ABSTRACT
Uncontrolled hedgehog (HH)/glioma-associated oncogene (GLI) and WNT/ß-catenin signaling are important events in the genesis of many cancers including skin cancer and are often implicated in tumor progression, invasion, and metastasis. However, because of the complexity and context dependency of both pathways, little is known about HH and WNT interactions in human carcinogenesis. In the current study, we provide evidence of HH/glioma-associated oncogene family zinc finger 2 (GLI2)-WNT/ß-catenin signaling crosstalk in human keratinocytes. Overexpression of GLI2ΔN in human keratinocytes resulted in cytoplasmic accumulation and nuclear relocalization of ß-catenin in vitro and in 3D organotypic cultures, accompanied by upregulation of WNT genes. Induction of GLI2ΔN enhanced the ß-catenin-dependent transcriptional activation and the subsequent activation of ß-catenin target genes including cyclin-D1. Additionally, GLI2 overexpression was associated with decreased E-cadherin protein levels; increased expression of SNAIL, matrix metalloproteinase 2, and integrin ß1; and increased cell invasion in 3D organotypic cultures. Invasion was reduced by WNT inhibition, thus unveiling the direct role of GLI2/WNT crosstalk in cell invasion. We show that GLI2 overexpression supported long-term epidermal regeneration in 3D organotypic cultures, and resulted in the manifestation of an undifferentiated basal/stem cell-associated phenotype in human keratinocytes. Both these observations are consistent with the role of ß-catenin and SNAIL in epidermal stem cell maintenance. This work suggests that GLI2 is a regulator of ß-catenin and provides insights into its role in tumorigenesis.
