J. Lipid Res. Neurobiology of Lipids (ISSN1683-5506)
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Journal of Lipid Research, Vol. 42, 1858-1864, November 2001
Copyright © 2001 by Lipid Research, Inc.

Differential effect of combined lipase deficiency (cld/cld) on human hepatic lipase and lipoprotein lipase secretion

Jennifer C. Boedekera, Mark H. Doolittlec, and Ann L. Whitea,b
a Center for Human Nutrition, University of Texas Southwestern Medical Center, Dallas, TX
b Department of Internal Medicine, University of Texas Southwestern Medical Center, Dallas, TX
c Lipid Research Laboratory, West Los Angeles VA Medical Center, Los Angeles, CA

Correspondence to: Ann L. White, at the Department of Internal Medicine, UT Southwestern Medical Center, 5323 Harry Hines Blvd., Dallas, TX 75390-9046., Ann.White{at}UTSouthwestern.edu (E-mail)

Combined lipase deficiency (cld) is a recessively inherited disorder in mice associated with a deficiency of LPL and hepatic lipase (HL) activity. LPL is synthesized in cld tissues but is retained in the endoplasmic reticulum (ER), whereas mouse HL (mHL) is secreted but inactive. In this study we investigated the effect of cld on the secretion of human HL (hHL) protein mass and activity. Differentiated liver cell lines were derived from cld mice and their normal heterozygous (het) littermates by transformation of hepatocytes with SV40 large T antigen. After transient transfection with lipase expression constructs, secretion of hLPL activity from cld cells was only 12% of that from het cells. In contrast, the rate of secretion of hHL activity and protein mass per unit of expressed hHL mRNA was identical for the two cell lines. An intermediate effect was observed for mHL, with a 46% reduction in secretion of activity from cld cells. The ER glucosidase inhibitor, castanospermine, decreased secretion of both hLPL and hHL from het cells by ~70%, but by only ~45% from cld cells. This is consistent with data suggesting that cld may result from a reduced concentration of the ER chaperone calnexin.

In conclusion, our results demonstrate a differential effect of cld on hLPL, mHL, and hHL secretion, suggesting differential requirements for activation and exit of the enzymes from the ER. — Boedeker, J. C., M. H. Doolittle, and A. L. White. Differential effect of combined lipase deficiency (cld/cld) on human hepatic lipase and lipoprotein lipase secretion. J. Lipid Res. 2001. 42: 1858–1864.

Supplementary key words: calnexin, castanospermine, endoplasmic reticulum, fetal hepatocytes, glucosidase enzymes


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