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Ligands that activate protein kinase-C differ in their ability to regulate basic fibroblast growth factor and
W L Lowe1, M A Yorek, R M Teasdale
1Department of Internal Medicine, University of Iowa College of Medicine, Iowa City 52246.
Abstract:
In this study, rat dermal fibroblasts were used as a model system to examine the ability of ligands that are known to activate protein kinase-C to regulate the levels of the mRNAs encoding basic fibroblast growth factor (bFGF) and insulin-like growth factor-I (IGF-I), two growth factors that are thought to be important in processes such as tissue repair and regeneration and wound healing. Treatment of fibroblasts with the phorbol ester phorbol 12-myristate 13-acetate (PMA), thrombin, bradykinin, serotonin, angiotensin-II, or bombesin increased protein kinase-C activity to a similar degree. Treatment of fibroblasts with 1 microM serotonin transiently increased bFGF mRNA levels about 3-fold compared to the level in control cells maintained in serum-free medium with 0.25% BSA and decreased IGF-I mRNA levels by approximately 50% compared to the level in control cells. This is similar to the previously described changes induced by bradykinin in these cells, but different from the more marked and sustained changes induced by thrombin and PMA. In contrast, angiotensin-II and bombesin had no effect on bFGF or IGF-I mRNA levels. The effects of serotonin, bradykinin, and PMA on bFGF and IGF-I mRNA levels were abrogated by preincubation of cells in 250 nM PMA to down-regulate protein kinase-C. In contrast, the effect of thrombin on bFGF mRNA levels was only partially inhibited by down-regulation of protein kinase-C, while its effect on IGF-I mRNA levels was unaffected. The activation of signaling pathways by the different ligands was further investigated to begin to determine the mechanism for the differences in the effects of thrombin vs. serotonin and bradykinin and in the effects of these three ligands vs. angiotensin-II and bombesin. All of the ligands activated phospholipase-D to a similar degree, suggesting that activation of this enzyme was not responsible for the differential effects of the ligands. In contrast, thrombin, serotonin, and bradykinin had marked effects on the hydrolysis of phosphatidylcholine and phosphatidylinositol, whereas bombesin and angiotensin-II had a small effect on phosphatidylcholine hydrolysis and no effect on phosphatidylinositol hydrolysis.(ABSTRACT TRUNCATED AT 400 WORDS)
Insights
Ligands activating protein kinase C differentially regulate basic fibroblast growth factor (bFGF) and insulin-like growth factor-I (IGF-I) mRNA in fibroblasts. Serotonin and bradykinin increased bFGF mRNA and decreased IGF-I mRNA, while angiotensin-II and bombesin had no effect.
Area of Science:
- Cell Biology
- Molecular Biology
- Biochemistry
Background:
- Basic fibroblast growth factor (bFGF) and insulin-like growth factor-I (IGF-I) are crucial for tissue repair and wound healing.
- Protein kinase C (PKC) activation is implicated in regulating growth factor gene expression.
Purpose of the Study:
- To investigate how ligands activating PKC modulate bFGF and IGF-I mRNA levels in rat dermal fibroblasts.
- To elucidate the signaling pathways involved in differential growth factor mRNA regulation.
Main Methods:
- Rat dermal fibroblasts were treated with various ligands known to activate PKC, including phorbol 12-myristate 13-acetate (PMA), thrombin, bradykinin, serotonin, angiotensin-II, and bombesin.
- mRNA levels for bFGF and IGF-I were quantified using techniques not specified in the abstract.
- Phospholipase D activity and hydrolysis of phosphatidylcholine and phosphatidylinositol were assessed.
Main Results:
- Serotonin and bradykinin transiently increased bFGF mRNA and decreased IGF-I mRNA levels.
- Thrombin and PMA induced more sustained changes in bFGF and IGF-I mRNA levels.
- Angiotensin-II and bombesin did not affect bFGF or IGF-I mRNA levels.
- PKC down-regulation abrogated the effects of serotonin, bradykinin, and PMA, but only partially inhibited thrombin's effect on bFGF mRNA.
- Differential hydrolysis of phosphatidylinositol was observed between effective (thrombin, serotonin, bradykinin) and ineffective (angiotensin-II, bombesin) ligands.
Conclusions:
- Ligand-induced PKC activation differentially regulates bFGF and IGF-I mRNA levels in fibroblasts.
- The distinct effects of ligands are partly mediated by differential activation of signaling pathways, including phosphatidylinositol hydrolysis.
- Thrombin's effects may involve PKC-independent mechanisms.