Cysteine 50 of the POU H domain determines the range of targets recognized by POU proteins

GSK3 Kinase Inhibitor, CHIR, Suppress Transcription of Tissue Specific POU2F1 Isoform in Burkitt Namalwa Lymphoma Cells

POU2F1 (Oct-1) is a transcription factor, the overexpression of which is found in many human malignant tumors; a significant increase in its level in cells determines the malignant potential of the tumor. POU2F1 is represented in cells by several isoforms that are transcribed from alternative promoters. In Burkitt's B-cell lymphoma Namalwa, the concentration of tissue-specific isoform Oct-1L is several times higher than in normal B cells. We tested the potential to inhibit the transcription of individual Oct-1 isoforms using the GSK3 kinase inhibitor CHIR, an aminopyrimidine derivative. We have shown that CHIR specifically affects the expression of the tissue-specific isoform Oct-1L, significantly reducing the level of mRNA and Oct-1L protein. However, CHIR does not change the amount of mRNA and protein of the ubiquitous isoform Oct-1A in Namalwa tumor cells. The results obtained show that it is possible to develop a system for selective inhibition of Oct-1 transcription factor isoforms in human cells to suppress drug resistance of tumor cells with a high POU2F1 content.

Differentiation of Monocytic Cells Is Accompanied by a Change in the Expression of the Set of Oct-1 Isoforms

Changes in the expression level of Oct-1A, Oct-1L, Oct-1X, and Oct-1Z isoforms and CD14 surface antigen during differentiation of HL-60 monocytic cells induced in vitro by dimethyl sulfoxide were studied, and the expression level of the four Oct-1 isoforms in vivo in human monocytes was determined.

The regulatory interplay between Oct-1 isoforms contributes to hematopoiesis and the isoforms imbalance correlates with a malignant transformation of B cells

Oct-1(POU2F1) is a DNA-binding transcription regulator and its level being highly increased in many human cancers. Oct-1 is present in the human cells as a family of functionally different isoforms which are transcribed from alternative promoters. Here, we have demonstrated that expression patterns of Oct-1 isoforms change during differentiation of hematopoetic progenitor cells (CD34+) (HPCs) to the B (CD19+) and T (CD3+) cells. While Oct-1L is expressed at a high level in the CD34+ HPCs, its expression level drops dramatically during the T-cell differentiation, although remains nearly the same in B-cells. We have described the novel human Oct-1R isoform which is conserved in mammals and is B cell-specific. Oct-1R was found in B cells, but not in HPCs. Oct-1R is transcribed from the same promoter as Oct-1L, another lymphocyte-specific isoform. Overexpression of Oct-1R and Oct-1L in the Namalwa cells leads to the repression of many genes involved in B-lymphocyte differentiation and signal transduction. Thus these isoforms may regulate the particular stages of development of normal B cells and maintain their proper differentiation status. However the extremely high level of Oct-1L isoform observed in the B-lymphoblast tumor cell lines indicated that the excess of Oct-L seem likely to considerably decrease the differentiation ability of these cells. Oct-1 may serve as a therapeutic target for many tumors, but it should be noted that in a tumor the content of a certain isoform Oct-1, rather than the total Oct-1 protein, can be increased.

Different N-terminal isoforms of Oct-1 control expression of distinct sets of genes and their high levels in Namalwa Burkitt's lymphoma cells affect a wide range of cellular processes

Oct-1 transcription factor has various functions in gene regulation. Its expression level is increased in several types of cancer and is associated with poor survival prognosis. Here we identified distinct Oct-1 protein isoforms in human cells and compared gene expression patterns and functions for Oct-1A, Oct-1L, and Oct-1X isoforms that differ by their N-terminal sequences. The longest isoform, Oct-1A, is abundantly expressed and is the main Oct-1 isoform in most of human tissues. The Oct-1L and the weakly expressed Oct-1X regulate the majority of Oct-1A targets as well as additional sets of genes. Oct-1X controls genes involved in DNA replication, DNA repair, RNA processing, and cellular response to stress. The high level of Oct-1 isoforms upregulates genes related to cell cycle progression and activates proliferation both in Namalwa Burkitt's lymphoma cells and primary human fibroblasts. It downregulates expression of genes related to antigen processing and presentation, cytokine-cytokine receptor interaction, oxidative metabolism, and cell adhesion, thus facilitating pro-oncogenic processes.

