Ski-interacting protein, a bifunctional nuclear receptor coregulator that interacts with N-CoR/SMRT and p300

RNA modification writer-based immunological profile and genomic landscape of tumor microenvironment in lung adenocarcinoma

BACKGROUND

Recent studies have highlighted the role of RNA modification, that is, the dysregulation of epitranscriptomics, in tumorigenesis and progression. The potential for undoing epigenetic changes may develop novel therapeutic and prognostic approaches. However, the roles of these RNA modifications in the tumor microenvironment (TME) are still unknown.

METHODS

We assessed the expression properties and genetic alterations of 26 RNA modification writers, including adenosine-to-inosine RNA editing, alternative polyadenylation, m1A, and m6A in 502 lung adenocarcinoma (LUAD) samples from the Cancer Genome Atlas (TCGA) datasets. Then, we used differentially expressed gene (DEGs) to develop a signature for predicting patient outcomes, which was dubbed the "writer score" for RNA-modified writers. In addition, we analyzed the association between TME features, molecular subtypes, treatment sensitivity, and immunotherapy efficacy.

RESULTS

We comprehensively evaluated the changes in multilayer RNA modification writers and identified the role of RNA modification writer expression imbalances in LUAD emergence and progression. Additionally, we constructed a risk-score model based on six LUAD prognosis-associated differentially expressed RNA modification writer genes. Kaplan-Meier (K-M) analyses revealed that the low risk-score signature had high overall patient survival. The predictive significance of the risk-score model was demonstrated using both univariate and multivariate Cox analyses. The risk-score model was positively correlated with the immune- and proliferation-related pathways. In response to anti-cancer treatment, high-risk score is related with high TMB, which has been discovered to correlate with immunotherapy effectiveness.

CONCLUSION

This study showed a strong correlation between the TME variety, level of complexity, and the four types of RNA modification writers. In addition, this scoring system could potentially predict effective immunotherapy and deepens our understanding of TME characteristics.

GmGAMYB-BINDING PROTEIN 1 promotes small auxin-up RNA gene transcription to modulate soybean maturity and height

Flowering time, maturity, and plant height are crucial agronomic traits controlled by photoperiod that affect soybean (Glycine max [L.] Merr.) yield and regional adaptability. It is important to cultivate soybean cultivars of earlier maturity that adapt to high latitudes. GAMYB-binding protein 1 (GmGBP1), a member of the SNW/SKIP family of transcriptional coregulators in soybean, is induced by short days and interacts with transcription factor GAMYB (GmGAMYB) during photoperiod control of flowering time and maturity. In the present study, GmGBP1:GmGBP1 soybean showed the phenotypes of earlier maturity and higher plant height. Chromatin immunoprecipitation sequencing (ChIP-seq) assays of GmGBP1-binding sites and RNA sequencing (RNA-seq) of differentially expressed transcripts in GmGBP1:GmGBP1 further identified potential targets of GmGBP1, including small auxin-up RNA (GmSAUR). GmSAUR:GmSAUR soybean also showed earlier maturity and higher plant height. GmGBP1 interacted with GmGAMYB, bound to the promoter of GmSAUR and promoted the expression of FLOWER LOCUS T homologs 2a (GmFT2a) and FLOWERING LOCUS D LIKE 19 (GmFDL19). Flowering repressors such as GmFT4 were negatively regulated, resulting in earlier flowering and maturity. Furthermore, the interaction of GmGBP1 with GmGAMYB increased the gibberellin (GA) signal to promote height and hypocotyl elongation by activating GmSAUR and GmSAUR bound to the promoter of the GA-positive activating regulator gibberellic acid-stimulated Arabidopsis 32 (GmGASA32). These results suggested a photoperiod regulatory pathway in which the interaction of GmGBP1 with GmGAMYB directly activated GmSAUR to promote earlier maturity and plant height in soybean.

Cyclophilins and Their Functions in Abiotic Stress and Plant-Microbe Interactions

Plants have developed a variety of mechanisms and regulatory pathways to change their gene expression profiles in response to abiotic stress conditions and plant–microbe interactions. The plant–microbe interaction can be pathogenic or beneficial. Stress conditions, both abiotic and pathogenic, negatively affect the growth, development, yield and quality of plants, which is very important for crops. In contrast, the plant–microbe interaction could be growth-promoting. One of the proteins involved in plant response to stress conditions and plant–microbe interactions is cyclophilin. Cyclophilins (CyPs), together with FK506-binding proteins (FKBPs) and parvulins, belong to a big family of proteins with peptidyl-prolyl cis-trans isomerase activity (Enzyme Commission (EC) number 5.2.1.8). Genes coding for proteins with the CyP domain are widely expressed in all organisms examined, including bacteria, fungi, animals, and plants. Their different forms can be found in the cytoplasm, endoplasmic reticulum, nucleus, chloroplast, mitochondrion and in the phloem space. They are involved in numerous processes, such as protein folding, cellular signaling, mRNA processing, protein degradation and apoptosis. In the past few years, many new functions, and molecular mechanisms for cyclophilins have been discovered. In this review, we aim to summarize recent advances in cyclophilin research to improve our understanding of their biological functions in plant defense and symbiotic plant–microbe interactions.

A novel SNW/SKIP domain-containing protein, Bx42, is involved in the antibacterial responses of Macrobrachium nipponense

Bx42, the homologue of SNW1 in mammals, is involved in pre-mRNA splicing and transcriptional regulation. However, the presence and function of Bx42 have remained poorly understood in invertebrates until now. In the current study, a novel SNW domain-containing protein (MnBx42) from Macrobrachium nipponense was identified, and its potential role in the immune response was investigated. The full-length MnBx42 was 7467 bp with an open reading frame of 1653 bp, encoding 550 amino acids. Real-time PCR analysis suggested that MnBx42 was predominantly expressed in the intestine, gills and hepatopancreas, and immunofluorescence assays indicated that it was located in the nucleus. Its expression level was significantly decreased in M. nipponense post-challenge with white spot syndrome virus (WSSV) as well as Aeromonas hydrophila and Staphylococcus aureus, implying its participation in the innate immune response. The knockdown of MnBx42 in vivo notably increased the susceptibility of the prawns to bacterial infection, markedly increased the bacterial load in the gills, and significantly attenuated the phagocytic activity of haemocytes. Dual-luciferase reporter assays illustrated that MnBx42 could activate the NF-κB pathway. Consistent with this, when MnBx42 was silenced in vivo, the expression levels of antimicrobial peptides (AMPs), including ALF2, ALF3, ALF4, ALF5, Cru1 and Cru2, and NF-κB signalling genes, including dorsal, relish, TAK1, TAB1, Ikkβ, and Ikkε, were significantly reduced. Taken together, these findings may provide new insights about Bx42 in crustaceans and pave the way for a better understanding of the crustacean innate immune system.

