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Reversible scavenging, the oceanographic process by which dissolved metals exchange onto and off sinking particles and are thereby transported to deeper depths, has been well established for the metal thorium for decades. Reversible scavenging both deepens the elemental distribution of adsorptive elements and shortens their oceanic residence times in the ocean compared to nonadsorptive metals, and scavenging ultimately removes elements from the ocean via sedimentation. Thus, it is important to understand which metals undergo reversible scavenging and under what conditions. Recently, reversible scavenging has been invoked in global biogeochemical models of a range of metals including lead, iron, copper, and zinc to fit modeled data to observations of oceanic dissolved metal distributions. Nonetheless, the effects of reversible scavenging remain difficult to visualize in ocean sections of dissolved metals and to distinguish from other processes such as biological regeneration. Here, we show that particle-rich "veils" descending from high-productivity zones in the equatorial and North Pacific provide idealized illustrations of reversible scavenging of dissolved lead (Pb). A meridional section of dissolved Pb isotope ratios across the central Pacific shows that where particle concentrations are sufficiently high, such as within particle veils, vertical transport of anthropogenic surface-dissolved Pb isotope ratios toward the deep ocean is manifested as columnar isotope anomalies. Modeling of this effect shows that reversible scavenging within particle-rich waters allows anthropogenic Pb isotope ratios from the surface to penetrate ancient deep waters on timescales sufficiently rapid to overcome horizontal mixing of deep water Pb isotope ratios along abyssal isopycnals. [ABSTRACT FROM AUTHOR]

Simple Summary: We sought to assess cancer cell viability in the context of glycolytic versus oxidative phosphorylation carbon source availability from cell lines and expression data from variably glycolytic human tumors. We performed an RNAi screen of genes consisting of the cytosolic machinery for ATP production and regulation of bioenergetic output in cancer cells in glycolytic or oxidative phosphorylation (OXPHOS) conditions. We identified the pentose phosphate pathway as requisite for viability under glycolytic conditions and mTOR signaling as requisite for viability under OXPHOS conditions. We then characterized gene sets within this panel to identify similarities and differences amongst RNA-seq profiles across variably glycolytic cancer types. This analysis identified glycolytic tumor profiles from non-glycolytic tumor profiles. Our analyses support classification of tumors by metabolic phenotype. Cancer cells utilize variable metabolic programs in order to maintain homeostasis in response to environmental challenges. To interrogate cancer cell reliance on glycolytic programs under different nutrient availabilities, we analyzed a gene panel containing all glycolytic genes as well as pathways associated with glycolysis. Using this gene panel, we analyzed the impact of an siRNA library on cellular viability in cells containing only glucose or only pyruvate as the major bioenergetic nutrient source. From these panels, we aimed to identify genes that elicited conserved and glycolysis-dependent changes in cellular bioenergetics across glycolysis-promoting and OXPHOS-promoting conditions. To further characterize gene sets within this panel and identify similarities and differences amongst glycolytic tumor RNA-seq profiles across a pan-cancer cohort, we then used unsupervised statistical classification of RNA-seq profiles for glycolytic cancers and non-glycolytic cancer types. Here, Kidney renal clear cell carcinoma (KIRC); Head and Neck squamous cell carcinoma (HNSC); and Lung squamous cell carcinoma (LUSC) defined the glycolytic cancer group, while Prostate adenocarcinoma (PRAD), Thyroid carcinoma (THCA), and Thymoma (THYM) defined the non-glycolytic cancer group. These groups were defined based on glycolysis scoring from previous studies, where KIRC, HNSC, and LUSC had the highest glycolysis scores, meanwhile, PRAD, THCA, and THYM had the lowest. Collectively, these results aimed to identify multi-omic profiles across cancer types with demonstrated variably glycolytic rates. Our analyses provide further support for strategies aiming to classify tumors by metabolic phenotypes in order to therapeutically target tumor-specific vulnerabilities. [ABSTRACT FROM AUTHOR]

