Identification of 13 Novel Loci in a Genome-Wide Association Study on Taiwanese with Hepatocellular Carcinoma.

Liver cancer is caused by complex interactions among genetic factors, viral infection, alcohol abuse, and metabolic diseases. We conducted a genome-wide association study and polygenic risk score (PRS) model in Taiwan, employing a nonspecific etiology approach, to identify genetic risk factors for hepatocellular carcinoma (HCC). Our analysis of 2836 HCC cases and 134,549 controls revealed 13 novel associated loci such as the FAM66C gene, noncoding genes, liver-fibrosis-related genes, metabolism-related genes, and HCC-related pathway genes. We incorporated the results from the UK Biobank and Japanese database into our study for meta-analysis to validate our findings. We also identified specific subtypes of the major histocompatibility complex that influence both viral infection and HCC progression. Using this data, we developed a PRS to predict HCC risk in the general population, patients with HCC, and HCC-affected families. The PRS demonstrated higher risk scores in families with multiple HCCs and other cancer cases. This study presents a novel approach to HCC risk analysis, identifies seven new genes associated with HCC development, and introduces a reproducible PRS model for risk assessment.

Efficacy of HMJ-38, a new quinazolinone analogue, against the gemcitabine-resistant MIA-PaCa-2 pancreatic cancer cells.

Gemcitabine is frequently utilized to treat pancreatic cancer. The purpose of our study was to create a gemcitabine-resistant MIA-PaCa-2 pancreatic cancer cell line (MIA-GR100) and to evaluate the anti-pancreatic cancer efficacy of HMJ-38, a new quinazolinone analogue. Compared to their parental counterparts, MIA-PaCa-2, established MIA-GR100 cells were less sensitive to gemcitabine. MIA-GR100 cell viability was not affected by 10, 50 and 100 nM gemcitabine concentrations. HMJ-38 reduced MIA-GR100 cell growth and induced autophagy and apoptosis. When stained with monodansylcadaverine (MDC), acridine orange (AO), and terminal deoxynucleotide transferase dUTP nick end labeling (TUNEL), MIA-GR100 cells shrunk, punctured their membranes, and produced autophagy vacuoles and apoptotic bodies. Combining chloroquine (CQ) and 3-methyladenine (3-MA) with HMJ-38 dramatically reduced cell viability, indicating that autophagy function as a cytoprotective mechanism. MIA-GR100 cells treated with both z-VAD-FMK and HMJ-38 were much more viable than those treated with HMJ-38 alone. HMJ-38 promotes apoptosis in MIA-GR100 cells by activating caspases. Epidermal growth factor receptor (EGFR) is one of HMJ-38's principal targets, as determined via in silico target screening with network prediction. HMJ-38 also inhibited EGFR kinase activity and EGFR-associated signaling in MIA-GR100 cells. HMJ-38 may be an effective chemotherapeutic adjuvant for gemcitabine-resistant pancreatic cancer cells, in which it induces an antitumor response.

Exploring RNA modifications, editing, and splicing changes in hyperuricemia and gout.

Hyperuricemia and gout are two of the most common metabolic disorders worldwide; their incidence is increasing with changes in lifestyle, and they are correlated with many diseases, including renal and cardiovascular diseases. The majority of studies on hyperuricemia and gout have focused on the discovery of the associated genes and their functions and on the roles of monocytes and neutrophils in the development of gout. Virtually no studies investigating the epigenomics of gout disease or exploring the clinical significance of such research have been conducted. In this study, we observed that the expression of enzymes involved in RNA modifications or RNA editing was affected in uric acid (UA)- or monosodium urate (MSU)-treated cell lines. RNA alternative splicing and splicing factors were also affected by UA or MSU treatment. We used transcriptome sequencing to analyze genome-wide RNA splicing and RNA editing and found significant changes in RNA splicing and RNA editing in MSU- or UA-treated THP-1 and HEK293 cells. We further found significant changes of RNA modifications, editing, and splicing in patients with gout. The data indicate that RNA modifications, editing, and splicing play roles in gout. The findings of this study may help to understand the mechanism of RNA splicing and modifications in gout, facilitating the development of new diagnostic and therapeutic strategies.

