Characterization of cDNA clones for the human c-yes gene

Plakophilin-2 induced EGFR phosphorylation: a focus on the intracellular activators of EGFR

The oncogenic role of EGFR in many tumors has attracted a great deal of attention in the recent years and initiated the development of several potent EGFR inhibitors, which are used clinically for cancer treatment. However, the current therapeutic inhibition of EGFR signaling is limited to monoclonal antibodies that bind to the EGFR extracellular domain or tyrosine kinase inhibitors that block EGFR kinase activation directly. Despite the great promise of these inhibitors, a certain percentage of patients develop resistance to these therapies, highlighting the necessity for alternative therapeutic strategies based on our most current knowledge of the mechanisms of EGFR signaling. We recently reported that Plakofilin-2 (PKP2) is a novel ligand-independent cytoplasmic activator of EGFR signaling. Here we focus on recent studies demonstrating important roles of intracellular EGFR activators, and propose targeted disruption of these activators as a novel avenue of therapeutic intervention to inhibit EGFR-mediated cancer development.

The Src family kinase c-Yes is required for maturation of West Nile virus particles

The role of cellular genes in West Nile virus (WNV) replication is not well understood. Examination of cellular transcripts upregulated during WNV infection revealed an increase in the expression of the src family kinase (SFK) c-Yes. WNV-infected cell lines treated with the SFK inhibitor PP2 demonstrated a 2- to 4-log decrease in viral titers, suggesting that SFK activity is required for completion of the viral replication cycle. RNA interference mediated knock-down of c-Yes, but not c-Src, and similarly reduced virus yield, specifically implicating c-Yes in WNV production. Interestingly, PP2 treatment did not reduce intracellular levels of either viral RNA or protein, suggesting that the drug does not act on the early stages of replication. However, endoglycosidase H (endoH) digestion of the viral envelope (E) glycoprotein revealed that the acquisition of endoH-resistant glycans by E, but not endogenous major histocompatibility complex class I, was reduced in PP2-treated cells, demonstrating that E specifically does not traffic beyond the endoplasmic reticulum in the absence of SFK activity. Electron microscopy further revealed that PP2-treated WNV-infected cells accumulated an increased number of virions in the ER compared to untreated cells. Therefore, we conclude that inhibition of SFK activity did not interfere with virus assembly but prevented transit of virions through the secretory pathway. These results identify c-Yes as a cellular protein that is involved in WNV assembly and egress.

High expression of methionine aminopeptidase 2 in human colorectal adenocarcinomas

PURPOSE

Several viral and eukaryotic proteins required for signal transduction and regulatory functions undergo lipophilic modification by the enzyme N-myristoyltransferase. Previously we reported that N-myristoyltransferase activity is higher in colon and gallbladder carcinoma than in the corresponding normal tissues. Methionine aminopeptidase 2 (MetAP2) is a bifunctional protein that plays a critical role in the regulation of post-translational processing and protein synthesis. To investigate whether MetAP2 contributes to the pathogenesis of colon carcinoma, we investigated the expression of MetAP2 in both normal and invasive tumor components of human samples.

EXPERIMENTAL DESIGN

We evaluated 50 cases of colon carcinoma for this study. In this report we analyzed 15 cases for MetAP2 activity and 13 cases for the expression of MetAP2 by Western blot in both the normal and in invasive tumor components of human samples. In addition, immunohistochemistry analysis was also carried out on samples from all patients.

RESULTS

MetAP activity was elevated in all cancerous tissues compared with normal tissues. Western blot analysis also showed the higher expression of MetAP2 in all cases of cancerous tissues. In addition, immunohistochemistry analysis revealed that all cases of colorectal adenocarcinoma showed moderate to strong cytoplasmic positivity for MetAP2 with increased intensity in the invasive component.

CONCLUSIONS

Elevated MetAP protein expression is associated with metastatic tumor progression and appears to be a strong molecular marker for clinical prognosis. MetAP2 inhibition may represent a potential target for therapeutic intervention in colorectal carcinoma.

Identification of expressed genes linked to malignancy of human colorectal carcinoma by parametric clustering of quantitative expression data

BACKGROUND

Individual human carcinomas have distinct biological and clinical properties: gene-expression profiling is expected to unveil the underlying molecular features. Particular interest has been focused on potential diagnostic and therapeutic applications. Solid tumors, such as colorectal carcinoma, present additional obstacles for experimental and data analysis.

RESULTS

We analyzed the expression levels of 1,536 genes in 100 colorectal cancer and 11 normal tissues using adaptor-tagged competitive PCR, a high-throughput reverse transcription-PCR technique. A parametric clustering method using the Gaussian mixture model and the Bayes inference revealed three groups of expressed genes. Two contained large numbers of genes. One of these groups correlated well with both the differences between tumor and normal tissues and the presence or absence of distant metastasis, whereas the other correlated only with the tumor/normal difference. The third group comprised a small number of genes. Approximately half showed an identical expression pattern, and cancer tissues were classified into two groups by their expression levels. The high-expression group had strong correlation with distant metastasis, and a poorer survival rate than the low-expression group, indicating possible clinical applications of these genes. In addition to c-yes, a homolog of a viral oncogene, prognostic indicators included genes specific to glial cells, which gives a new link between malignancy and ectopic gene expression.

CONCLUSIONS

The malignancy of human colorectal carcinoma is correlated with a unique expression pattern of a specific group of genes, allowing the classification of tumor tissues into two clinically distinct groups.

Nonreceptor tyrosine kinase c-Yes interacts with occludin during tight junction formation in canine kidney epithelial cells

Occludin is an integral membrane protein that is tyrosine phosphorylated when localized at tight junctions. When Ca(2+) was depleted from the culture medium, occludin tyrosine phosphorylation was diminished from Madin-Darby canine kidney epithelial cells in 2 min. This dephosphorylation was correlated with a significant reduction in transepithelial electrical resistance (TER), indicating a global loss of the tight junction barrier function. Reconstitution of Ca(2+) resulted in a robust tyrosine rephosphorylation of occludin that was temporally associated with an increase in TER. Moreover, we demonstrate in this study that occludin was colocalized with the nonreceptor tyrosine kinase c-Yes at cell junction areas and formed an immunoprecipitable complex with c-Yes in vivo. This complex dissociated when the cells were incubated in medium without Ca(2+) or treated with a c-Yes inhibitor, CGP77675. In the presence of CGP77675 after Ca(2+) repletion, occludin tyrosine phosphorylation was completely abolished and both tight junction formation and the increase of the TER were inhibited. Our study thus provides strong evidence that occludin tyrosine phosphorylation is tightly linked to tight junction formation in epithelial cells, and that the nonreceptor tyrosine kinase c-Yes is involved in the regulation of this process.

Fine-scale mapping of a locus for severe bipolar mood disorder on chromosome 18p11.3 in the Costa Rican population

We have searched for genes predisposing to bipolar disorder (BP) by studying individuals with the most extreme form of the affected phenotype, BP-I, ascertained from the genetically isolated population of the Central Valley of Costa Rica (CVCR). The results of a previous linkage analysis on two extended CVCR BP-I pedigrees, CR001 and CR004, and of linkage disequilibrium (LD) analyses of a CVCR population sample of BP-I patients implicated a candidate region on 18p11.3. We further investigated this region by creating a physical map and developing 4 new microsatellite and 26 single-nucleotide polymorphism markers for typing in the pedigree and population samples. We report the results of fine-scale association analyses in the population sample, as well as evaluation of haplotypes in pedigree CR001. Our results suggest a candidate region containing six genes but also highlight the complexities of LD mapping of common disorders.