Despite the Pacific being the location of the earliest seawater Cd studies, the processes which control Cd distributions in this region remain incompletely understood, largely due to the sparsity of data. Here, we present dissolved Cd and δ114Cd data from the US GEOTRACES GP15 meridional transect along 152°W from the Alaskan margin to the equatorial Pacific. Our examination of this region's surface ocean Cd isotope systematics is consistent with previous observations, showing a stark disparity between northern Cd‐rich high‐nutrient low‐chlorophyll waters and Cd‐depleted waters of the subtropical and equatorial Pacific. Away from the margin, an open system model ably describes data in Cd‐depleted surface waters, but atmospheric inputs of isotopically light Cd likely play an important role in setting surface Cd isotope ratios (δ114Cd) at the lowest Cd concentrations. Below the surface, Southern Ocean processes and water mass mixing are the dominant control on Pacific Cd and δ114Cd distributions. Cd‐depleted Antarctic Intermediate Water has a far‐reaching effect on North Pacific intermediate waters as far as 47°N, contrasting with northern‐sourced Cd signatures in North Pacific Intermediate Water. Finally, we show that the previously identified negative Cd* signal at depth in the North Pacific is associated with the PO4 maximum and is thus a consequence of an integrated regeneration signal of Cd and PO4 at a slightly lower Cd:P ratio than the deep ocean ratio (0.35 mmol mol−1), rather than being related to in situ removal processes in low‐oxygen waters. Key Points: Atmospheric inputs of isotopically light Cd play an important role in setting surface δ114Cd when surface Cd concentrations are lowStrong Southern Ocean control on subsurface Cd and δ114Cd distribution; Antarctic Intermediate Water influences δ114Cd of North Pacific intermediate watersA Cd* minimum at depth in the North Pacific is associated with the PO4 maximum, a consequence of integrated regeneration [ABSTRACT FROM AUTHOR]

Atmospheric deposition represents a major input for micronutrient trace elements (TEs) to the surface ocean and is often quantified indirectly through measurements of aerosol TE concentrations. Sea spray aerosol (SSA) dominates aerosol mass concentration over much of the global ocean, but few studies have assessed its contribution to aerosol TE loading, which could result in overestimates of "new" TE inputs. Low‐mineral aerosol concentrations measured during the U.S. GEOTRACES Pacific Meridional Transect (GP15; 152°W, 56°N to 20°S), along with concurrent towfish sampling of surface seawater, provided an opportunity to investigate this aspect of TE biogeochemical cycling. Central Pacific Ocean surface seawater Al, V, Mn, Fe, Co, Ni, Cu, Zn, and Pb concentrations were combined with aerosol Na data to calculate a "recycled" SSA contribution to aerosol TE loading. Only vanadium was calculated to have a SSA contribution averaging >1% along the transect (mean of 1.5%). We derive scaling factors from previous studies on TE enrichments in the sea surface microlayer and in freshly produced SSA to assess the broader potential for SSA contributions to aerosol TE loading. Maximum applied scaling factors suggest that SSA could contribute significantly to the aerosol loading of some elements (notably V, Cu, and Pb), while for others (e.g., Fe and Al), SSA contributions largely remained <1%. Our study highlights that a lack of focused measurements of TEs in SSA limits our ability to quantify this component of marine aerosol loading and the associated potential for overestimating new TE inputs from atmospheric deposition. Plain Language Summary: Sea spray aerosol (SSA) generated by breaking waves and bursting bubbles can dominate the particle population in the marine atmosphere. We investigated whether this mechanism could mobilize significant amounts of trace elements (TEs)—nutrient and pollutant elements present in the surface ocean in very low concentrations. Previous studies have suggested that TEs could become enriched on SSA during its formation, relative to their concentrations in seawater, and this could make the process a more significant source for aerosol concentrations of some elements. But for others, the SSA contribution is always likely to be insignificant. Our calculations based on sea salt and TE aerosol concentrations in the atmosphere and dissolved TEs in the surface ocean suggest that SSA does not contribute significantly to total aerosol TE loading, with the possible exception of vanadium, which has relatively higher concentrations in seawater than the other elements considered. This study highlights that this process remains poorly quantified due to limited direct measurements. Key Points: Sea spray aerosol (SSA) concentration was quantified along a meridional Pacific Ocean transect during low mineral aerosol conditionsSea spray‐derived aerosol trace elements (TEs) are negligible unless significant enrichment occurs during formation; only vanadium is >1%SSA contributions to aerosol TEs of >100% calculated by applying enrichments from earlier studies suggests these are not widely applicable [ABSTRACT FROM AUTHOR]

