Gpr48-deficience Effictively Inhibits The Formation Of Cutaneous Squamous Cell Carcinoma Via ERK Pathway

Skin is the body’s largest organ, bearing important physiological functions. It covers all parts of our body, its presence pretects the body tissues and organs against physical, chemical, mechanical injury, also the invasion of pathogenic microorganisms. In recent years, the incidence of skin cancer is increasing year by year, which has serious impact on people’s health. The skin cancer is caused due to the uncontrollable growth of epidermal cells. The skin cancer includes basal cell carcinoma(BCC), squamous cell carcinoma(SCC) and melanoma, which are originated from basal cells, squamous cell and melanoma cells respectively. BCC and SCC are called non-melanoma. Squamous cell carcinoma (SCC) is the second largest type of skin cancer, it is related to exposure ultraviolet radiation. In biological and medical research, the classic two-stage carcinogenesis to induce squamous cell carcinoma is usually used.GPCR (G-protein coupled receptor) superfamily is the largest family of cell surface molecules associated with signal transduction, and it is closely related to tumor growth and metastasis. GPR48/LGR4, also known as LGR4 (Leucine-rich repeat containing G-protein coupled receptor 4), is an orphan receptor. It is expressed in many tissues, and is involved in cell proliferation, differentiation, migration, and the regulation of various physiological activities of the cell. Whether GPR48/LGR4 plays an important role in the development of skin cancer is unknown.In our study, the classic DMBA/TPA two-stage carcinogenesis was used to induce Gpr48/Lgr4 wild-type and knockout mice to generate squamous cell carcinoma, trying to explore the role of Gpr48/Lgr4 in the initiation and promotion of skin cancer.Through 20 weeks of model establish experiments, we found that there were different size and number of papillomas on the back of wild-type mice, but none in knockout mice, suggesting that Gpr48/Lgr4 deficience can seriously impact on tumorgenesis. To further explore the mechanism of this phenomenon, we carried out a series of experiments in vivo and in vitro:in vivo, we used HE staining, immunohistochemical staining, Real-time PCR and Western blot to detect epidermal cell proliferation, the expression of inflammatory cytokines and ERK signaling pathway related proteins, we found that epidermal cell proliferation, inflammation and activation of the signaling pathway proteins was significantly higher in wild-type mice than that in knockout mice; In vitro, we selected human skin squamous cell carcinoma cell A431, using RNA interference to lower the expression of endogenous Gpr48/Lgr4, then investigated the A431 growth, colony formation, cell cycle and protein expression of ERK signaling pathway, the experiments showed that the lower expression of Gpr48/Lgr4 did reduce the growth of A431 and the colony forming efficiency, the activation of the ERK signaling pathway related proteins after TPA treatment was also affected.In summary, these findings reveal the pivotal important role of Gpr48/Lgr4 in skin tumor development induced by DMBA/TPA, probably Gpr48/Lgr4-deficience inhibits the formation of cutaneous squamous cell carcinoma via ERK Pathway, suggestting that this receptor may be served as a newbiomarker and therapeutic target in squamous cell carcinomas.