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PubMed1984

Expression of the Rous sarcoma virus src gene in avian macrophages fails to elicit transformed cell phenotype.

Infection of avian macrophages with Rous sarcoma virus does not induce any changes in the morphology, growth behavior, or expression of macrophage-specific proteins. The absence of cellular transformation does not result from a block in the synthesis of viral proteins, since infectious viruses are released from a majority of cells in the culture. In this report, we examine the synthesis, processing, and functional activity of pp60src in Rous sarcoma virus-infected macrophages to determine whether the absence of transformation is due to an alteration in the functional expression of pp60src. Although the absolute level of pp60src was reduced compared with fibroblasts, the protein exhibited the same phosphorylation pattern and subcellular distribution and was able to phosphorylate immunoglobulin in the immune complex-protein kinase assay. These results imply that the failure of Rous sarcoma virus to transform macrophage may be due to a restriction in the cellular response to a functional src protein, perhaps due to the absence of cellular products which are essential for mediating pp60src-induced transformation.

Animals↗
PubMed1984

The second oncogene mil of avian retrovirus MH2 is related to the src gene family.

The nucleotide sequence of a PstI fragment prepared from a cloned MH2 virus genome, pMH2-Hd, has been deduced using chemical and enzymatic methods. This fragment, 1862 nucleotides in length, starts with the gag gene, encodes the v-mil sequence and stops within the v-myc gene. This sequence shows that the v-mil gene is fused to the gag gene giving rise to a fused polyprotein of 98 000 daltons: 515 amino acids at the amino terminus would correspond to p10, p19, p27 and part of p12 determinants, 347 amino acids at the carboxy terminus correspond to the v-mil specific sequence. The mil protein shares homology with a number of onc proteins such as src, fes, fms, mos, yes, fps and erbB, as well as with the catalytic chain of the cAMP-dependent protein kinase. This PstI fragment also encodes the beginning of the myc gene which was integrated in MH2 along with the 3' end of the preceding intron placing an acceptor splice site in front of the used open reading frame. As deduced from the sequence, the MH2 myc protein is not identical to the MC29 myc protein. It differs at its amino terminus, which contains little or no gag determinants, depending on the ATG used to initiate translation.

Amino Acid Sequence↗
PubMed1990

Involvement of the membrane cytoskeletal proteins and the src gene product in growth cone adhesion and movement.

The neuronal growth cone is a highly motile and adhesive structure, leading to maintain and promote neurite outgrowth. Using immunocytochemical and biochemical techniques, we investigated the regional distribution of the membrane cytoskeletal proteins, such as alpha-actinin, calspectin (nonerythroid spectrin or fodrin) and actin, and the proto-oncogene product, pp60c-src, in the growth cone. During a course of this study, the two types of alpha-actinin, having Ca2(+)-sensitive and -insensitive actin-binding abilities, were identified. These three membrane cytoskeletal proteins and pp60c-src showed discrete differential distributions coinciding with the different functions of the growth cone substractures. Ca2(+)-sensitive alpha-actinin, calspectin and pp60c-src were observed to localize in the growth cone body and the distal portion of neurites, which are the adhesive sites of growth cone and neurite. By contrast, Ca2(+)-sensitive alpha-actinin and actin were densely concentrated in the filopodia. These results suggest that Ca2(+)-insensitive alpha-actinin, calspectin and pp60c-src may be involved in adhesiveness of growth cone, and Ca2(+)-sensitive alpha-actinin and actin in Ca2(+)-dependent filopodial movement. Furthermore, we will discuss the functional and structural similarities between the growth cone and the motile contact which is also the adhesive site of motile, transformed and cancer cells.

Animals↗
PubMed1985

Regulation of cellular morphology by the Rous sarcoma virus src gene: analysis of fusiform mutants.

We have been interested in how Rous sarcoma virus (RSV) influences transformed cell morphology and compared the molecular properties of chicken embryo cells (CEC) infected with mutants of RSV that induce the fusiform transformed cell morphology with those of CEC infected by wild-type RSV, which induces the more normal round transformed cell morphology. We looked for properties shared by all fusiform mutant-infected cells, because these may be responsible for maintaining the fusiform morphology. Five different fusiform mutants, two wild-type RSVs, and one wild-type back revertant of a fusiform mutant were studied. In the fusiform mutant-infected cells, the localization and myristylation of pp60src were determined and the extent of expression of the extracellular matrix protein fibronectin was examined at both the mRNA and protein levels. The phosphorylation of vinculin on tyrosine also was examined in the same CEC. Within all fusiform mutant-transformed CEC, pp60src was dramatically absent from the adhesion plaque sites normally seen in cells transformed with wild-type RSV, and these transformed CEC all expressed more fibronectin mRNA and protein in the extracellular matrix than did the wild-type RSV-transformed CEC. The absence of pp60src from the adhesion plaques was not due to lack of myristylation of the src protein, and tyrosine phosphorylation of vinculin was not related to fibronectin expression. These results suggest that the inverse relationship between pp60src in the adhesion plaques and fibronectin expression in the extracellular matrix may be interconnected phenomena and could be related to the maintenance of the fusiform transformed morphology.

Animals↗
PubMed1988

Transforming activity of ras proteins translocated to the plasma membrane by a myristoylation sequence from the src gene product.

Ras p21 proteins exert their biological functions when associated to the inner surface of the plasma membrane. This association is mediated by a lipid molecule which is covalently attached to the protein by a thioester bond through a cysteine at residue 186, at the carboxy end of the molecule. Deletion or substitution of the critical Cys186 residue of the Harvey-ras protein leads to ras-p21 mutants lacking the ability to translocate to the membrane and devoid of transforming activity (Willumsen et al., 1984a, 1984b). We have been able to regenerate both localization to the plasma membrane as well as transforming activity of such mutant ras p21 proteins by fusion of the amino-terminal 15 residues of the v-p60src protein, responsible for the covalent binding of myristic acid and its membrane association. Thus, while translocation to the plasma membrane is necessary for function of the transforming Harvey-ras p21 protein, it appears to be independent of a specific membrane insertion mechanism.

Animals↗
PubMed1980

Transformation-defective mutants of feline sarcoma virus which express a product of the viral src gene.

Mink cell cultures infected with the Snyder-Theilen strain of feline sarcoma-leukemia virus were cloned from single cells under conditions favoring single virus-single cell interactions. The primary colonies included (i) typical feline sarcoma virus (FeSV)-transformed nonproducer clones, one of which segregated revertants, and (ii) FeSV-infected, phenotypically normal clones, three of which spontaneously converted to the transformed phenotype. The revertants and spontaneous transformants were compared with parental and sister clones expressing the opposite phenotype. Transformed subclones formed colonies in agar, were tumorigenic in nude mice, and failed to bind epidermal growth factor, whereas flat sister subclones were indistinguishable from uninfected mink cells in each of these assays. Sister subclones derived from the same infectious event contained FeSV proviruses integrated at the same molecular site, regardless of which phenotype was expressed. One revertant clone, however, lacked most FeSV proviral DNA sequences but retained terminal portions of the FeSV genome which persisted at the original site of proviral DNA insertion. Two flat subclones expressed viral RNA and the phosphorylated "gag-x" polyprotein (pp78gag-x) encoded by the gag and src sequences of the FeSV genome. Both of these clones were susceptible to retransformation by FeSV. Although unable to induce foci, the viruses rescued from these cells contained as much FeSV RNA as the focus-forming viruses rescued from transformed sister subclones and could be retransmitted to mink cells, again inducing FeSV gene products without signs of morphological transformation. We conclude that these FeSV genomes represent transformation-defective mutants.

Animals↗