Over-expression of MSG1 transcriptional co-activator increases melanin in B16 melanoma cells: a possible role for MSG1 in melanogenesis

Whole Genome Resequencing Reveals Selection Signals Related to Wool Color in Sheep

Wool color is controlled by a variety of genes. Although the gene regulation of some wool colors has been studied in relative depth, there may still be unknown genetic variants and control genes for some colors or different breeds of wool that need to be identified and recognized by whole genome resequencing. Therefore, we used whole genome resequencing data to compare and analyze sheep populations of different breeds by population differentiation index and nucleotide diversity ratios (Fst and θπ ratio) as well as extended haplotype purity between populations (XP-EHH) to reveal selection signals related to wool coloration in sheep. Screening in the non-white wool color group (G1 vs. G2) yielded 365 candidate genes, among which PDE4B, GMDS, GATA1, RCOR1, MAPK4, SLC36A1, and PPP3CA were associated with the formation of non-white wool; an enrichment analysis of the candidate genes yielded 21 significant GO terms and 49 significant KEGG pathways (p < 0.05), among which 17 GO terms and 21 KEGG pathways were associated with the formation of non-white wool. Screening in the white wool color group (G2 vs. G1) yielded 214 candidate genes, including ABCD4, VSX2, ITCH, NNT, POLA1, IGF1R, HOXA10, and DAO, which were associated with the formation of white wool; an enrichment analysis of the candidate genes revealed 9 significant GO-enriched pathways and 19 significant KEGG pathways (p < 0.05), including 5 GO terms and 12 KEGG pathways associated with the formation of white wool. In addition to furthering our understanding of wool color genetics, this research is important for breeding purposes.

SISTEMA: A large and standardized collection of transcriptome data sets for human pluripotent stem cell research

Human pluripotent stem cells have ushered in an exciting new era for disease modeling, drug discovery, and cell therapy development. Continued progress toward realizing the potential of human pluripotent stem cells will be facilitated by robust data sets and complementary resources that are easily accessed and interrogated by the stem cell community. In this context, we present SISTEMA, a quality-controlled curated gene expression database, built on a valuable catalog of human pluripotent stem cell lines, and their derivatives for which transcriptomic analyses have been generated using a single experimental pipeline. SISTEMA functions as a one-step resource that will assist the stem cell community to easily evaluate the expression level for genes of interest, while comparing them across different hPSC lines, cell types, pathological conditions, or after pharmacological treatments.

•

SISTEMA is a curated gene expression database using human pluripotent stem cell lines

•

A single experimental and analytical pipeline are used for the transcriptomic analyses

•

SISTEMA is a user friendly Web portal designed for the stem cell community

Melanocyte-specific gene 1 promotes melanoma progression by enhancing the expression of Bcl-2

Malignant melanoma is a class of highly malignant tumors derived from melanocytes. At present, the dysregulated gene expression involved in the progression of melanoma has attracted much attention. In the present study, the gene expression profile of human melanoma tissue was screened using a cDNA microarray, and it was identified that melanocyte-specific gene 1 (MSG1) was significantly overexpressed in melanoma tissue compared with paired nevus tissues. The overexpression of MSG1 in melanoma was subsequently confirmed using immunohistochemistry in a set of melanoma tissues. It was additionally identified that the overexpression of MSG1 may promote cell viability and inhibit cell apoptosis in human melanoma A375 cells, thus promoting melanoma progression. Mechanistically, following screening of the expression of apoptosis-associated proteins, MSG1 was demonstrated to enhance the expression of the apoptosis inhibitor B-cell lymphoma 2 (Bcl-2) to inhibit melanoma cell apoptosis. Therefore, it was concluded that the overexpression of MSG1 inhibits apoptosis by enhancing Bcl-2 expression in malignant melanoma, thus promoting melanoma progression.

