Guanylyl cyclase C remodels metastatic architecture through vasodilator-stimulated phosphoprotein
Colon cancer is the 2nd leading cause of cancer mortality in United States and the world1. Mortality from colon cancer reflects metastatic disease progression. Indeed, the five year survival rate of patients with local disease is ∼90%, while that of patients with local or distant metastasis is ∼60% and ∼10%, respectively (ACS, 2005, Jemal, 2004). Maladaptive changes in tumor cell morphology and membrane architecture promoted by actin polymerization and cytoskeletal remodeling underlies key steps of the metastatic process, including extracellular matrix (ECM) degradation, migration and invasion. Guanylyl cyclase C (GCC), the intestinal epithelial cell receptor for diarrheagenic bacterial heat-stable enterotoxins (STs), and matrix metalloproteinase-9 (MMP-9), a collagenase mediating extracellular matrix remodeling, are functionally opposing regulators of these processes in colorectal cancer. MMP-9 activity is believed to promote metastasis through: (1) degradation of the extracellular matrix (ECM), which creates a physical space for tumor cells to invade and may result in the release of cytokines and growth factors, (2) promotion of metastatic seeding, and (3) regulation angiogenesis. Guanylyl cyclase C (GCC), the receptor for guanylin and uroguanylin in intestinal epithelial cells, maintains crypt-villus axis homeostasis by regulating enterocyte turnover and differentiation, and inhibiting tumorigenesis. Indeed, the most commonly lost gene products in colorectal cancer include guanylin and uroguanylin, suggesting that dysregulated GCC signaling may contribute to disease promotion and progression. Regulation of MMP-9 signaling by ligand activation of GCC in human colon carcinoma cells was examined in vitro by cell spreading and invasion and in vivo employing murine models of metastasis. Given its restricted expression, GCC-dependent inhibition of MMP-9 is limited to epithelial cells. Therefore, the pathological significance of tumor epithelial cell MMP-9 was evaluated in matched normal and tumor cell populations from patients by RT-PCR. Induction of GCC signaling by ST in cancer cells inhibited the secretion of MMP-9, suppressed cell spreading and invasion, and opposed hematogenous and peritoneal metastases in a MMP-9-dependent fashion. Over-expression of MMP-9 mRNA in cancer, compared to normal adjacent epithelial, cells significantly correlated with pericolic lymph node metastasis in patients. Notably, inhibition of MMP-9 was dependent on GCC signaling through the vasodilator-stimulated phosphoprotein (VASP), an important regulator of actin polymerization and membrane dynamics. Activation of GCC signaling induced VASP phosphorylation at serine 239 resulting in cytoplasmic redistribution of VASP and a reduction in the number and length of filopodia and invadopodia. Accordingly, GCC-mediated VASP phosphorylation nearly eliminated the ability of tumor cells to degrade ECM components, with a corresponding loss of matrix metalloproteinase-9 secretion. Taken together, these data demonstrate a novel role for the GCC-VASP signaling axis in cytoskeletal remodeling associated with invasion and metastasis and offer a novel approach, GCC hormone replacement therapy, for the treatment and prevention of metastatic colorectal cancer progression.