Chinese hamster ovary cell variants resistant to monensin, an ionophoric antibiotic. II. Growth requirement for insulin and altered insulin‐receptor activity

From the Chinese hamster ovary (CHO) cell, genetic variants (Mon^R–31 and Mon^R–32) relatively resistant to monensin, an ionophoric antibiotic, have been isolated. Growth of both Mon^R‐31 and Mon^R‐32 clones required higher doses of serum than CHO. Addition of insulin to media containing a low dose of serum restored full colony formation, but growth of Mon^R‐31 or Mon^R‐32 cells required more insulin than CHO cells. Specific binding of [¹²⁵l]insulin was observed in these cell lines. The two Mon^R clones bound about one‐half or less the [¹²⁵l]insulin bound by CHO cells. Scatchard analysis for [¹²⁵l]insulin binding at 4°C and 37°C showed altered number of binding sites, but not insulin affinity: The number of binding sites in the Mon^R cell was about a half or less that of the parental CHO cell. Down‐regulation of insulin receptor was assayed when both CHO and Mon^R cells were incubated with 1 μg/ml insulin. A 50–60% decrease in levels of insulin surface binding capacities was observed in CHC after exposure to insulin, whereas there was no decrease in Mon^R cell. The cellular uptake of 2‐[³H]deoxyglucose into CHO cells was significantly enhanced in the presence of insulin, but only slight, if any, increase was observed in Mon^R cells.