Triplication of a 21q22 region contributes to B cell transformation through HMGN1 overexpression and loss of histone H3 Lys27 trimethylation [Affymetrix]

Children with Down syndrome (DS) have a 20-fold increased risk of developing B cell acute lymphoblastic leukemia (B-ALL). Polysomy 21 (i.e., extra copies of chr.21) is also the most frequent somatic aneuploidy among all B-ALLs. Additional B-ALLs harbor intrachromosomal amplifications of chr.21q22 (iAMP21). Yet, the mechanistic links between chr.21q22 triplication and B-ALL remain undefined. Here we show that germline triplication of only 31 genes orthologous to human chr.21q22 is sufficient to confer murine B cell self-renewal in vitro, B cell maturation defects in vivo, and B-ALL in concert with either BCR-ABL or CRLF2 with activated JAK2. Chr.21q22 triplication suppresses H3K27me3 in murine progenitor B cells and B-ALLs, and bivalent genes with both H3K27me3 and H3K4me3 at their promoters in wild-type progenitor B cells are preferentially overexpressed in triplicated cells. Strikingly, human B-ALLs with polysomy 21 are distinguished by their overexpression of genes known to be marked with H3K27me3 in multiple cell types. Finally, overexpression of HMGN1, a nucleosome remodeling protein encoded on chr.21q22, suppresses H3K27me3 and promotes both B cell proliferation in vitro and B-ALL in vivo. These data implicate HMGN1 overexpression and loss of H3K27me3 in progenitor B cell transformation and suggest strategies to target leukemias with polysomy 21.

8

Lane AA, Chapuy B, Lin CY, Tivey T, Li H, Townsend EC, van Bodegom D, Day TA, Wu SC, Liu H, Yoda A, Alexe G, Schinzel AC, Sullivan TJ, Malinge S, Taylor JE, Stegmaier K, Jaffe JD, Bustin M, te Kronnie G, Izraeli S, Harris MH, Stevenson KE, Neuberg D, Silverman LB, Sallan SE, Bradner JE, Hahn WC, Crispino JD, Pellman D, Weinstock DM