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Originally published In Press as doi:10.1074/jbc.M108027200 on October 26, 2001
J. Biol. Chem., Vol. 277, Issue 3, 1816-1823, January 18, 2002
Monoacylglycerol Metabolism in Human Intestinal Caco-2 Cells
EVIDENCE FOR METABOLIC COMPARTMENTATION AND
HYDROLYSIS*
Shiu-Ying
Ho §,
Lissette
Delgado , and
Judith
Storch ¶
From the Department of Nutritional Sciences, Rutgers
University, New Brunswick, New Jersey 08901-8525
Free fatty acids (FFA) and
sn-2-monoacylglycerol (MG), the two major hydrolysis
products of dietary triacylglycerol (TG), are absorbed from the lumen
into polarized enterocytes that line the small intestine. Intensive
studies regarding FFA metabolism in the intestine have been published;
however, little is known regarding the metabolism of MG. In these
studies, we examined the metabolism of sn-2-monoolein
(sn-2-18:1) by human intestinal Caco-2 cells. To mimic the
physiological presentation of MG to the enterocyte, the metabolism of
[3H]sn-2-monoolein was examined by adding
taurocholate-mixed sn-2-18:1 and albumin-bound
sn-2-18:1 at the apical (AP) and basolateral (BL) surfaces
of the Caco-2 cell, respectively. The results demonstrate that more
sn-2-18:1 was incorporated into TG from AP
taurocholate-mixed sn-2-18:1, whereas more phospholipid
was synthesized from BL albumin-bound sn-2-18:1. The
TG:phospholipid ratio was ~5-fold higher for AP relative to BL MG
incubation. Qualitatively similar results were observed for bovine
serum albumin-bound MG added at the apical surface. It was also found
that substantial sn-2-18:1 radioactivity was recovered in
the FFA fraction, suggesting that sn-2-18:1 may be
directly hydrolyzed within the Caco-2. We therefore used reverse transcription-PCR with primers designed from the murine MG lipase (MGL)
gene, and detected the presence of MG lipase mRNA in Caco-2. The
human MGL gene was cloned and found to be 83% identical to the murine
MGL, and identical to a previously described lysophospholipase-like protein. Northern blot analysis showed the expression of MGL throughout Caco-2 differentiation. Thus, MG metabolism in Caco-2 cells may include
not only well established anabolic processes, but also catabolic
processes. Further, the observed polarity of MG metabolism suggests that, as for fatty acids, separate precursor and/or product pools of lipid may exist in the intestinal enterocyte.
*
This work was supported by Grant DK38389 from the National
Institutes of Health (to J. S.) and by state funds.The costs of publication of this
article were defrayed in part by the
payment of page charges. The article
must therefore be hereby marked
"advertisement" in
accordance with 18 U.S.C. Section
1734 solely to indicate this fact.
§
Current address: Dept. of Microbiology and Immunology, Kimmel
Cancer Center, Thomas Jefferson University, Philadelphia, PA 19107.
¶
To whom correspondence should be addressed: Dept. of
Nutritional Sciences, Rutgers University, 96 Lipman Dr., New Brunswick, NJ 08901-8525. Fax: 732-932-6837; E-mail:
storch@aesop.rutgers.edu.
Copyright © 2002 by The American Society for Biochemistry and Molecular Biology, Inc.

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Copyright © 2002 by the American Society for Biochemistry and Molecular Biology.
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