A potential role of alternative splicing in the regulation of the transcriptional activity of human GLI2 in gonadal tissues.

Mammalian Gli proteins are important transcription factors involved in the regulation of Sonic hedgehog signal transduction pathway. Association of Gli2 with mammalian development and human disease led us to study the structure and expression of the human GLI2. We show that the region encoding GLI2 repressor domain is subject to alternative splicing in the gonadal tissues and different cell lines. Two major alternatively spliced forms of GLI2 mRNA arise from skipping exon 3 (GLI2Delta3) or exons 4 and 5 (GLI2Delta4-5). Both forms contain premature translational stop codons in the GLI2 open reading frame (ORF) starting from exon 2. Translation of GLI2Delta3 and GLI2Delta4-5 in vitro, initiated from downstream AUG codons, produced N-terminally truncated proteins. In Gli-dependent transactivation assay, expression of GLI2Delta3 induced activation of the reporter gene similar to that of the full-length construct (GLI2fl) containing complete ORF. However, expression of the GLI2Delta4-5 resulted in about 10-fold increase in activation, suggesting that deletion of the major part of repressor domain was responsible for the enhanced activation of GLI2 protein. Our data suggest that in addition to proteolytic processing, alternative splicing may be another important regulatory mechanism for the modulation of repressor and activator properties of GLI2 protein.