Kelly A. Loffler

Conditional inactivation of the Men1 gene leads to pancreatic and pituitary tumorigenesis but does not affect normal development of these tissues

ABSTRACT Mutations of the MEN1 gene, encoding the tumor suppressor menin, predispose individuals to the cancer syndrome multiple endocrine neoplasia type 1, characterized by the development of tumors of the endocrine pancreas and anterior pituitary and parathyroid glands. We have targeted the murine Men1 gene by using Cre recombinase-loxP technology to develop both total and tissue-specific knockouts of the gene. Conditional homozygous inactivation of the Men1 gene in the pituitary gland and endocrine pancreas bypasses the embryonic lethality associated with a constitutional Men1 −/− genotype and leads to β-cell hyperplasia in less than 4 months and insulinomas and prolactinomas starting at 9 months. The pituitary gland and pancreas develop normally in the conditional absence of menin, but loss of this transcriptional cofactor is sufficient to cause β-cell hyperplasia in some islets; however, such loss is not sufficient to initiate pituitary gland tumorigenesis, suggesting that additional genetic events are necessary for the latter.

Genomic catastrophes frequently arise in esophageal adenocarcinoma and drive tumorigenesis

Oesophageal adenocarcinoma (EAC) incidence is rapidly increasing in Western countries. A better understanding of EAC underpins efforts to improve early detection and treatment outcomes. While large EAC exome sequencing efforts to date have found recurrent loss-of-function mutations, oncogenic driving events have been underrepresented. Here we use a combination of whole-genome sequencing (WGS) and single-nucleotide polymorphism-array profiling to show that genomic catastrophes are frequent in EAC, with almost a third (32%, n = 40/123) undergoing chromothriptic events. WGS of 22 EAC cases show that catastrophes may lead to oncogene amplification through chromothripsis-derived double-minute chromosome formation (MYC and MDM2) or breakage-fusion-bridge (KRAS, MDM2 and RFC3). Telomere shortening is more prominent in EACs bearing localized complex rearrangements. Mutational signature analysis also confirms that extreme genomic instability in EAC can be driven by somatic BRCA2 mutations. These findings suggest that genomic catastrophes have a significant role in the malignant transformation of EAC.

Broad tumor spectrum in a mouse model of multiple endocrine neoplasia type 1

Multiple endocrine neoplasia type 1 (MEN1) is an inherited cancer predisposition syndrome typified by development of tumors in parathyroid, pituitary and endocrine pancreas, as well as less common sites including both endocrine and nonendocrine organs. Deletion or mutation of the tumor suppressor gene MEN1 on chromosome 11 has been identified in many cases of MEN1 as well as in sporadic tumors. The molecular biology of menin, the protein encoded by MEN1, remains poorly understood. Here we describe a mouse model of MEN1 in which tumors were seen in pancreatic islets, pituitary, thyroid and parathyroid, adrenal glands, testes and ovaries. The observed tumor spectrum therefore includes types commonly seen in MEN1 patients and additional types. Pancreatic pathology was most common, evident in over 80% of animals, while other tumor types developed with lower frequency and generally later onset. Tumors of multiple endocrine organs were observed frequently, but progression to carcinoma and metastasis were not evident. Tumors in all sites showed loss of heterozygosity at the Men1 locus, though the frequency in testicular tumors was only 36%, indicating that a different molecular mechanism of tumorigenesis occurs in those Leydig tumors that do not show loss of the normal Men1 allele. Menin expression was below the level of detection in ovary, thyroid and testis, but loss of nuclear menin immunoreactivity was observed uniformly in all pancreatic islet adenomas and in some hyperplastic islet cells, suggesting that complete loss of Men1 is a critical point in islet tumor progression in this model.

Sex Determination: The Fishy Tale of Dmrt1

The idea that the Dmrt1 gene provides a unifying sex-determining mechanism in non-mammalian vertebrates is left high and dry by recent observations in fish.

