Mannose-6-phosphate/IGF-II receptors mediate the effects of IGF-1-induced latent transforming growth factor beta 1 on expression of type I collagen and collagenase in dermal fibroblasts.
We have previously shown that insulin-like growth factor-1 (IGF-1) induces the expression of latent transforming growth factor beta 1 (LTGF-beta 1) through activation of c-fos and c-jun oncogenes. In this study we investigated whether IGF-1 induced latent TGF-beta 1 has autocrine effects on dermal fibroblasts and described a possible mechanism. Human dermal fibroblasts were treated with either vehicle, IGF-1 alone, or IGF-1 with either anti-TGF-beta 1 neutralizing antibody or mannose-6-phosphate (M6P) and levels of mRNAs for TGF-beta 1, collagenase and the pro alpha 1(I) chain of type I collagen were then evaluated by Northern analysis. Conditioned medium was also collected from treated and untreated cells and assayed for TGF-beta 1 protein by enzyme-linked immunosorbent assay. The results of the Northern analysis revealed a differential effect on the expression of the pro alpha 1(I) chain of type I collagen and collagenase in dermal fibroblasts: mRNA for the former being significantly increased in response to IGF-1 treatment while that for collagenase was markedly suppressed. These effects of IGF-1 were blocked to a significant extent by TGF-beta 1 neutralizing antibody at a concentration of 0.5-2.0 micrograms/ml. As the TGF-beta 1 induced by IGF-1 is inactive in the traditionally used mink lung epithelial cell growth inhibition assay, we explored the possible role of IGF-II/M6P receptors in facilitating these autocrine effects. The results showed that the greater than two-fold increase (201.9 +/- 38 vs 81.8 +/- 13, p < 0.05) in mRNA for the pro alpha 1(I) chain of type I collagen induced by IGF-1 was at least 60% inhibited by M6P in a time-dependent fashion. A direct correlation between the expression of TGF-beta 1 and the pro alpha 1(I) chain of type I collagen was found in response to either IGF-1 alone or IGF-1 with M6P. Treatment of cell cultures with TGF-beta 1 neutralizing antibody mimicked the effect of M6P. In contrast to the effects on expression of type I collagen, the level of collagenase mRNA was markedly reduced by IGF-1 alone and was restored by the administration of M6P. The levels of TGF-beta 1 in conditioned medium from treated and untreated cells showed a similar pattern to that of the mRNA detected by Northern analysis. These findings suggest that IGF-1 induces latent TGF-beta 1 and that the matrix-modulating autocrine effects of LTGF-beta 1 on dermal fibroblasts are facilitated by M6P/IGF-II receptors on these cells.
Ghahary
A
A
Department of Surgery, University of Alberta, Edmonton, Canada.
Tredget
E E
EE
Shen
Q
Q
Kilani
R T
RT
Scott
P G
PG
Houle
Y
Y
D015152:Blotting, Northern; D002478:Cells, Cultured; D003094:Collagen / Q000096:biosynthesis* / Q000378:metabolism; D017364:Collagenases / Q000096:biosynthesis* / Q000378:metabolism; D004797:Enzyme-Linked Immunosorbent Assay; D005347:Fibroblasts / Q000378:metabolism; D006801:Humans; D007334:Insulin-Like Growth Factor I / Q000378:metabolism* / Q000502:physiology; D012333:RNA, Messenger / Q000032:analysis; D017527:Receptor, IGF Type 2 / Q000502:physiology*; D012867:Skin / Q000166:cytology / Q000378:metabolism*; D016212:Transforming Growth Factor beta / Q000096:biosynthesis* / Q000378:metabolism
D012333:RNA, Messenger; D017527:Receptor, IGF Type 2; D016212:Transforming Growth Factor beta; D007334:Insulin-Like Growth Factor I; D003094:Collagen; D017364:Collagenases