Over the past decade, the GEOTRACES and wider trace metal geochemical community has made substantial contributions towards constraining the marine cobalt (Co) cycle and its major biogeochemical processes. However, few Co speciation studies have been conducted in the North and equatorial Pacific Ocean, a vast portion of the world's oceans by volume and an important end-member of deep thermohaline circulation. Dissolved Co (dCo) samples, including total dissolved and labile Co, were measured at-sea during the GEOTRACES Pacific Meridional Transect (GP15) expedition along the 152 ∘ W longitudinal from 56 ∘ N to 20 ∘ S. Along this transect, upper-ocean dCo (σ0<26) was linearly correlated with dissolved phosphate (slope = 82±3 , µ mol : mol) due to phytoplankton uptake and remineralization. As depth increased, dCo concentrations became increasingly decoupled from phosphate concentrations due to co-scavenging with manganese oxide particles in the mesopelagic. The transect revealed an organically bound coastal source of dCo to the Alaskan Stream associated with low-salinity waters. An intermediate-depth hydrothermal flux of dCo was observed off the Hawaiian coast at the Loihi Seamount, and the elevated dCo was correlated with potential xs3 He at and above the vent site; however, the Loihi Seamount likely did not represent a major source of Co to the Pacific basin. Elevated concentrations of dCo within oxygen minimum zones (OMZs) in the equatorial North and South Pacific were consistent with the suppression of oxidative scavenging, and we estimate that future deoxygenation could increase the OMZ dCo inventory by 18 % to 36 % over the next century. In Pacific Deep Water (PDW), a fraction of elevated ligand-bound dCo appeared protected from scavenging by the high biogenic particle flux in the North Pacific basin. This finding is counter to previous expectations of low dCo concentrations in the deep Pacific due to scavenging over thermohaline circulation. Compared to a Co global biogeochemical model, the observed transect displayed more extreme inventories and fluxes of dCo than predicted by the model, suggesting a highly dynamic Pacific Co cycle. [ABSTRACT FROM AUTHOR]

Over the past decade, the GEOTRACES and wider trace metal geochemical community have made substantial contributions towards constraining the marine cobalt (Co) cycle and its major biogeochemical processes. However, few Co speciation studies have been conducted in the North and equatorial Pacific Ocean, a vast portion of the world's oceans by volume and an important endmember of deep thermohaline circulation. Dissolved Co (dCo) samples, including total dissolved and labile Co, were measured at-sea during the GEOTRACES Pacific meridional transect (GP15) along the 152° W longitudinal from 56° N to 20° S. Along this transect, upper ocean dCo was linearly correlated to dissolved phosphate (slope = 82 ± 2 µM:M) due to phytoplankton uptake and remineralization. As depth increased, dCo concentrations became increasingly decoupled from phosphate concentrations due to co-scavenging with manganese oxide particles in the mesopelagic. The transect revealed an organically-bound coastal source of dCo to the Alaskan Stream associated with low salinity waters. An intermediate-depth hydrothermal flux of dCo was observed off the Hawaiian coast at the Loihi Seamount, and the elevated dCo was correlated to estimated xs³He at and above the vent site; however, the Loihi Seamount likely did not represent a major source of Co to the Pacific basin. Elevated concentrations of dCo within oxygen minimum zones (OMZs) in the equatorial North and South Pacific were consistent with the suppression of oxidative scavenging, and we estimate that future deoxygenation could increase the OMZ dCo inventory by 13-28 % over the next century. In North Pacific Deep Water (NPDW), a fraction of elevated ligand-bound dCo appeared protected from scavenging by the high biogenic particle flux in the North Pacific basin. This finding is counter to previous expectations of low dCo concentrations in the deep Pacific due to scavenging over thermohaline circulation. Compared to a Co global biogeochemical model, the observed transect displayed more extreme inventories and fluxes of dCo than predicted by the model, suggesting a highly dynamic Pacific Co cycle. [ABSTRACT FROM AUTHOR]

