Partial characterization of a mitogenic factor with somatomedin-like activity produced by culture WI-38 human fibroblasts.

Conditioned serum-free medium (CSFM) obtained from WI-38 human fibroblasts was found to contain a mitogenic factor(s) with somatomedin (SM)-like activity. Treatment of the cells with cycloheximide eliminated the SM-like activity in CSFM, suggesting that these cells produce and release the activity. Gel filtration revealed that the fibroblast SM-like activity (FSLA) had a molecular size near 45,000. Isoelectric focusing of this FSLA yielded 2 bands of SM activity with pIs of 4.7 and 6.1, and corresponding molecular sizes of approximately 29,000 and 16,500, respectively. The FSLA obtained by gel filtration revealed parallel dose response curves with a basic SM in a SM radioreceptor and radioimmunoassay and stimulated: (1) 35So4 uptake by hypophysectomized rat cartilage; (2) (U-14C) glucose oxidation is isolated rat adipocytes; and (3) (3H) thymidine uptake and cell division in these same WI-38 fibroblasts. Out studies indicate that this FSLA and basic SM are similar but not identical.