Ini, a small nuclear protein that enhances the response of the connexin43 gene to estrogen

PHF5A promotes esophageal squamous cell carcinoma progression via stabilizing VEGFA

BACKGROUND

Esophageal squamous cell carcinoma (ESCC) is the main subtype of esophageal cancer. Current therapeutic effect is far from satisfaction. Hence, identifying susceptible genes and potential targets is necessary for therapy of ESCC patients.

METHODS

Plant homeodomain (PHD)-finger domain protein 5 A (PHF5A) expression in ESCC tissues was examined by immunohistochemistry. RNA interference was used for in vitro loss-of-function experiments. In vivo assay was performed using xenograft mice model by subcutaneous injection. Besides, microarray assay and co-immunoprecipitation experiments were used to study the potential downstream molecules of PHF5A in ESCC. The molecular mechanism between PHF5A and vascular endothelial growth factor A (VEGFA) was explored by a series of ubiquitination related assays.

RESULTS

We found that PHF5A was highly expressed in ESCC tissues compared to normal tissues and that was correlated with poor prognosis of ESCC. Loss-of-function experiments revealed that PHF5A silence remarkably inhibited cell proliferation, migration, and induced apoptosis as well as cell cycle arrest. Consistently, in vivo assay demonstrated that PHF5A deficiency was able to attenuate tumor growth. Furthermore, molecular studies showed that PHF5A silencing promoted VEGFA ubiquitination by interacting with MDM2, thereby regulating VEGFA protein expression. Subsequently, in rescue experiments, our data suggested that ESCC cell viability and migration promoted by PHF5A were dependent on intact VEGFA. Finally, PI3K/AKT signaling rescue was able to alleviate shPHF5A-mediated cell apoptosis and cell cycle arrest.

CONCLUSION

PHF5A is a tumor promoter in ESCC, which is dependent on VEGFA and PI3K/AKT signaling. PHF5A might serve as a potential therapeutic target for ESCC treatment.

Plant homeodomain-finger protein 5A: A key player in cancer progression

PHF5A is a member of the zinc-finger proteins. To advance knowledge on their role in carcinogenesis, data from experimental studies, animal models and clinical studies in different tumorigenesis have been reviewed. Furthermore, PHF5A as an oncogenic function, is frequently high expressed in tumor cells and a potential prognostic marker for different cancers. PHF5A is implicated in the regulation of cancer cell proliferation, invasion, migration and metastasis. Knockdown of PHF5A prevented the invasion and metastasis of tumor cells. Here, the role of PHF5A in different cancers and their possible mechanism in relation to recent literature is reviewed and discussed. There is an open promising perspective to their therapeutic management for different cancer types.

PHF5A as a new OncoTarget and therapeutic prospects

PHF5A (PHD-finger domain protein 5A) is a highly conserved protein comprised of 110 amino acids that belong to PHD zinc finger proteins and is ubiquitously expressed in entire eukaryotic nuclei from yeast to man. PHF5A is an essential component of the SF3B splicing complex regulating protein-protein or protein-DNA interactions; particularly involved in pre-mRNA splicing. Besides its basic spliceosome-associated attributes encompassing the regulation of alternative splicing of specific genes, PHF5A also plays a pivotal role in cell cycle regulation and morphological development of cells along with their differentiation into particular tissues/organs, DNA damage repair, maintenance of pluripotent embryonic stem cells (CSCs) embryogenesis and regulation of chromatin-mediated transcription. Presently identification of spliceosome and non-spliceosome-associated attributes of PHF5A needs great attention based on its key involvement in the pathogenesis of cancer malignancies including the prognosis of lung adenocarcinoma, endometrial adenocarcinoma, breast, and colorectal cancer. PHF5A is an essential splicing factor or cofactor actively participating as an oncogenic protein in tumorigenesis via activation of downstream signaling pathway attributed to its regulation of dysregulated splicing or abnormal alternative splicing of targeted genes. Further, the participation of PHF5A in regulating the growth of cancer stem cells might not be ignored. The current review briefly overviews the structural and functional attributes of PHF5A along with its hitherto described role in the propagation of cancer malignancies and its future concern as a potential therapeutic target for cancer management/treatment.

