Differential effect of transforming growth factor beta (TGF-beta) on the genes encoding hyaluronan synthases and utilization of the p38 MAPK pathway in TGF-beta-induced hyaluronan synthase 1 activation.

Karl M. Stuhlmeier,Christine Pollaschek

doi:10.1074/jbc.m303945200

Abstract

Unfettered hyaluronan (HA) production is a hallmark of rheumatoid arthritis. The discovery of three genes encoding hyaluronan synthases (HASs) allows for the investigation of the signaling pathways leading to the activation of these genes. Our objective is to further understanding of the regulation of these genes as well as to find ways to prevent undesired gene activation. Human fibroblast-like synoviocytes were used in these experiments. mRNA levels of HAS were monitored by reverse transcriptase-PCR. A series of specific kinase inhibitors were used to investigate intracellular pathways leading to the up-regulation of HAS1. Our experiments, testing a series of stimuli including tumor necrosis factor alpha (TNFalpha), demonstrate that TGF-beta is the most potent stimulus for HAS1 transcription. TGF-beta activates HAS1 in a dose-dependent manner with a maximum effect at a concentration of 0.5-1 ng/ml. TGF-beta-induced HAS1 mRNA can be detected within 60 min and reaches maximal levels at 6 h. Furthermore, TGF-beta treatment leads to an increase in synthase activity as determined by HA ELISA and by in vitro HA synthase assays. In contrast to the activatory effect on HAS1, TGF-beta dose-dependently suppresses HAS3 mRNA. As to the mode of action of TGF-beta-induced HAS1 mRNA activation, our experiments reveal that blocking p38 MAPK inhibited the TGF-beta effect by 90%, blocking the MEK pathway led to an inhibition by 40%, and blocking the JNK pathway had no effect. The presented data might contribute to a better understanding of the role of TGF-beta and of HA in the pathology of diseases.

Highlights

A hallmark of joint swelling associated with rheumatoid arthritis (RA)1 is the overproduction of hyaluronic acid (HA)
As to the mode of action of TGF-␤-induced HAS1 mRNA activation, our experiments reveal that blocking p38 mitogen-activated protein kinase (MAPK) inhibited the TGF-␤ effect by 90%, blocking the MAPK/extracellular signal-regulated kinase (MEK) pathway led to an inhibition by 40%, and blocking the JNK pathway had no effect
Time course experiments revealed that elevated levels of mRNA can be detected as early as 60 min following the addition of TGF-␤ (1 ng/ml) and that maximal levels of HAS1 mRNA in fibroblast-like synoviocytes (FS) are reached at 6 h

Summary

Introduction

A hallmark of joint swelling associated with rheumatoid arthritis (RA) is the overproduction of hyaluronic acid (HA) This polymer was first described by Meyer et al [1] in 1934. Low molecular weight degradation products of HA have been found to elicit various proinflammatory responses such as the stimulation and invasion of macrophages in affected joints [20, 21], as well as the functional maturation/activation of dendritic cells [22]. Low molecular weight HA molecules have been shown to act as a chemoattractant for many cell types as well as an angiogenic factor inducing the growth of blood vessels into joints, skin, and tumors [26, 27]

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Conclusion