The role of the annexin A2 heterotetramer in vascular fibrinolysis

The vascular endothelial cells line the inner surface of blood vessels and function to maintain blood fluidity by producing the protease plasmin that removes blood clots from the vasculature, a process called fibrinolysis. Plasminogen receptors play a central role in the regulation of plasmin activity. The protein complex annexin A2 heterotetramer (AIIt) is an important plasminogen receptor at the surface of the endothelial cell. AIIt is composed of 2 molecules of annexin A2 (ANXA2) bound together by a dimer of the protein S100A10. Recent work performed by our laboratory allowed us to clarify the specific roles played by ANXA2 and S100A10 subunits within the AIIt complex, which has been the subject of debate for many years. The ANXA2 subunit of AIIt functions to stabilize and anchor S100A10 to the plasma membrane, whereas the S100A10 subunit initiates the fibrinolytic cascade by colocalizing with the urokinase type plasminogen activator and receptor complex and also providing a common binding site for both tissue-type plasminogen activator and plasminogen via its C-terminal lysine residue. The AIIt mediated colocalization of the plasminogen activators with plasminogen results in the rapid and localized generation of plasmin to the endothelial cell surface, thereby regulating fibrinolysis.

Multiple core homeodomain binding motifs differentially contribute to transcriptional activity of the murine gonadotropin-releasing hormone receptor gene promoter

Multiple homeodomain (Hbox) proteins have been shown to organize expression of key markers of gonadotropes. Nine putative Hbox-binding sites, characterized by the homeospecific TAAT motif, are located within the proximal 600 bp of the murine GnRHR promoter. Homeoproteins bind separate Hbox sites within this promoter, supporting basal- and endocrine-directed transcription. The function of the most proximal sites (Hbox1 and Hbox2) in the murine GnRHR is unknown; thus, understanding of the global contribution of homeospecific TAAT sites to promoter function is incomplete. Site-directed mutagenesis revealed that loss of Hbox2 reduced promoter activity in a cell-specific manner, having no effect in alphaT3-1 cells but reducing promoter function in LbetaT2 cells, another gonadotrope-derived cell line representing a later developmental stage. In contrast, eliminating Hbox1 reduced basal activity in both lines. This region displayed specific binding to homeoprotein Oct-1. Mutagenesis of a previously identified Oct-1-binding site in concert with Hbox1 led to further reduction in activity. We suggest that the two most proximal homeodomain-binding sites in the murine GnRHR promoter may regulate the promoter in a developmentally dependent fashion and that Oct-1 acts at multiple but distinct TAAT sites to support basal transcription.

Ancient linkage of a POU class 6 and an anterior hox-like gene in cnidaria: implications for the evolution of homeobox genes

Linkage analyses in metazoan genomes suggest two ancestral arrays for the majority of homeobox genes. The related homeobox genes and chromosomal regions that are dispersed in extant species derived possibly from only two single common ancestor regions. One proposed ancestral array, designated as ANTP mega-array, contains most of the ANTP class homeobox genes; the second, named the contraHox super-paralogon, would consist of the classes PRD, POU, LIM, CUT, prospero, TALE and SIX. Here, we report the tight linkage of a POU class 6 gene to an anterior Hox-like gene in the hydrozoan Eleutheria dichotoma and discuss its possible significance for the evolution of homeobox genes. POU class 6 genes also seem to be ancestrally linked to the HoxC and A clusters in vertebrates, despite POU homeobox genes belonging to the contraHox paralogon. Hence, the much tighter linkage of a POU class 6 gene to an anterior Hox-like gene in a cnidarian is possibly the evolutionary echo of an ancestral genomic region from which most metazoan homeobox classes emerged.

Autoregulation of Oct-1 gene expression is mediated by two octa-sites in alternative promoter

Transcription of the oct-1 gene is regulated by two alternative promoters: U promoter and L promoter located upstream of the exons 1U and 1L, respectively. The L promoter contains two octamer sequences of opposite orientation: proximal (ATTTGCAT) and distal (ATGCAAAT), showing high affinity toward the Oct proteins. Binding of the Oct-1 protein to the octa-sites located in the L promoter region has been confirmed in footprinting experiments. Dual luciferase assay using wild-type and mutated promoters have indicated that mutations in the proximal octa-site resulted in significant transcription enhancement both in myeloma cell line NS/0 and in fibroblast cell line 3T3 (about twofold and fivefold, respectively), whereas mutations in the distal site decreased the promoter activity (about 10% and 40%, respectively). Mutations in both octa-sites enhanced the effect and increased transcription to about fourfold in myeloma cell line NS/0 and about sixfold in fibroblast cell line 3T3. These results demonstrate that transcription of the oct-1 gene may be autoregulated by two octa-sites within the L promoter. Different function and interactive tissue-specific effect of distal and proximal octamer sequences can be suggested.

