Calcitriol mediates the activity of SGLT1 through an extranuclear initiated mechanism that involves intracellular signaling pathways
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The present study explored whether calcitriol plays a role in the regulation of sodium-dependent glucose transporter protein 1 (SGLT1) activity. For this purpose, alpha-methyl glucoside (AMG) uptake in stable transfected Chinese hamster ovary (CHO-G6D3) cells expressing rabbit SGLT1 (rbSGLT1) was used. The involvement of second messengers, intracellular signaling pathways, and pro-inflammatory cytokines were examined using specific inhibitors before incubation with calcitriol for 15 min. The present study demonstrated the involvement of second messengers produced by phospholipase A2, phospholipase C, calmodulin, diacylglycerol kinase, and phosphoinositide 3 kinase on calcitriol-regulated AMG uptake. Pretreatment with inhibitors of the mitogen-activated protein kinase (MAPK) signaling pathway increased calcitriol-induced AMG uptake. In contrast, inhibition of the phosphoinositide 3-kinase PI3K/Akt/mTOR signaling pathway decreased the effect of calcitriol on AMG uptake. These findings suggest that calcitriol regulates rbSGLT1 activity through a rapid, extranuclear initiated mechanism of action stimulated by MAPK and inhibited by PI3K/Akt/mTOR. Another important finding was the effect of pro-inflammatory cytokines on calcitriol-induced AMG uptake. Interleukin-6 increased while tumor necrosis factor-α decreased calcitriol-induced AMG uptake. In conclusion, the present study demonstrates the involvement of calcitriol in the regulation of rbSGLT1 activity. This is due to the activation of intracellular signaling pathways triggered by second messenger molecules and cytokines after a short time (15 min) exposure to calcitriol.
KeywordsAMG uptake Calcitriol SGLT Non-genomic effect Second messengers Intracellular signaling
Arachidonyl trifluoromethyl ketone
Protein kinase B
Mitogen-activated protein kinase
Mammalian target of rapamycin
We acknowledge the financial support of the International Max Planck Research School in Chemical Biology, Dortmund, Germany.
- 9.Castaneda F (2009) Protein biosynthesis: a new method for functional expression of sodium-dependent glucose transporter (SGLT) to study inhibition of transport activity and drug discovery. In: Esterhouse TE, Petrinos LB (eds) Protein biosynthesis. Nova Science Publishers, New York, pp 267–284Google Scholar
- 17.Fernandez-Real JM, Vendrell J, Ricart W, Broch M, Gutierrez C, Casamitjana R, Oriola J, Richart C (2000) Polymorphism of the tumor necrosis factor-alpha receptor 2 gene is associated with obesity, leptin levels, and insulin resistance in young subjects and diet-treated type 2 diabetic patients. Diabetes Care 23:831–7CrossRefPubMedGoogle Scholar
- 28.Kimmich GA, Randles J (1981) alpha-Methylglucoside satisfies only Na+-dependent transport system of intestinal epithelium. Am J Physiol Cellular Physiol 241:C227–232Google Scholar
- 45.Schwartz Z, Ehland H, Sylvia VL, Larsson D, Hardin RR, Bingham V, Lopez D, Dean DD, Boyan BD (2002) 1alpha, 25-dihydroxyvitamin D(3) and 24R, 25-dihydroxyvitamin D(3) modulate growth plate chondrocyte physiology via protein kinase C-dependent phosphorylation of extracellular signal-regulated kinase 1/2 mitogen-activated protein kinase. Endocrinol 143:2775–2786CrossRefGoogle Scholar
- 47.Schwartz Z, Sylvia VL, Luna MH, Deveau P, Whetstone R, Dean DD, Boyan BD (2001) The effect of 24R, 25-(OH)(2)D(3) on protein kinase C activity in chondrocytes is mediated by phospholipase D whereas the effect of 1alpha, 25-(OH)(2)D(3) is mediated by phospholipase C. Steroids 66:683–694CrossRefPubMedGoogle Scholar
- 57.Vozarova B, Fernandez-Real JM, Knowler WC, Gallart L, Hanson RL, Gruber JD, Ricart W, Vendrell J, Richart C, Tataranni PA, Wolford JK (2003) The interleukin-6 (-174) G/C promoter polymorphism is associated with type-2 diabetes mellitus in Native Americans and Caucasians. Hum Genet 112:409–413PubMedGoogle Scholar