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 “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. Previou studies reported that CDK4/6 inhibitors induced DNA damage to activate the cGAS-STING pathway. However, the underlying mechanisms of how CDK4/6 inactivated the cGAS-STING pathway are still elusive. Here we revealed that treatment with CDK4/6 inhibitors enhance the anti-tumor effect of STING agonists in prostate cancer cells. Mechanically, CDK4/6 phosphorylated TBK1 at S527 to inactive the STING signaling pathway independent of RB1 in prostate cancer cell. Then, we also found that CDK4/6 phosphorylated RB1 at S249/T252 to induce 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 in prostate cancer cells. These insights provide the novel evidence for CDK4/6 suppressing the innate immune response of prostate cancer.