Mutational analysis of p27 (CDKN1B) and p18 (CDKN2C) in sporadic pancreatic endocrine tumors argues against tumor-suppressor function

Effects of RNAi-induced Skp2 inhibition on cell cycle, apoptosis and proliferation of endometrial carcinoma cells

The aim of the current study was to investigate the underlying mechanism of S-phase kinase associated protein 2 (Skp2) gene inhibition by lentivirus-mediated RNA interference (RNAi) on the cell cycle, apoptosis and proliferation of endometrial carcinoma HEC-1-A cells. A lentivirus shRNA vector targeting Skp2 was constructed and transfected into HEC-1-A cells. HEC-1-A cells transfected with a scramble sequence were used as negative controls. The mRNA and protein expression of Skp2, p27, cyclin D1 and caspase-3 were detected via reverse transcription-quantitative polymerase chain reaction and western blotting, respectively. The effects of Skp2 inhibition on the cell cycle, apoptosis and proliferation of HEC-1-A cells were detected using flow cytometry and a cell counting kit-8. Skp2 co-expression data was analyzed using Oncomine and TCGA databases. The positive recombinant viral clones were identified via PCR and confirmed via sequencing. The mRNA and protein expression of Skp2 were significantly decreased in HEC-1-A cells transfected with the lentiviral vectors compared with the negative control. In addition, there were no significant changes in the mRNA expression of p27 and cyclin D1; however, the protein levels of p27 and cyclin D1 were upregulated and downregulated, respectively, in HEC-1-A cells transfected with lentiviral vectors compared with negative controls. RNAi-induced Skp2 inhibition exerted an anti-proliferative effect by inducing cell cycle arrest, however cell apoptosis was not significantly affected. In the TCGA database, Skp2 expression positively associated with IGF2R, IGF2BP3, IGFBP1 and CCNF, while Skp2 expression negatively associated with IGF2, IGFBP6, IGFBP7 and IGFBP3. RNAi-induced Skp2 inhibition upregulated the protein expression of p27 and downregulated the protein expression of cyclin D1. The expression of Skp2 in endometrial cancer may therefore be regulated by the insulin-like growth factor 1 receptor signaling pathway.

MEN4 and CDKN1B mutations: the latest of the MEN syndromes

Multiple endocrine neoplasia (MEN) refers to a group of autosomal dominant disorders with generally high penetrance that lead to the development of a wide spectrum of endocrine and non-endocrine manifestations. The most frequent among these conditions is MEN type 1 (MEN1), which is caused by germline heterozygous loss-of-function mutations in the tumor suppressor gene MEN1 MEN1 is characterized by primary hyperparathyroidism (PHPT) and functional or nonfunctional pancreatic neuroendocrine tumors and pituitary adenomas. Approximately 10% of patients with familial or sporadic MEN1-like phenotype do not have MEN1 mutations or deletions. A novel MEN syndrome was discovered, initially in rats (MENX), and later in humans (MEN4), which is caused by germline mutations in the putative tumor suppressor CDKN1B The most common phenotype of the 19 established cases of MEN4 that have been described to date is PHPT followed by pituitary adenomas. Recently, somatic or germline mutations in CDKN1B were also identified in patients with sporadic PHPT, small intestinal neuroendocrine tumors, lymphoma and breast cancer, demonstrating a novel role for CDKN1B as a tumor susceptibility gene for other neoplasms. In this review, we report on the genetic characterization and clinical features of MEN4.

DNA methylation profiles distinguish different subtypes of gastroenteropancreatic neuroendocrine tumors

AIM

Most studies have considered gastroenteropancreatic neuroendocrine tumors (GEP-NETs) as a homogenous group of samples or distinguish only gastrointestinal from pancreatic endocrine tumors. This article investigates if DNA methylation patterns could distinguish subtypes of GEP-NETs.

MATERIALS & METHODS

The DNA methylation level of 807 cancer-related genes was investigated in insulinomas, gastrinomas, non-functioning pancreatic endocrine tumors and small intestine endocrine tumors.

RESULTS

DNA methylation patterns were found to be tumor type specific for each of the pancreatic tumor subtypes and identified two distinct methylation-based groups in small intestine endocrine tumors. Differences of DNA methylation levels were validated by pyrosequencing for 20 candidate genes and correlated with differences at the transcriptional level for four candidate genes.

CONCLUSION

The heterogeneity of DNA methylation patterns in the different subtypes of gastroenteropancreatic neuroendocrine tumors suggests different underlying pathways and, therefore, these tumors should be considered as distinct entities in molecular and clinical studies.

