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Suppression of the Protein Tyrosine Phosphatase LAR Reduces Apolipoprotein B Secretion by McA-RH7777 Rat Hepatoma Cells

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Abstract

Apolipoprotein B (apo B) secretion is reduced by insulin in rat hepatocytes. To evaluate possible mechanisms by which insulin action leads to inhibition of apo B secretion, we evaluated the effect of suppression of the protein-tyrosine phosphatase LAR on apo B secretion by McA-RH7777 (McA) rat hepatoma cells. A reduction in cellular LAR levels was accomplished by stable transfection of McA cells with LAR antisense cDNA. Previous studies indicate that LAR-antisense transfectants demonstrate increased insulin receptor signaling. In current studies, reduced LAR expression results in a 60% to 70% reduction in apo B secretion compared with null vector control. The reduction in apo B secretion correlated with a significant decrease in cellular apo B mRNA levels. Results suggests there is a relationship of protein tyrosine phosphorylation with regulation of apo B mRNA abundance in McA cells.

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Abbreviations used: Apo B, apolipoprotein BMcA, McA-RH7777; VLDL, very low density lipoprotein; BSA, bovine serum albumin; DMEM, Dulbecco's modified Eagle's medium; PTPase, protein tyrosine phosphatase; LAR, leukocyte common antigen-related; IRS-1 and IRS-2, insulin receptor substrates 1 and 2; GAPDH, glyceraldehyde 3-phosphate dehydrogenase; PI 3-K, phosphoinositide 3-kinase; MAPK, mitogen-activated protein kinase;

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