Transfection of the multiple endocrine neoplasia type 1 gene to a human endocrine pancreatic tumor cell line inhibits cell growth and affects expression of JunD, delta-like protein 1/preadipocyte factor-1, proliferating cell nuclear antigen, and QM/Jif-1.

In the absence of metastases or overgrowth to adjacent organs, the lack of reliable markers for malignancy is a well-recognized problem for clinicians managing patients with endocrine tumors. Apart from inactivation of the multiple endocrine neoplasia type 1 (MEN1) gene, the molecular mechanisms involved in tumorigenesis of the endocrine organs and MEN1-associated nonendocrine lesions are vastly unknown. To try to learn more about down-stream effects on MEN1 gene inactivation, we used the BON1 cells, showing low levels of endogenous menin, and transfected them with a MEN1 gene construct. On restoring the menin expression, we recorded inhibition of cell growth. We also performed macroarray and present data on differentially expressed genes in the transfected cells, after corroboration by Northern blots and quantitative PCR. JunD was up-regulated in menin-expressing clones, whereas delta-like protein 1/preadipocyte factor-1 (involved in differentiation and growth of the pancreatic endocrine cells), proliferating cell nuclear antigen, and QM/Jif-1 (a negative regulator of c-Jun) became down-regulated. These findings might contribute to the understanding of the tissue-specific features of MEN1. We also show that homozygous inactivation of the MEN1 gene statistically correlates to higher expression of delta-like protein 1/preadipocyte factor-1, proliferating cell nuclear antigen, and QM/Jif-1, as well as lower MEN1 expression, in a limited sample of malignant endocrine pancreatic tumors.

In situ RNA-RNA hybridisation of phospholipase C beta 3 shows lack of expression in neuroendocrine tumours.

BACKGROUND: Phospholipase C beta 3 (PLCB3) plays an important role in the signal transduction of the seven transmembrane receptors. The gene is located in the vicinity of the Multiple Endocrine Neoplasia type 1 (MEN1) gene on chromosome 11q13. Transfection of PLCB3 to neuroendocrine cell lines lacking expression suppresses the neoplastic phenotype and affects the gene expression of S100A3 and human mismatch repair protein, suggesting a role for PLCB3 in neuroendocrine tumorigenesis. MATERIALS AND METHODS: We used RNA-RNA in situ hybridisation for PLCB3 on a total of 82 samples including 34 from MEN1 patients. RESULTS: We show that the PLCB3 transcript is missing in 8 out of 14 MEN1-associated neoplasias as well as in 4 out of 10 bronchial carcinoids, 2 out of 10 exocrine pancreatic cancers and one sporadic adrenocortical carcinoma. CONCLUSION: Low or lack of PLCB3 expression in a subset of endocrine tumours, together with earlier published in vitro data on suppressor characteristics upon transfection, indicate that PLCB3 could be involved in the tumorigenesis in a subset of endocrine tumours.

Menin's interaction with glial fibrillary acidic protein and vimentin suggests a role for the intermediate filament network in regulating menin activity.

Recently the multiple endocrine neoplasia type 1 (MEN1) tumor suppressor gene was cloned. Its protein product, called menin, has been shown to associate with the AP1 transcription factor JunD and to repress JunD-mediated transcription. However, little is known concerning the regulation of menin. Here we report that menin interacts with the type III intermediate filament (IF) proteins glial fibrillary acidic protein (GFAP) and vimentin. Menin's interaction with these IF proteins was characterized and confirmed both in vitro and in vivo using GST pull-down analysis, co-immunoprecipitation experiments, and immunofluorescence studies. Deletion mutants of GFAP or vimentin involving the head domains of the molecules abolish the interaction with menin. Endogenous menin is colocalized with GFAP and vimentin in glioma cells as determined by confocal microscopy. Furthermore, a tailless GFAP deletion mutant, which disrupts the IF network, results in menin/GFAP/vimentin-containing aggregates. Triple immunofluorescence labeling studies with antibodies against menin, BrdU, and GFAP show that menin and GFAP colocalize in glioma cells at the S-G2 phase of the cell cycle, as measured by BrdU incorporation. Our data suggest that the intermediate filament network interacts with and may serve as a cytoplasmic sequestering network for menin at the S and early G2 phase of the cell cycle.

Effects of interferon alpha on the expression of p21cip1/waf1 and cell cycle distribution in carcinoid tumors.

Interferon alpha (IFN-alpha) has been shown to produce antitumor effects in 50-80% of carcinoid tumor patients and has demonstrated anti-proliferative effects in carcinoid tumor cells, but the mechanism is not well established. This study presents evidence that in a carcinoid tumor cell line, Bon1, IFN-alpha increases the expression of p21 and promotes nuclear translocation of endogenous p21. Furthermore, immunoprecipitation experiments demonstrated that p21 formed immuno-complexes with Stat1 and Stat2 in the nucleus of cells. Interferon alpha can decrease G1- and G2-phase cells, but increase S-phase population. The p21 mRNA expression is inversely correlated to the G1 population (r = -0.933, P < 0.05) and positively correlated to the S-phase population (r = 0.901, P < 0.05). In addition, IFN-alpha inhibited cyclin dependent kinases (CDK), CDK2-, CDK3-, CDK4-, and cyclin E- but not cyclin A-associated kinase activities. Immunodepletion of p21 resulted in a significant enhancement of CDK3 kinase activity (approximately 1.6-fold increase). These results suggest that the mechanism of antitumor and cell cycle regulation of IFN-alpha in carcinoid tumors may, at least in part, be p21-dependent. Based on these results, we conclude that IFN-alpha exerts antitumor effects by increased p21 expression in neuroendocrine tumors.