Features of the pp60v-src carboxyl terminus that are required for transformation

SRC64 regulates the localization of a Tec-family kinase required for Drosophila ring canal growth

Mutation of the Src64 gene of Drosophila results in ovarian ring canal defects and reduced female fertility. We used a dosage-sensitive modifier screen to search for downstream components of the SRC64 signaling pathway. We show that mutations affecting Tec29, an essential gene encoding a member of the Tec family of protein tyrosine kinases, dominantly enhance the Src64 ring canal phenotype. Loss of Tec29 function in the female germline results in a phenotype strikingly similar to that caused by the loss of Src64 function. In each case, the ring canals are reduced in size and phosphotyrosine content. We further demonstrate that TEC29 localizes to the ring canal, and this subcellular localization requires Src64 function. These data suggest that TEC29 is a downstream target of SRC64, and that regulating TEC29 localization during ring canal growth may be a crucial SRC64 function.

The VAB-1 Eph receptor tyrosine kinase functions in neural and epithelial morphogenesis in C. elegans

Mutations in the C. elegans vab-1 gene disrupt the coordinated movements of cells during two periods of embryogenesis. vab-1 mutants are defective in the movement of neuroblasts during closure of the ventral gastrulation cleft and in the movements of epidermal cells during ventral enclosure of the embryo by the epidermis. We show that vab-1 encodes a receptor tyrosine kinase of the Eph family. Disruption of the kinase domain of VAB-1 causes weak mutant phenotypes, indicating that VAB-1 may have both kinase-dependent and kinase-independent activities. VAB-1 is expressed in neurons during epidermal enclosure and is required in these cells for normal epidermal morphogenesis, demonstrating that cell-cell interactions are required between neurons and epidermal cells for epidermal morphogenesis.

C-terminal end of v-src protein interacts with peptide coded by gadd7/adapt15-like RNA in two-hybrid system

The significant differences in the metastatic properties of hamster fibroblasts transformed by the Rous sarcoma virus (RSV) were associated with mutations in the v-src carboxy-terminal region. To identify the capacity of this region for protein-protein interaction the two-hybrid system was used. The cDNA clone (vseap1), producing the protein specifically bound with the v-src C-terminal part in yeast cells in vivo and in GST-fusion system in vitro was isolated. Vseap1 shared 68% of homology with stressful agents induced RNA-gadd7/adapt15. Two vseap1 specific messenger RNAs were identified: 0.9-kbp RNA expressed in all transformed cells and three times less in embryo fibroblasts; 3.1-kbp transcript was deleted in the cells with suppressed v-src activity and H2O2 resistance.

Expression, characterization, and crystallization of the catalytic core of the human insulin receptor protein-tyrosine kinase domain

The deduced primary sequence of the cytoplasmic protein-tyrosine kinase domain of the insulin receptor contains a conserved kinase homology region (receptor residues 1002-1257) flanked by a juxtamembrane region and a C-terminal tail. A soluble 48-kDa derivative (residues 959-1355) containing these regions but lacking the first six residues of the juxtamembrane region had earlier been synthesized in Sf9 cells using a baculovirus expression system. The catalytic core of the kinase domain was studied first by proteolytic analysis of the 48-kDa kinase and then by expressing a series of truncated kinase domains in transiently transfected COS cells. Based on these studies, two core kinases of 34 (residues 985-1283) and 35 (residues 978-1283) kDa, respectively, were overexpressed in Sf9 cells. Biochemical characterization of the 35-kDa kinase revealed that the core kinase conserved the major functional properties of the native receptor kinase domain. Activity of the 35-kDa kinase toward a synthetic peptide increased more than 200-fold upon autophosphorylation, which occurred exclusively at Tyr-1158, Tyr-1162, and Tyr-1163; the largest increase was observed between bis- and trisphosphorylation of the kinase. The activated 35- and 48-kDa kinases were similar with respect to specific activity and ATP and Mg2+ requirements for peptide phosphorylation. Moreover, autophosphorylation appeared to initiate predominantly at Tyr-1162, immediately followed by phosphorylation at Tyr-1158 and then at Tyr-1163. The rate of autophosphorylation was dependent on enzyme concentration, consistent with a trans-phosphorylation mechanism. Finally, the 35-kDa kinase was crystallized, making possible elucidation of its three-dimensional structure by x-ray crystallography.

