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Adequate mass and function of adipose tissues (ATs) play essential roles in preventing metabolic perturbations. The pathological reduction of ATs in lipodystrophy leads to an array of metabolic diseases. Understanding the underlying mechanisms may benefit the development of effective therapies. Several cellular processes, including autophagy and vesicle trafficking, function collectively to maintain AT homeostasis. Here, we investigated the impact of adipocyte-specific deletion of the lipid kinase phosphatidylinositol 3-kinase catalytic subunit type 3 (PIK3C3) on AT homeostasis and systemic metabolism in mice. We report that PIK3C3 functions in all ATs and that its absence disturbs adipocyte autophagy and hinders adipocyte differentiation, survival, and function with differential effects on brown and white ATs. These abnormalities cause loss of white ATs, whitening followed by loss of brown ATs, and impaired “browning” of white ATs. Consequently, mice exhibit compromised thermogenic capacity and develop dyslipidemia, hepatic steatosis, insulin resistance, and type 2 diabetes. While these effects of PIK3C3 largely contrast previous findings with the autophagy-related (ATG) protein ATG7 in adipocytes, mice with a combined deficiency in both factors reveal a dominant role of the PIK3C3-deficient phenotype. We have also found that dietary lipid excess exacerbates AT pathologies caused by PIK3C3 deficiency. Surprisingly, glucose tolerance is spared in adipocyte-specific PIK3C3-deficient mice, a phenotype that is more evident during dietary lipid excess. These findings reveal a crucial yet complex role for PIK3C3 in ATs, with potential therapeutic implications.

The generation of a functional, self-tolerant T cell receptor (TCR) repertoire depends on interactions between developing thymocytes and antigen-presenting thymic epithelial cells (TECs). Cortical TECs (cTECs) rely on unique antigen-processing machinery to generate self-peptides specialized for T cell positive selection. In our current study, we focus on the lipid kinase Vps34, which has been implicated in autophagy and endocytic vesicle trafficking. We show that loss of Vps34 in TECs causes profound defects in the positive selection of the CD4 T cell lineage but not the CD8 T cell lineage. Utilizing TCR sequencing, we show that T cell selection in conditional mutants causes altered repertoire properties including reduced clonal sharing. cTECs from mutant mice display an increased abundance of invariant chain intermediates bound to surface MHC class II molecules, indicating altered antigen processing. Collectively, these studies identify lipid kinase Vps34 as an important contributor to the repertoire of selecting ligands processed and presented by TECs to developing CD4 T cells.

The PIK3C3/VPS34 subunit of the class III phosphatidylinositol 3-kinase (PtdIns3K) complex plays a role in both canonical and noncanonical autophagy, key processes that control immune-cell responsiveness to a variety of stimuli. Our previous studies found that PIK3C3 is a critical regulator that controls the development, homeostasis, and function of dendritic and T cells. In this study, we investigated the role of PIK3C3 in myeloid cell biology using myeloid cell-specific Pik3c3-deficient mice. We found that Pik3c3-deficient macrophages express increased surface levels of major histocompatibility complex (MHC) class I and class II molecules. In addition, myeloid cell-specific Pik3c3 ablation in mice caused a partial impairment in the homeostatic maintenance of macrophages expressing the apoptotic cell uptake receptor TIM-4. Pik3c3 deficiency caused phenotypic changes in myeloid cells that were dependent on the early machinery (initiation/nucleation) of the classical autophagy pathway. Consequently, myeloid cell-specific Pik3c3-deficient animals showed significantly reduced severity of experimental autoimmune encephalomyelitis (EAE), a primarily CD4(+) T-cell-mediated mouse model of multiple sclerosis (MS). This disease protection was associated with reduced accumulation of myelin-specific CD4(+) T cells in the central nervous system and decreased myeloid cell IL-1β production. Further, administration of SAR405, a selective PIK3C3 inhibitor, delayed disease progression. Collectively, our studies establish PIK3C3 as an important regulator of macrophage functions and myeloid cell-mediated regulation of EAE. Our findings also have important implications for the development of small-molecule inhibitors of PIK3C3 as therapeutic modulators of MS and other autoimmune diseases.