Vitamin D: Newer Concepts of Its Metabolism and Function at the Basic and Clinical Level

The interest in vitamin D continues unabated with thousands of publications contributing to a vast and growing literature each year. It is widely recognized that the vitamin D receptor (VDR) and the enzymes that metabolize vitamin D are found in many cells, not just those involved with calcium and phosphate homeostasis. In this mini review I have focused primarily on recent studies that provide new insights into vitamin D metabolism, mechanisms of action, and clinical applications. In particular, I examine how mutations in vitamin D metabolizing enzymes-and new information on their regulation-links vitamin D metabolism into areas such as metabolism and diseases outside that of the musculoskeletal system. New information regarding the mechanisms governing the function of the VDR elucidates how this molecule can be so multifunctional in a cell-specific fashion. Clinically, the difficulty in determining vitamin D sufficiency for all groups is addressed, including a discussion of whether the standard measure of vitamin D sufficiency, total 25OHD (25 hydroxyvitamin) levels, may not be the best measure-at least by itself. Finally, several recent large clinical trials exploring the role of vitamin D supplementation in nonskeletal diseases are briefly reviewed, with an eye toward what questions they answered and what new questions they raised.

SNW1 is a prognostic biomarker in prostate cancer

Background

SNW1 is a nuclear receptor co-activator involved in splicing and transcription control, including androgen receptor signaling. Overexpression of SNW1 has been linked to adverse prognosis in different cancer types, but studies on the role of SNW1 in prostate cancer are lacking.

Methods

Using immunohistochemistry, we analyzed SNW1 expression in 10,310 prostate cancers in a tissue microarray (TMA) with attached clinical and molecular data.

Results

The comparison with normal prostate tissue revealed an up regulation of SNW1 in a subset of cancer samples. SNW1 staining was considered weak in 31.5%, moderate in 37.7% and strong in 14% of cancers. Strong SNW1 expression was markedly more frequent in prostate cancers harboring the TMPRSS2:ERG fusion (24%) than in ERG negative cancers (7%, p < 0.0001). Significant associations with Gleason grade, stage, nodal status and early biochemical recurrence were observed in the ERG negative and positive subset. Multivariable modeling revealed that the prognostic value of SNW1 up regulation was independent from the established preoperative histopathological and clinical parameters.

Conclusion

These results demonstrate that SNW1 overexpression is an independent prognostic marker in prostate cancer with potential clinical utility.

Electronic supplementary material

The online version of this article (10.1186/s13000-019-0810-8) contains supplementary material, which is available to authorized users.

Enhancement of TGF-β-induced Smad3 activity by c-Abl-mediated tyrosine phosphorylation of its coactivator SKI-interacting protein (SKIP)

c-Abl is a non-receptor-type tyrosine kinase that plays an important role in cell proliferation, migration, apoptosis, and fibrosis. Furthermore, although c-Abl is involved in transforming growth factor-β (TGF-β) signaling, its molecular functions in TGF-β signaling are not fully understood. Here, we found that c-Abl phosphorylates SKI-interacting protein (SKIP), a nuclear cofactor of the transcription factor Smad3. The c-Abl inhibitor imatinib suppressed TGF-β-induced expression of Smad3 targets as well as SKIP/Smad3 interaction. TGF-β-stimulation induced tyrosine phosphorylation of SKIP, and this phosphorylation was suppressed by imatinib. Tyr²⁹², Tyr⁴³⁰, and Tyr⁴³³ residues in SKIP were shown to be involved in c-Abl-mediated phosphorylation. Phosphomimetic glutamic acid substitution at Tyr²⁹² in SKIP enhanced, whereas its phospho-dead phenylalanine substitution attenuated TGF-β-induced SKIP/Smad3 interaction. Moreover, the phosphomimetic mutant of SKIP augmented transcriptional activity of Smad3. Taken together, these results suggest that c-Abl phosphorylates SKIP mainly at Tyr²⁹² and promotes SKIP/Smad3 interaction for the full activation of TGF-β/Smad3 signaling.

Novel role for PINX1 as a coregulator of nuclear hormone receptors

Estrogen receptor alpha (ERα) has an established role in breast cancer biology. Transcriptional activation by ERα is a multistep process influenced by coactivator and corepressor proteins. This work shows that Pin2 interacting protein 1 (PINX1) interacts with the N-terminal domain of ERα and functions as a corepressor of ERα. Furthermore, it represses both AF-1 and AF-2 transcriptional activities. Chromatin immunoprecipitation assays verified that the interaction between ERα and PINX1 occurs on E2 regulated promoters and enhanced expression of PINX1 deregulates the expression of a number of genes that have a role in cell growth and proliferation in breast cancer. PINX1 overexpression decreases estrogen mediated proliferation of breast cancer cell lines, while its depletion shows the opposite effect. Taken together, these data show a novel molecular mechanism for PINX1 as an attenuator of estrogen receptor activity in breast cancer cell lines, furthering its role as a tumor suppressor gene in breast cancer.

Rice cyclophilin OsCYP18-2 is translocated to the nucleus by an interaction with SKIP and enhances drought tolerance in rice and Arabidopsis

Cyclophilin 18-2 (CYP18-2) genes, homologues of human peptidyl-prolyl isomerase-like 1 (PPiL1), are conserved across multicellular organisms and Schizosaccharomyces pombe. Although PPiL1 is known to interact with ski-interacting protein (SKIP), a transcriptional co-regulator and spliceosomal component, there have been no functional analyses of PPiL1 homologues in plants. Rice cyclophilin 18-2 (OsCYP18-2) bound directly to amino acids 56-95 of OsSKIP and its binding was independent of cyclosporin A, a cyclophilin-binding drug. Moreover, OsCYP18-2 exhibited PPIase activity regardless of its interaction with OsSKIP. Therefore, the binding site for OsCYP18-2's interaction with SKIP was distinct from the PPIase active site. OsCYP18-2's interaction with SKIP full-length protein enabled OsCYP18-2's translocation from the cytoplasm into the nucleus and AtSKIP interacted in planta with both AtCYP18-2 and OsCYP18-2. Drought and salt stress induced similar expression of OsCYP18-2 and OsSKIP. Overexpression of OsCYP18-2 in transgenic rice and Arabidopsis thaliana plants enhanced drought tolerance and altered expression and pre-mRNA splicing patterns of stress-related genes in Arabidopsis under drought conditions. Furthermore, OsCYP18-2 caused transcriptional activation with/without OsSKIP in the GAL4 system of yeast; thus the OsSKIP-OsCYP18-2 interaction has an important role in the transcriptional and post-transcriptional regulation of stress-related genes and increases tolerance to drought stress.

