REGULATION OF THE FIBROBLAST GROWTH-FACTOR RECEPTOR-3 PROMOTER AND INTRON-I ENHANCER BY SP1 FAMILY TRANSCRIPTION FACTORS

Fibroblast growth factor receptor 3 (FGFR3) has a complex spatial and temporal pattern of expression and is essential for the normal develop ment of a diverse set of tissues. Recently, mutations have been identi fied in FGFR3 that result in constitutive tyrosine kinase activity and cause a number of different human skeletal disorders. To examine the regulatory mechanisms governing FGFR3 expression, the promoter for the FGFR3 gene was identified and characterized. It resides in a CpG isla nd, which encompasses the 5' end of the FGFR3 gene and lacks classical cis-regulatory motifs. As little as 100 base pairs of sequence 5' to the initiation site can confer a 20-40-fold increase in transcriptiona l activity upon a promoter-less vector. The transcriptional activity o f these cia-regulatory sequences is further stimulated by elements fou nd within the first intron. Mapping of the enhancer activity found wit hin intron I identified two purine-rich sequence moths between +340 an d +395. Electrophoretic mobility shift assays demonstrated that sequen ces within this region bind members of the Spl family of transcription factors. In a background lacking Spl-like activity, we demonstrate th at Spl can enhance transcription of the minimal promoter (which contai ns five classical Spl sites), whereas both Spl and Sp3 can enhance tra nscription through the elements found in intron I. Although these tran scription factors are ubiquitously expressed, we demonstrate that the sequences between -220 and +609 of the FGFR3 gene are sufficient to pr omote the tissue-specific expression of a reporter gene in transgenic mice.