Research progress and therapeutic prospect of PHF5A acting as a new target for malignant tumors

PHD-finger domain protein 5A (PHF5A) is a member of the PHD-finger like protein superfamily and widely expressed in the nucleus of eukaryotes. The PHD-finger like domain is a protein-DNA or protein-protein interaction region. In addition to regulate alternative splicing of target genes as a spliceosome protein subunit, PHF5A is also involved in pluripotency maintenance of embryonic stem cells, chromatin remodeling, DNA damage repair, embryogenesis and histomorphological development. Recently, increasing studies have focused on exploring spliceosome-related and non-spliceosome-related functions of PHF5A and its relationship with the tumorigenesis, development and patient prognosis of various malignant tumors, such as breast cancer, lung cancer and colorectal cancer. The underlying mechanisms of PHF5A may include mediating aberrant alternative splicing of target genes, activating downstream signaling pathways as an oncogene/protein, and regulating abnormal gene transcription as a nuclear transcription factor or cofactor. Besides, PHF5A was also found to be involved in the growth regulation of cancer stem cells. In this review, we aimed to delineate the structural and functional characteristics of PHF5A, to summarize its role in the occurrence and development of malignant tumors hitherto described, and to provide potential targets for anti-tumor therapy.

Down-regulation of Cx43 expression on PIH-HUVEC cells attenuates monocyte-endothelial adhesion

INTRODUCTION

Pregnancy-induced hypertension (PIH) is the most common serious complication of pregnancy, resulting in significant maternal and fetal morbidity and mortality. Vasospasm is the main pathogenesis of PIH, which leads to the hemodynamic changes and the injury of vascular endothelial cells. However, the underlying mechanism is still unclear. Monocyte-endothelial adhesion is always considered to be one of the most important indicators of vascular endothelial cell injury. Connexin43 (Cx43) plays an important part in monocyte-endothelial adhesion. Thus, we explored effects of Cx43 on cell adhesion in PIH-induced vascular endothelial cells injury.

METHODS

We obtained human umbilical vein endothelial cells (HUVECs) from patients with or without PIH. Different methods, such as inhibitors: oleamide and Gap26, or specific siRNA were used to alter Cx43 channels function or protein expression in normal or PIH-HUVECs. U937-HUVECs adhesion, adhesion molecules expression, such as VCAM-1 and ICAM-1, and the activity of PI3K/AKT/NF-κB signaling pathway were determined.

RESULTS

Monocyte-endothelial adhesion on PIH-HUVECs was much more obvious than that on normal HUVECs. Inhibition of Cx43 protein expression could attenuate cell adhesion significantly, however, function of Cx43 channels had no effects on it. Alternation of Cx43 protein expression on PIH-HUVECs mediated VCAM-1 and ICAM-1 expression via regulating the activity of PI3K/AKT/NF-κB signaling pathway.

CONCLUSIONS

We firstly reported Cx43 protein expression on PIH-HUVECs was much higher than that on normal HUVECs. Elevation of Cx43 protein expression within the vasculature resulted in PI3K/AKT/NF-κB signaling pathway activation and VCAM-1 and ICAM-1 over-expression, which ultimately lead to monocyte-endothelial adhesion increase.

PHD-finger domain protein 5A functions as a novel oncoprotein in lung adenocarcinoma

BACKGROUND

PHD-finger domain protein 5A (PHF5A) is a highly conserved small transcriptional regulator also involved in pre-mRNA splicing; however, its biological functions and molecular mechanisms in non-small cell lung cancer (NSCLC) have not yet been investigated. The purpose of this study was to determine the functional relevance and therapeutic potential of PHF5A in lung adenocarcinoma (LAC).

