The role of cumulative growth hormone exposure in determining mortality and morbidity in acromegaly: a single centre study.

PURPOSE: Acromegaly has traditionally been associated with significant mortality and cardiovascular morbidity. The aim of this study was to assess the overall mortality and improvement in mortality and morbidity in acromegaly and correlate these with cumulative growth hormone exposure. METHODS: All patients treated for acromegaly at our centre until 2012 were analysed in this retrospective observational study. Baseline demographic details such as age at diagnoses, radiological features and pituitary status were obtained on these 167 patients. Cumulative GH levels (GHy) were calculated as a sum of average of GH readings in consecutive years. Mortality rates and development of new diabetes, hypertension and cardiovascular events (stroke, congestive cardiac failure and ischaemic heart disease) were assessed. RESULTS: The SMR for overall cohort was 1.6. There has been a significant improvement in SMR over the past two decades (SMR until 1992 2.5; SMR since 1992 1.0). Cumulative GH exposure was significantly high in patients who died (35.2 vs 24.1, p < 0.01) and in those with incident metabolic or vascular events during follow up (51.6 vs 24.4, p = 0.0001). The cardiovascular event rate of the 'new' cohort was significantly better than the 'old' cohort (8.0 vs. 29.1 %, p < 0.001). CONCLUSION: There has been significant improvement in mortality and morbidity associated with acromegaly, in the setting of routine care in a specialized endocrine unit. Early and effective treatment to 'control' acromegaly could reduce GH exposure and hence vascular comorbidities.

Epidrug mediated re-expression of miRNA targeting the HMGA transcripts in pituitary cells.

INTRODUCTION: Transgenic mice overexpressing the high mobility group A (HMGA) genes, Hmga1 or Hmga2 develop pituitary tumours and their overexpression is also a frequent finding in human pituitary adenomas. In some cases, increased expression of HMGA2 but not that of HMGA1 is consequent to genetic perturbations. However, recent studies show that down-regulation of microRNA (miRNA), that contemporaneously target the HMGA1 and HMGA2 transcripts, are associated with their overexpression. RESULTS: In a cohort of primary pituitary adenoma we determine the impact of epigenetic modifications on the expression of HMGA-targeting miRNA. For these miRNAs, chromatin immunoprecipitations showed that transcript down-regulation is correlated with histone tail modifications associated with condensed silenced genes. The functional impact of epigenetic modification on miRNA expression was determined in the rodent pituitary cell line, GH3. In these cells, histone tail, miRNA-associated, modifications were similar to those apparent in human adenoma and likely account for their repression. Indeed, challenge of GH3 cells with the epidrugs, zebularine and TSA, led to enrichment of the histone modification, H3K9Ac, associated with active genes, and depletion of the modification, H3K27me3, associated with silent genes and re-expression of HMGA-targeting miRNA. Moreover, epidrugs challenges were also associated with a concomitant decrease in hmga1 transcript and protein levels and concurrent increase in bmp-4 expression. CONCLUSIONS: These findings show that the inverse relationship between HMGA expression and targeting miRNA is reversible through epidrug interventions. In addition to showing a mechanistic link between epigenetic modifications and miRNA expression these findings underscore their potential as therapeutic targets in this and other diseases.

The EFEMP1 gene: a frequent target for epigenetic silencing in multiple human pituitary adenoma subtypes.