Mohawkis a novel homeobox gene expressed in the developing mouse embryo

Homeodomain-containing proteins comprise a superfamily of transcription factors that participate in the regulation of almost all aspects of embryonic development. Here, we describe the mouse embryonic expression pattern of Mohawk, a new member of the TALE superclass of atypical homeobox genes that is most-closely related to the Iroquois class. During mouse development, Mohawk was transcribed in cell lineages derived from the somites. As early as embryonic day 9.0, Mohawk was expressed in an anterior to posterior gradient in the dorsomedial and ventrolateral lips of the dermomyotome of the somites that normally give rise to skeletal muscle. Mohawk transcription in the dorsomedial region required the expression of the transcription factor paraxis. As somites matured, Mohawk transcription was observed in the tendon-specific syndetome and the sclerotome-derived condensing mesenchyme that prefigures the proximal ribs and vertebral bodies. In the limbs, Mohawk was expressed in a pattern consistent with the developing tendons that form along the dorsal and ventral aspect of the phalanges. Finally, Mohawk was detectable in the tips of the ureteric buds in the metanephric kidneys and the testis cords of the male gonad. Together, these observations suggest that Mohawk is an important regulator of vertebrate development.

The regulation of the Oct-1 gene transcription is mediated by two promoters

The ubiquitous transcription factor Oct-1 is a member of the POU domain family of regulatory proteins. Target genes controlled by Oct-1 include housekeeping genes, e.g. the genes encoding histon H2B or snRNAs, as well as tissue-specific genes, e.g. the genes encoding the light and heavy chains of immunoglobulines, some interleukins, and others. Oct-1 pre-mRNA may be spliced in several ways, resulting in production of several protein isoforms that may differ functionally. The 5'-end of the Oct-1 gene contains two exons-exon 1U and exon 1L that alternatively present in Oct-1 mRNA. We studied regulation of transcription of the Oct-1 gene using reporter gene assays of promoter-luciferase gene-constructs. It was shown that transcription of the Oct-1 gene is regulated by two promoters located upstream of the exon 1U and upstream of the exon 1L. The promoter located upstream of the exon 1U contains G/C-rich sequences and multiple Sp1 sites, while the promoter located upstream of the exon 1L contains A/T-rich motifs and autoregulation-related cis-elements: two octamer sites ATGCAAAT, two octamer related sites and multiple TAAT-core sites. Exons 1U and 1L in the human OTF-1 locus encoding the Oct-1 gene are located at the distance of 108 kbp. In the murine locus otf-1 the distance between exons 1U and 1L is 67 kbp. We suggest that the two promoters can differ functionally.

Androgen receptor interactions with Oct-1 and Brn-1 are physically and functionally distinct

POU domain proteins interact positively or negatively with steroid hormone receptors, depending on the precise array of these and other factors assembled on target gene promoters. Octamer transcription factor 1 (Oct-1), a ubiquitous POU factor, is implicated in androgen induction of the mouse sex-limited protein (Slp) gene based on protein-DNA interaction studies. However, direct evidence for a role of Oct-1 in the hormone response has been difficult to obtain. Brain 1 (Brn-1), another POU factor, is more tissue-specific, expressing in brain and also in kidney, which is a major site of Slp synthesis. We compared the interaction of the androgen receptor (AR) with Oct-1 and Brn-1 to reveal the more likely candidate for regulation of Slp. In transfection, addition of either Oct-1 or Brn-1 reduced AR activation, regardless of the presence of an octamer-like sequence in the enhancer, suggesting interference was indirect. However, when the octamer-like element was changed to a consensus octamer site, Brn-1, but not Oct-1, strongly enhanced androgen activation. This correlated with Brn-l's preference for the consensus octamer sequence in DNA binding assays. Direct interaction of AR with glutathione-S-transferase-(GST)-fused Oct-1 was DNA-dependent, while Brn-l-AR association was not. Chimeric Brn-1 and Oct-1 POU domains demonstrated that the DNA-dependent AR interaction relied on the origin of the POU homeodomain. However, in the context of full-length Brn-1 and Oct-1 chimeric proteins, the POU homedomain was not sufficient to confer the distinct behaviors of these factors in vivo, but instead revealed the importance of an N-terminal transactivation domain in Brn-1. These results demonstrate that functional interaction of Oct-1 and Brn-1 with AR is determined by the precise sequence of the octamer binding site, and by differential interaction of the POU factors with AR and other components of the transcriptional machinery.

