Targeted disruption of the CP2 gene, a member of the NTF family of transcription factors

TFCP2 is a transcriptional regulator of heparan sulfate assembly and melanoma cell growth

Heparan sulfate (HS) is a long, linear polysaccharide that is ubiquitously expressed in all animal cells and plays a key role in many cellular processes, including cell signaling and development. Dysregulation of HS assembly has been implicated in pathophysiological conditions, such as tumorigenesis and rare genetic disorders. HS biosynthesis occurs in a non-template-driven manner in the endoplasmic reticulum and Golgi through the activity of a large group of biosynthetic enzymes. While much is known about its biosynthesis, little is understood about the regulation of HS assembly across diverse tissue types and disease states. To address this gap in knowledge, we recently performed genome-wide CRISPR/Cas9 screens to identify novel regulatory factors of HS biosynthesis. From these screens, we identified the alpha globin transcription factor, TFCP2, as a top hit. To investigate the role of TFCP2 in HS assembly, we targeted TFCP2 expression in human melanoma cells using the CRISPR/Cas9 system. TFCP2 knockout cells exhibited decreased fibroblast growth factor binding to cell surface HS, alterations in HS composition, and slowed cell growth compared to wild-type cells. Additionally, RNA sequencing revealed that TFCP2 regulates the expression of multiple enzymes involved in HS assembly, including the secreted endosulfatase, SULF1. Pharmacological targeting of TFCP2 activity similarly reduced growth factor binding and increased SULF1 expression, and the knockdown of SULF1 expression in TFCP2 mutant cells restored melanoma cell growth. Overall, these studies identify TFCP2 as a novel transcriptional regulator of HS and highlight HS-protein interactions as a possible target to slow melanoma growth.

Transcription factor cellular promoter 2 is required for upstream binding protein 1 -mediated angiogenesis

OBJECTIVE

Angiogenesis is a key process of repairing tissue damage, and it is regulated by the delicate balance between anti-angiogenesis factors. In the present study, we investigate whether transcription factor cellular promoter 2 (TFCP2) is required for upstream binding protein 1 (UBP1)-mediated angiogenesis.

METHODS

Levels of UBP1 and TFCP2 in human umbilical vein endothelial cells (HUVECs) are detected by quantitative polymerase chain reaction (q-PCR) and Western blotting (WB). Effects of UBP1 on angiogenesis and migration are detected by tube-like network formation on matrigel assay and scratch assay. The interaction between UBP1 and TFCP2 is predicted and verified by STRING and Co-immunoprecipitation (Co-IP).

RESULTS

Firstly, the UBP1 expression level was up-regulated in the stimuli of vascular endothelial growth factor (VEGF) in HUVECs, and the knockdown of UBP1 inhibited angiogenesis and migration of HUVECs. Then, UBP1 interacted with TFCP2. Besides, the TFCP2 expression level was up-regulated in VEGF-stimulated HUVECs. Furthermore, knockdown of TFCP2 inhibited angiogenesis and migration in VEGF-stimulated HUVECs, and down-regulation of UBP1 enhanced the inhibition.

CONCLUSION

TFCP2 also plays a key role in UBP1 mediated angiogenesis of HUVECs stimulated by VEGF. These findings will provide a new theoretical basis for the treatment of angiogenic diseases.

Targeting the oncogene LSF with either the small molecule inhibitor FQI1 or siRNA causes mitotic delays with unaligned chromosomes, resulting in cell death or senescence

BACKGROUND

The oncogene LSF (encoded by TFCP2) has been proposed as a novel therapeutic target for multiple cancers. LSF overexpression in patient tumors correlates with poor prognosis in particular for both hepatocellular carcinoma and colorectal cancer. The limited treatment outcomes for these diseases and disappointing clinical results, in particular, for hepatocellular carcinoma in molecularly targeted therapies targeting cellular receptors and kinases, underscore the need for molecularly targeting novel mechanisms. LSF small molecule inhibitors, Factor Quinolinone Inhibitors (FQIs), have exhibited robust anti-tumor activity in multiple pre-clinical models, with no observable toxicity.

METHODS

To understand how the LSF inhibitors impact cancer cell proliferation, we characterized the cellular phenotypes that result from loss of LSF activity. Cell proliferation and cell cycle progression were analyzed, using HeLa cells as a model cancer cell line responsive to FQI1. Cell cycle progression was studied either by time lapse microscopy or by bulk synchronization of cell populations to ensure accuracy in interpretation of the outcomes. In order to test for biological specificity of targeting LSF by FQI1, results were compared after treatment with either FQI1 or siRNA targeting LSF.

RESULTS

Highly similar cellular phenotypes are observed upon treatments with FQI1 and siRNA targeting LSF. Along with similar effects on two cellular biomarkers, inhibition of LSF activity by either mechanism induced a strong delay or arrest prior to metaphase as cells progressed through mitosis, with condensed, but unaligned, chromosomes. This mitotic disruption in both cases resulted in improper cellular division leading to multiple outcomes: multi-nucleation, apoptosis, and cellular senescence.

