The same normal cell protein is phosphorylated after transformation by avian sarcoma viruses with unrelated transforming genes

Cell proliferation and carcinogenesis may share a common basis of permeable plasma membrane clusters

Wound potentials increase the surface potential of exposed areas of nearby cells. In these cells, soluble cytoplasmic bases are assumed gradually to move nearer the exposed area. Acidic molecules on the cell surface migrate to points opposite the bases. The image-charged species are mutually attracted to form transmembrane clusters. At clusters, membrane permeability increases and the cell is stimulated to cycle. When the wound heals, its clusters disperse, leaving a small 'permanent' residuum. Permanent clusters initiate cells to malignancy. They have (or develop) lipophilic molecules on both surfaces that help fix them in the membrane. Exposed cells contaminated with polycyclic aromatic hydrocarbon carcinogens (PAH) readily form permanent clusters. At mitosis, clusters on parental plasma membrane pass with that membrane to a daughter cell. Promotion results from many short-term or a single long-term exposure of initiated membranes to abnormal surface charge. Permanent clusters increase on the membrane after repeated wounding, proximity of charged foreign bodies like plastic film or asbestos, or oxidation of surface molecules. Progression requires acceleration of cluster growth so the daughter cell membranes become as leaky at maturity as was the parent membrane. One mechanism suggested involves reversible phosphorylation by membrane-bound kinases; another involves attraction of a basic protein (p36) to the membrane.

Calpactin I in the differentiating embryonic chicken lens: mRNA levels and protein distribution

Calpactin I, one of the EDTA-extractable proteins of the lens membrane, binds phospholipid and actin in a calcium-dependent manner. It is also known substrate of the pp60arc kinase. Analysis of embryonic chicken lens RNA with a bovine calpactin I-specific cDNA probe revealed the presence of a approximately 1.8 Kb calpactin mRNA in the lens cells. Six-day embryonic chicken lenses were microdissected into central epithelium, equatorial epithelium, and fiber cells. Total cytoplasmic RNA was isolated from these samples and calpactin I mRNA levels were determined by the polymerase chain reaction (PCR) following reverse transcription (RT). Quantitative PCR indicates that the calpactin I mRNA levels in the equatorial epithelium are greater than in the central epithelium by a factor of 12.7 +/- 2.7. Calpactin I mRNA in fiber cells is an additional 3.5 +/- 1.5 times greater than in the equatorial epithelium. Whole mounts of embryonic chicken lens epithelia and histological sections of whole lenses were also examined with an antibody directed against chicken calpactin I. Calpactin I was predominantly localized in a punctate distribution in equatorial epithelial cells and near the plasma membrane of elongate fiber cells. The elevated levels of calpactin I mRNA observed in the equatorial epithelium and fiber cells and the immunological localization of the protein suggest a possible role of calpactin I in the elongation of fiber cells during lens differentiation.

Identification and purification of a bovine corpora luteal membrane glycoprotein with [3H]prostaglandin F2-alpha binding properties

A bovine corpora luteal membrane glycoprotein which coelutes from multiple chromatographic procedures with bound tritiated prostaglandin F2a ([3H]PGF2 alpha) has been identified and purified to homogeneity. The properties of this molecule include: an apparent molecular mass by polyacrylamide gel electrophoresis (PAGE) of 135 kD; glycosylation which resists endoglycosidases D and H but is susceptible to cleavage by the exoglycosidase sialidase; binding of the molecule to Wheat Germ Agglutinin Sepharose but not to Concanavalin A Sepharose or Soybean Agglutinin Sepharose; migration on O'Farrell 2-D PAGE (pI 3-10) to the acidic side of the gel; binding to DEAE-Cellulose at pH 7.5 which can be displaced with NaCl at concentrations above approximately 100 mM; and, when solubilized with Triton X-100, binding to Phenyl-Sepharose or Octyl-Sepharose columns. Lastly, a rabbit polyclonal antibody against this [3H]PGF2 alpha binding protein has been made which allows both Western blotting of the 135 kD protein as well as immunohistochemical staining of ovarian tissue in a manner expected from previous binding studies. Problems associated with membrane solubilization of the receptor and receptor renaturation are discussed.

