Actin cytoskeleton remodelling in the anterior pituitary folliculostellate cell line TtT/GF: participation of the actin-binding protein cortactin

Abstract

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.

Cortactin/tyrosine‐phosphorylated cortactin interaction with connexin 43 in mouse seminiferous tubules

“…We have shown that cell-to-cell communication transiently increased following PKC-mediated Cx43 phosphorylation in Ser 368 (Meilleur et al, 2007); however, the persistent increase in P-Cx43 levels is accompanied by a reduced Cx43-mediated intercellular communication (Bao et al, 2004;Lampe et al, 2000;Meilleur et al, 2007). Cortactin phosphorylation in tyrosine 421 has been associated with increased actin polymerization (Tehrani et al, 2007) and cell adhesion stabilization (Well et al, 2004;Zheng et al, 2005). Thus, the Cx43 dephosphorylation and cortactin phosphorylation documented here early in development may reflect increasing intercellular junction-actin cytoskeleton interactions within the seminiferous epithelium during this period.…”

“…(4) Changes in form and phosphorylation status of the cortactin are stage-dependent. Cortactin is associated with cell migration (Huang et al, 2003;van Rossum et al, 2006;Zheng et al, 2005). Here, near the apex, the mature spermatids migrate from the seminiferous epithelium to the lumen of the tubule following completion of their differentiation.…”

Isoform B of myosin II heavy chain mediates actomyosin contractility during TNFα-induced apoptosis

“…1A, control, 24 to 96 hours). We have previously shown that the actin cytoskeleton of serum-cultured TtT/GF cells is characterised by its association with the subplasmalemmal region and by the presence of thin cytoplasmic actin cables (Zheng et al, 2005). Treatment of TtT/GF cells with TNFα for increasing periods of time (0-96 hours) induced the cells to acquire a rounded shape and to detach from the culture support (Fig.…”

“…The cytoskeleton fractions were dissolved in RIPA buffer (150 mM NaCl, 1% NP-40, 0.5% DOC, 0.1% SDS, 50 mM Tris pH 8). The characterisation of subcellular fractions had been be done and described before (Zheng et al, 2005).…”

Accelerators, Brakes, and Gears of Actin Dynamics in Dendritic Spines

“…Cortactin is located at sites of actin assembly in lamellipodia [101], and is likely involved in endosomal movement in fibroblasts [102]. It is also implicated in controlling shape-changes of folliculostellate cells of the anterior pituitary [103], and in aberrant cell motility, such as cancer cell migration and invasion [104,105].…”