Tyrosine kinase-dependent ubiquitination of CD16 zeta subunit in human NK cells following receptor engagement

We investigated whether aggregation of the low-affinity immunoglobulin G re ceptor (CD16) on human NK cells results in receptor ubiquitination. We foun d that the CD16 zeta subunit becomes ubiquitinated in response to receptor engagement. We then investigated whether protein tyrosine kinase (PTK) acti vation is required for CD16-mediated receptor ubiquitination. Pretreatment with the PTK inhibitor genistein substantially decreased ligand-induced zet a ubiquitination, suggesting a requirement for PTK activation in receptor u biquitination. We further analyzed PTK involvement in controlling receptor ubiquitination by using the vaccinia virus expression system. Overexpressio n of wild-type active lck, but not a kinase-deficient mutant, enhanced both ligand-induced tyrosine phosphorylation and ubiquitination of the CD16 zet a subunit. Taken together, our data demonstrate that CD16 engagement induce s zeta chain ubiquitination and strongly suggest a role for lck in regulati ng this modification.