The activity of the human interleukin-5 conserved lymphokine element 0 is regulated by octamer factors in human cells

Interleukin-5 (IL-5) controls the development of eosinophilia and contributes to a number of disease states including asthma. Expression of IL-5 is inducible under tight transcriptional regulation. This requires the contribution of several promoter elements; however, the conserved lymphokine element 0 (CLE0) in particular, is essential for expression of IL-5. In this study, we report the nuclear factors which regulate human IL-5 CLE0 activity in the human cell line PER-117. Using specific antibodies, we identified the transcriptional factors Oct-1 and Oct-2 binding to the 5' region of the CLE0 element. The involvement of Oct factors with CLE0 has not been reported previously in any of the lymphokines. In addition, the CLE0 element also appeared to complex with the transcriptional activator AP-1, consisting of the family members Jun D and Fra-2. We observed the binding of Oct-1 to be constitutive in comparison to Oct-2 and AP-1, both of which were induced in response to cell activation by PMA/A23187. Although the interaction of all three factors with CLE0 was closely linked and overlapping, residues critical to their binding were identified. We demonstrate, using site-directed mutagenesis and cotransfection experiments, that the CLE0 element is indispensable for IL-5 promoter activity and that Octamer factors contribute to the positive regulation of the hIL-5 gene.

OC-2, a novel mammalian member of the ONECUT class of homeodomain transcription factors whose function in liver partially overlaps with that of hepatocyte nuclear factor-6

Transcription factors of the ONECUT class, whose prototype is hepatocyte nuclear factor (HNF)-6, are characterized by the presence of a single cut domain and by a peculiar homeodomain (Lannoy, V. J., Bürglin, T. R., Rousseau, G. G., and Lemaigre, F. P. (1998) J. Biol. Chem. 273, 13552-13562). We report here the identification and characterization of human OC-2, the second mammalian member of this class. The OC-2 gene is located on human chromosome 18. The distribution of OC-2 mRNA in humans is tissue-restricted, the strongest expression being detected in the liver and skin. The amino acid sequence of OC-2 contains several regions of high similarity to HNF-6. The recognition properties of OC-2 for binding sites present in regulatory regions of liver-expressed genes differ from, but overlap with, those of HNF-6. Like HNF-6, OC-2 stimulates transcription of the hnf-3beta gene in transient transfection experiments, suggesting that OC-2 participates in the network of transcription factors required for liver differentiation and metabolism.

Isoforms of hepatocyte nuclear factor-6 differ in DNA-binding properties, contain a bifunctional homeodomain, and define the new ONECUT class of homeodomain proteins

Hepatocyte nuclear factor-6 (HNF-6) contains a single cut domain and a homeodomain characterized by a phenylalanine at position 48 and a methionine at position 50. We describe here two isoforms of HNF-6 which differ by the linker that separates these domains. Both isoforms stimulated transcription. The affinity of HNF-6alpha and HNF-6beta for DNA differed, depending on the target sequence. Binding of HNF-6 to DNA involved the cut domain and the homeodomain, but the latter was not required for binding to a subset of sites. Mutations of the F48M50 dyad that did not affect DNA binding reduced the transcriptional stimulation of constructs that do not require the homeodomain for DNA binding, but did not affect the stimulation of constructs that do require the homeodomain. Comparative trees of mammalian, Drosophila, and Caenorhabditis elegans proteins showed that HNF-6 defines a new class, which we call ONECUT, of homeodomain proteins. C. elegans proteins of this class bound to HNF-6 DNA targets. Thus, depending on their sequence, these targets determine for HNF-6 at least two modes of DNA binding, which hinge on the homeodomain and on the linker that separates it from the cut domain, and two modes of transcriptional stimulation, which hinge on the homeodomain.

Oct-1 promoter region contains octamer sites and TAAT motifs recognized by Oct proteins

The 5'-upstream region (1.3 kb) of the gene encoding the POU domain transcription factor Oct-1 was cloned and sequenced. CAT reporter gene analysis of this region has detected a functionally active promoter. This region contains 24 TAAT-core sites, arranged in five clusters (four to six sites in one cluster); two octamer sites (ATGCAAAT) are located in the first and second clusters; in the second one the CCAAT-box adjacent to the octamer overlaps with the TAAT-core site. As shown by gel retardation assay, Oct-1, Oct-2, and some unknown proteins from myeloma cell line NS/0 interact with the TAAT-core sites of these clusters. The results suggest autoregulation of Oct-1 gene expression that may also be controlled by other POU proteins, homeodomain proteins and CCAAT trans-action factors.