CONCLUSIONS

These data strongly support that cellular phenotypes observed upon FQI1 treatment are due specifically to the loss of LSF activity. Specific inhibition of LSF by either small molecules or siRNA results in severe mitotic defects, leading to cell death or senescence - consequences that are desirable in combating cancer. Taken together, these findings confirm that LSF is a promising target for cancer treatment. Furthermore, this study provides further support for developing FQIs or other LSF inhibitory strategies as treatment for LSF-related cancers with high unmet medical needs.

Grainyhead-like Protein 2: The Emerging Role in Hormone-Dependent Cancers and Epigenetics

In mammals, the grainyhead-like transcription factor (GRHL) family is composed of three nuclear proteins that are responsible for driving epithelial cell fate: GRHL1, GRHL2, and GRHL3. GRHL2 is important in maintaining proper tubulogenesis during development and in suppressing the epithelial-to-mesenchymal transition. Within the last decade, evidence indicates both tumor-suppressive and oncogenic roles for GRHL2 in various types of cancers. Recent studies suggest that GRHL2 may be especially important in hormone-dependent cancers, as correlative relationships exist between GRHL2 and various steroid receptors, such as the androgen and estrogen receptors. Acting as a pioneer factor and coactivator, GRHL2 may directly affect steroid receptor transcriptional activity. This review will highlight recent discoveries of GRHL2 activity in cancer and in maintaining the epithelial state, while also exploring recent literature on the role of GRHL2 in hormone-dependent cancers and epigenetics.

Neglected Functions of TFCP2/TFCP2L1/UBP1 Transcription Factors May Offer Valuable Insights into Their Mechanisms of Action

In recent years, the TFCP2 (transcription factor cellular promoter 2)/TFCP2L1 (TFCP2-like 1)/UBP1 (upstream binding protein 1) subfamily of transcription factors has been attracting increasing attention in the scientific community. These factors are very important in cancer, Alzheimer’s disease, and other human conditions, and they can be attractive targets for drug development. However, the interpretation of experimental results is complicated, as in principle, any of these factors could substitute for the lack of another. Thus, studying their hitherto little known functions should enhance our understanding of mechanisms of their functioning, and analogous mechanisms might govern their functioning in medically relevant contexts. For example, there are numerous parallels between placental development and cancer growth; therefore, investigating the roles of TFCP2, TFCP2L1, and UBP1 in the placenta may help us better understand their functioning in cancer, as is evidenced by the studies of various other proteins and pathways. Our review article aims to call the attention of the scientific community to these neglected functions, and encourage further research in this field. Here, we present a systematic review of current knowledge of the TFCP2/TFCP2L1/UBP1 subfamily in reproduction, embryonic development, renal function, blood-pressure regulation, brain function, and other processes, where their involvement has not been studied much until now.

TFCP2/TFCP2L1/UBP1 transcription factors in cancer

The TFCP2/Grainyhead family of transcription factors is divided into two distinct subfamilies, one of which includes the Grainyhead-like 1-3 (GRHL1-3) proteins and the other consists of TFCP2 (synonyms: CP2, LSF, LBP-1c), TFCP2L1 (synonyms: CRTR-1, LBP-9) and UBP1 (synonyms: LBP-1a, NF2d9). Transcription factors from the TFCP2/TFCP2L1/UBP1 subfamily are involved in various aspects of cancer development. TFCP2 is a pro-oncogenic factor in hepatocellular carcinoma, pancreatic cancer and breast cancer, may be important in cervical carcinogenesis and in colorectal cancer. TFCP2 can also act as a tumor suppressor, for example, it inhibits melanoma growth. Furthermore, TFCP2 is involved in epithelial-mesenchymal transition and enhances angiogenesis. TFCP2L1 maintains pluripotency and self-renewal of embryonic stem cells and was implicated in a wide variety of cancers, including clear cell renal cell carcinoma, breast cancer and thyroid cancer. Here we present a systematic review of current knowledge of this protein subfamily in the context of cancer. We also discuss potential challenges in investigating this family of transcription factors. These challenges include redundancies between these factors as well as their interactions with each other and their ability to modulate each other's activity.

Expression of TSG101 protein and LSF transcription factor in HPV-positive cervical cancer cells

Our previous study demonstrated a decreased expression of tumor susceptibility gene 101 (TSG101) in cervical cancer cells. To identify the mechanism responsible for TSG101 downregulation during cervical cancer development, we analyzed the TSG101 promoter using cis-element cluster finder software. One of the transcription factors whose binding site was detected in the TSG101 promoter was late SV40 factor (LSF). The aim of this study was to analyze the TSG101 protein and LSF expression levels during cervical cancer development. Immunohistochemical analysis confirmed a previously observed decreased expression of TSG101, whereas quantitative polymerase chain reaction (qPCR) and immunohistochemistry analysis revealed high expression of LSF in cervical, precancer and cancer cells compared with human papillomavirus (HPV)-negative non-cancer samples. High expression of LSF in cervical cancer HPV-positive cells suggests that this protein may be important in the regulation of TSG101 expression, as well as in cervical carcinogenesis. The role of LSF as a mediator in cervical cancer development must be confirmed in future studies.

