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C A Borgman

Publications and source records attributed to C A Borgman.

9 recordsLinked to original sources
PubMed1993

The protooncogene c-sea encodes a transmembrane protein-tyrosine kinase related to the Met/hepatocyte growth factor/scatter factor receptor.

c-sea is the cellular homologue of the avian erythroblastosis virus S13-encoded oncogene v-sea. We have isolated and determined the nucleotide sequence of overlapping chicken cDNAs that encode the putative c-sea protooncogene product. The predicted reading frame encoded a 1404-aa polypeptide that had the structure of a receptor-like protein-tyrosine kinase and exhibited the highest degree of sequence similarity with the Met/hepatocyte growth factor/scatter factor receptor. Analysis of steady-state RNA expression revealed that c-sea mRNA levels were elevated approximately 5-fold in chicken embryo cells transformed by activated variants of the src nonreceptor protein-tyrosine kinase gene but not in cells transformed by the nuclear oncogenes v-myc or v-rel. A survey of c-sea expression in a variety of chicken tissues indicated that the highest levels of mRNA were located in peripheral white blood cell populations and in the intestine.

Amino Acid Sequence↗
PubMed1993

Autonomous expression of a noncatalytic domain of the focal adhesion-associated protein tyrosine kinase pp125FAK.

Integrins play a central role in cellular adhesion and anchorage of the cytoskeleton and participate in the generation of intracellular signals, including tyrosine phosphorylation. We have recently isolated a cDNA encoding a unique, focal adhesion-associated protein tyrosine kinase (FAK) that is a component of an integrin-mediated signal transduction pathway. Here we report the isolation of cDNAs encoding the C-terminal, noncatalytic domain of the FAK kinase, termed FRNK (FAK-related nonkinase). Both the FAK- and FRNK-encoded polypeptides, pp125FAK and p41/p43FRNK, are expressed in normal chicken embryo cells. pp125FAK and p41/p43FRNK were localized to focal adhesions, suggesting that pp125FAK is directed to the focal adhesions by sequences within its C-terminal domain. We also show that the fibronectin-dependent increase in tyrosine phosphorylation of pp125FAK is accompanied by a concomitant posttranslational modification of p41FRNK.

Amino Acid Sequence↗
PubMed1992

pp125FAK a structurally distinctive protein-tyrosine kinase associated with focal adhesions.

Expression of the Rous sarcoma virus-encoded oncoprotein, pp60v-src, subverts the normal regulation of cell growth, which results in oncogenic transformation. This process requires the intrinsic protein-tyrosine kinase activity of pp60v-src and is associated with an increase in tyrosine phosphorylation of a number of cellular proteins, candidate substrates for pp60v-src. We report here the isolation of a cDNA encoding a protein, pp125, that is a major phosphotyrosine-containing protein in untransformed chicken embryo cells and exhibits an increase in phosphotyrosine in pp60v-src-transformed chicken embryo cells. This cDNA encodes a cytoplasmic protein-tyrosine kinase which, based upon its predicted amino acid sequence and structure, is the prototype for an additional family of protein-tyrosine kinases. Immunofluorescence localization experiments show that pp125 is localized to focal adhesions; hence, we suggest the name focal adhesion kinase.

Amino Acid Sequence↗
PubMed1986

On tight junction structure: Forssman glycolipid does not flow between MDCK cells in an intact epithelial monolayer.

One model of tight junction structure suggests that lipids might flow from cell to cell within shared exoplasmic membrane leaflets. We tested this proposal by co-culturing two clones of MDCK epithelial cells, which differed in their content of Forssman glycolipid, and then staining by immunofluorescence with rabbit anti-Forssman Ig. In co-cultures grown on glass cover slips and on nitrocellulose filters, positive Forssman staining was restricted to sharply demarcated clusters of cells formed by the Forssman-positive clone. Integrity of tight junctions between the two clones was indicated on cover slips by the presence of individual domes (hemicysts) composed of both clones and on filters by the generation of transepithelial potential differences. These results suggest that glycolipids in the exoplasmic leaflet of cells in a tight epithelium do not flow to adjacent cells.

Animals↗
PubMed1986

Isolation and characterization of two types of MDCK epithelial cell clones based on glycosphingolipid pattern.

The Madin-Darby canine kidney (MDCK) epithelial cell line was shown previously to be heterogeneous with marked differences reported between low-passage (strain I) and high-passage (strain II) cultures (Richardson, J.C.W., Scalera, V. and Simmons, N.L. (1981) Biochim. Biophys. Acta 673, 26-36). This report describes major differences in the glycolipids of the two subpopulations of cells that comprise strain I and strain II cultures. The majority of strain II cells were strongly positive for the Forssman glycolipid antigen, while strain I cells were Forssman-deficient. Upon finding that strain I cells were contaminated with mycoplasma, we rescued Forssman-deficient cells from strain II using an anti-Forssman plus complement lysis procedure. Clones of surviving cells consisted of two distinct cell types. The first were Forssman-deficient, non-ciliated, spindle-shaped cells which generated negative (apical to basolateral) transepithelial potential differences. Clones of the second type were strongly Forssman-positive, ciliated, and formed island-shaped clusters of cuboidal cells. These latter clones generated positive potential differences and grew more slowly than the spindle-shaped clones. Spindle cells were enriched in fucolipids, while cuboidal cells contained higher levels of sulfated glycolipids. These two types of clones should provide excellent model systems in which to study the processing and polarity of glycolipids in epithelial cells.

Animals↗
PubMed1986

Modes of shedding of glycosphingolipids from mouse lymphoma cells.

To characterize the process by which glycolipids are shed from cell membranes, the cellular and supernatant glycolipids were compared from a variant of the mouse lymphoma L5178Y which had been selected for strong expression of the neutral glycolipid gangliotriaosylceramide (GgOse3Cer). This glycolipid was present in three forms which differed in their fatty acid composition. Whereas the major cell-associated form of GgOse3Cer contained C24 fatty acids, the predominant form shed into the culture supernatant contained C16 fatty acids. Ultracentrifugation of the culture medium yielded a pellet with a GgOse3Cer profile similar to that of the cells and a supernatant enriched in the C16 fatty acid form. Gel filtration of the culture medium revealed two GgOse3Cer-containing pools. The first was excluded from Sepharose CL-2B and had a GgOse3Cer profile similar to that of the cells, while the second migrated with proteins in the range of 25,000-500,000 daltons and was enriched in the C16 fatty acid form. These results suggest two forms in which glycolipids are released from cell membranes. The first is in a large complex, possibly a membrane vesicle, which retains the glycolipid profile of the membrane of intact cells while the second form appears to result from the preferential release of particular glycolipid components.

Animals↗
PubMed1986

Short bed-continuous development thin-layer chromatography of glycosphingolipids.

The technique of short bed--continuous development chromatography has been utilized to increase the separation of glycosphingolipids on high performance thin-layer chromatography plates. The theoretical goal of increasing separation of bands by decreasing solvent strength was achieved within a practical time span as a result of the high solvent velocities in the short bed tank. Examples are given for increased separation of short and long chain neutral glycolipids, acetylated neutral glycolipids, and gangliosides.

Acetylation↗