The surface waters of the Arctic Ocean include an important inventory of freshwater from rivers, sea ice melt, and glacial meltwaters. While some freshwaters are mixed directly into the surface ocean, cryospheric reservoirs, such as snow, sea ice, and melt ponds act as incubators for trace metals, as well as potential sources to the surface ocean upon melting. The availability and reactivity of these metals depends on their speciation, which may vary across each pool or undergo transformation upon mixing. We present here baseline measurements of colloidal (~0.003-0.200 µm) iron (Fe), zinc (Zn), nickel (Ni), copper (Cu), cadmium (Cd), and manganese (Mn) in snow, sea ice, melt ponds, and the underlying seawater. We consider both the total concentration of colloidal metals ([cMe]) in each cryospheric reservoir and the contribution of cMe to the overall dissolved metal phase (%cMe). Notably, snow contained higher (cMe) as well as higher %cMe relative to seawater for metals such as Fe and Zn across most stations. Stations close to the North Pole had relatively high aerosol deposition, imparting high (cFe) and (cZn), as well as high %cFe, %cZn, %cMn, and %cCd (>80%). In contrast, surface seawater concentrations of Cd, Cu, Mn, and Ni were dominated by the soluble phase (<0.003 µm), suggesting little impact of cMe from the melting cryosphere, or rapid aggregation/disaggregation dynamics within surface waters leading to the loss of cMe. This has important implications for how trace metal biogeochemistry speciation and thus fluxes may change in a future ice-free Arctic Ocean. [ABSTRACT FROM AUTHOR]

Ocean time‐series sites are influenced by both temporal variability, as in situ conditions change, as well as spatial variability, as water masses move across the fixed observation point. To remove the effect of spatial variability, this study made sub‐daily Lagrangian observations of trace elements and isotopes (Al, Sc, Mn, Fe, Co, Ni, Cu, Zn, Cd, Pb, 232Th, and 230Th) in surface water over a 12‐day period (July–August 2015) in the North Pacific near the Hawaii Ocean Time‐series Station ALOHA. Additionally, a vertical profile in the upper 250 m was analyzed. This dataset is intercalibrated with GEOTRACES standards and provides a consistent baseline for trace element studies in the oligotrophic North Pacific. No diel changes in trace elements could be resolved, although day‐to‐day variations were resolved for some elements (Fe, Cu, and Zn), which may be related to organic matter cycling or ligand availability. Pb concentrations remained relatively constant during 1997–2015, presenting a change from previous decreases. Nutrient to trace element stoichiometric ratios were compared to those observed in phytoplankton as an indication of the extent of biological trace element utilization in this ecosystem, providing a basis for future ecological trace element studies. Key Points: A suite of 11 trace elements was analyzed in one patch of surface water at twice‐daily resolution for 12 days near Station ALOHANo diel patterns could be resolved; daily variations are suggestive of active biogeochemical cycling in this oligotrophic regionInterannual variations, in particular for Pb, and nutrient‐trace element stoichiometry with respect to prior observations was assessed [ABSTRACT FROM AUTHOR]

Defects in vesicular trafficking underlie a wide variety of human diseases. Genetic disruption of leucine-rich repeat kinase 2 (LRRK2) in rodents results in epithelial vesicular trafficking errors that can also be induced by treatment of animals with LRRK2 kinase inhibitors. Here we demonstrate that defects in human renal cells lacking LRRK2 phenocopy those seen in the kidneys of Lrrk2 knockout mice, characterized by accumulation of intracellular waste vesicles and fragmentation of the Golgi apparatus. This phenotype can be recapitulated by knockdown of N-ethylmaleimide-sensitive factor, which physically associates with LRRK2 in renal cells. Deficiency in either protein leads to a defect in trans-Golgi to lysosome protein trafficking, which compromises the capacity of lysosomes to degrade endocytic and autophagic cargo. In contrast, neither bulk endocytosis nor autophagic flux are impaired when LRRK2 is acutely knocked down in normal immortalized human kidney (HK2) cells. These data collectively suggest that the primary renal defect caused by LRRK2 deficiency is in protein trafficking between the Golgi apparatus and late endosome/lysosome, which leads to progressive impairments in lysosomal function. [ABSTRACT FROM AUTHOR]

