Inhibition of ciliogenesis promotes Hedgehog signaling, tumorigenesis, and metastasis in breast cancer

Primary cilia are chemosensors that play a dual role to either activate or repress Hedgehog signaling, depending on presence or absence of ligand, respectively. While inhibition of ciliogenesis has been shown to be characteristic of breast cancers, the functional consequence is unknown. Here, for the first time, inhibition of ciliogenesis led to earlier tumor formation, faster tumor growth rate, higher grade tumor formation, and increased metastasis in the polyoma middle T (PyMT) mouse model of breast cancer. In in vitro model systems, inhibition of ciliogenesis resulted in increased expression of Hedgehog-target genes through a mechanism involving loss of the repressor form of the GLI transcription factor (GLIR) and activation of Hedgehog target gene expression through cross-talk with TGF-alpha (TGFA) signaling. Bioinformatics analysis revealed that increased Hedgehog signaling is frequently associated with increased TGFA signaling in patients with triple-negative breast cancers (TNBC), a particularly aggressive breast cancer subtype. These results identify a previously unrecognized role for inhibition of ciliogenesis in breast cancer progression. This study identifies inhibition of ciliogenesis as an important event for activation of Hedgehog signaling and progression of breast cancer to a more aggressive, metastatic disease.