mTOR is a serine/threonine kinase that acts in two distinct complexes, mTORC1 and mTORC2, and is dysregulated in many diseases including cancer. mLST8 is a shared component of both mTORC1 and mTORC2, yet little is known regarding how mLST8 contributes to assembly and activity of the mTOR complexes. Here we assessed mLST8 loss in a panel of normal and cancer cells and observed little to no impact on assembly or activity of mTORC1. However, mLST8 loss blocked mTOR association with mTORC2 cofactors RICTOR and SIN1, thus abrogating mTORC2 activity. Similarly, a single pair of mutations on mLST8 with a corresponding mutation on mTOR interfered with mTORC2 assembly and activity without affecting mTORC1. We also discovered a direct interaction between mLST8 and the NH2-terminal domain of the mTORC2 cofactor SIN1. In PTEN-null prostate cancer xenografts, mLST8 mutations disrupting the mTOR interaction motif inhibited AKT S473 phosphorylation and decreased tumor cell proliferation and tumor growth in vivo. Together, these data suggest that the scaffolding function of mLST8 is critical for assembly and activity of mTORC2, but not mTORC1, an observation that could enable therapeutic mTORC2-selective inhibition as a therapeutic strategy. Significance: These findings show that mLST8 functions as a scaffold to maintain mTORC2 integrity and kinase activity, unveiling a new avenue for development of mTORC2-specific inhibitors.

PIK3C3/VPS34 is a key player in macroautophagy/autophagy and MAP1LC3/LC3-associated phagocytosis (LAP), which play critical roles in dendritic cell (DC) function. In this study, we assessed the contribution of PIK3C3 to DC function during experimental autoimmune encephalomyelitis (EAE), an animal model of multiple sclerosis (MS). We found that Pik3c3-deficient DCs exhibit attenuated capacity to reactivate encephalitogenic T cells in the central nervous system, leading to reduced incidence and severity of EAE in DC-specific Pik3c3-deficient mice. Additionally, animals with a DC-specific deficiency in Rb1cc1/Fip200 but not Rubcn were protected against EAE, suggesting that the EAE phenotype of DC-specific Pik3c3-deficient mice is due to defective canonical autophagy rather than LAP. Collectively, our studies have revealed a critical role of PIK3C3 in DC function and the pathogenicity of these cells during EAE, with important implications for the development of immunotherapies for autoimmune diseases such as MS. Abbreviations: ATG: autophagy-related; CNS: central nervous system; DC: dendritic cell; DEG: differentially expressed gene; EAE: experimental autoimmune encephalomyelitis; LAP: LC3-associated phagocytosis; MAP1LC3/LC3: microtubule-associated protein 1 light chain 3; MHC: major histocompatibility complex; MOG: myelin oligodendrocyte glycoprotein; MS: multiple sclerosis; PIK3C3/VPS34: phosphatidylinositol 3-kinase catalytic subunit type 3; ROS: reactive oxygen species

The PIK3C3/VPS34 subunit of the class III phosphatidylinositol 3-kinase (PtdIns3K) complex is a key early player in macroautophagy/autophagy. In this study, we assessed the contribution of PIK3C3 to T cell metabolism and function. We found that Pik3c3-deficient T cells exhibited impaired cellular metabolism, and Pik3c3-deficient CD4(+) T cells failed to differentiate into T helper 1 cells. These alterations were associated with reduced levels of active mitochondria upon T cell activation. In addition, conditional Pik3c3-deficient animals failed to mount autoreactive T cell responses and were resistant to experimental autoimmune encephalomyelitis (EAE). Interestingly, the deletion of Pik3c3 had little effect on the capacity of animals to clear tumor metastases. Collectively, our studies have revealed a critical role of PIK3C3 in T cell metabolism and the pathogenicity of these cells during EAE. Our findings also have important implications for the development of immunotherapies to treat multiple sclerosis and other inflammatory diseases by targeting PIK3C3. Abbreviations: CNS: central nervous system; DC: dendritic cell; DEG: differentially expressed gene; EAE: experimental autoimmune encephalomyelitis; ECAR: extracellular acidification rate; iNKT: invariant natural killer T; LAP: LC3-associated phagocytosis; LLC: Lewis lung carcinoma; MAP1LC3/LC3: microtubule-associated protein 1 light chain 3; MDSC: myeloid-derived suppressor cell; MOG: myelin oligodendrocyte glycoprotein; NK: natural killer; OCR: oxygen consumption rate; PI: propidium iodide; PIK3C3/VPS34: phosphatidylinositol 3-kinase catalytic subunit type 3; RNA-seq: RNA-sequencing; TCR: T cell receptor; TMRE: tetramethylrhodamine ethyl ester perchlorate

