PKCδ及下游靶分子介导放疗后肿瘤再增殖

After radiotherapy or chemotherapy, surviving tumor cells growth and reestablish the tumor is referred as tumor repopulation. Our previous studies demonstrated that radiotherapy- or chemotherapy-induced apoptotic cells significantly stimulate the proliferation of surviving tumor cells through the caspase 3-iPLA2-AA-PGE2 signaling pathway. My latest study showed that radiation-induced activation of caspase 3 could further activate protein kinase Cδ (PKCδ), which increases the phosphorylation of Akt in dying tumor cells, and the inhibition of PKCδ activity significantly decreased the growth-stimulating effect of dying tumor cells on surviving tumor cell repopulation both in vitro and in vivo. However, the downstream molecules mediated by PKCδ in tumor repopulation remains unclear. Since PI3K/Akt/mTOR signaling pathway could increase the expression of hypoxia-inducible factor 1α (HIF1α) to stimulate the production of vascular endothelial growth factor (VEGF), we assume that there may be a tumor cell repopulation-related caspase 3-PKCδ-PI3K/Akt/mTOR-HIF1α-VEGF signaling pathway presented in dying tumor cells. We intend to explore the relationship of PI3K/Akt/mTOR-HIF1α-VEGF with PKCδ as well as tumor cell repopulation, using the PKCδ dominant negative mutant-transduced tumor cells and the radiation-induced in vivo tumor repopulation model in Balb/c nude mice. This study will provide some new data for elucidating the mechanism of tumor repopulation.

肿瘤再增殖是指放化疗后残存的肿瘤细胞生长形成新的肿瘤的过程。课题组前期研究发现放化疗所致凋亡细胞可通过caspase 3-iPLA2-AA-PGE2通路刺激残存肿瘤细胞增殖。本人最近的研究发现放疗所致濒死肿瘤细胞中激活的caspase 3还可激活PKCδ，后者可增加Akt磷酸化。抑制PKCδ活性可在体内外显著抑制肿瘤再增殖！然而PKCδ是通过哪些下游分子调控肿瘤再增殖并不清楚。鉴于PI3K/Akt/mTOR通路可上调HIF1α促进VEGF生成，我们设想濒死肿瘤细胞可能存在caspase 3-PKCδ-PI3K/Akt/mTOR-HIF1α-VEGF通路，并与肿瘤细胞再增殖有关。我们拟在前期制备的PKCδ显性负性突变体细胞及裸鼠模型的基础上，研究PI3K/Akt/mTOR-HIF1α-VEGF与PKCδ及肿瘤再增殖的关系，为阐明肿瘤再增殖的分子机制提供新的实验证据。

肿瘤再增殖是指放化疗后残存的肿瘤细胞生长形成新的肿瘤的过程。课题组前期研究发现放化疗所致凋亡细胞可通过caspase-3/iPLA2/AA/PGE2通路刺激残存肿瘤细胞增殖。本人前期研究中发现放疗所致濒死肿瘤细胞中激活的caspase-3可激活PKCδ，抑制PKCδ活性可显著抑制体外和体内肿瘤再增殖。然而PKCδ调控肿瘤再增殖的机制目前尚不清楚。文献报道PKCδ的激活可激活Akt；Akt的激活被报道可上调HIF1α的表达进而促进VEGF的生成；而VEGF被大量的文献报道可直接刺激肿瘤细胞增殖。因此，我们设想濒死肿瘤细胞中可能存在caspase-3/PKCδ/Akt/HIF1α/VEGF通路参与调控肿瘤细胞再增殖。本研究中我们成功建立结直肠癌细胞体外和体内肿瘤再增殖模型，明确了放疗后濒死结直肠癌细胞在体外和体内均可显著刺激肿瘤再增殖；同时，我们证实caspase-3和caspase-7可促进PKCδ的切割激活来刺激肿瘤再增殖。caspase-3/PKCδ通路进一步促进Akt的激活，且Akt的激活也与肿瘤再增殖相关。濒死细胞最终通过caspase-3/PKCδ/Akt通路来调控VEGF-A的分泌（不依赖HIF1α），进而刺激肿瘤再增殖。最后，我们还发现PKCδ的核转移增多与结直肠癌肿瘤病人的预后显著负相关。综上，我们证实了caspase-3/PKCδ/Akt/VEGF-A信号通路在肿瘤再增殖中起关键的正向调控作用；另外，PKCδ核转移增多与肿瘤病人的预后显著负相关。这条新发现的caspase-3/PKCδ/Akt/VEGF-A信号通路有潜力作为干预放疗后肿瘤再增殖的靶点，同时，PKCδ的核转移增多有可能是预测结直肠癌病人预后的一个新的生物标志物。 ..项目成果论文已投稿于《Clinical Cancer Research》（IF：10.199，返修中）。