p62 dok Negatively Regulates CD2 Signaling in Jurkat Cells

Abstract

p62dok belongs to a newly identified family of adaptor proteins. In T cells, the two members that are predominantly expressed, p56dok and p62dok, are tyrosine phosphorylated upon CD2 or CD28 stimulation, but not upon CD3 ligation. Little is known about the biological role of Dok proteins in T cells. In this study, to evaluate the importance of p62dok in T cell function, we generated Jurkat clones overexpressing p62dok. Our results demonstrate that overexpression of p62dok in Jurkat cells has a dramatic negative effect on CD2-mediated signaling. The p62dok-mediated inhibition affects several biochemical events initiated by CD2 ligation, such as the increase of intracellular Ca2+, phospholipase Cγ1 activation, and extracellular signal-regulated kinase 1/2 activation. Importantly, these cellular events are not affected in the signaling cascade induced by engagement of the CD3/TCR complex. However, both CD3- and CD2-induced NF-AT activation and IL-2 secretion are impaired in p62dok-overexpressing cells. In addition, we show that CD2 but not CD3 stimulation induces p62dok and Ras GTPase-activating protein recruitment to the plasma membrane. These results suggest that p62dok plays a negative role at multiple steps in the CD2 signaling pathway. We propose that p62dok may represent an important negative regulator in the modulation of the response mediated by the TCR.