Purification and characterization of transcription factors

Transcription factors (TFs) are essential for the expression of all proteins, including those involved in human health and disease. However, TFs are resistant to proteomic characterization because they are frequently masked by more abundant proteins due to the limited dynamic range of capillary liquid chromatography-tandem mass spectrometry and protein database searching. Purification methods, particularly strategies that exploit the high affinity of TFs for DNA response elements (REs) on gene promoters, can enrich TFs prior to proteomic analysis to improve dynamic range and penetrance of the TF proteome. For example, trapping of TF complexes specific for particular REs has been achieved by recovering the element DNA-protein complex on solid supports. Additional methods for improving dynamic range include two- and three-dimensional gel electrophoresis incorporating electrophoretic mobility shift assays and Southwestern blotting for detection. Here we review methods for TF purification and characterization. We fully expect that future investigations will apply these and other methods to illuminate this important but challenging proteome.

Zebrafish grainyhead-like1 is a common marker of different non-keratinocyte epidermal cell lineages, which segregate from each other in a Foxi3-dependent manner

Grainyhead/CP2 transcription factor family members are widely conserved among the animal kingdom and have been implicated in different developmental processes. Thus far, nothing has been known about their roles in zebrafish. Here we identify seven zebrafish grainyhead-like (grhl) / cp2 genes, with focus on grhl1, which is expressed in the periderm and in epidermal ionocyte progenitors, but downregulated when ionocytes differentiate. In addition, expression was detected in other "non-keratinocyte" cell types of the epidermis, such as pvalb8-expressing cells, which according to our lineage tracing experiments are derived from the same pool of progenitor cells like keratinocytes and ionocytes. Antisense morpholino oligonucleotide-based loss-of-function analysis revealed that grhl1 is dispensable for the development and function of all investigated epidermal cell types, but required as a negative regulator of its own transcription during ionocyte differentiation. Knockdown of the transcription factor Foxi3a, which is expressed in a subset of the grhl1 population, caused a loss of ionocytes and a corresponding increase in the number of pvalb8-expressing cells, while leaving the number of grhl1-positive cells unaltered. We propose that grhl1 is a novel common marker of all or most "non-keratinocyte" epidermal progenitors, and that the sub-functionalisation of these cells is regulated by differential positive and negative effects of Foxi3 factors.

The evolutionary diversification of LSF and Grainyhead transcription factors preceded the radiation of basal animal lineages

Background

The transcription factors of the LSF/Grainyhead (GRH) family are characterized by the possession of a distinctive DNA-binding domain that bears no clear relationship to other known DNA-binding domains, with the possible exception of the p53 core domain. In triploblastic animals, the LSF and GRH subfamilies have diverged extensively with respect to their biological roles, general expression patterns, and mechanism of DNA binding. For example, Grainyhead (GRH) homologs are expressed primarily in the epidermis, and they appear to play an ancient role in maintaining the epidermal barrier. By contrast, LSF homologs are more widely expressed, and they regulate general cellular functions such as cell cycle progression and survival in addition to cell-lineage specific gene expression.

Results

To illuminate the early evolution of this family and reconstruct the functional divergence of LSF and GRH, we compared homologs from 18 phylogenetically diverse taxa, including four basal animals (Nematostella vectensis, Vallicula multiformis, Trichoplax adhaerens, and Amphimedon queenslandica), a choanoflagellate (Monosiga brevicollis) and several fungi. Phylogenetic and bioinformatic analyses of these sequences indicate that (1) the LSF/GRH gene family originated prior to the animal-fungal divergence, and (2) the functional diversification of the LSF and GRH subfamilies occurred prior to the divergence between sponges and eumetazoans. Aspects of the domain architecture of LSF/GRH proteins are well conserved between fungi, choanoflagellates, and metazoans, though within the Metazoa, the LSF and GRH families are clearly distinct. We failed to identify a convincing LSF/GRH homolog in the sequenced genomes of the algae Volvox carteri and Chlamydomonas reinhardtii or the amoebozoan Dictyostelium purpureum. Interestingly, the ancestral GRH locus has become split into two separate loci in the sea anemone Nematostella, with one locus encoding a DNA binding domain and the other locus encoding the dimerization domain.

Conclusions

In metazoans, LSF and GRH proteins play a number of roles that are essential to achieving and maintaining multicellularity. It is now clear that this protein family already existed in the unicellular ancestor of animals, choanoflagellates, and fungi. However, the diversification of distinct LSF and GRH subfamilies appears to be a metazoan invention. Given the conserved role of GRH in maintaining epithelial integrity in vertebrates, insects, and nematodes, it is noteworthy that the evolutionary origin of Grh appears roughly coincident with the evolutionary origin of the epithelium.