METHODS

The expression of PHF5A in LAC tissues and adjacent non-tumor (ANT) tissues was investigated using immunohistochemistry of a tissue microarray, qRT-PCR, western blot and bioinformatics. The function of PHF5A was determined using several in vitro assays and also in vivo assay by lentiviral vector-mediated PHF5A depletion in LAC cell lines.

RESULTS

PHF5A was highly upregulated in LAC tissues compared with the ANT counterparts, and closely associated with tumor progression and poor patient prognosis. These results were further confirmed by findings of the TCGA database. Moreover, functional studies demonstrated that PHF5A knockdown not only resulted in reduced cell proliferation, increased cell apoptosis, and cell cycle arrest, but also suppressed migration and invasion in LAC cells. PHF5A silencing was also found to inhibit LAC tumor growth in nude mice. Microarray and bioinformatics analyses revealed that PHF5A depletion led to dysregulation of multiple tumor signaling pathways; selected factors in key signaling pathways were verified in vitro.

CONCLUSIONS

The data suggest for the first time that PHF5A is an oncoprotein that contributes to LAC progression by regulating multiple signaling pathways, and may constitute a prognostic factor and potential new therapeutic target in NSCLC.

Curcumin Exerts its Anti-hypertensive Effect by Down-regulating the AT1 Receptor in Vascular Smooth Muscle Cells

Curcumin exerts beneficial effects on cardiovascular diseases, including hypertension. However, its mechanisms are unknown. We propose that curcumin prevents the development of hypertension by regulating AT₁ receptor (AT₁R) expression in arteries. The present study examined how curcumin regulates AT₁R expression in vascular smooth muscle cells and investigated the physiological significance of this regulation in angiotensin (Ang) II-induced hypertension. The results showed that curcumin decreased AT₁R expression in a concentration- and time-dependent manner in vascular smooth muscle cells. Using luciferase reporters with an entire AT₁ or a mutant AT₁R in A10 cells, the AT₁R promoter activity was inhibited by 10⁻⁶M curcumin, and the proximal element (from −61 to +25 bp) of the AT₁R promoter was crucial for curcumin-induced AT₁R down-regulation. An electrophoretic mobility shift assay showed that curcumin decreased specificity protein 1 (SP1) binding with the AT₁R promoter in A10 cells. Curcumin treatment reduced Ang II-induced hypertension in C57Bl/6J mice, which was accompanied by lower AT₁R expression in the arteries and decreased Ang II-mediated vasoconstriction in the mesenteric artery. These findings indicate that curcumin down-regulates AT₁R expression in A10 cells by affecting SP1/AT₁R DNA binding, thus reducing AT₁R-mediated vasoconstriction and subsequently prevents the development of hypertension in an Ang II-induced hypertensive model.

Serial interactome capture of the human cell nucleus

Novel RNA-guided cellular functions are paralleled by an increasing number of RNA-binding proteins (RBPs). Here we present 'serial RNA interactome capture' (serIC), a multiple purification procedure of ultraviolet-crosslinked poly(A)-RNA-protein complexes that enables global RBP detection with high specificity. We apply serIC to the nuclei of proliferating K562 cells to obtain the first human nuclear RNA interactome. The domain composition of the 382 identified nuclear RBPs markedly differs from previous IC experiments, including few factors without known RNA-binding domains that are in good agreement with computationally predicted RNA binding. serIC extends the number of DNA-RNA-binding proteins (DRBPs), and reveals a network of RBPs involved in p53 signalling and double-strand break repair. serIC is an effective tool to couple global RBP capture with additional selection or labelling steps for specific detection of highly purified RBPs.

