Epidermal growth factor activation of vinculin and beta 1-integrin gene transcription in quiescent Swiss 3T3 cells. Regulation through a protein kinase C-independent pathway

Growth activation of quiescent Swiss 3T3 fibroblasts leads to a rapid induction of vinculin and beta 1-integrin gene expression. Addition of serum, epidermal growth factor (EGF), or platelet-derived growth factor to serum-starved, density-arrested cells resulted in a rapid increase in vinculin and beta 1-integrin mRNA levels and a corresponding increase in vinculin synthesis. The increase in vinculin and beta 1-integrin mRNA expression by serum or EGF was not blocked by the inhibition of protein synthesis by cycloheximide. The kinetics of induction of vinculin and beta 1-integrin mRNAs by EGF are different: vinculin mRNA levels reached a peak of expression 4-5-fold greater than that measured in quiescent cells by 2 h after addition of growth factor, whereas beta 1-integrin mRNA levels increased more slowly and to a lesser extent, reaching peaks of 2-3-fold induction at 5 h poststimulation. Down-regulation of protein kinase C by prolonged pretreatment of cells with phorbol 1,2-myristate 1,3-acetate had no effect on the ability of EGF or platelet-derived growth factor to activate vinculin or beta 1-integrin mRNA expression. Furthermore, direct activation of protein kinase C with 1,2-myristate 1,3-acetate did not induce the expression of vinculin or beta 1-integrin mRNA, but did activate c-fos expression. In vitro nuclear "run-on" transcription assays demonstrate a greater than 7-fold increase in vinculin and beta 1-integrin transcription at 40-60 min after addition of EGF when compared with levels in quiescent cells. This activation was rapid and transient, but appeared to occur later than the increase in c-fos and actin transcription. These results demonstrate that vinculin and beta 1-integrin, important components of the cell adhesion apparatus, are members of a group of immediate early growth-responsive genes, along with c-fos, c-myc, actin, and fibronectin. In addition, regulation of these cell adhesion genes occurs exclusively through a protein kinase C-independent pathway in serum-deprived, density-arrested Swiss 3T3 cells.

Transient induction of vinculin gene expression in 3T3 fibroblasts stimulated by serum-growth factors

When stimulated with serum, quiescent Balb/C-3T3 fibroblasts were found to induce vinculin transcription transiently within 30 min, followed by accumulation of vinculin mRNA and protein synthesis between 2 and 4 h after stimulation and a decrease to the basal level by 6-8 h. Platelet-derived growth factor (PDGF), fibroblast growth factor (FGF), and 12-O-tetradecanoylphorbol-13-acetate (TPA) each could elicit a similar response, albeit to a lesser extent, whereas epidermal growth factor (EGF) was inefficient in inducing vinculin expression. In cells stimulated with serum and cycloheximide, vinculin expression was superinduced and vinculin mRNA levels persisted longer than in cells stimulated with serum alone. Cells arrested in the presence of serum by anchorage denial in methyl cellulose suspension culture also induced vinculin expression and formed large vinculin positive plaques when reattaching and spreading on the substrate in the presence of serum. Cells replated from suspension culture in the absence of serum on either plastic or extracellular matrix (ECM) components were capable of extensive spreading, but failed to elevate vinculin expression and displayed diffuse vinculin staining. The results indicate that the changes in vinculin organization and expression in response to growth factor stimulation may reflect either a necessary step in the progression through the cell cycle or a response related to complex cellular processes such as wound repair and embryogenesis.

Identification of two distinct functional domains on vinculin involved in its association with focal contacts

We report here on the identification of two distinct functional domains on chicken vinculin molecule, which can, independently, mediate its interaction with focal contacts in living cells. These findings were obtained by immunofluorescent labeling of COS cells transfected with a series of chicken vinculin-specific cDNA constructs derived from clones cVin1 and cVin5 (Bendori, R., D. Salomon, and B. Geiger. 1987. EMBO [Eur. Mol. Biol. Organ.] J. 6:2897-2905). These included a chimeric construct consisting of 5' sequences of cVin1 attached to the complementary 3' region of cVin5, as well as several constructs of either cVin1 or cVin5 from which 3' or 5' sequences were deleted. We show here that the products of both cVin1 and cVin5, and of the cVin1/cVin5 chimera, readily associated with focal contacts in transfected COS cells. Furthermore, 78 and 45 kD NH2-terminal fragments encoded by a deleted cVin1 and the 78-kD COOH-terminal portion of vinculin encoded by cVin5 were capable of binding specifically to focal contact areas. In contrast 3'-deletion mutants prepared from clone cVin5 and a 5'-deletion mutant of cVin1, lacking both NH2- and COOH-terminal sequences, failed to associate with focal contacts in transfected cells. The loss of binding was accompanied by an overall disarray of the microfilament system. These results, together with previous in vitro binding studies, suggest that vinculin contains at least two independent sites for binding to focal contacts; the NH2-terminal domain may contain the talin binding site while the COOH-terminal domain may mediate vinculin-vinculin interaction. Moreover, the disruptive effect of the double-deleted molecule (lacking the two focal-contact binding sites) on the organization of actin suggests that a distinct region involved in the binding of vinculin to the microfilament system is present in the NH2-terminal 45-kD region of the molecule.