Avian sarcoma viruses

Twelve independent isolates of avian sarcoma viruses (ASVs) can be divided into four groups according to the transforming genes harbored in the viral genomes. The first group is represented by viruses containing the transforming sequence, src, inserted in the viral genome as an independent gene; the other three groups of viruses contain transforming genes fps, yes or ros fused to various length of the truncated structural gene gag. These transforming sequences have been obtained by avian retroviruses from chicken cellular DNA by recombination. The src-containing viruses code for an independent polypeptide, p60src; and the representative fps, yes and ros-containing ASVs code for P140/130gag-fps, P90gag-yes and P68gag-ros fusion polypeptides respectively. All of these transforming proteins are associated with the tyrosine-specific protein kinase activity capable of autophosphorylation and phosphorylating certain foreign substrates. p60src and P68gag-ros are integral cellular membrane proteins and P140/130gag-fps and P90gag-yes are only loosely associated with the plasma membrane. Cells transformed by ASVs contain many newly phosphorylated proteins and in most cases have an elevated level of total phosphotyrosine. However, no definitive correlation between phosphorylation of a particular substrate and transformation has been established except that a marked increase of the tyrosine phosphorylation of a 34,000 to 37,000 dalton protein is observed in most ASV transformed cells. The kinase activity of ASV transforming proteins appears to be essential, but not sufficient for transformation. The N-terminal domain of p60src required for myristylation and membrane binding is also crucial for transformation. By contrast, the gag portion of the FSV P130gag-fps is dispensable for in vitro transformation and removal of it has only an attenuating effect on in vivo tumorigenicity. The products of cellular src, fps and yes proto-oncogenes have been identified and shown to also have tyrosine-specific protein kinase activity. The transforming potential of c-src and c-fps has been studied and shown that certain structural changes are necessary to convert them into transforming genes. Among the cellular proto-oncogenes related to the four ASV transforming genes, c-ros most likely codes for a growth factor receptor-like molecule. It is possible that the oncogene products of ASVs act through certain membrane receptor(s) or enzyme(s), such as protein kinase C, in the process of cell transformation.

Rous sarcoma virus mutant dlPA105 induces different transformed phenotypes in quail embryonic fibroblasts and neuroretina cells

dlPA105 is a spontaneous variant of Rous sarcoma virus, subgroup E, which carries a deletion in the N-terminal portion of the v-src gene coding sequence. This virus was isolated on the basis of its ability to induce proliferation of quiescent quail neuroretina cells. The altered v-src gene encodes a phosphoprotein of 45,000 daltons which possesses tyrosine kinase activity. DNA sequencing of the mutant v-src gene has shown that deletion extends from amino acid 33 to 126 of wild-type p60v-src. We investigated the tumorigenic and transforming properties of this mutant virus. dlPA105 induced fibrosarcomas in quails with an incidence identical to that induced by wild-type virus. Quail neuroretina cells infected with the mutant virus were morphologically transformed and formed colonies in soft agar. In contrast, dlPA105 induced only limited morphological alterations in quail fibroblasts and was defective in promoting anchorage-independent growth of these cells. Synthesis and tyrosine kinase activity of the mutant p45v-src were similar in both cell types. These data indicate that the portion of the v-src protein deleted in p45v-src is dispensable for the mitogenic and tumorigenic properties of wild-type p60v-src, whereas it is required for in vitro transformation of fibroblasts. The ability of dlPA105 to induce different transformation phenotypes in quail fibroblasts and quail neuroretina cells is a property unique to this Rous sarcoma virus mutant and provides evidence for the existence of cell-type-specific response to v-src proteins.

Isolation and characterization of three forms of 36-kDa Ca2+-dependent actin- and phospholipid-binding proteins from human placenta membrane

We purified three forms of 36-kDa proteins, two monomeric 36-kDa proteins, which had pIs of 7.5 (36K-I) and 6.4 (36K-II), and one 36-kDa complex (36K-C) consisting of two subunits, 36-kDa (pI 7.5) and 12-kDa (pI 5.8), from human placenta membrane. The 36-kDa subunit of 36K-C was identical to 36K-I as judged by pI, cyanogen bromide peptide mapping and immunological cross-reactivity. The three proteins showed F-actin- and phosphatidylserine-binding abilities dependent on Ca2+ concentrations at millimolar and micromolar levels, respectively. They all had phospholipase A2 inhibitory activity. Only 36K-II was phosphorylated extensively at tyrosine residue in Ca2+- and EGF- dependent manners in the membrane fraction of A431 cells. 36K-I was the best substrate for src kinase, whereas 36K-II was the best for fps kinase. However, 36K-C was not phosphorylated by any kinases used here.