Sequential extraction is commonly used to identify and quantify different forms of phosphorus (P) associated with particulate samples. Iron (Fe)-bound P is an important fraction of total particulate phosphorus because iron (Fe) is ubiquitous in natural environments. Three reductant solutions, i.e., sodium hydroxide (NaOH), dithionite, and ascorbic acid, have been used to extract solid phase reactive iron and associated phosphorus from sediments and soils. This study compares the efficiencies of three different methods in extracting Fe and Fe-bound P and evaluates the potential and limitation of each method. Based on the results of this comparative study it is recommended that the ascorbic acid reduction method is used for extraction of Fe-bound P in particulate samples, such as soil and sediment. [ABSTRACT FROM AUTHOR]

We previously performed an RNA interference (RNAi) screen and found that the knockdown of the catalytically inactive phosphatase, MK-STYX [MAPK (mitogen-activated protein kinase) phospho-serine/threonine/tyrosine-binding protein], resulted in potent chemoresistance. Our follow-up studies demonstrated that knockdown of MK-STYX prevents cells from undergoing apoptosis through a block in cytochrome c release, but that MK-STYX does not localize proximal to the molecular machinery currently known to control this process. In an effort to define its molecular mechanism, we utilized an unbiased proteomics approach to identify proteins that interact with MK-STYX. We identified the mitochondrial phosphatase, PTPMT1 (PTP localized to mitochondrion 1), as the most significant and unique interaction partner of MK-STYX. We previously reported that knockdown of PTPMT1, an important component of the cardiolipin biosynthetic pathway, is sufficient to induce apoptosis and increase chemosensitivity. Accordingly, we hypothesized that MK-STYX and PTPMT1 interact and serve opposing functions in mitochondrial-dependent cell death. We confirmed that MK-STYX and PTPMT1 interact in cells and, importantly, found that MK-STYX suppresses PTPMT1 catalytic activity. Furthermore, we found that knockdown of PTPMT1 resensitizes MK-STYX knockdown cells to chemotherapeutics and restores the ability to release cytochrome c. Taken together, our data support a model in which MK-STYX controls apoptosis by negatively regulating PTPMT1. Given the important role of PTPMT1 in the production of cardiolipin and other phospholipids, this raises the possibility that dysregulated mitochondrial lipid metabolism may facilitate chemoresistance. [ABSTRACT FROM AUTHOR]

Previous studies have shown that growth hormone (GH) recruits the adapter protein SH2B1β to the GH-activated, GH receptorassociated tyrosine kinase JAK2, implicating SH2B1β in GH-dependent actin cytoskeleton remodeling, and suggesting that phosphorylation at serines 161 and 165 in SH2B1β releases SH2B1β from the plasma membrane. Here, we examined the role of SH2B1β in GH regulation of macrophage migration. We show that GH stimulates migration of cultured RAW264.7 macrophages, and primary cultures of peritoneal and bone marrow-derived macrophages. SH2B1β overexpression enhances, whereas SH2B1 knockdown inhibits, GH-dependent motility of RAW macrophages. At least two independent mechanisms regulate the SH2B1β-mediated changes in motility. In response to GH, tyrosines 439 and 494 in SH2B1β are phosphorylated. Mutating these tyrosines in SH2B1β decreases both basal and GH-stimulated macrophage migration. In addition, mutating the polybasic nuclear localization sequence (NLS) in SH2B1β or creating the phosphomimetics SH2B1β(S161E) or SH2B1β(S165E), all of which release SH2B1β from the plasma membrane, enhances macrophage motility. Conversely, SH2B1β(S161/165A) exhibits increased localization at the plasma membrane and decreased macrophage migration. Mutating the NLS or the nearby serine residues does not alter GH-dependent phosphorylation on tyrosines 439 and 494 in SH2B1β. Mutating tyrosines 439 and 494 does not affect localization of SH2B1β at the plasma membrane or movement of SH2B1β into focal adhesions. Taken together, these results suggest that SH2B1β enhances GH-stimulated macrophage motility via mechanisms involving phosphorylation of SH2B1β on tyrosines 439 and 494 and movement of SH2B1β out of the plasma membrane (e.g. as a result of phosphorylation of serines 161 and 165). [ABSTRACT FROM AUTHOR]

