Functional cloning and characterization of a novel nonhomeodomain protein that inhibits the binding of PBX1-HOX complexes to DNA.
PBX1 is a homeodomain protein that functions in complexes with other homeodomain-containing proteins to regulate gene expression during developmental and/or differentiation processes. A yeast two-hybrid screen of a fetal liver-hematopoietic cDNA library using PBX1a as bait led to the discovery of a novel non-homeodomain-containing protein that interacts with PBX1 as well as PBX2 and PBX3. RNA analysis revealed it to be expressed in CD34(+) hematopoietic cell populations enriched in primitive progenitors, as is PBX1; search of the expressed sequence tag data base indicated that it is also expressed in other early embryonic as well as adult tissues. The full-length cDNA encodes a 731-amino acid protein that has no significant homology to known proteins. This protein that we have termed hematopoietic PBX-interacting protein (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.
Abramovich
C
C
Terry Fox Laboratory, British Columbia Cancer Agency, Vancouver, British Columbia V5Z 1L3, Canada.
Shen
W F
WF
Pineault
N
N
Imren
S
S
Montpetit
B
B
Largman
C
C
Humphries
R K
RK
D000595:Amino Acid Sequence; D000818:Animals; D051792:Basic Helix-Loop-Helix Proteins; D002471:Cell Transformation, Neoplastic; D003001:Cloning, Molecular; D056970:Co-Repressor Proteins; D004247:DNA / Q000378:metabolism*; D004268:DNA-Binding Proteins / Q000378:metabolism*; D006410:Hematopoiesis; D018398:Homeodomain Proteins / Q000378:metabolism*; D051379:Mice; D008969:Molecular Sequence Data; D000075062:Pre-B-Cell Leukemia Transcription Factor 1; D011518:Proto-Oncogene Proteins / Q000378:metabolism*; D014157:Transcription Factors / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism*; D015533:Transcriptional Activation / Q000187:drug effects; D014162:Transfection
D051792:Basic Helix-Loop-Helix Proteins; D056970:Co-Repressor Proteins; D004247:DNA; D004268:DNA-Binding Proteins; D018398:Homeodomain Proteins; D000075062:Pre-B-Cell Leukemia Transcription Factor 1; D011518:Proto-Oncogene Proteins; D014157:Transcription Factors; C413449:PBXIP1 protein, human; C407909:TCF3 protein, human; C083400:PBX1 protein, human