Interactions between carboxypeptidase M and kinin B1 receptor in endothelial cells

Introduction Carboxypeptidase M (CPM) is a glycosylphosphatidylinositol anchored enzyme that plays an important role in the kallikrein–kinin system (KKS). CPM catalytic domain hydrolyzes Arg from C-terminal peptides (i.e., bradykinin and kallidin), generating des-Arg-kinins, the agonists of B 1 receptor (B 1 R). It is known that CPM and kinin B 1 R are co-localized in the plasma membrane microdomains, where they interact with each other, facilitating receptor signaling. Aims We hypothesized here that this CPM-B 1 R interaction could also affect the activity of the enzyme. Methods Thus, in this work, we evaluated the impact of B 1 R presence or absence on CPM activity and expression, using primary culture of microvascular endothelial cells from wild-type, kinin B 1 R knockout mice (B 1 −/− ), and transgenic rats overexpressing B 1 receptor exclusively in the endothelium. In addition, HEK293T cells, as wells as B 1 −/− primary culture of endothelial cells, both transfected with B 1 R, were also used. Results CPM expression and activity were downregulated in cells of knockout mice compared to control and this reduction was rescued after B 1 R transfection. Cells overexpressing B 1 R presented higher levels of CPM mRNA, protein, and activity. This profile was reverted by pre-incubation with the B 1 R antagonist, R715, in highly expressing receptor cells. Conclusions Our data show that kinin B 1 R positively modulates both CPM expression and activity, suggesting that CPM-B 1 R interaction in membrane microdomains might affect enzyme activity, beyond interfering in receptors signaling. This work highlights the interactions among different components of KKS and contributes to a better understanding of its patho-physiological role.