An experimental study on membrane malignant phenotype of tumour cells and their reversion

A human promyelocytic leukemic cell line (HL-60 cells) was induced to differentiate along the myeloid pathway in vitro by 1.25% dimethylsulfoxide (DMSO) as an inducer. The membrane fluidity, the quantity of ConA binding sites on the cell membrane surface, and the protein tyrosine kinase (Tyr-PK) activity existing in NP-40 membrane extract and cytoplasma extract were determined respectively. The activity of tumour-derived immunosuppressive factor (TDSF) secreted by HL-60 cells into culture supernatant was also determined. The results demonstrated that: (1) HL-60 cells were capable of undergoing differentiation onto the myeloid pathway in the presence of DMSO. The growth of DMSO-treated HL-60 cells became slow and synthesis rate of DNA decreased by about 50%. (2) Both membrane fluidity and the quantity of ConA binding sites on membrane were obviously lower after induced with DMSO than those before induction. (3) The Tyr-PK activity in the NP-40 membrane extract increased during the period of induced differentiation. The phosphorylation level of endogenous protein in cytoplasma extract decreased with the process of induced differentiation. It may be reasoned that the phosphatase activity is much higher than the phosphorylase activity. (4) The secretive level of TDSF by HL-60 cells during the period of induced differentiation revealed no change. The preliminary results showed that the malignant phenotypes of tumour cells we used may undergo reversible changes with induced differentiation of tumour cells except the secretion of TDSF.