BACKGROUND/AIMS: In a genome-wide investigation we recently identified the EGF-containing fibulin-like extracellular matrix protein 1 gene, EFEMP1, as hypermethylated in growth hormone-secreting adenoma. METHODS: In an independent cohort we determined expression of EFEMP1, CpG island methylation and histone tail modification status. The causal consequences of epigenetic modification were determined through epidrug-induced reversal and enforced EFEMP1 expression in GH3 cells. RESULTS: The majority of adenomas, irrespective of subtype, show reduced EFEMP1 expression. However, epigenetic change, as determined by CpG island methylation, was not invariantly associated with decreased EFEMP1 expression. Conversely, chromatin immunoprecipitation assays revealed enrichment for modifications associated with either active or silenced genes in adenoma that did or did not express EFEMP1 respectively. In AtT-20 and GH3 cells a causal relationship between epigenetic silencing and expression of EFEMP1 was established where co-incubation with the epidrugs zebularine and TSA induced expression of EFEMP1 and concomitant histone tail modifications toward those associated with expressed genes. Enforced expression of EFEMP1 in GH3 cells was without effect on cell proliferation or apoptotic end-points, however inhibition of endogenous matrix metalloproteinase (MMP)-2 expression was apparent. Primary adenomas did not show this relationship, however a positive correlation was apparent with the MMP7 transcript and perhaps reflects cell or species differences. CONCLUSIONS: The protein product of the EFEMP1 gene, fibulin-3, is reported to impact on multiple pathways in a cell-specific context. Subtype-independent loss of EFEMP1 expression in the majority of primary adenomas should prompt more detailed investigation in this tumour type.

Genome-wide analysis in a murine Dnmt1 knockdown model identifies epigenetically silenced genes in primary human pituitary tumors.

DNA methylation at promoter CpG islands (CGI) is an epigenetic modification associated with inappropriate gene silencing in multiple tumor types. In the absence of a human pituitary tumor cell line, small interfering RNA-mediated knockdown of the maintenance methyltransferase DNA methyltransferase (cytosine 5)-1 (Dnmt1) was used in the murine pituitary adenoma cell line AtT-20. Sustained knockdown induced reexpression of the fully methylated and normally imprinted gene neuronatin (Nnat) in a time-dependent manner. Combined bisulfite restriction analysis (COBRA) revealed that reexpression of Nnat was associated with partial CGI demethylation, which was also observed at the H19 differentially methylated region. Subsequent genome-wide microarray analysis identified 91 genes that were significantly differentially expressed in Dnmt1 knockdown cells (10% false discovery rate). The analysis showed that genes associated with the induction of apoptosis, signal transduction, and developmental processes were significantly overrepresented in this list (P < 0.05). Following validation by reverse transcription-PCR and detection of inappropriate CGI methylation by COBRA, four genes (ICAM1, NNAT, RUNX1, and S100A10) were analyzed in primary human pituitary tumors, each displaying significantly reduced mRNA levels relative to normal pituitary (P < 0.05). For two of these genes, NNAT and S100A10, decreased expression was associated with increased promoter CGI methylation. Induced expression of Nnat in stable transfected AtT-20 cells inhibited cell proliferation. To our knowledge, this is the first report of array-based "epigenetic unmasking" in combination with Dnmt1 knockdown and reveals the potential of this strategy toward identifying genes silenced by epigenetic mechanisms across species boundaries.

Corticotropin tests for hypothalamic-pituitary- adrenal insufficiency: a metaanalysis.

CONTEXT: The diagnostic value of tests for detecting hypothalamic-pituitary adrenal insufficiency (HPAI) is controversial. OBJECTIVE: Our objective was to compare standard-dose and low-dose corticotropin tests for diagnosing HPAI. DATA SOURCES: We searched the PubMed database from 1966-2006 for studies reporting diagnostic value of standard-dose or low-dose corticotropin tests, with patient-level data obtained from original investigators. STUDY SELECTION: Eligible studies had more than 10 patients. All subjects were evaluated because of suspicion for chronic HPAI, and patient-level data were available. We excluded studies with no accepted reference standard for HPAI (insulin hypoglycemia or metyrapone test) if test subjects were in the intensive care unit or if only normal healthy subjects were used as controls. DATA EXTRACTION: We constructed receiver operator characteristic (ROC) curves using patient-level data from each study and then merged results to create summary ROC curves, adjusting for study size and cortisol assay method. Diagnostic value of tests was measured by calculating area under the ROC curve (AUC) and likelihood ratios. DATA SYNTHESIS: Patient-level data from 13 of 23 studies (57%; 679 subjects) were included in the metaanalysis. The AUC were as follows: low-dose corticotropin test, 0.92 (95% confidence interval 0.89-0.94), and standard-dose corticotropin test, 0.79 (95% confidence interval 0.74-0.84). Among patients with paired data (seven studies, 254 subjects), diagnostic value of low-dose corticotropin test was superior to standard-dose test (AUC 0.94 and 0.85, respectively; P<0.001). CONCLUSIONS: Low-dose corticotropin test was superior to standard-dose test for diagnosing chronic HPAI, although it has technical limitations.

