Caveolin-1 overexpression accelerates tumor growth and metastasis of embryonal rhabdomyosarcoma

Caveolin-1 (Cav-1) is a plasma membrane scaffolding protein that was shown to control the ERK pathway in muscle satellite cells. Oncogenic transformation of satellite cells is responsible of the generation of rhabdomyosarcoma (RMS), a soft tissue tumor affecting childhood and adolescence. We previously reported that Cav-1 is a marker of proliferating RMS cell lines and that its overexpression promotes increased malignancy of RMS cells in vitro and in vivo. Here we show that tail vein injection of the human embryonal RD cells with Cav-1 overexpression (RD Cav-1) into NOD/SCID mice resulted in formation of lung metastasis in about 9 weeks as compared to control cells that did not form metastasis. After performing ex vivo transplantation of lung metastases we isolated one cell population, termed lung metastatic RD1, which injected in mice again gave rise to lung metastases in 5 weeks; from these disseminated lungs we were able to isolate the lung metastatic RD2 cell population. All the distinct cell populations, including RD Cav-1 and lung metastatic RD1 and RD2 clones, retained high Cav-1 expression and showed high phosphorylation levels of ERK1/2, which completely prevented their ability to undergo myogenic differentiation. In addition, lung metastatic RD1 and RD2 clones exhibited an increased migration, adhesion and production of angiogenic stimuli in comparison to non-metastatic control RD and RD Cav-1 lines. Taken together, these data suggest a key role of Cav-1 in promoting both local tumor growth and metastasis of RMS through cooperation of the ERK signalling pathway.