Abstract 5015: Hcasz5, CASZ1 gene transcript variant 2 with 5 zinc fingers functions as a tumor suppressor in Neuroblastoma
Authors: Liu Zhihui , London Wendy B. , Maris John , Thiele Carol J. 
Published: February 2011

Neuroblastoma (NB) is a common childhood malignant tumor of the sympathetic nervous system. The human homolog of the Drosophila neural fate determination gene CASZ1, a zinc-finger transcription factor, maps to chromosome 1p36.22, a region implicated in NB tumorigenesis. We have previously reported that human CASZ1 gene encodes two major mRNA species, hcasz5 (CASZ1 gene transcript variant 2) and hcasz11 (CASZ1 gene transcript variant 1) because the predicted proteins have 5 and 11 zinc fingers, respectively. Quantitative PCR analysis showed that low expression of total CASZ1 is significantly correlated with decreased survival probability (p=0.0009). Functional in vitro and in vivo studies on the full length CASZ1 - hcasz11 show that it has tumor suppressor activity. To date the function of the short isoform - hcasz5 is unknown. In this study quantitative PCR analysis was performed using isoform specific primers that only recognize hcasz5. Low hcasz5 expression is significantly associated with older age (&gt;18 months), high-risk disease, 1p LOH, MYCN amplification and an undifferentiated histopathology (all p&lt;0.005). Using CASZ1 antibody that recognizes both hcasz5 and hcasz11 isoforms, we found hcasz5 and hcasz11 protein are co-expressed in the nucleus of all cell lines and mouse tissues examined. Retinoic acid (RA), a key embryonic morphogen, coordinately regulates hcasz5 and hcasz11 expression; moreover, the epigenetic modification agents 5-Aza-dC and HDAC inhibitors also induce both hcasz5 and hcasz11 expression. Bio-informatic analysis indicates that hcasz5 and hcasz11 utilize the same promoter and enhancer regulatory regions. However, the steady-state level of hcasz11 is higher than hcasz5 indicating different post-transcriptional mechanisms regulate specific isoforms. Frequently different isoforms have distinct functions or act as dominant negatives. However, expression profiling reveals that the majority of hcasz5 target genes overlap with hcasz11 targets and are also involved in cell movement, proliferation and developmental processes. Analysis of target gene expression revealed that neither hcas5 nor hcasz11 functioned synergistically or acted as a dominant negative when co-expressed in vitro. Functionally, specific restoration of hcasz5 in NB cells enhanced cell adhesion, inhibited migration and suppressed cell growth similar to the functional effects when hcasz11 expression is restored in NB cells. This study indicates that while both hcas5 and hcasz11 are lost in poor prognosis NB patient samples, the functional restoration of either isoform is sufficient to suppress tumor growth by MTS assay and soft agar cloning assay in vitro. We argue that the redundant expression and largely overlapping functions of hcasz5 and hcasz11 isoforms indicate that expression of the CASZ1 gene is an important regulator of neuroblast growth and differentiation during development.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 5015.