SLC35B4, an Inhibitor of Gluconeogenesis, Responds to Glucose Stimulation and Downregulates Hsp60 among Other Proteins in HepG2 Liver Cell Lines

Abstract

SLC35B4, solute receptor for UDP-N-acetylglucosamine and UDP-xylose, is associated with diabetes and predisposing conditions. This study investigated the localization of SLC35B4 and compared the differential expression between a knockdown of SLC35B4 and controls in HepG2. Responsiveness to glucose, expression, and localization were assayed using Western blot and immunostaining. Localization was confirmed using a proximity ligation assay. Two-dimensional (2D) gel electrophoresis and MALDI-TOF were used to identify differentially expressed proteins and pathway analysis was performed. SLC35B4 was increased by 60% upon glucose stimulation and localized in Golgi apparatus and endoplasmic reticulum. Presence of SLC35B4 in the Golgi apparatus suggests its involvement in the biosynthesis of glycoconjugate proteins. Four proteins were markedly under-expressed (Hsp60, HspA8, TUBA1A, and ENO1) and linked to the pathogenesis of diabetes or post-translationally modified by O-GlcNAc. Glucose levels activate SLC35B4 expression. This triggers a downstream effect via Hsp60 and other proteins. We hypothesize that the downstream effect on the proteins is mediated via altering the glycosylation pattern inside liver cells. The downstream cascade ultimately alters the ability of cultured liver cells to inhibit endogenous glucose production, and this could play a role in the association of the above-listed genes with the pathogenesis of diabetes.

Structural basis for the delivery of activated sialic acid into Golgi for sialyation

“…CSTs belongs to the Solute Carrier SLC35 family of Nucleotide Sugar Transporters (NST), which in humans translocate seven other essential sugars into the ER and/or Golgi for glycosylation in the form of GDP-fucose, UDPgalactose, UDP-glucose, UDP-xylose, UPD-GlcNAc, UDP-GalNAc and UDP-GlcA 8,10 . SLC35 activities are important to human physiology and have been associated with diseases such as obesity 11,12 . SLC35 members can influence the efficacy of anti-cancer drugs 13 , and also transport UDP-glucuronic acid into the liver ER for glucuronidation 14 , which is an essential process for the metabolism of many drugs, e.g., analgesics, nonsteroidal anti-inflammatory agents, antipsychotics, antivirals, and benzodiazepines 15 .…”

Structural basis for the delivery of activated sialic acid into Golgi for sialyation

“…activities are important to human physiology and have been associated with diseases such as obesity 11,12 . SLC35 members can influence the efficacy of anti-cancer drugs 13 , and also transport UDP-glucuronic acid into the liver ER for glucuronidation 14 , which is an essential process for the metabolism of many drugs, e.g., analgesics, nonsteroidal anti-inflammatory agents, antipsychotics, antivirals, and benzodiazepines 15 .…”