A P Iyer

Northwestern University, Evanston, IL, United States

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Publications (6)27.79 Total impact

  • K S Kochhar, A P Iyer
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    ABSTRACT: Hepatocyte growth factor (HGF), a mesenchyme derived growth factor, promotes cell growth, cell motility, and morphogenesis in a variety of epithelial cells. The diverse responses are transduced across the cell membrane by the met/HGF receptor, a product of c-met protooncogene. The met/HGF receptor recruits a variety of second messenger molecules which relay the diverse intracellular responses of HGF. In this study, we show that HGF autophosphorylates and activates met/HGF receptor. The activated met/HGF receptor then physically associates with and activates phospholipase C-gamma (PLC-gamma). Furthermore, upon ligand stimulation, tyrosine-autophosphorylated met/HGF receptor also activates Nck oncogene product. Taken together, our results suggest that the receptor activation leads to formation of a complex in which PLC-gamma and Nck oncogene product co-exist with the activated met/HGF receptor, and that the Nck oncogene product is an important component of HGF signaling in Calu-1 and A549 cells.
    Cancer Letters 08/1996; 104(2):163-9. · 5.02 Impact Factor
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    ABSTRACT: Hepatocyte growth factor (HGF) has been recently suggested to contribute to tumorigenesis by an autocrine mechanism in fibroblast cells overexpressing its receptor, the MET/HGFR protein. Since epithelial cells represent the primary physiologic target of HGF, we investigated whether inappropriate expression of HGF by epithelial cells which normally express MET/HGFR may also contribute to tumorigenesis. We have transfected a full length rat HGF gene into three mouse epithelial cell lines, one derived from breast (MM55) and two (BNL CL.2 and NMuLi) representing liver non-parenchymal epithelial cells (NPEC). We confirmed the presence of the transfected gene by Southern blot analysis, the production of HGF protein by immunofluorescence, and the preservation of HGF biologic activity by bio-assay. In comparison to untransfected cells, all three HGF-transfected cell lines displayed high level MET/HGFR autophosphorylation and increased ability to proliferate in media containing low serum. The two HGF-transfected liver NPEC lines, but not the HGF-transfected mammary cell line, displayed loss of cell contact growth-inhibition and acquired a markedly increased ability to form colonies in soft agar. Furthermore, the NPEC HGF-transfected cell lines formed much larger tumors in nude mice than the untransfected counterparts, with extensive invasion and sporadic lung metastases. These results demonstrate that overexpression of HGF in at least some epithelial cells contribute to tumorigenesis, and furthermore suggest a possible role for the HGF-MET/HGFR system in the progression of certain epithelial tumors.
    Cancer Letters 10/1995; 96(1):37-48. · 5.02 Impact Factor
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    ABSTRACT: We have investigated HGF-induced signal transduction in two normal mouse epithelial cell lines (M23 and MM55). Both cell lines display HGF-induced mitogenesis and high level HGF-induced autophosphorylation of MET/HGFR. In both M23 and MM55 cells, HGF induces association with MET/HGFR and increased tyrosine phosphorylation of the SH2-domain containing proteins PI3K, GAP and NCK. PLC-gamma exhibited neither HGF-induced increases in tyrosine phosphorylation nor an association with MET/HGFR in these cell lines. Additionally, HGF induced increased transcription of c-fos, c-jun, junB, junD, and c-myc early response genes in both cell lines. We therefore suggest that the second messenger proteins PI3K, GAP and NCK, and possibly the protein products of the c-fos, c-jun, junB, junD and c-myc genes, are important elements in the HGF-induced mitogenic pathway in the normal mouse epithelial cell lines M23 and MM55.
    Biochemistry and molecular biology international 08/1995; 36(3):465-74.
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    ABSTRACT: NIH-3T3 cells transformed with met/HGF receptor gene proliferate in the absence of serum and growth factors. Immunocytochemical staining with anti-HGF antibody revealed intense HGF staining in the transfected cells. Additionally, these cells secrete bioactive HGF as evidenced by the ability of the conditioned media to stimulate met/HGF receptor phosphorylation in epithelial cells, and to promote migration of bovine adrenal capillary endothelial cells in a modified Boyden chamber assay. The migration of endothelial cells could be specifically inhibited by anti-HGF antibody but not by an irrelevant antibody. Suramin, a drug known to disrupt ligand-receptor interactions, inhibits the serum and growth-factor free proliferation, and the endogenous phosphorylation of met/HGF receptor in the transformed cells. Taken together, our data suggests an autocrine mode of transformation in NIH-3T3 cells transfected with met/HGF receptor gene.
