SIRT6 phosphorylation - MDM2-mediated degradation of SIRT6 phosphorylated by AKT1 promotes tumorigenesis and trastuzumab resistance in breast cancer
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ABSTRACT: Sirtuin 6 (SIRT6) is associated with longevity and was recently established as a tumor suppressor. Hence, identifying the molecular regulators of SIRT6 might enable its activation therapeutically in cancer patients. We found that SIRT6 was phosphorylated by the kinase AKT1 at Ser338, which induces its interaction with and ubiquitination by MDM2, priming it for protease-dependent degradation. The survival of patients with breast cancers positively correlated with the abundance of SIRT6 and inversely correlated with the phosphorylation of SIRT6 at Ser338. In a large panel of breast tumor biopsies, SIRT6 abundance inversely correlated with the abundance of phosphorylated AKT. Inhibiting AKT or preventing SIRT6 phosphorylation by mutating Ser338 prevented the degradation of SIRT6 mediated by MDM2, suppressed the proliferation of breast cancer cells in culture, and inhibited the growth of breast tumor xenografts in mice. Overexpressing MDM2 decreased the abundance of SIRT6 in cells, whereas overexpressing an E3 ligase-deficient MDM2 or knocking down endogenous MDM2 increased SIRT6 abundance. Knocking down SIRT6 decreased the sensitivity of a breast cancer cell line to trastuzumab, whereas overexpression of a non-phosphorylatable SIRT6 mutant increased trastuzumab sensitivity in a resistant subculture. Thus, stabilizing SIRT6 may be a clinical strategy for overcoming trastuzumab resistance in breast cancer patients.
INSTRUMENT(S): Q TRAP
ORGANISM(S): Homo Sapiens (human)
TISSUE(S): Permanent Cell Line Cell, Hela Cell
DISEASE(S): Breast Cancer
SUBMITTER: Umadevi Thirumurthi
LAB HEAD: Mien-Chie Hung
PROVIDER: PXD001154 | Pride | 2016-07-06
REPOSITORIES: Pride
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