Biological effects of human insulin receptor substrate-1 overexpression in hepatocytes.
The human insulin receptor substrate-1 (hIRS-1) is a key intracellular protein involved in various cytokine signaling pathways associated with cell growth. We have previously demonstrated that stable transfection and overexpression of hIRS-1 in human hepatoblastoma cells in vitro leads to the constitutive activation of the mitogen-activated protein kinase (MAPK) cascade. In this setting, hIRS-1 acts as a dominant oncogene and will induce neoplastic transformation of NIH 3T3 cells. In the present study, the biologic effects of hIRS-1 overexpression in the liver was analyzed using both clinical tumor samples and a newly developed transgenic mouse model. We have found that approximately 40% of 22 human hepatocellular carcinoma (HCC) tumors had enhanced (>200%) hIRS-1 gene expression compared with adjacent non-involved liver tissue. There was a significant relationship between the level of hIRS-1 overexpression and the tumor size; this finding suggests a possible role for hIRS-1 in tumor progression. To determine if downstream signal transduction cascades were activated by overexpression of hIRS-1 in hepatocytes, we established a transgenic mouse model using an hIRS-1 construct driven by an albumin promoter/enhancer element to direct liver specific expression. The overexpressed hIRS-1 protein was found to be tyrosyl phosphorylated and interacted with downstream SH2-containing molecules such as the p85 subunit of phosphatidylinositol-3 kinase (PI3K), Grb2 adaptor, and SHP2 phosphatase proteins. The functional consequences of hIRS-1 overexpression were reflected by constitutive activation of both the MAPK and PI3K signal transduction cascades. More important, overexpression of hIRS-1 in the transgenic liver led to increased hepatocyte DNA synthesis. Our findings indicate that hIRS-1 overexpression induces downstream signaling molecules associated with hepatocyte growth and may potentially enhance tumor progression of HCC.
Tanaka
S
S
Molecular Hepatology, Massachusetts General Hospital Cancer Center and Harvard Medical School, Charlestown 02129, USA.
Mohr
L
L
Schmidt
E V
EV
Sugimachi
K
K
Wands
J R
JR
D016475:3T3 Cells; D000818:Animals; D017871:Calcium-Calmodulin-Dependent Protein Kinases / Q000378:metabolism*; D006528:Carcinoma, Hepatocellular / Q000378:metabolism*; D006801:Humans; D055504:Insulin Receptor Substrate Proteins; D007668:Kidney / Q000378:metabolism; D008099:Liver / Q000378:metabolism*; D008113:Liver Neoplasms / Q000378:metabolism*; D008168:Lung / Q000378:metabolism; D051379:Mice; D008822:Mice, Transgenic; D018482:Muscle, Skeletal / Q000378:metabolism; D009206:Myocardium / Q000378:metabolism; D019869:Phosphatidylinositol 3-Kinases; D010750:Phosphoproteins / Q000096:biosynthesis / Q000235:genetics / Q000502:physiology*; D017853:Phosphotransferases (Alcohol Group Acceptor) / Q000378:metabolism*; D016133:Polymerase Chain Reaction; D011994:Recombinant Proteins / Q000096:biosynthesis; D013154:Spleen / Q000378:metabolism
C526292:IRS1 protein, human; D055504:Insulin Receptor Substrate Proteins; C526295:Irs1 protein, mouse; D010750:Phosphoproteins; D011994:Recombinant Proteins; D019869:Phosphatidylinositol 3-Kinases; D017853:Phosphotransferases (Alcohol Group Acceptor); D017871:Calcium-Calmodulin-Dependent Protein Kinases