Basal-like/triple-negative breast cancers (TNBCs) are among the most aggressive forms of breast cancer, and disproportionally affects young premenopausal women and women of African descent. Patients with TNBC suffer a poor prognosis due in part to a lack of molecularly targeted therapies, which represents a critical barrier for effective treatment. Here, we identify EphA2 receptor tyrosine kinase as a clinically relevant target for TNBC. EphA2 expression is enriched in the basal-like molecular subtype in human breast cancers. Loss of EphA2 function in both human and genetically engineered mouse models of TNBC reduced tumor growth in culture and in vivo. Mechanistically, targeting EphA2 impaired cell cycle progression through S-phase via downregulation of c-Myc and stabilization of the cyclin-dependent kinase inhibitor p27/KIP1. A small molecule kinase inhibitor of EphA2 effectively suppressed tumor cell growth in vivo, including TNBC patient-derived xenografts. Thus, our data identify EphA2 as a novel molecular target for TNBC.

Mammalian target of rapamycin (mTOR) is a serine/threonine kinase that regulates a diverse array of cellular processes, including cell growth, survival, metabolism, and cytoskeleton dynamics. mTOR functions in two distinct complexes, mTORC1 and mTORC2, whose activities and substrate specificities are regulated by complex specific cofactors, including Raptor and Rictor, respectively. Little is known regarding the relative contribution of mTORC1 versus mTORC2 in vascular endothelial cells. Using mouse models of Raptor or Rictor gene targeting, we discovered that Rictor ablation inhibited vascular endothelial growth factor (VEGF)-induced endothelial cell proliferation and assembly in vitro and angiogenesis in vivo, whereas the loss of Raptor had only a modest effect on endothelial cells (ECs). Mechanistically, the loss of Rictor reduced the phosphorylation of AKT, protein kinase Cα (PKCα), and NDRG1 without affecting the mTORC1 pathway. In contrast, the loss of Raptor increased the phosphorylation of AKT despite inhibiting the phosphorylation of S6K1, a direct target of mTORC1. Reconstitution of Rictor-null cells with myristoylated AKT (Myr-AKT) rescued vascular assembly in Rictor-deficient endothelial cells, whereas PKCα rescued proliferation defects. Furthermore, tumor neovascularization in vivo was significantly decreased upon EC-specific Rictor deletion in mice. These data indicate that mTORC2 is a critical signaling node required for VEGF-mediated angiogenesis through the regulation of AKT and PKCα in vascular endothelial cells.

