Determinants of human apolipoprotein [a] secretion from mouse hepatocyte cultures.
Efforts to develop an in vitro model system to analyze apolipoprotein [a] (apo[a]) gene transcription, mRNA translation, and protein secretion have been complicated by the limited tissue and species distribution of apo[a] and the presence of regulatory DNA sequences remote from the apo[a] transcription start site. In the current study we examined primary hepatocytes cultured from apo[a] transgenic mice as a model system for analyzing apo[a] biogenesis. Hepatocytes from mice transgenic for a yeast artificial chromosome (YAC) encoding the entire apo[a] gene in its own genomic context (YAC-apo[a] hepatocytes) were unable to maintain apo[a] expression beyond 48 h of culture. This suggests that the apo[a] promoter was not active in cultured YAC-apo[a] hepatocytes. In contrast, apo[a] expression was maintained for at least 7 days in hepatocytes cultured from mice transgenic for an apo[a] cDNA under control of the mouse transferrin promoter (transferrin-apo[a] hepatocytes). Pulse-chase experiments established that more than 80% of apo[a] synthesized by both transferrin-apo[a] and YAC-apo[a] hepatocytes was degraded prior to secretion, independently of the coexpression of human apoB.Thus, low secretion efficiency appears to be a general characteristic of human apo[a] proteins in mouse liver. Apo[a] secretion was increased somewhat (from 18% to 32%) in the presence of lipoprotein-containing serum. Transformed cell lines derived from transferrin apo[a] hepatocytes retained characteristics of apo[a] secretion similar to those observed in primary cells. Primary and transformed apo[a] transgenic hepatocytes may provide valuable additional models with which to study posttranslational mechanisms regulating apo[a] secretion. - Wang, J., J. Boedeker, H. H. Hobbs, and A. L. White. Determinants of human apolipoprotein [a] secretion from mouse hepatocyte cultures. J. Lipid Res. 2001. 42: 60;-69.
Wang
J
J
Center for Human Nutrition, University of Texas Southwestern Medical Center at Dallas, Dallas, TX, USA.
Boedeker
J
J
Hobbs
H H
HH
White
A L
AL
D000818:Animals; D001053:Apolipoproteins / Q000187:drug effects / Q000235:genetics / Q000378:metabolism*; D001055:Apolipoproteins B / Q000235:genetics / Q000494:pharmacology; D053241:Apoprotein(a); D015152:Blotting, Northern; D002472:Cell Transformation, Viral; D002478:Cells, Cultured; D005786:Gene Expression Regulation; D022781:Hepatocytes / Q000166:cytology / Q000378:metabolism*; D006801:Humans; D015151:Immunoblotting; D017270:Lipoprotein(a) / Q000187:drug effects / Q000235:genetics / Q000378:metabolism*; D051379:Mice; D008822:Mice, Transgenic; D012333:RNA, Messenger / Q000378:metabolism
D001053:Apolipoproteins; D001055:Apolipoproteins B; D017270:Lipoprotein(a); D012333:RNA, Messenger; D053241:Apoprotein(a)