Insulin-like growth factors are mitogenic for human keratinocytes and a squamous cell carcinoma.
Normal adult human keratinocytes in monolayer culture and SCL-1, a skin-derived squamous-cell carcinoma cell line, were investigated for the expression of receptors for insulin-like growth factors (IGF) and insulin. As demonstrated by affinity crosslinking, radiolabeled IGF-1, IGF-2, and insulin bound specifically to both cell types. Each cell expressed type I IGF receptors, with affinity for IGF-1 greater than IGF-2 much greater than insulin. Insulin receptors, with highest affinity for insulin, were also present on both cells. However, keratinocytes and SCL-1 cells differed in 125I-IGF-2 binding. 125I-IGF-2-bound to both type I and type II IGF receptors in normal keratinocytes, but bound predominantly to membrane-associated IGF binding proteins in SCL-1. IGF-1 was slightly more potent than IGF-2 in stimulating growth of both keratinocytes and SCL-1 cells. In keratinocytes, concentrations of IGF-1 ranging from 5-100 ng/ml, and of IGF-2 from 50-100 ng/ml, resulted in a significant increase in cell number. At the maximum dose of 100 ng/ml, either IGF-1 or IGF-2 caused a 2.3-times increase in cell number. In SCL-1 cells, IGF-1 was more potent than IGF-2 or insulin at lower concentrations, but either IGF-1 or IGF-2 at the maximal concentration of 333 ng/ml stimulated a 4.7-times increase in thymidine incorporation. The stimulatory effect of insulin in SCL-1 was 10-50 times less potent than that of the IGF. The effect of either IGF on SCL-1 was completely inhibited by the type I IGF receptor antibody alpha IR-3, suggesting that both IGFs are mitogenic through the type I IGF receptor. Insulin action was partially blocked by alpha IR-3, suggesting that insulin can act through both the insulin and type I IGF receptors. It thus appears that IGF-1 and IGF-2 are mitogens for normal and transformed human keratinocytes and that their actions are primarily mediated through the type I IGF receptor, whereas insulin is a mitogen through both the IGF-1 receptor and the insulin receptor.
Neely
E K
EK
Department of Pediatrics, Stanford University School of Medicine, California.
Morhenn
V B
VB
Hintz
R L
RL
Wilson
D M
DM
Rosenfeld
R G
RG
D002294:Carcinoma, Squamous Cell; D002455:Cell Division / Q000187:drug effects*; D002460:Cell Line; D004261:DNA Replication / Q000187:drug effects; D006801:Humans; D007328:Insulin / Q000494:pharmacology; D007334:Insulin-Like Growth Factor I / Q000494:pharmacology*; D007335:Insulin-Like Growth Factor II / Q000378:metabolism / Q000494:pharmacology*; D015603:Keratinocytes / Q000166:cytology* / Q000187:drug effects; D007700:Kinetics; D008565:Membrane Proteins / Q000302:isolation & purification / Q000378:metabolism; D008934:Mitogens; D011972:Receptor, Insulin / Q000302:isolation & purification / Q000378:metabolism; D011956:Receptors, Cell Surface / Q000302:isolation & purification / Q000378:metabolism; D017451:Receptors, Somatomedin; D011994:Recombinant Proteins / Q000494:pharmacology; D012878:Skin Neoplasms; D013936:Thymidine / Q000378:metabolism
D007328:Insulin; D008565:Membrane Proteins; D008934:Mitogens; D011956:Receptors, Cell Surface; D017451:Receptors, Somatomedin; D011994:Recombinant Proteins; D007334:Insulin-Like Growth Factor I; D007335:Insulin-Like Growth Factor II; D011972:Receptor, Insulin; D013936:Thymidine