Male-Specific Long Noncoding RNA TTTY15 Inhibits Non-Small Cell Lung Cancer Proliferation and Metastasis via TBX4.

Gender affects cancer susceptibility. Currently, there are only a few studies on Y chromosome-linked long noncoding RNAs (lncRNAs), and the potential association between lncRNAs and cancers in males has not been fully elucidated. Here, we examined the expression of testis-specific transcript Y-linked 15 (TTTY15) in 37 males with non-small cell lung cancer (NSCLC), and performed circular chromosome conformation capture with next-generation sequencing to determine the genomic interaction regions of the TTTY15 gene. Our results showed that the expression levels of TTTY15 were lower in NSCLC tissues. Lower TTTY15 expression levels were associated with Tumor-Node-Metastasis (TNM) stage. A TTTY15 knockdown promoted malignant transformation of NSCLC cells. Based on the bioinformatics analysis of circular chromosome conformation capture data, we found that T-box transcription factor 4 (TBX4) may be a potential target gene of TTTY15. The RNA immunoprecipitation and chromatin immunoprecipitation results showed that TTTY15 may interact with DNA (cytosine-5)-methyltransferase 3A (DNMT3A), and the TTTY15 knockdown increased the binding of DNMT3A to the TBX4 promoter. We concluded that low TTTY15 expression correlates with worse prognosis among patients with NSCLC. TTTY15 promotes TBX4 expression via DNMT3A-mediated regulation. The identification of lncRNAs encoded by male-specific genes may help to identify potential targets for NSCLC therapy.

lncRNA NTT/PBOV1 Axis Promotes Monocyte Differentiation and Is Elevated in Rheumatoid Arthritis.

Monocytes/macrophages are important in orchestrating inflammatory responses. However, knowledge of the long noncoding RNA (lncRNA) regulation of monocytic cell differentiation and diseases remains limited. We aimed to elucidate the role of the 17 kb lncRNA noncoding transcript in T cells (NTT) in monocyte functions. Knockdown and chromatin immunoprecipitation (ChIP) assays in THP-1 cells (human monocytic leukemia cell line) revealed that NTT is regulated by the monocyte key transcription factor C/EBPß and that it binds to the promoter of nearby gene PBOV1 via hnRNP-U. Overexpression of PBOV1 in THP-1 cells resulted in cell cycle G1 arrest, differentiation into macrophages, a marked increase in IL-10 and CXCL10 mRNA levels, and upregulation of the costimulatory molecules. In contrast to the downregulated NTT observed in lipopolysaccharide (LPS)-treated THP-1 cells, the C/EBPß/NTT/PBOV1 axis was found to be hyperactivated in peripheral blood mononuclear cells (PBMCs) of first-time diagnosed untreated early rheumatoid arthritis (RA) patients, and their gene expression levels decreased markedly after treatment. Higher initial C/EBPß/NTT/PBOV1 expression levels were associated with a trend of higher disease activity DAS28 scores. In conclusion, our study suggests that the lncRNA NTT is a regulator of inflammation in monocytes, and its activation participates in monocyte/macrophage differentiation and the pathogenesis of RA.

Long noncoding RNA MIAT promotes non-small cell lung cancer proliferation and metastasis through MMP9 activation.

Long noncoding RNAs (lncRNAs) play crucial roles in carcinogenesis. Myocardial infarction-associated transcript (MIAT), originally isolated as a candidate gene for myocardial infarction, has been found to act as an oncogene in chronic lymphocytic leukaemias and neuroendocrine prostate cancer (NEPC); however, little is known about its expression pattern, biological function, and underlying mechanism in non-small cell lung cancer (NSCLC). In this study, we observed that MIAT expression was upregulated in NSCLC, and its overexpression was associated with advanced tumor stage. Moreover, MIAT knockdown decreased cell proliferation, migration, invasion, and cell cycle arrested in G1 phase. Mechanistic investigation revealed that MIAT could interact with histone methyltransferase mixed-lineage leukemia (MLL). MIAT silencing impeded the binding of MLL on the matrix metalloproteinase 9 (MMP9) promoter region and epigenetically reduced MMP9 transcriptional activity. Overall, our findings suggest that MIAT expression is associated with NSCLC and may be one of the critical targets in progression and metastasis in NSCLC.

