CLK1 Promotes Myeloid-Derived Suppressor Cell Trafficking and Reprograms the Tumor Microenvironment by Activating Hippo/YAP Signaling in Colorectal Cancer.

Colorectal cancer is a highly heterogeneous malignancy characterized by complex interactions between tumor cells and the immune system. The tumor microenvironment (TME) plays a crucial role in colorectal cancer progression and response to therapy. However, the mechanisms regulating TME composition remain poorly understood because of the genetic and phenotypic diversity of tumor cells. In this study, we investigated the tumor-intrinsic factors contributing to TME formation and evaluated genotype-based combination strategies to enhance the efficacy of immunotherapy in colorectal cancer. Using RNA sequencing, single-cell analysis, and immunohistochemistry (IHC), we identified pro-oncogenic proteins associated with low immune activation. Functional studies using in vitro co-culture systems, subcutaneous colorectal tumor models, flow cytometry, and IHC revealed a role for CDC-like kinase 1 (CLK1) in tumor progression and immunosuppressive TME remodeling. Mechanistically, CLK1 activation led to hyperactivation of the Hippo signaling pathway, promoting nuclear translocation of Yes-associated protein (YAP) and subsequent transcriptional upregulation of the chemokine CXCL1. Elevated CLK1 expression correlated with increased infiltration of myeloid-derived suppressor cells (MDSC) and impaired antitumor immune responses. Knockdown (KD) of CLK1 significantly reduced MDSC recruitment and restored CD8+ T-cell activity. Moreover, combined CLK1 KD and anti-PD-1 therapy enhanced intratumoral CD8+ T-cell infiltration to a greater extent and elicited robust antitumor responses in murine colorectal cancer models. Collectively, our findings identify the CLK1-Hippo/YAP-CXCL1 signaling axis as a regulator of immune evasion and TME remodeling in colorectal cancer and highlight the potential of therapeutically targeting this axis to improve the efficacy of immune checkpoint blockade.