src-related protein tyrosine kinases and their surface receptors

The CD4-p56lck and CD8-p56lck complexes have served as a paradym for an expanding number of interactions between src-family members (p56lck, p59fyn, p56lyn, p55blk) and surface receptors. These interactions implicate src-related kinases in the regulation of a variety of intracellular events, from lymphokine production and cytotoxicity to the expression of specific nuclear binding proteins. Different molecular mechanisms appear to have evolved to facilitate the receptor-kinase interactions, including the use of N-terminal regions, SH2 regions and kinase domains. Variation exists in stoichiometry, affinity and the nature of signals generated by these complexes in cells. The CD4-p56lck complex differs from receptor-tyrosine kinases in a number of important ways, including mechanisms of kinase domain regulation and recruitment of substrates such as PI 3-kinase. Furthermore, they may have a special affinity for receptor-substrates such as the TcR zeta, MB1/B29 or CD5 receptors, and act to recruit other SH2-carrying proteins, such as ZAP-70 to the receptor complexes. Receptor-src kinase interactions represent the first step in a cascade of intracellular events within the protein-tyrosine kinase/phosphatase cascade.

The gene involved in X-linked agammaglobulinaemia is a member of the src family of protein-tyrosine kinases

X-linked agammaglobulinaemia (XLA) is a human immunodeficiency caused by failure of pre-B cells in the bone marrow to develop into circulating mature B cells. A novel gene has been isolated which maps to the XLA locus, is expressed in B cells, and shows mutations in families with the disorder. The gene is a member of the src family of proto-oncogenes which encode protein-tyrosine kinases. This is, to our knowledge, the first evidence that mutations in a src-related gene are involved in human genetic disease.

An assessment of human insulin receptor phosphorylation and exogenous kinase activity following deletion of 69 residues from the carboxyl-terminus of the receptor beta-subunit

A mutant human insulin receptor with a carboxyl-terminal deletion of 69 amino acids (proreceptor residues 1287-1355) is expressed as a stable protein in transiently transfected COS cells. We find that in intact cells this mutant is phosphorylated in an insulin-dependent manner on core tyrosines 1158, 1163 and 1163. As expected, the carboxyl-terminal beta-subunit phosphorylation sites (serines 1305/6, tyrosines 1328/34 and threonine 1348) are absent from this mutant. However, the two major insulin-stimulated serine phosphopeptides remain. In intact cells, insulin stimulates exogenous substrate phosphorylation by the truncated receptor only approximately 1.9-fold (cf. approximately 9-fold for the wild-type receptor in these cells), a consequence of a approximately 4.8-fold elevation in basal insulin-independent kinase activity.

Use of antipeptide antibodies to probe the catalytic activity of p37v-mos

Several site-directed antipeptide antibodies were generated to probe the kinase function of p37v-mos. Anti-mos(37-55) antibodies allowed autophosphorylation of p37v-mos, as well as transphosphorylation of exogenously added purified bovine vimentin. Rabbit antipeptide antibodies against v-mos residues 158-70, 194-206, 260-271, and 363-374 and a mouse monoclonal antibody against residues 344-359 completely inhibited p37v-mos protein kinase activity in vitro. p37v-mos autophosphorylation and vimentin transphosphorylation were affected similarly. These results suggest important roles for insert and the carboxy-terminal domains in the catalytic activity of p37v-mos.

