Cellular retinoic acid-binding protein II is a direct transcriptional target of MycN in neuroblastoma.

Neuroblastoma is a heterogeneous disease in which 22% of tumors show MycN oncogene amplification and are associated with poor clinical outcome. MycN is a transcription factor that regulates the expression of a number of proteins that affect the clinical behavior of neuroblastoma. We report here that cellular retinoic acid-binding protein II (CRABP-II) is a novel MycN target, expressed at significantly higher levels in primary neuroblastoma tumors with mycN oncogene amplification as compared with non-MycN-amplified tumors. Moreover, regulated induction and repression of MycN in a neuroblastoma-derived cell line resulted in temporal and proportionate expression of CRABP-II. CRABP-II is expressed in several cancers, but its role in tumorigenesis has not been elucidated. We show that MycN binds to the promoter of CRABP-II and induces CRABP-II transcription directly. In addition, CRABP-II-transfected neuroblastoma cell lines show an increase in MycN protein levels resulting in increased cell motility. Gene expression profiling of CRABP-II-expressing cell lines uncovered increased expression of the HuB (Hel N1) gene. Hu proteins have been implicated in regulating the stability of MycN mRNA and other mRNAs by binding to their 3' untranslated regions. We did not, however, observe any change in MycN mRNA stability or protein half-life in response to CRABP-II expression. In contrast, de novo MycN protein synthesis was increased in CRABP-II-expressing neuroblastoma cells, thereby suggesting an autoregulatory loop that might exacerbate the effects of MycN gene amplification and affect the clinical outcome. Our findings also suggest that CRABP-II may be a potential therapeutic target for neuroblastoma.