Zheng Guifu, Solinet Sara, Pelletier R-Marc, Vitale María Leiza
Department of Pathology and Cell Biology, Faculty of Medicine, Université de Montréal, Montreal, Quebec, Canada.
J Mol Histol. 2005 Oct;36(8-9):461-74. doi: 10.1007/s10735-006-9021-1. Epub 2006 Apr 21.
We have previously shown that the folliculostellate (FS) cells of the anterior pituitary change their shape from stellate (type I) to polygonal (type II) coincidently with variations in the secretory activity of the pituitary. To elucidate the mechanisms involved in this switch in phenotypes, here we studied the impact of serum factors on the morphology of the FS cell line TtT/GF. TtT/GF cells cultured in serum-containing medium displayed elongated shapes and membrane ruffles similarly to type I cells. Serum deprivation caused the loss of plasma membrane activity and the acquisition by the cells of a sedentary phenotype and of a polygonal shape typical of type II FS cells. Addition of serum to the starved cells induced the reappearance of membrane raffles and lamellipodia. The switch in phenotypes and the maintenance of a motile phenotype depended on tyrosine kinase but not on Erk activity. Because the transition between phenotypes involved the tyrosine kinase-dependent reorganization of cortical actin filaments, we studied the participation of the actin-binding protein, cortactin, a tyrosine kinase substrate. Cortactin and its tyrosine-phosphorylated form, pY421-cortactin, localized to membrane ruffles and lamellipodia in serum-cultured TtT/GF cells, while they were evenly distributed over the whole cell cortex in serum-starved cells. Serum treatment of starved cells induced a transient increase in pY421-cortactin levels and the clustering of pY421-cortactin in membrane regions where protrusions were developing. Both serum responses were blocked by a tyrosine kinase inhibitor. Together, the results indicate that the transition from a polygonal to an elongated shape entails the acquisition of a dynamic cortical actin cytoskeleton that involves the tyrosine kinase-dependent phosphorylation of cortactin and the translocation of cortical pY421-cortactin to sites of ruffle formation at the plasma membrane.
我们之前已经表明，垂体前叶的滤泡星形（FS）细胞会随着垂体分泌活动的变化，将其形状从星形（I型）转变为多边形（II型）。为了阐明这种表型转换所涉及的机制，我们在此研究了血清因子对FS细胞系TtT/GF形态的影响。在含血清培养基中培养的TtT/GF细胞呈现出细长的形状和膜皱褶，类似于I型细胞。血清剥夺导致细胞膜活性丧失，细胞获得了静止的表型以及II型FS细胞典型的多边形形状。向饥饿的细胞中添加血清会诱导膜皱褶和片状伪足重新出现。表型的转换和运动表型的维持依赖于酪氨酸激酶，而不依赖于Erk活性。由于表型之间的转变涉及酪氨酸激酶依赖性的皮质肌动蛋白丝重组，我们研究了肌动蛋白结合蛋白cortactin（一种酪氨酸激酶底物）的参与情况。在血清培养的TtT/GF细胞中，cortactin及其酪氨酸磷酸化形式pY421-cortactin定位于膜皱褶和片状伪足，而在血清饥饿的细胞中，它们均匀分布在整个细胞皮质。用血清处理饥饿细胞会导致pY421-cortactin水平短暂升高，并且pY421-cortactin在突起正在形成的膜区域聚集。这两种血清反应均被酪氨酸激酶抑制剂阻断。总之，结果表明从多边形形状到细长形状的转变需要获得动态的皮质肌动蛋白细胞骨架，这涉及酪氨酸激酶依赖性的cortactin磷酸化以及皮质pY421-cortactin向质膜上皱褶形成位点的转位。
