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Identification of Growth arrest and DNA-damage-inducible gene beta (GADD45beta) as a Novel Tumor Suppressor in Pituitary Gonadotrope Tumors

ABSTRACT: Gonadotrope or null cell pituitary tumors present clinically with signs of hypogonadism and hypopituitarism, together with visual disturbances due to mass effects. Since there are no medical therapies, surgery and/or radiation are the only therapeutic options. To identify dysregulated genes and/or pathways that may play a role in tumorigenesis and/ or progression, molecular profiling was performed on 14 gonadotrope tumors and 9 normal human pituitaries from autopsy samples. Principle component analysis (PCA) revealed clear discrimination between tumor and normal pituitary gene expression profiles. Bioinformatic analysis identified specific genes and pathways that were highly differentially regulated, including a cohort of putative downstream effectors of p53 were repressed in gonadotrope pituitary tumors, including GADD45β, GADD45γ and Reprimo with concomitant downregulation of the upstream regulator, PLAGL1. PLAGL1 reexpression in gonadotrope cells did not directly modulate the downstream targets. Further functional analysis of GADD45β was performed. Overexpression of GADD45β in mouse gonadotrope cells blocked proliferation, increased rates of apoptosis in response to growth factor withdrawal and increased colony formation in soft agar. In contrast to prior studies with GADD45γ, methylation interference assays showed no evidence of epigenetic modification of the GADD45β promoter in pituitary tumors. Thus, our data suggest that many components downstream of p53 are suppressed in gonadotrope pituitary tumors. A novel candidate, GADD45β is low in tumors and reexpression blocks proliferation, survival and tumorigenesis in gonadotrope cells. Unlike GADD45γ, GADD45β is not methylated to block its expression. Together these studies identify new targets and mechanisms to explore concerning pituitary tumor initiation and progression.

ORGANISM(S): Homo sapiens

PROVIDER: GSE26966 | GEO | 2011/01/31

SECONDARY ACCESSION(S): PRJNA136983

REPOSITORIES: GEO

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Project description:Gonadotrope or null cell pituitary tumors present clinically with signs of hypogonadism and hypopituitarism, together with visual disturbances due to mass effects. Since there are no medical therapies, surgery and/or radiation are the only therapeutic options. To identify dysregulated genes and/or pathways that may play a role in tumorigenesis and/ or progression, molecular profiling was performed on 14 gonadotrope tumors and 9 normal human pituitaries from autopsy samples. Principle component analysis (PCA) revealed clear discrimination between tumor and normal pituitary gene expression profiles. Bioinformatic analysis identified specific genes and pathways that were highly differentially regulated, including a cohort of putative downstream effectors of p53 were repressed in gonadotrope pituitary tumors, including GADD45Î², GADD45Î³ and Reprimo with concomitant downregulation of the upstream regulator, PLAGL1. PLAGL1 reexpression in gonadotrope cells did not directly modulate the downstream targets. Further functional analysis of GADD45Î² was performed. Overexpression of GADD45Î² in mouse gonadotrope cells blocked proliferation, increased rates of apoptosis in response to growth factor withdrawal and increased colony formation in soft agar. In contrast to prior studies with GADD45Î³, methylation interference assays showed no evidence of epigenetic modification of the GADD45Î² promoter in pituitary tumors. Thus, our data suggest that many components downstream of p53 are suppressed in gonadotrope pituitary tumors. A novel candidate, GADD45Î² is low in tumors and reexpression blocks proliferation, survival and tumorigenesis in gonadotrope cells. Unlike GADD45Î³, GADD45Î² is not methylated to block its expression. Together these studies identify new targets and mechanisms to explore concerning pituitary tumor initiation and progression. To elucidate mechanisms involved in pituitary tumorigenesis and progression, we performed individual gene expression microarray analysis using Affy U133 Plus 2.0 GeneChips comparing 14 gonadotrope tumors with 9 normal pituitary samples obtained at autopsy.

Project description:The goals of this study is to enrich the population of ovine gonadotropes via adenovirus-mediated targeting and flow cytometry to compare NGS-derived transcriptome profiling (RNA-seq) of a gonadotrope-enriched cell population to the combined transcriptome of all anterior pituitary cells and apply enrichment method to query the transcriptome of sorted ovine pituitary cells in response to treatment with 10 nM estradiol (E2) for six hours. Methods: mRNA profiles of sheep anterior pituitary cells were generated by deep sequencing, in sextuplicates, using Illumina HiSeq. The sequence reads that passed quality filters were analyzed at the transcript level with GSNAP, followed by featureCounts and then followed by edgeR. qRT–PCR validation was performed using SYBR Green assays. Results: About 124 million sequence reads per sample were mapped to the sheep genome (Oar v.3.1) which identified 17,082 transcripts in the pituitaries. RNA-seq data confirmed overrepresentation of genes known to be expressed in pituitary in sorted samples; 11 of genes (5 gonadotrope-specific and 6 non gonadotrope-specific) were validated with qRT–PCR. RNA-seq data had a linear relationship with qRT–PCR. Approximately 7.2% of the transcripts showed differential expression between the sorted (gonadotropes) and unsorted (all anterior pituitary cells) pituitary cells, with a fold change ≥3 and FDR <0.05. Hierarchical clustering of differentially expressed genes uncovered several as yet uncharacterized genes that may contribute to gonadotrope function. 232 genes were detected as upregulated in the sorted GFP-positive cells treated with E2 (gonadotropes) and 31 were downregulated following E2 treatment with a fold change ≥1.5 and FDR <0.1. Conclusions: Our study represents the first detailed analysis of the gonadotrope transcriptome, with 6 biologic replicates, generated by RNA-seq technology. The data analysis workflows reported here should provide a framework for comparative investigations of gonadotrope expression profiles. This method was applied to determine differentially expressed genes in the sorted population of pituitary cells (gonadotropes) in response to 10 nM E2.

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Identification of Growth arrest and DNA-damage-inducible gene beta (GADD45beta) as a Novel Tumor Suppressor in Pituitary Gonadotrope Tumors

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