MiR-214 and N-ras regulatory loop suppresses rhabdomyosarcoma cell growth and xenograft tumorigenesis

Rhabdomyosarcoma (RMS) is a childhood malignant soft tissue cancer that is derived from myogenic progenitors trapped in a permanent mode of growth. Here, we report that miR-214 is markedly down-regulated in human RMS cell lines. Although not required for embryogenesis in mice, miR-214 suppresses mouse embryonic fibroblast (MEF) proliferation. When re-introduced into RD cells, a line of human embryonal RMS cells, miR-214 showed inhibition of tumor cell growth, induction of myogenic differentiation and apoptosis, as well as suppression of colony formation and xenograft tumorigenesis. We show that in the absence of miR-214, expression of proto-oncogene N-ras is markedly elevated in miR-214(-/-) MEFs, and manipulations of miR-214 levels using microRNA mimics or inhibitor in RD cells reciprocally altered N-ras expression. We further demonstrate that forced expression of N-ras from a cDNA that lacks its 3'-untranslated region neutralized the pro-myogenic and anti-proliferative activities of miR-214. Finally, we show that N-ras is a conserved target of miR-214 in its suppression of xenograft tumor growth, and N-ras expression is up-regulated in xenograft tumor models as well as actual human RMS tissue sections. Taken together, these data indicate that miR-214 is a bona fide suppressor of human RMS tumorigensis.