PATHWAY OF SIGNAL DELIVERY TO MURINE THYMOCYTES TRIGGERED BY CO-CROSS-LINKING CD3 AND THY-1 FOR CELLULAR DNA FRAGMENTATION AND GROWTH-INHIBITION

The signal delivery pathway triggered by crosslinking CD3 and Thy-1 to gether (CD3/Thy-1 crosslinkage) on murine thymocytes for cellular DNA fragmentation/growth inhibition was analyzed. The treatment of thymocy tes with herbimycin A as a specific tyrosine kinase inhibitor under su boptimum conditions before the CD3/Thy-1 crosslinkage partially but pr eferentially inhibited the otherwise promoted tyrosine phosphorylation of p40 and p56. Evidence was then provided that acceleration of the k inase activity of p56lck was involved in the CD3/Thy-1 crosslinkage-tr iggered signal. Partial characterization of p40 distinguished it from the p43 and p41 MAP kinases, the tyrosine phosphorylation of which was only marginally accelerated. Promotion of DNA fragmentation by the CD 3/Thy-1 crosslinkage-triggered signal was actually ablated by the trea tment with herbimycin, suggesting the obligatory involvement of the he rbimycin highly sensitive kinase activity in the signal pathway. The s ignal induced by co-crosslinkage of CD3 and Thy-1 was also shown to be negatively biased against mature T lymphocytes, suppressing their CD3 -mediated growth response. The negative signal was then found to parti ally attack the process of c-fos transcription as an earlier nuclear e vent. Interestingly, this c-fos suppression was prevented by the treat ment of thymocytes with herbimycin before stimulation, for accelerated expression of c-fos. It is suggested from these results that the CD3/ Thy-1 crosslinkage delivers protein tyrosine kinase-dependent negative signaling for inhibition of early and late nuclear events of both imm ature thymocytes and mature T lymphocytes.