Loss of CITED1, an MITF regulator, drives a phenotype switch in vitro and can predict clinical outcome in primary melanoma tumours

CITED1 is a non-DNA binding transcriptional co-regulator whose expression can distinguish the ‘proliferative’ from ‘invasive’ signature in the phenotype-switching model of melanoma. We have found that, in addition to other ‘proliferative’ signature genes, CITED1 expression is repressed by TGFβ while the ‘invasive’ signature genes are upregulated. In agreement, CITED1 positively correlates with MITF expression and can discriminate the MITF-high/pigmentation tumour molecular subtype in a large cohort (120) of melanoma cell lines. Interestingly, CITED1 overexpression significantly suppressed MITF promoter activation, mRNA and protein expression levels while MITF was transiently upregulated following siRNA mediated CITED1 silencing. Conversely, MITF siRNA silencing resulted in CITED1 downregulation indicating a reciprocal relationship. Whole genome expression analysis identified a phenotype shift induced by CITED1 silencing and driven mainly by expression of MITF and a cohort of MITF target genes that were significantly altered. Concomitantly, we found changes in the cell-cycle profile that manifest as transient G1 accumulation, increased expression of CDKN1A and a reduction in cell viability. Additionally, we could predict survival outcome by classifying primary melanoma tumours using our in vitro derived ‘CITED1-silenced’ gene expression signature. We hypothesize that CITED1 acts a regulator of MITF, functioning to maintain MITF levels in a range compatible with tumourigenesis.

Cited1 deficiency suppresses intestinal tumorigenesis

Conditional deletion of Apc in the murine intestine alters crypt-villus architecture and function. This process is accompanied by multiple changes in gene expression, including upregulation of Cited1, whose role in colorectal carcinogenesis is unknown. Here we explore the relevance of Cited1 to intestinal tumorigenesis. We crossed Cited1 null mice with Apc(Min/+) and AhCre(+)Apc(fl/fl) mice and determined the impact of Cited1 deficiency on tumour growth/initiation including tumour multiplicity, cell proliferation, apoptosis and the transcriptome. We show that Cited1 is up-regulated in both human and murine tumours, and that constitutive deficiency of Cited1 increases survival in Apc(Min/+) mice from 230.5 to 515 days. However, paradoxically, Cited1 deficiency accentuated nearly all aspects of the immediate phenotype 4 days after conditional deletion of Apc, including an increase in cell death and enhanced perturbation of differentiation, including of the stem cell compartment. Transcriptome analysis revealed multiple pathway changes, including p53, PI3K and Wnt. The activation of Wnt through Cited1 deficiency correlated with increased transcription of β-catenin and increased levels of dephosphorylated β-catenin. Hence, immediately following deletion of Apc, Cited1 normally restrains the Wnt pathway at the level of β-catenin. Thus deficiency of Cited1 leads to hyper-activation of Wnt signaling and an exaggerated Wnt phenotype including elevated cell death. Cited1 deficiency decreases intestinal tumourigenesis in Apc(Min/+) mice and impacts upon a number of oncogenic signaling pathways, including Wnt. This restraint imposed by Cited1 is consistent with a requirement for Cited1 to constrain Wnt activity to a level commensurate with optimal adenoma formation and maintenance, and provides one mechanism for tumour repression in the absence of Cited1.

Identification of estradiol/ERα-regulated genes in the mouse pituitary

Estrogen acts to prime the pituitary prior to the GnRH-induced LH surge by undiscovered mechanisms. This study aimed to identify the key components that mediate estrogen action in priming the pituitary. RNA extracted from the pituitaries of metestrous (low estrogen) and proestrus (high estrogen) stage mice, as well as from ovariectomized wild-type and estrogen receptor α (ERα) knockout mice treated with 17β-estradiol (E(2)) or vehicle, was used for gene expression microarray. Microarray data were then aggregated, built into a functional electronic database, and used for further characterization of E(2)/ERα-regulated genes. These data were used to compile a list of genes representing diverse biological pathways that are regulated by E(2) via an ERα-mediated pathway in the pituitary. This approach substantiates ERα regulation of membrane potential regulators and intracellular vesicle transporters, among others, but not the basic components of secretory machinery. Subsequent characterization of six selected genes (Cacna1a, Cacna1g, Cited1, Abep1, Opn3, and Kcne2) confirmed not only ERα dependency for their pituitary expression but also the significance of their expression in regulating GnRH-induced LH secretion. In conclusion, findings from this study suggest that estrogen primes the pituitary via ERα by equipping pituitary cells with critical cellular components that potentiate LH release on subsequent GnRH stimulations.