The role of the aryl hydrocarbon receptor-interacting protein gene in familial and sporadic pituitary adenomas.

CONTEXT: Mutations have been identified in the aryl hydrocarbon receptor-interacting protein (AIP) gene in familial isolated pituitary adenomas (FIPA). It is not clear, however, how this molecular chaperone is involved in tumorigenesis. OBJECTIVE: AIP sequence changes and expression were studied in FIPA and sporadic adenomas. The function of normal and mutated AIP molecules was studied on cell proliferation and protein-protein interaction. Cellular and ultrastructural AIP localization was determined in pituitary cells. PATIENTS: Twenty-six FIPA kindreds and 85 sporadic pituitary adenoma patients were included in the study. RESULTS: Nine families harbored AIP mutations. Overexpression of wild-type AIP in TIG3 and HEK293 human fibroblast and GH3 pituitary cell lines dramatically reduced cell proliferation, whereas mutant AIP lost this ability. All the mutations led to a disruption of the protein-protein interaction between AIP and phosphodiesterase-4A5. In normal pituitary, AIP colocalizes exclusively with GH and prolactin, and it is found in association with the secretory vesicle, as shown by double-immunofluorescence and electron microscopy staining. In sporadic pituitary adenomas, however, AIP is expressed in all tumor types. In addition, whereas AIP is expressed in the secretory vesicle in GH-secreting tumors, similar to normal GH-secreting cells, in lactotroph, corticotroph, and nonfunctioning adenomas, it is localized to the cytoplasm and not in the secretory vesicles. CONCLUSIONS: Our functional evaluation of AIP mutations is consistent with a tumor-suppressor role for AIP and its involvement in familial acromegaly. The abnormal expression and subcellular localization of AIP in sporadic pituitary adenomas indicate deranged regulation of this protein during tumorigenesis.

Mortality in patients with Cushing's disease more than 10 years after remission: a multicentre, multinational, retrospective cohort study.

BACKGROUND: No agreement has been reached on the long-term survival prospects for patients with Cushing's disease. We studied life expectancy in patients who had received curative treatment and whose hypercortisolism remained in remission for more than 10 years, and identified factors determining their survival. METHODS: We did a multicentre, multinational, retrospective cohort study using individual case records from specialist referral centres in the UK, Denmark, the Netherlands, and New Zealand. Inclusion criteria for participants, who had all been in studies reported previously in peer-reviewed publications, were diagnosis and treatment of Cushing's disease, being cured of hypercortisolism for a minimum of 10 years at study entry, and continuing to be cured with no relapses until the database was frozen or death. We identified the number and type of treatments used to achieve cure, and used mortality as our primary endpoint. We compared mortality rates between patients with Cushing's disease and the general population, and expressed them as standardised mortality ratios (SMRs). We analysed survival data with multivariate analysis (Cox regression) with no corrections for multiple testing. FINDINGS: The census dates on which the data were frozen ranged from Dec 31, 2009, to Dec 1, 2014. We obtained data for 320 patients with 3790 person-years of follow-up from 10 years after cure (female:male ratio of 3:1). The median patient follow-up was 11·8 years (IQR 17-26) from study entry and did not differ between countries. There were no significant differences in demographic characteristics, duration of follow-up, comorbidities, treatment number, or type of treatment between women and men, so we pooled data from both sexes for survival analysis. 51 (16%) of the cohort died during follow-up from study entry (10 years after cure). Median survival from study entry was similar for women (31 years; IQR 19-38) and men (28 years; 24-42), and about 40 years (IQR 30-48) from remission. The overall SMR for all-cause mortality was 1·61 (95% CI 1·23-2·12; p=0·0001). The SMR for circulatory disease was increased at 2·72 (1·88-3·95; p<0·0001), but deaths from cancer were not higher than expected (0·79, 0·41-1·51). Presence of diabetes, but not hypertension, was an independent risk factor for mortality (hazard ratio 2·82, 95% CI 1·29-6·17; p=0·0095). We noted a step-wise reduction in survival with increasing number of treatments. Patients cured by pituitary surgery alone had long-term survival similar to that of the general population (SMR 0·95, 95% CI 0·58-1·55) compared with those who were not (2·53, 1·82-3·53; p<0·0001). INTERPRETATION: Patients with Cushing's disease who have been in remission for more than 10 years are at increased risk of overall mortality compared with the general population, particularly from circulatory disease. However, median survival from cure is excellent at about 40 years of remission. Treatment complexity and an increased number of treatments, reflecting disease that is more difficult to control, appears to negatively affect survival. Pituitary surgery alone is the preferred treatment to secure an optimum outcome, and should be done in a centre of surgical excellence. FUNDING: None.

