Interactions between carboxypeptidase M and kinin B1 receptor in endothelial cells

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 B₁ receptor (B₁R). It is known that CPM and kinin B₁R are co-localized in the plasma membrane microdomains, where they interact with each other, facilitating receptor signaling.

We hypothesized here that this CPM-B₁R interaction could also affect the activity of the enzyme.

Thus, in this work, we evaluated the impact of B₁R presence or absence on CPM activity and expression, using primary culture of microvascular endothelial cells from wild-type, kinin B₁R knockout mice (B ₁ ^-/- ), and transgenic rats overexpressing B₁ receptor exclusively in the endothelium. In addition, HEK293T cells, as wells as B ₁ ^-/- primary culture of endothelial cells, both transfected with B₁R, were also used.

CPM expression and activity were downregulated in cells of knockout mice compared to control and this reduction was rescued after B₁R transfection. Cells overexpressing B₁R presented higher levels of CPM mRNA, protein, and activity. This profile was reverted by pre-incubation with the B₁R antagonist, R715, in highly expressing receptor cells.

Our data show that kinin B₁R positively modulates both CPM expression and activity, suggesting that CPM-B₁R 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.