Early induction of LDL receptor gene during rat liver regeneration

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Abstract
After partial hepatectomy in the rat, there is substantial lipid accumulation in the liver. No information is available on the possible role of receptor‐mediated endocytosis in this process. Since the low density lipoprotein (LDL) receptor is stimulated as a part of an early growth response in cell culture (Ellsworth et al.: Biochem. J. 279:175–187, 1991), the metabolism of this receptor during liver regeneration was studied. The mRNA and membrane protein level of the receptor were measured in the liver and in the adrenal glands at different times after partial hepatectomy, corresponding to different phases of the cell cycle. A discontinuous pattern of receptor expression is detectable in the regenerating liver; a large increase of mRNA and membrane protein occurs at an early time (2–4 h), suggesting that there is induction of LDL receptor gene transcription shortly after partial hepatectomy. This response seems specific for the liver following injury since the adrenal receptor does not show a different pattern in partially hepatectomized rats and sham‐operated controls. After returning to control levels, the LDL receptor again increases slightly above control at 24 h, a time when cell replication begins.