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Protein kinase CK2 (formerly known as casein kinase 2 or II), a ubiquitous and constitutively active enzyme, is widely recognized as one of the most pleiotropic serine/threonine kinases. It plays a critical role in numerous signaling pathways, with hundreds of bona fide substrates. However, despite considerable research efforts, our understanding of the entire CK2 substratome and its functional associations with the majority of these substrates is far from being completely deciphered. In this context, we aim to provide an overview of how CK2 recognizes its substrates. We will discuss the pros and cons of the existing methods to manipulate CK2 activity in cells, as well as exploring the dynamic response of substrate phosphorylation to CK2 modulation. [ABSTRACT FROM AUTHOR]

Abscisic acid (ABA) is an essential phytohormone for plant responses to complex and variable environmental conditions. The molecular basis of the ABA signaling pathway has been well elucidated. SnRK2.2 and SnRK2.3 are key protein kinases participating in ABA responses, and the regulation of their activity plays an important role in signaling. Previous mass spectroscopy analysis of SnRK2.3 suggested that ubiquitin and homologous proteins may bind directly to the kinase. Ubiquitin typically recruits E3 ubiquitin ligase complexes to target proteins, marking them for degradation by the 26S proteasome. Here, we show that SnRK2.2 and SnRK2.3 interact with ubiquitin but are not covalently attached to the protein, resulting in the suppression of their kinase activity. The binding between SnRK2.2, SnRK2.3, and ubiquitin is weakened under prolonged ABA treatment. Overexpression of ubiquitin positively regulated the growth of seedlings exposed to ABA. Our results thus demonstrate a novel function for ubiquitin, which negatively regulates ABA responses by directly inhibiting SnRK2.2 and SnRK2.3 kinase activity. [ABSTRACT FROM AUTHOR]

Clear cell carcinoma (CCC) is a rare subtype of ovarian cancer resistant to standard platinum chemotherapy, which leads to a poor prognosis for patients with CCC. Kinases are targets for anticancer drugs; few studies have profiled kinase activity to identify kinase inhibitors as novel anticancer drugs. In this study, we aimed to identify novel anticancer drugs for the treatment of CCC with comprehensive kinase activity assay and drug screening. Using ascites from a 51-year old patient, we established and characterized the NCC-cOV1-C1 cell line. We screened the antiproliferative effects of 152 small anticancer compounds and conducted comprehensive kinase activity assays with the PamStation12 platform. The NCC-cOV1-C1 cells harbor copy number variation of HFN1ß amplification, and exhibit constant growth, spheroid formation, and invasion capability. NCC-cOV1-C1 cells responded remarkably to idarubicin HCl and vorinostat. The kinase activity assay revealed that SRC and EGFR were highly activated in NCC-cOV1-C1 cells; the SRC inhibitor dasatinib and the EGFR inhibitor lapatinib exhibited antiproliferative effects and downregulation of downstream signaling. The NCC-cOV1-C1 cell line will be a useful tool for basic and preclinical study of CCC, and the clinical utility of idarubicin HCl, vorinostat, dasatinib, lapatinib is worthy of further investigation. [ABSTRACT FROM AUTHOR]

Src family kinases (SFKs) are non-receptor tyrosine kinases and are involved in various cellular functions (proliferation, differentiation, migration, survival and invasion) by regulating downstream pathways. Considerable evidence suggests that co- and post-translational modifications are highly related to the activation of SFKs and their downstream signals. How SFKs are activated and how their subsequent cascades were regulated has been reviewed in previous reports. However, the contribution of co- and post-translational modification to SFKs activation has not been fully elucidated. This review focuses on the effect of these modifications on SFKs activity according to structural and biochemical studies and uncovers the significance of co-and post-translational modifications in the regulation of SFKs activity. [ABSTRACT FROM AUTHOR]

Circadian rhythms exist in nearly all organisms. In mammals, transcriptional and translational feedback loops (TTFLs) are believed to underlie the mechanism of the circadian clock. Casein kinase 1δ/ε (CK1δ/ε) are key kinases that phosphorylate clock components such as PER proteins, determining the pace of the clock. Most previous studies of the biochemical properties of the key kinases CK1ε and CK1δ in vitro have focused on the properties of the catalytic domains from which the autoinhibitory C-terminus has been deleted (ΔC); those studies ignored the significance of self-inhibition by autophosphorylation. By comparing the properties of the catalytic domain of CK1δ/ε with the full-length kinase that can undergo autoinhibition, we found that recombinant full-length CK1 showed a sequential autophosphorylation process that induces conformational changes to affect the overall kinase activity. Furthermore, a direct relationship between the period change and the autokinase activity among CK1δ, CK1ε, and CK1ε-R178C was observed. These data implicate the autophosphorylation activity of CK1δ and CK1ε kinases in setting the pace of mammalian circadian rhythms and indicate that the circadian period can be modulated by tuning the autophosphorylation rates of CK1δ/ε. [ABSTRACT FROM AUTHOR]

