RS1 (RSC1A1) regulates the exocytotic pathway of Na⁺-d-glucose cotransporter SGLT1

Abstract

The product of gene RSC1A1, named RS1, participates in transcriptional and posttranscriptional regulation of the sodium-d-glucose cotransporter SGLT1. Using coexpression in oocytes of Xenopus laevis, posttranscriptional inhibition of human SGLT1 (hSGLT1) and some other transporters by human RS1 (hRS1) was demonstrated previously. In the present study, histidine-tagged hRS1 was expressed in oocytes or Sf9 cells and purified using nickel(II)-charged nitrilotriacetic acid-agarose. hRS1 protein was injected into oocytes expressing hSGLT1 or the human organic cation transporter hOCT2, and the effect on hSGLT1-mediated uptake of methyl-alpha-D-[14C]glucopyranoside ([14C]AMG) or hOCT2-mediated uptake of [14C]tetraethylammonium ([14C]TEA) was measured. Within 30 min after the injection of hRS1 protein, hSGLT1-expressed AMG uptake or hOCT2-expressed TEA uptake was inhibited by approximately 50%. Inhibition of AMG uptake was decreased when a dominant negative mutant of dynamin I was coexpressed and increased after stimulation of PKC. Inhibition remained unaltered when endocytosis was inhibited by chlorpromazine, imipramine, or filipin but was prevented when exocytosis was inhibited by botulinum toxin B or when the release of vesicles from the TGN and endosomes was inhibited by brefeldin A. Inhibition of hSGLT1-mediated AMG uptake and hOCT2-mediated TEA uptake by hRS1 protein were decreased at an enhanced intracellular AMG concentration. The data suggest that hRS1 protein exhibits glucose-dependent, short-term inhibition of hSGLT1 and hOCT2 by inhibiting the release of vesicles from the trans-Golgi network.

Tripeptides of RS1 (RSC1A1) Inhibit a Monosaccharide-dependent Exocytotic Pathway of Na+-d-Glucose Cotransporter SGLT1 with High Affinity

“…The observed changes in distribution correlated with functional data showing that RS1 down-regulates the transcrip-* This work was supported by Deutsche Forschungsgemeinschaft Grant SFB tion of SGLT1 in subconfluent LLC-PK 1 cells (25). In Xenopus oocytes, expression of SGLT1 was inhibited when human RS1 was coexpressed (23,24,27) or when purified RS1 protein was injected into SGLT1 expressing oocytes shortly before uptake measurements (21). This indicated that hSGLT1 was inhibited by hRS1 on the posttranscriptional level.…”

“…Cyclic AMP, protein kinase A, protein kinase C (PKC), 3 and phosphoinositol 3-kinase are involved in the regulatory pathways (13,14,16). It has been shown that SGLT1 can be regulated by changes in transcription (12,17,18), mRNA stability (19), intracellular trafficking (14,16,20,21), and transporter activity (22). However, the individual regulatory pathways, their cross-talk, and their physiological importance are not understood.…”

“…Previously, we identified the intracellular protein RS1 (human gene RSC1A1) that participates in the transcriptional and post-transcriptional regulation of SGLT1 (21,(23)(24)(25)(26)(27)(28). RSC1A1 is an intronless single copy gene that was only detected in mammals and codes for 67-68-kDa proteins in human, pig, rabbit, and mouse that exhibit about 70% amino acid identity.…”

Altered NMDA Receptor Trafficking in a Yeast Artificial Chromosome Transgenic Mouse Model of Huntington's Disease

“…Thus, acute recovery of NMDAR current after MK-801 block may reflect mainly recycling NMDARs, whereas accumulation of surface NMDARs in YAC72 MSNs over the 6 h chlorpromazine treatment likely represents newly synthesized receptors mobilized from the Golgi. The latter process is not expected to be affected by chlorpromazine (Wang et al, 1993;Veyhl et al, 2006), yet new receptor insertion was not observed in wt MSNs and was only modest in YAC72 MSNs over a 6 h period. Chlorpromazine may have additional effects on receptor forward trafficking or else homeostatic changes in receptor exocytosis may be induced in response to blockade of endocytosis, as shown previously for AMPARs over a timescale of minutes (Lledo et al, 1998;Man et al, 2000;Wang and Linden, 2000) (for review, see Groc and Choquet, 2006).…”

Risks and Benefits of Sweet Pee

“…1,6 Because SGLT1 and SGLT2 are regulated by several kinases [7][8][9][10][11][12][13] and the protein RS1, 14,15 glucosuria could, at least in theory, also result from deranged function of those signaling molecules. Moreover, Na ϩ -coupled glucose transport is affected by dietary Na ϩ , 16 hyperglycemia, 16 intracellular Na ϩ activity, 17 transplantation, 18 and exposure to cadmium.…”