Pre-B-cell leukemia homeobox interacting
protein 1 or human PBX1 interacting
protein (PBXIP1/
HPIP) is a
co-repressor of
pre-B-cell leukemia homeobox 1 (PBX1) and is also known to regulate
estrogen receptor functions by associating with the microtubule network. Despite its initial discovery in the context of hematopoietic cells, little is yet known about the role of
HPIP in hematopoiesis. Here, we show that lentivirus-mediated overexpression of
HPIP in human CD34(+) cells enhances hematopoietic colony formation in vitro, whereas
HPIP knockdown leads to a reduction in the number of such colonies. Interestingly, erythroid colony number was significantly higher in
HPIP-overexpressing cells. In addition, forced expression of
HPIP in K562 cells, a multipotent erythro-megakaryoblastic
leukemia cell line, led to an induction of erythroid differentiation.
HPIP overexpression in both CD34(+) and K562 cells was associated with increased activation of the PI3K/AKT pathway, and corresponding treatment with a PI3K-specific inhibitor,
LY-294002, caused a reduction in clonogenic progenitor number in
HPIP-expressing CD34(+) cells and decreased K562 cell differentiation. Combined, these findings point to an important role of the PI3K/AKT pathway in mediating
HPIP-induced effects on the growth and differentiation of hematopoietic cells. Interestingly,
HPIP gene expression was found to be induced in K562 cells in response to erythroid differentiation signals such as
DMSO and
erythropoietin. The erythroid lineage-specific
transcription factor GATA1 binds to the
HPIP promoter and activates
HPIP gene transcription in a
CCCTC-binding factor (CTCF)-dependent manner. Co-immunoprecipitation and co-localization experiments revealed the association of CTCF with GATA1 indicating the recruitment of CTCF/
GATA1 transcription factor complex onto the
HPIP promoter. Together, this study provides evidence that
HPIP is a target of GATA1 and CTCF in erythroid cells and plays an important role in erythroid differentiation by modulating the PI3K/AKT pathway.