Regulation of NR4A nuclear receptor expression by oncogenic BRAF in melanoma cells

Activating mutations in the MAPK pathway effectors, NRAS or BRAF, are detected in over 70% of melanomas. Accordingly, the identification of downstream targets of constitutive MAPK signalling in melanoma represents a major goal in understanding the genesis of this disease. We report here the regulation of members of the NR4A family of nuclear receptors by the BRAF-MEK-ERK cascade in melanoma cells. Expression profiling of melanoma cells in which both the NR4A1 and NR4A2 family members have been down-regulated by siRNA revealed alterations in genes associated with proliferation, survival and invasiveness of tumour cells. Notably, the up-regulation of Wnt/β-catenin pathway antagonists, DACT1 and CITED1, following NR4A1/2 ablation suggests a possible link between NR4A and β-catenin activity in melanoma cells. Taken together, these data suggest that dysregulation of NR4A nuclear receptors expression and function by the MAPK pathway may contribute to melanoma tumourigenicity.

Model cell culture system for defining the molecular and biochemical events mediating terminal differentiation of human melanoma cells

Cancer cells are commonly less differentiated than their normal progenitors; a phenotype that correlates with loss of specialized functions and an increased capability to self-renew. Melanoma is an ideal model to analyze cancer progression and differentiation since a well-characterized process of step-wise tumor progression has been defined. Our lab previously described a combinatorial in vitro treatment protocol to induce terminal differentiation of human melanoma cells using a low dose of the PKC activator Mezerein (Mez) combined with interferon-beta (IFN-beta), which also activates IFN-stimulated gene expression in addition to the re-differentiation program. In principle, using an alternate way to induce terminal differentiation not including IFN-beta would be more compatible with gene expression profiling. A higher concentration of Mez alone induced terminal differentiation of HO-1 human melanoma cells as measured by morphological, growth and biochemical assays. Pre-treatment with the PKC inhibitor GF109203x blocked changes associated with differentiation and inhibited the ability of Mez to force irreversible/terminal differentiation. By combining this efficient method of inducing terminal differentiation with microarray analyses we now identify potential regulators of this process and demonstrate utility of this novel in vitro model in which to study the molecular determinants and mechanisms of human melanoma differentiation.

An EGR2/CITED1 transcription factor complex and the 14-3-3sigma tumor suppressor are involved in regulating ErbB2 expression in a transgenic-mouse model of human breast cancer

Amplification and elevated expression of the ErbB2 receptor tyrosine kinase occurs in 20% of human breast cancers and is associated with a poor prognosis. We have previously demonstrated that mammary tissue-specific expression of activated ErbB2 under the control of its endogenous promoter results in mammary tumor formation. Tumor development was associated with amplification and overexpression of ErbB2 at both the transcript and protein levels. Here we demonstrate that the EGR2/Krox20 transcription factor and its coactivator CITED1 are coordinately upregulated during ErbB2 tumor induction. We have identified an EGR2 binding site in the erbB2 promoter and demonstrated by chromatin immunoprecipitation assays that EGR2 and CITED1 associate specifically with this region of the promoter. EGR2 and CITED1 were shown to associate, and expression from an erbB2 promoter-reporter construct was stimulated by EGR2 and was further enhanced by CITED1 coexpression. Furthermore, expression of the 14-3-3sigma tumor suppressor led to downregulation of ErbB2 protein levels and relocalization of EGR2 from the nucleus to the cytoplasm. Taken together, these observations suggest that, in addition to an increased gene copy number and upregulation of EGR2 and CITED1, an elevated erbB2 transcript level involves the loss of 14-3-3sigma, which sequesters a key transcriptional regulator of the erbB2 promoter.

