Involvement of matrix metalloproteinase-9 in stromal cell-derived factor-1/CXCR4 pathway of lung cancer metastasis

Lung caner cells have a striking tendency to metastasize to bone. The chemokine stromal cell-derived factor-1 (SDF-1) is constitutively secreted by osteoblasts and bone marrow stromal cells and plays a key role for homing of hematopoietic cells to the bone marrow. Reverse transcriptase–polymerase chain reaction and flow cytometry studies demonstrated SDF-1 receptor (CXCR4) messenger RNA (mRNA) and surface expression of CXCR4 in lung cancer cell lines, especially higher in those with high invasiveness (A549) as compared with lower level in H928 cells and H1299 cells. SDF-1, osteoblast-conditioned medium (OBCM) and stromal cell-conditioned medium all induced the invasiveness of lung cancer cells. Matrix metalloproteinase (MMP)-9 small interfering RNA inhibited the SDF-1α- or OBCM-induced MMP-9 expression and thereby significantly inhibited the SDF-1α- or OBCM-induced cell invasion. Furthermore, mitogen-activated protein kinase kinase inhibitor PD98059 suppressed SDF-1α-induced MMP-9 mRNA expression. Transient transfection with dominant-negative extracellular signal-regulated kinase (ERK) mutant also showed that the ERK-signaling pathway was involved in SDF-1α-induced MMP-9 expression. Moreover, nuclear factor-κB (NF-κB) decoy oligodeoxynucleotide suppressed the MMP-9 promoter activity enhanced by SDF-1α. Both mitogen-activated protein kinase kinase inhibitor and ERK mutant also antagonized SDF-1α-induced NF-κB-driven luciferase promoter activity. Taken together, our results indicated that bone marrow-derived-SDF-1α enhances the invasiveness of lung cancer cells by increasing MMP-9 expression through the CXCR4/ERK/NF-κB signal transduction pathway.