Hsp90 directly modulates the spatial distribution of AF9/MLLT3 and affects target gene expression
Description
Chromosomal translocations involving the Mixed Lineage Leukemia (MLL) gene give rise to poor prognosis in infants. The MLL-AF9 translocation, t(9;11)(p22;q23) is a common one involving a less studied partner, AF9. AF9/MLLT3 contributes to the regulation of the gene encoding the epithelial sodium channel alpha, ENaCalpha, in renal tubular cells. Increases in AF9 protein lead to a reduction in ENaCalpha expression and changes in AF9 activity appear to be an important component of aldosterone signaling in the kidney. While AF9 is found in the nucleus where it interacts with the histone H3 lysine 79 methyltransferase, Dot1, AF9 is also present in the cytoplasm. Data presented in this dissertation indicate that the heat shock protein Hsp90 directly and specifically interacts with AF9. Experimental manipulation of Hsp90 function by the inhibitor novobiocin, but not 17-AAG, results in redistribution of AF9 from a primarily nuclear to cytoplasmic location. Knock-down of Hsp90 with siRNA mimics the effect elicited by novobiocin. As expected, a shift in AF9 from the nucleus to the cytoplasm in response to Hsp90 interference leads to increased ENaCalpha expression. This is accompanied by a decrease in AF9 occupancy and a slight decrease of H3K79 hypermethylation at the ENaCalpha promoter. Our data suggest that the interaction of Hsp90 and its co-chaperones with AF9 is necessary for the proper subnuclear localization and activity of AF9