Endocrine Abstracts

The proto-oncogene pituitary tumor-transforming gene-binding factor (PBF) is upregulated in multiple tumours including thyroid cancer. PBF overexpression mediates tumorigenic processes such as cell motility and accelerates thyroid cancer cell invasion. We have recently shown that both PBF phosphorylation at tyrosine 174 (Y174) and PBF endocytosis are required for PBF-stimulated thyroid and breast cancer cell migration and invasion. This prompted further investigation into a physiological role for PBF in cell motility. We utilised a novel Pbf knockout (Pbf-/-) mouse model to determine the impact of Pbf deletion on cell motility. Mouse embryonic fibroblasts (MEFs) were isolated at embryonic day 13.5 and used as primary cultures within 3 passages. Pbf-/- MEFs showed a significant reduction in migration compared with wild-type (Pbf+/+) MEFs. Interestingly, the loss of one functional copy of Pbf in heterozygote MEFs (Pbf+/-) resulted in an intermediate decrease in migration suggesting a gene-dosage effect. Immunofluorescent studies of Pbf-/- MEFs identified alterations in focal adhesions (FAs). FAs are structures that link the extracellular matrix with the intracellular actin cytoskeleton, and the turnover of FAs plays a crucial role in cell motility. In Pbf+/+ MEFs focal adhesion kinase (FAK) and paxillin staining highlighted FA structures that were normally elongated and aligned with actin stress fibres. In contrast, Pbf-/- MEFs demonstrated a significant reduction in FAK and paxillin staining with smaller, punctate, and more radially distributed FAs. These studies demonstrate a physiological role for PBF in cell adhesion and migration and further elucidate the mechanism by which PBF induces cell motility in tumour progression.