Molecular Diagnostic Laboratory of Cancer Center, Shanghai General Hospital, Shanghai Jiao Tong University School of Medicine, Shanghai, China.
Department of Pathology, Shanghai General Hospital, Shanghai Jiao Tong University School of Medicine, Shanghai, China.
Clin Cancer Res. 2019 Jun 15;25(12):3732-3743. doi: 10.1158/1078-0432.CCR-18-3001. Epub 2019 Mar 19.
Tumor repopulation is known as a major cause of treatment failure and/or tumor recurrence after radiotherapy. The underlying mechanism remains unclear. Our previous study demonstrated that irradiated apoptotic cells mediated tumor repopulation, in which caspase-3 played an important role. Herein, we investigated downstream effectors of caspase-3 involved in this process.
A dominant-negative protein kinase Cδ (DN_PKCδ) mutant that could not be cleaved by caspase-3 and therefore could not be activated by irradiation-induced apoptosis was constructed. DN_PKCδ stably transduced tumor cells were compared with wild-type tumor cells for their growth stimulation effects in and tumor repopulation models. Downstream effectors of caspase-3 and PKCδ were investigated. The role of PKCδ was further verified in human colorectal tumor specimens.
Inactivation of caspase-3 or caspase-7 attenuated tumor repopulation and weakened PKCδ cleavage. Both DN_PKCδ and PKCδ inhibitors restrained tumor repopulation both and . Phosphorylated Akt was attenuated in caspase-3-, caspase-7-, or PKCδ-inactivated tumor cells. Furthermore, expression of vascular endothelial growth factor (VEGF)-A but not hypoxia-inducible factor 1α (HIF1α) was decreased in PKCδ- or Akt-inactivated tumor cells. In addition, inhibition of p-Akt, HIF1α, VEGF-A, or VEGF-A receptor reduced tumor repopulation significantly. Finally, increased nuclear translocation of PKCδ in colorectal tumor specimens was associated with worse patient prognosis.
The caspase-3/PKCδ/Akt/VEGF-A axis is involved in tumor repopulation and could be exploited as a potential target to enhance the efficacy of radiotherapy.
肿瘤再增殖是放疗后治疗失败和/或肿瘤复发的主要原因。其潜在机制尚不清楚。我们之前的研究表明，辐射诱导的凋亡细胞介导肿瘤再增殖，其中半胱天冬酶-3（caspase-3）起着重要作用。在此，我们研究了 caspase-3 参与这一过程的下游效应物。
构建了一种无法被 caspase-3 切割因而不能被辐射诱导凋亡激活的蛋白激酶 Cδ（PKCδ）的显性失活突变体（DN_PKCδ）。将稳定转染 DN_PKCδ 的肿瘤细胞与野生型肿瘤细胞进行比较，在 和 肿瘤再增殖模型中观察其对肿瘤生长的刺激作用。研究了 caspase-3 和 PKCδ 的下游效应物。进一步在人结直肠肿瘤标本中验证了 PKCδ 的作用。
caspase-3 或 caspase-7 的失活减弱了肿瘤再增殖，并削弱了 PKCδ 的切割。DN_PKCδ 和 PKCδ 抑制剂均能抑制 和 肿瘤的再增殖。失活 caspase-3、caspase-7 或 PKCδ 的肿瘤细胞中磷酸化 Akt 减弱。此外，在失活 PKCδ 或 Akt 的肿瘤细胞中，血管内皮生长因子（VEGF）-A 的表达减少，但缺氧诱导因子 1α（HIF1α）的表达不变。此外，抑制 p-Akt、HIF1α、VEGF-A 或 VEGF-A 受体可显著抑制肿瘤再增殖。最后，结直肠肿瘤标本中 PKCδ 的核转位增加与患者预后不良有关。
caspase-3/PKCδ/Akt/VEGF-A 轴参与肿瘤再增殖，可作为增强放疗效果的潜在靶点。
