Prostaglandins differently regulate FGF-2 and FGF receptor expression and induce nuclear translocation in osteoblasts via MAPK kinase

Abstract

We have previously reported that prostaglandin F_2α (PGF_2α) and its selective agonist fluprostenol increase basic fibroblast growth factor (FGF-2) mRNA and protein production in osteoblastic Py1a cells. The present report extends our previous studies by showing that Py1a cells express FGF receptor-2 (FGFR2) and that treatment with PGF_2α or fluprostenol decreases FGFR2 mRNA. We have used confocal and electron microscopy to show that, under PGF_2α stimulation, FGF-2 and FGFR2 proteins accumulate near the nuclear envelope and colocalize in the nucleus of Py1a cells. Pre-treatment with cycloheximide blocks nuclear labelling for FGF-2 in response to PGF_2α. Treatment with SU5402 does not block prostaglandin-mediated nuclear internalization of FGF-2 or FGFR2. Various effectors have been used to investigate the signal transduction pathway. In particular, pre-treatment with phorbol 12-myristate 13-acetate (PMA) prevents the nuclear accumulation of FGF-2 and FGFR2 in response to PGF_2α. Similar results are obtained by pre-treatment with the protein kinase C (PKC) inhibitor H-7. In addition, cells treated with PGF_2α exhibit increased nuclear labelling for the mitogen-activated protein kinase (MAPK), p44/ERK2. Pre-treatment with PMA blocks prostaglandin-induced ERK2 nuclear labelling, as confirmed by Western blot analysis. We conclude that PGF_2α stimulates nuclear translocation of FGF-2 and FGFR2 by a PKC-dependent pathway; we also suggest an involvement of MAPK/ERK2 in this process.