Regulation of Trib2 gene expression in normal and AML cells

The mammalian Trib family consists of Trib1, Trib2 and Trib3.Elevated levels of Trib2 have been linked with murine AML andassociates with a specific subset of human AML with Notch1mutations and dysregulated C/EBPa. However the regulation of Tribexpression is poorly understood; understanding this regulation isimportant both physiologically and pathologically.Promoter analyses indicated that several possible E2F1 bindingsites exist within the Trib2 promoter region. A complex regulatoryrelationship exists between C/EBPa and E2F1, and proliferationarrest mediated by C/EBPa involves repression of E2F1-target genes.Luciferase assays using a Trib2 promoter construct demonstratedthat E2F1 is a positive regulator of Trib2 and that this positiveinduction was dependent on E2F1’s ability to bind directly to DNA.Further analyses revealed that this activation is repressed by wild type C/EBPa. Importantly, C/EBPap30, an N-terminal truncateddominant negative C/EBPa isoform commonly associated with AMLco-operated with E2F1 to induce Trib2 promoter activity. Bioinfor-matic analysis of human AML datasets revealed a negativecorrelation between Trib2 and C/EBPa expression, and a positivecorrelation between Trib2 and Notch1 expression. These resultscorrespond with our previous findings that Trib2 is a Notch1 targetgene and functions to degrade and inhibit wild type C/EBPa. Furtheranalyses demonstrated a positive correlation between Trib2 and E2F1expression in the human AML dataset supporting our findings.Together these data indicate a positive regulatory pathway forTrib2 expression mediated by E2F1 and C/EBPap30, and a negativeregulatory pathway involving E2F1 and wild type C/EBPa.