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Increased expression of the negative growth factor, galactoside-binding protein, gene in transformed thyroid cells and in human thyroid carcinomas.

Murine beta-galactoside-binding protein has been shown to be a cell growth regulatory molecule and a cytostatic factor. We analysed the beta-galactoside-binding protein gene expression in a thyroid cell system including two normal cell lines (FRTL-5 and PC Cl 3) and the same cells transfected by several oncogenes that induce different degrees of malignancy and differentiation. We show that beta-galactoside-binding protein mRNA levels correlate with the expression of the malignant phenotype. Run-on experiments suggest that a transcriptional effect accounts at least in part for such a difference. We also show that the beta-galactoside-binding protein gene expression is increased in most human papillary thyroid carcinomas compared with normal thyroid.

Adenovirus E1A Proteins↗

Alternative splicing in the human lck gene leads to the deletion of exon 1' and results in a new type II lck transcript.

In this study we describe a new lck mRNA transcribed from the type II promoter, resulting from alternative splicing, in the deletion of exon 1' which comprises the AUG initiation codon. In this type IIB lck transcript, as a consequence of exon 1' deletion, a new AUG codon in exon 1, located 35 nt upstream from the regular initiation codon in exon 1', and normally out of frame, is now in frame with exon 2 and the following lck coding sequence. In this type IIB lck transcript, 10 residues encoded by exon 1 from the new AUG codon replace the first 35 residues encoded by exon 1'. Strikingly, in this new N-terminal amino acid sequence, a glycine residue, needed for myristylation and anchorage in the plasma membrane, is present at position 2. This alternative splicing has been observed in T-cell lines, normal mature T cells and in peripheral blood lymphocytes from different leukemic patients. Different ratios of regular type IIA lck mRNA (with exon 1') to spliced type IIB lck mRNA (without exon 1') have been observed depending on the patient.

Alternative Splicing↗

Wocko, a neurological mutant generated in a transgenic mouse pedigree.

Naturally occurring mutations involving the nervous system have provided virtually all of our current understanding of the genetic regulation of neural development (Caviness and Rakic, 1978). The difficulty of isolating the corresponding genes, however, has precluded a molecular analysis of these mutants. Insertional mutagenesis, induced by microinjection of DNA into fertilized ova to produce transgenic animals, provides a molecular tag that marks the site of the mutational event. In this article, we describe a transgenic neurological mutation, designated wocko (Wo), which disrupts the development of the inner ear. These mutant mice display a dominant behavioral phenotype that consists of circling, hyperactivity, and head tossing, reminiscent of the shaker/waltzer class of mutants, and they display a recessive homozygous sublethal phenotype. Anatomical analyses showed that both structural and neural components of the vestibular system were disrupted, while analyses of mutant fetuses showed that these morphological abnormalities were due to aberrant development. Although low levels of transgene expression were detected using a sensitive PCR assay, several nonmutant pedigrees that contain the same construct also expressed the transgene in the inner ear, suggesting that low levels of transgene expression alone were not responsible for the wocko phenotype. Because the integrated transgene provides a marker to clone the wocko mutation, the analysis of this mutant will give unique insight into the molecular genetics of inner ear development and into a broad class of neurological mutations that affect the inner ear.

Animals↗

Activation of transcription via AP-1 or CREB regulatory sites is blocked by protein tyrosine phosphatases.

Transcriptional activation endowed by AP-1 or CREB binding sites can be significantly reduced in transient transfection tests by expression from the corresponding cloned cDNAs of protein tyrosine phosphatases. Both the protein tyrosine phosphatase 1B and the T-cell protein tyrosine phosphatase, as well as a novel form of this latter protein generated by an alternative splicing even show this activity. The effect is specific, as none of the protein tyrosine phosphatases alters transcriptional activation by either the estrogen receptor, GAL4, or a GAL4-VP16 fusion protein. Furthermore, the activities of the SV40 early gene promoter and a Moloney murine leukemia virus long terminal repeat promoter are not reduced by these phosphatases. We conclude that a yet to be identified protein phosphorylated on tyrosine is necessary for a full transcriptional response via AP-1 or CREB binding sites.

Amino Acid Sequence↗

Expression of a novel form of the fyn proto-oncogene in hematopoietic cells.

The fyn proto-oncogene encodes a 59-kD membrane-associated protein-tyrosine kinase that is implicated in the control of cell growth. We report here that there are two distinct fyn-encoded transcripts that exhibit mutually exclusive expression patterns; one form is found in thymocytes, splenocytes, and some hematolymphoid cell lines, while a second form accumulates principally in brain. The thymocyte and brain forms of p59fyn differ in their kinase domains, and are generated by mutually exclusive alternative splicing of a single exon. Immunoprecipitation followed by in vitro autophosphorylation demonstrates that both forms of p59fyn are enzymatically active. Our results define a novel form of the p59fyn protein-tyrosine kinase, with an altered catalytic domain, that apparently participates in a specialized signal transduction pathway in hematopoietic cells.

Amino Acid Sequence↗

Critical genetic determinants and molecular events in multistage skin carcinogenesis.

