Dataset Information

Galpha(i1) and Galpha(i3) are required for epidermal growth factor-mediated activation of the Akt-mTORC1 pathway.

ABSTRACT: The precise mechanism whereby epidermal growth factor (EGF) activates the serine-threonine kinase Akt and the mammalian target of rapamycin (mTOR) complex 1 (mTORC1) remains elusive. Here, we report that the alpha subunits of the heterotrimeric guanine nucleotide-binding proteins (G proteins) Galpha(i1) and Galpha(i3) are critical for this activation process. Both Galpha(i1) and Galpha(i3) formed complexes with growth factor receptor binding 2 (Grb2)-associated binding protein 1 (Gab1) and the EGF receptor (EGFR) and were required for the phosphorylation of Gab1 and its subsequent interaction with the p85 subunit of phosphatidylinositol 3-kinase in response to EGF. Loss of Galpha(i1) and Galpha(i3) severely impaired the activation of Akt and of p70 S6 kinase and 4E-BP1, downstream targets of mTORC1, in response to EGF, heparin-binding EGF-like growth factor, and transforming growth factor alpha, but not insulin, insulin-like growth factor, or platelet-derived growth factor. In addition, ablation of Galpha(i1) and Galpha(i3) largely inhibited EGF-induced cell growth, migration, and survival and the accumulation of cyclin D1. Overall, this study suggests that Galpha(i1) and Galpha(i3) lie downstream of EGFR, but upstream of Gab1-mediated activation of Akt and mTORC1, thus revealing a role for Galpha(i) proteins in mediating EGFR signaling.

SUBMITTER: Cao C

PROVIDER: S-EPMC4138699 | biostudies-literature | 2009 Apr

REPOSITORIES: biostudies-literature

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Galpha(i1) and Galpha(i3) are required for epidermal growth factor-mediated activation of the Akt-mTORC1 pathway.

Cao Cong C Huang Xuesong X Han Yuyuan Y Wan Yinsheng Y Birnbaumer Lutz L Feng Geng-Sheng GS Marshall John J Jiang Meisheng M Chu Wen-Ming WM

Science signaling 20090428 68

The precise mechanism whereby epidermal growth factor (EGF) activates the serine-threonine kinase Akt and the mammalian target of rapamycin (mTOR) complex 1 (mTORC1) remains elusive. Here, we report that the alpha subunits of the heterotrimeric guanine nucleotide-binding proteins (G proteins) Galpha(i1) and Galpha(i3) are critical for this activation process. Both Galpha(i1) and Galpha(i3) formed complexes with growth factor receptor binding 2 (Grb2)-associated binding protein 1 (Gab1) and the E ...[more]

PMID: 19401591

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Project description:Mutational activation of the epidermal growth factor receptor (EGFR) is a major player in the pathogenesis of non-small cell lung cancer (NSCLC). NSCLC patients with constitutively active EGFR mutations eventually develop drug resistance against EGFR tyrosine-kinase inhibitors; therefore, better understandings of key components of mutant EGFR (mtEGFR) signaling are required. Here, we initially observed aberrantly high expression of protein kinase C? (PKC?) in lung adenocarcinomas, especially those with EGFR mutations, and proceeded to examine the role of PKC? in the regulation of the signaling pathways downstream of mtEGFR. The results showed that NSCLC cell lines with constitutively active EGFR mutations tend to have very or moderately high PKC? levels. Furthermore, PKC? was constitutively activated in HCC827 and H4006 cells which have an EGFR deletion mutation in exon 19. Interestingly, mtEGFR was not required for the induction of PKC? at protein and message levels suggesting that the increased levels of PKC? are due to independent selection. On the other hand, mtEGFR activity was required for robust activation of PKC?. Loss of functions studies revealed that the NSCLC cells rely heavily on PKC? for the activation of the mTORC1 signaling pathway. Unexpectedly, the results demonstrated that PKC? was required for activation of Akt upstream of mTOR but only in cells with the mtEGFR and with the increased expression of PKC?. Functionally, inhibition of PKC? in HCC827 led to caspase-3-dependent apoptosis and a significant decrease in cell survival in response to cellular stress induced by serum starvation. In summary, the results identified important roles of PKC? in regulating mTORC1 activity in lung cancer cells, whereby a primary switching occurs from PKC?-independent to PKC?-dependent signaling in the presence of EGFR mutations. The results present PKC? as a potential synergistic target of personalized treatment for NSCLC with constitutively active mutant forms of EGFR and constitutively active PKC?.