DNA-Sensing and Nuclease Gene Expressions as Markers for Colorectal Cancer Progression.

OBJECTIVE: Oncogene-driven stress-related DNA damage has been observed in lesions of colon cancer. Furthermore, DNA sensors and nucleases are stimulated during active DNA damage and replication. However, their changes and influences with respect to cancer remain largely unknown. METHODS: The gene expression levels of cGAS, IFI16, STING, TBK1, IFNB1, TREX1, SAMHD1, RNASEH2A, RNASEH2B, and RNASEH2C were examined in the paired colorectal cancer and adjacent normal part tissues of 53 patients. Their associations with the clinical stages of cancer were then analyzed. RESULTS: All cytosolic DNA-sensing and nuclease-related genes except cGAS, RNASEH2A, and RNASEH2B showed lower mRNA expressions in the colorectal tumor tissues. Moreover, cGAS upregulation was found to be associated with early-stage colorectal cancers, while higher expressions of RNASEH2B, RNASEH2C, and SAMHD1 correlated with metastasis. RNASEH2C knockdown in a colon cancer cell line impaired cell migration, and analysis of the cancer RNA-seq data from The Cancer Genome Atlas (TCGA) database revealed a negative correlation between RNASEH2C expression and E-cadherin levels. CONCLUSIONS: In contrast to DNA-sensing events in viral infections or autoimmunity, cGAS-STING-IFNB signaling is disrupted in colorectal cancer. The expression levels of cGAS, RNASEH2B, RNASEH2C, and SAMHD1 could be prognostic markers of colorectal cancer.

Preclinical Investigation of the Novel Histone Deacetylase Inhibitor AR-42 in the Treatment of Cancer-Induced Cachexia.

BACKGROUND: Cancer cachexia is a debilitating condition that impacts patient morbidity, mortality, and quality of life and for which effective therapies are lacking. The anticachectic activity of the novel HDAC inhibitor AR-42 was investigated in murine models of cancer cachexia. METHODS: The effects of AR-42 on classic features of cachexia were evaluated in the C-26 colon adenocarcinoma and Lewis lung carcinoma (LLC) models. Effects on survival in comparison with approved HDAC inhibitors (vorinostat, romidepsin) were determined. The muscle metabolome and transcriptome (by RNA-seq), as well as serum cytokine profile, were evaluated. Data were analyzed using mixed effects models, analysis of variance, or log-rank tests. All statistical tests were two-sided. RESULTS: In the C-26 model, orally administered AR-42 preserved body weight (23.9±2.6 grams, AR-42-treated; 20.8±1.3 grams, vehicle-treated; P = .005), prolonged survival (P < .001), prevented reductions in muscle and adipose tissue mass, muscle fiber size, and muscle strength and restored intramuscular mRNA expression of the E3 ligases MuRF1 and Atrogin-1 to basal levels (n = 8). This anticachectic effect, confirmed in the LLC model, was not observed after treatment with vorinostat and romidepsin. AR-42 suppressed tumor-induced changes in inflammatory cytokine production and multiple procachexia drivers (IL-6, IL-6Rα, leukemia inhibitory factor, Foxo1, Atrogin-1, MuRF1, adipose triglyceride lipase, uncoupling protein 3, and myocyte enhancer factor 2c). Metabolomic analysis revealed cachexia-associated changes in glycolysis, glycogen synthesis, and protein degradation in muscle, which were restored by AR-42 to a state characteristic of tumor-free mice. CONCLUSIONS: These findings support further investigation of AR-42 as part of a comprehensive therapeutic strategy for cancer cachexia.

Loading of PAX3 to Mitotic Chromosomes Is Mediated by Arginine Methylation and Associated with Waardenburg Syndrome.