Association of three chicken proteins with the 34 kD target of Rous sarcoma virus tyrosine kinase

Transformation of chicken embryo fibroblasts by avian retroviruses induces the tyrosine phosphorylation of a 34-39 kD cellular protein (p34). In vitro, p34 isolated from intestine interacts with F-actin in a Ca2+-dependent manner. We report here that, in the absence of Ca2+ chelators, three proteins co-purified with p34 extracted from a cytosolic or membrane fraction of chicken embryo fibroblasts; these two fractions account respectively for 10-20% and 50% of the total cellular p34. Isolated from the cytosoluble fraction of fibroblasts by sucrose gradient centrifugation and hydrophobic chromatography, p34 and the other proteins behaved as a homogeneous species upon non-denaturing gel electrophoresis, gel filtration, and CsCl density gradient centrifugation, thus indicating a strong association. Moreover, an analysis by electron microscopy following uranyl acetate staining revealed particles with a raspberry-like shape. This association was always disrupted by the calcium-chelating agent, EGTA.

Identification of the EDTA-extractable protein in lens as calpactin I

The EDTA-extractable protein (EEP) is a major extrinsic protein of lens membrane. The 35 kilodalton (kDa) polypeptide of the EEP cross-reacted to antibody prepared against calpactin I, a substrate for the src protein and an inhibitor of phospholipase A2. Calpactin I is also thought to play a structural role in linking cytoskeleton to membrane. The 35 kDa protein in bovine lens contained phosphotyrosine residues that can be detected by affinity purified antibody to this moiety. Although there is some microheterogeneity of EEP using two dimensional gel electrophoresis, at least one of the chick polypeptides, immunoreactive for calpactin I, can be phosphorylated in whole lens culture. These results suggest a regulatory function for the EEP in lens.

Primary structure of bovine calpactin I heavy chain (p36), a major cellular substrate for retroviral protein-tyrosine kinases: homology with the human phospholipase A2 inhibitor lipocortin

An amplified Okayama-Berg plasmid cDNA library was constructed from total poly(A)+ RNA isolated from the Madin-Darby bovine kidney cell line MDBK. This library was screened with a partial murine calpactin I heavy chain (p36) cDNA clone, the identification of which was based on bovine p36 tryptic peptide sequences generated during the course of these studies. The largest p36 cDNA insert (p36/6 of 1.6 kilobase pairs) was fully sequenced by the dideoxy method. The DNA sequence of this insert had an open reading frame of 1014 base pairs and coded for a protein with a molecular weight of 38 481. The deduced protein sequence of 338 residues was concordant with 173 residue positions of p36 determined at the protein level. The 5'- and 3'-ends of p36/6 contained 54 and 307 base pairs of untranslated sequence, respectively. Examination of poly(A)+ RNA prepared from the Madin-Darby cell line indicated a p36 mRNA species of about 1.6 kilobases. Four regions of internal homology, each about 70 amino acid residues in length, were observed in the deduced protein sequence for p36. Thirty-three of the 70 residue positions were conserved in at least three of the four repeating units. A comparison of derived amino acid sequence for bovine p36 with that previously determined for human lipocortin [Wallner, B. P., Mattaliano, R. J., Hession, C., Cate, R. L., Tizard, R., Sinclair, L. K., Foeller, C., Chow, E. P., Browning, J. L., Ramachandran, K. L., & Pepinsky, R. B. (1986) Nature (London) 320, 77-81] revealed extensive homology (66% overall) and the presence of four repetitive regions in the lipocortin structure.(ABSTRACT TRUNCATED AT 250 WORDS)

The cDNA sequence for the protein-tyrosine kinase substrate p36 (calpactin I heavy chain) reveals a multidomain protein with internal repeats

We have isolated and sequenced a full-length cDNA clone for the protein-tyrosine kinase substrate p36 (calpactin I heavy chain). This sequence predicts a 339 amino acid (Mr 38,493) protein containing an N-terminal region of 20 amino acids, known to interact with a 10 kd protein (light chain), and a C-terminal region, found to contain two Ca2+/phospholipid-binding sites, that can be aligned as four 70 amino acid repeats. A single p36 gene was detected in the mouse genome, and a major p36 mRNA of 1.6 kb was found to be expressed in different mouse tissues. Unexpectedly, p36 and the phospholipase A2 inhibitor lipocortin I were found to be 50% identical in sequence over the C-terminal 300 residues. The function of p36 and its relation to other proteins are discussed.