Protein Tyrosine Phosphatase localized to the Mitochondrion 1 (PTPMT1) is a dual specificity phosphatase exclusively localized to the mitochondria, and has recently been shown to be a critical component in the cardiolipin biosynthetic pathway. The downregulation of PTPMT1 in pancreatic beta cells has been shown to increase cellular ATP levels and insulin production, however, the generalized role of PTPMT1 in cancer cells has not been characterized. Here we report that downregulation of PTPMT1 activity is sufficient to induce apoptosis of cancer cells. Additionally, the silencing of PTPMT1 decreases cardiolipin levels in cancer cells, while selectively increasing ATP levels in glycolytic media. Additionally, sublethal downregulation of PTPMT1 synergizes with low doses of paclitaxel to promote cancer cell death. Our data suggest that inhibition of PTPMT1 causes a metabolic crisis in cancer cells that induces cell death, and may be a mechanism by which cancer cells can be sensitized to currently available therapies. [ABSTRACT FROM AUTHOR]

Degenerative joint disease, also known as osteoarthritis, is the most common joint disorder in human beings. The molecular mechanism underlying this disease is not fully understood. Here, we report that disruption of mitogen-inducible gene 6 (Mig-6) in mice by homologous recombination leads to early onset degenerative joint disease, which is revealed by simultaneous enlargement and deformity of multiple joints, degradation of articular cartilage, and the development of bony outgrowths or osteophyte formation within joint space. The osteophyte formation appears to be derived from proliferation of mesenchymal progenitor cells followed by differentiation into chondrocytes. Absence of the Rag2 gene does not rescue the joint phenotype, excluding a role for the acquired immune system in the development of this disease. Our results provide insight into the mechanism of osteoarthritis by showing that loss of Mig-6 leads to early onset of this disease, implying that this gene or its pathway is important in normal joint maintenance. Because of the striking similarity of osteoarthritis in humans and mice, the Mig-6 mutant mouse should provide a useful animal model for studying the mechanism of this disease and for testing drugs or therapies for treating osteoarthritis. [ABSTRACT FROM AUTHOR]

The ability to detect and respond to hypoxia within a developing tumor appears to be a common feature amongst most cancers. This hypoxic response has many molecular drivers, but none as widely studied as Hypoxia-Inducible Factor 1 (HIF-1). Recent evidence suggests that HIF-1 biology within lung adenocarcinoma (LUAD) may be associated with expression levels of adenylate kinases (AKs). Using LUAD patient transcriptome data, we sought to characterize AK gene signatures related to lung cancer hallmarks, such as hypoxia and metabolic reprogramming, to identify conserved biological themes across LUAD tumor progression. Transcriptomic analysis revealed perturbation of HIF-1 targets to correlate with altered expression of most AKs, with AK4 having the strongest correlation. Enrichment analysis of LUAD tumor AK4 gene signatures predicts signatures involved in pyrimidine, and by extension, nucleotide metabolism across all LUAD tumor stages. To further discriminate potential drivers of LUAD tumor progression within AK4 gene signatures, partial least squares discriminant analysis was used at LUAD stage-stage interfaces, identifying candidate genes that may promote LUAD tumor growth or regression. Collectively, these results characterize regulatory gene networks associated with the expression of all nine human AKs that may contribute to underlying metabolic perturbations within LUAD and reveal potential mechanistic insight into the complementary role of AK4 in LUAD tumor development. [ABSTRACT FROM AUTHOR]

