Bakin Andrei V, Safina Alfiya, Rinehart Cammie, Daroqui Cecilia, Darbary Huferesh, Helfman David M
Department of Cancer Genetics, Roswell Park Cancer Institute, Buffalo, NY 14263, USA.
Mol Biol Cell. 2004 Oct;15(10):4682-94. doi: 10.1091/mbc.e04-04-0353. Epub 2004 Aug 18.
We have investigated transforming growth factor beta (TGF-beta)-mediated induction of actin stress fibers in normal and metastatic epithelial cells. We found that stress fiber formation requires de novo protein synthesis, p38Mapk and Smad signaling. We show that TGF-beta via Smad and p38Mapk up-regulates expression of actin-binding proteins including high-molecular-weight tropomyosins, alpha-actinin and calponin h2. We demonstrate that, among these proteins, tropomyosins are both necessary and sufficient for TGF-beta induction of stress fibers. Silencing of tropomyosins with short interfering RNAs (siRNAs) blocks stress fiber assembly, whereas ectopic expression of tropomyosins results in stress fibers. Ectopic-expression and siRNA experiments show that Smads mediate induction of tropomyosins and stress fibers. Interestingly, TGF-beta induction of stress fibers was not accompanied by changes in the levels of cofilin phosphorylation. TGF-beta induction of tropomyosins and stress fibers are significantly inhibited by Ras-ERK signaling in metastatic breast cancer cells. Inhibition of the Ras-ERK pathway restores TGF-beta induction of tropomyosins and stress fibers and thereby reduces cell motility. These results suggest that induction of tropomyosins and stress fibers play an essential role in TGF-beta control of cell motility, and the loss of this TGF-beta response is a critical step in the acquisition of metastatic phenotype by tumor cells.
我们研究了转化生长因子β（TGF-β）介导的正常上皮细胞和转移性上皮细胞中肌动蛋白应力纤维的诱导作用。我们发现应力纤维的形成需要从头合成蛋白质、p38丝裂原活化蛋白激酶（p38Mapk）和Smad信号传导。我们表明，TGF-β通过Smad和p38Mapk上调肌动蛋白结合蛋白的表达，包括高分子量原肌球蛋白、α-辅肌动蛋白和钙调蛋白h2。我们证明，在这些蛋白质中，原肌球蛋白对于TGF-β诱导应力纤维既是必需的也是充分的。用小干扰RNA（siRNA）沉默原肌球蛋白可阻断应力纤维组装，而原肌球蛋白的异位表达则导致应力纤维形成。异位表达和siRNA实验表明，Smads介导原肌球蛋白和应力纤维的诱导。有趣的是，TGF-β诱导应力纤维并不伴随着丝切蛋白磷酸化水平的变化。在转移性乳腺癌细胞中，Ras-ERK信号传导显著抑制TGF-β诱导的原肌球蛋白和应力纤维。抑制Ras-ERK途径可恢复TGF-β诱导的原肌球蛋白和应力纤维，从而降低细胞运动性。这些结果表明，原肌球蛋白和应力纤维的诱导在TGF-β对细胞运动性的控制中起重要作用，而这种TGF-β反应的丧失是肿瘤细胞获得转移表型的关键步骤。