A synthetic peptide analog of the putative substrate-binding motif activates protein kinase C

A 29-residue synthetic peptide, Leu530-Leu-Tyr-Glu-Met-Leu-Ala-Gly-Gln-Ala-Pro-Phe-Glu-Gly-Glu-Asp -Glu-Asp- Glu-Leu-Phe-Gln-Ser-Ile-Met-Glu-His-Asn-Val-NH2(558), corresponding to part of the catalytic domain of protein kinase C, is a potent activator of the enzyme, with a Ka of approx. 10 microM. Activation was 59 +/- 4% of that observed with phosphatidylserine, predominantly due to an increased Vmax, partially calcium-dependent, observed with all three isoenzymes (alpha, beta, gamma), and resulted in autophosphorylation. It is proposed that the region between Gly528 and Arg583 is part of the protein substrate binding region of protein kinase C and synthetic peptide analogs of this region activate the enzyme by blocking the action of the enzyme's basic pseudosubstrate autoregulatory region.

Purified maturation promoting factor phosphorylates pp60c-src at the sites phosphorylated during fibroblast mitosis

We have previously shown that overexpressed chicken pp60c-src has retarded mobility, novel serine/threonine phosphorylation, and enhanced kinase activity during NIH 3T3 cell mitosis. Here we show that novel mitotic phosphorylations occur at Thr 34, Thr 46, and Ser 72. The possibility, previously raised, that Ser 17 is dephosphorylated during mitosis is excluded. The phosphorylated sites lie in consensus sequences for phosphorylation by p34cdc2, the catalytic component of maturation promoting factor (MPF). Furthermore, highly purified MPF from metaphase-arrested Xenopus eggs phosphorylated both wild-type and kinase-defective pp60c-src at these sites. Altered phosphorylation alone is sufficient to account for the large retardation in mitotic pp60c-src electrophoretic mobility: phosphorylation of normal pp60c-src by MPF retarded mobility and dephosphorylation of mitotic pp60c-src restored normal mobility. These results suggest that pp60c-src is one of the targets for MPF action, which may account in part for the pleiotropic changes in protein phosphorylation and cellular architecture that occur during mitosis.

Transduction of the cellular src gene and 3' adjacent sequences in avian sarcoma virus PR2257

When injected into chickens, a transformation-defective mutant of the Prague C strain of Rous sarcoma virus induced tumors at low incidence and after a long latency. One such tumor released a replication-defective virus designated PR2257. We molecularly cloned and sequenced the proviral DNA from quail fibroblasts transformed by PR2257. Comparison of PR2257 sequence with that of Prague C, cellular src, and 3' adjacent cellular DNA showed that the spliced version of the c-src gene and about 950 base pairs (bp) of 3'-flanking cellular DNA were transduced into PR2257. This transduction eliminated nearly all replicative genes, since the gag gene splice donor site was linked to the splice acceptor site of the src gene and, on the 3' side, recombination occurred in the end of env gene. Insertion of two extra cytosines 23 bp before and 19 bp after the c-src stop codon resulted in an extension of the coding portion up to 587 amino acids, divergence of sequences after Pro-525 and replacement of Tyr-527 by a valine residue. In addition, it appears that the 5' and 3' untranslated regions of PR2257 result from multiple recombinations between exogenous and endogenous virus genomes. Limited digestion of p66src encoded by PR2257 with Staphylococcus aureus V8 protease yielded a V2 peptide (C-terminal moiety) with an apparent molecular mass of 31 kilodaltons, consistent with the 5.7-kilodalton increase expected from the DNA sequence. The structure of PR2257 suggests that the first step in the capture of c-src gene by avian lymphomatosis viruses is the trans splicing of the viral leader mRNA to exon 1 of c-src.

Oncogenes, protooncogenes, and signal transduction: toward a unified theory?

