Tissue invasion by tumor cells involves their migration across basement membranes through coordinated activation of matrix degradation and cell motility mechanisms. Chemokine binding to their receptors provides chemotactic cues guiding cells to specific tissues and organs, and therefore they could potentially participate in tumour cell dissemination. In the present study we show that several human melanoma cell lines and melanoma cells from infiltrated lymph nodes express the chemokine receptors CXCR4 and CXCR3. Moreover, we show that CXCL12 and CXCL9, the ligands for these receptors, promote invasion of melanoma cells across basement membranes. The proteolytic activity of MT1-MMP was necessary for these invasions, and an increase in the expression of MT1-MMP was triggered by CXCL12. Furthermore, CXCL12 and CXCL9 triggered the activation of GTPases RhoA and Rac, and expression of dominant negative forms of these GTPases substantially impaired the invasion of transfectants in response to both chemokines. We found that melanoma cells express Vav1 and Vav2, which are GEF proteins that catalyze the activation of Rho GTPases. Moreover, CXCL12 promoted the activation of Vav1 and Vav2, and interfering the expression of these GEFs resulted in inhibition of RhoA and Rac activation, up-regulation of MT1-MMP expression, and invasion of melanoma cells in response to CXCL12. In addition, CXCR4 expression on melanoma cells was notably augmented by TGF-β1, a basement membrane component, whereas anti-TGF-β1 antibodies inhibited increases in CXCR4 expression and melanoma cell invasion towards CXCL12. Stimulation by CXCL12 of Vav/Rho GPTase/MT1-MMP pathway in melanoma cells, as well as regulation of CXCR4 expression, constitute mechanisms that contribute to melanoma cell invasion towards CXCL12. Our results could provide the basis for future investigations on therapies addressing inhibition of melanoma cell dissemination. The α4 integrins are cell surface receptors expressed mostly on leukocytes that mediate cell-cell and cell-extracellular matrix adhesion. A characteristic feature of α4 integrins is that their adhesive activity can be rapidly modulated during migration. We reported that TGF-β1 rapidly and transiently up-regulates α4 integrin-dependent cell adhesion to their ligands VCAM-1 and CS-1/fibronectin. Herein, we show that TGF-β1 rapidly activates GTPase RhoA and p38 MAP kinase, but enhanced adhesion does not require activation of both signalling molecules. Instead, polymerization of actin cytoskeleton triggered by TGF-β1 is necessary for α4 integrin-dependent up-regulated adhesion, and elevation of intracellular cAMP levels opposes both actin polymerization and enhaced adhesion. Moreover, TGF-β1 further increases α4 integrin-mediated cell adhesion stimulated by CXCL12. These data suggest that TGF-β1 can potentially contribute to cell migration by dynamically regulating cell adhesion mediated by α4 integrins.

Formación y especialización en líneas de investigación de interésindustrial 2000-2001. CSIC-GLAXO WELLCOME 2001-2004.

130 p.-40 fig.-2 tab.

Peer reviewed