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

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Abstract
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 ∼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.