IDENTIFICATION OF A TRUNCATED FORM OF THE CC-CHEMOKINE CK-BETA-8 DEMONSTRATING GREATLY ENHANCED BIOLOGICAL-ACTIVITY

A new CC chemokine, designated CK beta-8 or myeloid progenitor inhibit or factor-1, was recently identified in a large scale sequencing effor t and was cloned from a human aortic endothelial library. CK beta-8 cD NA encodes a signal sequence of 21 amino acids, followed by a 99-amino acid predicted mature form. CK beta-8 was expressed and purified from a baculovirus insect cell expression system, which resulted in the id entification of different N-terminal variants of the secreted chemokin e. The three major forms (containing amino acids 1-99, 24-99, and 25-9 9 of the secreted chemokine) showed a large variation in potency. CK b eta-8 activated both monocytes and eosinophils to mobilize intracellul ar calcium; however, the shortest form of CK beta-8 (25-99) was >2 ord ers of magnitude more potent than the longest form. Cross-desensitizat ion experiments in both monocytes and eosinophils suggested that the C CR1 receptor was probably the predominant receptor that mediates this chemokine's physiologic response. However, incomplete desensitization was encountered in both cell systems, suggesting involvement of an add itional receptor(s). Interestingly, the short form of CK beta-8 was th e most potent chemotactic chemokine that we have ever evaluated in the monocyte system (EC50 = 54 pM). However, in contrast to its action on monocytes, CK beta-8 was a very poor chemotactic factor for eosinophi ls.