Phosphatidylinositol-3-OH kinase signalling is spatially organized at endosomal compartments by microtubule-associated protein 4

A p85 isoform switch enhances PI3K activation on endosomes by a MAP4- and PI3P-dependent mechanism

Phosphatidylinositol 3-kinase α (PI3Kα) is a heterodimer of p110α catalytic and p85 adaptor subunits that is activated by agonist-stimulated receptor tyrosine kinases. Although p85α recruits p110α to activated receptors on membranes, p85α loss, which occurs commonly in cancer, paradoxically promotes agonist-stimulated PI3K/Akt signaling. p110α localizes to microtubules via microtubule-associated protein 4 (MAP4), facilitating its interaction with activated receptor kinases on endosomes to initiate PI3K/Akt signaling. Here, we demonstrate that in response to agonist stimulation and p85α knockdown, the residual p110α, coupled predominantly to p85β, exhibits enhanced recruitment with receptor tyrosine kinases to endosomes. Moreover, the p110α C2 domain binds PI3-phosphate, and this interaction is also required to recruit p110α to endosomes and for PI3K/Akt signaling. Stable knockdown of p85α, which mimics the reduced p85α levels observed in cancer, enhances cell growth and tumorsphere formation, and these effects are abrogated by MAP4 or p85β knockdown, underscoring their role in the tumor-promoting activity of p85α loss.

Role of tumor-derived exosomes mediated immune cell reprograming in cancer

Tumor-derived exosomes (TDEs), as topologies of tumor cells, not only carry biological information from the mother, but also act as messengers for cellular communication. It has been demonstrated that TDEs play a key role in inducing an immunosuppressive tumor microenvironment (TME). They can reprogram immune cells indirectly or directly by delivering inhibitory proteins, cytokines, RNA and other substances. They not only inhibit the maturation and function of dendritic cells (DCs) and natural killer (NK) cells, but also remodel M2 macrophages and inhibit T cell infiltration to promote immunosuppression and create a favorable ecological niche for tumor growth, invasion and metastasis. Based on the specificity of TDEs, targeting TDEs has become a new strategy to monitor tumor progression and enhance treatment efficacy. This paper reviews the intricate molecular mechanisms underlying the immunosuppressive effects induced by TDEs to establish a theoretical foundation for cancer therapy. Additionally, the challenges of TDEs as a novel approach to tumor treatment are discussed.

EVA1A reverses lenvatinib resistance in hepatocellular carcinoma through regulating PI3K/AKT/p53 signaling axis

Lenvatinib is a commonly used first-line drug for the treatment of advanced hepatocellular carcinoma (HCC). However, its clinical efficacy is limited due to the drug resistance. EVA1A was a newly identified tumor suppressor, nevertheless, the impact of EVA1A on resistance to lenvatinib treatment in HCC and the potential molecular mechanisms remain unknown. In this study, the expression of EVA1A in HCC lenvatinib-resistant cells is decreased and its low expression was associated with a poor prognosis of HCC. Overexpression of EVA1A reversed lenvatinib resistance in vitro and in vivo, as demonstrated by its ability to promote cell apoptosis and inhibit cell proliferation, invasion, migration, EMT, and tumor growth. Silencing EVA1A in lenvatinib-sensitive parental HCC cells exerted the opposite effect and induced resistance to lenvatinib. Mechanistically, upregulated EVA1A inhibited the PI3K/AKT/MDM2 signaling pathway, resulting in a reduced interaction between MDM2 and p53, thereby stabilizing p53 and enhancing its antitumor activity. In addition, upregulated EVA1A suppressed the PI3K/AKT/mTOR signaling pathway and promoted autophagy, leading to the degradation of mutant p53 and attenuating its oncogenic impact. On the contrary, loss of EVA1A activated the PI3K/AKT/MDM2 signaling pathway and inhibited autophagy, promoting p53 proteasomal degradation and mutant p53 accumulation respectively. These findings establish a crucial role of EVA1A loss in driving lenvatinib resistance involving a mechanism of modulating PI3K/AKT/p53 signaling axis and suggest that upregulating EVA1A is a promising therapeutic strategy for alleviating resistance to lenvatinib, thereby improving the efficacy of HCC treatment.

Endocytic vesicles act as vehicles for glucose uptake in response to growth factor stimulation

Glycolysis is a fundamental cellular process, yet its regulatory mechanisms remain incompletely understood. Here, we show that a subset of glucose transporter 1 (GLUT1/SLC2A1) co-endocytoses with platelet-derived growth factor (PDGF) receptor (PDGFR) upon PDGF-stimulation. Furthermore, multiple glycolytic enzymes localize to these endocytosed PDGFR/GLUT1-containing vesicles adjacent to mitochondria. Contrary to current models, which emphasize the importance of glucose transporters on the cell surface, we find that PDGF-stimulated glucose uptake depends on receptor/transporter endocytosis. Our results suggest that growth factors generate glucose-loaded endocytic vesicles that deliver glucose to the glycolytic machinery in proximity to mitochondria, and argue for a new layer of regulation for glycolytic control governed by cellular membrane dynamics.

DTX3L Accelerates Pancreatic cancer Progression via FAK/PI3K/AKT Axis

DTX3L (Deltex E3 ubiquitin ligase 3 L) is an E3 ubiquitin ligase, a member of the deltex family. It is also known as B-lymphoma and BAL-associated protein (BBAP). DTX3L has been proven to play an important role in various tumor development; however, its role in pancreatic cancer remains unknown. So, we analyzed the DTX3L expression in pancreatic cancer based on the TCGA database and verified it in our samples by qRT‑PCR and western blot. We identified that DTX3L was highly expressed in pancreatic cancer, and its expression level was significantly negatively correlated with patients' survival. Using CCK8, colony formation, transwell, and wound healing assays, we found that upregulated DTX3L promotes pancreatic cancer cell proliferation, invasion, and migration. Mechanically, DTX3L combined with EGFR (epidermal growth factor receptor) and prevented the ubiquitination degradation of it. Upregulated EGFR activated the FAK/PI3K/Akt pathway and promoted the progression of pancreatic cancer. Moreover, we found that DTX3L can weaken pancreatic cancer cells' sensitivity to chemotherapy using the orthotopic implant tumor model. In conclusion, DTX3L accelerates pancreatic cancer progression by EGFR dependent FAK/PI3K/Akt pathway activation and may become a potential target for pancreatic cancer treatment.

