Molecular cloning and characterization of rat chemokine-like factor 1 and 2.

Chemokine-like factor 1(CKLF1) is a newly cloned cytokine with three RNA splicing isoforms. It has chemotactic activities on leukocytes and plays an important role in skeletal muscle regeneration. Here we have isolated two rat homologues of human chemokine-like factors by expressed sequence tag assembly, which are designated as rat chemokine-like factor 1 and 2 (rat CKLF1, CKLF2). The full-length cDNAs of rat CKLF1 and -2 contain 523 and 682 nucleotides and the open reading frames encoding 98 and 151 amino acids, respectively. Rat CKLF1 and -2 share about 54.1 and 59.6% homologies with human CKLF1 and -2 at the amino acid level; both rat CKLF1 and -2 contain a CX3C motif at their C-terminal regions while human CKLFs have a CC motif at the same regions. Rat CKLFs are highly expressed in testis, while human CKLFs have a broad expression spectrum across multiple tissues. Recombinant rat CKLF1 can be secreted into the cell culture supernatants and has chemotactic effects on neutrophils, macrophages and lymphocytes, which is similar to human CKLF1, while recombinant rat CKLF2 has weaker chemotactic effects on these cells. These findings show that rat CKLFs have similar bioactivity with human CKLFs, although they are different in tissue distribution and contain different characteristic motifs.