Vitamin D and alternative splicing of RNA

The active form of vitamin D (1α,25-dihydroxyvitamin D, 1,25(OH)2D) exerts its genomic effects via binding to a nuclear high-affinity vitamin D receptor (VDR). Recent deep sequencing analysis of VDR binding locations across the complete genome has significantly expanded our understanding of the actions of vitamin D and VDR on gene transcription. However, these studies have also promoted appreciation of the extra-transcriptional impact of vitamin D on gene expression. It is now clear that vitamin D interacts with the epigenome via effects on DNA methylation, histone acetylation, and microRNA generation to maintain normal biological functions. There is also increasing evidence that vitamin D can influence pre-mRNA constitutive splicing and alternative splicing, although the mechanism for this remains unclear. Pre-mRNA splicing has long been thought to be a post-transcription RNA processing event, but current data indicate that this occurs co-transcriptionally. Several steroid hormones have been recognized to coordinately control gene transcription and pre-mRNA splicing through the recruitment of nuclear receptor co-regulators that can both control gene transcription and splicing. The current review will discuss this concept with specific reference to vitamin D, and the potential role of heterogeneous nuclear ribonucleoprotein C (hnRNPC), a nuclear factor with an established function in RNA splicing. hnRNPC, has been shown to be involved in the VDR transcriptional complex as a vitamin D-response element-binding protein (VDRE-BP), and may act as a coupling factor linking VDR-directed gene transcription with RNA splicing. In this way hnRNPC may provide an additional mechanism for the fine-tuning of vitamin D-regulated target gene expression. This article is part of a Special Issue entitled '17th Vitamin D Workshop'.

SKIP and BIR-1/Survivin have potential to integrate proteome status with gene expression

SKIP and BIR are evolutionarily conserved proteins; SKIP (SKP-1) is a known transcription and splicing cofactor while BIR-1/Survivin regulates cell division, gene expression and development. Their loss of function induces overlapping developmental phenotypes. We searched for SKP-1 and BIR-1 interaction on protein level using yeast two-hybrid screens and identified partially overlapping categories of proteins as SKIP-1 and BIR-1 interactors. The interacting proteins included ribosomal proteins, transcription factors, translation factors and cytoskeletal and motor proteins suggesting involvement in multiple protein complexes. To visualize the effect of BIR-1 on the proteome in Caenorhabditis elegans we induced a short time pulse BIR-1 overexpression in synchronized L1 larvae. This led to a dramatic alteration of the whole proteome pattern indicating that BIR-1 alone has the capacity to alter the chromatographic profile of many target proteins including proteins found to be interactors in yeast two hybrid screens. The results were validated for ribosomal proteins RPS3 and RPL5, non-muscle myosin and TAC-1, a transcription cofactor and a centrosome associated protein. Together, these results suggest that SKP-1 and BIR-1 are multifunctional proteins that form multiple protein complexes in both shared and distinct pathways and have the potential to connect proteome signals with the regulation of gene expression.

BIOLOGICAL SIGNIFICANCE

The genomic organization of the genes encoding BIR-1 and SKIP (SKP-1) in C. elegans have suggested that these two factors, each evolutionarily conserved, have related functions. However, these functional connections have remained elusive and underappreciated in light of limited information from C. elegans and other biological systems. Our results provide further evidence for a functional link between these two factors and suggest they may transmit proteome signals towards the regulation of gene expression.

Up-regulation of SKIP relates to retinal ganglion cells apoptosis after optic nerve crush in vivo

Cell cycle re-entry is one of the key processes in neuronal apoptosis. Previous studies have shown that Ski-interacting protein (SKIP) played an important role in cell cycle re-entry. However, its expression and function in optic nerve injury are still with limited acquaintance. To investigate whether SKIP is involved in retinal ganglion cells (RGCs) death, we performed an optic nerve crush (ONC) model in adult rats. Western blot analysis revealed that up-regulation of SKIP was present in retina at 5 days after ONC. Immunofluorescent labeling indicated that up-regulated SKIP was found mainly in RGCs. We also investigated co-localization of SKIP with active-caspase-3 and TUNEL (apoptotic markers) -positive cells in the retina after ONC. In addition, the expression of SKIP was increased in parallel with P53 and P21 in retina after ONC. All these results suggested that up-regulation of SKIP in the retina was associated with RGCs death after ONC.

Expression and prognostic role of SKIP in human breast carcinoma

Ski-interacting protein (SKIP) is a nuclear hormone receptor-interacting cofactor, interactions with the proto-oncogene Ski, appears to modulate a number of signalling pathways involved in control of cell proliferation and differentiation, and may play a critical role in oncogenesis. In the present study, to investigate the potential roles of SKIP in breast cancer, expression patterns, interaction and the correlation with clinical/prognostic factors of SKIP and Ki-67 were examined among patients with breast cancer. Immunohistochemistry and Western blot analysis were performed for SKIP in 85 breast carcinoma samples. The data were correlated with clinicopathological features. The univariate and multivariate survival analyses were also performed to determine their prognostic significance. We found that SKIP was over expressed in breast carcinoma as compared with the adjacent normal tissues. High expression of SKIP was positively associated with histological grade (P = 0.01) and Ki-67 (P = 0.004). Univariate analysis showed that SKIP expression was associated with a poor prognosis (P = 0.006). While in vitro, following release of breast cancer cell lines from serum starvation, the expression of SKIP was up-regulated, whereas p27 was down-regulated. In addition, we employed small interfering RNA (siRNA) technique to knock down SKIP expression and observed it effects on MDA-MB-231 cells growth. SKIP depletion by siRNA inhibited cell proliferation, blocked S phase and decreased cyclin A and cyclin B levels. On the basis of these results, we suggested that SKIP overexpression was involved in the pathogenesis of breast cancer, which might serve as a future target for breast cancer.

