Data from PH-Binding Motif in PAR<sub>4</sub> Oncogene: From Molecular Mechanism to Drug Design

While the role of G-protein–coupled receptors (GPCR) in cancer is acknowledged, their underlying signaling pathways are understudied. Protease-activated receptors (PAR), a subgroup of GPCRs, form a family of four members (PAR_1–4) centrally involved in epithelial malignancies. PAR₄ emerges as a potent oncogene, capable of inducing tumor generation. Here, we demonstrate identification of a pleckstrin-homology (PH)-binding motif within PAR₄, critical for colon cancer growth. In addition to PH–Akt/PKB association, other PH-containing signal proteins such as Gab1 and Sos1 also associate with PAR₄. Point mutations are in the C-tail of PAR₄ PH-binding domain; F347 L and D349A, but not E346A, abrogate these associations. Pc(4–4), a lead backbone cyclic peptide, was selected out of a mini-library, directed toward PAR_2&4 PH-binding motifs. It effectively attenuates PAR_2&4–Akt/PKB associations; PAR₄ instigated Matrigel invasion and migration in vitro and tumor development in vivo. EGFR/erbB is among the most prominent cancer targets. AYPGKF peptide ligand activation of PAR₄ induces EGF receptor (EGFR) Tyr-phosphorylation, effectively inhibited by Pc(4–4). The presence of PAR₂ and PAR₄ in biopsies of aggressive breast and colon cancer tissue specimens is demonstrated. We propose that Pc(4–4) may serve as a powerful drug not only toward PAR-expressing tumors but also for treating EGFR/erbB-expressing tumors in cases of resistance to traditional therapies. Overall, our studies are expected to allocate new targets for cancer therapy. Pc(4–4) may become a promising candidate for future therapeutic cancer treatment.