The clock gene BHLHE40 and atypical CCNG2 control androgen-induced cellular senescence as a novel tumor suppressive pathway in prostate cancer

The androgen receptor (AR) is a therapeutic target of prostate cancer (PCa). Targeted AR therapy commonly uses androgen deprivation therapy (ADT) and AR antagonists to reduce androgen levels and inhibit tumor growth. Surprisingly, treatment with supraphysiological androgen level (SAL) can also inhibit the growth of PCa. SAL (R1881) was shown to induce cellular senescence in PCa. Knockdown of BHLHE40 in C4-2 and LNCaP cell lines indicates that BHLHE40 mediates SAL-induced cellular senescence as a possible tumor suppressive pathway. The RNA-seq from BHLHE40 knocked down C4-2 cells confirmed that BHLHE40 regulates cellular senescence and associated pathways. Interestingly, a large overlap of differentially expressed gene sets was identified between BHLHE40 regulated transcriptome and the SAL-changed transcriptome leading to four classes of up-and downregulated BHLHE40 transcriptome landscapes overlapping with that of AR. Further RNA-seq analyses revealed that the tumor suppressive cyclin G2 (CCNG2) emerged as a novel downstream target of BHLHE40. Knockdown of CCNG2 suggests that it mediates SAL-induced cellular senescence providing evidence of a novel pathway by the AR-BHLHE40-CCNG2 axis to mediate androgen-induced cellular senescence as a novel tumor suppressive pathway in PCa cells.