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Regulation of the ovine intestinal Na+/glucose co-transporter (SGLT1) is dissociated from mRNA abundance.

ABSTRACT: We have investigated the mechanisms of regulation of the Na+/glucose co-transporter (SGLT1) in a ruminant animal, which is an exceptional model system for studying intestinal glucose transport. Pre-ruminant lambs absorb glucose, produced by hydrolysis of the milk sugar lactose, in the intestine via apical SGLT1 and basolateral facilitative glucose transporters (GLUT2). Weaning coincides with the development of the rumen, and consequently the amount of hexoses reaching the small intestine of the ruminant sheep is undetectable. During development, SGLT1 activity and abundance in intestinal brush-border membranes decreased by over 200-fold, and either maintaining lambs on a milk replacer diet or infusing sheep intestine with D-glucose restored co-transporter activity and expression. We have measured ovine intestinal SGLT1 mRNA levels during development, with changes in diet and after direct infusion of D-glucose or methyl alpha-D-glucopyranoside into the intestinal lumen, in order to determine the level of regulation. During development, mRNA levels decreased only 4-fold. Lambs maintained on a milk replacer diet showed no change in mRNA levels relative to age-matched controls. Finally, upon infusion of the intestine of the ruminant sheep with sugars, D-glucose infusion increased SGLT1 mRNA, but only by 2-fold, compared with a 60-90-fold increase in co-transporter number and activity. Since the change in Na(+)-dependent glucose transport activity is correlated with SGLT1 protein abundance, and since changes in mRNA levels do not account for the dramatic changes in protein abundance, we conclude that the principal level of SGLT1 regulation by luminal sugar is translational or post-translational.

SUBMITTER: Lescale-Matys L

PROVIDER: S-EPMC1132544 | biostudies-other | 1993 Apr

REPOSITORIES: biostudies-other

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Project description:LEFTY2 (endometrial bleeding associated factor; EBAF or LEFTYA), a cytokine released shortly before menstrual bleeding, is a negative regulator of cell proliferation and tumour growth. LEFTY2 down-regulates Na+/H+ exchanger activity with subsequent inhibition of glycolytic flux and lactate production in endometrial cancer cells. Glucose can be utilized not only for glycolysis but also for glycogen formation. Both glycolysis and glycogen formation require cellular glucose uptake which could be accomplished by the Na+ coupled glucose transporter-1 (SGLT1; SLC5A1). The present study therefore explored whether LEFTY2 modifies endometrial SGLT1 expression and activity as well as glycogen formation. Ishikawa and HEC1a cells were exposed to LEFTY2, SGLT1 and glycogen synthase (GYS1) transcript levels determined by qRT-PCR. SGLT1, GYS1 and phospho-GYS1 protein abundance was quantified by western blotting, cellular glucose uptake from 2-(N-(7-Nitrobenz-2-oxa-1,3-diazol-4-yl)Amino)-2-Deoxyglucose (2-NBDG) uptake, and cellular glycogen content utilizing an enzymatic assay and subsequent colorimetry. As a result, a 48-hour treatment with LEFTY2 significantly increased SGLT1 and GYS1 transcript levels as well as SGLT1 and GYS1 protein abundance in both Ishikawa and HEC1a cells. 2-NBDG uptake and cellular glycogen content were upregulated significantly in Ishikawa (type 1) but not in type 2 endometrial HEC1a cells, although there was a tendency of increased 2-NBDG uptake. Further, none of the effects were seen in human benign endometrial cells (HESCs). Interestingly, in both Ishikawa and HEC1a cells, a co-treatment with TGF-? reduced SGLT1, GYS and phospho-GYS protein levels, and thus reduced glycogen levels and again HEC1a cells had no significant change. In conclusion, LEFTY2 up-regulates expression and activity of the Na+ coupled glucose transporter SGLT1 and glycogen synthase GYS1 in a cell line specific manner. We further show the treatment with LEFTY2 fosters cellular glucose uptake and glycogen formation and TGF-? can negate this effect in endometrial cancer cells.

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Regulation of the ovine intestinal Na+/glucose co-transporter (SGLT1) is dissociated from mRNA abundance.

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