Ski-interacting protein (SKIP) interacts with androgen receptor in the nucleus and modulates androgen-dependent transcription

Background

The androgen receptor (AR) is a member of the nuclear receptor (NR) superfamily of ligand-inducible DNA transcription factors, and is the major mediator of male sexual development, prostate growth and the pathogenesis of prostate cancer. Cell and gene specific regulation by the AR is determined by availability of and interaction with sets of key accessory cofactors. Ski-interacting protein (SKIP; SNW1, NCOA62) is a cofactor shown to interact with several NRs and a diverse range of other transcription factors. Interestingly, SKIP as part of the spliceosome is thought to link mRNA splicing with transcription. SKIP has not been previously shown to interact with the AR.

Results

The aim of this study was to investigate whether SKIP interacts with the AR and modulates AR-dependent transcription. Here, we show by co-immunoprecipitation experiments that SKIP is in a complex with the AR. Moreover, SKIP increased 5α-dihydrotestosterone (DHT) induced N-terminal/C-terminal AR interaction from 12-fold to almost 300-fold in a two-hybrid assay, and enhanced AR ligand-independent AF-1 transactivation. SKIP augmented ligand- and AR-dependent transactivation in PC3 prostate cancer cells. Live-cell imaging revealed a fast (half-time=129 s) translocation of AR from the cytoplasm to the nucleus upon DHT-stimulation. Förster resonance energy transfer (FRET) experiments suggest a direct AR-SKIP interaction in the nucleus upon translocation.

Conclusions

Our results suggest that SKIP interacts with AR in the nucleus and enhances AR-dependent transactivation and N/C-interaction supporting a role for SKIP as an AR co-factor.

Spatiotemporal expression of SKIP after rat sciatic nerve crush

Ski-interacting protein (SKIP) is a highly conserved protein from yeast to Human. As an essential spliceosomal component and transcriptional co-regulator it plays an important role in preinitiation, splicing and polyadenylation. SKIP can also combine with Ski to overcome the G1 arrest and the growth-suppressive activities of pRb. Furthermore SKIP has the capacity to augment TGF-β dependent transcription. While the distribution and function of SKIP in peripheral nervous system lesion and regeneration remain unclear. Here, we investigated the spatiotemporal expression of SKIP in an acute sciatic nerve crush model in adult rats. Western Blot analysis revealed that SKIP was expressed in normal sciatic nerves. It gradually increased, reached a peak at 1 week after crush, and then returned to the normal level at 4 weeks. Besides, we observed that up-regulation of SKIP was approximately in parallel with Proliferating cell nuclear antigen (PCNA), and numerous Schwann cells (SCs) expressing SKIP were PCNA and Ki-67 positive. Collectively, we hypothesized peripheral nerve crush induced up-regulation of SKIP in the sciatic nerve, which was associated with SCs proliferation.

Regulation of bone and cartilage development by network between BMP signalling and transcription factors

Bone morphogenetic protein(s) (BMP) are very powerful cytokines that induce bone and cartilage formation. BMP also stimulate osteoblast and chondrocyte differentiation. During bone and cartilage development, BMP regulates the expression and/or the function of several transcription factors through activation of Smad signalling. Genetic studies revealed that Runx2, Osterix and Sox9, all of which function downstream of BMP, play essential roles in bone and/or cartilage development. In addition, two other transcription factors, Msx2 and Dlx5, which interact with BMP signalling, are involved in bone and cartilage development. The importance of these transcription factors in bone and cartilage development has been supported by biochemical and cell biological studies. Interestingly, BMP is regulated by several negative feedback systems that appear necessary for fine-tuning of bone and cartilage development induced by BMP. Thus, BMP harmoniously regulates bone and cartilage development by forming network with several transcription factors.

Vitamin D resistance and colon cancer prevention

Observational studies have been largely consistent in showing an inverse association between vitamin D and an individual's risk of developing colorectal cancer. Vitamin D protection is further supported by a range of preclinical colon cancer models, including carcinogen, genetic and dietary models. A large number of mechanistic studies in both humans and rodents point to vitamin D preventing cancer by regulating cell proliferation. Counterbalancing this mostly positive data are the results of human intervention studies in which supplemental vitamin D was found to be ineffective for reducing colon cancer risk. One explanation for these discrepancies is the timing of vitamin D intervention. It is possible that colon lesions may progress to a stage where they become unresponsive to vitamin D. Such a somatic loss in vitamin D responsiveness bears the hallmarks of an epigenetic change. Here, we review data supporting the chemopreventive effectiveness of vitamin D and discuss how gene silencing and other molecular changes somatically acquired during colon cancer development may limit the protection that may otherwise be afforded by vitamin D via dietary intervention. Finally, we discuss how understanding the mechanisms by which vitamin D protection is lost might be used to devise strategies to enhance its chemopreventive actions.

SKIP counteracts p53-mediated apoptosis via selective regulation of p21Cip1 mRNA splicing

The Ski-interacting protein SKIP/SNW1 functions as both a splicing factor and a transcriptional coactivator for induced genes. We showed previously that transcription elongation factors such as SKIP are dispensable in cells subjected to DNA damage stress. However, we report here that SKIP is critical for both basal and stress-induced expression of the cell cycle arrest factor p21(Cip1). RNAi chromatin immunoprecipitation (RNAi-ChIP) and RNA immunoprecipitation (RNA-IP) experiments indicate that SKIP is not required for transcription elongation of the gene under stress, but instead is critical for splicing and p21(Cip1) protein expression. SKIP interacts with the 3' splice site recognition factor U2AF65 and recruits it to the p21(Cip1) gene and mRNA. Remarkably, SKIP is not required for splicing or loading of U2AF65 at other investigated p53-induced targets, including the proapoptotic gene PUMA. Consequently, depletion of SKIP induces a rapid down-regulation of p21(Cip1) and predisposes cells to undergo p53-mediated apoptosis, which is greatly enhanced by chemotherapeutic DNA damage agents. ChIP experiments reveal that SKIP is recruited to the p21(Cip1), and not PUMA, gene promoters, indicating that p21(Cip1) gene-specific splicing is predominantly cotranscriptional. The SKIP-associated factors DHX8 and Prp19 are also selectively required for p21(Cip1) expression under stress. Together, these studies define a new step that controls cancer cell apoptosis.

