Menin expression is regulated by transforming growth factor beta signaling in leukemia cells

Background Menin is a ubiquitously expressed protein encoded by the multiple endocrine neoplasia type 1 (MEN1) gene. Besides its importance in endocrine organs, menin has been shown to interact with the mixed lineage leukemia (MLL) protein, a histone H3 lysine 4 methyltransferase, and plays a critical role in hematopoiesis and leukemogenesis. Previous studies have shown that menin promotes transforming growth factor beta (TGF-beta) signaling in endocrine cells. However, little is known regarding the impact of TGF-beta pathway on menin in hematopoietic system. Here, with leukemia cell lines generated from conditional MEN1 or TGF-beta receptor (T beta RII) knockout mouse models, we investigated the possible cross-talk of these two pathways in leukemia cells. Methods MEN1 or T beta RII conditional knockout mice were bred and the bone marrow cells were transduced with retroviruses expressing oncogeneic MLL-AF9 (a mixed lineage leukemia fusion protein) to generate two leukemia cell lines. Cell proliferation assays were performed to investigate the effect of TGF-beta treatment on MLL-AF9 transformed leukemia cells with/without MEN1 or T beta RII excision. Menin protein was detected with Western blotting and mRNA levels of cell proliferation-related genes Cyclin A(2) and Cyclin E(2) were examined with real-time RT-PCR for each treated sample. In vivo effect of TGF-beta signal on menin expression was also investigated in mouse liver tissue after T beta RII excision. Results TGF-beta not only inhibited the proliferation of wild type MLL-AF9 transformed mouse bone marrow cells, but also up-regulated menin expression in these cells. Moreover, TGF-beta failed to further inhibit the proliferation of Men1-null cells as compared to Men1-expressing control cells. Furthermore, excision of T beta RII, a vital component in TGF-beta signaling pathway, down-regulated menin expression in MLL-AF9 transformed mouse bone marrow cells. In vivo data also confirmed that menin expression was decreased in liver samples of conditional T beta RII knockout mice after T beta RII excision. Conclusion These results provided the first piece of evidence of cross-talk between menin and TGF-beta signaling pathways in regulating proliferation of leukemia cells, suggesting that manipulating the cross-talk of the two pathways may lead to a novel therapy for leukemia. Chin Med J 2011;124(10):1556-1562