Loss of expression of the growth inhibitory gene GADD45gamma, in human pituitary adenomas, is associated with CpG island methylation.

Inappropriate expression of cell-cycle regulatory genes and/or their protein products are a frequent finding in pituitary tumours; however, genetic changes associated with or responsible for their dysregulation are in general uncommon. In a search for novel genes, and employing cDNA-representational difference analysis, the gene encoding GADD45gamma was recently isolated and identified as being under-represented in pituitary adenomas. GADD45gamma is a member of a family of genes that are induced by DNA damage and function in the negative regulation of cell growth. In this study, we further confirm this initial report that the majority of pituitary adenomas (22 of 33; 67%) do not express GADD45gamma as determined by RT-PCR analysis. Loss of expression was not associated with either loss of heterozygosity or mutations within the coding region of this gene. In marked contrast, epigenetic change, namely methylation of the GADD45gamma genes CpG island, was a frequent finding (19 of 33 adenoma; 58%) and was significantly associated with tumours in which GADD45gamma transcript was not expressed (18 of 22; 82%; P=0.002). In common with the primary tumours, methylation-associated gene silencing of the GADD45gamma gene was also found in the pituitary tumour cell line AtT20. The treatment of AtT20 cells with the demethylating agent, 5-Aza-2'-deoxycytidine, induced the re-expression of this gene. These findings show that silencing of the GADD45gamma gene in pituitary tumours is primarily associated with methylation of the genes CpG island. Methylation has functional importance since reversal of this epigenetic change in a pituitary-derived cell line is associated with re-expression. Silencing of GADD45gamma, a negative regulator of cell growth, is most likely responsible for conferring a selective growth advantage during tumour evolution and outgrowth.

Molecular pathology shows p16 methylation in nonadenomatous pituitaries from patients with Cushing's disease.

