GLI3 mutations in human disorders mimic Drosophila Cubitus interruptus protein functions and localization

Truncation mutations of the GL13 zinc finger transcription factor can cause Greig cephalopolysyndactyly syndrome (GCPS), Pallister-Hall syndrome (PHS) , and postaxial polydactyly type A (PAP-A). GLI3 is homologous to Drosophil a Cubitus interruptus (Ci), which regulates the patched (ptc), gooseberry ( gsb), and decapentaplegic (dpp) genes. Ci is sequestered in the cytoplasm a nd is subject to posttranslational processing whereby the full-length trans criptional activator form (Ci(155)) can be cleaved to a repressor form (Ci( 75)). Under hedgehog signaling, the Ci(155) form translocates to the nucleu s whereas in the absence of hedgehog, the Ci(75) form translocates to the n ucleus. Based on the correlation of GLI3 truncation mutations and the human phenotypes, He hypothesized that GLI3 shows transcriptional activation or repression activity and subcellular localization similar to Ci. Here we sho w that full-length GLI3 localizes to the cytoplasm and activates PTCH1 expr ession, which is similar to full-length Ci(155), PHS mutant protein (GLI3-P HS) localizes to the nucleus and represses GLI3-activated PTCH1 expression, which is similar to Ci(75). The GCPS mutant protein has no effect on GLI3- activated PTCH1 transcription, consistent with the role of haploinsufficien cy in this disorder. The PAP-A mutant protein (GLD-P;SP-A) showed less spec ific subcellular localization but still inhibited GLI3-activated PTCH1 tran scription, suggesting it may be a weaker allele than the GLI3-PHS mutation. These data show that GL13 mutations in humans mimic functional effects of the Drosophila ci gene and correlate with the distinct effects of these mut ations on human development.