Selective Expression of Hepatocellular Membrane Proteins in Mice Homozygous for a Lethal Chromosomal Deletion

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Abstract
Previous studies of mice homozygous for one of several overlapping radiation-induced deletions in chromosome 7 revealed reduced expression of a number of hepatocyte proteins. These proteins include the plasma membrane receptors for insulin, epidermal growth factor, and glucagon, all of which are reduced in number by over 70% with no change in apparent affinity constants. It is not known whether all or only select liver cell surface proteins are so affected in newborn deletion homozygotes. In the present study, we investigated expression of two additional, functionally distinct intrinsic hepatocellular membrane binding proteins: the hepatic binding protein (HBP; the receptor for asialoglycoproteins), and the organic anion binding protein (OABP) which may play a role in organic anion transport. Immunoblot analysis showed the content of OABP and HBP in neonatal mutants to be identical to that in controls. As compared to adults, neonates showed levels of only about 8% of HBP and 75% of OABP binding proteins. Assays of HBP binding activities confirmed these results. The normal levels of these hepatocyte binding proteins in the deletion homozygotes suggest that the DNA sequences deleted in these mutants do not regulate all genes encoding sugh proteins but only a selected number of them.