Carcinogenesis can be operationally and mechanistically divided into at least three major stages--initiation, promotion, and progression. Variations among stocks and strains of mice to susceptibility to multistage skin and liver carcinogenesis appear to be more related to alterations in tumor promotion than tumor initiation; however, the critical events have not been determined. In the mouse skin model the first stage is thought to involve the interaction of a tumor initiator with the genetic material of stem cells leading to an alteration in some aspect of growth control, differentiation, or both. The major effect of tumor promoters, regardless of the type, is the specific expansion of the initiated stem cells in the skin. This appears to occur by both direct and indirect mechanisms that involve the loss of glucocorticoid receptors, differentiation alterations, a direct growth stimulation of the initiated cells, or selective cytotoxicity. The progression stage is characterized by a high level of genetic instability that produces a number of chromosomal alterations. These changes may be responsible for the loss of the high-molecular-weight keratin proteins and filaggrin, increase in gamma-glutamyl-transpeptidase activity, and changes in oncogene expression in squamous cell carcinomas. We have found that a high percentage of squamous cell carcinomas have a trisomy in chromosome 2 that carries both src and abl genes and an increased expression of src and abl. We have also found increased Ha-ras on RNA expression in both papillomas and squamous cell carcinomas. We suggest that the genetic instability of the initiated cells is responsible for most observed changes during skin carcinogenesis.

Animals↗

CaLB: a 43 amino acid calcium-dependent membrane/phospholipid binding domain in p120 Ras GTPase-activating protein.

CaLB was originally observed as a conserved sequence motif in various calcium-responsive signalling proteins and also in p120 Ras GTPase activating protein (p120GAP) (Clark et al. Cell 65: 1043-1051, 1991). Here we show the 43 residue CaLB motif in p120GAP is a functional protein domain that when expressed as a fusion protein in vitro confers Ca(2+)-dependent interactions with cellular membranes and phosphatidylserine and phosphatidylinositol vesicles. p120GAP, but not a mutant lacking the CaLB domain, associates with the particulate fraction of cells in response to elevated intracellular Ca2+ suggesting that p120GAP may be regulated in part by calcium signals. Addition of the p120GAP CaLB domain was able to restore transforming activity and particulate localization to an otherwise transformation-defective and cytosolic mutant v-Sre tyrosine kinase. The CaLB domain appears to be a prevalent protein module that may affect the molecular interactions and subcellular localization of signalling proteins.

3T3 Cells↗

Alteration of in vivo DNA synthesis in the alpha globin locus of chick embryo fibroblasts due to in vivo activity of Rous sarcoma virus pp60src.

Globin gene transcription is activated in chick embryo fibroblasts (CEF) transformed by Rous sarcoma virus (RSV). To determine whether this activation is correlated with a change in the replication of the alpha D globin locus we used a nuclear runoff replication assay. Density labeling of nuclei showed that replication of the alpha D globin gene in normal and RSV-transformed CEF (RSV-CEF) is in the transcriptional direction. However, in RSV-CEF the signal from a specific restriction fragment between the alpha D and alpha A globin genes was lower in the replicated DNA. This decrease was selective in that the signal of this restriction fragment was not diminished in the unreplicated DNA in the same nuclei. When CEF transformed by temperature sensitive RSV were grown at the restrictive temperature for pp60src activity the loss of transformed cell morphology correlated with the reappearance of the replicated alpha globin DNA fragments in their normal stoichiometry. By comparison, histone H5 gene expression was not seen in CEF or in RSV-CEF, and H5 gene replication was not perturbed by viral transformation. These results suggest that the viral pp60src protein can activate transcription of the alpha D globin gene and change the replication of alpha globin chromatin.

Animals↗

Evaluation of protein kinase inhibitors in an assay system containing multiple protein kinase activities.

Specificities of several known protein kinase inhibitors were evaluated using an assay system in which activities of protein kinase A, protein kinase C, protein tyrosine kinase and calmodulin-dependent protein kinase III were simultaneously detected. Inhibitory spectra of H-89, K252a, H-7, staurosporine, tyrphostin and herbimycin A observed in the assay system were similar to those reported in the purified protein kinase assay systems. It was also found that KN-62 selectively inhibited calmodulin-dependent protein kinase III activity. These data suggest that the assay system may be effective and practicable in evaluating specificities and screening of new protein kinase inhibitors.

1-(5-Isoquinolinesulfonyl)-2-Methylpiperazine↗

Rous sarcoma virus genome stably integrated into mouse ascites sarcoma cells.

The organization of RSV genes present in the mouse ascites sarcoma cells was analysed. The transformed cells kept in vivo and in vitro for a long time continued to contain intact RSV genome and the cellular integration site was unchanged. RSV was recovered by transfection of chick embryo cells with these cellular DNA. As these cells, especially in ascites form, grow very rapidly and it is easy to obtain a large amount of cells at a time, they are useful for further study as RSV-transformants derived from mouse cells.

Animals↗

Molecular cloning and analysis of cDNA encoding the murine c-yes tyrosine protein kinase.

The cellular yes (c-yes) gene is a member of the class of proto-oncogenes that encode non-receptor tyrosine protein kinases. In this report we describe the isolation of cDNAs that encode the murine c-yes gene product and analysis of the nucleotide sequence of the murine c-yes cDNA clones. The reading frame encodes a protein of 541 amino acids with a calculated molecular mass of 60.63 kDa that is reactive with anti-Yes antisera and possesses protein kinase activity.

Amino Acid Sequence↗