Natural biology of polyomavirus middle T antigen

"It has been commented by someone that 'polyoma' is an adjective composed of a prefix and suffix, with no root between--a meatless linguistic sandwich" (C. J. Dawe). The very name "polyomavirus" is a vague mantel: a name given before our understanding of these viral agents was clear but implying a clear tumor life-style, as noted by the late C. J. Dawe. However, polyomavirus are not by nature tumor-inducing agents. Since it is the purpose of this review to consider the natural function of middle T antigen (MT), encoded by one of the seemingly crucial transforming genes of polyomavirus, we will reconsider and redefine the virus and its MT gene in the context of its natural biology and function. This review was motivated by our recent in vivo analysis of MT function. Using intranasal inoculation of adult SCID mice, we have shown that polyomavirus can replicate with an MT lacking all functions associated with transformation to similar levels to wild-type virus. These observations, along with an almost indistinguishable replication of all MT mutants with respect to wild-type viruses in adult competent mice, illustrate that MT can have a play subtle role in acute replication and persistence. The most notable effect of MT mutants was in infections of newborns, indicating that polyomavirus may be highly adapted to replication in newborn lungs. It is from this context that our current understanding of this well-studied virus and gene is presented.

N-myristoyltransferase

Myristoylation refers to the co-translational addition of a myristoyl group to an amino-terminal glycine residue of a protein by an ubiquitously distributed enzyme myristoyl-CoA:protein N-myristoyltransferase (NMT, EC 2.3.1.97). This review describes the basic enzymology, molecular cloning and regulation of NMT activity in various pathophysiological processes such as colon cancer and diabetes.

A tyrosine kinase profile of prostate carcinoma

Tyrosine kinases play central roles in the growth and differentiation of normal and tumor cells. In this study, we have analyzed the general tyrosine kinase expression profile of a prostate carcinoma (PCA) xenograft, CWR22. We describe here an improved reverse transcriptase-PCR approach that permits identification of nearly 40 different kinases in a single screening; several of these kinases are newly cloned kinases and some are novel. According to this, there are 11 receptor kinases, 9 nonreceptor kinases, and at least 7 dual kinases expressed in the xenograft tissue. The receptor kinases include erbB2, erbB3, Ret, platelet-derived growth factor receptor, sky, nyk, eph, htk, sek (eph), ddr, and tkt. The nonreceptor kinases are lck, yes, abl, arg, JakI, tyk2, and etk/bmx. Most of the dual kinases are in the mitogen-activating protein (MAP) kinase-kinase (MKK) family, which includes MKK3, MKK4, MEK5, and a novel one. As a complementary approach, we also analyzed by specific reverse transcriptase-PCR primers the expression profile of erbB/epidermal growth factor receptor family receptors in a variety of PCA specimens, cell lines, and benign prostatic hyperplasia. We found that erbB1, -2, and -3 are often coexpressed in prostate tissues, but not in erbB4. The information established here should provide a base line to study the possible growth and oncogenic signals of PCA.

Small Maf proteins heterodimerize with Fos and may act as competitive repressors of the NF-E2 transcription factor

The maf oncogene encodes a bZip nuclear protein which recognizes sequences related to an AP-1 site either as a homodimer or as heterodimers with Fos and Jun. We describe here a novel maf-related gene, mafG, which shows extensive homology with two other maf-related genes, mafK and mafF. These three maf-related genes encode small basic-leucine zipper proteins lacking the trans-activator domain of v-Maf. Bacterially expressed small Maf proteins bind to DNA as homodimers with a sequence recognition profile that is virtually identical to that of v-Maf. As we have previously described, the three small Maf proteins also dimerize with the large subunit of NF-E2 (p45) to form an erythroid cell-specific transcription factor, NF-E2, which has distinct DNA-binding specificity. This study shows that the small Maf proteins can also dimerize among themselves and with Fos and a newly identified p45-related molecule (Ech) but not with v-Maf or Jun. Although the small Maf proteins preferentially recognize the consensus NF-E2 sequence as heterodimers with either NF-E2 p45, Ech, or Fos, these heterodimers seemed to be different in their transactivation potentials. Coexpression of Fos and small Mafs could not activate a promoter with tandem repeats of the NF-E2 site. These results raise the possibility that tissue-specific gene expression and differentiation of erythroid cells are regulated by competition among Fos, NF-E2 p45, and Ech for small Maf proteins and for binding sites.

Rapid and efficient purification of Src homology 2 domain-containing proteins: Fyn, Csk and phosphatidylinositol 3-kinase p85

To analyse the regulation of Src family tyrosine kinases in vitro, we have purified Fyn and Csk, a kinase capable of regulating Fyn activity by phosphorylation, from baculovirus-infected insect cells. The proteins were purified by affinity purification over a phosphotyrosine column. Highly purified proteins were eluted from the resin by a salt gradient and further purified by ion-exchange chromatography. This purification scheme was successfully applied to a third, unrelated protein that also contains the Src homology 2 (SH2) domain, namely the 85 kDa subunit of phosphatidylinositol 3-kinase, indicating that this method is versatile and should prove applicable to any protein with an accessible SH2 domain. The binding of Csk to different phosphopeptides was tested, and specificity for the autophosphorylation site of Fyn was demonstrated. Pure Csk was used to phosphorylate Fyn and down-regulate its kinase activity, and the kinetic parameters of both the active and the repressed forms of Fyn were determined. Repression of Fyn activity by Csk reduced binding of Fyn to phosphopeptides to undetectable levels, supporting the model that predicts an intramolecular interaction of the Fyn SH2 domain with a C-terminal phosphotyrosine residue.

Oncogenic activation of the Lck protein accompanies translocation of the LCK gene in the human HSB2 T-cell leukemia

The tyrosine protein kinase p56lck transduces signals important for antigen-induced T-cell activation. In transgenic mice, p56lck is oncogenic when overexpressed or expressed as a mutant, catalytically activated enzyme. In humans, the LCK gene is located at the breakpoint of the t(1;7)(p34;q34) chromosomal translocation. This translocation positions the beta T-cell receptor constant region enhancer upstream of the LCK gene without interrupting the LCK coding sequences, and a translocation of this sort occurs in both the HSB2 and the SUP-T-12 T-cell lines. We have found that, although the level of the p56lck protein in HSB2 cells is elevated approximately 2-fold in comparison with that in normal T-cell lines, total cellular tyrosine protein phosphorylation is elevated approximately 10-fold. Increased levels of phosphotyrosine in HSB2 cells resulted from mutations in the LCK gene that activated its function as a phosphotransferase and converted it into a dominant transforming oncogene. The oncogenic p56lck in HSB2 cells contained one amino acid substitution within the CD4/CD8-binding domain, two substitutions in the kinase domain, and an insertion of Gln-Lys-Pro (QKP) between the SH2 and kinase domains. In NIH 3T3 fibroblasts, three of these mutations cooperated to produce the fully oncogenic form of this p56lck variant. These results suggest that mutation of LCK may contribute to some human T-cell leukemias.

