| The MEN1 tumor suppressor is inactivated in the cancer syndrome multiple endocrine neoplasia type 1. This dissertation dissects the role of menin in the cell, in order to understand how its absence leads to cancer.; To investigate menin function, interacting proteins were identified. Menin interacts with an MLL2-containing histone methyltransferase (HMTase) complex. The complex methylates H3K4, a mark that is involved in gene activation. Some patient-derived menin point mutants fail to interact with HMTase activity, suggesting involvement of the HMTase complex in menin's tumor suppressor activity. Menin transcriptionally activates Hoxc6 and Hoxc8 and binds the Hoxc8 promoter, leading to a model in which menin targets HMTase activity to specific genes, methylating H3K4, enhancing RNA polymerase II transcription.; Menin interacts both with MLL and MLL2, but not with MLL family proteins generally. The interaction domain of MLL was mapped to amino acids 380--441 of menin. Menin also interacts with HMTase activity in the absence Mll, suggesting that MLL2 is a true HMTase protein. Finally, patient-derived menin point mutants that fail to associate with HMTase activity fail to bind to MLL.; Menin was shown to regulate the expression of the cyclin-dependent kinases p18Ink4c and p27Kip1. Both menin and MLL are involved in regulating the expression of these genes, as absence of either gene results in downregulation of Cdkn2c and Cdkn1b . Menin appears to target MLL to these genes, because menin interacts with the promoters in the absence of MLL, whereas MLL will not interact with these promoters in the absence of menin.; Several post-translational modifications of menin are described: two phosphorylation sites, at S543 and S583, and an acetylation site at K502. The involvement of these modifications in the binding of menin to MLL was tested, both via ablation mutants and by the generation of 'phospho-mimics'. The absence of phosphorylation does not prevent menin from binding to MLL, nor does a negative charge at either phospho-site prevent binding.; Together, these data demonstrate that menin interacts with H3K4 historic methyltransferase complexes to regulate genes involved in development and the cell cycle. When menin is absent, these genes are misregulated, leading to tumorigenesis. |