Somatic Mutations and Genetic Heterogeneity at the CDKN1B Locus in Small Intestinal Neuroendocrine Tumors

BACKGROUND

Until recently, the genetic landscape of small intestinal neuroendocrine tumors (SI-NETs) was limited to recurrent copy number alterations, most commonly a loss on chromosome 18. Intertumor heterogeneity with nonconcordant genotype in paired primary and metastatic lesions also is described, further contributing to the difficulty of unraveling the genetic enigma of SI-NETs. A recent study analyzing 55 SI-NET exomes nominated CDKN1B (p27) as a haploinsufficient tumor suppressor gene.

METHODS

This study aimed to determine the frequency of CDKN1B inactivation and to investigate genotype-phenotype correlations. It investigated 362 tumors from 200 patients. All samples were resequenced for mutations in CDKN1B using automated Sanger sequencing. The expression of p27 was investigated in 12 CDKN1B mutant and nine wild type tumors.

RESULTS

Some 8.5 % (17/200) of patients had tumors with pathogenic mutations in CDKN1B including 13 insertion deletions, four nonsense variants, and one stop-loss variant. All variants with available nontumoral DNA were classified as somatic. Inter- and intratumor heterogeneity at the CDKN1B locus was detected respectively in six of ten and two of ten patients. Patients with CDKN1B mutated tumors had both heterogeneous disease presentation and diverse prognosis. Expression of the p27 protein did not correlate with CDKN1B mutation status, and no differences in the clinical characteristics between CDKN1B mutated and CDKN1B wild type tumor carriers were found.

CONCLUSION

This study corroborates the finding of CDKN1B as a potential haplo-insufficient tumor suppressor gene characterized by inter- and intratumor heterogeneity in SI-NETs.

Functional characterization of a rare germline mutation in the gene encoding the cyclin-dependent kinase inhibitor p27Kip1 (CDKN1B) in a Spanish patient with multiple endocrine neoplasia-like phenotype

OBJECTIVE

The aim of this study was to investigate the presence of germline mutations in the CDKN1B gene that encodes the cyclin-dependent kinase (Cdk) inhibitor p27 in multiple endocrine neoplasia 1 (MEN1)-like Spanish index patients. The CDKN1B gene has recently been identified as a tumor susceptibility gene for MEN4, with six germline mutations reported so far in patients with a MEN-like phenotype but negative for MEN1 mutations.

DESIGN AND METHODS

Fifteen Spanish index cases with MEN-like symptoms were screened for mutations in the CDKN1B gene and the mutant variant was studied functionally by transcription/translation assays in vitro and in transiently transfected HeLa cells.

RESULTS

We report the identification of a heterozygous GAGA deletion in the 5'-UTR of CDKN1B, NM_004064.3:c.-32_-29del, in a patient affected by gastric carcinoid tumor and hyperparathyroidism. This deletion falls inside the region that is responsible for CDKN1B transcription and is predicted to destroy a secondary stem and loop structure that includes the GAGAGA element responsible for ribosome recruitment. Accordingly, in vitro studies of coupled transcription/translation assays and transient transfection in HeLa cells showed that the GAGA deletion in the CDKN1B 5'-UTR significantly impairs the transcription of downstream reporter luciferase (of ∼40-60%) and, possibly, the translation of the corresponding mRNA. This mutation was associated with a significant reduction in the amount of CDKN1B mRNA in peripheral blood leukocytes from the patient, as demonstrated by quantitative real-time PCR.

CONCLUSIONS

Our results confirm that germline CDKN1B mutations may predispose to a human MEN4 condition and add novel evidence that alteration in the transcription/translation rate of CDKN1B mRNA might be the mechanism implicated in tumor susceptibility.

Somatic mutation and germline sequence abnormalities in CDKN1B, encoding p27Kip1, in sporadic parathyroid adenomas

CONTEXT

Typical nonfamilial (sporadic) parathyroid adenomas are common endocrine tumors for which no predisposing germline DNA variants and only a few clonally altered genes that drive parathyroid tumorigenesis have been identified. CDKN1B, encoding cyclin-dependent kinase inhibitor p27(kip1), has recently been implicated in a multiple endocrine tumor phenotype in rats and, rarely, in a human familial MEN1 (multiple endocrine neoplasia type 1)-like disorder.

OBJECTIVE

We sought to determine whether mutation of CDKN1B might contribute to the development of common sporadic parathyroid adenomas.

