CDK4/6 inhibition suppresses p73 phosphorylation and activates DR5 to potentiate chemotherapy and immune checkpoint blockade. CDK4/6 inhibition suppresses p73 phosphorylation and activates DR5 to potentiate chemotherapy and immune checkpoint blockade

Targeting cyclin-dependent kinases 4 and 6 (CDK4/6) is a successful therapeutic approach against breast and other solid tumors. Inhibition of CDK4/6 halts cell cycle progression and promotes antitumor immunity. However, the mechanisms underlying the antitumor activity of CDK4/6 inhibitors are not fully understood. We found that CDK4/6 bind and phosphorylate the p53 family member p73 at threonine 86, which sequesters p73 in the cytoplasm. Inhibition of CDK4/6 led to dephosphorylation and nuclear translocation of p73, which transcriptionally activated death receptor 5 (DR5), a cytokine receptor and key component of the extrinsic apoptotic pathway. p73-mediated induction of DR5 by CDK4/6 inhibitors promoted immunogenic cell death (ICD) of cancer cells. Deletion of DR5 in cancer cells in vitro and in vivo abrogated the potentiating effects of CDK4/6 inhibitors on immune cytokine TNF-related apoptosis-inducing ligand (TRAIL), 5-fluorouracil (5-FU) chemotherapy, and anti-PD-1 immunotherapy. Together, these results reveal a previously unrecognized consequence of CDK4/6 inhibition, which may be critical for potentiating the killing and immunogenic effects on cancer cells. Overall design: mRNA profiles of HCT116 cells, HCT116 cells treated with palbociclib for 24 hours, HCT116 cells transfected with siRNA against CDK4 for 24 hours.

靶向细胞周期蛋白依赖性激酶4和6（cyclin-dependent kinases 4 and 6, CDK4/6）是治疗乳腺癌及其他实体瘤的成熟治疗策略。CDK4/6抑制剂可阻断细胞周期进程并增强抗肿瘤免疫，但其抗肿瘤活性的潜在分子机制尚未完全阐明。本研究发现，CDK4/6可结合并在苏氨酸86位点磷酸化p53家族成员p73，进而将p73滞留于细胞质内。CDK4/6抑制剂处理可促使p73发生去磷酸化并发生核转位，后者可转录激活死亡受体5（death receptor 5, DR5）——一种参与外源性凋亡通路的关键细胞因子受体。CDK4/6抑制剂通过p73介导的DR5上调，可促进癌细胞发生免疫原性细胞死亡（immunogenic cell death, ICD）。体外及体内实验均证实，敲除癌细胞中的DR5可消除CDK4/6抑制剂对免疫细胞因子肿瘤坏死因子相关凋亡诱导配体（TNF-related apoptosis-inducing ligand, TRAIL）、5-氟尿嘧啶（5-fluorouracil, 5-FU）化疗以及抗PD-1免疫治疗的增敏作用。综上，本研究揭示了CDK4/6抑制此前未被报道的生物学效应，该效应或对增强癌细胞杀伤及免疫原性作用至关重要。实验整体设计：本研究包含三组样本的mRNA转录组谱分析，分别为未处理的HCT116细胞、经帕博西尼（palbociclib）处理24小时的HCT116细胞、转染靶向CDK4的小干扰RNA（siRNA）24小时的HCT116细胞。