Non-catalytic role of phosphoinositide 3-kinase in mesenchymal cell migration through non-canonical induction of p85β/AP2-mediated endocytosis

Class IA phosphoinositide 3-kinase (PI3K) galvanizes fundamental cellular processes such as migration, proliferation, and differentiation. To enable these multifaceted roles, the catalytic subunit p110 utilizes the multi-domain, regulatory subunit p85 through its inter SH2 domain (iSH2). In cell migration, its product PI(3,4,5)P3 generates locomotive activity. While non-catalytic roles are also implicated, underlying mechanisms and their relationship to PI(3,4,5)P3 signaling remain elusive. Here, we report that a disordered region of iSH2 contains AP2 binding motifs which can trigger clathrin and dynamin-mediated endocytosis independent of PI3K catalytic activity. The AP2 binding motif mutants of p85 aberrantly accumulate at focal adhesions and increase both velocity and persistency in fibroblast migration. We thus propose the dual functionality of PI3K in the control of cell motility, catalytic and non-catalytic, arising distinctly from juxtaposed regions within iSH2.

MAP4 acts as an oncogene and prognostic marker and affects radioresistance by mediating epithelial-mesenchymal transition in lung adenocarcinoma

PURPOSE

To explore the effect of microtubule-associated protein 4 (MAP4) on lung adenocarcinoma cells in vitro and evaluate its prognostic value. Radioresistance, indicated by reduced efficiency of radiotherapy, is a key factor in treatment failure in lung adenocarcinoma (LADC). This study aims to explore the primary mechanism underlying the relationship between MAP4 and radiation resistance in lung adenocarcinoma.

METHODS

We analysed the expression of MAP4 in lung adenocarcinoma by real-time quantitative polymerase chain reaction (RT‒qPCR), immunohistochemistry (IHC) and bioinformatics online databases, evaluated the prognostic value of MAP4 in lung adenocarcinoma and studied its relationship with clinicopathological parameters. Cox regression analysis and least absolute shrinkage and selection operator (LASSO) regression analysis identified independent prognostic factors associated with lung adenocarcinoma that were used to construct a nomogram, internal validation was performed. We then evaluated the accuracy and clinical validity of the model using a receiver operating characteristic (ROC) curve, time-dependent C-index analysis, a calibration curve, and decision curve analysis (DCA). Scratch assays and transwell assays were used to explore the effect of MAP4 on the migration and invasion of lung adenocarcinoma cells. Bioinformatics analysis, RT‒qPCR, Cell Counting Kit-8 (CCK-8) assays and Western blot experiments were used to study the relationship between MAP4, epithelial-mesenchymal transition (EMT) and radiation resistance in lung adenocarcinoma.

RESULTS

MAP4 expression in lung adenocarcinoma tissues was significantly higher than that in adjacent normal lung tissues. High expression of MAP4 is associated with poorer overall survival (OS) in patients with lung adenocarcinoma. Univariate Cox regression analysis showed that pT stage, pN stage, TNM stage and MAP4 expression level were significantly associated with poorer OS in LADC patients. Multivariate Cox regression analysis and LASSO regression analysis showed that only the pT stage and MAP4 expression level were associated with LADC prognosis. The nomogram constructed based on the pT stage and MAP4 expression showed good predictive accuracy. ROC curves, corrected C-index values, calibration curves, and DCA results showed that the nomogram performed well in both the training and validation cohorts and had strong clinical applicability. The results of in vitro experiments showed that the downregulation of MAP4 significantly affected the migration and invasion of lung adenocarcinoma cells. MAP4 was strongly correlated with EMT-related markers. Further studies suggested that the downregulation of MAP4 can affect the viability of lung adenocarcinoma cells after irradiation and participate in the radiation resistance of lung adenocarcinoma cells by affecting EMT.

CONCLUSION

MAP4 is highly expressed in lung adenocarcinoma; it may affect prognosis by promoting the migration and invasion of cancer cells. We developed a nomogram including clinical factors and MAP4 expression that can be used for prognosis prediction in patients with lung adenocarcinoma. MAP4 participates in radiation resistance in lung adenocarcinoma by regulating the radiation-induced EMT process. MAP4 may serve as a biomarker for lung adenocarcinoma prognosis evaluation and as a new target for improving radiosensitivity.

CHKB-AS1 enhances proliferation and resistance to NVP-BEZ235 of renal cancer cells via regulating the phosphorylation of MAP4 and PI3K/AKT/mTOR signaling

Targeted therapy is pivotal in renal carcinoma treatment, and the dual-inhibitor NVP-BEZ235 has emerged as a promising candidate in preliminary studies. Its effectiveness against renal carcinoma and the mechanisms underlying potential resistance, however, warrant further exploration. This study aims to elucidate these aspects, enhancing our understanding of NVP-BEZ235's future clinical utility. To investigate resistance mechanisms, renal cancer cell lines were exposed to progressively increasing concentrations of NVP-BEZ235, leading to the development of stable resistance. These resistant cells underwent extensive RNA-sequencing analysis. We implemented gene interference techniques using plasmid vectors and lentivirus and conducted regular IC50 assessments. To pinpoint the role of LncRNAs, we utilized FISH and immunofluorescence staining assays, supplemented by RNA pull-down and RIP assays to delineate interactions between LncRNA and its RNA-binding protein (RBP). Further, Western blotting and qRT-PCR were employed to examine alterations in signaling pathways, with an animal model providing additional validation. Our results show a marked increase in the IC50 of NVP-BEZ235 in resistant cell lines compared to their parental counterparts. A significant revelation was the role of LncRNA-CHKB-AS1 in mediating drug resistance. We observed dysregulated expression of CHKB-AS1 in both clinical samples of clear cell renal cell carcinoma (ccRCC) and cell lines. In vivo experiments further substantiated our findings, showing that CHKB-AS1 overexpression significantly enhanced tumor growth and resistance to NVP-BEZ235 in a subcutaneous tumorigenesis model, as evidenced by increased tumor volume and weight, whereas CHKB-AS1 knockdown led to a marked reduction in these parameters. Critically, CHKB-AS1 was identified to interact with MAP4, a key regulator in the phosphorylation of the PI3k/Akt/mTOR pathway. This interaction contributes to a diminished antitumor effect of NVP-BEZ235, highlighting the intricate mechanism through which CHKB-AS1 modulates drug resistance pathways, potentially impacting therapeutic strategies against renal carcinoma.

