Caveolin-1 overexpression in the human embryonal rhabdomyosarcoma RD cells increases tumor growth and metastasis in vivo through a phospho-ERK-dependent signaling pathway

Caveolin-1 (Cav-1) represents the principal component of caveolae, flask-shaped invaginations of the plasma membrane controlling different processes like endocytosis, mechanoprotection and signal transduction. Cav-1 expression and/or function is often dysregulated in cancer, being associated to an increased or decreased tumor cell behavior depending on the cell context. We proposed Cav-1 as a marker of poorly differentiated cells in rhabdomyosarcoma (RMS), a class of childhood soft tissue sarcomas characterized by expression of myogenic markers. In addition, we have further shown that increasing or depleting Cav-1 expression levels in the human embryonal RD cells correlates with an augmented or decreased tumor cell behavior, respectively. In the attempt to further characterize the role of Cav-1 in RMS in vivo, here we demonstrate that injecting subcutaneously Cav-1-overexpressing RD cells in SCID nude mice led to rapid growth of huge RMS tumors in comparison to control mice; in addition, tail vein injection was followed by rapid lung metastasis formation. Ex vitro transplantation of lung metastatic cells followed by re-injection in the tail vein of SCID mice allowed us to isolate two clonal metastatic RD populations (named F1 and F2) characterized by increased ability to disseminate in a shorter time as compared to controls. FACS analyses revealed that both Cav-1 overexpressing RD cells and the metastatic F1-F2 populations exhibited a rapid G1 phase transition, characterized by massive activation of the phosphorylated ERK1/2 pathway. As a result, treatment of these cells with a pharmacological inhibitor of ERK phosphorylation (PD098059) was sufficient to prevent in vitro the increased proliferation and migration associated to the high Cav-1 levels. Overall, these data establish an important connection between the levels of Cav-1 and the activation of the ERK1/2 pathway underlying the augmented cell aggressiveness in RMS cells.