Connexin-mediated regulation of the pulmonary vasculature

Pulmonary arterial hypertension (PAH) is a complex, multi-factorial disorder characterized by both constriction and remodelling of the distal pulmonary vasculature. This leads to increased pulmonary pressures and eventually right heart failure. Current drugs, which primarily target the vasoconstriction, serve only to prolong life and novel therapies targeting both the vasoconstriction and the remodelling are required. Aberrant signalling between cells of the pulmonary vasculature has been associated with the development of PAH. In particular, endothelial dysfunction can lead to hyperplasia of the underlying medial layer. Connexins are a family of transmembrane proteins which can form intercellular communication channels known as gap junctions. This review will discuss recent evidence which shows that connexins play a role in regulation of the pulmonary vasculature and that dysregulation of connexins may contribute to PAH pathogenesis. Interaction of connexins with signalling pathways relevant to the pathogenesis of PAH, such as bone morphogenetic protein (BMP), serotonin and oestrogen are discussed.

Eventual proapoptotic or anti-apoptotic impact of aberrantly expressed Cx43 and Cx26 can depend on ER-alpha overexpression in human endometrioid adenocarcinoma

Estrogen receptor (ER) and progesterone receptor (PgR) accumulations lead to impairment of gap junctional intercellular communication in endometrial cancer. The task of this study was to explore relationships of Cx26 and Cx43 with anti-apoptotic protein Bcl-xL and proapoptotic agent Bak in ER-alpha and PgR negative or variably positive endometrioid adenocarcinomas. Cx26, Cx43, Bak, Bcl-xL, PgR and ER-alpha were detected in 78 endometrioid adenocarcinomas with immunohistochemistry. There was a remarkable cellular re-distribution of Cx26 and Cx43 from normally membranous location in normal endometrium to aberrantly cytoplasmic expression in endometrioid adenocarcinomas, thus suggesting the decrease of functional membranous gap junctions in the malignancy. Bak failed to correlate with Cx43 regardless of either PgR or ER-alpha status of tumors, while Bcl-xL positively correlated with Cx43 in ER-alpha positive tumors (p = 0.001, r = 0.427) and both PgR positive (p = 0.019, r = 0.312) and negative (p = 0.015, r = 0.509) cancers. Similarly, Bcl-xL significantly associated with Cx26 in ER-alpha positive tumors (p = 0.036, r = 0.267) and both PgR positive (p = 0.026, r = 0.297) and negative (p = 0.046, r = 0.429) cancers. On the contrary, Bak exclusively correlated with Cx26 only in ER-alpha negative tumors (p = 0.027, r = 0.551). ER-alpha status of endometrioid adenocarcinomas could restrict eventual proapoptotic or anti-apoptotic impact of aberrantly expressed Cx43 and Cx26 in these tumors.

Genome-wide RNAi screens in human brain tumor isolates reveal a novel viability requirement for PHF5A

To identify key regulators of human brain tumor maintenance and initiation, we performed multiple genome-wide RNAi screens in patient-derived glioblastoma multiforme (GBM) stem cells (GSCs). These screens identified the plant homeodomain (PHD)-finger domain protein PHF5A as differentially required for GSC expansion, as compared with untransformed neural stem cells (NSCs) and fibroblasts. Given PHF5A's known involvement in facilitating interactions between the U2 snRNP complex and ATP-dependent helicases, we examined cancer-specific roles in RNA splicing. We found that in GSCs, but not untransformed controls, PHF5A facilitates recognition of exons with unusual C-rich 3' splice sites in thousands of essential genes. PHF5A knockdown in GSCs, but not untransformed NSCs, astrocytes, or fibroblasts, inhibited splicing of these genes, leading to cell cycle arrest and loss of viability. Notably, pharmacologic inhibition of U2 snRNP activity phenocopied PHF5A knockdown in GSCs and also in NSCs or fibroblasts overexpressing MYC. Furthermore, PHF5A inhibition compromised GSC tumor formation in vivo and inhibited growth of established GBM patient-derived xenograft tumors. Our results demonstrate a novel viability requirement for PHF5A to maintain proper exon recognition in brain tumor-initiating cells and may provide new inroads for novel anti-GBM therapeutic strategies.

