Soluble CD109 binds TGF-ß and antagonizes TGF-ß signalling and responses.

Transforming growth factor-ß (TGF-ß) is a multifunctional cytokine implicated in many diseases, including tissue fibrosis and cancer. TGF-ß mediates diverse biological responses by signalling through type I and II TGF-ß receptors (TßRI and TßRII). We have previously identified CD109, a glycosylphosphatidylinositol (GPI)-anchored protein, as a novel TGF-ß co-receptor that negatively regulates TGF-ß signalling and responses and demonstrated that membrane-anchored CD109 promotes TGF-ß receptor degradation via a SMAD7/Smurf2-mediated mechanism. To determine whether CD109 released from the cell surface (soluble CD109 or sCD109) also acts as a TGF-ß antagonist, we determined the efficacy of recombinant sCD109 to interact with TGF-ß and inhibit TGF-ß signalling and responses. Our results demonstrate that sCD109 binds TGF-ß with high affinity as determined by surface plasmon resonance (SPR) and cell-based radioligand binding and affinity labelling competition assays. SPR detected slow dissociation kinetics between sCD109 and TGF-ß at low concentrations, indicating a stable and effective interaction. In addition, sCD109 antagonizes TGF-ß-induced Smad2/3 phosphorylation, transcription and cell migration. Together, our results suggest that sCD109 can bind TGF-ß, inhibit TGF-ß binding to its receptors and decrease TGF-ß signalling and TGF-ß-induced cellular responses.

Atypical methylmalonic aciduria: frequency of mutations in the methylmalonyl CoA epimerase gene (MCEE).

Methylmalonic aciduria is known to result from defects in the enzyme methylmalonyl CoA mutase (MCM) (mut complementation group) and from defects in the synthesis of the MCM cofactor adenosylcobalamin (cblA, cblB, cblC, cblD, and cblF groups). Two patients who excrete methylmalonic acid have recently been shown to have a homozygous nonsense mutation in the gene coding for methylmalonyl CoA epimerase (MCEE). To further understand the cause of methylmalonic acid excretion, the MCEE gene was sequenced in 229 patients with elevations of methylmalonic acid excretion for which no cause was known. Mutations in MCEE were detected in five patients: two patients homozygous for c.139C>T, p.R47X, one patient homozygous for c.178A>C, p.K60Q, and two patients heterozygous for c.427C>T, p.R143C. Fusion of fibroblast lines from two patients homozygous for c.139C>T, p.R47X did not result in correction of [(14)C]propionate incorporation toward control values while the defect in these fibroblasts was complemented by mut, cblA, and cblB fibroblasts. Infection with wild-type MCEE cDNA resulted in correction of the biochemical phenotype in cells from both patients.