Lack of augmentation of tumor spectrum or severity in dual heterozygous Men1 and Rb1 knockout mice

To identify possible genetic interactions between the mechanisms of tumor suppression of menin and pRb, we intercrossed mice with targeted deletions of Men1 and Rb1, and compared tumor development in cohorts of animals carrying single or dual mutations of these tumor-suppressor genes. In mice lacking one copy of Men1, pancreatic islet and anterior pituitary adenomas are common. In animals lacking one copy of Rb1, intermediate pituitary and thyroid tumors occur at high frequency, with less frequent development of pancreatic islet hyperplasia and parathyroid lesions. In mice heterozygous for both Men1 and Rb1, pancreatic hyperplasia and tumors of the intermediate pituitary and thyroid occurred at high frequency. Serum measurements of calcium and glucose did not vary significantly between genotypic groups. Loss of heterozygosity at the Rb1 locus was common in pituitary and thyroid tumors, whereas loss of menin was observed in pancreatic and parathyroid lesions. The tumor spectrum in the double heterozygotes was a combination of pathologies seen in each of the individual heterozygotes, without decrease in age of onset, indicating independent, non-additive effects of the two mutations. Together with the lack of increased tumor spectrum, this suggests that menin and pRb function in a common pathway of tumor suppression.

BRAF mutation status is an independent prognostic factor for resected stage IIIB and IIIC melanoma: Implications for melanoma staging and adjuvant therapy

BACKGROUND 5-year survival for melanoma metastasis to regional lymph nodes (American Joint Committee on Cancer stage III) is <50%. Knowledge of outcomes following therapeutic lymphadenectomy for stage III melanoma related to BRAF status may guide adjuvant use of BRAF/MEK inhibitors along with established and future therapies. AIMS To determine patterns of melanoma recurrence and survival following therapeutic lymph node dissection (TLND) associated with oncogenic mutations. METHODS DNA was obtained from patients who underwent TLND and had ⩾2 positive nodes, largest node >3cm or extracapsular invasion. Mutations were detected using an extended Sequenom MelaCARTA panel. RESULTS Mutations were most commonly detected in BRAF (57/124 [46%] patients) and NRAS (26/124 [21%] patients). Patients with BRAF mutations had higher 3-year recurrence rate (77%) versus 54% for BRAF wild-type patients (hazard ratio (HR) 1.8, p=0.008). The only prognostically significant mutations occurred in BRAF: median recurrence-free (RFS) and disease-specific survival (DSS) for BRAF mutation patients was 7 months and 16 months, versus 19 months and not reached for BRAF wild-type patients, respectively. Multivariate analysis identified BRAF mutant status and number of positive lymph nodes as the only independent prognostic factors for RFS and DSS. CONCLUSIONS Patients with BRAF mutations experienced rapid progression of metastatic disease with locoregional recurrence rarely seen in isolation, supporting incorporation of BRAF status into melanoma staging and use of BRAF/MEK inhibitors post-TLND.

Global expression profiling of murine MEN1-associated tumors reveals a regulatory role for menin in transcription, cell cycle and chromatin remodelling

Although the identification of menin‐interacting partners and other evidence support a role for menin, the multiple endocrine neoplasia type 1 gene (MEN1) product, in regulating gene expression, little is known about the cellular pathways dysregulated by menin loss during tumorigenesis. The mouse models of MEN1 accurately mimic the human syndrome and provide an opportunity to assess the transcriptional effects of Men1 deletion in different endocrine tumor types to identify common pathway aberrations underlying tumorigenesis in MEN1‐affected tissues. We compared the global gene expression profiles of pituitary adenomas and pancreatic islet tumors with control tissues from wild‐type littermates. Amongst the 551 differentially expressed genes was significant over‐representation of genes associated with chromatin remodelling, transcription and cell cycling, including some genes known to encode menin‐binding partners, e.g., Rhox5 and Mll1. Consistent with increased cell‐cycle transition from G1 to S phase was an elevation of Cdc7 expression in the tumors, which was confirmed by qRT‐PCR using independent samples. In support of previous findings in islet tumors, we found down‐regulation of the cell‐cycle regulator, p18, in both the pancreatic islet and pituitary adenomas, suggesting that reduced p18 levels may be important for Men1‐related tumorigenesis in multiple tissues. Surprisingly, we identified increased p16 transcript in pancreatic islet and pituitary tumors. This was accompanied by increased cytoplasmic localization p16 protein in tumor cells. The specific genes and general pathways we have found to be commonly dysregulated in MEN1 tumors, provide a platform for determining their roles in endocrine tumorigenesis.