Functional annotation of novel lineage-specific genes using co-expression and promoter analysis

Background

The diversity of placental architectures within and among mammalian orders is believed to be the result of adaptive evolution. Although, the genetic basis for these differences is unknown, some may arise from rapidly diverging and lineage-specific genes. Previously, we identified 91 novel lineage-specific transcripts (LSTs) from a cow term-placenta cDNA library, which are excellent candidates for adaptive placental functions acquired by the ruminant lineage. The aim of the present study was to infer functions of previously uncharacterized lineage-specific genes (LSGs) using co-expression, promoter, pathway and network analysis.

Results

Clusters of co-expressed genes preferentially expressed in liver, placenta and thymus were found using 49 previously uncharacterized LSTs as seeds. Over-represented composite transcription factor binding sites (TFBS) in promoters of clustered LSGs and known genes were then identified computationally. Functions were inferred for nine previously uncharacterized LSGs using co-expression analysis and pathway analysis tools. Our results predict that these LSGs may function in cell signaling, glycerophospholipid/fatty acid metabolism, protein trafficking, regulatory processes in the nucleus, and processes that initiate parturition and immune system development.

Conclusions

The placenta is a rich source of lineage-specific genes that function in the adaptive evolution of placental architecture and functions. We have shown that co-expression, promoter, and gene network analyses are useful methods to infer functions of LSGs with heretofore unknown functions. Our results indicate that many LSGs are involved in cellular recognition and developmental processes. Furthermore, they provide guidance for experimental approaches to validate the functions of LSGs and to study their evolution.

Transactivation activity of LBP-1 proteins and their dimerization in living cells

LBP-1 proteins form dimers and act as transcription factors that activate a number of genes related to cell growth and differentiation. LBP-1a and LBP-1c are localized in the cytoplasm when transiently expressed in cultured cells, but translocated into the nucleus after forming heterodimers with LBP-1b, which is a splicing variant of LBP-1a with an intrinsic nuclear localization signal (NLS). Here, we report that LBP-1b showed potent transactivation activity, and that forcibly expressed LBP-1a and LBP-1c in the nucleus essentially exhibited very little or no transactivation activity. Mutations in the NLS that abolished the NLS activity of LBP-1b also abrogated the transactivation activity. We have found that LBP-1 proteins contain a putative sterile alpha motif domain indispensable for their dimerization capability in the C-terminal region. To demonstrate whether homo- and heterodimers composed of LBP-1a and/or LBP-1c are generated in the nucleus, we applied the FLIM-based fluorescence resonance energy transfer imaging technique to living cells. It revealed that dimers composed of LBP-1a and LBP-1c were re-formed probably by a partner-exchange of LBP-1b-containing heterodimers.

Transcription factors LSF and E2Fs: tandem cyclists driving G0 to S?

Cell cycle progression in mammalian cells from G(1) into S phase requires sensing and integration of multiple inputs, in order to determine whether to continue to cellular DNA replication and subsequently, to cell division. Passage to S requires transition through the restriction point, which at a molecular level consists of a bistable switch involving E2Fs and pRb family members. At the G(1)/S boundary, a number of genes essential for DNA replication and cell cycle progression are upregulated, promoting entry into S phase. Although the activating E2Fs are the most extensively characterized transcription factors driving G(1)/S expression, LSF is also a transcription factor essential for stimulating G(1)/S gene expression. A critical LSF target gene at this stage, Tyms, encodes thymidylate synthetase. In investigating how LSF is activated in a cell cycle-dependent manner, we recently identified a novel time delay mechanism for regulating its activity during G(1) progression, which is apparently independent of the E2F/pRb axis. This involves inhibition of LSF in early G(1) by two major proliferative signaling pathways: ERK and cyclin C/CDK, followed by gradual dephosphorylation during mid- to late-G(1). Whether LSF and E2F act independently or in concert to promote G(1)/S progression remains to be determined.

Low dose, low dose rate photon radiation modifies leukocyte distribution and gene expression in CD4(+) T cells

A better understanding of low dose radiation effects is needed to accurately estimate health risks. In this study, C57BL/6 mice were gamma-irradiated to total doses of 0, 0.01, 0.05, and 0.1 Gy ((57)Co; ~0.02 cGy/h). Subsets per group were euthanized at the end of irradiation (day 0) and on days 4 and 21 thereafter. Relative spleen mass and splenic white blood cell (WBC) counts, major leukocyte populations, and spontaneous DNA synthesis were consistently higher in the irradiated groups on day 0 compared to 0 Gy controls, although significance was not always obtained. In the spleen, all three major leukocyte types were significantly elevated on day 0 (P < 0.05). By day 21 post-irradiation the T, B, and natural killer (NK) cell counts, as well as CD4(+) T cells and CD4:CD8 T cell ratio, were low especially in the 0.01 Gy group. Although blood analyses showed no significant differences in leukocyte counts or red blood cell and platelet characteristics, the total T cells, CD4(+) T cells, and NK cells were increased by day 21 after 0.01 Gy (P < 0.05). Gene analysis of CD4(+) T cells negatively isolated from spleens on day 0 after 0.1 Gy showed significantly enhanced expression of Il27 and Tcfcp2, whereas Inha and Socs5 were down-regulated by 0.01 Gy and 0.1 Gy, respectively (P < 0.05). A trend for enhancement was noted in two additional genes (Il1r1 and Tbx21) in the 0.1 Gy group (P < 0.1). The data show that protracted low dose photons had dose- and time-dependent effects on CD4(+) T cells after whole-body exposure.