Expression patterns of Phf5a/PHF5A and Gja1/GJA1 in rat and human endometrial cancer

Endometrial adenocarcinoma is the most frequently diagnosed cancer of the female genital tract in the western world. Studies of complex diseases can be difficult to perform on human tumor samples due to the high genetic heterogeneity in human. The use of rat models is preferable since rat has similarities in pathogenesis and histopathological properties to that of human.

A genomic region including the highly conserved Phf5a gene associated to development of EAC has previously been identified in an association study. PHF5A has been suggested to acts as a transcription factor or cofactor in the up regulation of expression of Gja1 gene in the presence of estrogen. It has earlier been shown that the Phf5a gene is down regulated in rat EAC derived cell lines by means of expression microarrays.

We analyzed the expression of Phf5a and Gja1 by qPCR, and potential relations between the two genes in EAC tumors and non-malignant cell lines derived from the BDII rat model. In addition, the expression pattern of these genes was compared in rat and human EAC tumor samples.

Changes in expression for Phf5a/PHF5A were found in tumors from both rat and human even though the observed pattern was not completely consistent between the two species. By separating rat EAC cell lines according to the genetic background, a significant lower expression of Phf5a in one of the two cross backgrounds was revealed, but not for the other. In contrast to other studies, Phf5a/PHF5A regulation of Gja1/GJA1 was not revealed in this study.

EGCG attenuates high glucose-induced endothelial cell inflammation by suppression of PKC and NF-κB signaling in human umbilical vein endothelial cells

AIMS

Vascular inflammation is a key factor in the pathogenesis of diabetes-related vascular complications. Our previous study showed that (-)-epigallocatechin-3-gallate (EGCG) inhibits high glucose-induced vascular smooth muscle cell proliferation, thus it may have beneficial effects in diabetes and its complications. However, the effect of EGCG on inflammation in diabetes is not known. In the present study, we investigated whether EGCG suppresses the vascular inflammation induced by high glucose in human umbilical vein endothelial cells (HUVECs).

MAIN METHODS

The inhibitory effect of EGCG on high glucose-induced up-regulation of the expression of vascular cell adhesion molecule 1 (VCAM-1) was measured using enzyme-linked immunosorbent, RT-PCR, immunoblotting and cell adhesion assays. The effect of EGCG on high glucose-induced nuclear factor-kappa B (NF-κB) activation was investigated by immunoblotting, immunofluorescence and electrophoretic mobility shift assays.

KEY FINDINGS

High glucose increased VCAM-1 expression and enhanced the adhesion of monocytes to HUVECs. Pretreatment with EGCG in a concentration-dependent manner (1.0-50 μM) significantly attenuated these effects. High glucose (25 mM)-mediated vascular inflammation was blocked by PKC pseudosubstrate (PKC inhibitor 19-31) or the NF-κB inhibitor pyrrolidine dithiocarbamate (PDTC). Stimulation with high glucose increased the NF-κB translocation from the cytoplasm to the nucleus, and increased IκB-α phosphorylation, decreased its expression, and in the presence of EGCG, the effect of high glucose on NF-κB and IκB-α were blocked.

SIGNIFICANCE

EGCG suppresses high glucose-induced vascular inflammatory process via the inhibition of PKC and NF-κB activation in HUVECs, suggesting that EGCG may be a potential candidate for the treatment and prevention of diabetic vascular complications.

Angiotensin II AT(2) receptor decreases AT(1) receptor expression and function via nitric oxide/cGMP/Sp1 in renal proximal tubule cells from Wistar-Kyoto rats

BACKGROUND

The renin-angiotensin (Ang) system controls blood pressure, in part, by regulating renal tubular sodium transport. In the kidney, activation of the angiotensin II type 1 (AT(1)) receptor increases renal sodium reabsorption, whereas the angiotensin II type 2 (AT(2)) receptor produces the opposite effect. We hypothesized that the AT(2) receptor regulates AT(1) receptor expression and function in the kidney.

