Allan E H, Martin T J
St. Vincent's Institute of Medical Research, Melbourne, Victoria, Australia.
J Cell Physiol. 1995 Dec;165(3):521-9. doi: 10.1002/jcp.1041650310.
The bone resorbing agent, prostaglandin E2 (PGE2), was found to alter several components of the plasminogen activator (PA)/plasmin pathway in primary cultures of rat neonatal osteoblast-like cells. The mRNA and activities of both urokinase-type PA (uPA) and tissue-type PA (tPA) were enhanced by PGE2 treatment. The presence of mRNA for the uPA receptor (uPAR) has been demonstrated in these cells and steady-state levels shown to be greatly enhanced, the response being rapid and sustained for at least 24 hours. mRNA for plasminogen activator inhibitor 1 (PAI-1) was modulated in a biphasic manner, with inhibition of the constitutive level apparent at 4 hours of treatment and stimulation apparent at 12 hours and longer, while PAI-1 protein, measured by an ELISA assay for rat PAI-1, was diminished over this period. Neither PAI-2 mRNA nor mRNA for the broad spectrum protease inhibitor, protease nexin-1 (PN-1), was found to be modulated by PGE2. Therefore, PGE2 is likely to stimulate cell surface proteolytic activity, since uPA mRNA and cell-associated activity were elevated, as was mRNA for the cellular receptor for uPA. Although it was not possible to measure uPAR number and affinity it seems likely that elevated uPAR mRNA would translate into increased uPARs which would localize the increased uPA activity to the pericellular region. tPA mRNA and activity were also increased transiently with the activity inhibited with prolonged incubations, apparently by PAI-1. Elevation of tPA mRNA and activity may result in elevated activity within the extracellular matrix as tPA has been reported to associate with several matrix proteins. Thus the early effect of PGE2 would be to promote proteolysis, both pericellularly and in the extracellular matrix. The inhibition of PAI-1 mRNA and protein, which would contribute to the elevation of activity, is due to PGE2, but the later stimulatory effect on PAI-1 mRNA may be due to feedback regulation by transforming growth factor beta (TGF beta), secreted by osteoblasts and activated by elevated levels of PA.
骨吸收剂前列腺素E2（PGE2）被发现可改变大鼠新生成骨细胞样细胞原代培养物中纤溶酶原激活物（PA）/纤溶酶途径的几个成分。PGE2处理可增强尿激酶型PA（uPA）和组织型PA（tPA）的mRNA及活性。在这些细胞中已证实存在uPA受体（uPAR）的mRNA，且稳态水平显著增强，该反应迅速且至少持续24小时。纤溶酶原激活物抑制剂1（PAI-1）的mRNA以双相方式被调节，处理4小时时组成型水平受到抑制，12小时及更长时间时受到刺激，而通过大鼠PAI-1的ELISA测定法测量的PAI-1蛋白在此期间减少。未发现PGE2调节PAI-2 mRNA或广谱蛋白酶抑制剂蛋白酶连接蛋白-1（PN-1）的mRNA。因此，PGE2可能刺激细胞表面蛋白水解活性，因为uPA mRNA和细胞相关活性升高，uPA细胞受体的mRNA也是如此。尽管无法测量uPAR的数量和亲和力，但uPAR mRNA升高似乎可能转化为uPAR增加，这会使增加的uPA活性定位于细胞周区域。tPA mRNA和活性也会短暂增加，长时间孵育后活性受到抑制，显然是被PAI-1抑制。tPA mRNA和活性的升高可能导致细胞外基质内活性升高，因为据报道tPA与几种基质蛋白相关。因此，PGE2的早期作用是促进细胞周和细胞外基质中的蛋白水解。PAI-1 mRNA和蛋白的抑制有助于活性升高，这是由PGE2引起的，但对PAI-1 mRNA的后期刺激作用可能是由于成骨细胞分泌并由PA水平升高激活的转化生长因子β（TGFβ）的反馈调节。
