CLONING OF ATAC, AN ACTIVATION-INDUCED, CHEMOKINE-RELATED MOLECULE EXCLUSIVELY EXPRESSED IN CD8(-LYMPHOCYTES() T)

A cDNA clone, designated ATAC, was isolated from a collection of human T cell activation genes. Analysis of tissue distribution determined t hat ATAC mRNA of approxiamtely 0.9 kb is exclusively expressed in acti vated CD8(+) T cells. Induction of the ATAC gene requires stimulation by both phorbol 12-myristate 13-acetate and Ca2+ ionophore A23187 (''t wo-signal gene'') and is fully abrogated by the immunosuppressive agen t cyclosporin A. Upon stimulation, ATAC mRNA is detectable within 30 m in, maximal expression is seen after 4 h. The polypeptide encoded by t he open reading frame of ATAC mRNA is 114 amino acids long with a calc ulated M(r) of 12.52 kDa. The structural features predict the cleavage and secretion of a mature ATAC protein of approximately 10 kDa from t he 12.52-kDa precursor. ATAC is highly similar to a very recently iden tified murine molecule designated lymphotactin both at the cDNA (73.8% identity) and the protein (61.4% identity) levels, and related to mem bers of the C-C and C-X-C chemokine families. Two variants of the ATAC protein were expressed and tested for chemotaxis and Ca2+ release on a variety of target cells. The ATAC gene was located to chromosome 1q2 3.