Serine-Arginine-rich Protein p30 Directs Alternative Splicing of Glucocorticoid Receptor Pre-mRNA to Glucocorticoid Receptor β in Neutrophils *

Glucocorticoid (GC) insensitivity is a major clinical challenge in the treatment of many inflammatory diseases. It has been shown previously that GC insensitivity, in several inflammatory cell types, is due to an overabundance of the β isoform of the glucocorticoid receptor (GCRβ) relative to the ligand binding isoform, GCRα. GCRβ functions as a dominant inhibitor of GCRα action. A number of GCR isoforms are created from the same pre-mRNA transcript via alternative splicing, and the factor or factors that control alternative splicing of GCR pre-mRNA are of great importance. In the current study, we have identified the predominant alternative splicing factor present in human neutrophils, which is known to be exceptionally GC-insensitive. The predominant alternative splicing factor in neutrophils is SRp30c, which is one of several highly conserved serine-arginine-rich (SR) proteins that are involved in both constitutive and alternative splicing in eukaryotic cells. Inhibition of SRp30c expression with antisense oligonucleotide strongly inhibited expression of GCRβ and stimulated expression of GCRα. Antisense molecules targeted to other SR proteins had no effect. Our data indicate that SRp30c is necessary for alternative splicing of the GCR pre-mRNA to create mRNA encoding GCRβ.