Regulation of alternative pre-mRNA splicing by the ERK MAP-kinase pathway

Differential gene expression through alternative pre-mRNA splicing is cruci al to various physiological and pathological conditions. Upon activation of B and T lymphocytes during an immune response, variant isoforms of the cel l surface molecule CD44 are generated by alternative pre-mRNA splicing. We show here that in primary mouse T cells as well as in the murine LB-17 T-ce ll line upregulation of variant CD44 mRNA species upon T-cell activation re quires activation of the MEK-ERK pathway. By employing mutant signaling mol ecules and a novel luciferase-based splice reporter system we demonstrate t hat the Ras-Raf-MEK-ERK signaling cascade, but not the p38 MAP-kinase pathw ay, activates a mechanism that retains variant CD44 exon v5 sequence in mat ure mRNA. The findings demonstrate that a highly conserved pleiotropic sign aling pathway links extracellular cues to splice regulation, providing an a venue for tissue-specific, developmental or pathology-associated splicing d ecisions.