Stuhlmeier Karl M, Pollaschek Christine
Ludwig Boltzmann Institute for Rheumatology and Balneology, 1100 Vienna, Austria.
J Biol Chem. 2005 Dec 30;280(52):42766-73. doi: 10.1074/jbc.M503374200. Epub 2005 Oct 28.
It has become increasingly clear that hyaluronan is more than the simple matrix molecule it was once thought to be but instead takes part in a multitude of biological functions. Three genes encode for hyaluronan synthases (HAS). We demonstrated earlier that HAS2 and HAS3 are constitutively activated in type-B synoviocytes (fibroblast-like synoviocytes) and, furthermore, that the only gene that readily responds to stimulation with a series of proinflammatory cytokines is HAS1. Here we probe the involvement of the transcription factor NF-kappaB in induced and noninduced HAS activation. Transforming growth factor (TGF) beta1 as well as interleukin (IL)-1beta are both strong inducers of HAS1 transcription. Stimulation of fibroblast-like synoviocytes with IL-1beta resulted in rapid degradation of IkappaBalpha, an event that was preceded by IkappaBalpha phosphorylation. Interestingly, TGFbeta1 neither affected IkappaBalpha levels, nor did it cause phosphorylation of IkappaBalpha. In addition, TGFbeta1 had no effect on IkappaBbeta and IkappaBepsilon levels. Electrophorectic mobility shift assays demonstrate that IL-1beta is a potent inducer of NF-kappaB translocation; however, TGFbeta1 treatment did not result in shifting bands. Two adenovirus constructs were used to further clarify differences in TGFbeta1- and IL-1beta-induced HAS1 activation. Overexpressing IkappaBalpha completely abolished the IL-1beta effect on HAS1 but did not interfere with TGFbeta1-induced HAS1 mRNA accumulation. Identical results were obtained when a dominant negative IKK was overexpressed. Interestingly, neither overexpression of IkappaBalpha nor of IKK had any effect on HAS2 and HAS3 mRNA levels. Taken together, HAS1 can be activated by distinct pathways; IL-1beta utilizes NF-kappaB, and TGFbeta1 does not. Furthermore, HAS2 and HAS3 are activated without the involvement of NF-kappaB.
越来越清楚的是，透明质酸不仅仅是曾经被认为的简单基质分子，而是参与了多种生物学功能。有三个基因编码透明质酸合酶（HAS）。我们之前证明，HAS2和HAS3在B型滑膜细胞（成纤维样滑膜细胞）中持续被激活，此外，对一系列促炎细胞因子刺激易于产生反应的唯一基因是HAS1。在此，我们探究转录因子核因子-κB在诱导和非诱导的HAS激活中的作用。转化生长因子（TGF）β1以及白细胞介素（IL）-1β都是HAS1转录的强诱导剂。用IL-1β刺激成纤维样滑膜细胞导致IκBα迅速降解，这一事件之前有IκBα磷酸化。有趣的是，TGFβ1既不影响IκBα水平，也不引起IκBα磷酸化。此外，TGFβ1对IκBβ和IκBε水平没有影响。电泳迁移率变动分析表明，IL-1β是核因子-κB易位的有效诱导剂；然而，TGFβ1处理并未导致条带迁移。使用两种腺病毒构建体进一步阐明TGFβ1和IL-1β诱导的HAS1激活的差异。过表达IκBα完全消除了IL-1β对HAS1的作用，但不干扰TGFβ1诱导的HAS1 mRNA积累。当过表达显性负性IKK时获得了相同的结果。有趣的是，IκBα或IKK的过表达对HAS2和HAS3 mRNA水平均无任何影响。综上所述，HAS1可通过不同途径被激活；IL-1β利用核因子-κB，而TGFβ1则不然。此外，HAS2和HAS3的激活不涉及核因子-κB。