Conformational changes associated to sensing mechanisms of heme-based protein sensors are a key molecular event that seems to modulate not only the protein activity but also the potential of the Fe III/II redox couple of the heme domain. In this work, midpoint potentials ( E m ) assigned to the Fe III/II redox couple of the heme domain of FixL from Rhizobium etli ( Re FixL) in the unliganded and liganded states were determined by spectroelectrochemistry in the presence of inorganic mediators. In comparison to the unliganded Re FixL protein (+ 19 mV), the binding to ligands that switch off the kinase activity induces a negative shift, i. e. E m = − 51, − 57 and − 156 mV for O 2 , imidazole and CN − , respectively. Upon binding to CO, which does not affect the kinase active, E m was observed at + 21 mV. The potential values observed for Fe III/II of the heme domain of Re FixL upon binding to CO and O 2 do not follow the expected trend based on thermodynamics, assuming that positive potential shift would be expected for ligands that bind to and therefore stabilize the Fe II state. Our results suggest that the conformational changes that switch off kinase activity upon O 2 binding have knock-on effects to the local environment of the heme, such as solvent rearrangement, destabilize the Fe II state and counterbalances the Fe II -stabilizing influence of the O 2 ligand. [ABSTRACT FROM AUTHOR]

Pseudokinases are classified by the lack of one or several of the highly conserved motifs involved in nucleotide (nt) binding or catalytic activity of protein kinases (PKs). Pseudokinases represent ∼10% of the human kinome and they are found in all evolutionary classes of kinases. It has become evident that pseudokinases, which were initially considered somewhat peculiar dead kinases, are important components in several signalling cascades. Furthermore, several pseudokinases have been linked to human diseases, particularly cancer, which is raising interest for therapeutic approaches towards these proteins. The ATP-binding pocket is a well-established drug target and elucidation of the mechanism and properties of nt binding in pseudokinases is of significant interest and importance. Recent studies have demonstrated that members of the pseudokinase family are very diverse in structure as well as in their ability and mechanism to bind nts or perform phosphoryl transfer reactions. This diversity also precludes prediction of pseudokinase function, or the importance of nt binding for said function, based on primary sequence alone. Currently available data indicate that ∼40% of pseudokinases are able to bind nts, whereas only few are able to catalyse occasional phosphoryl transfer. Pseudokinases employ diverse mechanisms to bind nts, which usually occurs at low, but physiological, affinity. ATP binding serves often a structural role but in most cases the functional roles are not precisely known. In the present review, we discuss the various mechanisms that pseudokinases employ for nt binding and how this often low-affinity binding can be accurately analysed. [ABSTRACT FROM AUTHOR]

Key message: Arabidopsis BIK1 negatively regulates EIN3-depedent gene expression as an immediate cellular response. BIK1 localizes to the plasma membrane and its autophosphorylation and kinase activity involves in EIN3 repression. Abstract: BOTRYTIS INDUCED KINASE1 (BIK1) is a multifunctional receptor-like kinase that involves in ethylene-mediated plant defense signaling. The loss of function BIK1 becomes insensitive to ethylene, but it still accumulates a higher level of ETHYLENE INSENSITIVE3 (EIN3) that serves as the key transcription activator in ethylene signaling. To unequivocally elucidate BIK1 function on EIN3 regulation in ethylene signaling, we took a combined approach of transient expression assay and stable expression analysis of BIK1. In our cell-based functional assay BIK1 destabilized EIN3 and down-regulated EIN3-dependent transcription. Membrane localization and autophosphorylation of BIK1 were required for full repression of EIN3 function, but its kinase activity potential compromised such regulatory action. Consistently, the analysis of transgenic plants verified BIK1 function on EIN3 repression. Our findings have clarified that autophosphorylated BIK1 in the plasma membrane negatively regulates EIN3-dependent gene expression. Thus, ethylene insensitivity in bik1 appears to be an indirect or a feedback long-term response. [ABSTRACT FROM AUTHOR]

