Down-regulation of caveolin-1 in mouse Lewis lung cancer P29 is a causal factor for the malignant properties in a high-metastatic subline

In order to analyze molecular mechanisms for cancer metastasis, we established a high-metastatic subline H7-Lu from a subline H7 of mouse Lewis lung cancer (P29) by repeated injection into tail veins. H7-Lu exhibited increased proliferation and invasion activity. Analysis of gene expression profiles between the parent H7 and H7-Lu revealed that several genes were down-regulated in H7-Lu. One of them, caveolin-1, was a component of lipid/rafts. After confirming the down-regulation of caveolin-1 mRNA by real-time RT-PCR and reduction of the protein by immunoblotting, respectively, H7 was transfected with siRNA for caveolin-1 to examine the role of caveolin-1 in H7-Lu. mRNA of the caveolin-1 gene was suppressed to approximately one third of the original level in H7 cells transfected with siRNA. The transfectant cells showed significantly increased cell proliferation and motility when analyzed by MTT assay and scratching wound healing assay, respectively. In the siRNA-transfectant cells, both ERK1/2 and Akt showed stronger phosphorylation than the mock-transfectant cells indicating that both of these signaling pathways were activated in caveolin-1-suppressed cells. These situations seem to reflect some aspects of the cellular changes in the high metastatic subline H7-Lu. Thus, down-regulation of caveolin-1 in a high-metastatic subline of Lewis lung cancer as defined by DNA array is really a causal factor for the increased malignant properties.