Identification of the CIMP-like subtype and aberrant methylation of members of the chromosomal segregation and spindle assembly pathways in esophageal adenocarcinoma

Summary This study describes the esophageal cancer methylation landscape and its impact on gene expression. Genes aberrantly methylated suggest a mechanism that could lead to genomic instability and chromothripsis. A CpG island methylator phenotype-like subtype with potentially worse clinical outcome was also identified.

Global expression profiling of sex cord stromal tumors from Men1 heterozygous mice identifies altered TGF-beta signaling, decreased Gata6 and increased Csf1r expression.

Heterozygous disruption of the Men1 gene predisposes mice to the development of multiple endocrine tumors, accurately mimicking the human MEN1 cancer predisposition syndrome. Additionally, Men1+/– mice frequently develop sex cord adenomas. The mechanism underlying the susceptibility of these mice to sex cord tumor development has not been fully determined, but data suggest it may involve transcriptional regulation of key growth promoting/repressing genes. To identify potential menin‐regulated genes that may be important for tumor suppression in sex cord cells, we compared the global gene expression profiles of testis and ovary adenomas with other endocrine tumors of the pancreas and pituitary from Men1 heterozygous mice and with control tissues. Gonadal tumors clustered separately from pancreas and pituitary tumors with only a few genes (e.g., Cdkn2c) commonly dysregulated in all tumor types. Testis and ovary tumors displayed a higher level of transcriptional similarity to each other than they did to their respective control tissues. Among genes that had decreased expression in tumors was significant over‐representation of genes associated with the TGF‐β, hedgehog and Wnt signaling, indicating that loss of menin function affects these pathways at the level of transcription. Aberrant protein expression in Leydig and granulosa cells of 2 transcriptionally dysregulated gene products, Gata6 and Csf1r were confirmed by immunohistochemistry. We propose that sex cord tumor susceptibility in Men1+/– mice involves deregulated cell proliferation due to dysregulation of multiple cell growth regulating genes including: reduced Cdkn2c transcription, loss of TGF‐β pathway tumor suppressor function (e.g., Gata6) and transcriptional activation of Csf1r.

Alterations in gene expression in MEN1-associated insulinoma development.

Objectives: To identify gene expression alterations associated with insulinoma formation and progression in 2 mouse models of multiple endocrine neoplasia type 1. Methods: Mice were killed at 12 or 16 months, and pancreatic islets were isolated by enzymatic and physical disruption. Islets were separated by size representing control, normal, hyperplastic, and adenomous islets. RNA was isolated from these islets and profiled on Sentrix Mouse-6 Expression version 1 BeadChips. Array data were analyzed in GeneSpring. Results: One hundred and one genes that were significantly (P ≤ 0.05) altered in hyperplastic islets and insulinomas compared with normal islets were identified. Of these, 64 gene elements showed reduced messenger RNA levels and 37 gene elements had increased gene expression compared with control islets. Altered expression of 3 genes, namely, Gata6, Tspan8, and s100a8, was confirmed by quantitative reverse transcription-polymerase chain reaction, and aberrant levels of Tspan8 and Lmo2 protein measured by Western blot correlated with the changes in messenger RNA levels. Conclusions: These results suggest that alterations in gene expression of Gata6, Tspan8, S100a8, and Lmo2 may act via novel pathways that play functionally important roles in Men1-associated tumor progression.