This paper has reviewed, in a broad sense, the potential involvement of the oncogenes and their progenitors, the protooncogenes, in signal transduction pathways. The membrane-associated oncogene products appear to be connected with the generation and/or regulation of secondary messengers, particularly those associated with Ca2+/phospholipid-dependent activation of the serine/threonine kinase protein kinase C. Activation of transmembrane receptors, either through binding their native ligand or through point mutations that lead to constitutive expression, results in the expression of their intrinsic tyrosine-specific protein kinases. In PDGF-stimulated cells, this results in the increased turnover of phosphatidylinositols and the subsequent release of IP3 (Habenicht et al., 1981; Berridge et al., 1984). This coincides with activation of a PI kinase activity (Kaplan et al., 1987). Likewise, the fms product, which is the receptor for CSF-1, induces a guanine nucleotide-dependent activation of phospholipase C (Jackowski et al., 1986). Receptor functions are potentially regulated through differential binding of ligands (as proposed with PDGF), through interactions with other receptors, and through the "feedback" regulation mediated by protein kinase C. PDGF stimulation leads to modulation of the EGF receptor through protein kinase C (Bowen-Pope et al., 1983; Collins et al., 1983; Davis and Czech, 1985). Similarly, the neu product becomes phosphorylated on tyrosine residues following treatment of cells with EGF, although the neu protein does not bind EGF itself (King et al., 1988; Stern and Kamps, 1988). The tyrosine kinases of the src family are not receptors themselves, although they may mediate specific receptor-generated signals. The clck product is physically and functionally associated with the T-cell receptors CD4 and CD8, and becomes active upon specific stimulation of cells expressing those markers (Veillette et al., 1988a,b). The precise physiological role of the src family products has not been established, but their kinase activity is intrinsic to that function. The v- and c-src products are hyperphosphorylated during mitosis (Chackalaparampil and Shalloway, 1988), which correlates with periods of reduced cell-to-cell adhesion and communication (Warren and Nelson, 1987; Azarnia et al., 1988). Furthermore, pp60c-src is associated with a PI kinase activity when complexed with MTAg of polyoma virus, suggesting a function in stimulating increased turnover of the phosphatidylinositols (Heber and Courtneidge, 1987; Kaplan et al., 1987).(ABSTRACT TRUNCATED AT 400 WORDS)

Altered phosphorylation and activation of pp60c-src during fibroblast mitosis

At least half the pp60c-src in NIH 3T3-derived c-src overexpresser cells in modified by novel threonine and, possibly, serine phosphorylation within its amino 16 kd region during mitosis. At the same time, the tryptic phosphopeptide containing Ser 17, the site of cyclic AMP-dependent phosphorylation, is either modified or dephosphorylated. While the amount of pp60c-src is not significantly altered, the in vitro-specific kinase activity of modified pp60c-src is enhanced 4- to 7-fold. Modified pp60c-src has the same tyrosine-containing tryptic phosphopeptides as pp60c-src from unsynchronized cells, indicating that activation is independent of Tyr 416/Tyr 527 phosphorylation. Electrophoretic mobility retardations indicated that endogenous pp60c-src and pp60v-src are similarly modified during mitosis. The modifications and enhanced activity disappear near the time of cell division. These results suggest that pp60c-src is regulated by and, in turn, may regulate mitosis-specific events in fibroblasts.

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.

Efficient transformation by Prague A Rous sarcoma virus plasmid DNA requires the presence of cis-acting regions within the gag gene

A region in addition to and outside the long terminal repeats (LTRs) in the gag gene of the Prague A strain of Rous sarcoma virus was found to be essential in cis for efficient cell transformation by cloned viral DNA. Transformation in chicken embryo fibroblasts, which requires infectious virus production and reinfection, was facilitated in cis by sequences between nucleotides 630 and 1659. Efficient transformation of NIH 3T3 cells in which secondary spread of virus is not necessary (as it is in chicken embryo fibroblasts) required sequences between nucleotides 630 and 1149. A src cDNA clone which also lacks this region demonstrated low transformation efficiency, indicating that the role of the cis element cannot be attributed to interference with RNA splicing. The gag gene segment required in cis for transformation, between nucleotides 630 and 1149, could substitute for the simian virus 40 enhancer in either orientation, and cells transfected with Rous sarcoma virus LTR-driven plasmids containing the gag cis element had a two- to threefold increase in steady-state viral RNA levels compared with plasmids lacking this region. Thus, additional cis-acting regulatory elements located outside the viral LTRs may modulate viral gene expression and contribute to the efficiency of cell transformation.

