Menard Raymond E, Jovanovski Andrew P, Mattingly Raymond R
Department of Pharmacology, Wayne State University, 540 East Canfield Avenue, Detroit, MI 48201, USA.
Neoplasia. 2005 Jul;7(7):638-45. doi: 10.1593/neo.04736.
The protein kinase, PAK1, is overexpressed in human breast cancer and may contribute to malignancy through induction of proliferation and invasiveness. In this study, we examined the role of PAK1 in the survival of detached MCF10A breast epithelial cells to test whether it may also regulate the early stages of neoplasia. MCF10A cells undergo anoikis, as measured by the cleavage of caspase 3 and poly(ADP-ribose) polymerase (PARP), after more than 8 hours of detachment. Endogenous Akt, PAK1, and BAD are phosphorylated in attached MCF10A cells, but these phosphorylation events are all lost during the first 8 hours of detachment. Expression of constitutively active PAK1 or Akt suppresses the cleavage of caspase 3 and PARP in detached MCF10A cells. Co-overexpression of active PAK1 with dominant-negative Akt, or of active Akt with dominant-negative PAK1, still suppresses anoikis. Thus, Akt and PAK1 enhance survival through pathways that are at least partially independent. PAK1-dependent regulation of anoikis is likely to occur early in the apoptotic cascade as expression of dominant-negative PAK1 increased the cleavage of the upstream caspase 9, while constitutively active PAK1 inhibited caspase 9 activation. These results support a role for activated PAK1 in the suppression of anoikis in MCF10A epithelial cells.
蛋白激酶PAK1在人类乳腺癌中过表达，可能通过诱导增殖和侵袭性而促进恶性肿瘤的发生。在本研究中，我们检测了PAK1在脱离贴壁的MCF10A乳腺上皮细胞存活中的作用，以测试它是否也可能调节肿瘤形成的早期阶段。脱离贴壁超过8小时后，通过半胱天冬酶3和聚（ADP-核糖）聚合酶（PARP）的裂解来检测，MCF10A细胞会发生失巢凋亡。在贴壁的MCF10A细胞中，内源性Akt、PAK1和BAD被磷酸化，但在脱离贴壁的最初8小时内，这些磷酸化事件全部消失。组成型活性PAK1或Akt的表达可抑制脱离贴壁的MCF10A细胞中半胱天冬酶3和PARP的裂解。活性PAK1与显性阴性Akt共过表达，或活性Akt与显性阴性PAK1共过表达，仍然可抑制失巢凋亡。因此，Akt和PAK1通过至少部分独立的途径增强细胞存活。PAK1依赖的失巢凋亡调节可能发生在凋亡级联反应的早期，因为显性阴性PAK1的表达增加了上游半胱天冬酶9的裂解，而组成型活性PAK1抑制了半胱天冬酶9的激活。这些结果支持活化的PAK1在抑制MCF10A上皮细胞失巢凋亡中的作用。