Evasion of apoptosis is a significant problem affecting an array of cancers. In order to identify novel regulators of apoptosis, we performed an RNA interference (RNAi) screen against all kinases and phosphatases in the human genome. We identified MK-STYX (STYXL1), a catalytically inactive phosphatase with homology to the mitogen-activated protein kinase (MAPK) phosphatases. Despite this homology, MK-STYX knockdown does not significantly regulate MAPK signaling in response to growth factors or apoptotic stimuli. Rather, RNAi-mediated knockdown of MK-STYX inhibits cells from undergoing apoptosis induced by cellular stressors activating mitochondrion-dependent apoptosis. This MK-STYX phenotype mimics the loss of Bax and Bak, two potent guardians of mitochondrial apoptotic potential. Similar to loss of both Bax and Bak, cells without MK-STYX expression are unable to release cytochrome c. Proapoptotic members of the BCL-2 family (Bax, Bid, and Bim) are unable to trigger cytochrome c release in MK-STYX-depleted cells, placing the apoptotic deficiency at the level of mitochondrial outer membrane permeabilization (MOMP). MK-STYX was found to localize to the mitochondria but is neither released from the mitochondria upon apoptotic stress nor proximal to the machinery currently known to control MOMP, indicating that MK-STYX regulates MOMP using a distinct mechanism. [ABSTRACT FROM AUTHOR]

Wnt signaling is essential for both the development and homeostasis of diverse cellular lineages, including hematopoietic stem cells. Organism-wide, Wnt signals are tightly regulated, as overactivation of the pathway can lead to tumorigenesis. Although numerous Wnt ligands and Frizzled (Fzd) receptors exist, how particular Wnt/Fzd pairings are established and how their signals are regulated is poorly understood. We have previously identified the requirements of the cognate pairing of Wnt9a and Fzd9b for early hematopoietic stem cell proliferation. However, the specific signals governing activation, but equally important, the molecular mechanisms required to turn the signal 'off,' are unknown. Here, we show that the E3 ubiquitin ligase Trip12 (thyroid hormone receptor interactor 12) is specifically required to ubiquitinate the third intracellular loop of Fzd9b at K437, targeting it for lysosomal degradation. In contrast to other ubiquitin ligases described to regulate the cell surface availability of multiple Fzds broadly, our data indicate that Trip12 is selective for Fzd9b. We further demonstrate that this occurs through ubiquitination at K437 of Fzd9b in the third intracellular loop, ultimately leading to a decrease in Fzd9b receptor availability and in Wnt9a/Fzd9b signaling that impacts hematopoietic stem cell proliferation in zebrafish. Our results point to specific mechanisms driving the availability of different Fzd receptors. Determining how particular Fzd abundance is regulated at the membrane will be critical to developing specific therapies for human intervention.

The complexes of the electron transport chain and ATP synthase comprise the oxidative phosphorylation (OXPHOS) system. The reactions of OXPHOS generate the mitochondrial membrane potential, drive the majority of ATP production in respiring cells, and contribute significantly to cellular reactive oxygen species (ROS). Regulation of OXPHOS is therefore critical to maintain cellular homeostasis. OXPHOS machinery subunits have been found to be highly phosphorylated, implicating this post-translational modification as a means whereby OXPHOS is regulated. Multiple lines of evidence now reveal the diverse mechanisms by which phosphorylation of OXPHOS machinery serve to regulate individual complex stability and activity as well as broader cellular functions. From these mechanistic studies of OXPHOS machinery phosphorylation, it is now clear that many aspects of human health and disease are potentially impacted by phosphorylation of OXPHOS complexes. This mini-review summarizes recent studies that provide robust mechanistic detail related to OXPHOS subunit phosphorylation.