PURPOSE: The majority of cases of Cushing's disease are due to the presence of a corticotroph microadenoma. Less frequently no adenoma is found and histology shows either corticotroph hyperplasia, or apparently normal pituitary. In this study we have used molecular pathology to determine whether the tissue labeled histologically as "normal" is indeed abnormal. EXPERIMENTAL DESIGN: Tissue from 31 corticotroph adenomas and 16 nonadenomatous pituitaries were subject to methylation-sensitive PCR to determine the methylation status of the p16 gene CpG island. The proportion of methylated versus unmethylated CpG island was determined using combined bisulphite restriction analysis. Methylation status was correlated with immunohistochemical detection of p16. RESULTS: Seventeen of 31 adenomas (54.8%), 4 of 6 cases of corticotroph hyperplasia, and 7 of 10 apparently normal pituitaries showed p16 methylation. Ten of 14 (71%; P = 0.01) adenomas and 2 of 3 cases of corticotroph hyperplasia, which were methylated, failed to express p16 protein. However, only 2 of 7 apparently normal pituitaries that were methylated failed to express p16 protein. Quantitative analysis of methylation using combined bisulphite restriction analysis showed only unmethylated CpG islands in postmortem normal pituitaries; however, in adenomas 80-90% of the cells within a specimen were methylated. The reverse was true for corticotroph hyperplasia and apparently normal pituitaries where only 10-20% of the cells were methylated. Thus, the decreased proportion of cells that were methylated, particularly in those cases of apparently normal pituitary, is the most likely explanation for the lack of association between this change and loss of cognate protein in these cases. CONCLUSIONS: To our knowledge this is the first report that describes an intrinsic molecular change, namely methylation of the p16 gene CpG island, common to all three histological patterns associated with Cushing's disease. Thus, the use of molecular pathology reveals abnormalities undetected by routine pathological investigation. In cases of "apparently" normal pituitaries it is not possible to determine whether the change is associated with adenoma cells "scattered" throughout the gland, albeit few in number, or with the ancestor-clonal origin of these tumor cells.

Isolation and characterization of a novel pituitary tumor apoptosis gene.

To determine mechanisms for pituitary neoplasia we used methylation-sensitive arbitrarily primed-PCR to isolate novel genes that are differentially methylated relative to normal pituitary. We report the isolation of a novel differentially methylated chromosome 22 CpG island-associated gene (C22orf3). Sodium bisulfite sequencing of pooled tumor cohorts, used in the isolation of this gene, showed that only a proportion of the adenomas within the pools were methylated; however, expression analysis by quantitative RT-PCR of individual adenoma irrespective of subtype showed the majority (30 of 38; 79%) failed to express this gene relative to normal pituitary. Sodium bisulfite sequencing of individual adenomas showed that 6 of 30 (20%) that failed to express pituitary tumor apoptosis gene (PTAG) were methylated; however, genetic change as determined by loss of heterozygosity and sequence analysis was not apparent in the remaining tumors that failed to express this gene. In those cases where the CpG island of these genes was methylated it was invariably associated with loss of transcript expression. Enforced expression of C22orf3 in AtT20 cells had no measurable effects on cell proliferation or viability; however, in response to bromocriptine challenge (10-40 microm) cells expressing this gene showed a significantly augmented apoptotic response as determined by both acridine orange staining and TUNEL labeling. The apoptotic response to bromocriptine challenge was inhibited in coincubation experiments with the general caspase inhibitor z-VAD-fmk. In addition, in time course experiments, direct measurement of active caspases by fluorochrome-labeled inhibition of caspases, showed an augmented increase (approximately 2.4 fold) in active caspases in response to bromocriptine challenge in cells expressing C22orf3 relative to those harboring an empty vector control. The pituitary tumor derivation and its role in apoptosis of this gene led us to assign the acronym PTAG to this gene and its protein product. The ability of cells, showing reduced expression of PTAG, to evade or show a blunted apoptotic response may underlie oncogenic transformation in both the pituitary and other tumor types.

Excess mortality associated with hypopituitarism in adults: a meta-analysis of observational studies.

