Heterogeneity of insulin and insulin-like growth factor I binding in a human Burkitt type ALL cell line during the cell cycle and in three Burkitt type ALL sublines.

The expression of hormonal and growth factor receptors in leukemic cell lines might be heterogeneous due to the admixture of different cell cycle phases and the presence of yet unidentified sublines. Therefore, cell cycle-specific separation of Burkitt type ALL cells was performed by counterflow elutriation, and by limited dilution procedure three sublines of this cell line were obtained. Counterflow elutriation enriched to 60-80% purity for G1-, S-, and G2-phase which was shown by DNA flow cytometry. Insulin and insulin-like growth factor I (IGF-I) binding was investigated in the G1, S, and G2 phase. Insulin binding sites decreased from 10 to 15,000 per cell in G1 to 1,000-5,000 in S and increased to 40-50,000 in G2. The affinity of insulin binding remained constant during the cell cycle. IGF-I binding sites increased from 2,000 per cell in G1 to 5,000 in S and 15,000 in G2. The affinity of IGF-I binding decreased from G1 toward S and then remained constant in G2. The three isolated clonal sublines differed in numbers of insulin and IGF-I binding sites/cell without differences in affinity. The fact that IGF-I shows higher affinity binding during G1 than during S and G2 Burkitt type ALL cells suggests that IGF-I might be important for initiation of proliferation. The reduction in insulin binding sites during S-phase may indicate refractoriness of the cell to insulin during DNA replication.