ENHANCEMENT OF HIV-1-INDUCED SYNCYTIUM FORMATION IN T-CELLS BY THE TYROSYL KINASE P56(LCK)

The CD4 glycoprotein is the primary cellular receptor for human immuno deficiency virus type 1 (HIV-1) and has also been reported to be physi cally associated with p56(lck), a tyrosyl protein kinase. p56(lck) is a member of the src family of nonreceptor protein-tyrosine kinases and is expressed predominantly in T lymphocytes. Our objective was to stu dy the effect of p56(lck) on the biology of HIV-1. For this purpose, w e have stably transfected two human p56(lck)-negative T cell lines (C8 166-45 and MT-2) with plasmids encoding for this cellular protein. Fol lowing coculture with HIV-1-infected cells or infection with cell-free virus, p56(lck)-expressing cell lines showed a greater propensity for virus-mediated syncytium formation than parental p56(lck)-negative ce lls. The enhancement of HIV-1-induced syncytium formation was not asso ciated with the kinase activity of p56(lck), as demonstrated by experi ments using a kinase-deficient mutant. However, the physical interacti on between CD4 and p56(lck) was shown to be necessary to obtain the en hancement of syncytium formation since a mutated version of p56(lck), which is deficient in its capacity to associate with CD4, did not lead to an increase in virus-mediated cell-to-cell fusion events. Finally, we determined that cells transfected with wild-type and kinase-negati ve mutant p56(lck) showed a reduced rate of CD4 endocytosis compared t o parental p56(lck)-negative cells. Together, these results suggest th at p56(lck) can be seen as an accessory molecule facilitating HIV-1-me diated syncytium formation in T cells by a mechanism involving the sta bilization of the CD4 molecule at the cell surface. (C) 1997 Academic Press.