OBJECTIVETo investigate the effect of down-expression of inhibitor of differentiation-1 (Id-1) on the differentiation of dendritic cell sarcoma (DCS) cells in vitro.

METHODSDown-regulation of the expression of Id-1 in DCS cells was performed by RNAi, and confirmed by protein and mRNA quantitative analyses. Cellular differentiation and biological behavior including malignant phenotypes of the cells were evaluated. All experiments included negative (no treatment group and no-target siRNA) and positive (induction-differentiation drug sodium butyrate) controls.

RESULTSWhen the expression of Id-1 was down regulated, the DCS cells showed more mature morphology including cell enlargement, longer cellular extensions, more branches, and decreased nuclear/plasma ratio. Differentiation marker expression (Id-2 and CD86) was also increased. RNAi treated cells at 24 and 48 hours, showed increase percentage of cells at G0/G1 phase and less cells at S phase (P < 0.01). Importantly, the abilities of cell proliferation, colony formation and invasiveness were significantly decreased (P < 0.01), as evidenced by MTT, colony formation and transwell assays respectively.

CONCLUSIONRNAi inhibition of Id-1 protein can induce differentiation of malignant solid tumor cells along with reversion of their malignant phenotype.