Fucosylation is a type of glycosylation, a form of post-transcriptional regulation of
proteins, involved in
cancer and
inflammation. It involves the attachment of a
fucose residue to N-
glycans, O-
glycans, and
glycolipids, which is catalyzed by a family of
enzymes called
fucosyltransferases (Futs). Among the many Futs, α-1,6-fucosyltransferase (Fut8) is the only
enzyme that produces α-1,6-fucosylated
oligosaccharides (core
fucose). In the human liver, the expression and activity of Fut8 are frequently elevated during progression of chronic
liver diseases.
Proprotein convertase subtilisin/kexin type 9 (PCSK9) is a well-known negative regulator of the
low-density lipoprotein receptor (LDLR). Here, we found that loss of core
fucose in immortalized hepatocytes led to LDLR downregulation through a dramatic induction of PCSK9. We used the immortalized hepatocytes derived from Fut8 knockout mice or a Fut8 knockdown AML12 hepatocyte cell line. Using these cells, we investigated the effects of Fut8 on hepatocyte
cholesterol influx. Both cell lines had reduced LDLR
protein levels, resulting from marked increases in PCSK9 expression. Intracellular
cholesterol levels were significantly lower and
LDL cholesterol uptake was suppressed in Fut8-KO cells.
Hepatocyte nuclear factor 1α accumulated in nuclei of Fut8-KO hepatocytes, which mediated increases in PCSK9
mRNA expression. Our findings demonstrated that loss of core fucosylation promoted degradation of LDLR and impaired
cholesterol uptake, which is a novel mechanism that regulates
cholesterol influx, suggesting that Fut8 might be a novel causative gene for
familial hypercholesterolemia.