CD2-MEDIATED ACTIVATION OF THE TEC-FAMILY TYROSINE KINASE ITK IS CONTROLLED BY PROLINE-RICH STRETCH-4 OF THE CD2 CYTOPLASMIC TAIL

Ligation of the CD2 co-stimulatory receptor on human T lymphocytes ind uces tyrosine phosphorylation and activation of the Tee-family tyrosin e kinase, ITK, To examine whether any of several proline-rich (PR) str etches of the CD2 cytoplasmic tail are necessary for ITK activation we introduced wild-type and mutated versions of rat CD2, each missing at least one PR stretch of the tail, into human Jurkat T leukemia cells, The influence of cytoplasmic tail mutations was then studied followin g stimulation of transfectants with the rat CD2 mAb pair, OX54/OX55, A s predicted, wild-type rat CD2 was able to activate ITK in Jurkat cell s. In addition, a truncation mutant, lacking the most membrane-distal PR stretch, PR6, was able to activate ITK. By contrast, all other stud ied truncation mutants, each of which is missing at least PR4-PR6, wer e unable to induce ITK activation. Of deletion mutants, deletion of th e membrane-proximal PR stretches, PR1-PR3, did not impair rat CDP-medi ated ITK activation. However, additional deletion of PR4 from a tail m issing PR1 and PR2, deletion of PR2 and PR4, and deletion of PR4 alone from rat CD2 abrogated an ability to activate ITK, Thus, these result s identify PR4 as an element of the CD2 tail that is required for acti vation of ITK, Furthermore, we show that, unlike wild-type rat CD2, PR 4-deleted rat CD2 is unable to induce IL-2 secretion from Jurkat cells . This is consistent with the view that PR4-mediated activation of ITK is important for downstream signaling events induced by CD2 co-stimul ation.