    Growth Factors 02/1995; 12(4):303-13. · 2.20 Impact Factor
  • K S Kochhar, D Linnekin, A P Iyer
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    ABSTRACT: We have previously reported that c-met protooncogene, a member of a new class of receptor tyrosine-kinase gene family, is transforming when overexpressed in NIH-3T3 cells. In this paper, we report that the c-met protooncogene-transformed cells proliferate in a serum- and growth factor-free medium and exhibit constitutive tyrosine phosphorylation of several cellular proteins including the met protooncogene-encoded p145 and p185. Further investigations revealed platelet-derived growth factor (PDGF)-independent phosphorylation of PDGF-beta receptors in the transformed cells. Phosphoamino acid analysis revealed phosphorylation of PDGF receptors at tyrosine and serine residues. The PDGF receptor phosphorylation is unlikely to occur via autocrine production of PDGF since we could not detect PDGF activity both at the RNA level and at a functional protein level. Additionally, phospholipase C-gamma (PLC-gamma) a substrate of activated PDGF receptors, was found to be physically associated with PDGF receptors in the absence of PDGF stimulation in transformed cells. Furthermore, PDGF receptors coimmunoprecipitated along with PLC-gamma. Taken together, our results demonstrate a PDGF-independent phosphorylation and activation of PDGF-beta receptor in NIH-3T3 cells transformed by c-met protooncogene.
    Experimental Cell Research 07/1994; 212(2):414-21. · 3.56 Impact Factor
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    ABSTRACT: Hepatocyte growth factor is the most potent mitogen known for hepatocytes, and increasing evidence suggests that hepatocyte growth factor plays an important role in liver regeneration. However, hepatocytes are not the only liver epithelial cell population that proliferates during regeneration. Experimental and clinical data indicate that the regenerative liver response also includes the participation of nonparenchymal epithelial cells. The possible role of hepatocyte growth factor in this nonparenchymal epithelial cell regenerative response has not been explored. We studied the effects of hepatocyte growth factor with a model of two normal mouse nonparenchymal epithelial cell-derived cell lines with varying differentiation potentials. Addition of hepatocyte growth factor induced mitogenesis and scattering of colonies growing on culture dishes in both cell lines. Furthermore, hepatocyte growth factor was found to exert a profound morphogenic effect on cells growing in collagen matrixes. Hepatocyte growth factor-treated embryonic BNL CL.2 cell colonies developed elaborately branching elongated cords with only minimal tubularization. Hepatocyte growth factor-treated postnatal NMuLi cell colonies developed a network of anastomosing tubules with wide lumens. These morphological changes were not inhibitable by transforming growth factor-beta and were not induced by other hepatocellular growth factors including epidermal growth factor, transforming growth factor-alpha, acidic fibroblast growth factor and insulin. Histological sections of the hepatocyte growth factor-treated BNL CL.2 cell colonies resembled neocholangioles, believed to include facultative stem cells, which proliferate after submassive and massive hepatic necrosis. Sections of hepatocyte growth factor-treated NMuLi colonies resembled ductules proliferating in biliary tract obstruction from a wide variety of causes. This work represents the first examples of hepatocyte growth factor-induced mitogenesis, scattering and morphogenesis in the same cell lines. More important, our data suggest that hepatocyte growth factor mediates liver response to injury not only by acting on hepatocytes but also by exerting mitogenic and morphogenic influences on nonparenchymal epithelial cell components.
    Hepatology 07/1993; 17(6):1052-61. · 12.00 Impact Factor

Publication Stats

117 Citations
27.79 Total Impact Points

Institutions

  • 1994–1996
    • Northwestern University
      • Department of Pathology
      Evanston, IL, United States
  • 1993–1995
    • Rush Medical College
      Chicago, Illinois, United States