Project description:When skin tissue is damaged, the wound microenvironment is hypoxic or anoxic due to the rupture of blood vessels and the high oxygen consumption of related cells; so far, it is not clear whether such hypoxic microenvironment will promote epidermal cell migration and the underlying molecular regulatory mechanisms of this effect remains unclear. Studies to date have shown that, immortal keratinocyte cell line HaCaT and primary human keratinocytes are maintained under conditions of hypoxia (1% oxygen) or normoxia. The researchers would adopt methods such as live cell imaging system, Western blotting, transwell assays and wound scratch assays etc. to study the changes of cell migration. Expression profile of mRNAs in HaCaT cells from 3 hypoxia and 3 normoxic conditions were analyzed by the Clariom D microarray assay. Gene Ontology (GO) and KEGG genomics analyses were performed to identify significant functions, pathways, and the associations of differentially expressed mRNAs. Moreover, the potential mechanism is discussed and studied. According to relevant results, the epidermal cell migration is promoted in the early hypoxia. Furthermore, experiment showed that 1456 mRNAs showed differential expression between the hypoxia and normoxic conditions, which included 537 upregulated and 919 downregulated mRNAs. These results also shown that all G proteins are upregulated. At the same time, GO analysis indicated that most upregulated mRNA are in connection with cell inflammation and migration. Pathway analysis indicated that 20 pathways corresponded to the upregulated mRNA and 6 pathways corresponded to the upregulated mRNA. These pathway analyses have indicated that genes involved in inflammation, migration and PI3K-Akt signaling are potentially regulated. Combine with microarray assay, we further shown that G protein accelerates epidermal cell migration via activation of PI3K/Akt-dependent mTORC1 signaling under the condition of hypoxia. Based on this evidence, researchers can further reveal the molecular and cellular mechanisms of local wound hypoxia, and for improving the wound healing.

Project description:BackgroundThe signaling pathways imposing hormonal control over adipocyte differentiation are poorly understood. While insulin and Akt signaling have been found previously to be essential for adipogenesis, the relative importance of their many downstream branches have not been defined. One direct substrate that is inhibited by Akt-mediated phosphorylation is the tuberous sclerosis complex 2 (TSC2) protein, which associates with TSC1 and acts as a critical negative regulator of the mammalian target of rapamycin (mTOR) complex 1 (mTORC1). Loss of function of the TSC1-TSC2 complex results in constitutive mTORC1 signaling and, through mTORC1-dependent feedback mechanisms and loss of mTORC2 activity, leads to a concomitant block of Akt signaling to its other downstream targets.Methodology/principal findingsWe find that, despite severe insulin resistance and the absence of Akt signaling, TSC2-deficient mouse embryo fibroblasts and 3T3-L1 pre-adipocytes display enhanced adipocyte differentiation that is dependent on the elevated mTORC1 activity in these cells. Activation of mTORC1 causes a robust increase in the mRNA and protein expression of peroxisome proliferator-activated receptor gamma (PPARgamma), which is the master transcriptional regulator of adipocyte differentiation. In examining the requirements for different Akt-mediated phosphorylation sites on TSC2, we find that only TSC2 mutants lacking all five previously identified Akt sites fully block insulin-stimulated mTORC1 signaling in reconstituted Tsc2 null cells, and this mutant also inhibits adipogenesis. Finally, renal angiomyolipomas from patients with tuberous sclerosis complex contain both adipose and smooth muscle-like components with activated mTORC1 signaling and elevated PPARgamma expression.Conclusions/significanceThis study demonstrates that activation of mTORC1 signaling is a critical step in adipocyte differentiation and identifies TSC2 as a primary target of Akt driving this process. Therefore, the TSC1-TSC2 complex regulates the differentiation of mesenchymal cell lineages, at least in part, through its control of mTORC1 activity and PPARgamma expression.

Dataset Information

Galpha(i1) and Galpha(i3) are required for epidermal growth factor-mediated activation of the Akt-mTORC1 pathway.

Publications

Galpha(i1) and Galpha(i3) are required for epidermal growth factor-mediated activation of the Akt-mTORC1 pathway.

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