Oncogenic activation of the Lck protein accompanies translocation of the LCK gene in the human HSB2 T-cell leukemia

The tyrosine protein kinase p56lck transduces signals important for antigen-induced T-cell activation. In transgenic mice, p56lck is oncogenic when overexpressed or expressed as a mutant, catalytically activated enzyme. In humans, the LCK gene is located at the breakpoint of the t(1;7)(p34;q34) chromosomal translocation. This translocation positions the beta T-cell receptor constant region enhancer upstream of the LCK gene without interrupting the LCK coding sequences, and a translocation of this sort occurs in both the HSB2 and the SUP-T-12 T-cell lines. We have found that, although the level of the p56lck protein in HSB2 cells is elevated approximately 2-fold in comparison with that in normal T-cell lines, total cellular tyrosine protein phosphorylation is elevated approximately 10-fold. Increased levels of phosphotyrosine in HSB2 cells resulted from mutations in the LCK gene that activated its function as a phosphotransferase and converted it into a dominant transforming oncogene. The oncogenic p56lck in HSB2 cells contained one amino acid substitution within the CD4/CD8-binding domain, two substitutions in the kinase domain, and an insertion of Gln-Lys-Pro (QKP) between the SH2 and kinase domains. In NIH 3T3 fibroblasts, three of these mutations cooperated to produce the fully oncogenic form of this p56lck variant. These results suggest that mutation of LCK may contribute to some human T-cell leukemias.

Inactivation of c-Yes tyrosine kinase by elevation of intracellular calcium levels

We have previously shown that the c-Src tyrosine kinase is activated four- to fivefold when cultured keratinocytes differentiate following the elevation of intracellular calcium levels. In contrast to c-Src, another Src family tyrosine kinase, c-Yes, was rapidly inactivated in these same cells, despite its marked similarity in structure and enzymatic activity to c-Src. The inactivation of c-Yes was independent of the protein kinase C pathway, which is usually activated by elevation of intracellular calcium levels. The protein levels of c-Src and c-Yes were not altered, but the phosphotyrosine content of both proteins was greatly reduced. As has been demonstrated for c-Src, in vitro dephosphorylation of c-Yes by incubation with protein tyrosine phosphatases also resulted in its activation, not inactivation. In vitro reconstitution experiments showed that c-Yes can be inactivated by preincubation with a Ca(2+)-supplemented cell extract and that this inhibition was reversed by the addition of EGTA [ethylene glycol-bis(beta-aminoethyl ether)-N,N,N',N'-tetraacetic acid]. Gradient sedimentation of cell lysates showed that in cells treated with calcium and ionophore, c-Yes formed complexes with two distinct cellular proteins, whereas similar complexes were not seen in c-Src immunoprecipitates. One of these two proteins has the ability to inhibit c-Yes kinase activity in vitro. Finally, the Ca(2+)-dependent inactivation of c-Yes was observed in kidney tubular cells and fibroblasts, suggesting that the Ca(2+)-dependent regulation of c-Yes tyrosine kinase is not unique to keratinocytes. We postulate that c-Yes is inactivated through a Ca2+ -dependent association with cellular proteins, which seems to override its activation resulting from tyrosine dephosphorylation.

Inactivation of c-Yes tyrosine kinase by elevation of intracellular calcium levels

We have previously shown that the c-Src tyrosine kinase is activated four- to fivefold when cultured keratinocytes differentiate following the elevation of intracellular calcium levels. In contrast to c-Src, another Src family tyrosine kinase, c-Yes, was rapidly inactivated in these same cells, despite its marked similarity in structure and enzymatic activity to c-Src. The inactivation of c-Yes was independent of the protein kinase C pathway, which is usually activated by elevation of intracellular calcium levels. The protein levels of c-Src and c-Yes were not altered, but the phosphotyrosine content of both proteins was greatly reduced. As has been demonstrated for c-Src, in vitro dephosphorylation of c-Yes by incubation with protein tyrosine phosphatases also resulted in its activation, not inactivation. In vitro reconstitution experiments showed that c-Yes can be inactivated by preincubation with a Ca(2+)-supplemented cell extract and that this inhibition was reversed by the addition of EGTA [ethylene glycol-bis(beta-aminoethyl ether)-N,N,N',N'-tetraacetic acid]. Gradient sedimentation of cell lysates showed that in cells treated with calcium and ionophore, c-Yes formed complexes with two distinct cellular proteins, whereas similar complexes were not seen in c-Src immunoprecipitates. One of these two proteins has the ability to inhibit c-Yes kinase activity in vitro. Finally, the Ca(2+)-dependent inactivation of c-Yes was observed in kidney tubular cells and fibroblasts, suggesting that the Ca(2+)-dependent regulation of c-Yes tyrosine kinase is not unique to keratinocytes. We postulate that c-Yes is inactivated through a Ca2+ -dependent association with cellular proteins, which seems to override its activation resulting from tyrosine dephosphorylation.

A conserved helix motif complements the protein kinase core

Residues 40-300 of the mammalian catalytic (C) subunit of cAMP-dependent protein kinase define a conserved bilobal catalytic core shared by all eukaryotic protein kinases. Contiguous to the core is an extended amphipathic alpha-helix (A helix). Trp30, a prominent feature of this helix, fills a deep hydrophobic pocket between the two lobes on the surface opposite to the active site. The C subunit in Dictyostelium discoideum shows sequence conservation of residues 40-350 with the mouse enzyme but contains an N-terminal extension of 332 residues. A sequence corresponding to the A helix contiguous to the core is absent. However, we have now identified a remote A-helix motif (residues 77-98). When the core of the Dictyostelium C subunit was modeled, based on the mouse C subunit, complementarity between this putative A helix and the surface of the core was found to be conserved. Analysis of other protein kinases reveals that the A-helix motif is not restricted to cAMP-dependent protein kinase. In the Src-related family of protein kinases, for example, an A helix is very likely contiguous to the core, thus serving as a linker between the conserved catalytic core and the Src homology 2 domain. We predict that an A-helix motif complementary to the core will be a conserved feature of most eukaryotic protein kinases.

Alteration of a yeast SH3 protein leads to conditional viability with defects in cytoskeletal and budding patterns

Mutations in genes necessary for survival in stationary phase were isolated to understand the ability of wild-type Saccharomyces cerevisiae to remain viable during prolonged periods of nutritional deprivation. Here we report results concerning one of these mutants, rvs167, which shows reduced viability and abnormal cell morphology upon carbon and nitrogen starvation. The mutant exhibits the same response when cells are grown in high salt concentrations and other unfavorable growth conditions. The RVS167 gene product displays significant homology with the Rvs161 protein and contains a SH3 domain at the C-terminal end. Abnormal actin distribution is associated with the mutant phenotype. In addition, while the budding pattern of haploid strains remains axial in standard growth conditions, the budding pattern of diploid mutant strains is random. The gene RVS167 therefore could be implicated in cytoskeletal reorganization in response to environmental stresses and could act in the budding site selection mechanism.

