Pre-B-cell Leukemia Homeobox Interacting Protein 1 (PBXIP1)

PBXIP1 is a regulator of pre-B-cell leukemia transcription factors (BPXs) function. It inhibits the binding of PBX1-HOX complex to DNA and blocks the transcriptional activity of E2A-PBX1. PBXIP1 also tethers estrogen receptor-alpha (ESR1) to microtubules and allows them to influence estrogen receptors-alpha signaling. HPIP is mainly localized in the cytosol and in small amounts in the nucleus. The region of PBX that interacts with HPIP includes both the homeodomain and immediate N-terminal flanking sequences. Strikingly, electrophoretic mobility shift assays revealed that HPIP inhibits the ability of PBX-HOX heterodimers to bind to target sequences. Moreover, HPIP strongly inhibits the transactivation activity of E2A-PBX. Together these findings suggest that HPIP is a new regulator of PBX function.