MEN1 is an autosomal dominant cancer syndrome characterized by multiple tumors of the parathyroid, anterior pituitary and GI (gastrointestinal) endocrine tissues. We have shown earlier that mutations in the MEN1 gene are responsible for the disease. We find that the MEN1 encoded nuclear protein, Menin, resides primarily in the nucleus, binds the transcription factors JunD and NFkB, and can repress JunD and NFkB-induced transcription. We find that interaction with menin is required for the growth suppressor function(s) of JunD. Menin was found to interact many other proteins including RPA2, a protein component in a replication complex. ? We have developed both conventional and conditional mouse knockout models, which yield phenotypes that are remarkably similar to the human MEN1 disease, and have allowed us to delineate the stages in development of the pancreatic endocrine tumors. Tissue specificity of the tumor development was evident from the studies that conditional knockout of menin in liver was well tolerated, a tissue not affected in MEN1 syndrome, whereas similar loss in parathyroid or pancreatic islets resulted in tumors of the respective tissues. In addition, we have developed tissue specific menin-inducible transgenic mouse models. Expression changes associated with menin in cell lines and during tumorigenesis have been evaluated. Mouse fibroblasts lacking menin affected changes in the expression of extracellular matrix proteins, and expression changes for a fraction of these genes was also mediated by TGF-β. Expression changes associated with the loss of menin in ES (embryonic stem) cells suggest that menin may mediate early differentiation of these cells. In order to pursue specific role of menin in differentiation, we are overexpressing menin in mouse P19 cells and evaluating its effect on differentiation into neuronal, meso- and endodermal lineages. ? Identification of the promoters of the genes with which menin is associated was studied, using ChIP on chip approach. Included among thousands of genes/promoters that menin was associated were hox genes. This is particularly relevant in light of the recent demonstration that menin is a critical component of a huge protein complex that includes MLL (mixed lineage leukemia), which plays key role in transcriptional regulation by methylation of Histone H3, and plays a critical role in hematopoiesis by modulating hox gene expression. Therefore, we tested hematopoietic differentiation of mouse ES cells lacking menin and found that this process was severely affected. We find that not only menin but also hoxa9 can rescue the deficiency in hematopoiesis. This indicates that menin also mediates its role in hematopoiesis via hoxa9, similar to that by MLL. We are exploring the specific role(s) of menin in hematopoiesis in mouse ES cells; the role of menin in hematopoiesis (and other developmental events) in zebrafish and Xenopus laevis, are also being explored. We could bring down the the Men1 mRNA and menin protein levels in zebrafish and Xenopus by injection of antisense oligonucleotides (morpholino derivatives) designed to complement splice junctions and the region around ATG. There was not any apparent effect such a reduction in menin levels in early development in zebrafish. We are evaluating the effect of germline Men1 mutations in zebrafish. In addition, tissue specific transgenic expression and knockout models for MEN1 are developed in Drosophila. These models should help to understand the functional role(s) of menin.? Apart from studies associated with menin, we are also evaluation genomic changes associated with breast and colon cancer using high-resolution BAC arrays. The TRMT12 gene encoding an enzyme in the biosynthetic pathway of a modified base, wybutosine (yW) in tRNA Phe was amplified and overexpressed in breast cancer. Application of such high-resolution techniques for evaluation of genomic changes are likely to lead to the identification of novel targets that may serve a s better diagnostic tools or open up novel therapeutic avenues.
Showing the most recent 10 out of 19 publications