Alteration of a yeast SH3 protein leads to conditional viability with defects in cytoskeletal and budding patterns

Mutations in genes necessary for survival in stationary phase were isolated to understand the ability of wild-type Saccharomyces cerevisiae to remain viable during prolonged periods of nutritional deprivation. Here we report results concerning one of these mutants, rvs167, which shows reduced viability and abnormal cell morphology upon carbon and nitrogen starvation. The mutant exhibits the same response when cells are grown in high salt concentrations and other unfavorable growth conditions. The RVS167 gene product displays significant homology with the Rvs161 protein and contains a SH3 domain at the C-terminal end. Abnormal actin distribution is associated with the mutant phenotype. In addition, while the budding pattern of haploid strains remains axial in standard growth conditions, the budding pattern of diploid mutant strains is random. The gene RVS167 therefore could be implicated in cytoskeletal reorganization in response to environmental stresses and could act in the budding site selection mechanism.

Physical and functional association of p56lck with Fc gamma RIIIA (CD16) in natural killer cells

The transmembrane receptor for immunoglobulin G immune complexes on natural killer (NK) cells and macrophages, Fc gamma RIIIA (CD16), mediates cellular activation through a tyrosine kinase-dependent pathway. We show that Fc gamma RIII crosslinking results in activation of the src-related kinase p56lck in NK cells and demonstrate a physical association of p56lck with Fc gamma RIIIA in immunoprecipitates from NK cells obtained using anti-Fc gamma RIII antibodies or immune complexes. Our studies show that the zeta chain, the signal transducing subunit of Fc gamma RIIIA and of T cell receptor, associates with p56lck and, in NK cells, is a substrate for this kinase. Such direct association of p56lck with the zeta subunit as confirmed by demonstrating the interaction in heterologous cells transfected with cDNA expressing p56lck and zeta. Our findings demonstrate both functional and physical association of p56lck with Fc gamma RIIIA, through direct interaction of the kinase with the zeta and/or the gamma signal transducer subunits of the receptor. These data suggest a possible mechanism by which activation via Fc gamma RIIIA occurs.

Two additional protein-tyrosine kinases expressed in human lung: fourth member of the fibroblast growth factor receptor family and an intracellular protein-tyrosine kinase

The expression of protein-tyrosine kinases (PTKs; ATP:protein-tyrosine O-phosphotransferase, EC 2.7.1.112) was studied in normal human lung and various tumors by PCR followed by molecular cloning and sequence analysis. Six known PTKs (YES, FGR, LYN, HCK, PDGFB-R, and CSF1-R), as well as two additional members of this enzyme family, were detected in lung. One of the newly discovered sequences appears to represent a group of cytosolic PTKs. The cDNA sequence of the second unknown PTK revealed that it is a fourth member of the fibroblast growth factor receptor family. It was therefore called TKF (tyrosine kinase related to fibroblast growth factor receptor). Among a wide variety of cells and tissues tested, including human lymphocytes and macrophages, TKF was only found expressed in lung. Apart from normal lung, TKF expression could be demonstrated in some tumors of lung origin, but also in malignancies not derived from lung tissues. As fibroblast growth factors are generally involved in a variety of functions such as mitogenesis, angiogenesis, and wound healing, the specific expression of a receptor-related gene in lung only may point to yet another special function of this group of proteins.

Alternatively spliced murine lyn mRNAs encode distinct proteins

Two lyn proteins of 56 and 53 kDa have been observed in immunoprecipitates from a variety of murine and human cell lines and tissues. We report the cloning and nucleotide sequence of two distinct murine lyn cDNAs isolated from an FDC-P1 cDNA library. One of the cDNAs, designated lyn11, encodes a protein of 56 kDa which shares 96% similarity with human lyn. The other cDNA, designated lyn12, encodes a protein of 53 kDa. The proteins differ in the presence or absence of a 21-amino-acid sequence located 24 amino acids C terminal of the translational initiation codon. Using RNase protection analysis, we have identified mRNAs corresponding to both cDNAs in murine cell lines and tissues. Sequence analysis of murine genomic clones suggests that the distinct mRNAs are alternatively spliced transcripts derived from a single gene. Expression of both cDNAs in COS cells leads to the production of lyn proteins with the same molecular weight as the two forms of lyn proteins immunoprecipitated from extracts of FDC-P1 cells and mouse spleen. Subcellular fractionation studies and Western immunoblotting analysis suggest that both isoforms of lyn are membrane associated. The association of both lyn isoforms with the membrane fraction supports the notion that lyn, like other src-related kinases, may interact with the intracellular domain of cell surface receptors.

Alternatively spliced murine lyn mRNAs encode distinct proteins

Two lyn proteins of 56 and 53 kDa have been observed in immunoprecipitates from a variety of murine and human cell lines and tissues. We report the cloning and nucleotide sequence of two distinct murine lyn cDNAs isolated from an FDC-P1 cDNA library. One of the cDNAs, designated lyn11, encodes a protein of 56 kDa which shares 96% similarity with human lyn. The other cDNA, designated lyn12, encodes a protein of 53 kDa. The proteins differ in the presence or absence of a 21-amino-acid sequence located 24 amino acids C terminal of the translational initiation codon. Using RNase protection analysis, we have identified mRNAs corresponding to both cDNAs in murine cell lines and tissues. Sequence analysis of murine genomic clones suggests that the distinct mRNAs are alternatively spliced transcripts derived from a single gene. Expression of both cDNAs in COS cells leads to the production of lyn proteins with the same molecular weight as the two forms of lyn proteins immunoprecipitated from extracts of FDC-P1 cells and mouse spleen. Subcellular fractionation studies and Western immunoblotting analysis suggest that both isoforms of lyn are membrane associated. The association of both lyn isoforms with the membrane fraction supports the notion that lyn, like other src-related kinases, may interact with the intracellular domain of cell surface receptors.

Specific proto-oncogenic tyrosine kinases of src family are enriched in cell-to-cell adherens junctions where the level of tyrosine phosphorylation is elevated

To approach the transmembrane signaling pathway in the cell-to-cell adherens junctions (AJ), AJ-specific tyrosine phosphorylation was analyzed. When various types of rat adult tissues were pretreated with sodium orthovanadate, a potent inhibitor of tyrosine phosphatase, immunofluorescence microscopy showed that anti-phosphotyrosine polyclonal antibody specifically stained the undercoat of the cell-to-cell AJ. This indicates that the tyrosine kinase activity is elevated at the undercoat of the cell-to-cell AJ of adult tissues. To identify tyrosine kinases responsible for the high level of tyrosine phosphorylation at AJ, we have performed in vitro phosphorylation experiments with cell-to-cell AJ isolated from rat liver (Tsukita, Sh. and Sa. Tsukita. 1989. J. Cell Biol. 108:31-41) and immunoblotting analyses with specific antibodies for tyrosine kinases. As a result, three proto-oncogenic tyrosine kinases of src family, c-yes, c-src, and lyn kinases, were identified as major tyrosine kinases in the cell-to-cell AJ of hepatocytes. Furthermore, it was immunofluorescently shown that at least two of these kinases, c-yes and c-src kinases, were enriched at the cell-to-cell AJ of various types of cells including hepatocytes. Based on these findings, it is concluded that, in various types of cells, specific proto-oncogenic tyrosine kinases of src-family (c-yes and c-src) are enriched to work as signal mediators in the cell-to-cell AJ where the level of tyrosine phosphorylation is elevated.

