Characterization of the Cancer-Associated Meprin Beta eta Variants G45R and G89R

Meprin beta is a metalloprotease associated with neurodegeneration, inflammation, extracellular matrix homeostasis, transendothelial cell migration, and cancer. In this study, we investigated two melanoma-associated variants of meprin beta, both exhibiting a single amino acid exchange, namely, meprin beta G45R and G89R. Based on the structural data of meprin beta and with regard to the position of the amino acid exchanges, we hypothesized an increase in proteolytic activity in the case of the G45R variant due to the induction of a potential new activation site and a decrease in proteolytic activity from the G89R variant due to structural instability. Indeed, the G89R variant showed, overall, a reduced expression level compared to wild-type meprin beta, accompanied by decreased activity and lower cell surface expression but strong accumulation in the endoplasmic reticulum. This was further supported by the analysis of the shedding of the interleukin-6 receptor (IL-6R) by meprin beta and its variants. In transfected HEK cells, the G89R variant was found to generate less soluble IL-6R, whereas the expression of meprin beta G45R resulted in increased shedding of the IL-6R compared to wild-type meprin beta and the G89R variant. A similar tendency of the induced shedding capacity of G45R was seen for the well-described meprin beta substrate CD99. Furthermore, employing an assay for cell migration in a collagen IV matrix, we observed that the transfection of wild-type meprin beta and the G45R variant resulted in increased migration of HeLa cells, while the G89R variant led to diminished mobility.