Histone methylase MLL1 has critical roles in tumor growth and angiogenesis and its knockdown suppresses tumor growth in vivo.

Mixed lineage leukemias (MLLs) are human histone H3 lysine-4-specific methyl transferases that have critical roles in gene expression, epigenetics and cancer. Herein, we demonstrated that antisense-mediated knockdown of MLL1 induced cell-cycle arrest and apoptosis in cultured cells. Intriguingly, application of MLL1 antisense specifically knocked down MLL1 in vivo and suppressed the growth of xenografted cervical tumor implanted in nude mouse. MLL1 knockdown downregulated various growth and angiogenic factors, such as HIF1α, VEGF and CD31, in tumor tissue affecting tumor growth. MLL1 is overexpressed along the line of vascular network and localized adjacent to endothelial cell layer expressing CD31, indicating potential roles of MLL1 in vasculogenesis. MLL1 is also overexpressed in the hypoxic regions along with HIF1α. Overall, our studies demonstrated that MLL1 is a key factor in hypoxia signaling, vasculogenesis and tumor growth, and its depletion suppresses tumor growth in vivo, indicating its potential in novel cancer therapy.

Mixed lineage leukaemia-4 regulates cell-cycle progression and cell viability and its depletion suppresses growth of xenografted tumour in vivo.

BACKGROUND: Mixed lineage leukaemia-4 (MLL4) is one of the MLL family of histone H3 lysine-4 (H3K4)-specific methyl transferases that have critical roles in gene expression and epigenetics in human. Though MLLs are well recognised as crucial players in histone methylation and gene regulation; little is known about the biochemical functions of MLL4 and its roles in cancer. METHODS: Herein, we have investigated the roles of MLL4 in cell viability, cell-cycle progression and explored its potential roles in tumour growth using antisense-mediated knockdown experiments, flow-cytometry analysis, chromatin immunoprecipitation, immunofluorescence staining and animal models. RESULTS: Our studies demonstrated that knockdown of MLL4 severely affects cell-cycle progression and induces apoptotic cell death in cultured tumour cells. Knockdown of MLL4 induced nuclear condensation, fragmentation, cytochrome-c release from mitochondria to cytosol and activated caspase-3/7 indicating apoptotic cell death. The MLL4 regulates expression of various critical cell-cycle regulatory genes such as cyclin D, cyclin E, p27, HOXA5 and HOXB7 via histone H3K4 trimethylation and recruitment of RNA polymerase II. Interestingly, application of MLL4 antisense suppressed tumour growth in vivo in colon cancer xenograft implanted in nude mouse. The MLL4 antisense specifically knocked down MLL4 in tumour tissue and also downregulated the expression of various growth and angiogenic factors resulting in tumour suppression. CONCLUSION: Our results demonstrated that MLL4 is a crucial player in cell viability, cell-cycle progression and is critical for tumour growth in vivo.