CONTEXT: Several previous observational studies showed an association between hypopituitarism and excess mortality. Reports on reduction of standard mortality ratio (SMR) with GH replacement have been published recently. OBJECTIVE: This meta-analysis assessed studies reporting SMR to clarify mortality risk in hypopituitary adults and also the potential benefit conferred by GH replacement. DATA SOURCES: A literature search was performed in Medline, Embase, and Cochrane library up to March 31, 2014. ELIGIBILITY CRITERIA: Studies with or without GH replacement reporting SMR with 95% confidence intervals (95% CI) were included. DATA EXTRACTION AND ANALYSIS: Patient characteristics, SMR data, and treatment outcomes were independently assessed by two authors, and with consensus from third author, studies were selected for analysis. Meta-analysis was performed in all studies together, and those without and with GH replacement separately, using the statistical package metafor in R. RESULTS: Six studies reporting a total of 19 153 hypopituiatary adults with a follow-up duration of more than 99,000 person years were analyzed. Hypopituitarism was associated with an overall excess mortality (weighted SMR, 1.99; 95% CI, 1.21-2.76) in adults. Female hypopituitary adults showed higher SMR compared with males (2.53 vs 1.71). Onset of hypopituitarism at a younger age was associated with higher SMR. GH replacement improved the mortality risk in hypopituitary adults that is comparable to the background population (SMR with GH replacement, 1.15; 95% CI, 1.05-1.24 vs SMR without GH, 2.40; 95% CI, 1.46-3.34). GH replacement conferred lower mortality benefit in hypopituitary women compared with men (SMR, 1.57; 95% CI, 1.38-1.77 vs 0.95; 95% CI, 0.85-1.06). LIMITATIONS: There was a potential selection bias of benefit of GH replacement from a post-marketing data necessitating further evidence from long-term randomized controlled trials. CONCLUSIONS: Hypopituitarism may increase premature mortality in adults. Mortality benefit from GH replacement in hypopituitarism is less pronounced in women than men.

A paradigm shift in the monitoring of patients with acromegaly: last available growth hormone may overestimate risk.

CONTEXT: Acromegaly is associated with reduced life expectancy, which has been reported to be normalized if treatment is successful in controlling GH/IGF-I levels. OBJECTIVE: Most previous studies have invariably used the last available GH/IGF-I, which may be biased as it only assesses exposure at a single point in time. We compared the last available GH/IGF-I analysis to a "time-dependent" and cumulative method, during follow-up to assess risk of mortality in the West Midlands Acromegaly study (n = 501). RESULTS: Using the last available GH, there was a statistically significant increase in mortality comparing groups as low as GH ≤ 1 µg/L vs >1 µg/L (relative risks [RR] 1.8, P = .03). This was not the case when using the "time-dependent method," where only comparisons of GH values of GH ≤5 µg/L vs >5 µg/L were suggestive of being associated with an increased risk of mortality (RR = 1.5, P = .08). When the time-dependent GH method of analysis was used, the RR of mortality at each level was lower and the associated P value was less significant. Irrespective of using the last available or time-dependent method, when IGF-I was divided into levels according to quartile or arbitrary cutoffs, there was no significant increase in mortality with higher levels. CONCLUSIONS: This study emphasizes the potential bias of using the latest available GH/IGF-I levels to predict mortality. Our study again highlights the limitations of IGF-I in predicting mortality.

Preincubation of pituitary tumor cells with the epidrugs zebularine and trichostatin A are permissive for retinoic acid-augmented expression of the BMP-4 and D2R genes.

Retinoic acid (RA)-induced expression of bone morphogenetic protein-4 (BMP-4) inhibits in vitro and in vivo cell proliferation and ACTH synthesis in corticotroph-derived tumor cells. Reduced expression of BMP-4 in this adenoma subtype is associated with epigenomic silencing, and similar silencing mechanisms are also associated with the RA-responsive dopamine D2 receptor (D2R) in somatolactotroph cells. We now show that preincubation with the epidrugs zebularine and trichostatin A is obligate and permissive for RA-induced expression of the BMP-4 and the D2R genes in pituitary tumor cells. Combined epidrug challenges are associated with marginal reduction in CpG island methylation. However, significant change to histone tail modifications toward those associated with expression-competent genes is apparent, whereas RA challenge alone or in combined incubations does not have an impact on these modifications. Epidrug-mediated and RA-augmented expression of endogenous BMP-4 increased or decreased cell proliferation and colony-forming efficiency in GH3 and AtT-20 pituitary tumor cells, respectively, recapitulating recent reports of challenges of these cells with exogenous ligand. The specificity of the BMP-4-mediated effects was further supported by knock-down experiments of the BMP-4 antagonist noggin (small interfering RNA [siRNA]). Knock-down of noggin, in the absence and the presence of epidrugs, induced and augmented BMP-4 expression, respectively. In cell proliferation assays, challenge with either epidrugs or siRNA led to significant increase in cell numbers at the 72-hour time point; however, in siRNA-treated cells coincubated with epidrugs, a significant increase was apparent at the 48-hour time point. These studies show the potential of combined drug challenges as a treatment option, where epidrug renders silenced genes responsive to conventional therapeutic options.

