Elis Winfried, Triantafellow Ellen, Wolters Natalie M, Sian Katie R, Caponigro Giordano, Borawski Jason, Gaither L Alex, Murphy Leon O, Finan Peter M, Mackeigan Jeffrey P
Van Andel Research Institute, Grand Rapids, MI 49503, USA.
Mol Cancer Res. 2008 Apr;6(4):614-23. doi: 10.1158/1541-7786.MCR-07-0262.
Members of the phosphoinositide 3-kinase (PI3K) family collectively control multiple cellular responses, including proliferation, growth, chemotaxis, and survival. These diverse effects can partly be attributed to the broad range of downstream effectors being regulated by the products of these lipid kinases, the 3'-phosphoinositides. However, an additional layer of complexity is introduced by the existence of multiple PI3K enzyme isoforms. Much has been learned over the last years on the roles of the classes I and III PI3K members in cellular signaling, but little is known about the isoform-specific tasks done by the class II PI3Ks (C2alpha, beta, and gamma). In this study, we used quantitative reverse transcription-PCR and RNA interference in mammalian cells to gain further insight into the function of these lesser studied PI3K enzymes. We find that PI3K-C2alpha, but not PI3K-C2beta, has an important role in controlling cell survival and by using a panel of RNA interference reagents, we were able to determine a critical threshold of PI3K-C2alpha mRNA levels, below which the apoptotic program is switched on, via the intrinsic cell death pathway. In addition, knockdown of PI3K-C2alpha to levels that by themselves do not induce apoptosis sensitize cells to the anticancer agent Taxol (paclitaxel). Lastly, we report that lowering the levels of PI3K-C2alpha in a number of cancer cell lines reduces their proliferation and cell viability, arguing that PI3K inhibitors targeting not only the class Ialpha isoform but also class IIalpha may contribute to an effective anticancer strategy.
磷酸肌醇3激酶（PI3K）家族成员共同控制多种细胞反应，包括增殖、生长、趋化性和存活。这些多样的效应部分可归因于这些脂质激酶的产物3'-磷酸肌醇所调控的广泛下游效应器。然而，多种PI3K酶亚型的存在引入了另一层复杂性。在过去几年里，关于I类和III类PI3K成员在细胞信号传导中的作用已有很多了解，但对于II类PI3K（C2α、β和γ）所执行的亚型特异性任务却知之甚少。在本研究中，我们在哺乳动物细胞中使用定量逆转录PCR和RNA干扰，以进一步深入了解这些研究较少的PI3K酶的功能。我们发现PI3K-C2α而非PI3K-C2β在控制细胞存活方面具有重要作用，并且通过使用一组RNA干扰试剂，我们能够确定PI3K-C2α mRNA水平的临界阈值，低于该阈值，凋亡程序通过内源性细胞死亡途径被开启。此外，将PI3K-C2α敲低至本身不会诱导凋亡的水平会使细胞对抗癌药物紫杉醇敏感。最后，我们报告在多种癌细胞系中降低PI3K-C2α的水平会降低其增殖和细胞活力，这表明不仅靶向Iα类亚型而且靶向IIα类的PI3K抑制剂可能有助于制定有效的抗癌策略。