PAX3 is a transcription factor critical to gene regulation in mammalian development. Mutations in PAX3 are associated with Waardenburg syndrome (WS), but the mechanism of how mutant PAX3 proteins cause WS remains unclear. Here, we found that PAX3 loads on mitotic chromosomes using its homeodomain. PAX3 WS mutants with mutations in homeodomain lose the ability to bind mitotic chromosomes. Moreover, loading of PAX3 on mitotic chromosomes requires arginine methylation, which is regulated by methyltransferase PRMT5 and demethylase JMJD6. Mutant PAX3 proteins that lose mitotic chromosome localization block cell proliferation and normal development of zebrafish. These results reveal the molecular mechanism of PAX3s loading on mitotic chromosomes and the importance of this localization pattern in normal development. Our findings suggest that PAX3 WS mutants interfere with the normal functions of PAX3 in a dominant negative manner, which is important to the understanding of the pathogenesis of Waardenburg syndrome.

Targeting of multiple oncogenic signaling pathways by Hsp90 inhibitor alone or in combination with berberine for treatment of colorectal cancer.

There is a wide range of drugs and combinations under investigation and/or approved over the last decade to treat colorectal cancer (CRC), but the 5-year survival rate remains poor at stages II-IV. Therefore, new, more-efficient drugs still need to be developed that will hopefully be included in first-line therapy or overcome resistance when it appears, as part of second- or third-line treatments in the near future. In this study, we revealed that heat shock protein 90 (Hsp90) inhibitors have high therapeutic potential in CRC according to combinative analysis of NCBI's Gene Expression Omnibus (GEO) repository and chemical genomic database of Connectivity Map (CMap). We found that second generation Hsp90 inhibitor, NVP-AUY922, significantly downregulated the activities of a broad spectrum of kinases involved in regulating cell growth arrest and death of NVP-AUY922-sensitive CRC cells. To overcome NVP-AUY922-induced upregulation of survivin expression which causes drug insensitivity, we found that combining berberine (BBR), a herbal medicine with potency in inhibiting survivin expression, with NVP-AUY922 resulted in synergistic antiproliferative effects for NVP-AUY922-sensitive and -insensitive CRC cells. Furthermore, we demonstrated that treatment of NVP-AUY922-insensitive CRC cells with the combination of NVP-AUY922 and BBR caused cell growth arrest through inhibiting CDK4 expression and induction of microRNA-296-5p (miR-296-5p)-mediated suppression of Pin1-ß-catenin-cyclin D1 signaling pathway. Finally, we found that the expression level of Hsp90 in tumor tissues of CRC was positively correlated with CDK4 and Pin1 expression levels. Taken together, these results indicate that combination of NVP-AUY922 and BBR therapy can inhibit multiple oncogenic signaling pathways of CRC.

Berberine inhibits the metastatic ability of prostate cancer cells by suppressing epithelial-to-mesenchymal transition (EMT)-associated genes with predictive and prognostic relevance.

BACKGROUND: Over 70% of cancer metastasis from prostate cancer develops bone metastases that are not sensitive to hormonal therapy, radiation therapy, or chemotherapy. The epithelial-to-mesenchymal transition (EMT) genetic program is implicated as a significant contributor to prostate cancer progression. As such, targeting the EMT represents an important therapeutic strategy for preventing or treating prostate cancer metastasis. Berberine is a natural alkaloid with significant antitumor activities against many types of cancer cells. In this study, we investigated the molecular mechanism by which berberine represses the metastatic potential of prostate cancer. METHODS: The effects of berberine on cell migration and invasion were determined by transwell migration assay and Matrigel invasion assay. Expressions of EMT-related genes were determined by an EMT PCR Array and a quantitative RT-PCR. The prognostic relevance of berberine's modulation of EMT-related genes in prostate cancer was evaluated using Kaplan-Meier survival analysis. RESULTS: Berberine exerted inhibitory effects on the migratory and invasive abilities of highly metastatic prostate cancer cells. These inhibitory effects of berberine resulted in significant repression of a panel of mesenchymal genes that regulate the developmental EMT. Among EMT-related genes downregulated by berberine, high BMP7, NODAL and Snail gene expressions of metastatic prostate cancer tissues were associated with shorter survival of prostate cancer patients and provide potential therapeutic interventions. CONCLUSIONS: We concluded that berberine should be developed as a pharmacological agent for use in combination with other anticancer drug for treating metastatic prostate cancer.

