Ablation of LGR4 signaling enhances radiation sensitivity of prostate cancer cells

Aim: Our previous study has shown that leucine-rich repeat containing GPCR-4 (LGR4, or GPR48) LGR4 plays a role in cell migration, invasion, proliferation and Apoptosis of prostate Cancer (PCa). In this study, we aimed to explore whether LGR4 would affect radiation response in PCa.

Materials and methods: LGR4 expression was silenced by shRNA transfection. qRT-PCR was employed to determine mRNA expression of LGR4 and DNA damage repair genes. Western blot was used to evaluate protein expression of LGR4, RSPO1-4, Androgen Receptor (AR), cyclic AMP response-element binding protein (CREB1), γH2A.X, and H2A.X. Cell proliferation was detected by CCK-8 assay and Apoptosis was assayed by flow cytometry. Additionally, a xenograft model was also established to validate the role of LGR4 in PCa cells after radiation.

Key findings: LGR4 expression was enhanced in PCa cells by radiation treatment in dose- and time-dependent means. RSPO1-4 were also upregulated post-radiation. Furthermore, LGR4 knockdown exacerbated Apoptosis, reduced cell viabilities and strengthened nuclear γH2A.X staining in AR positive PCa cells but not in AR negative cells in the presence of radiation. Likewise, LGR4 ablation diminished AR and CREB1 expression induced by radiation. In contrast, RSPO1 stimulation augmented cell viabilities, promoted AR and CREB1 expression, and upregulated DNA repair gene expression, which could be reversed by enzalutamide, except for AR expression. Additionally, LGR4 knockdown further suppressed tumor growth and AR/CREB1 expression but enhanced γH2A.X expression in xenografts.

Significance: In all, our study suggested that LGR4 might serve as an important regulator of radiation sensitivity in PCa.