Dataset Information

Identification of Syntaxin 7 and 12 as the first selective substrates for SGK3

ABSTRACT: Deregulation of the PI3K/Akt pathway is a common feature in many types of cancer. Recent data has demonstrated that prolonged inhibition of breast cancer cell lines with PI3K and Akt inhibitors leads to up-regulation and increased activity of the AGC kinase Serum and glucocorticoid activated kinase 3, SGK3, which in turn substitutes for Akt and leads to activation of mTORC1. SGK3 and Akt exhibit similar substrate specificity for Ser/Thr residues in the RxRxxS/T motif. However, SGK3 can be regulated by both PI3K class I and class III and possesses a unique PX domain, enabling it to bind to PI(3)P lipids in endosomes. Still, the known SGK3 substrates are either shared or have not been tested whether Akt can phosphorylate them. In the present study, we undertook genetic and pharmacologic phosphoproteomic screens to search for selective SGK3 substrates. We identified a significant number of potential in vivo SGK3 selective substrates, including the endosomal proteins STX7, STX12, RFIP4 and WDR44. In vitro phosphorylation studies demonstrated that these substrates were directly phosphorylated at the sites identified in vivo by SGK3 but, unlike all other SGK3 substrates reported, not by Akt. We provide evidence that endogenous STX7 and STX12 are physiological SGK3 substrates whose phosphorylation is potently stimulated by IGF1. Our data pinpoint that STX7 and STX12 are the first selective SGK3 substrates in vivo and this phosphorylation enhances their interaction with the respective SNARE complexes. Finally, we suggest that STX7 and STX12 phosphorylation can be utilised as in vivo biomarkers for SGK3 activity.

INSTRUMENT(S): Orbitrap Fusion

ORGANISM(S): Homo Sapiens (human)

TISSUE(S): Cell Culture

SUBMITTER: Raja Sekhar Nirujogi

LAB HEAD: Prof Matthias Trost

PROVIDER: PXD014561 | Pride | 2020-05-26

REPOSITORIES: Pride

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Publications

Phosphoproteomics reveals that the hVPS34 regulated SGK3 kinase specifically phosphorylates endosomal proteins including Syntaxin-7, Syntaxin-12, RFIP4 and WDR44.

Malik Nazma N Nirujogi Raja S RS Peltier Julien J Macartney Thomas T Wightman Melanie M Prescott Alan R AR Gourlay Robert R Trost Matthias M Alessi Dario R DR Karapetsas Athanasios A

The Biochemical journal 20191001 20

The serum- and glucocorticoid-regulated kinase (SGK) isoforms contribute resistance to cancer therapies targeting the PI3K pathway. SGKs are homologous to Akt and these kinases display overlapping specificity and phosphorylate several substrates at the same residues, such as TSC2 to promote tumor growth by switching on the mTORC1 pathway. The SGK3 isoform is up-regulated in breast cancer cells treated with PI3K or Akt inhibitors and recruited and activated at endosomes, through its phox homology ...[more]

PMID: 31665227

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Project description:Hyperactivation of the PI3K/AKT pathway is observed in most NSCLCs, promoting proliferation, migration and resistance to therapy. AKT can be activated through several mechanisms that include loss of the negative regulator PTEN, activating mutations of the catalytic subunit of the positive regulator phosphatydil-inositol-3â phosphate kinase (PIK3CA) and/or mutations of AKT1 itself. However, whereas the effects of AKT activation on mRNAs and proteins in the cell are fairly clear, the role of miRNAs as downstream targets of activated PI3K/AKT signalling is still poorly defined so far. To identify miRNAs that are targets of constitutive signalling of PI3K/AKT in lung cancer cells, we performed miRNA profiling of human lung epithelial cells expressing active mutant AKT1 (E17K), active mutant PI3KCA (E545K) or that are silenced for PTEN. We identified 28 differentially expressed miRNAs (8 up-regulated, 20 down-regulated) that were common to BEAS-AKT1-E17K, BEAS-PIK3CA-E545K and BEAS-shPTEN cells. Among the 8 up-regulated miRNAs that were common to all the alterations, the miRNA most consistently up-regulated by activation of the PI3K/AKT pathway in BEAS-2B cells was miR-196a. The results reported here demonstrate that miR-196a acts as oncogene downstream the PI3K/AKT pathway, mediating the proliferative, pro-migratory and tumorigenic activity of this pathway in NSCLC cells by targeting FoxO1 and p27 expression. By adoptive expression of miR-196a in BEAS-2B cells, we demonstrated that miR-196a stimulates anchorage-dependent and -independent proliferation, migration and tumorigenicity in BEAS-2B cells. On the other hand, by use of antimir-196a in NCI-H460 cells to silence the endogenous expression of miR-196a, we demonstrate that miR-196a plays a pivotal role in mediating the stimulation of proliferation, migration and tumorigenicity induced by aberrant activation of PI3K/AKT signalling. Accordingly, we found that miR-196a was significantly overexpressed in human NSCLC-derived cell lines (n=6) and primary lung cancer samples (n=28). Finally, based on predicted binding sites for miR-196a by microRNA analysis software, we found that miR-196a affects protein levels of FoxO1 and p27 in NSCLC cells.

Dataset Information

Identification of Syntaxin 7 and 12 as the first selective substrates for SGK3

Publications

Phosphoproteomics reveals that the hVPS34 regulated SGK3 kinase specifically phosphorylates endosomal proteins including Syntaxin-7, Syntaxin-12, RFIP4 and WDR44.

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