Caveolin-1 (CAV1) Is a Target of EWS/FLI-1 and a Key Determinant of the Oncogenic Phenotype and Tumorigenicity of Ewing's Sarcoma Cells

Abstract

Tumors of the Ewing's sarcoma family (ESFT), such as Ewing's sarcoma (EWS) and primitive neuroectodermal tumors (PNET), are highly aggressive malignancies predominantly affecting children and young adults. ESFT express chimeric transcription factors encoded by hybrid genes fusing the EWS gene with several ETS genes, most commonly FLI-1. EWS/FLI-1 proteins are responsible for the malignant phenotype of ESFT, but only few of their transcriptional targets are known. Using antisense and short hairpin RNA-mediated gene expression knockdown, array analyses, chromatin immunoprecipitation methods, and reexpression studies, we show that caveolin-1 (CAV1) is a new direct target of EWS/FLI-1 that is overexpressed in ESFT cell lines and tumor specimens and is necessary for ESFT tumorigenesis. CAV1 knockdown led to up-regulation of Snail and the concomitant loss of E-cadherin expression. Consistently, loss of CAV1 expression inhibited the anchorage-independent growth of EWS cells and markedly reduced the growth of EWS cell-derived tumors in nude mice xenografts, indicating that CAV1 promotes the malignant phenotype in EWS carcinogenesis. Reexpression of CAV1 or E-cadherin in CAV1 knockdown EWS cells rescued the oncogenic phenotype of the original EWS cells, showing that the CAV1/Snail/E-cadherin pathway plays a central role in the expression of the oncogenic transformation functions of EWS/ FLI-1. Overall, these data identify CAV1 as a key determinant of the tumorigenicity of ESFT and imply that targeting CAV1 may allow the development of new molecular therapeutic strategies for ESFT patients.

GSTM4 is a microsatellite-containing EWS/FLI target involved in Ewing's sarcoma oncogenesis and therapeutic resistance

“…Through these cross-platform comparisons, we identified genes that have all of the characteristics we sought. These genes include previously identified EWS/ FLI targets such as NR0B1, FCGRT and CAV1 (Tirado et al, 2006;. In addition, we identified glutathione S-transferase mu 4 (GSTM4) as a potential new EWS/FLI target gene in Ewing's sarcoma.…”

Upstream of the mammalian target of rapamycin: do all roads pass through mTOR?

“…The suggested mechanism is that p53 activates TSC1/2 and mTOR in response to energy stress through the 5 0 adenosine monophosphate-activated protein kinase (AMPK) (see below for a discussion of AMPK) (Feng et al, 2005). However, two other seemingly conflicting possibilities have also been suggested, as it has also been proposed that p53 acts parallel to mTOR (Jones et al, 2005), and downstream of mTOR as one of its substrates (Castedo et al, 2002;Tirado et al, 2003). Given the complexity of p53 regulation in different cell types, at different stages of the cell cycle, and in response to different agonists, considerable future investigation is required to determine its true physiological role with respect to mTOR.…”

Caveolin-1 Up-regulation during Epithelial to Mesenchymal Transition Is Mediated by Focal Adhesion Kinase

“…Clues that caveolin-1 may be serving a tumor promoter effect first arose with the observation that prostate cancer tissue expresses more caveolin-1 than does normal tissue (15). The list has since expanded and includes esophageal squamous cell carcinoma, multiple myeloma, Ewing's sarcoma family tumors, clear cell renal carcinoma, urinary bladder tumors, and non-small cell lung cancer (4,8,16,17). This suppressor/promoter discrepancy could be due to the examination of various cell types, cancer stages, variations in in vitro versus in vivo data, or an indicator that caveolin can serve different roles depending on the context in which its function is being examined.…”