A model system for activation-induced alternative splicing of CD45 Pre-mRNA in T cells implicates protein kinase C and Ras

Multiple isoforms of the protein tyrosine phosphatase CD45 are expressed on the surface of human T cells. Interestingly, the expression of these isofo rms has been shown to vary significantly upon T-cell activation. In this re port, we describe a novel cell line-based model system in which we can mimi c the activation-induced alternative splicing of CD45 observed in primary T cells. Of the many proximal signaling events induced by T-cell stimulation , we show that activation of protein kinase C and activation of Ras are imp ortant for the switch toward the exclusion of CD45 variable exons, whereas events related to Ca2+ flux are not. In addition, the ability of cyclohexim ide to block the activation-induced alternative splicing of CD45 suggests a requirement for de novo protein synthesis. We further demonstrate that seq uences which have previously been implicated in the tissue-specific regulat ion of CD45 variable exons are likewise necessary and sufficient for activa tion-induced splicing. These results provide an initial understanding of th e requirements for CD45 alternative splicing upon T-cell activation, and th ey confirm the importance of this novel cell line in facilitating a more de tailed analysis of the activation-induced regulation of CD45 than has been previously possible.