Cancer initiation and malignant progression are multistep processes that involve loss of growth control, evasion of apoptosis, sustained angiogenesis, tissue invasion, and metastasis (1). Developing cancer cells stochastically acquire and selectively accumulate mutations in the genes that encode oncoproteins, tumor suppressors, and their regulators. Receptor tyrosine kinases (RTKs) are important regulators of signal transduction pathways that promote cell growth, survival, invasion, and motility during malignant progression of solid tumors (2). Dysregulation of RTKs, such as EGF receptor family members, by mutation, amplification, or overexpression, can result in increased kinase activity and ultimately oncogenic transformation. The generality of this paradigm of gain-of-function RTK signaling in cancer has been recently challenged by the discovery of the dual roles of the EPH receptors in both promoting and inhibiting oncogenesis and tumor progression in cell lines and mouse models. To date, there has been insufficient evidence from patient outcome-based studies to verify the findings from mechanistic analyses in tumor models. EPH receptors and their membrane-bound ligands, the ephrins, were originally discovered in the 1990s as axonal guidance molecules, and since that time, the EPH proteins have been found to constitute the largest family of RTKs and to be key regulators of cell–cell communication both in development and disease (3,4). The role of EPH receptors in cancer models is complex; they can either promote or inhibit malignancy, depending on ligand stimulation, signaling cross-talk, and other contextual factors (5–8). For example, EPHA2 overexpression is associated with worsened survival in human breast, prostate, and lung cancers and in glioblastoma multiforme (9–17). Overexpression of EPHA2 can induce ligand-independent signaling, resulting in increased tumor cell malignancy in vitro and accelerated tumor growth and metastasis in vivo (18,19). In keeping with these findings, reduced EPHA2 expression in the presence of short interfering RNA or targeted gene deletion inhibited tumor initiation and metastatic progression (19–21). However, ligand-dependent signaling by EPHA2 in both breast cancer and glioblastoma cell lines inhibited their malignant behavior in vitro and tumor growth in vivo (21,22). The conundrum posed by these findings is not completely resolved, and mechanisms that account for these opposing activities are just beginning to be investigated. Recently, “next-generation” DNA sequencing using large cohorts of human lung cancer samples identified various mutations in EPH receptor genes. Notably, somatic mutations in EPHA3, the gene for EPHA3, were present in 5% to 10% of lung adenocarcinomas (23–26). However, those mutations are associated with amino acid substitutions scattered throughout the receptor, and it is unclear whether these nonrecurrent mutations are “driver” or biologically neutral “passenger” genetic alterations. In addition, because EPH receptor signaling can cause either tumor promotion or tumor suppression, the biological impact of somatically mutated variants of EPHA3 in lung cancer remains unclear. In this report, we sought to characterize the functional effects of EPHA3 mutations identified in primary tumors to distinguish between the oncogenic and tumor-suppressive roles of the protein that EPHA3 encodes. We used a combination of genomic and mutational analyses in cell lines and tumor specimens to investigate the role of EPHA3 and its somatic mutations in non–small cell lung cancer (NSCLC). We performed cell proliferation and apoptosis assays in NSCLC cell lines and used mouse xenograft models to assess the function of EPHA3 in vivo. Finally, we identified molecular mechanisms by which EPHA3 regulates tumorigenicity.

Despite the success of treating EGFR-mutant lung cancer patients with EGFR tyrosine kinase inhibitors (TKI), all patients eventually acquire resistance to these therapies. Although various resistance mechanisms have been described, there are currently no FDA-approved therapies that target alternative mechanisms to treat lung tumors with acquired resistance to first-line EGFR TKI agents. Here we found that EPHA2 is overexpressed in EGFR TKI-resistant tumor cells. Loss of EPHA2 reduced the viability of erlotinib-resistant tumor cells harboring EGFRT790M mutations in vitro and inhibited tumor growth and progression in an inducible EGFRL858R+T790M-mutant lung cancer model in vivo. Targeting EPHA2 in erlotinib-resistant cells decreased S6K1-mediated phosphorylation of cell death agonist BAD, resulting in reduced tumor cell proliferation and increased apoptosis. Furthermore, pharmacologic inhibition of EPHA2 by the small-molecule inhibitor ALW-II-41-27 decreased both survival and proliferation of erlotinib-resistant tumor cells and inhibited tumor growth in vivo. ALW-II-41-27 was also effective in decreasing viability of cells with acquired resistance to the third-generation EGFR TKI AZD9291. Collectively, these data define a role for EPHA2 in the maintenance of cell survival of TKI-resistant, EGFR-mutant lung cancer and indicate that EPHA2 may serve as a useful therapeutic target in TKI-resistant tumors. Cancer Res; 76(2); 305–18. ©2016 AACR.

Angiogenic remodeling during embryonic development and in adult tissue homeostasis is orchestrated by cooperative signaling between several distinct molecular pathways, which are often exploited by tumors. Indeed, tumors upregulate proangiogenic molecules while simultaneously suppressing angiostatic pathways to recruit blood vessels for growth, survival, and metastatic spread. Understanding how cancers exploit proangiogenic and antiangiogenic signals is a key step in developing new, molecularly targeted antiangiogenic therapies. While EphA2, a receptor tyrosine kinase (RTK), is required for VEGF-induced angiogenesis, the mechanism through which these pathways intersect remains unclear. Slit2 expression is elevated in EphA2-deficient endothelium, and here it is reported that inhibiting Slit activity rescues VEGF-induced angiogenesis in cell culture and in vivo, as well as VEGF-dependent tumor angiogenesis, in EphA2-deficient endothelial cells and animals. Moreover, blocking Slit activity or Slit2 expression in EphA2-deficient endothelial cells restores VEGF-induced activation of Src and Rac, both of which are required for VEGF-mediated angiogenesis. These data suggest that EphA2 suppression of Slit2 expression and Slit angiostatic activity enables VEGF-induced angiogenesis in vitro and in vivo, providing a plausible mechanism for impaired endothelial responses to VEGF in the absence of EphA2 function. Implications: Modulation of angiostatic factor Slit2 by EphA2 receptor regulates endothelial responses to VEGF-mediated angiogenesis and tumor neovascularization. Mol Cancer Res; 13(3); 524–37. ©2014 AACR.