Two novel protein-tyrosine kinases, each with a second phosphotransferase-related catalytic domain, define a new class of protein kinase

The protein-tyrosine kinases (PTKs) are a burgeoning family of proteins, each of which bears a conserved domain of 250 to 300 amino acids capable of phosphorylating substrate proteins on tyrosine residues. We recently exploited the existence of two highly conserved sequence elements within the catalytic domain to generate PTK-specific degenerate oligonucleotide primers (A. F. Wilks, Proc. Natl. Acad. Sci. USA 86:1603-1607, 1989). By application of the polymerase chain reaction, portions of the catalytic domains of several novel PTKs were amplified. We describe here the primary sequence of one of these new PTKs, JAK1 (from Janus kinase), a member of a new class of PTK characterized by the presence of a second phosphotransferase-related domain immediately N terminal to the PTK domain. The second phosphotransferase domain bears all the hallmarks of a protein kinase, although its structure differs significantly from that of the PTK and threonine/serine kinase family members. A second member of this family (JAK2) has been partially characterized and exhibits a similar array of kinase-related domains. JAK1 is a large, widely expressed membrane-associated phosphoprotein of approximately 130,000 Da. The PTK activity of JAK1 has been located in the C-terminal PTK-like domain. The role of the second kinaselike domain is unknown.

Two novel protein-tyrosine kinases, each with a second phosphotransferase-related catalytic domain, define a new class of protein kinase

The protein-tyrosine kinases (PTKs) are a burgeoning family of proteins, each of which bears a conserved domain of 250 to 300 amino acids capable of phosphorylating substrate proteins on tyrosine residues. We recently exploited the existence of two highly conserved sequence elements within the catalytic domain to generate PTK-specific degenerate oligonucleotide primers (A. F. Wilks, Proc. Natl. Acad. Sci. USA 86:1603-1607, 1989). By application of the polymerase chain reaction, portions of the catalytic domains of several novel PTKs were amplified. We describe here the primary sequence of one of these new PTKs, JAK1 (from Janus kinase), a member of a new class of PTK characterized by the presence of a second phosphotransferase-related domain immediately N terminal to the PTK domain. The second phosphotransferase domain bears all the hallmarks of a protein kinase, although its structure differs significantly from that of the PTK and threonine/serine kinase family members. A second member of this family (JAK2) has been partially characterized and exhibits a similar array of kinase-related domains. JAK1 is a large, widely expressed membrane-associated phosphoprotein of approximately 130,000 Da. The PTK activity of JAK1 has been located in the C-terminal PTK-like domain. The role of the second kinaselike domain is unknown.

A distinctive family of embryonic protein-tyrosine kinase receptors

Two closely related protein-tyrosine kinases with the characteristics of growth factor receptors were identified by screening a chicken embryo cDNA expression library with anti-phosphotyrosine antibodies and were designated Cek2 and Cek3 (chicken embryo kinases 2 and 3). Cek2 and Cek3 are structurally related to Cek1, a chicken basic fibroblast growth factor receptor, and presumably represent receptors for basic fibroblast growth factor-related molecules. The identification of Cek2 and Cek3 establishes the existence of a family of protein-tyrosine kinases that includes Cek1 and that is likely to be implicated in the control of developmental processes. Among protein-tyrosine kinases, this family of receptors, which may include other as yet unknown members, is most closely related to the protooncogene product Ret and the platelet-derived growth factor receptor family.

Transformation of chicken embryo fibroblast cells by avian retroviruses containing the human Fyn gene and its mutated genes

The transforming activity of the human fyn protein, p59fyn, which is a kinase of the src family, was investigated by testing the effect of recombinant avian retrovirus (Fyn virus) expressing p59fyn on chickens or cultured chicken embryo fibroblast (CEF) cells. The Fyn virus did not induce transformed foci. After several passages of the virus stock on CEF cells, however, a few foci were detected in the presence of dimethyl sulfoxide. Chickens inoculated with Fyn virus at the stage of 12-day-old embryos developed fibrosarcomas 3 to 6 weeks after hatching. The viruses obtained from these foci and from one of the tumor tissues showed high transforming activity in the presence of dimethyl sulfoxide, suggesting that these viruses carry spontaneous mutations of the fyn gene. Four fyn genes from CEF DNAs infected with transforming viruses were molecularly cloned, and their products were confirmed to possess transforming activity. DNA sequence analysis of the fyn genes showed that two of the four mutants have Thr instead of Ile at position 338 in the kinase domain. The other two mutants carry deletions of 78 and 108 base pairs, respectively, which result in complete loss of region C of SH2. The overall level of proteins containing phosphotyrosine was significantly higher in transformed cells than in normal CEF cells. Our data indicate that when expressed at high levels in a retrovirus, normal p59fyn cannot cause cellular transformation, but that mutant p59fyn with either a single amino acid substitution in the kinase domain or a deletion including region C produces a transforming protein, perhaps due to enhanced tyrosine kinase activity. This is the first observation that deletion of region C can unmask the potential transforming activity of a src family kinase.

Transformation of chicken embryo fibroblast cells by avian retroviruses containing the human Fyn gene and its mutated genes

The transforming activity of the human fyn protein, p59fyn, which is a kinase of the src family, was investigated by testing the effect of recombinant avian retrovirus (Fyn virus) expressing p59fyn on chickens or cultured chicken embryo fibroblast (CEF) cells. The Fyn virus did not induce transformed foci. After several passages of the virus stock on CEF cells, however, a few foci were detected in the presence of dimethyl sulfoxide. Chickens inoculated with Fyn virus at the stage of 12-day-old embryos developed fibrosarcomas 3 to 6 weeks after hatching. The viruses obtained from these foci and from one of the tumor tissues showed high transforming activity in the presence of dimethyl sulfoxide, suggesting that these viruses carry spontaneous mutations of the fyn gene. Four fyn genes from CEF DNAs infected with transforming viruses were molecularly cloned, and their products were confirmed to possess transforming activity. DNA sequence analysis of the fyn genes showed that two of the four mutants have Thr instead of Ile at position 338 in the kinase domain. The other two mutants carry deletions of 78 and 108 base pairs, respectively, which result in complete loss of region C of SH2. The overall level of proteins containing phosphotyrosine was significantly higher in transformed cells than in normal CEF cells. Our data indicate that when expressed at high levels in a retrovirus, normal p59fyn cannot cause cellular transformation, but that mutant p59fyn with either a single amino acid substitution in the kinase domain or a deletion including region C produces a transforming protein, perhaps due to enhanced tyrosine kinase activity. This is the first observation that deletion of region C can unmask the potential transforming activity of a src family kinase.

Expression of the yes proto-oncogene in cerebellar Purkinje cells

To identify the kinds of cells in the brain that express the yes proto-oncogene, we examined chicken brains by using immunofluorescent staining and in situ hybridization. Both approaches showed that the highest level of the yes gene product was in cerebellar Purkinje cells. In addition, we analyzed Purkinje cell degeneration (pcd) mutant mice. The level of yes mRNA in cerebella of pcd mutants was four times lower than that found in cerebella of normal littermates. Our studies point to Purkinje cells as an attractive model for functional studies of the yes protein.