Epigenomic silencing of the BMP-4 gene in pituitary adenomas: a potential target for epidrug-induced re-expression.

Bone morphogenetic protein (BMP)-4 is a key mediator of anterior pituitary organogenesis. However, through inappropriate expression patterns, BMP-4 is also pathogenic in a pituitary adenoma subtype-specific context. In these cases, increase or decrease in BMP-4 in lactotroph- and corticotroph-derived adenomas, respectively, is consistent with a bifunction role for this protein toward either promotion or inhibition of cell proliferation and hormone secretion. To gain insight into the aberrations responsible for differential expression, we examined BMP-4 transcript and protein expression patterns in the major adenomas subtypes. BMP-4 transcript and protein are differentially expressed and show increase in the majority of prolactinomas relative to normal pituitary, whereas the majority of other adenoma subtypes show reduced expression relative to both prolactinoma and normal pituitaries. Reduced expression of BMP-4 is not associated with change in CpG island methylation status. However, histone tail modifications are apparent, as enrichment for a modification associated with silent genes, H3K27me3, and depletion of a modification associated with active genes, H3K9Ac. In pituitary cell lines, reduced BMP-4 expression is also associated with similar histone tail modifications and contemporaneous increase in CpG island methylation. In these cells, coincubation with the demethylating agent zebularine and histone deacetylase inhibitor, trichostatin A, reversed epigenetic changes and restored expression of BMP-4. These studies show that, in contrast to prolactinomas, other adenoma subtypes show reduced expression of BMP-4 where epidrug induced reexpression, alone or in combination with conventional therapies, may offer new treatment strategies.

The pituitary tumour epigenome: aberrations and prospects for targeted therapy.

Global and gene-specific changes in the epigenome are hallmarks of most tumour types, including those of pituitary origin. In contrast to genetic mutations, epigenetic changes (aberrant DNA methylation and histone modifications) are potentially reversible. Drugs that specifically target or inhibit DNA methyltransferases (DNMTs) and histone deacetylases (HDACs) can be used to restore the expression of epigenetically silenced genes. These drugs can potentially increase the sensitivity of tumour cells to conventional treatment modalities, such as chemotherapy and radiotherapy. Drug-induced reversal of transcriptional silencing can also be used to restore dopamine-D(2)-receptor-negative, hormone-refractory tumours to their previous receptor-positive, hormone-responsive status. Synergy between HDAC and DNMT inhibitors makes these pharmacological agents more therapeutically effective when administered in combination than when used alone. Studies in pituitary tumour cell lines show that drug-induced re-expression of the epigenetically silenced dopamine D(2) receptor leads to an increase in apoptosis mediated by a receptor agonist. Collectively, the use of drugs to directly or indirectly reverse gene-specific epigenetic changes, in combination with conventional therapeutic interventions, has potential for the clinical management of multiple tumour types-including those of pituitary origin. Furthermore, these drugs can be used to identify epigenetically regulated genes that could be novel, tumour-specific therapeutic targets.

Quantitative, genome-wide analysis of the DNA methylome in sporadic pituitary adenomas.

