Okadaic acid induces transcription of junB through a CCAAT Box and NF-Y

The shellfish toxin, okadaic acid (OA), is a potent tumor promoter that ind uces expression of the proto-oncogene junB in mouse keratinocyte 308 cells. Here we show, through deletion analysis of the junB promoter, that sequenc es near the TATA box conferred transcriptional induction by OA. Transient t ransfections of luciferase constructs bearing the junB promoter with single mutations in various cis elements demonstrated that a promoter containing a mutated CCAAT box could not be induced by OA. When this CCAAT box was ins erted into a heterologous promoter construct, OA induction was dependent on an intact CCAAT box. Flanking cis elements located near the CCAAT box, alt hough not required for OA inducibility, did play a role in the basal level of transcription. NF-Y was shown by EMSA to bind to the CCAAT box. OA induc tion from the junB CCAAT box was blocked by dominant negative NF-YA as well as the CCAAT box-dependent anticancer drug, ET-473. Expression of a lexA/N F-YA chimeric protein demonstrated that OA induction was dependent on the b inding of NF-Y family members. These studies demonstrate that OA can mediat e transcriptional activation of junB through the classical CCAAT box and th at transcription factor NF-Y plays a functional role in the induction. (C) 2001 Elsevier Science B.V. All rights reserved.