Division of Molecular Cell Biology, Institute for Molecular Bioscience, University of Queensland, Brisbane, QLD 4072, Australia.
J Mol Histol. 2009 Oct;40(5-6):395-405. doi: 10.1007/s10735-010-9253-y. Epub 2010 Feb 16.
Cell-cell interactions influence epithelial morphogenesis through an interplay between cell adhesion, trafficking and the cytoskeleton. These cellular processes are coordinated, often by cell signals found at cell-cell contacts. One such contact-based signal is the phosphatidylinositol 3'-kinase (PI3-kinase; PI3K) pathway. PI3-kinase is best understood for its role in mitogenic signalling, where it regulates cell survival, proliferation and differentiation. Its precise morphogenetic impacts in epithelia are, in contrast, less well-understood. Using phosphoinositide-specific biosensors we confirmed that E-cadherin-based cell-cell contacts are enriched in PIP(3), the principal product of PI3-kinase. We then used pharmacologic inhibitors to assess the morphogenetic impact of PI3-kinase in MDCK and MCF7 monolayers. We found that inhibiting PI3-kinase caused a reduction in epithelial cell height that was reversible upon removal of the drugs. This was not attributable to changes in E-cadherin expression or homophilic adhesion. Nor were there detectable changes in cell polarity. While Myosin II has been implicated in regulating keratinocyte height, we found no effect of PI3-kinase inhibition on apparent Myosin II activity; nor did direct inhibition of Myosin II alter epithelial height. Instead, in pursuing signalling pathways downstream of PI3-kinase we found that blocking Rac signalling, but not mTOR, reduced epithelial cell height, as did PI3-kinase inhibition. Overall, our findings suggest that PI3-kinase exerts a major morphogenetic impact in simple cultured epithelia through preservation of cell height. This is independent of potential effects on adhesion or polarity, but may occur through PI3-kinase-stimulated Rac signaling.
细胞间的相互作用通过细胞间的黏附、运输和细胞骨架之间的相互作用来影响上皮形态发生。这些细胞过程是协调的，通常是通过细胞信号在细胞-细胞接触处发现的。这样的基于接触的信号之一是磷脂酰肌醇 3'-激酶（PI3-kinase；PI3K）途径。PI3K 最被理解的是其在有丝分裂信号中的作用，它调节细胞存活、增殖和分化。相比之下，它在上皮组织中的精确形态发生影响则不太为人所知。使用磷酸肌醇特异性生物传感器，我们证实基于 E-钙粘蛋白的细胞-细胞接触富含 PIP(3)，PI3-kinase 的主要产物。然后，我们使用药理抑制剂来评估 PI3-kinase 在 MDCK 和 MCF7 单层中的形态发生影响。我们发现抑制 PI3-kinase 会导致上皮细胞高度降低，而在去除药物后可恢复。这不是由于 E-钙粘蛋白表达或同质黏附的变化所致。也没有检测到细胞极性的变化。虽然肌球蛋白 II 被认为参与调节角质形成细胞的高度，但我们发现 PI3-kinase 抑制对明显的肌球蛋白 II 活性没有影响；直接抑制肌球蛋白 II 也不会改变上皮细胞高度。相反，在追寻 PI3-kinase 下游的信号通路时，我们发现阻断 Rac 信号通路，但不是 mTOR，会降低上皮细胞高度，而 PI3-kinase 抑制也是如此。总的来说，我们的研究结果表明，PI3-kinase 通过维持细胞高度在上皮的简单培养物中发挥主要的形态发生作用。这与对黏附和极性的潜在影响无关，但可能通过 PI3-kinase 刺激的 Rac 信号发生。
