Cowden syndrome-associated germline SDHD variants alter PTEN nuclear translocation through SRC-induced PTEN oxidation.
Bottom Line: However, very little is known about the underlying crosstalk between SDHD and PTEN in CS-associated thyroid cancer.We show that SRC inhibition could rescue SDHD dysfunction-induced cellular phenotype and tumorigenesis only when wild-type PTEN is expressed, in thyroid cancer lines.Patient lymphoblast cells carrying either SDHD-G12S or SDHD-H50R also show increased nuclear PTEN and more oxidized PTEN after hydrogen peroxide treatment.
Affiliation: Genomic Medicine Institute, Learner Research Institute.Show MeSH
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Mentions: We then examined activation of SRC in LCL cells derived from a series of CS/CSL patients carrying either SDHD-G12S or SDHD-H50R variants. Compared with three LCLs derived from controls without SDHD germline variants, phosphorylation of tyrosine 418 on SRC, representing activated SRC, was dramatically higher in the SDHD variant-positive CS/CSL patients (Supplementary Material, Fig. S2A). PTEN western blot of the LCL nuclear and cytoplasmic fractionated proteins showed more nuclear PTEN in SDHD-variant carriers compared with those of the controls (Supplementary Material, Fig. S2B). Next, we pretreated the LCL cells with bosutinib before exposing them to H2O2. H2O2-induced oxidized PTEN was abolished by bosutinib pretreatment of the LCL cells derived from the CS patients (Fig. 6A). Fluorescence-activated cell sorting (FACS) analysis after propidium iodine staining showed that although H2O2 treatment could induce apoptosis in both healthy control LCL cells and patient LCL cells, the induced level of apoptosis in LCL from SDHD variant-positive patients was much lower than in control LCL cells. With bosutinib pretreatment, LCLs from CS patients have a greater increase of apoptosis rate with H2O2 exposure compared with cells without bosutinib treatment (Fig. 6B). Finally, we compared the effect of bosutinib on apoptotic rates in LCLs from CS patients with only SDHD variants and LCLs from CS patients with both SDHD variants and PTEN mutations. Bosutinib induced apoptosis in LCLs with SDHD variants (G12S or H50R). However, in three LCLs with both SDHD variants (either G12S or H50R) and PTEN mutations (insertion, truncation or early translation termination), which dramatically abolished PTEN function, no significant induction of apoptosis was observed (Fig. 6C). These data utilizing patient-derived cells further confirmed our in vitro cell line observation that SRC kinase inhibitor rescues tumorigenic phenotype required wild-type PTEN expression.Figure 6.
Affiliation: Genomic Medicine Institute, Learner Research Institute.