PATIENTS AND DESIGN

We sequenced the CDKN1B gene in 86 parathyroid adenomas from patients with typical, sporadic presentations of primary hyperparathyroidism. Identified alterations were categorized as somatic or germline, and their functional consequences were examined.

RESULTS

CDKN1B sequence abnormalities were identified in four parathyroid adenomas. Acquired biallelic alteration of CDKN1B, resulting from somatic mutation plus loss of heterozygosity, was detected in one tumor. Germline origin was documented in two cases despite nonfamilial presentations. None of the observed alterations were found in 240 CDKN1B alleles from normal individuals, nor among more than 2,000 previously reported alleles. Most identified variants reduced p27(kip1) protein levels or altered in vitro stability.

CONCLUSIONS

In typical, sporadic parathyroid adenomas, CDKN1B mutation can be somatic and clonal, indicative of a directly conferred selective advantage in parathyroid tumorigenesis. Additionally, the identification of germline CDKN1B variants in patients with sporadic presentations provides evidence for CDKN1B as a susceptibility gene in the development of typical parathyroid adenomas.

MEN-4 and other multiple endocrine neoplasias due to cyclin-dependent kinase inhibitors (p27(Kip1) and p18(INK4C)) mutations

Cyclin-dependent kinase inhibitors (CDKIs) are known targets to become deregulated in various tumour types, including endocrine tumours. Typically, these cell cycle regulators are somatically inactivated in sporadic endocrine tumours. Recently, it became known that certain CDKI genes cause inherited susceptibility to endocrine neoplasia. Multiple endocrine neoplasia type 4 (MEN4) emerged as a novel form of multiple endocrine neoplasia, caused by mutations in the CDKI gene CDKN1B/p27(Kip1). The MEN4 phenotype remains unclear, but all MEN4 patients identified thus far present with parathyroid involvement, and less typically with pituitary adenomas and other endocrine features. Moreover, the CDKI gene CDKN2C/p18(INK4C) has been also implicated in endocrine neoplasia susceptibility. This review presents the recent advances in these novel MEN-related states and summarises the current knowledge of how these CDKIs may be implicated in endocrine neoplasia. In addition, it briefly presents data from Cdkn1b/p27(Kip1) and Cdkn2c/p18(INK4C) murine models, which strongly support the protective role of these inhibitors against endocrine tumourigenesis.

The War on Cancer rages on

In 1971, the "War on Cancer" was launched by the US government to cure cancer by the 200-year anniversary of the founding of the United States of America, 1976. This article briefly looks back at the progress that has been made in cancer research and compares progress made in other areas of human affliction. While progress has indeed been made, the battle continues to rage on.

Neoplasia: the second decade

This issue marks the end of the 10-year anniversary of Neoplasia where we have seen exciting growth in both number of submitted and published articles in Neoplasia. Neoplasia was first published in 1999. During the past 10 years, Neoplasia has dynamically adapted to the needs of the cancer research community as technologies have advanced. Neoplasia is currently providing access to articles through PubMed Central to continue to facilitate rapid broad-based dissemination of published findings to the scientific community through an Open Access model. This has in part helped Neoplasia to achieve an improved impact factor this past year, demonstrating that the manuscripts published by Neoplasia are of great interest to the overall cancer research community. This past year, Neoplasia received a record number of articles for review and has had a 21% increase in the number of published articles.

Assessment of p27 (cyclin-dependent kinase inhibitor 1B) and aryl hydrocarbon receptor-interacting protein (AIP) genes in multiple endocrine neoplasia (MEN1) syndrome patients without any detectable MEN1 gene mutations

OBJECTIVE

Germline mutations in the MEN1 gene predispose to the multiple endocrine neoplasia (MEN1) syndrome; however, approximately 10-20% of patients with MEN1 do not have a detectable MEN1 mutation. A rat strain with multiple endocrine tumours, a phenotypic overlap of both MEN1 and MEN2, has been reported to have a homozygous germline p27 (CDKN1B) mutation. Recently, two MEN1 mutation-negative MEN1 syndrome patients have been identified to harbour a germline CDKN1B mutation. The recently identified gene AIP can also cause familial isolated pituitary adenoma, but no other specific tumour is associated with this syndrome. The objective of this study was to evaluate the possible contribution of CDKN1B and AIP germline mutations in a cohort of MEN1 mutation-negative MEN1 syndrome patients.

