GSE135118
CD28 regulation of global alternative splicing changes in activated human CD4+ T cells
Alternative splicing consists of exons that are selectively either included or excluded from the mature mRNA transcript. Previous studies have demonstrated that ~10-15% of alternatively spliced genes undergo signal-induced changes in isoform abundance in activated primary human CD4+ T cells. In the past, signal-induced alternative splicing changes in T cells have been characterized in the context of CD3 and CD28 activation. CD3 is a component of the T Cell Receptor (TCR) which is responsible for recognizing foreign peptides presented on antigen presenting cells. CD28 enhances various signaling events downstream of the TCR to boost the survival of T cells and is required for full T cell stimulation.  The contribution of CD28 signaling to transcriptional changes has been well documented, but the impact on splicing has not been investigated. Here we test the hypothesis that CD28 exerts some of its functional impact through the enhancement of splicing changes in stimulated T cells. We utilized poly(A) RNA-seq and the MAJIQ alternative splicing algorithm to analyze splicing events of human CD4+ T cells stimulated with through CD3 in the presence and absence of co-stimulation with CD28. Consistent with previous studies, we identified approximately 400 and 1,000 significant splicing events induced by CD3/CD28 stimulation at 8 and 48 hours of culture, respectively. Alternative splicing changes induced by CD3 and CD3/CD28 stimuli are highly correlative, however, approximately 23% of alternative splicing changes are further enhanced with additional CD28 costimulation at 8 hours of culture.  This enhancement drops to 8% of alternative splicing events by 48 hours. Therefore, we conclude that CD28 costimulation increases the magnitude of splicing during T cell activation, in a manner that is eventually compensated for over time with CD3 stimulation alone. Overall design: From 2 female and 1 male donors, naïve CD4+ T cells were isolated with magnetic beads, then stimulated with aCD3, aCD28, or both for 0, 8 or 48 hours