Upregulated BMP-Smad signaling activity in the glucuronyl C5-epimerase knock out MEF cells

• Glucuronyl C5-epimerase (Hsepi) catalyzes the conversion of glucuronic acid to iduronic acid in the process of heparan sulfate biosynthesis. Targeted interruption of the gene, Glce,in mice resulted in neonatal lethality with varied defects in organ development. To understand the molecular mechanisms of the phenotypes, we used mouse embryonic fibroblasts (MEF) as a model to examine selected signaling pathways. Our earlier studies found reduced activities of FGF-2, GDNF, but increased activity of sonic hedgehog in the mutant cells. In this study, we focused on the bone morphogenetic protein (BMP) signaling pathway. Western blotting detected substantially elevated endogenous Smad1/5/8 phosphorylation in the Hsepi mutant (KO) MEF cells, which is reverted by re-expression of the enzyme in the KO cells. The mutant cells displayed an enhanced proliferation and elevated alkaline phosphatase activity, marking higher differentiation, when cultured in osteogenic medium. The high level of Smad1/5/8 phosphorylation was also found in primary calvarial cells isolated from the KO mice. Analysis of the genes involved in the BMP signaling pathway revealed upregulation of a number of BMP ligands, but reduced expression of several Smads and BMP antagonist (Grem1) in the KO MEF cells. The results suggest that Hsepi expression modulates BMP signaling activity, which, at least partially, is associated with defected molecular structure of heparan sulfate expressed in the cells.   

Ämnesord

MEDICIN OCH HÄLSOVETENSKAP  -- Medicinska och farmaceutiska grundvetenskaper -- Cell- och molekylärbiologi (hsv//swe)

MEDICAL AND HEALTH SCIENCES  -- Basic Medicine -- Cell and Molecular Biology (hsv//eng)

MEDICIN OCH HÄLSOVETENSKAP  -- Medicinsk bioteknologi -- Medicinsk bioteknologi (hsv//swe)

MEDICAL AND HEALTH SCIENCES  -- Medical Biotechnology -- Medical Biotechnology (hsv//eng)

Nyckelord

BMP signaling

Heparan sulfate

MEF cells

Smad

Glucuronyl C5-epimerase

Bone Morphogenetic Protein

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