Dissection of receptor functions through the generation of a tcu-PA cleavage resistant u-PAR: a u-PA independent active u-PAR

receptor;internalization;fibrinolysis;plasminogen activation;urokinase receptor

Nieves, Evelyn

关键词: receptor;    internalization;    fibrinolysis;    plasminogen activation;    urokinase receptor;   

Others  :  https://www.ideals.illinois.edu/bitstream/handle/2142/42459/Evelyn_Nieves.pdf?sequence=1&isAllowed=y

美国|英语

来源: The Illinois Digital Environment for Access to Learning and Scholarship

【 摘 要 】

The regulation of protease activity is essential for physiological events, such as angiogenesis, inflammation, wound healing, and tumor invasion.Urokinase plasminogen activator receptor (u-PAR) has been widely studied in both systemic and cellular processes. Systemic roles for u-PAR include angiogenesis, inflammation and cancer while cellular roles include cell proliferation, survival, adhesion, migration, and localizing activation of plasminogen (Pg) (Blasi, Behrendt et al. 1990; Ellis, Behrendt et al. 1991; Nguyen, Hussaini et al. 1998; Chapman, Wei et al. 1999). u-PAR exerts its effects through both proteolytic and non-proteolytic mechanisms that are inter-related. Both functions are directly affected by the activation of u-PAR through the binding of its cognate ligand, urokinase plasminogen activator (u-PA).u-PAR is a glycosidylphosphatidylinsotol (GPI)-anchored receptor that has the ability to activate Pg through localization of u-PA to the cell surface. In malignant cells, the increased glycosylation of u-PAR confers resistance to cleavage by two-chain urokinase plasminogen activator (tcu-PA) (Montuori, Rossi et al. 1999).Interestingly, the presence of highly glycosylated receptor prevents the tcu-PA from cleaving domain 1 (D1) by decreasing u-PA’s affinity for u-PAR.The central hypothesis of the work described here involves the sensitive balance that is created by the binding of u-PA to u-PAR for both the activation and functional regulation of these proteins. u-PAR has the ability to localize u-PA to the cell surface to initiate Pg activation.tcu-PA also has the ability to cleave D1 of u-PAR from the rest of the protein, which prevents localization of u-PA on the cell-surface.To explore and characterize this relationship, we engineered a mutant u-PAR that prevents cleavage of D1, and studied the effects on the activation of Pg, u-PAR dependent cellular migration and proliferation.Mutation of residues Arg 83 and Arg 89 in u-PAR leads to conformational changes that resemble the active conformation of u-PAR previously observed in crystal structures (Llinas, Le Du et al. 2005; Barinka, Parry et al. 2006; Huai, Mazar et al. 2006).Although our studies indicate that the initiation of the Pg activation cascade of our u-PAR mutants is essentially indistinguishable from wild type wt u-PAR, we also show an acceleration of the rate at which u-PA-PAI-1 complexes are cleared by 2-macroglobulin receptor/ low-density lipoprotein receptor-related protein (LRP) through u-PAR binding. In addition, we observe an increase in cell proliferation, cell migration and changes in cell morphology that correlates with an increase in ERK signaling.The u-PAR:LRP interaction we identified was remarkably novel, although one publication related u-PAR to LRP via binding the u-PA-PAI-1 complex, with u-PAR with minimal interaction via domain 3 of u-PAR (Czekay, Kuemmel et al. 2001).The u-PAR:LRP interaction we observed was supported by an increase in u-PAR detection when the mutant receptor was co-immunoprecipitated with an antibody against LRP. A similar increase was not observed with wt u-PAR.We also observed a direct impact on cell migration, adhesion and proliferation that are known to be u-PA dependent.The ability of u-PAR to aid in cellular motility in response to local environment is intriguing, in light of the fact that there is a correlation between plasma levels and the amount of intact su-PAR found in cancer patients (Bifulco, Longanesi-Cattani et al. 2011). The ability of highly glycosylated u-PAR molecules to increase proliferative events is also of interest. Over-glycosylation of u-PAR leads to resistance to cleavage by its cognate ligand, tcu-PA (Sier, Nicoletti et al. 2004). In addition, this effect is pronounced in highly metastatic anaplastic thyroid carcinoma (Montuori, Rossi et al. 1999).Studying the mechanisms used by u-PAR in vitro and in vivo provides great insight into which u-PAR activities are important in cancer. The expression of u-PAR in both neoplastic cells and tumor-associated cells from ovary, colon, lung, breast, endometrium, macrophages, endothelial cells, and fibroblasts indicates that u-PAR may be a useful therapeutic target since researchers have been able to correlate prognosis and u-PAR expression levels (Mazar 2001; Wang, Mao et al. 2001; Ge and Elghetany 2003; Sidenius and Blasi 2003; Mazzieri and Blasi 2005). Furthermore, u-PAR may be useful as a prognostic marker for cancer and to detect metastasis at an early stage. Generation of a non-cleavable u-PAR provides information regarding what relative roles are played by the intact and cleaved forms of the receptor.