Phosphorylation by cyclin C/cyclin-dependent kinase 2 following mitogenic stimulation of murine fibroblasts inhibits transcriptional activity of LSF during G1 progression

Transcription factor LSF is required for progression from quiescence through the cell cycle, regulating thymidylate synthase (Tyms) expression at the G(1)/S boundary. Given the constant level of LSF protein from G(0) through S, we investigated whether LSF is regulated by phosphorylation in G(1). In vitro, LSF is phosphorylated by cyclin E/cyclin-dependent kinase 2 (CDK2), cyclin C/CDK2, and cyclin C/CDK3, predominantly on S309. Phosphorylation of LSF on S309 is maximal 1 to 2 h after mitogenic stimulation of quiescent mouse fibroblasts. This phosphorylation is mediated by cyclin C-dependent kinases, as shown by coimmunoprecipitation of LSF and cyclin C in early G(1) and by abrogation of LSF S309 phosphorylation upon suppression of cyclin C with short interfering RNA. Although mouse fibroblasts lack functional CDK3 (the partner of cyclin C in early G(1) in human cells), CDK2 compensates for this absence. By transient transfection assays, phosphorylation at S309, mediated by cyclin C overexpression, inhibits LSF transactivation. Moreover, overexpression of cyclin C and CDK3 inhibits induction of endogenous Tyms expression at the G(1)/S transition. These results identify LSF as only the second known target (in addition to pRb) of cyclin C/CDK activity during progression from quiescence to early G(1). Unexpectedly, this phosphorylation prevents induction of LSF target genes until late G(1).

Functional interaction of CP2 with GATA-1 in the regulation of erythroid promoters

We observed that binding sites for the ubiquitously expressed transcription factor CP2 were present in regulatory regions of multiple erythroid genes. In these regions, the CP2 binding site was adjacent to a site for the erythroid factor GATA-1. Using three such regulatory regions (from genes encoding the transcription factors GATA-1, EKLF, and p45 NF-E2), we demonstrated the functional importance of the adjacent CP2/GATA-1 sites. In particular, CP2 binds to the GATA-1 HS2 enhancer, generating a ternary complex with GATA-1 and DNA. Mutations in the CP2 consensus greatly impaired HS2 activity in transient transfection assays with K562 cells. Similar results were obtained by transfection of EKLF and p45 NF-E2 mutant constructs. Chromatin immunoprecipitation with K562 cells showed that CP2 binds in vivo to all three regulatory elements and that both GATA-1 and CP2 were present on the same GATA-1 and EKLF regulatory elements. Adjacent CP2/GATA-1 sites may represent a novel module for erythroid expression of a number of genes. Additionally, coimmunoprecipitation and glutathione S-transferase pull-down experiments demonstrated a physical interaction between GATA-1 and CP2. This may contribute to the functional cooperation between these factors and provide an explanation for the important role of ubiquitous CP2 in the regulation of erythroid genes.

Human LBP-32/MGR is a repressor of the P450scc in human choriocarcinoma cell line JEG-3

Steroid hormones regulate a wide range of physiologic functions in humans. The cholesterol side-chain cleavage enzyme P450scc regulates the initial step of biosynthesis of all steroid hormones. We investigated the expression of P450scc by studying a potential regulator of P450scc, LBP-32/MGR. Using a Northern blot, we found that LBP-32/MGR mRNA was expressed mainly in the human placenta. Using radiation hybrid mapping, we identified LBP-32/MGR on human chromosome 2p25. Recombinant LBP-32/MGR protein bound preferentially to a DNA fragment from the promoter of P450scc in vitro and exhibited clear nuclear localization in transfected cells. Luciferase reporter gene assays showed that LBP-32/MGR specifically repressed transcriptional activation of the human P450scc promoter. Because placental P450scc expression is essential for pregnancy and steroid biosynthesis, the placental expression and transcriptional repressor activity of LBP-32/MGR in JEG-3 cells suggest it has a role as a transcriptional modulator of steroid biosynthesis.

