Figure 4.

DNA synthesis response of cells expressing mutant forms of IGFBP-5. To determine whether the cells that were transfected with mutant forms of IGFBP-5 that resulted in less IGFBP-5 in their extracellular matrix would respond similarly to IGF-I, confluent, quiescent cultures were exposed to increasing concentrations of IGF-I for 36 h in DMEM containing 0.2% PPP. After 36 h, [³H]thymidine incorporation into DNA was determined as described in MATERIALS AND METHODS. Each point represents the mean of triplicate determinations. The cultures expressing the wild-type IGFBP-5 (•—•) responded to IGF-I better than the mock-transfected cultures (▪—▪). Those synthesizing the R201A/K202N/K206N/K208N (○—○) mutant responded equally well. In contrast, the cultures synthesizing the K202A/K206A/K207A (○- · -○) or K211N/R214A/K217N/R218A (×- - -×) mutants had attenuated responses to IGF-I. The experiment was repeated three times with similar results.