Expression of insulin-like growth factor binding protein-3 (IGFBP-3) in human keratinocytes is regulated by EGF and TGFbeta1.
Insulin-like growth factor-I (IGF-I) is essential for normal epidermal homeostasis; however, the role of IGF binding proteins (IGFBPs), regulators of IGF action, remains unclear. Here we examine the regulation of human keratinocyte-produced IGFBPs by epidermal growth factor (EGF), transforming growth factor beta 1 (TGFbeta1), and IGF-I, growth factors known to be active in skin. In the absence of added growth factors, IGFBP-3 was the major binding protein secreted into the medium by primary keratinocytes. Addition of EGF or TGFbeta1 to keratinocyte cultures resulted in a significant decrease in IGFBP-3 abundance in conditioned medium when compared with control, untreated cells. Specifically, EGF (50 ng/ml) and TGFbeta1 (50 ng/ml) reduced IGFBP-3 abundance to 15+/-6% and 22+/-9%, respectively. Using Northern blot analysis, we found EGF and TGFbeta1 (50 ng/ml) to reduce IGFBP-3 mRNA levels in keratinocytes to 51+/-12% and 50+/-38%, respectively, when compared with control, untreated cells. Treatment with IGF-I or its analogue des(1-3)IGF-I did not lead to any consistent change in IGFBP-3 abundance. However, both IGF-I and des(1-3)IGF-I at 100 ng/ml led to a modest increase in IGFBP-3 mRNA levels in keratinocytes, suggesting posttranscriptional regulation of IGFBP-3 abundance. We propose that local modulation of IGFBP-3 abundance may represent another level of regulation of growth factor action in the epidermis, where EGF and TGFbeta1 and possibly other local growth factors specifically regulate the availability of IGF-I to its keratinocyte receptors.
Edmondson
S R
SR
Centre for Hormone Research, Royal Children's Hospital, Parkville, Victoria, Australia.
Murashita
M M
MM
Russo
V C
VC
Wraight
C J
CJ
Werther
G A
GA
D017077:Culture Media, Conditioned / Q000494:pharmacology; D004815:Epidermal Growth Factor / Q000494:pharmacology*; D005786:Gene Expression Regulation / Q000187:drug effects; D006801:Humans; D018972:Insulin-Like Growth Factor Binding Protein 3 / Q000235:genetics* / Q000378:metabolism; D007334:Insulin-Like Growth Factor I / Q000494:pharmacology; D015603:Keratinocytes / Q000187:drug effects / Q000378:metabolism*; D010446:Peptide Fragments / Q000494:pharmacology; D012333:RNA, Messenger / Q000378:metabolism; D012867:Skin / Q000187:drug effects; D016212:Transforming Growth Factor beta / Q000494:pharmacology*
D017077:Culture Media, Conditioned; D018972:Insulin-Like Growth Factor Binding Protein 3; D010446:Peptide Fragments; D012333:RNA, Messenger; D016212:Transforming Growth Factor beta; C058957:insulin-like growth factor 1, des-(1-3)-; D004815:Epidermal Growth Factor; D007334:Insulin-Like Growth Factor I