Proteolytic Cleavage of Chemerin Protein Is Necessary for Activation to the Active Form, Chem157S, Which Functions as a Signaling Molecule in Glioblastoma

Chemerin is a chemoattractant involved in innate and adaptive immunity as well as an adipokine implicated in adipocyte differentiation. Chemerin circulates as an inactive precursor in blood whose bioactivity is closely regulated through proteolytic processing at its C terminus. We developed methodology for production of different recombinant chemerin isoforms (chem163S, chem157S, and chem155A) which allowed us to obtain large quantities of these proteins with purity of >95%. Chem158K was generated from chem163S by plasmin cleavage. Characterization by mass spectrometry and Edman degradation demonstrated that both the N and C termini were correct for weach isoform. Ca2+ mobilization assays showed that the EC50 values for chem163S and chem158K were 54.2 +/- 19.9 nM and 65.2 +/- 13.2 nM, respectively, whereas chem157S had a similar to 50-fold higher potency with an EC50 of 1.2 +/- 0.7 nM. Chem155A had no agonist activity and weak antagonist activity, causing a 50% reduction of chem157S activity at a molar ratio of 100:1. Similar results were obtained in a chemotaxis assay. Because chem158K is the dominant form in cerebrospinal fluid from patients with glioblastoma (GBM), we examined the significance of chemerin in GBM biology. In silico analysis showed chemerin mRNA was significantly increased in tissue from grade III and IV gliomas. Furthermore, U-87 MG cells, a human GBM line, express the chemerin receptors, chemokine-like receptor 1 and chemokine receptor-like 2, and chem157S triggered Ca2+ flux. This study emphasized the necessity of appropriate C-terminal proteolytic processing to generate the likely physiologic form of active chemerin, chem157S, and suggested a possible role in malignant GBM.