Identification of a HoxA10 Activation Domain Necessary for Transcription of the Gene Encoding β3 Integrin during Myeloid Differentiation

Abstract

Transcription of the ITGB3 gene, which encodes ␤3 integrin, increases during myeloid differentiation. ␣v␤3 integrin mediates adhesion to fibronectin or vitronectin and regulates various aspects of the inflammatory response in mature phagocytes. In these studies, we found that the homeodomain transcription factor HoxA10 interacted with a specific ITGB3 cis element and activated transcription of this gene during myeloid differentiation. We also found that increased fibronectin adhesion in differentiating myeloid cells was dependent upon this HoxA10-induced increase in ␤3 integrin expression. We determined that activation of ITGB3 transcription required a HoxA10 domain that was not identical to the "hexapeptide" that mediates interaction of Hox and Pbx proteins. This activation domain was also not identical to a previously identified HoxA10 repression domain that mediates interaction with transcriptional co-repressors. Instead, this HoxA10 activation domain had homology to "PQ" protein-protein interaction domains that have been described previously in other transcription factors. Consistent with this, we found that the HoxA10 PQ-like domain recruited the CREB-binding protein (CBP) to the ITGB3 promoter. This was associated with an increase in local histone acetylation in vivo. In immature myeloid cells, we previously determined that HoxA10 repressed transcription of the CYBB and NCF2 genes, which encode the phagocyte oxidase proteins gp91 PHOX and p67 PHOX , respectively. Therefore, our studies indicated that HoxA10 either activates or represses gene transcription at various points during myelopoiesis. Our studies also suggested that HoxA10 is a bifunctional protein that is involved in dynamic regulation of multiple aspects of phagocyte phenotype and function.

HoxA10 Protein Regulates Transcription of Gene Encoding Fibroblast Growth Factor 2 (FGF2) in Myeloid Cells

“…We also found that HoxA10 activates ITGB3 transcription in myeloid progenitor cells and differentiating phagocytes (the gene encoding ␤3 integrin) (20). Our studies suggested that increased ␣v␤3 integrin in HoxA10-overexpressing myeloid progenitor cells facilitated expansion of these cells via interaction with vitronectin and fibronectin in bone marrow stroma.…”

“…Our studies suggested that increased ␣v␤3 integrin in HoxA10-overexpressing myeloid progenitor cells facilitated expansion of these cells via interaction with vitronectin and fibronectin in bone marrow stroma. Increased ␣v␤3 integrin expression on HoxA10-overexpressing myeloid progenitor cells leads to an increase in activation of Syk protein-tyrosine kinase, substantiating this hypothesis (20).…”

The Leukemia-associated Mll-Ell Oncoprotein Induces Fibroblast Growth Factor 2 (Fgf2)-dependent Cytokine Hypersensitivity in Myeloid Progenitor Cells

“…The HoxA9 cDNA was generated by reverse transcription and PCR from U937 cells as described (37). These cDNAs were subcloned into the mammalian expression vector pcDNAamp (Invitrogen) and the murine retroviral vector pMSCVpuro (Clontech, Mountain View, CA), as described (21,22). A vector with the Mll-Ell fusion protein was obtained from D. E. Zhang (University of California, San Diego, CA).…”

“…Oligonucleotides probes were prepared, and DNA binding was analyzed by electrophoretic mobility shift assay (EMSA) and DNA affinity purification techniques as described (18,(21)(22)(23)(24)(25)(26). For EMSA, antibody to HoxA9 or HoxA10 (or irrelevant control antibody) was included in binding assays.…”

“…We used chromatin immunoprecipitation-based screening techniques to identify HoxA10 target genes that might be relevant to leukemogenesis (21)(22)(23)(24)(25)(26). In these studies we identified the gene encoding fibroblast growth factor 2 (Fgf2, or basic Fgf) as a HoxA10 target gene (26).…”