Identification of CASZ1 nuclear export signal (NES) reveals potential mechanisms for loss of CASZ1 tumor suppressor activity in neuroblastoma

As a transcription factor, localization to the nucleus and the recruitment of co-factors to regulate gene transcription is essential. Nuclear localization and nucleosome remodeling and histone deacetylase (NuRD) complex binding are required for the zinc finger transcription factor CASZ1 to function as neuroblastoma (NB) tumor suppressor. However, the critical amino acids (AAs) that are required for CASZ1 interaction with NuRD complex and the regulation of CASZ1 subcellular localization have not been characterized. Through alanine scanning, immunofluorescence cell staining and co-immunoprecipitation we define a critical region at the CASZ1 N-terminus (AA23-40) that mediates the CASZ1b nuclear localization and NuRD interaction. Furthermore, we identify a nuclear export signal (NES) at the N-terminus (AA176-192) that contributes to CASZ1 nuclear-cytoplasmic shuttling in a chromosomal maintenance 1 (CRM1)-dependent manner. An analysis of CASZ1 protein expression in a primary neuroblastoma tissue microarray shows that high nuclear CASZ1 staining is detected in tumors from NB patients with good prognoses. In contrast, cytoplasmic-restricted CASZ1 staining or low nuclear CASZ1 staining is found in tumors from patients with poor prognoses. These findings provide insight into mechanisms by which CASZ1 regulates transcription, and suggests that regulation of CASZ1 subcellular localization may impact its function in normal development and pathologic conditions such as neuroblastoma tumorigenesis.