A new paradigm for regulation of protein phosphatase 2A function via Src and Fyn kinase–mediated tyrosine phosphorylation

Sontag, Jean‐Marie; Schuhmacher, Diana; Taleski, Goce; Jordan, A. M.; Khan, Sarah; Hoffman, Alexander; Gomez, Rey J.; Mazalouskas, Matthew D.; Hanks, Steven K.; Spiller, Benjamin W.; Sontag, Estelle; Wadzinski, Brian E.

doi:10.1016/j.jbc.2022.102248

Cited by 8 publications

(9 citation statements)

References 63 publications

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“…It has been shown that the carboxymethylation at Leu 309 is associated with PP2A activation, whereas phosphorylation of Thr 304 and Tyr 307 has been, in both cases, associated with PP2A inactivation ( 37 ). In addition, phosphorylation of Tyr 127 and Tyr 284 has been identified in response to Src family kinase activation, which further promotes the dissociation of the regulatory Bα subunit and alters PP2A substrate specificity ( 40 ). Here, we saw that phosphorylated (T304 and Y307) and carboxymethylated (L309) PP2Ac were rarely detected in purified CF-PP2Ac protein, indicating that the three repeated Flag-tags fused to the C terminus may block the PTMs of PP2Ac C-tail (Fig.…”

Section: Resultsmentioning

confidence: 99%

PTEN deficiency facilitates gemcitabine efficacy in cancer by modulating the phosphorylation of PP2Ac and DCK

et al. 2023

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Gemcitabine is a nucleoside analog that has been successfully used in the treatment of multiple cancers. However, intrinsic or acquired resistance reduces the chemotherapeutic potential of gemcitabine. Here, we revealed a previously unappreciated mechanism by which phosphatase and tensin homolog (PTEN), one of the most frequently mutated genes in human cancers, dominates the decision-making process that is central to the regulation of gemcitabine efficacy in cholangiocarcinoma (CCA). By investigating a gemcitabine-treated CCA cohort, we found that PTEN deficiency was correlated with the improved efficacy of gemcitabine-based chemotherapy. Using cell-based drug sensitivity assays, cell line–derived xenograft, and patient-derived xenograft models, we further confirmed that PTEN deficiency or genetic-engineering down-regulation of PTEN facilitated gemcitabine efficacy both in vitro and in vivo. Mechanistically, PTEN directly binds to and dephosphorylates the C terminus of the catalytic subunit of protein phosphatase 2A (PP2Ac) to increase its enzymatic activity, which further dephosphorylates deoxycytidine kinase (DCK) at Ser 74 to diminish gemcitabine efficacy. Therefore, PTEN deficiency and high phosphorylation of DCK predict a better response to gemcitabine-based chemotherapy in CCA. We speculate that the combination of PP2A inhibitor and gemcitabine in PTEN-positive tumors could avoid the resistance of gemcitabine, which would benefit a large population of patients with cancer receiving gemcitabine or other nucleoside analogs.

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Section: Resultsmentioning

confidence: 99%

PTEN deficiency facilitates gemcitabine efficacy in cancer by modulating the phosphorylation of PP2Ac and DCK

et al. 2023

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“…These findings suggested that SRC phosphorylates MAGI1 Y373 and thereby inhibits PP2AC through posttranslational modifications. Given a recent report that Y127 and Y284 on PP2AC act as additional phospho-acceptor sites upon SRC activation and the lack of consensus on the specificity of PP2AC pY307 antibody ( 34 ), it remains unclear how the interplay of the phosphorylation at these three sites control overall activity of PP2A.…”

Section: Resultsmentioning

confidence: 99%

SRC inhibition enables formation of a growth suppressive MAGI1-PP2A complex in isocitrate dehydrogenase-mutant cholangiocarcinoma

Luk,

Bridgwater,

et al. 2024

Sci. Transl. Med.

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Intrahepatic cholangiocarcinoma (ICC) is an aggressive bile duct malignancy that frequently exhibits isocitrate dehydrogenase ( IDH1/IDH2 ) mutations. Mutant IDH (IDHm) ICC is dependent on SRC kinase for growth and survival and is hypersensitive to inhibition by dasatinib, but the molecular mechanism underlying this sensitivity is unclear. We found that dasatinib reduced p70 S6 kinase (S6K) and ribosomal protein S6 (S6), leading to substantial reductions in cell size and de novo protein synthesis. Using an unbiased phosphoproteomic screen, we identified membrane-associated guanylate kinase, WW, and PDZ domain containing 1 (MAGI1) as an SRC substrate in IDHm ICC. Biochemical and functional assays further showed that SRC inhibits a latent tumor-suppressing function of the MAGI1–protein phosphatase 2A (PP2A) complex to activate S6K/S6 signaling in IDHm ICC. Inhibiting SRC led to activation and increased access of PP2A to dephosphorylate S6K, resulting in cell death. Evidence from patient tissue and cell line models revealed that both intrinsic and extrinsic resistance to dasatinib is due to increased phospho-S6 (pS6). To block pS6, we paired dasatinib with the S6K/AKT inhibitor M2698, which led to a marked reduction in pS6 in IDHm ICC cell lines and patient-derived organoids in vitro and substantial growth inhibition in ICC patient-derived xenografts in vivo. Together, these results elucidated the mechanism of action of dasatinib in IDHm ICC, revealed a signaling complex regulating S6K phosphorylation independent of mTOR, suggested markers for dasatinib sensitivity, and described a combination therapy for IDHm ICC that may be actionable in the clinic.

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“…HEK-293T cells were maintained in DMEM supplemented with 10% FBS. Cell lines were maintained in an incubator at 37 • C under moistened air atmosphere with 5% CO 2 and used in a low cell passage (8)(9)(10)(11)(12)(13)(14)(15)(16)(17)(18)(19)(20).…”

Section: Cell Culturesmentioning

confidence: 99%

“…Indeed, there are nearly 100 heterotrimeric holoenzymes, as result of the combination of different isoforms expressed for each subunit [8,9]. PP2A activity is further regulated by post-translational mechanisms, including reversible PP2A-C carboxymethylation [10,11], and PP2A-C or B subunit phosphorylation [9,12]. In addition, several endogenous polypeptides inhibit PP2A by direct interaction [13].…”

Section: Introductionmentioning

confidence: 99%

C-glycosides analogues of the okadaic acid central fragment exert neuroprotection via restoration of PP2A-phosphatase activity: A rational design of potential drugs for Alzheimer's disease targeting tauopathies

Arribas

Viejo

Bravo

et al. 2023

European Journal of Medicinal Chemistry

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A new paradigm for regulation of protein phosphatase 2A function via Src and Fyn kinase–mediated tyrosine phosphorylation

Cited by 8 publications

References 63 publications

PTEN deficiency facilitates gemcitabine efficacy in cancer by modulating the phosphorylation of PP2Ac and DCK

PTEN deficiency facilitates gemcitabine efficacy in cancer by modulating the phosphorylation of PP2Ac and DCK

SRC inhibition enables formation of a growth suppressive MAGI1-PP2A complex in isocitrate dehydrogenase-mutant cholangiocarcinoma

C-glycosides analogues of the okadaic acid central fragment exert neuroprotection via restoration of PP2A-phosphatase activity: A rational design of potential drugs for Alzheimer's disease targeting tauopathies

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