Structure and expression of STK, a src-related gene in the simple metazoan Hydra attenuata

Both cDNA clones and a genomic DNA clone encoding a 509-amino-acid protein that is 64% similar to chicken pp60c-src were isolated from the simple metazoan Hydra attenuata. We have designated this gene STK, for src-type kinase. Features of the amino acid sequence of the protein encoded by the STK gene suggest that it is likely to be myristoylated and regulated by phosphorylation in a manner similar to that found for pp60c-src. The genomic sequence encoding the protein was found to be interrupted by at least two introns, one of which was located in a position identical to that of one of the introns in the chicken src gene. The STK gene was expressed during early development of H. attenuata and at high levels in the epithelial cells of adult polyps. Probing of Hydra proteins with an antibody to phosphotyrosine indicated that the major phosphotyrosine-containing protein in H. attenuata may be the STK protein itself. H. attenuata is the simplest organism from which a protein-tyrosine kinase gene has been isolated. The presence of such a gene in the evolutionarily ancient phylum Cnidaria suggests that protein-tyrosine kinase genes arose concomitantly with or shortly after the appearance of multicellular organisms.

Expression of the fgr protooncogene product as a function of myelomonocytic cell maturation

The fgr protooncogene is a member of the src family of protein tyrosine kinases. Recent studies have shown that normal myelomonocytic cells and tissue macrophages are the major sites of fgr mRNA expression. In the present study, we have identified the fgr protooncogene protein product in HL60 cells and have examined its expression as a function of HL60 cell maturation. Whether induced toward monocytic or granulocytic lineages, p55c-fgr accumulated in HL60 cells during maturation. In differentiated cells, the protein was active as a protein tyrosine kinase and was localized to peripheral cell membranes. Demonstration that a myristyl group was covalently bound to the protein probably accounted for its subcellular distribution. These findings establish developmental regulation of p55c-fgr in a lineage that represents its natural site of expression.

Expression of the yes proto-oncogene in cerebellar Purkinje cells

To identify the kinds of cells in the brain that express the yes proto-oncogene, we examined chicken brains by using immunofluorescent staining and in situ hybridization. Both approaches showed that the highest level of the yes gene product was in cerebellar Purkinje cells. In addition, we analyzed Purkinje cell degeneration (pcd) mutant mice. The level of yes mRNA in cerebella of pcd mutants was four times lower than that found in cerebella of normal littermates. Our studies point to Purkinje cells as an attractive model for functional studies of the yes protein.

Structure and expression of STK, a src-related gene in the simple metazoan Hydra attenuata

Both cDNA clones and a genomic DNA clone encoding a 509-amino-acid protein that is 64% similar to chicken pp60c-src were isolated from the simple metazoan Hydra attenuata. We have designated this gene STK, for src-type kinase. Features of the amino acid sequence of the protein encoded by the STK gene suggest that it is likely to be myristoylated and regulated by phosphorylation in a manner similar to that found for pp60c-src. The genomic sequence encoding the protein was found to be interrupted by at least two introns, one of which was located in a position identical to that of one of the introns in the chicken src gene. The STK gene was expressed during early development of H. attenuata and at high levels in the epithelial cells of adult polyps. Probing of Hydra proteins with an antibody to phosphotyrosine indicated that the major phosphotyrosine-containing protein in H. attenuata may be the STK protein itself. H. attenuata is the simplest organism from which a protein-tyrosine kinase gene has been isolated. The presence of such a gene in the evolutionarily ancient phylum Cnidaria suggests that protein-tyrosine kinase genes arose concomitantly with or shortly after the appearance of multicellular organisms.

Evidence that the leukocyte-common antigen is required for antigen-induced T lymphocyte proliferation

The leukocyte-common antigen (L-CA) is a family of large molecular weight glycoproteins uniquely expressed on the surface of all nucleated cells of hematopoietic origin. The glycoprotein consists of a heavily glycosylated exterior domain, a single membrane spanning region, and a large cytoplasmic domain that contains tyrosine phosphatase activity. To investigate the function of this family, we generated T cell clones that lacked L-CA (L-CA-). The expression of the alpha beta T cell receptor, CD3, CD4, IL-2 receptor (p55), LFA-1, Thy-1, and Pgp-1 (CD44) was normal. The L-CA- T cell clones failed to proliferate in response to antigen or cross-linked CD3; however, they could still proliferate in response to IL-2. An L-CA+ revertant was obtained and the ability to proliferate in response to antigen and cross-linked CD3 was restored. These data indicate that L-CA is required for T cells to enter into cell cycle in response to antigen.

Identification of a developmentally regulated protein-tyrosine kinase by using anti-phosphotyrosine antibodies to screen a cDNA expression library

To identify the protein-tyrosine kinases that are expressed during chicken embryonic development, a 10-day chicken embryo cDNA expression library was screened with anti-phosphotyrosine antibodies. Of the positive clones isolated, many encoded the same protein-tyrosine kinase, which we designate Cek1 (chicken embryo kinase 1). Its amino acid sequence suggests that the Cek1 protein is a transmembrane tyrosine kinase and presumably the receptor for an unknown ligand. Antibodies prepared to the cloned Cek1 kinase recognize, in immunoblotting experiments, two protein bands with apparent molecular weights of 100,000 and 110,000. The Cek1 protein was detected in many chicken embryonic tissues, but not in the corresponding adult tissues (with the exception of brain). The Cek1 kinase appears to be very closely related to two protein-tyrosine kinases whose partial sequences have been recently determined, human Flg and mouse Bek. Cloning using anti-phosphotyrosine antibodies has allowed us to detect, in addition to Cek1, several other protein-tyrosine kinases that are expressed during chicken embryonic development, some of which have not been previously identified.

Tissue-specific expression and developmental regulation of the human fgr proto-oncogene

In this study, we show that c-fgr proto-oncogene expression is limited to normal peripheral blood granulocytes, monocytes, and alveolar macrophages, all of which contain 50 to 100 copies of c-fgr mRNA per cell. The c-fgr RNA molecules in these cells consisted of partially spliced transcripts containing intron 7 and completely spliced molecules capable of encoding the predicted p55 c-fgr protein. The splicing of intron 7 appeared to occur after the splicing of most of the other introns; partially spliced molecules containing intron 7 did not appear to be transported into the cytoplasm. Very low levels of fgr transcripts were also present in U937 promonocytic cells and increased in abundance with 12-O-tetradecanoylphorbol-13-acetate (TPA)-induced differentiation. The level of fgr transcripts began to increase 2 to 4 h after TPA addition, peaked at 8 h, and subsequently declined. Since we found that the half-life of fgr mRNA was longer than 8 h, these changes are best explained by transient transcriptional activation of fgr during TPA-induced differentiation, although nuclear runoff experiments were not sensitive enough to detect this event. Cycloheximide also caused accumulation of c-fgr transcripts in U937 cells; no superinduction was observed when TPA and cycloheximide were added at the same time. Induction by either agent was blocked with actinomycin D. These results demonstrate that the c-fgr gene is expressed in a tissue- and development-specific fashion and suggest that constitutive expression of c-fgr in U937 cells is regulated by a labile transcriptional repressor.

Two putative protein-tyrosine kinases identified by application of the polymerase chain reaction

The pivotal role that protein-tyrosine kinases (PTKs) play in the growth regulation of eukaryotic cells is manifest in the frequent appearance of members of the PTK family as growth factor receptors or as the transforming agents of acutely transforming retroviruses. A feature common to all members of the PTK family is a highly conserved catalytic domain which is characteristic of the group as a whole and whose activity appears to be tightly regulated within the cell by other domains of the PTK. Degenerate oligonucleotide probes corresponding to two invariant amino acid sequence motifs within the catalytic domains of all PTK family members were synthesized and employed in the polymerase chain reaction (PCR) to amplify cDNA sequences between them. An M13 PCR library was produced in this way from cDNA prepared against mRNA from the murine hemopoietic cell line FDC-P1. The PCR library was then screened by DNA sequencing for PTK-related sequences. Two sequences were identified that, on the basis of sequence comparison with known PTKs, may encode representatives of a new class of PTK.

