Estrogen dependence of synthesis and secretion of apolipoprotein B-containing lipoproteins in the chicken hepatoma cell line, LMH-2A

Abstract

The chicken hepatoma cell line LMH-2A, which permanently overexpresses the chicken estrogen receptor, was used to study the synthesis and secretion of lipoproteins in response to treatment with estrogen. In the absence of the hormone, only small amounts of apolipoprotein B (apoB) and no apolipoprotein VLDL II (apoII) were found in cell extracts. After treatment of cells with moxestrol, a stable estrogen derivative, for 24 to 48 h, a dramatic increase in the quantities of these lipoproteins was observed both in cell extracts and in the medium. As determined by pulse-chase experiments, both proteins also showed enhanced rates of synthesis after estrogen induction, and secretion of the newly synthesized proteins was essentially complete by 6 h. The secreted apoB-containing lipoprotein particles have a density corresponding to that of very low density lipoprotein (VLDL). Furthermore, in estrogen-stimulated cells, the secreted particles also contain apoII, as shown by co-immunoprecipitation of apoII, and apoB. It appears that vitellogenin, the product of another estrogen-regulated gene in egg-laying species, is not synthesized by LMH-2A cells. Taken together, the data suggest that LMH-2A cells provide a new and promising cell system to investigate lipoprotein synthesis, assembly, and secretion in an estrogen-dependent manner.