CDK4/6 inhibits the STING signaling axis through RB1-dependent and RB1-independent pathways in prostate cancer

The efficacy of immunotherapy in prostate cancer is not satisfactory due to the heterogeneity of this cancer, the “cold” tumor microenvironment and the paucity of neoantigens. The STING-TBK1-IRF3 signaling axis as core molecules of the innate immune system is increasingly recognized as a candidate target for cancer immunotherapy. Inhibition of CDK4/6 has been reported to r increase T-cell activation to enhance antitumor immunity. However, little is known about the relationship between CDK4/6 and innate immune-related STING signaling. In this study, we revealed that combination treatment with CDK4/6 inhibitors and STING agonists is significantly more effective than treatment with STING agonists alone in eliminating prostate cancer cells. Then, we demonstrated that CDK4/6 phosphorylate TBK1 at S527 to inactive the STING signaling pathway independent of RB1 in prostate cancer cell. On the other hand, CDK4/6 phosphorylate RB1 at S249/T252 to promote the interaction of RB1 with TBK1 and diminish the phosphorylation of TBK1 at S172, which also suppresses the activation of the STING pathway. Collectively, we found that CDK4/6 inhibits the STING/TBK1/IRF3 axis through RB1-dependent and RB1-independent pathways and elucidated the detailed mechanism. These insights lay a solid foundation for the synergistic application of CDK4/6 inhibitors with STING activators in prostate cancer patients.