METHODS AND RESULTS

In immortalized renal proximal tubule (RPT) cells from Wistar-Kyoto rats, CGP42112, an AT(2) receptor agonist, decreased AT(1) receptor mRNA and protein expression (P < 0.05), as assessed by reverse transcriptase-polymerase chain reaction and immunoblotting. The inhibitory effect of the AT(2) receptor on AT(1) receptor expression was blocked by the AT(2) receptor antagonist, PD123319 (10 (-6)mol/l), the nitric oxide synthase inhibitor N(w)-nitro-L-arginine methyl ester (10(-4) mol/l), or the nitric oxide-dependent soluble guanylate cyclase inhibitor 1H-[1,2,4] oxadiazolo-[4,3-a] quinoxalin-1-one (10(-5) mol/l), indicating that both nitric oxide and cyclic guanosine monophosphate (cGMP) were involved in the signaling pathway. Furthermore, CGP42112 decreased Sp1 serine phosphorylation and reduced the binding of Sp1 to AT(1) receptor DNA. Stimulation with Ang II (10(-11) mol/l per 30 min) enhanced Na(+)-K(+)-ATPase activity in RPT cells, which was prevented by pretreatment with CGP42112 (10(-7) mol/l per 24 h) (P < 0.05). The above-mentioned results were confirmed in RPT cells from AT(2) receptor knockout mice; AT(1) receptor expression and Ang II-stimulated Na-K-ATPase activity were greater in these cells than in RPT cells from wild-type mice (P < 0.05). AT(1)/AT(2) receptors co-localized and co-immunoprecipitated in RPT cells; short-term CGP42112 (10 mol/l per 30 min) treatment increased AT(1)/AT(2) receptor co-immunoprecipitation (P < 0.05).

CONCLUSIONS

These results indicate that the renal AT(2) receptor, via nitric oxide/cGMP/Sp1 pathway, regulates AT(1 )receptor expression and function, which may be important in the regulation of sodium excretion and blood pressure.

Minireview: regulation of gap junction dynamics by nuclear hormone receptors and their ligands

Gap junctions are plasma membrane channels comprising connexin proteins that mediate intercellular permeability and communication. The presence, composition, and function of gap junctions can be regulated by diverse sets of physiological signals. Evidence from many hormone-responsive tissues has shown that connexin expression, modification, stability, and localization can be targeted by nuclear hormone receptors and their ligands through both transcriptional and nontranscriptional mechanisms. The focus of this review is to discuss molecular, cellular, and physiological studies that directly link receptor- and ligand-triggered signaling pathways to the regulation of gap junction dynamics.

Regulation of connexin expression by transcription factors and epigenetic mechanisms

Gap junctions are specialized cell-cell junctions that directly link the cytoplasm of neighboring cells. They mediate the direct transfer of metabolites and ions from one cell to another. Discoveries of human genetic disorders due to mutations in gap junction protein (connexin [Cx]) genes and experimental data on connexin knockout mice provide direct evidence that gap junctional intercellular communication is essential for tissue functions and organ development, and that its dysfunction causes diseases. Connexin-related signaling also involves extracellular signaling (hemichannels) and non-channel intracellular signaling. Thus far, 21 human genes and 20 mouse genes for connexins have been identified. Each connexin shows tissue- or cell-type-specific expression, and most organs and many cell types express more than one connexin. Connexin expression can be regulated at many of the steps in the pathway from DNA to RNA to protein. In recent years, it has become clear that epigenetic processes are also essentially involved in connexin gene expression. In this review, we summarize recent knowledge on regulation of connexin expression by transcription factors and epigenetic mechanisms including histone modifications, DNA methylation, and microRNA. This article is part of a Special Issue entitled: The communicating junctions, roles and dysfunctions.

