Biomedical subjects

D L Faletto

Publications and source records attributed to D L Faletto.

6 recordsLinked to original sources

PubMed1993

Signal transduction in c-met mediated motogenesis.

We have begun characterizing the signal transduction pathways used by the c-met receptor in cells in which ligand (HGF-SF) stimulates motogenesis in the absence of mitogenesis. Primary targets (within 10-15 minutes) were identified as PI-3 kinase, GAP, PLC gamma, src, and MAP kinase, substrates which are also activated upon growth factor activation of mitogenic receptor systems. Following HGF-SF treatment, the 85 kD subunit of PI-3 kinase is phosphorylated on tyrosine and PI-3 kinase activity rapidly associates with the c-met receptor. A number of these substrates are implicated in cytoskeletal rearrangements and may be important in the motogenic response to the factor. We have also identified a number of colon carcinoma lines which express unamplified levels of constitutively tyrosine phosphorylated c-met protein. In these and other (gastric) cell lines which express amplified levels of activated receptor protein, we have determined that receptor activation is not due to the autocrine production of ligand.

Animals↗

PubMed1992

The met proto-oncogene receptor and lumen formation.

The met proto-oncogene product (Met) and its ligand, hepatocyte growth factor/scatter factor (HGF/SF), have been implicated in cell mitogenic response, cell motility, and the promotion of the ordered spatial arrangement of tissue. By means of confocal laser-scanning microscopy, it was shown that Met is expressed in cells bordering lumen-like structures that resemble ducts in the human mammary cell line T47D. In human breast tissue biopsies, Met staining was intense in normal cells bordering mammary ducts but was reduced in adjacent tumor tissue. Met staining in lumen-forming organs colocalizes with staining of antibody to phosphotyrosine, which suggests that the Met receptor and its substrates may be activated in lumen structures or ducts. HGF/SF treatment of human epithelial carcinoma cell lines resulted in the formation of lumen-like structures in vitro. Reduced expression of Met could be related to the extent of tumor cell differentiation.

Adenocarcinoma↗

PubMed1992

Evidence for non-covalent clusters of the c-met proto-oncogene product.

The met proto-oncogene is a member of the tyrosine kinase growth factor receptor family and is the receptor for hepatocyte growth factor (HGF) or scatter factor. The primary met product is a 150 kDa precursor that is glycosylated to generate a 170 kDa (p170met) proreceptor protein. The mature form of the receptor is generated by cleavage of p170met to yield a disulfide-linked 140 kDa beta-subunit (p140met) and a 45 kDa alpha-subunit (p45met). Both products are glycosylated. Under non-reducing conditions both p170met and the alpha, beta-disulfide-linked protein are detected as a 185 kDa product (p185met), but only alpha-beta heterodimeric p185met is cross-linked and rendered resistant to disulfide reduction with membrane-impermeable 6.4 A linker length cross-linking reagents. These data indicate that the p170 precursor is not on the cell surface. Cross-linking experiments using 12-A linker reagents yield multimeric forms of alpha-beta heterodimeric p185met greater than 500 kDa in size. These multimeric forms are produced in all cell lines tested regardless of the levels of protein expressed. These data suggest that alpha-beta heterodimeric p185met occurs in clusters or patches on the cell surface. Immunohistochemical analysis of met protein in the absence of ligand reveals a clustered staining pattern on the cell surface.

Animals↗

PubMed1991

Identification of the hepatocyte growth factor receptor as the c-met proto-oncogene product.

Hepatocyte growth factor (HGF) is a plasminogen-like protein thought to be a humoral mediator of liver regeneration. A 145-kilodalton tyrosyl phosphoprotein observed in rapid response to HGF treatment of intact target cells was identified by immunoblot analysis as the beta subunit of the c-met proto-oncogene product, a membrane-spanning tyrosine kinase. Covalent cross-linking of 125I-labeled ligand to cellular proteins of appropriate size that were recognized by antibodies to c-met directly established the c-met product as the cell-surface receptor for HGF.

Cell Line↗

PubMed1985

The role of Ca2+ in dimethyl sulfoxide-induced differentiation of Friend erythroleukemia cells.

Cultured Friend cells can be induced by dimethyl sulfoxide (Me2SO) and several other agents to mature along the erythroid pathway. Evidence has been presented that an increase in Ca2+ influx is an early and necessary prelude to the commitment to maturation by these cells (Levenson, R., Housman, D., and Cantley, L. (1980) Proc. Natl. Acad. Sci. U.S.A. 77, 5948-5952). The simplest hypothesis supporting all the available data is that Me2SO and other inducers elevate the cytosolic Ca2+ concentration. We have now measured cytosolic Ca2+ using the fluorescent indicator quin-2, and find, contrary to expectation, a small decrease upon treatment of cells with Me2SO. Cytosolic Ca2+ was increased by raising the Ca2+ in the medium, but was not dramatically altered by addition of ouabain or monensin or by incubation in Na+-free medium. Measurement of total cell Ca2+ by a triple-labeling technique using 3H2O and 125I-albumin to determine cell water and extracellular space, respectively, revealed no significant change upon treatment with Me2SO for up to 40 h. A decrease in the initial rate of 45Ca2+ influx was observed in Me2SO-treated cells, when measured at 4 degrees C. These data do not support the hypothesis that an increase in cell Ca2+ is necessary for the induction of Friend cell differentiation or that Na+/Ca2+ exchange is a significant regulator of cytosolic Ca2+ in Friend cells.

Aminoquinolines↗

PubMed1985

An early decrease in phosphatidylinositol turnover occurs on induction of Friend cell differentiation and precedes the decrease in c-myc expression.

Phosphatidylinositol turnover has recently been implicated in the regulation of proliferation and transformation. Its role in differentiation has now been investigated using Friend erythroleukemia cells, which can be induced to differentiate along the erythroid pathway by dimethylsulfoxide and certain other agents. We have found that levels of the phosphatidylinositol metabolites inositol-trisphosphate and diacylglycerol significantly decrease within 2 hr of induction of Friend cell differentiation. These decreases precede decreased expression of the c-myc proto-oncogene and its protein product. Phorbol 12-myristate, 13-acetate, which can mimic diacylglycerol, blocked differentiation without reversing the decrease in phosphatidylinositol metabolite levels. Two synthetic diacylglycerols, L-alpha-1-oleoyl-2-acetoyl-sn-3-glycerol and sn-1,2-dioctanoylglycerol, also blocked differentiation and commitment. Diacylglycerol regulation of kinase C activity may play a key role in control of c-myc expression and Friend cell differentiation.

Animals↗