PAX3 loads onto pericentromeric heterochromatin during S phase through PARP1.

BACKGROUND: Proper re-establishment of heterochromatin after each round of DNA replication is critical to the preservation of cell identity. Paired box 3 (PAX3), a transcription factor important in embryonic development, was found to mediate the formation of pericentromeric heterochromatin. However, how PAX3 recognizes the heterochromatic environment and re-establishes it after DNA replication remains unclear. MATERIALS AND METHODS: Cell-cycle synchronization, fluorescence microscopic analyses, and co-immunoprecipitation were used to analyze the heterochromatic localization of PAX3 in HEK 293 cells and NIH 3T3 cells. RESULTS: We found that PAX3 binds pericentromeric heterochromatin during middle-to-late S phase. Loading of PAX3 onto pericentromeric heterochromatin requires poly(ADP-ribose) polymerase 1 (PARP1). Furthermore, loss of PAX3 or PARP1 delays cell-cycle progression through the S phase. CONCLUSION: Our results reveal how PAX3 recognizes and maintains pericentromeric heterochromatin at the S phase of the cell cycle.

AMPK reverses the mesenchymal phenotype of cancer cells by targeting the Akt-MDM2-Foxo3a signaling axis.

In cancer cells, the epithelial-mesenchymal transition (EMT) confers the ability to invade basement membranes and metastasize to distant sites, establishing it as an appealing target for therapeutic intervention. Here, we report a novel function of the master metabolic kinase AMPK in suppressing EMT by modulating the Akt-MDM2-Foxo3 signaling axis. This mechanistic link was supported by the effects of siRNA-mediated knockdown and pharmacologic activation of AMPK on epithelial and mesenchymal markers in established breast and prostate cancer cells. Exposure of cells to OSU-53, a novel allosteric AMPK activator, as well as metformin and AICAR, was sufficient to reverse their mesenchymal phenotype. These effects were abrogated by AMPK silencing. Phenotypic changes were mediated by Foxo3a activation, insofar as silencing or overexpressing Foxo3a mimicked the effects of AMPK silencing or OSU-53 treatment on EMT, respectively. Mechanistically, Foxo3a activation led to the transactivation of the E-cadherin gene and repression of genes encoding EMT-inducing transcription factors. OSU-53 activated Foxo3a through two Akt-dependent pathways, one at the level of nuclear localization by blocking Akt- and IKKß-mediated phosphorylation, and a second at the level of protein stabilization via cytoplasmic sequestration of MDM2, an E3 ligase responsible for Foxo3a degradation. The suppressive effects of OSU-53 on EMT had therapeutic implications illustrated by its ability to block invasive phenotypes in vitro and metastatic properties in vivo. Overall, our work illuminates a mechanism of EMT regulation in cancer cells mediated by AMPK, along with preclinical evidence supporting a tractable therapeutic strategy to reverse mesenchymal phenotypes associated with invasion and metastasis.

Targeting the Warburg effect with a novel glucose transporter inhibitor to overcome gemcitabine resistance in pancreatic cancer cells.