Transforming proteins of fujinami and PRCII avian sarcoma viruses have different subcellular locations

The subcellular locations of transforming proteins encoded by the related avian sarcoma viruses, PRCII and Fujinami sarcoma virus (FSV), were compared by cell fractionation and by indirect immunofluorescence. Whereas both viruses encode gag-fps proteins associated with tyrosine-specific kinase activity, FSV is more highly tumorigenic than PRCII in vivo. Cell fractionation studies showed that the PRCII transforming protein, P105, became associated with the high-speed particulate fraction shortly after synthesis. However, PRCII P105 did not fractionate with the plasma membrane marker, but rather with high-density membranes. It is unique in this subcellular localization among viral tyrosine kinases. This membrane association was found to be relatively insensitive to salt concentration and did not require divalent cations. Immunofluorescent studies, using anti-fps serum, showed that the PRCII protein was present in discrete, large, cytoplasmic patches, as well as in a juxtanuclear location. In contrast, FSV-encoded P130 was found to fractionate with the plasma membrane marker when cells were analyzed in low salt in the presence of magnesium. However, at higher salt concentrations and in the absence of magnesium, the bulk of P130 was found to be soluble. Immunofluorescent staining of FSV P130 revealed a diffuse, cytoplasmic pattern that was distinct from that of the PRCII product. The observed difference in the subcellular localization of these transforming proteins may be the cause of the difference in tumorigenicity between the two viruses.

The effect of quercetin on the phosphorylation activity of the Rous sarcoma virus transforming gene product in vitro and in vivo

The phosphotransferase activity of the Rous sarcoma virus src gene product, pp60src, was inhibited both in vitro and in vivo by the bioflavonoid quercetin. The Ki for the inhibitory effect was in the range of 6-11 microM under conditions in vitro. The inhibitory effect of quercetin was competitive towards the nucleotides ATP and GTP as substrates for pp60src and was non-competitive towards alpha-casein as the protein substrate of this kinase activity. In contrast, studies in vitro of the phosphotransferase activity of the catalytic subunit of the cAMP-dependent protein kinase showed that this flavonoid did not inhibit the phosphorylation of physiological substrates of this enzyme. In cultured cells the half-maximal inhibition of tyrosine phosphorylation of pp60src as well as the phosphorylation of the Mr = 34000 protein, a physiological substrate of pp60src, was in the range 0.06-0.08 mM.

Immunological study of a cellular 35K phosphorylated polypeptide detected in Rous sarcoma virus transformed cells

We have immunoprecipitated a phosphoprotein of 35K daltons (35K) common to RSV-transformed chick embryo fibroblasts (CEF) and rodent cells. The phosphorylation of this antigen depends on the expression of the v-src gene and contains phosphotyrosine. The pre-existing 35K protein, of CEF infected de novo, was further shown to become phosphorylated shortly after the appearance of active pp60v-src, and about 1 day before morphological transformation. The experiments with RSV-transformed rodent cells have shown that the 35K phosphoprotein is associated with the cellular framework. Another phosphoprotein of 37K was found in the RSV-transformed rodent cells, but not in the transformed CEF. However, this protein was not phosphorylated at tyrosine residues and its phosphorylation persisted, at the restrictive temperature, in cells transformed by a ts mutant of RSV.

Phorbol ester receptors and the in vitro effects of tumor promoters

The evidence for the multistage nature of tumor promotion in vivo and for multiple subclasses of phorbol ester receptors in vitro argues that multiple mechanisms of tumor promotion exist. The existence of multiple mechanisms suggests that brute force assay for tumor promoters in vivo may be inadequate and that understanding of mechanisms may be essential. The interest in the phorbol esters is not primarily that they are environmental hazards for man, but rather that they provide a probe for phorbol ester receptors. These receptors are found in people, and modulation of their activity may play a role in tumor promotion in man.

Transformation by avian sarcoma viruses leads to phosphorylation of multiple cellular proteins on tyrosine residues

Phosphoamino acid compositions were determined for 10 size classes of cellular proteins, separated by electrophoresis through one-dimensional sodium dodecyl sulfate-polyacrylamide gels. Phosphotyrosine-containing proteins were observed in uninfected chicken embryo fibroblasts in every size class analyzed, ranging from approximately 20,000 to greater than 200,000 daltons. Transformation of chicken embryo fibroblasts by Rous sarcoma virus or PRC II avian sarcoma virus led to increases in phosphorylation of proteins at tyrosine residues in all of these size classes. A large fraction of the phosphotyrosine-containing protein molecules observed in Rous sarcoma virus-transformed cells was larger than 100,000 daltons with a second broad peak in the 35,000- to 60,000-dalton range. This study suggests that there are a number of substrates of viral or cellular tyrosine-specific protein kinases, which have not yet been identified by other methods.