Regulation of Cell Adhesion and Migration via Microtubule Cytoskeleton Organization, Cell Polarity, and Phosphoinositide Signaling

The capacity for cancer cells to metastasize to distant organs depends on their ability to execute the carefully choreographed processes of cell adhesion and migration. As most human cancers are of epithelial origin (carcinoma), the transcriptional downregulation of adherent/tight junction proteins (e.g., E-cadherin, Claudin and Occludin) with the concomitant gain of adhesive and migratory phenotypes has been extensively studied. Most research and reviews on cell adhesion and migration focus on the actin cytoskeleton and its reorganization. However, metastasizing cancer cells undergo the extensive reorganization of their cytoskeletal system, specifically in originating/nucleation sites of microtubules and their orientation (e.g., from non-centrosomal to centrosomal microtubule organizing centers). The precise mechanisms by which the spatial and temporal reorganization of microtubules are linked functionally with the acquisition of an adhesive and migratory phenotype as epithelial cells reversibly transition into mesenchymal cells during metastasis remains poorly understood. In this Special Issue of "Molecular Mechanisms Underlying Cell Adhesion and Migration", we highlight cell adhesion and migration from the perspectives of microtubule cytoskeletal reorganization, cell polarity and phosphoinositide signaling.

Multiple forms of cell death: A focus on the PI3K/AKT pathway

Cell death is a natural biological process that occurs in living organisms. Since 1963, extensive research has shed light on the occurrence, progress, and final outcome of cell death. According to different cell phenotypes, it is classified into different types, including apoptosis, pyroptosis, necroptosis, autophagy, ferroptosis, cuproptosis, and so on. However, regardless of the form of cell death, what we ultimately expect is the disappearance of abnormal cells, such as tumor cells, while normal cells survive. As a result, it is vital to investigate the details of cell death, including death triggers, potent regulators, and executioners. Although significant progress has been made in understanding molecular pathways of cell death, many aspects remain unclear because of the complex regulatory networks in cells. Among them, the phosphoinositide-3-kinase (PI3K)/protein kinase B(AKT) pathway is discovered to be a crucial regulator of the cell death process. AKT, as a proto-oncogene, has become a major focus of attention in the medical community due to its role in regulating a multiplicity of cellular functions counting metabolism, immunity, proliferation, survival, transcription, and protein synthesis. Here, we explored the connection between the PI3K/AKT pathway and cell death, aiming to enhance our comprehension of the mechanism underlying this process. Such knowledge may pave the way for the subsequent development of more effective disease treatments, such as finding suitable targets for drug intervention.

Regulation of Phosphoinositide Signaling by Scaffolds at Cytoplasmic Membranes

Cytoplasmic phosphoinositides (PI) are critical regulators of the membrane-cytosol interface that control a myriad of cellular functions despite their low abundance among phospholipids. The metabolic cycle that generates different PI species is crucial to their regulatory role, controlling membrane dynamics, vesicular trafficking, signal transduction, and other key cellular events. The synthesis of phosphatidylinositol (3,4,5)-triphosphate (PI3,4,5P3) in the cytoplamic PI3K/Akt pathway is central to the life and death of a cell. This review will focus on the emerging evidence that scaffold proteins regulate the PI3K/Akt pathway in distinct membrane structures in response to diverse stimuli, challenging the belief that the plasma membrane is the predominant site for PI3k/Akt signaling. In addition, we will discuss how PIs regulate the recruitment of specific scaffolding complexes to membrane structures to coordinate vesicle formation, fusion, and reformation during autophagy as well as a novel lysosome repair pathway.

Epidermal growth factor receptor promotes infectious spleen and kidney necrosis virus invasion via PI3K-Akt signaling pathway

Infectious spleen and kidney necrosis virus disease (ISKNVD) caused significant economic losses to the fishery industry. Epidermal growth factor receptor (EGFR), phosphatidylinositide 3-kinase (PI3K) played an important role in ISKNV invasion. However, the molecular regulatory mechanisms among EGFR, PI3K-Akt, and ISKNV invasion are not clear. In this study, ISKNV infection rapidly induced EGFR activation. While, EGFR activation promoted virus entry, but EGFR inhibitors and specific RNA (siRNA) decreased virus invasion. The PI3K-Akt as downstream signalling of EGFR was activated upon ISKNV infection. Consistent with the trends of EGFR, Akt activation increased ISKNV entry into cells, Akt inhibition by specific inhibitor or siRNA decreased ISKNV invasion. Akt silencing combination with EGFR activation showed that EGFR activation regulation ISKNV invasion is required for activation of the Akt signalling pathway. Those data demonstrated that ISKNV-induced EGFR activation positively regulated virus invasion by PI3K-Akt pathway and provided a better understanding of the mechanism of EGFR-PI3K-Akt involved in ISKNV invasion.

Endocytic vesicles act as vehicles for glucose uptake in response to growth factor stimulation

Glycolysis is a fundamental cellular process, yet its regulatory mechanisms remain incompletely understood. Here, we show that a subset of glucose transporter 1 (GLUT1/SLC2A1) co-endocytoses with platelet-derived growth factor (PDGF) receptor (PDGFR) upon PDGF-stimulation. Furthermore, multiple glycolytic enzymes localize to these endocytosed PDGFR/GLUT1-containing vesicles adjacent to mitochondria. Contrary to current models, which emphasize the importance of glucose transporters on the cell surface, we find that PDGF-stimulated glucose uptake depends on receptor/transporter endocytosis. Our results suggest that growth factors generate glucose-loaded endocytic vesicles that deliver glucose to the glycolytic machinery in proximity to mitochondria, and argue for a new layer of regulation for glycolytic control governed by cellular membrane dynamics.