Gemcitabine resistance remains a significant clinical challenge. Here, we used a novel glucose transporter (Glut) inhibitor, CG-5, as a proof-of-concept compound to investigate the therapeutic utility of targeting the Warburg effect to overcome gemcitabine resistance in pancreatic cancer. The effects of gemcitabine and/or CG-5 on viability, survival, glucose uptake and DNA damage were evaluated in gemcitabine-sensitive and gemcitabine-resistant pancreatic cancer cell lines. Mechanistic studies were conducted to determine the molecular basis of gemcitabine resistance and the mechanism of CG-5-induced sensitization to gemcitabine. The effects of CG-5 on gemcitabine sensitivity were investigated in a xenograft tumor model of gemcitabine-resistant pancreatic cancer. In contrast to gemcitabine-sensitive pancreatic cancer cells, the resistant Panc-1 and Panc-1(GemR) cells responded to gemcitabine by increasing the expression of ribonucleotide reductase M2 catalytic subunit (RRM2) through E2F1-mediated transcriptional activation. Acting as a pan-Glut inhibitor, CG-5 abrogated this gemcitabine-induced upregulation of RRM2 through decreased E2F1 expression, thereby enhancing gemcitabine-induced DNA damage and inhibition of cell survival. This CG-5-induced inhibition of E2F1 expression was mediated by the induction of a previously unreported E2F1-targeted microRNA, miR-520f. The addition of oral CG-5 to gemcitabine therapy caused greater suppression of Panc-1(GemR) xenograft tumor growth in vivo than either drug alone. Glut inhibition may be an effective strategy to enhance gemcitabine activity for the treatment of pancreatic cancer.

Identification of kazinol Q, a natural product from Formosan plants, as an inhibitor of DNA methyltransferase.

DNA methylation plays a pivotal role in the epigenetic regulation of the transcription of a number of cancer-related genes, thereby representing an important target for cancer prevention and treatment. In our search for DNA methyltransferase (DNMT) inhibitors from Formosan plants, by screening against a library consisting of 12 structurally distinct natural products, we identified kazinol Q {4-[6-(1,1-dimethyl-allyl)-7-hydroxy-chroman-2-yl]-3,6-bis-(3-methyl-but-2-enyl)-benzene-1,2-diol} as an inhibitor of recombinant DNMT1 with IC50 of 7 µM. The effect of kazinol Q on DNMT inhibition was validated by its ability to reactivate the expression of a DNA methylation-silenced gene, E-cadherin, in MDA-MB-231 breast cancer cells. Moreover, kazinol Q suppressed the proliferation of MCF-7 breast and LNCaP prostate cancer cells, in part, through apoptosis induction. The role of DNMT1 inhibition in mediating kazinol Q's antiproliferative effect was supported by the protective effect of ectopic expression of DNMT1 on kazinol Q-induced cell death. Molecular modeling analysis suggests that kazinol Q inhibited DNMT activity by competing with cytosine binding, a mechanism similar to that described for (-)-epigallocatechin-3-gallate (EGCG). Relative to EGCG, kazinol Q exhibits several desirable features for drug development, including chemical stability and increased hydrophobicity, and might have therapeutic relevance to cancer treatment.

Activation of silenced tumor suppressor genes in prostate cancer cells by a novel energy restriction-mimetic agent.

BACKGROUND: Targeting tumor metabolism by energy restriction-mimetic agents (ERMAs) has emerged as a strategy for cancer therapy/prevention. Evidence suggests a mechanistic link between ERMA-mediated antitumor effects and epigenetic gene regulation. METHODS: Microarray analysis showed that a novel thiazolidinedione-derived ERMA, CG-12, and glucose deprivation could suppress DNA methyltransferase (DNMT)1 expression and reactivate DNA methylation-silenced tumor suppressor genes in LNCaP prostate cancer cells. Thus, we investigated the effects of a potent CG-12 derivative, CG-5, vis-à-vis 2-deoxyglucose, glucose deprivation and/or 5-aza-deoxycytidine, on DNMT isoform expression (Western blotting, RT-PCR), DNMT1 transcriptional activation (luciferase reporter assay), and expression of genes frequently hypermethylated in prostate cancer (quantitative real-time PCR). Promoter methylation was assessed by pyrosequencing analysis. SiRNA-mediated knockdown and ectopic expression of DNMT1 were used to validate DNMT1 as a target of CG-5. RESULTS: CG-5 and glucose deprivation upregulated the expression of DNA methylation-silenced tumor suppressor genes, including GADD45a, GADD45b, IGFBP3, LAMB3, BASP1, GPX3, and GSTP1, but also downregulated methylated tumor/invasion-promoting genes, including CD44, S100A4, and TACSTD2. In contrast, 5-aza-deoxycytidine induced global reactivation of these genes. CG-5 mediated these epigenetic effects by transcriptional repression of DNMT1, which was associated with reduced expression of Sp1 and E2F1. SiRNA-mediated knockdown and ectopic expression of DNMT1 corroborated DNMT1's role in the modulation of gene expression by CG-5. Pyrosequencing revealed differential effects of CG-5 versus 5-aza-deoxycytidine on promoter methylation in these genes. CONCLUSIONS: These findings reveal a previously uncharacterized epigenetic effect of ERMAs on DNA methylation-silenced tumor suppressor genes, which may foster novel strategies for prostate cancer therapy.

