Tyrosine phosphorylation of a low molecular weight protein induced by RANTES in T-lymphocytes

The beta-chemokine RANTES, a T-lymphocyte activator, chemoattractant, and i nducer of homotypic aggregation, is considered to exert extensive effects o n T lymphocytes through either G protein-coupled or protein tyrosine kinase (PTK) signaling pathway. In the present study, we analyzed RANTES-induced signal transduction through PTK as an early event in T-lymphocyte activatio n. Tyrosine phosphorylation is detected by immunoblots in the human T-cell line H9 after incubation with human recombinant RANTES. The tyrosine phosph orylation of a protein with a molecular mass of about 25 kD is measurable a s early as 30 s and maximal at 1-5 min; and is a dose-dependent effect. The phosphorylation response can be abrogated by the tyrosine-kinase inhibitor herbimycin A (HA) but is insensitive to heterotrimeric G, protein inhibito r pertussis toxin (Ptx). This phenomenon is also observed in a visible homo typic aggregation response after incubation serum-starved H9 cells with RAN TES. The phosphorylation response can not be down-regulated by preincubatio n with either anti-CC chemokine receptor 5 (CCR5) antibody or HIV-1(Bal) su pernatants. Our results suggest that tyrosine phosphorylation of a protein with molecular mass of about 25 kD via Src-family PTK(s) is an early event in T-lymphocyte activation associated with the homotypic aggregation in res ponse to RANTES. (C) 1999 Elsevier Science B.V. All rights reserved.