Nuclear localization of GLI1 and elevated expression of FOXC2 in breast cancer is associated with the basal-like phenotype

Aberrant sonic hedgehog (SHH)/glioma-associated oncogene (GLI) signaling has been shown in the development of many tumors. The aims of the present study are to determine the expression of two SHH signaling molecules, the glioma-associated oncogene homolog 1 (GLI1) and forkhead box C2 (FOXC2), in invasive breast cancers (IBC), to evaluate their association with clinicopathological parameters, and to determine their prognostic significance in breast cancer patients. Expression of GLI1 and FOXC2 were assessed by immunohistochemical analysis of a tissue microarray containing 262 unselected IBC cases. A statistical analysis was performed to assess the correlation of GLI1 and FOXC2 expression with the patients' clinicopathological parameters, postoperative survival rate, and molecular subtypes. Immunoreactivity of GLI1 and FOXC2 was observed in 84% and 75% of all breast cancer tissues, respectively. There was a significant correlation between nuclear FOXC2 and GLI1 expressions in these breast cancers, which was associated with estrogen receptor (ER) negativity. Furthermore, there was a significant association between nuclear expression of GLI1 and FOXC2 and a basal-like breast cancer phenotype. Patients with nuclear GLI1 or FOXC2-expressing tumors had a significantly shorter survival time than those without nuclear FOXC2 or GLI1 expression. Multivariate analysis showed that nuclear GLI1 or FOXC2 expression was an independent factor for predicting the prognosis of basal-like breast cancer. In conclusion, there was a significant correlation between expression of nuclear GLI1 or FOXC2 and human breast cancer. More specifically, elevated levels of these proteins were associated with the basal-like breast cancer phenotype and with a poor rate of disease-free survival. These data suggest that GLI1 and FOXC2 are involved in tumorigenesis and that they may be useful as diagnostic and therapeutic targets for human basal-like breast cancers. Additional studies are warranted to better understand the biological significance of GLI1 and FOXC2, to further refine statistics related to patient prognosis, and to optimize treatment of patients with basal-like breast cancer.