{'fraction_non_alphanumeric': 0.02804878048780488, 'fraction_numerical': 0.01097560975609756, 'mean_word_length': 5.239543726235741, 'pattern_counts': {'":': 0, '<': 0, '<?xml version=': 0, '>': 0, 'https://': 0, 'lorem ipsum': 0, 'www.': 0, 'xml': 0}, 'pii_count': 0, 'substrings_counts': 0, 'word_list_counts': {'cursed_substrings.json': 0, 'profanity_word_list.json': 0, 'sexual_word_list.json': 0, 'zh_pornsignals.json': 0}}
Sequential addition of platelet factor and plasma to BALB/c 3T3 fibroblast cultures stimulates somatomedin-C binding early in cell cycle.

Recent studies have shown that confluent cultured fibroblasts must be rendered competent by a factor contained in platelets before they can respond to plasma components and progress from G0 to S phase of the cell cycle. Somatomedin-C is one of the components of platelet-poor plasma necessary for cell cycle progression, but other factors present in somatomedin-C-deficient plasma are also required. Because both competence and progression factors contained in somatomedin-C-deficient serum modulate somatomedin-C action in fibroblasts, this study was undertaken to examine their possible influence on the binding of 125I-labeled somatomedin-C. Exposure of BALB/c 3T3 fibroblasts to high concentrations of platelet-derived growth factor alone prevented the time-dependent decrease in somatomedin-C binding which occurs in serum-free medium. Lower concentrations of the growth factor or 5% (vol/vol) platelet-poor plasma reduced but did not abolish this decrease. In contrast, sequential addition of platelet-derived growth factor followed by platelet-poor plasma resulted in a 75% increase in 125I-labeled somatomedin-C binding over basal levels during the first 2 hr. Binding increased by 125% when somatomedin-C-deficient platelet-poor plasma was substituted for normal platelet-poor plasma. The hormonal induction of somatomedin-C receptors appears to be a mechanism whereby peptide growth factors such as platelet-derived growth factor may condition the cell to respond optimally to somatomedin-C.