The regulatory role of PI3K in ageing-related diseases

Ageing is a physiological/pathological process accompanied by the progressive damage of cell function, triggering various ageing-related disorders. Phosphatidylinositol 3-kinase (PI3K), which serves as one of the central regulators of ageing, is closely associated with cellular characteristics or molecular features, such as genome instability, telomere erosion, epigenetic alterations, and mitochondrial dysfunction. In this review, the PI3K signalling pathway was firstly thoroughly explained. The link between ageing pathogenesis and the PI3K signalling pathway was then summarized. Finally, the key regulatory roles of PI3K in ageing-related illnesses were investigated and stressed. In summary, we revealed that drug development and clinical application targeting PI3K is one of the focal points for delaying ageing and treating ageing-related diseases in the future.

Ketamine Induces Delirium-Like Behavior and Interferes With Endosomal Tau Trafficking

BACKGROUND

Ketamine is an intravenous anesthetic. However, whether ketamine can induce neurotoxicity and neurobehavioral deficits remains largely unknown. Delirium is a syndrome of acute brain dysfunction associated with anesthesia and surgery in patients, and tau protein may contribute to postoperative delirium. Finally, ketamine may affect the function of the endosome, the key organelle for tau release from neurons. Therefore, we set out to determine the effects of ketamine on delirium-like behavior in mice and on tau trafficking in cultured cells.

METHODS

We used the buried-food test, open-field test, and Y-maze test in adult mice to assess the presence of delirium-like behavior in mice. We quantified tau amounts in the serum of mice. We used cell fraction methods to determine the effects of ketamine on tau intracellular trafficking, extracellular release, and endosome trafficking in cultured cells.

RESULTS

Ketamine induced delirium-like behavior in mice and increased tau amounts in serum of mice. The ketamine treatments also led to increased accumulation of endosomes, as evidenced by increased endosomal markers Rab5 and Rab7. Moreover, ketamine inhibited endosome maturation, demonstrated by decreased membrane-bound but increased cytoplasm amounts of Rab5 and Rab7. Consequently, ketamine increased tau in the endosomes of cultured cells and the cell culture medium.

CONCLUSIONS

These data suggest that ketamine may interfere with intracellular tau trafficking and induce delirium-like behavior, promoting future research regarding the potential neurotoxicity of anesthetics.

PI3K-alpha translocation mediates nuclear PtdIns(3,4,5)P3 effector signaling in colorectal cancer

The canonical view of phosphatidylinositol 3-kinase alpha (PI3Kα) signaling describes PtdIns(3,4,5)P₃ generation and activation of downstream effectors at the plasma membrane or at microtubule-bound endosomes. Here, we show that colorectal cancer (CRC) cell lines exhibit a diverse plasma membrane-nuclear distribution of PI3Kα, controlling corresponding levels of subcellular PtdIns(3,4,5)P₃ pools. PI3Kα nuclear translocation was mediated by the importin β-dependent nuclear import pathway. By PtdIns(3,4,5)P₃ affinity capture mass spectrometry done in the presence of SDS on CRC cell lines with PI3Kα nuclear localization, we identified 867 potential nuclear PtdIns(3,4,5)P₃ effector proteins. Nuclear PtdIns(3,4,5)P₃ interactome proteins were characterized by non-canonical PtdIns(3,4,5)P₃ binding domains and showed overrepresentation for nuclear membrane, nucleolus and nuclear speckles. The nuclear PtdIns(3,4,5)P₃ interactome was enriched for proteins related to RNA metabolism, with splicing reporter assays and SC-35 foci staining suggesting a role of EGF-stimulated nuclear PI3Kα signaling in modulating pre-mRNA splicing. In patient tumors, nuclear p110α staining was associated with lower T stage and mucinous histology. These results indicate that PI3Kα translocation mediates nuclear PtdIns(3,4,5)P₃ effector signaling in human CRC, modulating signaling responses.

Microtubule-associated protein 4 promotes epithelial mesenchymal transition in hepatocellular cancer cells via regulating GSK3β/β-catenin pathway

Metastasis is a major obstacle in the treatment of hepatocellular carcinoma (HCC). Microtubule-associated protein 4 (MAP4) plays an important role as a coordinator between microtubules and microfilaments. However, the role of MAP4 in HCC migration and epithelial mesenchymal transition (EMT) is unclear. We compared the protein and mRNA levels of MAP4 in human HCC and adjacent normal tissues using western blotting, immunohistochemistry and RT-qPCR. The migration and invasion abilities and the levels of EMT markers (E-Cadherin, N-Cadherin, Vimentin, and Snail) were compared between MAP4-knockdown and MAP4-overexpressed HCC cells. Finally, we examined whether β-catenin and glycogen synthase kinase 3β (GSK3β) are involved in the stimulatory effects of MAP4 on HCC migration, invasion and EMT. The results revealed that MAP4 levels were higher in the HCC tissues than in the normal hepatic tissues. More importantly, MAP4 knockdown suppressed migration and invasion abilities and EMT processes in HCC cells, which were confirmed by the stimulatory effects of MAP4 overexpression on EMT processes in HCC cells. Further evidence demonstrated that the up-regulation of β-catenin activity induced by the interaction between MAP4 and GSK3β possibly accounted for the pro-migration and pro-EMT effects of MAP4 on HCC cells. Taken together, these results suggest that MAP4 promotes migration, invasion, and EMT in HCC cells by regulating the GSK3β/β-catenin pathway.

PI(3,5)P 2 Controls the Signaling Activity of Class I PI3K

3'-Phosphoinositides are ubiquitous cellular lipids that play pivotal regulatory roles in health and disease. Generation of 3'-phosphoinositides are driven by three families of phosphoinositide 3-kinases (PI3K) but the mechanisms underlying their regulation and cross-talk are not fully understood. Among 3'-phosphoinositides, phosphatidylinositol-3,5-bisphosphate (PI(3,5)P 2 ) remains the least understood species in terms of its spatiotemporal dynamics and physiological function due to the lack of specific probes. By means of spatiotemporally resolved in situ quantitative imaging of PI(3,5)P 2 using a newly developed ratiometric PI(3,5)P 2 sensor we demonstrate that a special pool of PI(3,5)P 2 is generated on lysosomes and late endosomes in response to growth factor stimulation. This PI(3,5)P 2 pool, the formation of which is mediated by Class II PI3KC2β and PIKFyve, plays a crucial role in terminating the activity of growth factor-stimulated Class I PI3K, one of the most frequently mutated proteins in cancer, via specific interaction with its regulatory p85 subunit. Cancer-causing mutations of Class I PI3K inhibit the p85-PI(3,5)P 2 interaction and thereby induce sustained activation of Class I PI3K. Our results unravel a hitherto unknown tight regulatory interplay between Class I and II PI3Ks mediated by PI(3,5)P 2 , which may be important for controlling the strength of PI3K-mediated growth factor signaling. These results also suggest a new therapeutic possibility of treating cancer patients with p85 mutations.