The carboxy-terminal sequence of p56lck can regulate p60c-src

A chimera containing the coding region for residues 1 to 516 of p60c-src and residues 495 to 509 (the carboxy terminus) of p56lck was constructed and expressed in mouse fibroblasts. The chimeric protein appeared to be phosphorylated and regulated in the same fashion as p60c-src.

A mutation in v-src that removes a single conserved residue in the SH-2 domain of pp60v-src restricts transformation in a host-dependent manner

The v-src oncogene of Rous sarcoma virus (RSV) is able to transform both avian and mammalian cells, but the mutant allele v-src-L displays a host range dependence for transformation, transforming chicken but not rat cells with wild-type efficiency. This host range restriction can be detected by measuring growth in low serum, saturation density, and anchorage independent growth. In addition, rat cells expressing v-src-L do not form tumors in syngeneic rats or nude mice, but RSV carrying the mutant allele causes tumors in chicks, although at a reduced efficiency and with increased latency. To determine the lesion responsible for this phenotype, we sequenced the entire v-src gene from the parental B77 strain of RSV, as well as the mutant allele. v-src-L is missing 3 nucleotides present in the wild-type parent, RSV B31, eliminating Phe-172, an invariant residue in a conserved region of src-related proteins known as SH-2. The kinase activity of pp60v-src-L was indistinguishable from that of the wild type in chicken cells but was significantly reduced in rat cells as assayed by an in vitro immune complex assay; in vivo phosphorylation of one specific substrate, p36 (calpactin I heavy chain); and total phosphotyrosine-containing proteins. In addition, the pattern of phosphotyrosine-containing proteins in rat cells was qualitatively different when cells containing pp60v-src-L were compared with cells with wild-type pp60v-src, even though both pp60v-src proteins were membrane associated. The data are consistent with a role for the SH-2 region in substrate specificity.

Tissue-specific expression and developmental regulation of the human fgr proto-oncogene

In this study, we show that c-fgr proto-oncogene expression is limited to normal peripheral blood granulocytes, monocytes, and alveolar macrophages, all of which contain 50 to 100 copies of c-fgr mRNA per cell. The c-fgr RNA molecules in these cells consisted of partially spliced transcripts containing intron 7 and completely spliced molecules capable of encoding the predicted p55 c-fgr protein. The splicing of intron 7 appeared to occur after the splicing of most of the other introns; partially spliced molecules containing intron 7 did not appear to be transported into the cytoplasm. Very low levels of fgr transcripts were also present in U937 promonocytic cells and increased in abundance with 12-O-tetradecanoylphorbol-13-acetate (TPA)-induced differentiation. The level of fgr transcripts began to increase 2 to 4 h after TPA addition, peaked at 8 h, and subsequently declined. Since we found that the half-life of fgr mRNA was longer than 8 h, these changes are best explained by transient transcriptional activation of fgr during TPA-induced differentiation, although nuclear runoff experiments were not sensitive enough to detect this event. Cycloheximide also caused accumulation of c-fgr transcripts in U937 cells; no superinduction was observed when TPA and cycloheximide were added at the same time. Induction by either agent was blocked with actinomycin D. These results demonstrate that the c-fgr gene is expressed in a tissue- and development-specific fashion and suggest that constitutive expression of c-fgr in U937 cells is regulated by a labile transcriptional repressor.

Primary structure of the brain alpha-spectrin

We have determined the nucleotide sequence coding for the chicken brain alpha-spectrin. It is derived both from the cDNA and genomic sequences, comprises the entire coding frame, 5' and 3' untranslated sequences, and terminates in the poly(A)-tail. The deduced amino acid sequence was used to map the domain structure of the protein. The alpha-chain of brain spectrin contains 22 segments of which 20 correspond to the repeat of the human erythrocyte spectrin (Speicher, D. W., and V. T. Marchesi. 1984. Nature (Lond.). 311:177-180.), typically made of 106 residues. These homologous segments probably account for the flexible, rod-like structure of spectrin. Secondary structure prediction suggests predominantly alpha-helical structure for the entire chain. Parts of the primary structure are excluded from the repetitive pattern and they reside in the middle part of the sequence and in its COOH terminus. Search for homology in other proteins showed the presence of the following distinct structures in these nonrepetitive regions: (a) the COOH-terminal part of the molecule that shows homology with alpha-actinin, (b) two typical EF-hand (i.e., Ca2+-binding) structures in this region, (c) a sequence close to the EF-hand that fulfills the criteria for a calmodulin-binding site, and (d) a domain in the middle of the sequence that is homologous to a NH2-terminal segment of several src-tyrosine kinases and to a domain of phospholipase C. These regions are good candidates to carry some established as well as some yet unestablished functions of spectrin. Comparative analysis showed that alpha-spectrin is well conserved across the species boundaries from Xenopus to man, and that the human erythrocyte alpha-spectrin is divergent from the other spectrins.

The first seven amino acids encoded by the v-src oncogene act as a myristylation signal: lysine 7 is a critical determinant

The transforming protein of Rous sarcoma virus, pp60v-src, is covalently coupled to myristic acid by an amide linkage to glycine 2. Myristylation promotes the association of pp60v-src with cellular membranes, and this subcellular location is essential for transforming activity. The findings presented here, in conjunction with the previous reports of others, imply that the seventh amino acid encoded by v-src might be important in the myristylation reaction. Replacement of lysine 7 by asparagine greatly reduced the myristylation, membrane association, and transforming activity of pp60v-src. In contrast, substitution of arginine at residue 7 had no effect on any of these properties of pp60v-src. Addition of amino acids 1 to 7 encoded by v-src was sufficient to cause myristylation of a src-pyruvate kinase fusion protein. We conclude that the recognition sequence for myristylation of pp60v-src comprises amino acids 1 to 7 and that lysine 7 is a critical component of this sequence.

The carboxy-terminal sequence of p56lck can regulate p60c-src

A chimera containing the coding region for residues 1 to 516 of p60c-src and residues 495 to 509 (the carboxy terminus) of p56lck was constructed and expressed in mouse fibroblasts. The chimeric protein appeared to be phosphorylated and regulated in the same fashion as p60c-src.

The carboxy terminus of pp60c-src is a regulatory domain and is involved in complex formation with the middle-T antigen of polyomavirus

A large number of mutations were introduced into the carboxy-terminal domain of pp60c-src. The level of phosphorylation on Tyr-416 and Tyr-527, the transforming activity (as measured by focus formation on NIH 3T3 cells), kinase activity, and the ability of the mutant pp60c-src to associate with the middle-T antigen of polyomavirus were examined. The results indicate that Tyr-527 is a major carboxy-terminal element responsible for regulating pp60c-src in vivo. A good but not perfect correlation exists between lack of phosphorylation at Tyr-527 and increased phosphorylation at Tyr-416, between elevated phosphorylation on Tyr-416 and activated kinase activity, and between activated kinase activity and transforming activity. Phosphorylation of Tyr-527 was insensitive to the mutation of adjacent residues, indicating that the primary sequence only has a minor role in recognition by kinases or phosphatases which regulate it in vivo. Three mutants which have in common a modified Glu-524 residue were phosphorylated on Tyr-416 and Tyr-527 and were weakly transforming. This suggests that other mechanisms besides complete dephosphorylation of Tyr-527 can lead to increased phosphorylation of Tyr-416 and activation of the transforming activity of pp60c-src. Furthermore, the residues between Asp-518 and Pro-525 were required to form a stable complex with middle-T antigen. The proximity of these sequences to Tyr-527 suggests a model in which middle-T activates pp60c-src by binding directly to this region of the molecular and thereby preventing phosphorylation of Tyr-527. Alternatively, middle-T binding may mediate a conformational change in this region, which in turn induces an alteration in the level of phosphorylation at Tyr-527 and Tyr-416.