Expression of the transcriptional coactivator CITED1 in the adult and developing murine brain

The transcription coactivator CITED1 is an important mediator of transcriptional events regulated by estrogen or TGF-beta. We used in situ hybridization to delineate the distribution of CITED1 mRNA in the adult and developing murine brain and found robust CITED1 expression in ventral hypothalamus and midbrain raphe. The distribution of CITED1 in these regions overlapped the reported expression of estrogen receptors alpha and beta. Less intense expression of CITED1 was also evident in medial preoptic area, subfornical organ, thalamus and cerebral cortex. CITED1 mRNA in the arcuate nucleus (an area of active transcriptional modulation by TGF-beta) was evident in postmigratory neurons as early as embryonic day 16. Expression of CITED1 in arcuate continued throughout postnatal development. CITED1 in developing cerebellum was first evident in external granule cells and was transiently expressed in the Purkinje cell/granule cell layer in a temporal pattern similar to estrogen receptor-beta. The spatial and temporal distribution of CITED1 mRNA reported here is consistent with a role for CITED1 in the modulation of transcriptional events mediated by steroid hormone and cytokine signaling pathways.

CITED1 homozygous null mice display aberrant pubertal mammary ductal morphogenesis

Expression microarray analysis identified CITED1 among a group of genes specifically upregulated in the pubertal mouse mammary gland. At puberty, CITED1 localizes to the luminal epithelial cell population of the mammary ducts and the body cells of the terminal end buds. Generation of CITED1 gene knockout mice showed that homozygous null mutants exhibit retarded mammary ductal growth at puberty and, in addition, dilated ductal structures with a lack of spatial restriction of the subtending branches. Analysis of CITED1 homozygous null and heterozygous null mammary gland gene expression using microarrays suggested that the mammary-specific phenotype seen in the homozygous null females is due to a disturbance in the transcription of a number of key mediators of pubertal ductal morphogenesis. These include estrogen and TGFbeta responsive genes, such as the EGFR/ErbB2 ligand, amphiregulin, whose transcription we suggest is directly or indirectly regulated by CITED1.

Transcription factor Ap-2α is necessary for development of embryonic melanophores, autonomic neurons and pharyngeal skeleton in zebrafish

The genes that control development of embryonic melanocytes are poorly defined. Although transcription factor Ap-2alpha is expressed in neural crest (NC) cells, its role in development of embryonic melanocytes and other neural crest derivatives is unclear because mouse Ap-2alpha mutants die before melanogenesis. We show that zebrafish embryos injected with morpholino antisense oligonucleotides complementary to ap-2alpha (ap-2alpha MO) complete early morphogenesis normally and have neural crest cells. Expression of c-kit, which encodes the receptor for the Steel ligand, is reduced in these embryos, and, similar to zebrafish c-kit mutant embryos, embryonic melanophores are reduced in number and migration. The effects of ap-2alpha MO injected into heterozygous and homozygous c-kit mutants support the notion that Ap-2alpha works through C-kit and additional target genes to mediate melanophore cell number and migration. In contrast to c-kit mutant embryos, in ap-2alpha MO-injected embryos, melanophores are small and under-pigmented, and unexpectedly, analysis of mosaic embryos suggests Ap-2alpha regulates melanophore differentiation through cell non-autonomous targets. In addition to melanophore phenotypes, we document reduction of other neural crest derivatives in ap-2alpha MO-injected embryos, including jaw cartilage, enteric neurons, and sympathetic neurons. These results reveal that Ap-2alpha regulates multiple steps of melanophore development, and is required for development of other neuronal and non-neuronal neural crest derivatives.