Histone deacetylase 10 relieves repression on the melanogenic program by maintaining the deacetylation status of repressors.

HDAC10 belongs to the class II histone deacetylase family; however, its functions remain enigmatic. We report here that the HDAC10 protein complex contained deacetylated chaperone protein hsc70, and HDAC10 relieved repression of melanogenesis by decreasing the repressional activity of two transcriptional regulators, paired box protein 3 (Pax3) and KRAB-associated protein 1 (KAP1). HDAC10 physically interacted with Pax3 and KAP1 in a ternary complex and maintained Pax3 and KAP1 in a deacetylated state. Deacetylated Pax3 and KAP1 derepressed promoters of microphthalmia-associated transcription factor (MITF) and melanocyte-specific tyrosinase-related protein 1 and 2 (TRP-1 and TRP-2), three genes of the melanogenesis cascade, in a trichostatin A-sensitive manner. Co-occupancy of melanogenic promoters by HDAC10, Pax3, and KAP1 only happened in cells of the melanocyte lineage, and KAP1 facilitated nuclear enrichment of HDAC10. Finally, cellular melanin content correlated directly with the expression level and activity of HDAC10. Our results not only show that HDAC10 regulates melanogenesis but also demonstrate that the transcriptional activities of Pax3 and KAP1 are intimately linked to their acetylation status.

Transcriptional and subcellular regulation of the TRIP-Br family.

TRIP-Brs are a recently discovered set of proteins whose functions remain poorly characterized. Here we report the identification of TRIP-Br3 as a member of the TRIP-Br family along with evidence showing that TRIP-Brs interact with bromodomain-containing transcriptional cofactors PCAF, STAF65gamma, and KAP1. PCAF, a histone acetyltransferase; STAF65gamma, a protein associated with histone acetylation activity; and KAP1, a corepressor, influence the transcriptional activity of TRIP-Brs differentially. Finally, while all three TRIP-Brs are localized to the nucleus, TRIP-Br2 and TRIP-Br3 are also present in the cytoplasm through interaction with CRM1. Our results suggest that different TRIP-Brs function by interacting with a wide variety of bromodomain-containing transcriptional regulators in different subcellular locales.

Transcriptional repression activity of PAX3 is modulated by competition between corepressor KAP1 and heterochromatin protein 1.

Pax3 is a transcription factor crucial for normal development and tumorigenesis. Pax3 has been known to cause Waardenburg syndrome and pediatric alveolar rhabdomyosarcoma, but how Pax3 regulates transcription is not clear. Here, we report that Pax3 represses transcription and selectively interacts with heterochromatin protein 1 (HP1) and KAP1. KAP1 functions as a transcriptional corepressor by recruiting HP1 to facilitate the formation of a closed chromatin through histone deacetylation and methylation. We found that KAP1 is a corepressor for Pax3 by augmenting the repressional activity of Pax3. Unexpectedly, HP1gamma diminishes the repressional activity of Pax3. On target promoters, KAP1 and HP1gamma compete for binding with Pax3 on the N-terminal paired domain, and the C-terminal domain of Pax3 governs the subcellular localization of Pax3. Taken together, our results indicate that Pax3 represses transcription through a novel mechanism involving competition between corepressor KAP1 and the heterochromatin-binding protein HP1gamma.