Non-catalytic role of phosphoinositide 3-kinase in mesenchymal cell migration through non-canonical induction of p85β/AP-2-mediated endocytosis

Class IA phosphoinositide 3-kinase (PI3K) galvanizes fundamental cellular processes such as migration, proliferation, and differentiation. To enable multifaceted roles, the catalytic subunit p110 utilizes a multi-domain, regulatory subunit p85 through its inter SH2 domain (iSH2). In cell migration, their product PI(3,4,5)P3 generates locomotive activity. While non-catalytic roles are also implicated, underlying mechanisms and its relationship to PI(3,4,5)P3 signaling remain elusive. Here, we report that a disordered region of iSH2 contains previously uncharacterized AP-2 binding motifs which can trigger clathrin and dynamin-mediated endocytosis independent of PI3K catalytic activity. The AP-2 binding motif mutants of p85 aberrantly accumulate at focal adhesions and upregulate both velocity and persistency in fibroblast migration. We thus propose the dual functionality of PI3K in the control of cell motility, catalytic and non-catalytic, arising distinctly from juxtaposed regions within iSH2.

Non-catalytic role of phosphoinositide 3-kinase in mesenchymal cell migration through non-canonical induction of p85β/AP-2-mediated endocytosis

Class IA phosphoinositide 3-kinase (PI3K) galvanizes fundamental cellular processes such as migration, proliferation, and differentiation. To enable multifaceted roles, the catalytic subunit p110 utilizes a multidomain, regulatory subunit p85 through its inter SH2 domain (iSH2). In cell migration, their product PI(3,4,5)P3 generates locomotive activity. While non-catalytic roles are also implicated, underlying mechanisms and its relationship to PI(3,4,5)P3 signaling remain elusive. Here, we report that a disordered region of iSH2 contains previously uncharacterized AP-2 binding motifs which can trigger clathrin and dynamin-mediated endocytosis independent of PI3K catalytic activity. The AP-2 binding motif mutants of p85 aberrantly accumulate at focal adhesions and upregulate both velocity and persistency in fibroblast migration. We thus propose the dual functionality of PI3K in the control of cell motility, catalytic and non-catalytic, arising distinctly from juxtaposed regions within iSH2.

NUF2 overexpression contributes to epithelial ovarian cancer progression via ERBB3-mediated PI3K-AKT and MAPK signaling axes

Introduction

NDC80 kinetochore complex component (NUF2) is upregulated and plays an important role in various human cancers. However, the function and mechanism of NUF2 in epithelial ovarian cancer (EOC) remain unclear.

Methods

NUF2 expression was detected in EOC tissues and cell lines. The effects of NUF2 downregulation on cell proliferation, migration and invasion in EOC were analyzed by CCK-8 and Transwell assays. Meanwhile, the effect of NUF2 downregulation on tumor growth in vivo was determined by xenograft tumor models. The mechanisms by which NUF2 regulates EOC progression were detected by RNA sequencing and a series of in vitro assays.

Results

We showed that NUF2 was significantly upregulated in EOC tissues and cell lines, and high NUF2 expression was associated with FIGO stage, pathological grade and poor EOC prognosis. NUF2 downregulation decreased cell proliferation, migration, invasion and tumor growth in nude mice. RNA sequencing studies showed that NUF2 knockdown inhibited several genes enriched in the phosphatidylinositol-4,5-bisphosphate 3-kinase (PI3K)-AKT serine/threonine kinase (AKT) and mitogen-activated protein kinase (MAPK) signaling pathways. Erb-B2 receptor tyrosine kinase 3 (ERBB3) was the key factor involved in both of the above pathways. We found that ERBB3 silencing could inhibit EOC progression and repress activation of the PI3K-AKT and MAPK signaling pathways. Furthermore, the exogenous overexpression of ERBB3 partially reversed the inhibitory effects on EOC progression induced by NUF2 downregulation, while LY294002 and PD98059 partially reversed the effects of ERBB3 upregulation.

Conclusion

These results showed that NUF2 promotes EOC progression through ERBB3-induced activation of the PI3K-AKT and MAPK signaling axes. These findings suggest that NUF2 might be a potential therapeutic target for EOC.

Regulation of EGF-stimulated activation of the PI-3K/AKT pathway by exocyst-mediated exocytosis

The phosphoinositide-3 kinase (PI-3K)/AKT cell survival pathway is an important pathway activated by EGFR signaling. Here we show, that in addition to previously described critical components of this pathway, i.e., the docking protein Gab1, the PI-3K/AKT pathway in epithelial cells is regulated by the exocyst complex, which is a vesicle tether that is essential for exocytosis. Using live-cell imaging, we demonstrate that PI(3,4,5)P₃ levels fluctuate at the membrane on a minutes time scale and that these fluctuations are associated with local PI(3,4,5)P₃ increases at sites where recycling vesicles undergo exocytic fusion. Supporting a role for exocytosis in PI(3,4,5)P₃ generation, acute promotion of exocytosis by optogenetically driving exocyst-mediated vesicle tethering up-regulates PI(3,4,5)P₃ production and AKT activation. Conversely, acute inhibition of exocytosis using Endosidin2, a small-molecule inhibitor of the exocyst subunit Exo70 (also designated EXOC7), or inhibition of exocyst function by siRNA-mediated knockdown of the exocyst subunit Sec15 (EXOC6), impairs PI(3,4,5)P₃ production and AKT activation induced by EGF stimulation of epithelial cells. Moreover, prolonged inhibition of EGF signaling by EGFR tyrosine kinase inhibitors results in spontaneous reactivation of AKT without a concomitant relief of EGFR inhibition. However, this reactivation can be negated by acutely inhibiting the exocyst. These experiments demonstrate that exocyst-mediated exocytosis-by regulating PI(3,4,5)P₃ levels at the plasma membrane-subserves activation of the PI-3K/AKT pathway by EGFR in epithelial cells.