[The role of vitamin D in the prevention and the additional therapy of cancers]

The active metabolite of vitamin D apart from a crucial role in maintaining mineral homeostasis and skeletal functions, has antiproliferative, apoptosis and differentiation inducing as well as immunomodulatory effects in cancer. It is well known that with increasing sunshine exposure the incidence of breast, prostate and colorectal cancer is decreasing. A number of in vitro and in vivo experiments documented the effects of vitamin D in the inhibition of the tumorigenesis. In studying the role of vitamin D in cancer, it is imperative to examine the potential pathways that control local tissue levels of vitamin D. The enzyme 24-hydroxylase converts the active vitamin D to inactive metabolite. Extra-renal production of this enzyme is observed and has been increasingly recognized as present in cancer cells. This enzyme is rate limiting for the amount of local vitamin D in cancer tissues and elevated expression is associated with an adverse prognosis. 24-hydroxylase may be a predictive marker of vitamin D efficacy in patients with cancer as an adjunctive therapy. There are many vitamin D analogs with no pronounced hypercalcemizing effects. Some analogs are in phase 1 and 2 clinical test, and they might have a role in the therapy of several types of cancer. At present our main task is to make an effort to decrease the vitamin D deficiency in Hungary. Speer G. The D-day. The role of vitamin D in the prevention and the additional therapy of cancers.

Assembly of a Notch transcriptional activation complex requires multimerization

Notch transmembrane receptors direct essential cellular processes, such as proliferation and differentiation, through direct cell-to-cell interactions. Inappropriate release of the intracellular domain of Notch (N(ICD)) from the plasma membrane results in the accumulation of deregulated nuclear N(ICD) that has been linked to human cancers, notably T-cell acute lymphoblastic leukemia (T-ALL). Nuclear N(ICD) forms a transcriptional activation complex by interacting with the coactivator protein Mastermind-like 1 and the DNA binding protein CSL (for CBF-1/Suppressor of Hairless/Lag-1) to regulate target gene expression. Although it is well understood that N(ICD) forms a transcriptional activation complex, little is known about how the complex is assembled. In this study, we demonstrate that N(ICD) multimerizes and that these multimers function as precursors for the stepwise assembly of the Notch activation complex. Importantly, we demonstrate that the assembly is mediated by N(ICD) multimers interacting with Skip and Mastermind. These interactions form a preactivation complex that is then resolved by CSL to form the Notch transcriptional activation complex on DNA.

Cooperative activation of cyclin D1 and progesterone receptor gene expression by the SRC-3 coactivator and SMRT corepressor

Although the ability of coactivators to enhance the expression of estrogen receptor-alpha (ERalpha) target genes is well established, the role of corepressors in regulating 17beta-estradiol (E2)-induced gene expression is poorly understood. Previous studies revealed that the silencing mediator of retinoic acid and thyroid hormone receptor (SMRT) corepressor is required for full ERalpha transcriptional activity in MCF-7 breast cancer cells, and we report herein the E2-dependent recruitment of SMRT to the regulatory regions of the progesterone receptor (PR) and cyclin D1 genes. Individual depletion of SMRT or steroid receptor coactivator (SRC)-3 modestly decreased E2-induced PR and cyclin D1 expression; however, simultaneous depletion revealed a cooperative effect of this coactivator and corepressor on the expression of these genes. SMRT and SRC-3 bind directly in an ERalpha-independent manner, and this interaction promotes E2-dependent SRC-3 binding to ERalpha measured by co-IP and SRC-3 recruitment to the cyclin D1 gene as measured by chromatin IP assays. Moreover, SMRT stimulates the intrinsic transcriptional activity of all of the SRC family (p160) coactivators. Our data link the SMRT corepressor directly with SRC family coactivators in positive regulation of ERalpha-dependent gene expression and, taken with the positive correlation found for SMRT and SRC-3 in human breast tumors, suggest that SMRT can promote ERalpha- and SRC-3-dependent gene expression in breast cancer.

Reciprocal roles of SIRT1 and SKIP in the regulation of RAR activity: implication in the retinoic acid-induced neuronal differentiation of P19 cells

Human sirtuin 1 (SIRT1) is a NAD⁺-dependent deacetylase that participates in cell death/survival, senescence and metabolism. Although its substrates are well characterized, no direct regulators have been defined. Here, we show that SIRT1 associates with SKI-interacting protein (SKIP) and modulates its activity as a coactivator of retinoic acid receptor (RAR). Binding assays indicated that SKIP interacts with RAR in a RA-dependent manner, through a region that overlaps the binding site for SIRT1. SKIP augmented the transcriptional activation activity of RAR by cooperating with SRC-1, and SIRT1 suppressed SKIP/SRC-1-enhanced RAR transactivation activity. The suppression was dependent on the deacetylase activity of SIRT1 and was enhanced by a SIRT1 activator, resveratrol. In contrast, the suppression was relieved by SIRT1 knockdown, overexpression of SKIP and treatment with a SIRT1 inhibitor, splitomicin. Upon SKIP overexpression, the recruitment of SIRT1 to the endogenous RARβ2 promoter was severely impaired, and SKIP was recruited to the promoter instead. Finally, resveratrol treatment inhibited RA-induced neuronal differentiation of P19 cells, accompanied by reductions in the neuronal marker nestin and a RAR target gene, RARβ2. This inhibition was relieved by either knockdown of SIRT1 or overexpression of SKIP. These data suggest that SIRT1 and SKIP play reciprocal roles in the regulation of RAR activity, which is implicated in the regulation of RA-induced neuronal differentiation of P19 cells.

A homolog of human ski-interacting protein in rice positively regulates cell viability and stress tolerance

Abiotic stresses are major limiting factors for growth, development, and productivity of crop plants. Here, we report on OsSKIPa, a rice homolog of human Ski-interacting protein (SKIP) that can complement the lethal defect of the knockout mutant of SKIP homolog in yeast and positively modulate cell viability and stress tolerance of rice. Suppression of OsSKIPa in rice resulted in growth arrest and reduced cell viability. The expression OsSKIPa is induced by various abiotic stresses and phytohormone treatments. Transgenic rice overexpressing OsSKIPa exhibited significantly improved growth performance in the medium containing stress agents (abscisic acid, salt, or mannitol) and drought resistance at both the seedling and reproductive stages. The OsSKIPa-overexpressing rice showed significantly increased reactive oxygen species-scavenging ability and transcript levels of many stress-related genes, including SNAC1 and rice homologs of CBF2, PP2C, and RD22, under drought stress conditions. More than 30 OsSKIPa-interacting proteins were identified, but most of these proteins have no matches with the reported SKIP-interacting proteins in animals and yeast. Together, these data suggest that OsSKIPa has evolved a specific function in positive modulation of stress resistance through transcriptional regulation of diverse stress-related genes in rice.