Conserved regulatory motifs at phenylethanolamine N-methyltransferase (PNMT) are disrupted by common functional genetic variation: an integrated computational/experimental approach

The adrenomedullary hormone epinephrine transduces environmental stressors into cardiovascular events (tachycardia and hypertension). Although the epinephrine biosynthetic enzyme PNMT genetic locus displays both linkage and association to such traits, genetic variation underlying these quantitative phenotypes is not established. Using an integrated suite of computational and experimental approaches, we elucidate a functional mechanism for common (minor allele frequencies > 30%) genetic variants at PNMT. Transcription factor binding motif prediction on mammalian PNMT promoter alignments identified two variant regulatory motifs, SP1 and EGR1, disrupted by G-367A (rs3764351), and SOX17 motif created by G-161A (rs876493). Electrophoretic mobility shifts of approximately 30-bp oligonucleotides containing ancestral versus variant alleles validated the computational hypothesis. Queried against chromaffin cell nuclear protein extracts, only the G-367 and -161A alleles shifted. Specific antibodies applied in electrophoretic gel shift experiments confirmed binding of SP1 and EGR1 to G-367 and SOX17 to -161A. The in vitro allele-specific binding was verified in cella through promoter reporter assays: lower activity for -367A haplotypes cotransfected by SP1 (p = 0.002) and EGR1 (p = 0.034); and enhanced inhibition of -161A haplotypes (p = 0.0003) cotransfected with SP1 + SOX17. Finally, we probed cis/trans regulation with endogenous factors by chromatin immunoprecipitation using SP1/EGR1/SOX17 antibodies. We describe the systematic application of complementary computational and experimental techniques to detect and document functional genetic variation in a trait-associated regulatory region. The results provide insight into cis and trans transcriptional mechanisms whereby common variation at PNMT can give rise to quantitative changes in human physiological and disease traits. Thus, PNMT variants in cis may interact with nuclear factors in trans to govern adrenergic activity.

Solution structure of the U2 snRNP protein Rds3p reveals a knotted zinc-finger motif

Rds3p, a component of the U2 snRNP subcomplex SF3b, is essential for pre-mRNA splicing and is extremely well conserved in all eukaryotic species. We report here the solution structure of Rds3p, which reveals an unusual knotted fold unrelated to previously known knotted proteins. Rds3p has a triangular shape with a GATA-like zinc finger at each vertex. Pairs of cysteines contributing to each finger are arranged nonsequentially in a permuted arrangement reminiscent of domain-swapping but which here involves segments of subdomains within a single chain. We suggest that the structure arose through a process of segment swapping after gene duplication. The fingers are connected through beta-strands and loops, forming an overall topology strongly resembling a "triquetra knot." The conservation and surface properties of Rds3p suggest that it functions as a platform for protein assembly within the multiprotein SF3b complex of U2 snRNP. The recombinant protein used for structure determination is biologically active, as it restores splicing activity in a yeast splicing extract depleted of native Rds3p.

Treatment with an inhibitor of catechol-O-methyltransferase activity reduces preterm birth and impedes cervical resistance to stretch in pregnant rats

Catechol-O-methyltransferase (COMT) enzyme catalyzes the methylation of the 2- or 4-hydroxyestrogens to 2- or 4-methoxyestrogens. Both the hydroxyestrogens and methoxyestrogens have been shown to block or enhance the effects of estrogen respectively. Our objective was to investigate the potential role of COMT in parturition and cervical ripening using a rat model. Immunohistochemistry was conducted to detect and localize the COMT protein in rat uterine tissues during pregnancy. We measured the longitudinal changes in urinary 2-hydroxyestrogen before, during, and after pregnancy in rats. Animal studies were conducted to determine the effect of treatment with a selective COMT inhibitor on (1) mifepristone-induced preterm birth and (2) cervical resistance to stretch in pregnant rats. The intensity of staining for the COMT protein differed within the luminal epithelium, uterine gland epithelium, endometrium, and myometrium during pregnancy. Levels of staining for the COMT protein in rat myometrium were highest on day 1 and lowest on days 8 and 13, but high levels returned by days 16 and 19 of pregnancy. The levels of urinary 2-hydroxyestrogen gradually increased in the first 2 weeks of pregnancy, peaked from days 16 to 18 of pregnancy, and then gradually returned to pre-pregnancy levels after delivery. The percentage of pups retained in the uterus of pregnant rats treated with both mifepristone and COMT inhibitor (48 ± 15%) was significantly higher (P< 0.05) when compared with the value of pregnant rats treated with mifepristone alone (12 ± 4%). The resistance to stretch was significantly higher (P< 0.05) in cervical tissues from the pregnant rats treated with COMT inhibitor (0.28) when compared with cervical tissues taken from rats treated with vehicle control (0.18). Modulation of COMT activity may play a role in the regulation of myometrial contractility and cervical ripening during pregnancy.

