A critical role of CXCR2 PDZ-mediated interactions in endothelial progenitor cell homing and angiogenesis.

Bone marrow-derived endothelial progenitor cells (EPCs) contribute to neovessel formation in response to growth factors, cytokines, and chemokines. Chemokine receptor CXCR2 and its cognate ligands are reported to mediate EPC recruitment and angiogenesis. CXCR2 possesses a consensus PSD-95/DlgA/ZO-1 (PDZ) motif which has been reported to modulate cellular signaling and functions. Here we examined the potential role of the PDZ motif in CXCR2-mediated EPC motility and angiogenesis. We observed that exogenous CXCR2 C-tail significantly inhibited in vitro EPC migratory responses and angiogenic activities, as well as in vivo EPC angiogenesis. However, the CXCR2 C-tail that lacks the PDZ motif (ΔTTL) did not cause any significant changes of these functions in EPCs. In addition, using biochemical assays, we demonstrated that the PDZ scaffold protein NHERF1 specifically interacted with CXCR2 and its downstream effector, PLC-ß3, in EPCs. This suggests that NHERF1 might cluster CXCR2 and its relevant signaling molecules into a macromolecular signaling complex modulating EPC cellular functions. Taken together, our data revealed a critical role of a PDZ-based CXCR2 macromolecular complex in EPC homing and angiogenesis, suggesting that targeting this complex might be a novel and effective strategy to treat angiogenesis-dependent diseases.

CXCR2 macromolecular complex in pancreatic cancer: a potential therapeutic target in tumor growth.

The signaling mediated by the chemokine receptor CXC chemokine receptor 2 (CXCR2) plays an important role in promoting the progression of many cancers, including pancreatic cancer, one of the most lethal human malignancies. CXCR2 possesses a consensus PSD-95/DlgA/ZO-1 (PDZ) motif at its carboxyl termini, which might interact with potential PDZ scaffold/adaptor proteins. We have previously reported that CXCR2 PDZ motif-mediated protein interaction is an important regulator for neutrophil functions. Here, using a series of biochemical assays, we demonstrate that CXCR2 is physically coupled to its downstream effector phospholipase C-ß3 (PLC-ß3) that is mediated by PDZ scaffold protein Na(+)/H(+) exchange regulatory factor 1 (NHERF1) into a macromolecular signaling complex both in vitro and in pancreatic cancer cells. We also observe that disrupting the CXCR2 complex, by gene delivery or peptide delivery of exogenous CXCR2 C-tail, significantly inhibits the biologic functions of pancreatic cancer cells (i.e., proliferation and invasion) in a PDZ motif-dependent manner. In addition, using a human pancreatic tumor xenograft model, we show that gene delivery of CXCR2 C-tail sequence (containing the PDZ motif) by adeno-associated virus type 2 viral vector potently suppresses human pancreatic tumor growth in immunodeficient mice. In summary, our results suggest the existence of a physical and functional coupling of CXCR2 and PLC-ß3 mediated through NHERF1, forming a macromolecular complex that is critical for efficient and specific CXCR2 signaling in pancreatic cancer progression. Disrupting this CXCR2 complex could represent a novel and effective treatment strategy against pancreatic cancer.