Regulation of cyclin D1 RNA stability by SNIP1

Cyclin D1 expression represents one of the key mitogen-regulated events during the G(1) phase of the cell cycle, whereas Cyclin D1 overexpression is frequently associated with human malignancy. Here, we describe a novel mechanism regulating Cyclin D1 levels. We find that SNIP1, previously identified as a regulator of Cyclin D1 expression, does not, as previously thought, primarily function as a transcriptional coactivator for this gene. Rather, SNIP1 plays a critical role in cotranscriptional or posttranscriptional Cyclin D1 mRNA stability. Moreover, we show that the majority of nucleoplasmic SNIP1 is present within a previously undescribed complex containing SkIP, THRAP3, BCLAF1, and Pinin, all proteins with reported roles in RNA processing and transcriptional regulation. We find that this complex, which we have termed the SNIP1/SkIP-associated RNA-processing complex, is coordinately recruited to both the 3' end of the Cyclin D1 gene and Cyclin D1 RNA. Significantly, SNIP1 is required for the further recruitment of the RNA processing factor U2AF65 to both the Cyclin D1 gene and RNA. This study shows a novel mechanism regulating Cyclin D1 expression and offers new insight into the role of SNIP1 and associated proteins as regulators of proliferation and cancer.

Ankyrin repeats-containing cofactors interact with ADA3 and modulate its co-activator function

ANCO (ankyrin repeats-containing cofactor)-1 and ANCO-2 are a family of unique transcriptional co-regulators with dual properties: they interact with both the co-activators and the co-repressors [Zhang, Yeung, Li, Tsai, Dinh, Wu, Li and Chen (2004) J. Biol. Chem. 279, 33799-33805]. Specifically, ANCO-1 is thought to recruit HDACs (histone deacetylases) to the p160 co-activator to repress transcriptional activation by nuclear receptors. In the present study, we provide new evidence to suggest further that ANCO-1 and ANCO-2 also interact with the co-activator ADA3 (alteration/deficiency in activation 3). The interaction occurs between the conserved C-terminal domain of ANCO-1 and the N-terminal transactivation domain of ADA3. Several subunits of the P/CAF {p300/CBP [CREB (cAMP-response-element-binding protein)-binding protein]-associated factor} complex, including ADA3, ADA2alpha/beta and P/CAF, showed co-localization with ANCO-1 nuclear dots, indicating an in vivo association of ANCO-1 with the P/CAF complex. Furthermore, a transient reporter assay revealed that both ANCO-1 and ANCO-2 repress ADA3-mediated transcriptional co-activation on nuclear receptors, whereas ANCO-1 stimulated p53-mediated transactivation. These data suggest that ADA3 is a newly identified target of the ANCO proteins, which may modulate co-activator function in a transcription-factor-specific manner.

Modulation of VEGF signalling output by the Notch pathway

The formation of blood vessels within the vascular system entails a variety of cellular processes, including proliferation, migration and differentiation. In many cases, these diverse processes need to be finely coordinated among neighbouring endothelial cells in order to establish a functional vascular network. For instance, during angiogenic sprouting specialized endothelial tip cells follow guidance cues and migrate extensively into avascular tissues while trailing stalk cells must stay connected to the patent blood vessel. The vascular endothelial growth factor (VEGF) and Notch signalling pathways have emerged as the major players in governing these different cellular behaviours. In particular, recent work indicates an important role for Notch signalling in determining how an endothelial cell responds to VEGF. In this review, we provide an overview of these biochemically distinct pathways and discuss how they may interact during endothelial cell differentiation and angiogenesis.

Notch signaling in the developing cardiovascular system

The Notch proteins encompass a family of transmembrane receptors that have been highly conserved through evolution as mediators of cell fate. Recent findings have demonstrated a critical role of Notch in the developing cardiovascular system. Notch signaling has been implicated in the endothelial-to-mesenchymal transition during development of the heart valves, in arterial-venous differentiation, and in remodeling of the primitive vascular plexus. Mutations of Notch pathway components in humans are associated with congenital defects of the cardiovascular system such as Alagille syndrome, cerebral autosomal dominant arteriopathy with subcortical infarcts and leukoencephalopathy (CADASIL), and bicuspid aortic valves. This article focuses on the role of the Notch pathway in the developing cardiovascular system and congenital human cardiovascular diseases.

Rbm15 modulates Notch-induced transcriptional activation and affects myeloid differentiation

RBM15 is the fusion partner with MKL in the t(1;22) translocation of acute megakaryoblastic leukemia. To understand the role of the RBM15-MKL1 fusion protein in leukemia, we must understand the normal functions of RBM15 and MKL. Here, we show a role for Rbm15 in myelopoiesis. Rbm15 is expressed at highest levels in hematopoietic stem cells and at more moderate levels during myelopoiesis of murine cell lines and primary murine cells. Decreasing Rbm15 levels with RNA interference enhances differentiation of the 32DWT18 myeloid precursor cell line. Conversely, enforced expression of Rbm15 inhibits 32DWT18 differentiation. We show that Rbm15 alters Notch-induced HES1 promoter activity in a cell type-specific manner. Rbm15 inhibits Notch-induced HES1 transcription in nonhematopoietic cells but stimulates this activity in hematopoietic cell lines, including 32DWT18 and human erythroleukemia cells. Moreover, the N terminus of Rbm15 coimmunoprecipitates with RBPJkappa, a critical factor in Notch signaling, and the Rbm15 N terminus has a dominant negative effect, impairing activation of HES1 promoter activity by full-length-Rbm15. Thus, Rbm15 is differentially expressed during hematopoiesis and may act to inhibit myeloid differentiation in hematopoietic cells via a mechanism that is mediated by stimulation of Notch signaling via RBPJkappa.

Signal integration during development: mechanisms of EGFR and Notch pathway function and cross-talk

Metazoan development relies on a highly regulated network of interactions between conserved signal transduction pathways to coordinate all aspects of cell fate specification, differentiation, and growth. In this review, we discuss the intricate interplay between the epidermal growth factor receptor (EGFR; Drosophila EGFR/DER) and the Notch signaling pathways as a paradigm for signal integration during development. First, we describe the current state of understanding of the molecular architecture of the EGFR and Notch signaling pathways that has resulted from synergistic studies in vertebrate, invertebrate, and cultured cell model systems. Then, focusing specifically on the Drosophila eye, we discuss how cooperative, sequential, and antagonistic relationships between these pathways mediate the spatially and temporally regulated processes that generate this sensory organ. The common themes underlying the coordination of the EGFR and Notch pathways appear to be broadly conserved and should, therefore, be directly applicable to elucidating mechanisms of information integration and signaling specificity in vertebrate systems.