Repression of human gamma-globin gene expression by a short isoform of the NF-E4 protein is associated with loss of NF-E2 and RNA polymerase II recruitment to the promoter

Binding of the stage selector protein (SSP) to the stage selector element (SSE) in the human gamma-globin promoter contributes to the preferential expression of the gamma-gene in fetal erythroid cells. The SSP contains the transcription factor CP2 and an erythroid-specific partner, NF-E4. The NF-E4 gene encodes a 22-kDa polypeptide employing a non-AUG initiation codon. Antisera specific to NF-E4 detects this species and an additional 14 kDa protein, which initiates from an internal methionine. Enforced expression of p14 NF-E4 in the K562 fetal/erythroid cell line, and in primary erythroid cord blood progenitors, results in repression of gamma-gene expression. Biochemical studies reveal that p14 NF-E4 interacts with CP2, resulting in diminished association of CP2 with the SSE in chromatin immunoprecipitation assays. p45 NF-E2 recruitment to the gamma-promoter is also lost, resulting in a reduction in RNA polymerase II and TBP binding and a fall in promoter transcriptional activity. This effect is specific, as enforced expression of a mutant form of p14 NF-E4, which fails to interact with CP2, also fails to repress gamma-gene expression in K562 cells. These findings provide one potential mechanism that could contribute to the autonomous silencing of the human gamma-genes in adult erythroid cells.

Gene trap screening as an effective approach for identification of Wnt-responsive genes in the mouse embryo

In this study, we examined whether gene trap methodology, which would be available for systematic identification and functional analysis of genes, is effective for screening of Wnt-responsive genes during mouse development. We screened out two individual clones among 794 gene-trapped embryonic stem cell lines by their in vitro response to WNT-3A proteins. One gene was mainly expressed in the ductal epithelium of several developing organs, including the kidney and the salivary glands, and the other gene was expressed in neural crest cells and the telencephalic flexure. The spatial and temporal expression of these two genes coincided well with that of several Wnt genes. Furthermore, the expression of these two genes was significantly decreased in embryos deficient for Wnts or in cultures of embryonic tissues treated with a Wnt signal inhibitor. These results indicate that the gene trap is an effective method for systematic identification of Wnt-responsive genes during embryogenesis.

Heterodimerization with LBP-1b is necessary for nuclear localization of LBP-1a and LBP-1c

The LBP-1 family consists of four proteins, which act as transcription factors in the formation of dimers with a member of this family. LBP-1a and LBP-1b are splicing variants from one gene, and LBP-1c and LBP-1d also arise from the alternative splicing of another gene. Investigation of subcellular localization of LBP-1 proteins fused to YFP revealed that the LBP-1b was localized in the nucleus, whereas LBP-1a and LBP-1c were exclusively localized in the cytosol. The peptide of 36 amino acids encoded by exon 6, a specific exon used only for LBP-1b, possessed the function of a nuclear localization signal (NLS). Nuclear localization of LBP-1a and LBP-1c occurred when LBP-1b was co-expressed, suggesting that heterodimerization of LBP-1a and LBP-1c with LBP-1b is important for their nuclear transport. Transiently expressed LBP-1 proteins in COS-7 cells formed speckles in the nucleus. Most speckles overlapped with the PML body. The activity of LBP-1a for accumulation in the PML body was mapped in the N-terminal region.

Erythroid cell-specific alpha-globin gene regulation by the CP2 transcription factor family

We previously demonstrated that ubiquitously expressed CP2c exerts potent erythroid-specific transactivation of alpha-globin through an unknown mechanism. This mechanism is reported here to involve specific CP2 splice variants and protein inhibitor of activated STAT1 (PIAS1). We identify a novel murine splice isoform of CP2, CP2b, which is identical to CP2a except that it has an additional 36 amino acids encoded by an extra exon. CP2b has an erythroid cell-specific transcriptional activation domain, which requires the extra exon and can form heteromeric complexes with other CP2 isoforms, but lacks the DNA binding activity found in CP2a and CP2c. Transcriptional activation of alpha-globin occurred following dimerization between CP2b and CP2c in erythroid K562 and MEL cells, but this dimerization did not activate the alpha-globin promoter in nonerythroid 293T cells, indicating that an additional erythroid factor is missing in 293T cells. PIAS1 was confirmed as a CP2 binding protein by the yeast two-hybrid screen, and expression of CP2b, CP2c, and PIAS1 in 293T cell induced alpha-globin promoter activation. These results show that ubiquitously expressed CP2b exerts potent erythroid cell-specific alpha-globin gene expression by complexing with CP2c and PIAS1.

Lineage-specific and ubiquitous biological roles of the mammalian transcription factor LSF

Transcriptional regulation in mammalian cells is driven by a complex interplay of multiple transcription factors that respond to signals from either external or internal stimuli. A single transcription factor can control expression of distinct sets of target genes, dependent on its state of post-translational modifications, interacting partner proteins, and the chromatin environment of the cellular genome. Furthermore, many transcription factors can act as either transcriptional repressors or activators, depending on promoter and cellular contexts [Alvarez, M., Rhodes, S.J., Bidwell, J.P., 2003. Context-dependent transcription: all politics is local. Gene 313, 43-57]. Even in this light, the versatility of LSF (Late SV40 Factor) is remarkable. A hallmark of LSF is its unusual DNA binding domain, as evidenced both by lack of homology to any other established DNA-binding domains and by its DNA recognition sequence. Although a dimer in solution, LSF requires additional multimerization with itself or partner proteins in order to interact with DNA. Transcriptionally, LSF can function as an activator or a repressor. It is a direct target of an increasing number of signal transduction pathways. Biologically, LSF plays roles in cell cycle progression and cell survival, as well as in cell lineage-specific functions, shown most strikingly to date in hematopoietic lineages. This review discusses how the unique aspects of LSF DNA-binding activity may make it particularly susceptible to regulation by signal transduction pathways and may relate to its distinct biological roles. We present current progress in elucidation of both tissue-specific and more universal cellular roles of LSF. Finally, we discuss suggestive data linking LSF to signaling by the amyloid precursor protein and to Alzheimer's disease, as well as to the regulation of latency of the human immunodeficiency virus (HIV).

