Kim Minji, Datta Anirban, Brakeman Paul, Yu Wei, Mostov Keith E
Departments of Anatomy, and Biochemistry and Biophysics, University of California School of Medicine, San Francisco, CA 94158, USA.
J Cell Sci. 2007 Jul 15;120(Pt 14):2309-17. doi: 10.1242/jcs.007443.
Epithelial cells are polarized, with an apical surface facing a lumen or outer surface and a basolateral surface facing other cells and extracellular matrix (ECM). Hallmarks of epithelial carcinogenesis include loss of polarity, as well as uncontrolled proliferation and resistance to apoptosis. Are these features controlled by a common molecular mechanism? The partitioning-defective 3 (PAR3)-PAR6-atypical PKC (aPKC) complex is a master regulator that controls polarization in many animal cells. Here we show that PAR6 is involved in apoptosis by regulating aPKC and glycogen synthase kinase 3beta (GSK-3beta) activity. During epithelial morphogenesis in 3D culture of Madin-Darby canine kidney (MDCK) cells, expression of an N-terminally deleted PAR6 (PAR6DeltaN) leads to a significant increase in caspase-dependent cell death by downregulating aPKC activity. Accordingly, inhibition of aPKC in wild-type (WT) MDCK cells with either a cell-permeable PKCzeta pseudosubstrate or RNAi promotes apoptosis, which suggests that PAR6 regulates apoptosis via an aPKC-mediated pathway. GSK-3beta, a substrate of aPKC, is hyper-activated by expressing PAR6DeltaN. GSK-3beta inhibitors block PAR6DeltaN-induced apoptosis while expression of constitutively active GSK-3beta (S9A) promotes apoptosis, which is rescued by ectopic expression of aPKC. We conclude that a PAR6-aPKC-GSK-3beta mechanism links cell polarity and apoptosis.
上皮细胞是极化的，其顶端表面朝向管腔或外表面，基底外侧表面朝向其他细胞和细胞外基质（ECM）。上皮癌发生的标志包括极性丧失、不受控制的增殖以及对细胞凋亡的抵抗。这些特征是否由共同的分子机制控制？分区缺陷3（PAR3）-PAR6-非典型蛋白激酶C（aPKC）复合物是一种主要调节因子，可控制许多动物细胞的极化。在这里，我们表明PAR6通过调节aPKC和糖原合酶激酶3β（GSK-3β）的活性参与细胞凋亡。在Madin-Darby犬肾（MDCK）细胞的三维培养上皮形态发生过程中，N端缺失的PAR6（PAR6DeltaN）的表达通过下调aPKC活性导致半胱天冬酶依赖性细胞死亡显著增加。因此，用细胞可渗透的PKCζ假底物或RNAi抑制野生型（WT）MDCK细胞中的aPKC会促进细胞凋亡，这表明PAR6通过aPKC介导的途径调节细胞凋亡。aPKC的底物GSK-3β通过表达PAR6DeltaN而过度激活。GSK-3β抑制剂可阻断PAR6DeltaN诱导的细胞凋亡，而组成型活性GSK-3β（S9A）的表达则促进细胞凋亡，异位表达aPKC可挽救这种凋亡。我们得出结论，PAR6-aPKC-GSK-3β机制将细胞极性与细胞凋亡联系起来。
