Defining the Cooperative Genetic Changes That Temporally Drive Alveolar Rhabdomyosarcoma

Abstract

Rhabdomyosarcoma (RMS) is the most common soft tissue sarcoma of childhood and adolescence. Despite advances in therapy, patients with a histologic variant of RMS known as alveolar (aRMS) have a 5-year survival rate of <30%. aRMS tissues exhibit a number of genetic changes, including lossof-function of the p53 and Rb tumor suppressor pathways, amplification of MYCN, stabilization of telomeres, and most characteristically, reciprocal translocation of loci involving the PAX and FKHR genes, generating the PAX7-FKHR or PAX3-FKHR fusion proteins. We previously showed that PAX3-FKHR expression in primary human myoblasts, cells that can give rise to RMS, cooperated with loss of p16INK4A to promote extended proliferation. To better understand the genetic events required for aRMS formation, we then stepwise converted these cells to their transformed counterpart. PAX3-FKHR, the catalytic unit of telomerase hTERT, and MycN, in cooperation with down-regulation of p16 INK4A /p14 ARF expression, were necessary and sufficient to convert normal human myoblasts into tumorigenic cells that gave rise to aRMS tumors. However, the order of expression of these transgenes was critical, as only those cells expressing PAX3-FKHR early could form tumors. We therefore suggest that the translocation of PAX3 to FKHR drives proliferation of myoblasts, and a selection for loss of p16 INK4A /p14 ARF . These early steps, coupled with MycN amplification and telomere stabilization, then drive the cells to a fully tumorigenic state. [Cancer Res 2008;68(23):9583-8]

AKT and PAX3-FKHR cooperation enforces myogenic differentiation blockade in alveolar rhabdomyosarcoma cell

“…Several studies have reported phosphorylation in the PAX3 domain of PAX3-FKHR in association with its transcriptional activity. 1,[54][55][56][57][58] However, none of the above studies reported phosphorylation-induced we did perceive, during the assessment of PAX3-FKHR transactivation potency in ARMS cells, that PAX3-FKHR appears as a doublet of a faster and slower migrating form. Interestingly, the data showed the shift of PAX3-FKHR to a slower migrating form in ARMS cells grown in DM.…”

“…Mathivanan Jothi, 1 Kochi Nishijo, 2, † Charles Keller 3 and Asoke K. Mal 1, transactivation power and relaxed target specificity, leading to deregulated expression of downstream targets that cause ARMS phenotype. A typical feature of ARMS also includes the myogenic phenotype with expression of MyoD, 14 a bona fide target of PAX3-FKHR, 13,15 which acts as a key regulator of myogenic gene expression, leading to terminal differentiation.…”

“…The latter responds poorly to treatment and, thus, has a poor prognosis. 1 The majority of ARMS are characterized by the presence of the pathogenetic chromosomal translocation t(2;13), 2,3 which generates the chimeric transcription factor PAX3-FKHR consisting of the intact DNA binding domain of PAX3 and the potent transactivation domain of FKHR (FOXO1A). 3 The transcription factor PAX3 plays an essential role in regulating the skeletal muscle differentiation program.…”

Lineage of origin in rhabdomyosarcoma informs pharmacological response

“…Rhabdomyosarcoma is a disease that has a steady incidence throughout childhood (aRMS contrasts dramatically with eRMS, the latter of which peaks with toddler and adolescent growth spurts) (Ognjanovic et al 2009). Suggestion of Myf6 + prenatal or postnatal myogenic cells, possibly a terminally differentiating subpopulation, as an aRMS cell of origin was first reported by our group (Keller et al 2004a,b) and later complemented by in vitro studies of human postnatal myoblasts transformed by PAX3:FOXO1 and other cooperative initiating mutations (Naini et al 2008). Congenital fusion-positive aRMS is rarely reported, and congenital aRMS is generally fusion-negative (Godambe and Rawal 2000;Grundy et al 2001;Sueters et al 2005), although the PAX3:FOXO1 translocation has been detected in rare neonatal instances (Rodriguez-Galindo et al 2001).…”

Uncovering metabolism in rhabdomyosarcoma

“…34,35 Pax3-Foxo1 is found in 70% ARMS cases and is considered a strong predictor of poor prognosis, while fusion-negative ARMS have better resolution and are clinically and molecularly indistinguishable from the larger group of ERMS in the majority of patients. 36 Because of the ability of Pax3-Foxo1 to drive the transcription of genes like fibroblast growth factor receptor 4 (FGFR4) and insulin-like growth factor 2 (IGF-2), fusionpositive RMS are characterized by sustained activation of the RTK/RAS/phosphatidylinositol-3-kinase (PI3K) axis; 33 in addition, these tumors often carry high copy number of N-Myc gene [37][38][39] and exhibit IGF-2 overexpression due to loss of imprinting (LOI) at 11p15.5 locus 40 (Fig. 2).…”