STAMP, a novel predicted factor assisting TIF2 actions in glucocorticoid receptor-mediated induction and repression

The coactivator TIF2 was predicted to interact with an unknown factor to modify both the relative inhibition in glucocorticoid receptor (GR)-mediated gene repression and several parameters of agonists and antisteroids in GR-regulated induction. Here, we describe the isolation and characterization of the predicted factor as a new 1,277-amino-acid endogenous protein (STAMP). STAMP associates with coactivators (TIF2 and SRC-1) and is selective for a subset of the steroid/nuclear receptors including GRs. Transfected STAMP increases the effects of TIF2 in GR-mediated repression and induction. Conversely, the levels of both induction and repression of endogenous genes are reduced when STAMP small interfering RNAs are used to lower the level of endogenous STAMP. Endogenous STAMP colocalizes with GR in intact cells and is recruited to the promoters of endogenous GR-induced and -repressed genes. We suggest that STAMP is an important new, downstream component of GR action in both gene activation and gene repression.

SLIRP, a small SRA binding protein, is a nuclear receptor corepressor

Steroid receptor RNA activator (SRA), the only known RNA coactivator, augments transactivation by nuclear receptors (NRs). We identified SLIRP (SRA stem-loop interacting RNA binding protein) binding to a functional substructure of SRA, STR7. SLIRP is expressed in normal and tumor tissues, contains an RNA recognition motif (RRM), represses NR transactivation in a SRA- and RRM-dependent manner, augments the effect of Tamoxifen, and modulates association of SRC-1 with SRA. SHARP, a RRM-containing corepressor, also binds STR7, augmenting repression with SLIRP. SLIRP colocalizes with SKIP (Chr14q24.3), another NR coregulator, and reduces SKIP-potentiated NR signaling. SLIRP is recruited to endogenous promoters (pS2 and metallothionein), the latter in a SRA-dependent manner, while NCoR promoter recruitment is dependent on SLIRP. The majority of the endogenous SLIRP resides in the mitochondria. Our data demonstrate that SLIRP modulates NR transactivation, suggest it may regulate mitochondrial function, and provide mechanistic insight into interactions between SRA, SLIRP, SRC-1, and NCoR.

Conditional knockout mice reveal distinct functions for the global transcriptional coactivators CBP and p300 in T-cell development

The global transcriptional coactivators CREB-binding protein (CBP) and the closely related p300 interact with over 312 proteins, making them among the most heavily connected hubs in the known mammalian protein-protein interactome. It is largely uncertain, however, if these interactions are important in specific cell lineages of adult animals, as homozygous null mutations in either CBP or p300 result in early embryonic lethality in mice. Here we describe a Cre/LoxP conditional p300 null allele (p300flox) that allows for the temporal and tissue-specific inactivation of p300. We used mice carrying p300flox and a CBP conditional knockout allele (CBPflox) in conjunction with an Lck-Cre transgene to delete CBP and p300 starting at the CD4- CD8- double-negative thymocyte stage of T-cell development. Loss of either p300 or CBP led to a decrease in CD4+ CD8+ double-positive thymocytes, but an increase in the percentage of CD8+ single-positive thymocytes seen in CBP mutant mice was not observed in p300 mutants. T cells completely lacking both CBP and p300 did not develop normally and were nonexistent or very rare in the periphery, however. T cells lacking CBP or p300 had reduced tumor necrosis factor alpha gene expression in response to phorbol ester and ionophore, while signal-responsive gene expression in CBP- or p300-deficient macrophages was largely intact. Thus, CBP and p300 each supply a surprising degree of redundant coactivation capacity in T cells and macrophages, although each gene has also unique properties in thymocyte development.

CHES1/FOXN3 interacts with Ski-interacting protein and acts as a transcriptional repressor

Checkpoint Suppressor 1 (CHES1; FOXN3) encodes a member of the forkhead/winged-helix transcription factor family. The human CHES1 cDNA was originally identified by its ability to function as a high-copy suppressor of multiple checkpoint mutants of Saccharomyces cerevisiae. Accumulating expression profile data suggest that CHES1 plays a role in tumorigenicity and responses to cancer treatments, though nothing is known regarding the transcriptional function of CHES1 or other FOXN proteins in human cells. In this report, we find that the carboxyl terminus of CHES1 fused to a heterologous DNA binding domain consistently represses reporter gene transcription in cell lines derived from tumor tissues. Using a cytoplasmic two-hybrid screening approach, we find that this portion of CHES1 interacts with Ski-interacting protein (SKIP; NCoA-62), which is a transcriptional co-regulator known to associate with repressor complexes. We verify this interaction through co-immunoprecipitation experiments performed in mammalian cells. Further analysis of the CHES1/SKIP interaction indicates that CHES1 binds to a region within the final 66 hydrophobic residues of SKIP thus defining a new protein-protein interaction domain of SKIP. These data suggest that CHES1 recruits SKIP to repress genes important for tumorigenesis and the response to cancer treatments.

Smads and chromatin modulation

Smad proteins are critical intracellular effector proteins and regulators of transforming growth factor type beta (TGFbeta) modulated gene transcription. They directly convey signals that initiate at ligand-bound receptor complexes and end in the nucleus with changes in programs of gene expression. Activated Smad proteins seem to recruit chromatin modifying proteins to target genes besides cooperating with DNA-bound transcription factors. We survey here the current and still emerging knowledge on Smad-binding factors, and their different mechanisms of chromatin modification in particular, in Smad-dependent TGFbeta signaling.

Profiling estrogen-regulated gene expression changes in normal and malignant human ovarian surface epithelial cells

Estrogens regulate normal ovarian surface epithelium (OSE) cell functions but also affect epithelial ovarian cancer (OCa) development. Little is known about how estrogens play such opposing roles. Transcriptional profiling using a cDNA microarray containing 2400 named genes identified 155 genes whose expression was altered by estradiol-17beta (E2) in three immortalized normal human ovarian surface epithelial (HOSE) cell lines and 315 genes whose expression was affected by the hormone in three established OCa (OVCA) cell lines. All but 19 of the genes in these two sets were different. Among the 19 overlapping genes, five were found to show discordant responses between HOSE and OVCA cell lines. The five genes are those that encode clone 5.1 RNA-binding protein (RNPS1), erythrocyte adducin alpha subunit (ADD1), plexin A3 (PLXNA3 or the SEX gene), nuclear protein SkiP (SKIIP), and Rap-2 (rap-2). RNPS1, ADD1, rap-2, and SKIIP were upregulated by E2 in HOSE cells but downregulated by estrogen in OVCA cells, whereas PLXNA3 showed the reverse pattern of regulation. The estrogen effects was observed within 6-18 h of treatment. In silicon analyses revealed presence of estrogen response elements in the proximal promoters of all five genes. RNPS1, ADD1, and PLXNA3 were underexpressed in OVCA cell lines compared to HOSE cell lines, while the opposite was true for rap-2 and SKIIP. Functional studies showed that RNPS1 and ADD1 exerted multiple antitumor actions in OVCA cells, while PLXNA3 only inhibited cell invasiveness. In contrast, rap-2 was found to cause significant oncogenic effects in OVCA cells, while SKIIP promotes only anchorage-independent growth. In sum, gene profiling data reveal that (1) E2 exerts different actions on HOSE cells than on OVCA cells by affecting two distinct transcriptomes with few overlapping genes and (2) among the overlapping genes, a set of putative oncogenes/tumor suppressors have been identified due to their differential responses to E2 between the two cell types. These findings may explain the paradoxical roles of estrogens in regulating normal and malignant OSE cell functions.