Spatially resolved phosphoproteomics reveals fibroblast growth factor receptor recycling-driven regulation of autophagy and survival

Receptor Tyrosine Kinase (RTK) endocytosis-dependent signalling drives cell proliferation and motility during development and adult homeostasis, but is dysregulated in diseases, including cancer. The recruitment of RTK signalling partners during endocytosis, specifically during recycling to the plasma membrane, is still unknown. Focusing on Fibroblast Growth Factor Receptor 2b (FGFR2b) recycling, we reveal FGFR signalling partners proximal to recycling endosomes by developing a Spatially Resolved Phosphoproteomics (SRP) approach based on APEX2-driven biotinylation followed by phosphorylated peptides enrichment. Combining this with traditional phosphoproteomics, bioinformatics, and targeted assays, we uncover that FGFR2b stimulated by its recycling ligand FGF10 activates mTOR-dependent signalling and ULK1 at the recycling endosomes, leading to autophagy suppression and cell survival. This adds to the growing importance of RTK recycling in orchestrating cell fate and suggests a therapeutically targetable vulnerability in ligand-responsive cancer cells. Integrating SRP with other systems biology approaches provides a powerful tool to spatially resolve cellular signalling.

Spatially resolved phosphoproteomics reveals fibroblast growth factor receptor recycling-driven regulation of autophagy and survival

Receptor Tyrosine Kinase (RTK) endocytosis-dependent signalling drives cell proliferation and motility during development and adult homeostasis, but is dysregulated in diseases, including cancer. The recruitment of RTK signalling partners during endocytosis, specifically during recycling to the plasma membrane, is still unknown. Focusing on Fibroblast Growth Factor Receptor 2b (FGFR2b) recycling, we reveal FGFR signalling partners proximal to recycling endosomes by developing a Spatially Resolved Phosphoproteomics (SRP) approach based on APEX2-driven biotinylation followed by phosphorylated peptides enrichment. Combining this with traditional phosphoproteomics, bioinformatics, and targeted assays, we uncover that FGFR2b stimulated by its recycling ligand FGF10 activates mTOR-dependent signalling and ULK1 at the recycling endosomes, leading to autophagy suppression and cell survival. This adds to the growing importance of RTK recycling in orchestrating cell fate and suggests a therapeutically targetable vulnerability in ligand-responsive cancer cells. Integrating SRP with other systems biology approaches provides a powerful tool to spatially resolve cellular signalling.

Glutamyl-prolyl-tRNA synthetase 1 coordinates early endosomal anti-inflammatory AKT signaling

The AKT signaling pathway plays critical roles in the resolution of inflammation. However, the underlying mechanisms of anti-inflammatory regulation and signal coordination remain unclear. Here, we report that anti-inflammatory AKT signaling is coordinated by glutamyl-prolyl-tRNA synthetase 1 (EPRS1). Upon inflammatory activation, AKT specifically phosphorylates Ser999 of EPRS1 in the cytoplasmic multi-tRNA synthetase complex, inducing release of EPRS1. EPRS1 compartmentalizes AKT to early endosomes via selective binding to the endosomal membrane lipid phosphatidylinositol 3-phosphate and assembles an AKT signaling complex specific for anti-inflammatory activity. These events promote AKT activation-mediated GSK3β phosphorylation, which increase anti-inflammatory cytokine production. EPRS1-deficient macrophages do not assemble the early endosomal complex and consequently exacerbate inflammation, decreasing the survival of EPRS1-deficient mice undergoing septic shock and ulcerative colitis. Collectively, our findings show that the housekeeping protein EPRS1 acts as a mediator of inflammatory homeostasis by coordinating compartment-specific AKT signaling.

The orchestrated signaling by PI3Kα and PTEN at the membrane interface

The oncogene PI3Kα and the tumor suppressor PTEN represent two antagonistic enzymatic activities that regulate the interconversion of the phosphoinositide lipids PI(4,5)P2 and PI(3,4,5)P3 in membranes. As such, they are defining components of phosphoinositide-based cellular signaling and membrane trafficking pathways that regulate cell survival, growth, and proliferation, and are often deregulated in cancer. In this review, we highlight aspects of PI3Kα and PTEN interplay at the intersection of signaling and membrane trafficking. We also discuss the mechanisms of PI3Kα- and PTEN- membrane interaction and catalytic activation, which are fundamental for our understanding of the structural and allosteric implications on signaling at the membrane interface and may aid current efforts in pharmacological targeting of these proteins.

A p53-phosphoinositide signalosome regulates nuclear AKT activation

The tumour suppressor p53 and PI3K-AKT pathways have fundamental roles in the regulation of cell growth and apoptosis, and are frequently mutated in cancer. Here, we show that genotoxic stress induces nuclear AKT activation through a p53-dependent mechanism that is distinct from the canonical membrane-localized PI3K-AKT pathway. Following genotoxic stress, a nuclear PI3K binds p53 in the non-membranous nucleoplasm to generate a complex of p53 and phosphatidylinositol 3,4,5-trisphosphate (PtdIns(3,4,5)P₃), which recruits AKT, PDK1 and mTORC2 to activate AKT and phosphorylate FOXO proteins, thereby inhibiting DNA damage-induced apoptosis. Wild-type p53 activates nuclear AKT in an on/off fashion following stress, whereas mutant p53 dose-dependently stimulates high basal AKT activity. The p53-PtdIns(3,4,5)P₃ complex is dephosphorylated to p53-phosphatidylinositol 4,5-bisphosphate by PTEN to inhibit AKT activation. The nuclear p53-phosphoinositide signalosome is distinct from the canonical membrane-localized pathway and insensitive to PI3K inhibitors currently in the clinic, which underscores its therapeutic relevance.