The mechanism of transduction of proto-oncogene c-src by avian retroviruses

Chicken c-src sequences have been transduced by avian leukosis viruses (ALV) and by partial src-deletion (td) mutants of Rous sarcoma virus in several independent events. Analyses of the recombination junctions in the genomes of src-containing viruses and the c-src DNA have shed light on the mechanism of transduction, which involves at least two steps of recombination. The initial recombination between a viral genome and the 5' region of c-src appears to occur at the DNA level. This step does not require extensive homology and can be mediated by stretches of sequences with only partial homology. The 5' recombination junction can also be formed by splicing between viral and c-src sequences. The second recombination is presumed to occur between the transducing ALV or td viral RNA and the viral-c-src hybrid RNA molecule generated from the initial recombination. This step involving recombination at the 3' ends of those molecules restores the 3' viral sequences essential for replication to the viral-c-src hybrid molecule. High frequency of c-src transduction by partial td mutants suggests that the second recombination is greatly enhanced when there is sequence homology between the transducing virus and the 3' region of c-src. Incorporation of the c-src sequences into an ALV genome results in greatly elevated expression of the gene. However, increased expression of c-src alone is insufficient to activate its transforming potential. Structural changes in c-src are necessary to convert it into a transforming gene. The changes can be as small as single nucleotide changes resulting in single amino aid substitutions at certain positions. Mutations can occur rapidly during viral replication after c-src is incorporated into the viral genome. Therefore, it is most likely that transduction of c-src by ALV is followed by subsequent mutation and selection for the sarcomagenic virus. In the case of transduction by td viruses that retain certain src sequences, joining of these sequences with the transduced c-src apparently is sufficient to activate its transforming potential.

Cell transformation by pp60c-src mutated in the carboxy-terminal regulatory domain

We introduced two mutations into the carboxy-terminal regulatory region of chicken pp60c-src. One, F527, replaces tyrosine 527 with phenylalanine. The other, Am517, produces a truncated pp60c-src protein lacking the 17 carboxy-terminal amino acids. Both mutant proteins were phosphorylated at tyrosine 416 in vivo. The specific activity of the Am517 mutant protein kinase was similar to that of wild-type pp60c-src whereas that of the F527 mutant was 5- to 10-fold higher. Both mutant c-src genes induced focus formation on NIH 3T3 cells, but the foci appeared at lower frequency, and were smaller than foci induced by polyoma middle tumor antigen (mT). The wild-type or F527 pp60c-src formed a complex with mT, whereas the Am517 pp60c-src did not. The results suggest that one, inability to phosphorylate tyrosine 527 increases pp60c-src protein kinase activity and transforming ability; two, transformation by mT involves other events besides lack of phosphorylation at tyrosine 527 of pp60c-src; three, activation of the pp60c-src protein kinase may not be required for transformation by the Am517 mutant; and four, the carboxyl terminus of pp60c-src appears to be required for association with mT.

Activation and suppression of pp60c-src transforming ability by mutation of its primary sites of tyrosine phosphorylation

pp60c-src is phosphorylated in vivo at tyrosine 527, a residue not present in pp60v-src (its transforming homolog), and not at tyrosine 416, its site of in vitro autophosphorylation. To test the hypothesis that tyrosine phosphorylation regulates pp60c-src biological activity, we constructed and studied pp60c-src mutants in which Tyr 527 and Tyr 416 were separately or coordinately altered to phenylalanine. Tyr----Phe 527 mutation strongly activated pp60c-src transforming and kinase activities, whereas the additional introduction of a Tyr----Phe 416 mutation suppressed these activities. Tyr----Phe 416 mutation of normal pp60c-src eliminated its partial transforming activity, which suggests that transient or otherwise restricted phosphorylation of Tyr 416 is important for pp60c-src function even though stable phosphorylation is not observed in vivo.