PATIENTS

Eighteen sporadic and three familial cases of MEN1 mutation-negative MEN1 syndrome were studied (18 pituitary adenomas, 12 hyperparathyroidism, 10 neuroendocrine tumours including 2 ACTH-secreting lesions and one adrenal nodular hyperplasia). Clinical data and genomic DNA were analysed for mutations in the CDKN1B and AIP genes.

RESULTS

There were no mutations in the coding region or exon/intron junction of the CDKN1B and AIP genes in any patient. Although we have a limited number of patients in our cohort, our data is consistent with others in the literature suggesting that CDKN1B and AIP mutations are extremely rare in MEN1 syndrome.

CONCLUSION

Our results suggest that mutations in the CDKN1B and AIP genes are relatively uncommon in MEN1 mutation-negative MEN1 syndrome patients.

Expression of p18(INK4C) is down-regulated in human pituitary adenomas

Cyclin-dependent kinase inhibitors represented by the INK4 family comprising p16(INK4A), p15(INK4B), p18(INK4C), and p19(INK4D) are regulators of the cell cycle shown to be aberrant in many types of cancer. Mice lacking p18(Ink4c) exhibit a series of phenotypes including the development of widespread organomegaly and pituitary adenomas. The objective of our study is to examine the role of p18(INK4C) in the pathogenesis of human pituitary tumors. The protein and mRNA levels of p18(INK4C) were examined by immunohistochemistry and real-time reverse transcription-polymerase chain reaction, respectively. The methylation status of the p18(INK4C) gene promoter and somatic mutations of the p18(INK4C) gene were also investigated. p18(INK4C) protein expression was lost or significantly reduced in 64% of pituitary adenomas compared with levels in normal pituitary glands. p18(INK4C) mRNA levels were low in all ACTH adenomas and non-functioning (NF)-FSH and in 42%, 70% and 66% of GH, PRL, and subtype 3 adenomas, respectively. p18(INK4C) mRNA levels were significantly associated with p18(INK4C) protein levels. Neither methylated promoters in pituitary adenomas, except in one NF-FSH adenoma, nor somatic mutations of the p18(INK4C) gene in any pituitary adenomas were detected. The down-regulation of p18(INK4C) expression may contribute to the tumorigenesis of pituitary adenomas.

Menin regulates endocrine diseases by controlling histone modification and gene transcription

Multiple endocrine neoplasia type 1 (MEN1), a human familial tumor syndrome, results from mutations in the Men1 gene. Although much progress has been made in demonstrating the definitive role for menin in suppressing tumorigenesis in endocrine organs, the molecular pathways responsible for menin action in normal tissues and tumors remain poorly defined. Here, we review the recent progress on the molecular functions of menin in controlling cell proliferation, apoptosis, and DNA repair. The majority of these functions are largely executed by menin-mediated influencing of histone modifications and chromatin structure. These findings lead to a new model of understanding menin's tumor-suppressing function, providing insights into understanding of how menin regulates cell proliferation and the development of endocrine tumors. The new knowledge could also be translated into new strategies to improve therapeutic interventions against MEN1 and other endocrine diseases including diabetes.

Repression of Ah receptor and induction of transforming growth factor-beta genes in DEN-induced mouse liver tumors

The aryl hydrocarbon receptor (AHR) is a ligand-activated transcription factor that mediates the biologic and toxic effects of its xenobiotic ligands. In recent years it has become evident that in the absence of ligand the AHR promotes cell cycle progression and that its activation by high-affinity ligands results in interactions with the retinoblastoma protein (RB) that lead to perturbation of the cell cycle, G0/G1 arrest, diminished capacity for DNA replication and inhibition of cell proliferation. Hence, the AHR has diametrically opposed pro-proliferative and anti-proliferative functions that have yet to be reconciled at the molecular level. Work from our own and from other laboratories suggests that the AHR may function as a tumor suppressor gene that becomes silenced in the process of tumor formation. To develop preliminary support for a more thorough examination of this hypothesis we characterized the expression levels of various tumor suppressor genes, transforming growth factor-beta (Tgfb) genes and the Ahr gene in liver tumor samples from mice with a liver-specific RB ablation and their wild-type littermates. In tumors arising in RB-positive livers, Cdkn2d and Tgfb1 were repressed and Cdkn2c, Tgfb2, Tgfb3 and Pai1 were induced, whereas in RB-negative tumors, only Cdkn2c and Tgfb3 were induced. Ahr was significantly repressed in tumors from both sets of mice, supporting the concept that Ahr silencing may be associated with cancer progression.