Characteristic overexpression of the forkhead box transcription factor Foxf1 in Patched-associated tumors

Patients with nevoid basal cell carcinoma syndrome carry germline mutations in the tumor suppressor gene Patched 1 (PTCH1) and are predisposed to develop basal cell carcinoma (BCC), medulloblastoma (MB), and rhabdomyosarcoma (RMS). These tumors are also present in the murine model for Ptch1 deficiency, the Ptch1neo67/+ mouse. Previous studies, including those from our laboratory, have shown that the forkhead box transcription factor Foxf1 is highly expressed in RMS of human and murine origin. We report on a more common role of Foxf1 in Ptch1-associated tumorigenesis, since we found a striking up-regulation of Foxf1 expression in Ptch1-associated BCC and MB compared with the respective non-neoplastic tissue. This overexpression was accompanied by increased levels of the Hedgehog target gene Gli1 as well as the putative Foxf1 targets Bmi1 and Notch2 in these tumors. We also describe a striking Foxf1 activation in Ptch1 null embryos. In contrast, basal expression levels of Foxf1, Gli1, Bmi1 and Notch2 were detected in a variety of adult mouse tissues, such as liver, kidney, spleen, lung, heart and brain. In conclusion, our study suggests that Foxf1 expression is characteristically up-regulated in tumors with a constitutively activated Hedgehog signaling pathway thereby defining a key role for Foxf1 in Hedgehog-associated tumorigenesis.