Defective extraembryonic angiogenesis in mice lacking LBP-1a, a member of the grainyhead family of transcription factors

LBP-1a and CP2 are ubiquitously expressed members of the grainyhead transcription factor family, sharing significant sequence homology, a common DNA binding motif, and modulating a range of key regulatory and structural genes. We have reported previously that CP2-null mice are viable with no obvious abnormality. LBP-1a provides redundant function in this context. We show here that mice lacking LBP-1a expression develop intrauterine growth retardation at embryonic day 10.5, culminating in death 1 day later. No focal intraembryonic cause for this CP2-independent defect is evident. In contrast, a significant reduction in the thickness of the labyrinthine layer of the placenta is observed in LBP-1a(-/-) animals. However, expression of trophoblast differentiation markers is unperturbed in this context, and complementation studies utilizing tetraploid wild-type cells failed to rescue or ameliorate the LBP-1a(-/-) phenotype, excluding a primary trophoblast defect. An explanation for these observations is provided by the prominent angiogenic defect observed in the mutant placentas. LBP-1a(-/-) allantoic blood vessels fail to penetrate deeply and branch into the complex embryonic vasculature characteristic of the normal placenta. Interestingly, a similar defect in angiogenesis is observed in the yolk sac vasculature, primary endothelial cell-lined capillary tubes, although present, failed to connect into a characteristic intricate vascular network. Collectively, these results demonstrate that LBP-1a plays a critical role in the regulation of extraembryonic angiogenesis.

Mammalian transcription factor LSF is a target of ERK signaling

LSF is a mammalian transcription factor that is rapidly and quantitatively phosphorylated upon growth induction of resting, peripheral human T cells, as assayed by a reduction in its electrophoretic mobility. The DNA-binding activity of LSF in primary T cells is greatly increased after this phosphorylation event (Volker et al. [1997]: Genes Dev 11:1435-1446). We demonstrate here that LSF is also rapidly and quantitatively phosphorylated upon growth induction in NIH 3T3 cells, although its DNA-binding activity is not significantly altered. Three lines of experimentation established that ERK is responsible for phosphorylating LSF upon growth induction in both cell types. First, phosphorylation of LSF by ERK is sufficient to cause the reduced electrophoretic mobility of LSF. Second, the amount of ERK activity correlates with the extent of LSF phosphorylation in both primary human T cells and NIH 3T3 cells. Finally, specific inhibitors of the Ras/Raf/MEK/ERK pathway inhibit LSF modification in vivo. This phosphorylation by ERK is not sufficient for activation of LSF DNA-binding activity, as evidenced both in vitro and in mouse fibroblasts. Nonetheless, activation of ERK is a prerequisite for the substantial increase in LSF DNA-binding activity upon activation of resting T cells, indicating that ERK phosphorylation is necessary but not sufficient for activation of LSF in this cell type.

Expression of the human oestrogen receptor-alpha gene is regulated by promoter F in MG-63 osteoblastic cells

(O)estrogen receptor-alpha (ERalpha), a hormone-dependent transcription factor belonging to the steroid/thyroid-hormone-receptor superfamily, plays an essential role in the development and maintenance of the skeleton. Here we report the analysis of an unexplored sequence inside the bone-specific distal promoter F (PF) with respect to the regulation of ERalpha gene expression in bone. This sequence, 785 bp in size, is localized upstream of the assigned transcription start site of exon F, at -117140 bp from the originally described transcription start site +1. It contains a TA reach box, a conventional CAAT box and potential regulatory elements for many transcription factors, including Cbfa1 [OSE2 (osteoblast-specific element) core binding factor], GATA-1 [(A/T)GATA(A/G) binding protein], Sox5 [sex-determining region Y (SRY)-type HMG bOX protein, belonging to a subfamily of DNA-binding proteins with an HMG domain], Sry, AP1 (activator protein 1) and CP2 (activator of gamma-globin). It is able to strongly activate the luciferase reporter gene in MG-63 osteoblastic-like cells, but not in MCF7 breast-cancer cells. This is in agreement with different transcripts that we found in the two cell types. The footprinting and electrophoretic mobility-shift assays (EMSAs) showed that, inside the region analysed, there were some sequences that specifically reacted to nuclear proteins isolated from MG-63 cells. In particular, we identified two regions, named PF a and PF b, that do not present binding sites for known transcription factors and that are involved in a strong DNA-protein interaction in MG-63, but not in MCF7, cells. The analysis of three transcription factors (GATA-1, Sry and Sox) that might bind the identified footprinted areas suggested a possible indirect role of these proteins in the regulation of ERalpha gene expression in bone. These data provide evidence for different promoter usage of the ERalpha gene through the recruitment of tissue-specific transcription activators and co-regulators.

