Regulation of cell cycle by the novel GATA1/TAL1/Sphingomyelin Synthase 1 ( SGMS1 ) transcriptional axis. Implications for anti-leukemic strategies

Sphingomyelin Synthase 1 (gene name: SGMS1 ) participates in regulation of sphingolipid levels by synthesizing sphingomyelin from ceramide and phosphatidylcholine. Evidence have supported SGMS1’s functions in regulating proliferation, cell cycle, cell death and migration. While its functions have begun to be explored, very little is known about upstream regulators. Here, we demonstrate that SGMS1 is a direct gene target of the GATA1-TAL1 transcriptional complex in K562 erythroleukemic cells. A predicted GATA1 consensus DNA binding sequence was identified with in a newly characterized alternative SGMS1 promoter (TSS-7 promoter) and ChIP analysis confirmed GATA1 occupancy on the promoter. Down-regulation of GATA1 in K562 cells significantly decreased SGMS1 expression and enzymatic activity, and ChIP-Seq analysis from ENCODE showed colocalized peaks for GATA1 and TAL1 ( a well-established GATA1 DNA binding partner) on the SGMS1 gene. Analysis of publicly available datasets shows that elevated GATA1, TAL1 and SGMS1 expression not only clusters GATA1 positive chronic myelogenous leukemia cells (like K562), but also selectively identifies acute erythrocytic and megakaryocytic leukemias (M6 and M7 AML, respectively). Microarray gene expression analysis after down-regulation of SGMS1 in M6 AML Hel cells revealed alteration of genes regulating G2/M check point and mitotic spindle formation. This phenotype was functionally confirmed by the significant delay in G2/M cell cycle progression of cells with SGMS1 downregulation and sensitization to the clinically relevant anti-mitotic agent, Taxol. Altogether, these results identify SGMS1 as a novel target of GATA1/TAL1 transcriptional complex and they support a role for the GATA1/TAL1/SGMS1 axis in regulating transit through G2/M. Importantly, results also point to combination of anti-mitotic agents and inhibition of SGMS1 as a potential novel therapeutic approach against the aggressive and resilient M6 AMLs.