PBX1 Is a Favorable Prognostic Biomarker as It Modulates 13-cis Retinoic Acid–Mediated Differentiation in Neuroblastoma

Purpose: Neuroblastoma is an embryonic childhood cancer with high mortality. 13- cis retinoic acid (13- cis RA) improves survival for some patients, but many recur, suggesting clinical resistance. The mechanism of resistance and the normal differentiation pathway are poorly understood. Three–amino-acid loop extension (TALE) family genes are master regulators of differentiation. Because retinoids promote differentiation in neuroblastoma, we evaluated TALE family gene expression in neuroblastoma. Experimental Design: We evaluated expression of TALE family genes in RA-sensitive and -resistant neuroblastoma cell lines, with and without 13- cis RA treatment, identifying genes whose expression correlates with retinoid sensitivity. We evaluated the roles of one gene, PBX1 , in neuroblastoma cell lines, including proliferation and differentiation. We evaluated PBX1 expression in primary human neuroblastoma samples by qRT-PCR, and three independent clinical cohort microarray datasets. Results: We confirmed that induction of PBX1 expression, and no other TALE family genes, was associated with 13- cis RA responsiveness in neuroblastoma cell lines. Exogenous PBX1 expression in neuroblastoma cell lines, mimicking induced PBX1 expression, significantly impaired proliferation and anchorage-independent growth, and promoted RA-dependent and -independent differentiation. Reduced PBX1 protein levels produced an aggressive growth phenotype and RA resistance. PBX1 expression correlated with histologic neuroblastoma subtypes, with highest expression in benign ganglioneuromas and lowest in high-risk neuroblastomas. High PBX1 expression is prognostic of survival, including in multivariate analysis, in the three clinical cohorts. Conclusions: PBX1 is an essential regulator of differentiation in neuroblastoma and potentiates retinoid-induced differentiation. Neuroblastoma cells and tumors with low PBX1 expression have an immature phenotype with poorer prognosis, independent of other risk factors. Clin Cancer Res; 20(16); 4400–12. ©2014 AACR .