Carboxypeptidase Z (CPZ) modulates Wnt signaling and regulates the development of skeletal elements in the chicken

Carboxypeptidase Z (CPZ) is a secreted Zn-dependent enzyme whose biological function is largely unknown. CPZ has a bipartite structure consisting of an N-terminal cysteine-rich domain (CRD) and a C-terminal catalytic domain. In the early chicken embryo CPZ is initially expressed throughout the somites and subsequently becomes restricted to the sclerotome. To initiate a functional analysis of CPZ, a CPZ producing retroviral vector was applied to the presomitic mesoderm at the level of the future wing. This resulted in a loss of the scapular blade and of rostral ribs. Such dysmorphogenesis is preceded by ectopic Pax3 expression in the hypaxial part of the dermomyotome, a region from which the blade of the scapula normally derives. A mutant CPZ, lacking a critical active site glutamate, fails to induce Pax3 expression and does not cause skeletal defects. The induction of Pax3, a Wnt-responsive gene in somites, and the presence of a CRD prompted us to examine whether CPZ affects Wnt signaling. In an in vitro assay we found that CPZ, but not its inactive mutant form, enhances the Wnt-dependent induction of the homeobox gene Cdx1. In addition, immunoprecipitation experiments suggest that the CRD of CPZ acts as a binding domain for Wnt. Taken together these data provide the first evidence for CPZ playing a role in Wnt signaling.