Phosphoenolpyruvate-dependent inhibition of collagen biosynthesis, alpha2beta1 integrin and IGF-I receptor signaling in cultured fibroblasts.
ABSTRACT The mechanism of collagen biosynthesis regulation is not fully understood. The finding that prolidase plays an important role in collagen biosynthesis and phosphoenolpyruvate inhibits prolidase activity "in vitro" led to evaluate its effect on collagen biosynthesis in cultured human skin fibroblasts. Confluent fibroblasts were treated with millimolar concentrations (1-4 mM) of phosphoenolpyruvate monopotassium salt (PEP) for 24 h. It was found that PEP-dependent decrease in prolidase activity and expression was accompanied by parallel decrease in collagen biosynthesis. However, the experiments with inhibitor of PEP production, 3-mercaptopicolinate revealed no direct correlation between collagen biosynthesis and prolidase activity and expression. Since insulin-like growth factor (IGF-I) is the most potent stimulator of both collagen biosynthesis and prolidase activity, and prolidase is regulated by beta(1) integrin signaling, the effect of PEP on IGF-I receptor (IGF-IR) and beta(1) integrin receptor expressions were evaluated. It was found that the exposure of the cells to 4 mM PEP contributed to a decrease in IGF-IR and beta(1) integrin receptor expressions. The data suggest that PEP-dependent decrease of collagen biosynthesis in cultured human skin fibroblasts may undergo through depression of alpha(2)beta(1) integrin and IGF-IR signaling. The hypothetical mechanism of the role of prolidase in IGF-IR, beta(1) integrin receptor expressions, and clinical significance of the process are discussed.
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ABSTRACT: Transforming growth factor beta 1 (TGF β1) is a protein that in most cells control proliferation and differentiation. One of the best characterized functions of TGF β1 is stimulation of collagen biosynthesis that may lead to tissue fibrosis. Several reports suggest that prolidase, through regulation of expression of growth factors and transcription factors, e.g. vascular endothelial growth factor (VEGF) and hypoxia-inducible factor-1α (HIF-1 α) may be important in many physiologic and pathophysiologic processes like: wound healing, inflammation and angiogenesis. We found that inhibitors of prolidase activity (N-benzyloxycarbonyl-l-proline, Cbz-Pro and phosphoenolopyruvate, PEP) induced decrease in TGF β1 and its receptor expressions. On the other hand, products of prolidase catalytic activity, proline (Pro) and hydroxyproline (HyPro) induced increase in the amount of TGF β1 and TGF β receptors. Simultaneously, inhibitors of prolidase induced down-regulation of expression of the phospho-AKT. An addition of Pro or HyPro to the cells induced increase in the expression of phospho-AKT. An important transcription factor involved in signal induced by TGF β receptor is mammalian target of rapamycin (mTOR). We found that prolidase inhibitors induced decrease in the expression of phospho-mTOR, while Pro or HyPro counteracted the effect. Rapamycin (pharmacological inhibitor of mTOR) resulted in decrease in prolidase activity. The down-regulation of phospho-mTOR by rapamycin contributed to down-regulation of prolidase activity suggesting its important role in prolidase-dependent function. It seems, that products of prolidase activity, Pro or HyPro may act as an interface between mTOR and phospho-mTOR in regulation of numerous TGF β receptor-dependent functions.European journal of pharmacology 12/2010; 649(1-3):115-9. DOI:10.1016/j.ejphar.2010.09.034 · 2.59 Impact Factor