Sall4, a Stem Cell Factor, Promotes Chemoresistance by Regulates the Side Population Cell Phenotype.

Abstract 3093

Poster Board III-30

The side population (SP) phenotype, defined as the verapamil-blockable ability to efflux the nucleic acid dye Hoechst 33342, has been used to enrich for stem cells in several human normal tissues, cancers, and multiple cell lines including blood cells, and thus may be useful for the identification and isolation of cancer stem cells, which has emerged as a new therapeutic target for cancer treatment. However, the molecular mechanism(s) operating in SP cells remain unclear. Previous studies show that the stem cell factor, SALL4 plays a central role in the self-renewal of embryonic and leukemic stem cells. In this study, we determined the role of SALL4 in side population (SP). Using FACS sorting, we found the presence of SP fractions in four leukemic cell lines: HL-60, NB-4, RPMI8226 and KG1a. SALL4 expression was more abundant in SP cells compared with non-SP cells by 2- 4 fold in these leukemic cell lines. Knockdown of SALL4 in purified SP cells resulted in a reduction of SP population, indicating that SALL4 is required for the self-renewal of SP cells in this culture system. Since the side population phenotype is known to be mediated by the ATP-binding cassette proteins, we further investigated whether SALL4 could regulate the ATP transporters in SP cells. Chromatin immunoprecipitation (ChIP), luciferase assays and real-time PCR analysis demonstrated that SALL4 could bind to the promoter region of ABCA3, one of the ABC transporters, and activated its expression. In addition, while overexpression of SALL4 led to drug resistance in cell lines, SALL4-knockdown cells displayed more sensitive to drug treatments than the control cells. Further more, SALL4 expression was associated with primary AML treatment status (N= 64 cases), with higher SALL4 mRNA expression seen in drug resistance and partial remission patients than that from complete remission cases. Taken together, our results suggest that SALL4 plays an important in the sensitivity to drug treatment, at least in part, through the maintenance of SP cells, and is responsible for drug-resistance in leukemia.