Primary sequence and domain structure of chicken vinculin

We have determined the complete sequence of chick vinculin from two overlapping cDNA clones. The vinculin mRNA consists of 262 bp of 5' untranslated sequence, an open reading frame of 3195 bp (excluding the initiation codon) and a long 3' untranslated sequence (greater than 2 kb). Chick vinculin contains 1066 amino acid residues, and has a deduced molecular mass of 116,933 Da. Analysis of the domain structure of vinculin shows that the molecule can be cleaved by V8 proteinase into a 90 kDa globular head and a 32 kDa tail region, the latter of which could further be cleaved into a 27 kDa polypeptide. The 90 kDa globular head contains the N-terminus of vinculin, three 112-residue repeats (residues 259-589), and extends to approximately residue 850. Gel overlay experiments show that it also contains a binding site for the cytoskeletal protein talin. The talin-binding domain was further localized to the N-terminal 398 amino acid residues of the protein by expression in vitro of this region from a vinculin cDNA cloned into the Bluescript SK+ vector. The head and tail domains are apparently separated by a proline-rich region that contains V8-proteinase-cleavage sites and a candidate tyrosine (822)-phosphorylation site. Secondary-structure prediction suggests that the head and tail domains contain alpha-helical regions separated by short stretches of turn/coil. Comparison of the chick with a partial human sequence reveals that vinculin is a highly conserved protein. In chickens Southern-blot analysis is consistent with a single vinculin gene, and it is therefore likely that vinculin, and its higher-molecular-mass isoform termed metavinculin, arise through alternative splicing.

Changes in p53 mRNA expression during terminal differentiation of murine erythroleukemia cells

The protein p53 is functionally implicated in the normal regulation of cell proliferation. We have previously reported that the rate of p53 protein synthesis is reduced during the cessation of cellular proliferation which accompanies the in vitro induced differentiation of Friend-erythroleukemia cells. In this work we followed the p53 mRNA expression during the differentiation of these cells. We report on a new type of p53 mRNA with a slower electrophoretic mobility on gels, which appeared in the cytoplasmic fraction of the erythroleukemia cells between 1 to 3 days following induction of differentiation and persisted in the cells until Day 7. The larger type of p53 mRNA was found associated with polysomes, suggesting that it is translatable in cells. The difference in size between the noninduced and the differentiation-specific type of p53 mRNAs (about 200 nucleotides) was not abrogated following the deadenylation of the mRNAs, thus excluding the possibility that the altered size might result from a longer poly(A) tract. S1 nuclease mapping of the 3' termini of the p53 mRNAs revealed that the 3' ends of both p53 mRNA types were identical, suggesting that either alternative splicing or a longer 5' noncoding region could cause this heterogeneity in p53 mRNA transcripts.

Contact-dependent regulation of vinculin expression in cultured fibroblasts: a study with vinculin-specific cDNA probes

Vinculin specific cDNA clones were isolated from chicken embryo fibroblast (CEF) cDNA library in lambda gt11. The clones, ranging in size from 2.8 to 5.0 kb, were initially selected by rabbit antibodies to vinculin. Their identity was further confirmed by their specific reactivities with a battery of different vinculin-specific monoclonal antibodies. Southern blot analysis of restriction enzyme digested chicken spleen DNA suggested that all the isolated cDNA clones correspond to the same gene(s). Northern blot hybridization revealed that the vinculin-specific cDNA clones react with a single 6.5 kb mRNA in total cellular RNA preparations of CEF, whole chicken embryos and chicken gizzard smooth muscle. Moreover, fractionation of CEF poly(A)+ RNA by sucrose gradient centrifugation followed by translation in cell free system indicated that the mRNA coding for vinculin has a size of about 6.0-7.0 kb. The identity of these clones was finally confirmed by selection hybridization assay. The isolated vinculin-specific cDNA probes were subsequently used in order to study the effect of substrate adhesiveness on the expression of vinculin. We show here that cells cultured on highly adhesive substrate, such as endothelial extracellular matrix (ECM), form large vinculin-rich focal contacts, while cells grown on poorly adhesive substrate poly(2-hydroxyethyl methacrylate) [poly(HEMA)] contain only small distorted vinculin spots. These morphological differences were accompanied by over 5-fold reduction in vinculin synthesis in cells growing on poly(HEMA), compared to those cultured on the ECM and over 7.5-fold decrease in the levels of vinculin-specific mRNA.(ABSTRACT TRUNCATED AT 250 WORDS)

Molecular interactions in adherens-type contacts

Adherens junctions are members of a molecularly and structurally heterogeneous family of cell contacts sharing a common association with the microfilament system. Various topics related to the biogenesis of these cellular contacts and the molecular interactions involved in their formation are discussed. The role of vinculin, a cytoplasmic 'plaque' component present in all adherens junctions tested to date and its possible interactions with the other junctional domains have been investigated by both biochemical analyses and studies of molecular dynamics in microinjected living cells. The importance of A-CAM, which apparently functions as a 'junctional receptor' is emphasized and its roles in junction formation in cell cultures and in developing embryos are discussed. In addition, its relationship to other Ca2+-dependent cell adhesion molecules (in particular L-CAM) is considered. The evidence indicating that the level of expression of vinculin-specific mRNA is affected by culture conditions and may be markedly modulated by changes in the adhesiveness of the substratum on which the cells grow is reviewed.