Abstract
Mutations in SPOP E3 ligase gene are reportedly associated with genome-wide DNA hypermethylation in prostate cancer (PCa) although the underlying mechanisms remain elusive. Here, we demonstrate that SPOP binds and promotes polyubiquitination and degradation of histone methyltransferase and DNMT interactor GLP. SPOP mutation induces stabilization of GLP and its partner protein G9a and aberrant upregulation of global DNA hypermethylation in cultured PCa cells and primary PCa specimens. Genome-wide DNA methylome analysis shows that a subset of tumor suppressor genes (TSGs) including FOXO3, GATA5, and NDRG1, are hypermethylated and downregulated in SPOP-mutated PCa cells. DNA methylation inhibitor 5-azacytidine effectively reverses expression of the TSGs examined, inhibits SPOP-mutated PCa cell growth in vitro and in mice, and enhances docetaxel anti-cancer efficacy. Our findings reveal the GLP/G9a-DNMT module as a mediator of DNA hypermethylation in SPOP-mutated PCa. They suggest that SPOP mutation could be a biomarker for effective treatment of PCa with DNA methylation inhibitor alone or in combination with taxane chemotherapeutics.
Highlights
Mutations in SPOP E3 ligase gene are reportedly associated with genome-wide DNA hypermethylation in prostate cancer (PCa) the underlying mechanisms remain elusive
We found that compared to the empty vector (EV), expression of SPOP mutants Y87C, F102C, F133V, and Q165P invariably increased DNA methylation in 22Rv1 cells and the differences are statistically significant (Fig. 1a–c)
Only 56% of SPOP-WT tumors had strong or intermediate 5mC signals (Fig. 1h, i, Supplementary Data 1). These findings are consistent with the detection of increased DNA methylation in SPOP-mutated PCa patient specimens[3,8], and provide direct evidence that SPOP mutations play a causal role in induction of DNA hypermethylation in PCa cells
Summary
Mutations in SPOP E3 ligase gene are reportedly associated with genome-wide DNA hypermethylation in prostate cancer (PCa) the underlying mechanisms remain elusive. SPOP mutation induces stabilization of GLP and its partner protein G9a and aberrant upregulation of global DNA hypermethylation in cultured PCa cells and primary PCa specimens. DNA methylation inhibitor 5-azacytidine effectively reverses expression of the TSGs examined, inhibits SPOP-mutated PCa cell growth in vitro and in mice, and enhances docetaxel anti-cancer efficacy. GLP (encoded by EHMT1) and G9a (encoded by EHMT2) form a protein complex and function as a euchromatic histone methyltransferase (HMTase) to catalyze mono- and di-methylation of histone H3K9 (H3K9me1/2), resulting in epigenetic silencing of target genes[22,23]. Mutations in SPOP result in elevation of GLP and its partner protein G9a, DNA hypermethylation and silencing of a subset of TSGs. Treatment of the DNA methylation inhibitor 5-azacytidine reverses these processes, and sensitizes SPOPmutated PCa cells to the first-line chemotherapy agent taxane
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