DNA methylation is one of the several epigenetic modifications that together with genetic aberrations are hallmarks of tumorigenesis including those emanating from the pituitary gland. In this study, we examined DNA methylation across 27 578 CpG sites spanning more than 14 000 genes in the major pituitary adenoma subtypes. Genome-wide changes were first determined in a discovery cohort comprising non-functioning (NF), growth hormone (GH), prolactin (PRL)-secreting and corticotroph (CT) adenoma relative to post-mortem pituitaries. Using stringent cut-off criteria, we validated increased methylation by pyrosequencing in 12 of 16 (75%) genes. Overall, these criteria identified 40 genes in NF, 21 in GH, six in PRL and two in CT that were differentially methylated relative to controls. In a larger independent cohort of adenomas, for genes in which hypermethylation had been validated, different frequencies of hypermethylation were apparent, where the KIAA1822 (HHIPL1) and TFAP2E genes were hypermethylated in 12 of 13 NF adenomas whereas the COL1A2 gene showed an increase in two of 13 adenomas. For genes showing differential methylation across and between adenoma subtypes, pyrosequencing confirmed these findings. In three of 12 genes investigated, an inverse relationship between methylation and transcript expression was observed where increased methylation of EML2, RHOD and HOXB1 is associated with significantly reduced transcript expression. This study provides the first genome-wide survey of adenoma, subtype-specific epigenomic changes and will prove useful for identification of biomarkers that perhaps predict or characterise growth patterns. The functional characterisation of identified genes will also provide insight of tumour aetiology and identification of new therapeutic targets.

Reversal of endogenous dopamine receptor silencing in pituitary cells augments receptor-mediated apoptosis.

Dopamine (DA)-agonist targeting of the DA D(2) receptor (D2R) in prolactinomas is the first-line treatment choice for suppression of prolactin and induction of tumor shrinkage. Resistance to DA agonists seems to be related to receptor number. Using the MMQ and GH3 pituitary cell lines, that either do or do not express D2R, respectively, we explored the epigenetic profile associated with the presence or absence of D2R in these cells lines. These studies led us to explore pharmacological strategies designed to restore receptor expression and thereby potentially augment DA agonist-mediated apoptosis. We show in GH3 cells that the D2R harbors increased CpG island-associated methylation and enrichment for histone H3K27me3. Conversely, MMQ cells and normal pituitaries show enrichment for H3K9Ac and barely detectable H3K27me3. Coculture of GH3 cells with the demethylating agent zebularine and the histone deacetylase inhibitor trichostatin A was responsible for a decrease in CpG island methylation and enrichment for the histone H3K9Ac mark. In addition, challenge of GH3 cells with zebularine alone or coculture with both agents led to expression of endogenous D2R in these cells. Induced expression D2R in GH3 cells was associated with a significant increase in apoptosis indices to challenge with either DA or bromocriptine. Specificity of a receptor-mediated response was established in coincubations with specific D2R antagonist and siRNA approaches in GH3 cell and D2R expressing MMQ cell lines. These studies point to the potential efficacy of combined treatment with epigenetic drugs and DA agonists for the medical management of different pituitary tumor subtypes, resistant to conventional therapies.

Primary colorectal tumors fail to express the proapoptotic mediator PTAG and its reexpression augments drug-induced apoptosis.

Genes implicated in tumor evolution and progression, including those in apoptotic pathways, are associated with methylation-associated gene silencing in different tumor types. By exploiting differential methylation we recently isolated a novel pituitary tumor derived apoptosis gene (PTAG) that augments drug-induced apoptosis. The importance of PTAG was determined in other tumor types, and these studies show that the majority of primary colorectal tumors fail to express the PTAG gene, indicating an important role for PTAG in colorectal tumorigenesis. The effects of expression of PTAG were examined through stable transfection of the colorectal cell lines HCT116 and SW480. Expression of PTAG, per se, had no discernible effects on cell viability or cell kinetics. In contrast to these findings, in cells subject to drug challenges that engaged either a death-receptor mediated or mitochondrial pathway, all of the experiments indicated a role for PTAG in the intrinsic pathway of apoptosis. Loss of PTAG therefore contributes to a blunted apoptotic response and is likely to predispose cells toward malignant transformation and resistance to chemotherapeutic interventions.