Previous studies have shown that growth hormone (GH) recruits the adapter protein SH2B1β to the GH-activated, GH receptor-associated tyrosine kinase JAK2, implicating SH2B1β in GH-dependent actin cytoskeleton remodeling, and suggesting that phosphorylation at serines 161 and 165 in SH2B1β releases SH2B1β from the plasma membrane. Here, we examined the role of SH2B1β in GH regulation of macrophage migration. We show that GH stimulates migration of cultured RAW264.7 macrophages, and primary cultures of peritoneal and bone marrow-derived macrophages. SH2B1β overexpression enhances, whereas SH2B1 knockdown inhibits, GH-dependent motility of RAW macrophages. At least two independent mechanisms regulate the SH2B1β-mediated changes in motility. In response to GH, tyrosines 439 and 494 in SH2B1β are phosphorylated. Mutating these tyrosines in SH2B1β decreases both basal and GH-stimulated macrophage migration. In addition, mutating the polybasic nuclear localization sequence (NLS) in SH2B1β or creating the phosphomimetics SH2B1β(S161E) or SH2B1β(S165E), all of which release SH2B1β from the plasma membrane, enhances macrophage motility. Conversely, SH2B1β(S161/165A) exhibits increased localization at the plasma membrane and decreased macrophage migration. Mutating the NLS or the nearby serine residues does not alter GH-dependent phosphorylation on tyrosines 439 and 494 in SH2B1β. Mutating tyrosines 439 and 494 does not affect localization of SH2B1β at the plasma membrane or movement of SH2B1β into focal adhesions. Taken together, these results suggest that SH2B1β enhances GH-stimulated macrophage motility via mechanisms involving phosphorylation of SH2B1β on tyrosines 439 and 494 and movement of SH2B1β out of the plasma membrane (e.g. as a result of phosphorylation of serines 161 and 165).

The adaptor protein SH2B1β participates in regulation of the actin cytoskeleton during processes such as cell migration and differentiation. Here, we identify SH2B1β as a new focal adhesion protein. We provide evidence that SH2B1β is phosphorylated in response to phorbol 12-myristate 13-acetate (PMA)-induced protein kinase C (PKC) activation and show that PMA induces a rapid redistribution of SH2B1β out of focal adhesions. We also show that growth hormone (GH) increases cycling of SH2B1β into and out of focal adhesions. Ser161 and Ser165 in SH2B1β fall within consensus PKC substrate motifs. Mutating these two serine residues into alanine residues abrogates PMA-induced redistribution of SH2B1β out of focal adhesions, decreases SH2B1β cycling into and out of focal adhesions in control and GH-stimulated cells, and increases the size of focal adhesions. By contrast, mutating Ser165 into a glutamate residue decreases the amount of SH2B1β in focal adhesions and increases the number of focal adhesions per cell. These results suggest that activation of PKC regulates SH2B1β focal adhesion localization through phosphorylation of Ser161 and/or Ser165. The finding that phosphorylation of SH2B1β increases the number of focal adhesions suggests a mechanism for the stimulatory effect on cell motility of SH2B1β.

Mitochondrial processes play an important role in tumor initiation and progression. In this review, we focus on three critical processes by which mitochondrial function may contribute to cancer: through alterations in glucose metabolism, the production of reactive oxygen species (ROS) and compromise of intrinsic apoptotic function. Alterations in cancer glucose metabolism include the Warburg effect, leading to a shift in metabolism away from aerobic respiration toward glycolysis, even when sufficient oxygen is present to support respiration. Such alterations in cellular metabolism may favor tumor cell growth by increasing the availability of biosynthetic intermediates needed for cellular growth and proliferation. Mutations in specific metabolic enzymes, namely succinate dehydrogenase, fumarate hydratase and the isocitrate dehydrogenases, have been linked to human cancer. Mitochondrial ROS may contribute to cancer via DNA damage and the activation of aberrant signaling pathways. ROS-dependent stabilization of the transcription factor hypoxia-inducible factor (HIF) may be a particularly important event for tumorigenesis. Compromised function of intrinsic apoptosis removes an important cellular safeguard against cancer and has been implicated in tumorigenesis, tumor metastasis, and chemoresistance. Each of the major mitochondrial processes is linked. In this review, we outline the connections between them and address ways these mitochondrial pathways may be targeted for cancer therapy.