Reducing PDK1/Akt Activity: An Effective Therapeutic Target in the Treatment of Alzheimer's Disease

Alzheimer’s disease (AD) is a common age-related neurodegenerative disease that leads to memory loss and cognitive function damage due to intracerebral neurofibrillary tangles (NFTs) and amyloid-β (Aβ) protein deposition. The phosphoinositide-dependent protein kinase (PDK1)/protein kinase B (Akt) signaling pathway plays a significant role in neuronal differentiation, synaptic plasticity, neuronal survival, and neurotransmission via the axon–dendrite axis. The phosphorylation of PDK1 and Akt rises in the brain, resulting in phosphorylation of the TNF-α-converting enzyme (TACE) at its cytoplasmic tail (the C-terminal end), changing its internalization as well as its trafficking. The current review aimed to explain the mechanisms of the PDK1/Akt/TACE signaling axis that exerts its modulatory effect on AD physiopathology. We provide an overview of the neuropathological features, genetics, Aβ aggregation, Tau protein hyperphosphorylation, neuroinflammation, and aging in the AD brain. Additionally, we summarized the phosphoinositide 3-kinase (PI3K)/PDK1/Akt pathway-related features and its molecular mechanism that is dependent on TACE in the pathogenesis of AD. This study reviewed the relationship between the PDK1/Akt signaling pathway and AD, and discussed the role of PDK1/Akt in resisting neuronal toxicity by suppressing TACE expression in the cell membrane. This work also provides a perspective for developing new therapeutics targeting PDK1/Akt and TACE for the treatment of AD.

Fyn and TOM1L1 are recruited to clathrin-coated pits and regulate Akt signaling

The epidermal growth factor (EGF) receptor (EGFR) controls many aspects of cell physiology. EGF binding to EGFR elicits the membrane recruitment and activation of phosphatidylinositol-3-kinase, leading to Akt phosphorylation and activation. Concomitantly, EGFR is recruited to clathrin-coated pits (CCPs), eventually leading to receptor endocytosis. Previous work uncovered that clathrin, but not receptor endocytosis, is required for EGF-stimulated Akt activation, and that some EGFR signals are enriched in CCPs. Here, we examine how CCPs control EGFR signaling. The signaling adaptor TOM1L1 and the Src-family kinase Fyn are enriched within a subset of CCPs with unique lifetimes and protein composition. Perturbation of TOM1L1 or Fyn impairs EGF-stimulated phosphorylation of Akt2 but not Akt1. EGF stimulation also triggered the TOM1L1- and Fyn-dependent recruitment of the phosphoinositide 5-phosphatase SHIP2 to CCPs. Thus, the recruitment of TOM1L1 and Fyn to a subset of CCPs underlies a role for these structures in the support of EGFR signaling leading to Akt activation.

PI3K/AKT Signaling Tips the Balance of Cytoskeletal Forces for Cancer Progression

The PI3K/AKT signaling pathway plays essential roles in multiple cellular processes, which include cell growth, survival, metabolism, and motility. In response to internal and external stimuli, the PI3K/AKT signaling pathway co-opts other signaling pathways, cellular components, and cytoskeletal proteins to reshape individual cells. The cytoskeletal network comprises three main components, which are namely the microfilaments, microtubules, and intermediate filaments. Collectively, they are essential for many fundamental structures and cellular processes. In cancer, aberrant activation of the PI3K/AKT signaling cascade and alteration of cytoskeletal structures have been observed to be highly prevalent, and eventually contribute to many cancer hallmarks. Due to their critical roles in tumor progression, pharmacological agents targeting PI3K/AKT, along with cytoskeletal components, have been developed for better intervention strategies against cancer. In our review, we first discuss existing evidence in-depth and then build on recent advances to propose new directions for therapeutic intervention.

IQGAP1 scaffolding links phosphoinositide kinases to cytoskeletal reorganization

IQGAP1 is a multidomain scaffold protein that coordinates the direction and impact of multiple signaling pathways by scaffolding its various binding partners. However, the spatial and temporal resolution of IQGAP1 scaffolding remains unclear. Here, we use fluorescence imaging and correlation methods that allow for real-time live-cell changes in IQGAP1 localization and complex formation during signaling. We find that IQGAP1 and PIPKIγ interact on both the plasma membrane and in cytosol. Epidermal growth factor (EGF) stimulation, which can initiate cytoskeletal changes, drives the movement of the cytosolic pool toward the plasma membrane to promote cytoskeletal changes. We also observe that a significant population of cytosolic IQGAP1-PIPKIγ complexes localize to early endosomes, and in some instances form aggregated clusters which become highly mobile upon EGF stimulation. Our imaging studies show that PIPKIγ and PI3K bind simultaneously to IQGAP1, which may accelerate conversion of PI4P to PI(3,4,5)P₃ that is required for cytoskeletal changes. Additionally, we find that IQGAP1 is responsible for PIPKIγ association with two proteins associated with cytoskeletal changes, talin and Cdc42, during EGF stimulation. These results directly show that IQGAP1 provides a physical link between phosphoinositides (through PIPKIγ), focal adhesion formation (through talin), and cytoskeletal reorganization (through Cdc42) upon EGF stimulation. Taken together, our results support the importance of IQGAP1 in regulating cell migration by linking phosphoinositide lipid signaling with cytoskeletal reorganization.

Pulling back the curtain: The hidden functions of receptor tyrosine kinases in development

Receptor tyrosine kinases (RTKs) are a conserved superfamily of transmembrane growth factor receptors that drive numerous cellular processes during development and in the adult. Upon activation, multiple adaptors and signaling effector proteins are recruited to binding site motifs located within the intracellular domain of the RTK. These RTK-effector interactions drive subsequent intracellular signaling cascades involved in canonical RTK signaling. Genetic dissection has revealed that alleles of Fibroblast Growth Factor receptors (FGFRs) that lack all canonical RTK signaling still retain some kinase-dependent biological activity. Here we examine how genetic analysis can be used to understand the mechanism by which RTKs drive multiple developmental processes via canonical signaling while revealing noncanonical activities. Recent data from both FGFRs and other RTKs highlight potential noncanonical roles in cell adhesion and nuclear signaling. The data supporting such functions are discussed as are recent technologies that have the potential to provide valuable insight into the developmental significance of these noncanonical activities.