Vitamin D

The vitamin D endocrine system plays an essential role in calcium homeostasis and bone metabolism, but research during the past two decades has revealed a diverse range of biological actions that include induction of cell differentiation, inhibition of cell growth, immunomodulation, and control of other hormonal systems. Vitamin D itself is a prohormone that is metabolically converted to the active metabolite, 1,25-dihydroxyvitamin D [1,25(OH)(2)D]. This vitamin D hormone activates its cellular receptor (vitamin D receptor or VDR), which alters the transcription rates of target genes responsible for the biological responses. This review focuses on several recent developments that extend our understanding of the complexities of vitamin D metabolism and actions: the final step in the activation of vitamin D, conversion of 25-hydroxyvitamin D to 1,25(OH)(2)D in renal proximal tubules, is now known to involve facilitated uptake and intracellular delivery of the precursor to 1alpha-hydroxylase. Emerging evidence using mice lacking the VDR and/or 1alpha-hydroxylase indicates both 1,25(OH)(2)D(3)-dependent and -independent actions of the VDR as well as VDR-dependent and -independent actions of 1,25(OH)(2)D(3). Thus the vitamin D system may involve more than a single receptor and ligand. The presence of 1alpha-hydroxylase in many target cells indicates autocrine/paracrine functions for 1,25(OH)(2)D(3) in the control of cell proliferation and differentiation. This local production of 1,25(OH)(2)D(3) is dependent on circulating precursor levels, providing a potential explanation for the association of vitamin D deficiency with various cancers and autoimmune diseases.

A human splicing factor, SKIP, associates with P-TEFb and enhances transcription elongation by HIV-1 Tat

HIV-1 Tat binds human CyclinT1 and recruits the CDK9/P-TEFb complex to the viral TAR RNA in a step that links RNA polymerase II (RNAPII) C-terminal domain (CTD) Ser 2 phosphorylation with transcription elongation. Previous studies have suggested a connection between Tat and pre-mRNA splicing factors. Here we show that the splicing-associated c-Ski-interacting protein, SKIP, is required for Tat transactivation in vivo and stimulates HIV-1 transcription elongation, but not initiation, in vitro. SKIP associates with CycT1:CDK9/P-TEFb and Tat:P-TEFb complexes in nuclear extracts and interacts with recombinant Tat:P-TEFb:TAR RNA complexes in vitro, indicating that it may act through nascent RNA to overcome pausing by RNAPII. SKIP also associates with U5snRNP proteins and tri-snRNP110K in nuclear extracts, and facilitates recognition of an alternative Tat-specific splice site in vivo. The effects of SKIP on transcription elongation, binding to P-TEFb, and splicing are mediated through the SNW domain. HIV-1 Tat transactivation is accompanied by the recruitment of P-TEFb, SKIP, and tri-snRNP110K to the integrated HIV-1 promoter in vivo, whereas the U5snRNPs associate only with the transcribed coding region. These findings suggest that SKIP plays independent roles in transcription elongation and pre-mRNA splicing.

Coordinate transcriptional regulation of bile acid homeostasis and drug metabolism

Drugs and bile acids are taken up into hepatocytes by specialized transport proteins localized at the basolateral membrane, e.g., organic anion transporting polypeptides . Following intracellular metabolism by cytochrome P450 (CYP) enzymes, drug metabolites are excreted into bile or urine via ATP-dependent multidrug resistance proteins (MDR1 and MRPs). Bile acids are excreted mainly via the bile salt export pump (BSEP, ABCB11). The genes coding for drug and bile acid transporters and CYP enzymes are regulated by a complex network of transcriptional cascades, notably by the ligand-activated nuclear receptors FXR, PXR, and CAR and by the ligand-independent nuclear receptor HNF-4alpha. The bile acid synthesizing enzymes CYP7A1, CYP8B1, and CYP27A1 are subject to negative feedback regulation by bile acids, which is partly mediated through the transcriptional repressor SHP. The role of transcriptional cofactors, such as SRC-1 and PGC-1, in mediating the gene-specific effects of individual nuclear receptors is becoming increasingly evident.

Paricalcitol

Paricalcitol (Zemplar) is a synthetic vitamin D(2) analogue that inhibits the secretion of parathyroid hormone (PTH) through binding to the vitamin D receptor. It is approved in the US and in most European nations for intravenous use in the prevention and treatment of secondary hyperparathyroidism associated with chronic renal failure in adult, and in the US paediatric, patients. Paricalcitol effectively reduced elevated serum PTH levels and was generally well tolerated in children and adults with secondary hyperparathyroidism associated with chronic renal failure. In well designed clinical trials, paricalcitol was as effective as calcitriol and as well tolerated in terms of the incidence of prolonged hypercalcaemia and/or elevated calcium-phosphorus product (Ca x P). Thus, paricalcitol is a useful option for the management of secondary hyperparathyroidism in adults and children with chronic renal failure.

The human Ski-interacting protein functionally substitutes for the yeast PRP45 gene

The PRP45 gene has been identified as encoding a protein involved in mRNA splicing that is essential in Saccharomyces cerevisiae. PRP45's human homolog SKIP has been identified as a mediator of transcriptional programming in a variety of signal transduction pathways including TGFbeta, nuclear hormones, Notch, and retinoblastoma signaling. However, Skip has been also identified in purified spliceosomal complexes but an explicit role in splicing has not been identified in mammalian cells. To determine if the Skip protein could function as a splicing factor we investigated if the SKIP gene could functionally complement the yeast PRP45 gene. We show that SKIP complements the PRP45 deletion and rescues the lethal phenotype. These results show that the human SKIP gene can functionally substitute for the mRNA splicing gene PRP45 of S. cerevisiae.