Molecular cloning and characterization of four isoforms of mCKLF, mouse homologues of human chemokine-like factor.

Chemokine-like factor1 (CKLF1), and its three isoforms (CKLF2, 3 and 4), are recently identified human cytokines. CKLF1 is a potent chemoattractant for human leukocytes and can stimulate inflammation and the regeneration of murine skeletal muscle. CKLF2 can promote proliferation and differentiation of C2C12 muscle cells directly by inducing expression of myogenin and activating transcription factors. In the present study, we cloned CKLF murine homologues, and based on their biological and structural features, named them murine chemokine-like factor 2, 4, 5 and 6 (mCKLF2, 4, 5 and 6). mCKLF2, 4, 5 and 6 encode 152, 120, 122 and 86 amino-acid proteins, respectively. mCKLFs map to mouse chromosome 8 and have high sequence similarity to human CKLFs. Compared to human CKLFs, which have a CC motif in the C-terminal region, mCKLF2 and 4 contain a CX3C motif. Using a PCR-based approach, it appeared mCKLF2 and 5 mRNA were highly expressed in adult testis, while mCKLF4 mRNA was detected only in differentiated C2C12 cells, a pattern different from human CKLFs. Conditioned media from COS-7 cells transfected with mCKLF2 and 4 was chemotactic for mouse neutrophils, macrophages and lymphocytes. Our results show that mCKLF2, 4, 5 and 6 are four splicing variants which are homologues of human CKLFs and murine CKLFs possess distinct features compared to their human counterparts.