Activation Mechanisms of the VPS34 Complexes

Phosphatidylinositol-3-phosphate (PtdIns(3)P) is essential for cell survival, and its intracellular synthesis is spatially and temporally regulated. It has major roles in two distinctive cellular pathways, namely, the autophagy and endocytic pathways. PtdIns(3)P is synthesized from phosphatidylinositol (PtdIns) by PIK3C3C/VPS34 in mammals or Vps34 in yeast. Pathway-specific VPS34/Vps34 activity is the consequence of the enzyme being incorporated into two mutually exclusive complexes: complex I for autophagy, composed of VPS34/Vps34-Vps15/Vps15-Beclin 1/Vps30-ATG14L/Atg14 (mammals/yeast), and complex II for endocytic pathways, in which ATG14L/Atg14 is replaced with UVRAG/Vps38 (mammals/yeast). Because of its involvement in autophagy, defects in which are closely associated with human diseases such as cancer and neurodegenerative diseases, developing highly selective drugs that target specific VPS34/Vps34 complexes is an essential goal in the autophagy field. Recent studies on the activation mechanisms of VPS34/Vps34 complexes have revealed that a variety of factors, including conformational changes, lipid physicochemical parameters, upstream regulators, and downstream effectors, greatly influence the activity of these complexes. This review summarizes and highlights each of these influences as well as clarifying key questions remaining in the field and outlining future perspectives.

Revising Endosomal Trafficking under Insulin Receptor Activation

The endocytosis of ligand-bound receptors and their eventual recycling to the plasma membrane (PM) are processes that have an influence on signalling activity and therefore on many cell functions, including migration and proliferation. Like other tyrosine kinase receptors (TKR), the insulin receptor (INSR) has been shown to be endocytosed by clathrin-dependent and -independent mechanisms. Once at the early endosome (EE), the sorting of the receptor, either to the late endosome (LE) for degradation or back to the PM through slow or fast recycling pathways, will determine the intensity and duration of insulin effects. Both the endocytic and the endosomic pathways are regulated by many proteins, the Arf and Rab families of small GTPases being some of the most relevant. Here, we argue for a specific role for the slow recycling route, whilst we review the main molecular mechanisms involved in INSR endocytosis, sorting and recycling, as well as their possible role in cell functions.

Endosomes as Signaling Platforms for IL-6 Family Cytokine Receptors

Interleukin-6 (IL-6) is the name-giving cytokine of a family of eleven members, including IL-6, CNTF, LIF, and IL-27. IL-6 was first recognized as a B-cell stimulating factor but we now know that the cytokine plays a pivotal role in the orchestration of inflammatory processes as well as in inflammation associated cancer. Moreover, IL-6 is involved in metabolic regulation and it has been shown to be involved in major neural activities such as neuroprotection, which can help to repair and to reduce brain damage. Receptor complexes of all members formed at the plasma membrane contain one or two molecules of the signaling receptor subunit GP130 and the mechanisms of signal transduction are well understood. IL-6 type cytokines can also signal from endomembranes, in particular the endosome, and situations have been reported in which endocytosis of receptor complexes are a prerequisite of intracellular signaling. Moreover, pathogenic GP130 variants were shown to interfere with spatial activation of downstream signals. We here summarize the molecular mechanisms underlying spatial regulation of IL-6 family cytokine signaling and discuss its relevance for pathogenic processes.

Endosomal mTORC2 Is Required for Phosphoinositide-Dependent AKT Activation in Platelet-Derived Growth Factor-Stimulated Glioma Cells

Simple Summary

The full activation of AKT, which is necessary for cell physiological changes, is achieved through the phosphorylation of Thr308 and Ser473 in human AKT. Here, we have addressed how AKT activation at early endosomes occurs during growth factor stimulation and how mTORC2 is recruited into endosomes and associated with AKT. The explanation comes from the discovery of three important events: (1) the physical association of mSIN and Rictor, critical components for mTORC2 assembly and activity, with early endosomes; (2) the control of the recruitment of mSIN to endosomes by PtdIns(3,4)P₂; and (3) the PtdIns(3,4)P₂-mediated endosomal AKT activation through phosphorylation at Ser473 to control a subset of AKT substrates.

Abstract

The serine/threonine kinase AKT is a major effector during phosphatidylinositol 3-kinase (PI3K)-driven cell signal transduction in response to extracellular stimuli. AKT activation mechanisms have been extensively studied; however, the mechanism underlying target of rapamycin complex 2 (mTORC2) phosphorylation of AKT at Ser473 in the cellular endomembrane system remains to be elucidated. Here, we demonstrate that endocytosis is required for AKT activation through phosphorylation at Ser473 via mTORC2 using platelet-derived growth factor-stimulated U87MG glioma cells. mTORC2 components are localized to early endosomes during growth factor activation, and the association of mTORC2 with early endosomes is responsible for the local activation of AKT, which is critical for specific signal transduction through glycogen synthase kinase-3 beta and forkhead box O1/O3 phosphorylation. Furthermore, endosomal phosphoinositide, represented by PtdIns(3,4)P₂, provides a binding platform for mTORC2 to phosphorylate AKT Ser473 in endosomes through mammalian Sty1/Spc1-interacting protein (mSIN), a pleckstrin homology domain-containing protein, and is dispensable for AKT phosphorylation at Thr308. This PtdIns(3,4)P₂-mediated endosomal AKT activation provides a means to integrate PI3K activated by diverse stimuli to mTORC2 assembly. These early endosomal events induced by endocytosis, together with the previously identified AKT activation by PtdIns(3,4,5)P₃, contribute to the strengthening of the transduction of AKT signaling through phosphoinositide.

Modulation of Pathological Pain by Epidermal Growth Factor Receptor

Chronic pain has been widely recognized as a major public health problem that impacts multiple aspects of patient quality of life. Unfortunately, chronic pain is often resistant to conventional analgesics, which are further limited by their various side effects. New therapeutic strategies and targets are needed to better serve the millions of people suffering from this devastating disease. To this end, recent clinical and preclinical studies have implicated the epidermal growth factor receptor signaling pathway in chronic pain states. EGFR is one of four members of the ErbB family of receptor tyrosine kinases that have key roles in development and the progression of many cancers. EGFR functions by activating many intracellular signaling pathways following binding of various ligands to the receptor. Several of these signaling pathways, such as phosphatidylinositol 3-kinase, are known mediators of pain. EGFR inhibitors are known for their use as cancer therapeutics but given recent evidence in pilot clinical and preclinical investigations, may have clinical use for treating chronic pain. Here, we review the clinical and preclinical evidence implicating EGFR in pathological pain states and provide an overview of EGFR signaling highlighting how EGFR and its ligands drive pain hypersensitivity and interact with important pain pathways such as the opioid system.

MAPping PI3K signaling to endosomes

The microtubule-associated protein MAP4 recruits PI3Kα from the plasma membrane to endosomes to activate Akt signaling.