Ca(2+)-inactivated K+ current is modulated by endothelin-1 in B-16 murine melanoma cells

It is well established that endothelin-1 (ET-1) plays a role in differentiation and proliferation in a variety of cells such as fibroblasts and human melanoma cells via a receptor-mediated mechanism. However, whether ET-1 modulates ion channel activity in these cell types is still unknown. In this report, we recorded the voltage-dependent outward K+ current in cultured B16 melanoma cells using the patch-clamp technique. Biophysical and pharmacological properties of the K+ current, and the effect of ET-1 on the K+ current were investigated. When cells were loaded with a Ca(2+)-chelating agent (EGTA or BAPTA), the K+ current amplitude gradually increased with time after establishment of the whole cell configuration. Replacement of Ca2+ with Co2+ in the extracellular medium caused no significant modulation of the K+ current amplitude. Addition of BaCl2 or quinidine to the extracellular solution reduced the K+ current amplitude, whereas the K+ current was insensitive to tetraethylammonium. ET-1 (10 nM) reversibly decreased the K+ current amplitude and accelerated the decay of the K+ current. The ET-1-induced inhibitory effect displayed no desensitization following repeated ET-1 application. Pretreatment with pertussis toxin (PTX) or perfusion of cells with the protein kinase C (PKC) inhibitor H-7 abolished the inhibitory effect of ET-1 on the K+ current. We conclude that the outward K+ current recorded in murine B-16 melanoma cells represents a Ca(2+)-inactivated K+ current, and that the inhibitory effect of ET-1 on the K+ current may reveal a novel mechanism to control the differentiation and proliferation of melanoma cells.

Pediatric liver tumors and hepatic ontogenesis: common and distinctive pathways

Several types of pediatric liver tumors exhibit structural features apparently reflecting processes which normally occur during hepatic ontogenesis: some hepatoblastomas mimic distinct phases of hepatogenesis, including the formation of mesenchymal structures closely associated with immature epithelia, and there are tumors almost exclusively consisting of complex mesenchymal patterns. Current classifications of hepatoblastomas refer to the identification of more or less mature (differentiated) single or mixed components seen in histologic preparations. These do not, however, attempt to integrate ontogenic pathways, in contrast for example, to nephroblastoma and associated lesions, where such a view has proved to be highly fruitful. Based on the fact that an enormous amount of knowledge has recently been accumulated regarding hepatic ontogenesis, time may have come to look at these tumors with a new eye. In what follows, we aim at trying to analyze distinct features of pediatric hepatic tumors (except vascular tumors) within the background of ontogenesis. Some key steps of hepatogenesis and the regulatory factors involved may, in the future, deliver an armamentarium to search for novel molecular mechanisms involved in tumorigenic pathways.

Type I gamma-GT mRNA is expressed in B16 melanoma and levels correlate with pigmentation

Gamma-glutamyl transpeptidase (gamma-GT), an ectoenzyme involved mainly in glutathione metabolism, is expressed in B16 melanoma cells. B16 melanoma cells under continuous culture conditions show a phenotypic drift from melanotic to amelanotic and re-melanotic stages. We have investigated the regulation of gamma-GT in B16 melanoma cells under such different pigmentary conditions. High levels of gamma-GT messenger RNA (mRNA) and activity were detected in pigmented B16 melanoma cells, whereas in amelanotic B16 melanoma cells the levels were very low. Treatment with lactic acid, a known inhibitor of tyrosinase gene expression, also led to the down-regulation of gamma-GT mRNA and activity. Thus our results indicate that gamma-GT regulation depends on the pigmentation status in pigment cells. We have also assessed the levels of gamma-GT in normal murine melanocytes (melan-a cells). It was seen that melan-a cells express very low levels of gamma-GT. As gamma-GT is known to be regulated in a tissue-specific manner, and is expressed from as many as six promoters giving rise to six different types of mRNAs each having unique 5' ends, we have further investigated the type of gamma-GT mRNA expressed in B16 melanoma and melan-a cells. In this study, we have conclusively demonstrated that type I mRNA transcript of gamma-GT is expressed in B16 melanoma and melan-a cells.