Abstract
Proline-rich Gla protein 2 (PRGP2) is one of four known vertebrate transmembrane gamma-carboxyglutamic acid (Gla) proteins. Members of this protein family are broadly expressed in fetal and adult human tissues and share a common architecture consisting of a predicted propeptide and Gla domain, a single-pass transmembrane segment, and tandem Pro/Leu-Pro-Xaa-Tyr (PY) motifs near their C termini. Using a methodology developed for the regulated expression of enzymatically biotinylated proteins in mammalian cells, we demonstrate that PRGP2 undergoes gamma-glutamyl carboxylation in a manner that is both dependent upon the presence of a proteolytically cleavable propeptide and sensitive to warfarin, a vitamin K antagonist that is widely used as an antithrombotic agent. When expressed at physiologically relevant levels, the majority of PRGP2 is present in the gamma-glutamyl carboxylated, propeptide-cleaved (mature) form. We additionally demonstrate, by Western blotting and flow cytometry, that mature PRGP2 is predominantly located on the cell surface with the Gla domain exposed extracellularly. In a yeast two-hybrid screen that used the C-terminal cytoplasmic region of PRGP2 as bait, we identified the WW domain-containing transcriptional coactivator Yes-associated protein (YAP) as a binding partner for PRGP2. In GST pull-down experiments, both PRGP2 PY motifs and both YAP WW domains were essential for complex formation, as were residues proximal to the core sequence of the first PY motif. These findings suggest that PRGP2 may be involved in a signal transduction pathway, the impairment of which may be an unintended consequence of warfarin therapy.