Qiu D, Owen K, Gray K, Bass R, Ellis V
Biomedical Research Centre, School of Biological Sciences, University of East Anglia, Norwich NR4 7TJ, UK.
Biochem Soc Trans. 2007 Jun;35(Pt 3):583-7. doi: 10.1042/BST0350583.
Pericellular proteolytic activity affects many aspects of cellular behaviour, via mechanisms involving processing of the extracellular matrix, growth factors and receptors. The serine proteases have exquisitely sensitive regulatory mechanisms in this setting, involving both receptor-bound and transmembrane proteases. Receptor-bound proteases are exemplified by the uPA (urokinase plasminogen activator)/uPAR (uPAR receptor) plasminogen activation system. The mechanisms initiating the activity of this proteolytic system on the cell surface, a critical regulatory point, are poorly understood. We have found that the expression of the TTSP (type II transmembrane serine protease) matriptase is highly regulated in leucocytes, and correlates with the presence of active uPA on their surface. Using siRNA (small interfering RNA), we have demonstrated that matriptase specifically activates uPAR-associated pro-uPA. The uPA/uPAR system has been implicated in the activation of the plasminogen-related growth factor HGF (hepatocyte growth factor). However, we find no evidence for this, but instead that HGF can be activated by both matriptase and the related TTSP hepsin in purified systems. Hepsin is of particular interest, as the proteolytic cleavage sequence of HGF is an 'ideal substrate' for hepsin and membrane-associated hepsin activates HGF with high efficiency. Both of these TTSPs can be activated autocatalytically at the cell surface, an unusual mechanism among the serine proteases. Therefore these TTSPs have the capacity to be true upstream initiators of proteolytic activity with subsequent downstream effects on cell behaviour.
细胞周围的蛋白水解活性通过涉及细胞外基质、生长因子和受体加工的机制影响细胞行为的许多方面。在这种情况下，丝氨酸蛋白酶具有极其敏感的调节机制，涉及受体结合型和跨膜蛋白酶。受体结合型蛋白酶以uPA（尿激酶型纤溶酶原激活剂）/uPAR（uPAR受体）纤溶酶原激活系统为代表。启动该蛋白水解系统在细胞表面活性的机制，这一关键调节点，目前了解甚少。我们发现，II型跨膜丝氨酸蛋白酶（TTSP）胃蛋白酶在白细胞中表达受到高度调节，并且与其表面活性uPA的存在相关。使用小干扰RNA（siRNA），我们证明胃蛋白酶特异性激活与uPAR相关的pro-uPA。uPA/uPAR系统与纤溶酶原相关生长因子HGF（肝细胞生长因子）的激活有关。然而，我们没有发现这方面的证据，而是发现HGF在纯化系统中可以被胃蛋白酶和相关的TTSP组织蛋白酶激活。组织蛋白酶特别令人感兴趣，因为HGF的蛋白水解切割序列是组织蛋白酶的“理想底物”，并且膜相关的组织蛋白酶能高效激活HGF。这两种TTSP都可以在细胞表面自催化激活，这在丝氨酸蛋白酶中是一种不寻常的机制。因此，这些TTSP有能力成为蛋白水解活性真正的上游启动因子，随后对细胞行为产生下游影响。