Eph receptor tyrosine kinases (RTKs) and their ligands, ephrins, play critical roles in development, tissue homeostasis, and cancer. Because Eph receptors are expressed in most adult stem cell niches and in many types of cancers, it has been long suspected that this family of RTKs may also regulate the function of cancer stem-like cells (CSCs). This review will focus on recent studies to elucidate the contribution of Eph/ephrin molecules in CSC self-renewal and tumorigenicity, as well as describe efforts to target these molecules in cancer. Because CSCs are often resistant to therapeutic intervention and have been shown to depend on Eph RTKs for self-renewal, targeting Eph receptors may hold promise for the treatment of drug-resistant cancers.

Recent genome-wide analyses in human lung cancer revealed that EPHA2 receptor tyrosine kinase is overexpressed in non–small cell lung cancer (NSCLC), and high levels of EPHA2 correlate with poor clinical outcome. However, the mechanistic basis for EPHA2-mediated tumor promotion in lung cancer remains poorly understood. Here, we show that the JNK/c-JUN signaling mediates EPHA2-dependent tumor cell proliferation and motility. A screen of phospho-kinase arrays revealed a decrease in phospho-c-JUN levels in EPHA2 knockdown cells. Knockdown of EPHA2 inhibited p-JNK and p-c-JUN levels in approximately 50% of NSCLC lines tested. Treatment of parental cells with SP600125, a c-JUN-NH2-kinase (JNK) inhibitor, recapitulated defects in EPHA2-deficient tumor cells, whereas constitutively activated JNK mutants were sufficient to rescue phenotypes. Knockdown of EPHA2 also inhibited tumor formation and progression in xenograft animal models in vivo. Furthermore, we investigated the role of EPHA2 in cancer stem–like cells (CSC). RNA interference-mediated depletion of EPHA2 in multiple NSCLC lines decreased the ALDH+ cancer stem–like population and tumor spheroid formation in suspension. Depletion of EPHA2 in sorted ALDH+ populations markedly inhibited tumorigenicity in nude mice. Furthermore, analysis of a human lung cancer tissue microarray revealed a significant, positive association between EPHA2 and ALDH expression, indicating an important role for EPHA2 in human lung CSCs. Collectively, these studies revealed a critical role of JNK signaling in EPHA2-dependent lung cancer cell proliferation and motility and a role for EPHA2 in CSC function, providing evidence for EPHA2 as a potential therapeutic target in NSCLC. Cancer Res; 74(9); 2444–54. ©2014 AACR.

VAPB (VAMP- associated protein B) is an ER protein that regulates multiple biological functions. Although aberrant expression of VAPB is associated with breast cancer, its function in tumor cells is poorly understood. In this report, we provide evidence that VAPB regulates breast tumor cell proliferation and AKT activation. VAPB protein expression is elevated in primary and metastatic tumor specimens, and VAPB mRNA expression levels correlated negatively with patient survival in two large breast tumor datasets. Overexpression of VAPB in mammary epithelial cells increased cell growth, whereas VAPB knockdown in tumor cells inhibited cell proliferation in vitro and suppressed tumor growth in orthotopic mammary gland allografts. The growth regulation of mammary tumor cells controlled by VAPB appears to be mediated, at least in part, by modulation of AKT activity. Overexpression of VAPB in MCF10A-HER2 cells enhances phosphorylation of AKT. In contrast, knockdown of VAPB in MMTV-Neu tumor cells inhibited pAKT levels. Pharmacological inhibition of AKT significantly reduced three-dimensional spheroid growth induced by VAPB. Collectively, the genetic, functional and mechanistic analyses suggest a role of VAPB in tumor promotion in human breast cancer.