The recruitment of signaling proteins into activated receptor tyrosine kinases (RTKs) to produce rapid, high-fidelity downstream response is exposed to the ambiguity of random diffusion to the target site. Liquid-liquid phase separation (LLPS) overcomes this by providing elevated, localized concentrations of the required proteins while impeding competitor ligands. Here, we show a subset of phosphorylation-dependent RTK-mediated LLPS states. We then investigate the formation of phase-separated droplets comprising a ternary complex including the RTK, (FGFR2); the phosphatase, SHP2; and the phospholipase, PLCγ1, which assembles in response to receptor phosphorylation. SHP2 and activated PLCγ1 interact through their tandem SH2 domains via a previously undescribed interface. The complex of FGFR2 and SHP2 combines kinase and phosphatase activities to control the phosphorylation state of the assembly while providing a scaffold for active PLCγ1 to facilitate access to its plasma membrane substrate. Thus, LLPS modulates RTK signaling, with potential consequences for therapeutic intervention. [Display omitted] • Phosphorylated RTKs undergo phase separation with downstream effectors • Phosphorylation-dependent multivalent interaction drives FGFR2-SHP2 phase separation • The FGFR2-SHP2 complex colocalizes PLCγ1 to its plasma membrane substrate • Enzymatic activities are regulated within the FGFR2-SHP2-PLCγ1 membraneless droplets Lin et al. demonstrate that phosphorylated RTKs undergo liquid-liquid phase separation upon the recruitment of downstream proteins. Focusing on the RTK FGFR2, this process is shown to modulate enzymatic activities within the subcellular membraneless compartment. [ABSTRACT FROM AUTHOR]

Kinases play a key role in cellular signaling, and the overactivation or overexpression of these kinases has been linked to a variety of cancers. Tyrosine kinase inhibitors treat the mechanism of these cancers by targeting the specific kinases that are overactive. Some patients, however, do not respond to these inhibitors or develop resistance to these inhibitors during treatment. Additionally, even within cancers of the same tissue type, different kinases may be overactive in different patients. For example, some lung cancers overexpress epidermal growth factor receptor (EGFR) and respond to EGFR inhibitors, whereas other lung cancers do not overexpress EGFR and receive no benefit from this treatment. Even among patients exhibiting EGFR overexpression, some do not respond to EGFR kinase inhibitors because other kinases, such as Met kinase, are also overactivated. Here we describe a quantitative and specific multiplexed microfluidic assay using a hydrogel immobilized substrate for measuring the kinase activity of Met and Abl kinase from cancer cells. We immobilized kinase-specific substrates on macroporous hydrogel micropillars in microchannels. These microchannels were incubated with 6 μl of a kinase reaction solution containing cancer cell lysate, and we measured kinase activity via fluorescence detection of a phosphotyrosine antibody. We showed that the assay can specifically measure the activity of both Met and Abl kinase within one microchannel and has the potential to measure the activity of as many as five kinases within one microchannel. The assay also detected Met kinase inhibition from lysates of cancer cells grown in the Met kinase inhibitor PHA665752. [Figure not available: see fulltext.] [ABSTRACT FROM AUTHOR]

Abstract: Brassinosteroids (BRs) are steroid hormones that participate in multiple biological processes. In this paper, we characterized a classic rice mutant Fn189 (dwarf54, d54) showing semi-dwarf stature and erect leaves. The coleoptile elongation and root growth was less affected in Fn189 than wild-type plant by the exogenous application of eBL, the most active form of BRs. Lamina joint inclination assay and morphological analysis in darkness further showed that Fn189 mutant plant was insensitive to exogenous eBL. Through map-based cloning, Fn189 was found to be a novel allelic mutant of the DWARF 61 (D61) gene, which encodes the putative BRs receptor OsBRI1. A single base mutation caused the I834F substitution in the OsBRI1 kinase domain. Consequently, kinase activity of OsBRI1 was found to decrease dramatically. Taken together, the kinase activity of OsBRI1 is essential for brassinosteroids to regulate normal plant growth and development in rice. [Copyright &y& Elsevier]

MAPK (mitogen-activated protein kinase) pathways have been implicated in stress signalling in plants. In the present study, we performed yeast two-hybrid screening to identify partner MAPKs for OsMKK (Oryza sativa MAPK kinase) 6, a rice MAPK kinase, and revealed specific interactions of OsMKK6 with OsMPK3 and OsMPK6. OsMPK3 and OsMPK6 each co-immunoprecipitated OsMKK6, and both were directly phosphorylated by OsMKK6 in vitro. An MBP (myelin basic protein) kinase assay of the immunoprecipitation complex indicated that OsMPK3 and OsMPK6 were activated in response to a moderately low temperature (12°C), but not a severely low temperature (4°C) in rice seedlings. A constitutively active form of OsMKK6, OsMKK6DD, showed elevated phosphorylation activity against OsMPK3 and OsMPK6 in vitro. OsMPK3, but not OsMPK6, was constitutively activated in transgenic plants overexpressing OsMKK6DD, indicating that OsMPK3 is an in vivo target of OsMKK6. Enhanced chilling tolerance was observed in the transgenic plants overexpressing OsMKK6DD. Taken together, our data suggest that OsMKK6 and OsMPK3 constitute a moderately low-temperature signalling pathway and regulate cold stress tolerance in rice. [ABSTRACT FROM AUTHOR]