Acquisition of transforming properties by FYN, a normal SRC-related human gene

The SRC gene is the prototype for a family of closely related genes whose products have protein-tyrosine kinase activity. We recently described another member of this family, designated FYN, whose cDNA was isolated from normal human fibroblasts. To examine the possible role of FYN as an oncogene, we investigated the effects of FYN overexpression on NIH 3T3 cells. Our findings demonstrate that normal FYN overexpression induces morphologic transformation and anchorage-independent growth. In addition, at relatively low frequency, FYN acquired properties of a dominant-acting oncogene capable of inducing the fully tumorigenic phenotype. Genetic changes associated with the conversion of normal FYN cDNA into a transforming gene with high focus-forming activity were localized to the carboxyl-terminal region of its translational product.

The first seven amino acids encoded by the v-src oncogene act as a myristylation signal: lysine 7 is a critical determinant

The transforming protein of Rous sarcoma virus, pp60v-src, is covalently coupled to myristic acid by an amide linkage to glycine 2. Myristylation promotes the association of pp60v-src with cellular membranes, and this subcellular location is essential for transforming activity. The findings presented here, in conjunction with the previous reports of others, imply that the seventh amino acid encoded by v-src might be important in the myristylation reaction. Replacement of lysine 7 by asparagine greatly reduced the myristylation, membrane association, and transforming activity of pp60v-src. In contrast, substitution of arginine at residue 7 had no effect on any of these properties of pp60v-src. Addition of amino acids 1 to 7 encoded by v-src was sufficient to cause myristylation of a src-pyruvate kinase fusion protein. We conclude that the recognition sequence for myristylation of pp60v-src comprises amino acids 1 to 7 and that lysine 7 is a critical component of this sequence.

Mutation of a site of tyrosine phosphorylation in the lymphocyte-specific tyrosine protein kinase, p56lck, reveals its oncogenic potential in fibroblasts

p56lck, a cellular tyrosine protein kinase (EC 2.7.1.112) of the src family, is expressed in essentially all T cells and in some B cells. Expression in nonlymphoid cells is observed only rarely. We have found that mutation of a carboxyl-terminal phosphorylation site, tyrosine-505, reveals an oncogenic activity of this protein. Infection of fibroblasts with a retrovirus encoding wild-type p56lck is without consequence. In contrast, infection with a virus encoding the mutant protein leads to greatly increased phosphorylation of cellular proteins on tyrosine, morphological transformation, and anchorage-independent growth. This suggests that the tyrosine protein kinase activity and the oncogenic potential of p56lck are normally suppressed in vivo by phosphorylation of tyrosine-505. Since similar results were obtained previously with an analogous mutant of c-src, our results suggest that the protein kinase activity of all members of the src family of cytoplasmic tyrosine protein kinases will prove to be regulated by tyrosine phosphorylation at a conserved residue near the carboxyl terminus. Because p56lck is normally expressed only in lymphoid cells, it was possible that p56lck would be without effect in other tissues. The transformation of fibroblasts by mutant p56lck shows that this lymphoid protein can interact productively with nonlymphoid polypeptide substrates.

Nucleotide sequence and chromosomal mapping of the human c-yes-2 gene

We molecularly characterized the second gene, c-yes-2, of two copies of yes-related genes which we previously found to contain in the human genome. First, nucleotide sequence analysis revealed that the c-yes-2 gene is a pseudogene of the c-yes-1 gene. Second, by using two independent methods, hybridization of both DNAs from sorted chromosomes and metaphase spreads with c-yes-2 DNA, we assigned the c-yes-2 gene to chromosome 22q11.2. This chromosomal localization is consistent with that given in our previous report. The failure of proper mapping in our experiment might have been caused by instability of hybrid cell clones.

The carboxy terminus of pp60c-src is a regulatory domain and is involved in complex formation with the middle-T antigen of polyomavirus

A large number of mutations were introduced into the carboxy-terminal domain of pp60c-src. The level of phosphorylation on Tyr-416 and Tyr-527, the transforming activity (as measured by focus formation on NIH 3T3 cells), kinase activity, and the ability of the mutant pp60c-src to associate with the middle-T antigen of polyomavirus were examined. The results indicate that Tyr-527 is a major carboxy-terminal element responsible for regulating pp60c-src in vivo. A good but not perfect correlation exists between lack of phosphorylation at Tyr-527 and increased phosphorylation at Tyr-416, between elevated phosphorylation on Tyr-416 and activated kinase activity, and between activated kinase activity and transforming activity. Phosphorylation of Tyr-527 was insensitive to the mutation of adjacent residues, indicating that the primary sequence only has a minor role in recognition by kinases or phosphatases which regulate it in vivo. Three mutants which have in common a modified Glu-524 residue were phosphorylated on Tyr-416 and Tyr-527 and were weakly transforming. This suggests that other mechanisms besides complete dephosphorylation of Tyr-527 can lead to increased phosphorylation of Tyr-416 and activation of the transforming activity of pp60c-src. Furthermore, the residues between Asp-518 and Pro-525 were required to form a stable complex with middle-T antigen. The proximity of these sequences to Tyr-527 suggests a model in which middle-T activates pp60c-src by binding directly to this region of the molecular and thereby preventing phosphorylation of Tyr-527. Alternatively, middle-T binding may mediate a conformational change in this region, which in turn induces an alteration in the level of phosphorylation at Tyr-527 and Tyr-416.

Primary structure of the human fgr proto-oncogene product p55c-fgr

Normal human c-fgr cDNA clones were constructed by using normal peripheral blood mononuclear cell mRNA as a template. Nucleotide sequence analysis of two such clones revealed a 1,587-base-pair-long open reading frame which predicted the primary amino acid sequence of the c-fgr translational product. Homology of this protein with the v-fgr translational product stretched from codons 128 to 516, where 32 differences among 388 codons were observed. Sequence similarity with human c-src, c-yes, and fyn translational products began at amino acid position 76 of the predicted c-fgr protein and extended nearly to its C-terminus. In contrast, the stretch of 75 amino acids at the N-terminus demonstrated a greatly reduced degree of relatedness to these same proteins. To verify the deduced amino acid sequence, antibodies were prepared against peptides representing amino- and carboxy-terminal regions of the predicted c-fgr translational product. Both antibodies specifically recognized a 55-kilodalton protein expressed in COS-1 cells transfected with a c-fgr cDNA expression plasmid. Moreover, the same protein was immunoprecipitated from an Epstein-Barr virus-infected Burkitt's lymphoma cell line which expressed c-fgr mRNA but not in its uninfected fgr mRNA-negative counterpart. These findings identified the 55-kilodalton protein as the product of the human fgr protooncogene.