Late Simian virus 40 transcription factor is a target of the phosphoinositide 3-kinase/Akt pathway in anti-apoptotic Alzheimer's amyloid precursor protein signalling

The association of familial Alzheimer's disease (FAD) with mutations in Alzheimer's amyloid precursor protein (APP) suggests important functions for APP in the central nervous system. Mutations in APP impair its function to confer resistance to apoptosis in cells under stress, and this may contribute to neurodegeneration in Alzheimer's disease (AD) brain, but the mechanisms involved are unknown. We examined the role of the late Simian virus 40 transcription factor (LSF), in anti-apoptotic APP pathways. We show that in APP-deficient B103 cells, expression of wild-type human APP (hAPPwt), but not of FAD-mutant APP, inhibited staurosporine (STS)-induced apoptosis. This inhibition was further enhanced by expression of LSFwt, although LSFwt alone was not sufficient to inhibit STS-induced apoptosis. In contrast, expression of dominant-negative LSF led to a marked increase in STS-induced cell death that was significantly blocked by hAPPwt. These effects of APP were accompanied by LSF nuclear translocation and dependent gene transcription. The activation of LSF is dependent on the expression of hAPPwt and is inhibited by the expression of dominant-negative forms of either phosphoinositide 3-kinase or Akt. These results demonstrate that LSF activation is required for the neuroprotective effects of APP via phosphoinositide 3-kinase/Akt signalling. Alterations in this pathway by aberrations in APP and/or LSF could promote neuronal loss in AD brain, due to secondary insults. Thus a link is established between APP and LSF and AD.

A highly conserved novel family of mammalian developmental transcription factors related to Drosophila grainyhead

The Drosophila transcription factor Grainyhead regulates several key developmental processes. Three mammalian genes, CP2, LBP-1a and LBP-9 have been previously identified as homologues of grainyhead. We now report the cloning of two new mammalian genes (Mammalian grainyhead (MGR) and Brother-of-MGR (BOM)) and one new Drosophila gene (dCP2) that rewrite the phylogeny of this family. We demonstrate that MGR and BOM are more closely related to grh, whereas CP2, LBP-1a and LBP-9 are descendants of the dCP2 gene. MGR shares the greatest sequence homology with grh, is expressed in tissue-restricted patterns more comparable to grh and binds to and transactivates the promoter of the human Engrailed-1 gene, the mammalian homologue of the key grainyhead target gene, engrailed. This sequence and functional conservation indicates that the new mammalian members of this family play important developmental roles.

Regulation of the globin genes

The a- and b-globin gene clusters are subject to several levels of regulation. They are expressed exclusively in the erythroid cells, only during defined periods of development and in a perfectly tuned way, assuring, at any stage of ontogeny, a correct balance in the availability of a- and b-globin chains for hemoglobin assembling. Such a tight control is dependent on regulatory regions of DNA located either in proximity or at great distances from the globin genes in a region characterized by the presence of several DNAse I hypersensitive sites and known as the Locus Control Region. All these sequences exert stimulatory, inhibitory or more complex activities by interacting with transcription factors that bridge these regions of DNA to the RNA polymerase machinery. Many of these factors have now been cloned and the corresponding mouse genes inactivated, shading new light on the metabolic pathways they control. It is increasingly recognized that such factors are organized into hierarchies according to the number of genes and circuits they regulate. Some genes such as GATA-1 and 2 are master regulators that act on large numbers of genes at early stage of differentiation whereas others, like EKLF, stand on the lowest step and control only single or limited number of genes at late stages of differentiation. We will review recent data gathered from expression studies in cell cultures, in transgenic or K.O. murine models as well as from a clinical settings. We will also discuss the development of novel theories on the regulation of the a- and b-globin genes and clusters.

Binding of the RING polycomb proteins to specific target genes in complex with the grainyhead-like family of developmental transcription factors

The Polycomb group (PcG) of proteins represses homeotic gene expression through the assembly of multiprotein complexes on key regulatory elements. The mechanisms mediating complex assembly have remained enigmatic since most PcG proteins fail to bind DNA. We now demonstrate that the human PcG protein dinG interacts with CP2, a mammalian member of the grainyhead-like family of transcription factors, in vitro and in vivo. The functional consequence of this interaction is repression of CP2-dependent transcription. The CP2-dinG interaction is conserved in evolution with the Drosophila factor grainyhead binding to dring, the fly homologue of dinG. Electrophoretic mobility shift assays demonstrate that the grh-dring complex forms on regulatory elements of genes whose expression is repressed by grh but not on elements where grh plays an activator role. These observations reveal a novel mechanism by which PcG proteins may be anchored to specific regulatory elements in developmental genes.