CDK4 Mediates Cisplatin Resistance in Renal Cell Carcinoma (RCC) Cells by Regulating the ASH1L-CTR1 Axis

Objectives: Cisplatin resistance is a major obstacle in the treatment of renal cell carcinoma (RCC), severely compromising therapeutic efficacy and patient prognosis. This study aimed to clarify the role and molecular mechanism of cyclin-dependent kinase 4 (CDK4) in cisplatin resistance of RCC. Methods: Immunohistochemistry (IHC) was used to detect the expression of CDK4 in cisplatin-resistant RCC tissues. In RCC cells and their drug-resistant sublines, CDK4 overexpression/knockdown assays were performed to evaluate the effects on cisplatin resistance and malignant progression. An in vivo model was established, to verify the in vivo function of CDK4. Transcriptome sequencing (RNA-seq), Cleavage Under Targets and Tagmentation (CUT&Tag), chromatin immunoprecipitation (ChIP) and dual-luciferase reporter assays were applied to elucidate the downstream regulatory mechanism of CDK4. Results: CDK4 was highly expressed in Tumor-Drug Resistant (Tumor-DR) tissues, which was significantly correlated with poor patient prognosis. CDK4 overexpression enhanced cisplatin resistance and malignant phenotypes of RCC cells, whereas CDK4 knockdown reversed these effects and sensitized cells to cisplatin. In vivo experiments confirmed that CDK4 promoted cisplatin resistance and tumor growth of A498 cells, and this effect was validated under both CIS and GEM intervention. Mechanistically, CDK4 directly bound to the promoter region of the ASH1L (ASH1-Like Histone Lysine Methyltransferase) gene to promote its transcription; by upregulating ASH1L, CDK4 inhibited the expression of copper transporter 1 (CTR1), thereby mediating cisplatin resistance. Targeted inhibition of CDK4 or ASH1L enhanced the cisplatin sensitivity of RCC cells. Conclusions: This study identifies the critical role of the CDK4-ASH1L-CTR1 axis in cisplatin resistance of RCC.