Regulation of connexin expression

Gap junctions contain cell-cell communicating channels that consist of multimeric proteins called connexins and mediate the exchange of low-molecular-weight metabolites and ions between contacting cells. Gap junctional communication has long been hypothesized to play a crucial role in the maintenance of homeostasis, morphogenesis, cell differentiation, and growth control in multicellular organisms. The recent discovery that human genetic disorders are associated with mutations in connexin genes and experimental data on connexin knockout mice have provided direct evidence that gap junctional communication is essential for tissue functions and organ development. Thus far, 21 human genes and 20 mouse genes for connexins have been identified. Each connexin shows tissue- or cell-type-specific expression, and most organs and many cell types express more than one connexin. Cell coupling via gap junctions is dependent on the specific pattern of connexin gene expression. This pattern of gene expression is altered during development and in several pathological conditions resulting in changes of cell coupling. Connexin expression can be regulated at many of the steps in the pathway from DNA to RNA to protein. However, transcriptional control is one of the most important points. In this review, we summarize recent knowledge on transcriptional regulation of connexin genes by describing the structure of connexin genes and transcriptional factors that regulate connexin expression.

Redefining the structure of the mouse connexin43 gene: selective promoter usage and alternative splicing mechanisms yield transcripts with different translational efficiencies

The connexin43 (cx43) gene was originally described as consisting of two exons, one coding for most of the 5'-untranslated region (5'-UTR), and the other for the protein sequence and 3'-UTR. We now report that in mouse four additional exons are expressed, all coding for novel 5'-UTRs. Altogether, we found nine different cx43 mRNA species (GenBank accession numbers NM010288, and AY427554 through AY427561) generated by differential promoter usage and alternative splicing mechanisms. The relative abundance of these different mRNAs varied with the tissue source. In addition, the different transcripts showed varying translational efficiencies in several cell lines, indicating the presence of cis-RNA elements that regulate cx43 translation. We propose that it is the promoter driving the expression of the cx43 gene that determines exon choice in the downstream splicing events in a cell-type-dependent fashion. This in turn will affect the translation efficiency of the transcript orchestrating the events that lead to the final expression profile of cx43. Since a similar organization of the cx43 gene was also observed in rat it is likely that the complex regulation of cx43 expression involving transcription, splicing and translation mechanisms is a common trait conserved during evolution.

A novel RING-finger-like protein Ini1 is essential for cell cycle progression in fission yeast

We have cloned a fission yeast (Schizosaccharomyces pombe) homologue of Ini, a novel RING-finger-like protein recently identified in rat that interacts with the connexin43 (cx43) promoter and might be important for the response of the cx43 gene to estrogen. S. pombe cells deleted for ini1(+) fail to form colonies and arrest with an elongated cell phenotype, indicating a cell cycle block. Cell cycle arrest is dependent on expression of Wee1, but not Rad3, suggesting that it occurs independently of the DNA damage checkpoint control. Analysis of mRNA intermediates in cells depleted for Ini1 demonstrates that Ini1 is required for pre-mRNA splicing. We observe an accumulation of pre-mRNA for six of seven genes analysed, suggesting that Ini1 is required for general splicing activity. Interestingly, loss of Ini1 results in cell death that is partially suppressed by elimination of the Wee1 kinase. Therefore, Wee1 might promote cell death in the absence of Ini1.