The local expression of bone morphogenetic protein-2 (BMP-2) during pituitary development mediates the commitment of undifferentiated cells to the gonadotroph lineage. In the current study, we have used alphaT3-1 and LbetaT2 cells, which represent different stages of gonadotroph development to examine BMP-2 receptor (BMPR) expression and effects of BMP-2 on cell signalling pathways and cell proliferation. In bone, signal transduction via BMPRs requires heteromeric complexing between Type I (alpha or beta) and Type II Rs with the mode of oligomerisation determining different signalling pathways.
Using subtype and isoform-specific primers and antibodies, we have demonstrated expression of mRNA and protein for BMPR-I alpha and II Rs in both cell lines with Type I beta present only in ?T3-1 cells. Type II mRNA was 2-fold less than Type I alpha although protein levels of each R were similar. Treatment of alphaT3-1 cells with BMP-2 (200 ng/ml) showed a time dependent increase in phospho Akt (part of the PI3 kinase cascade) with a peak at 5 min and a 3-fold increase over unstimulated cells, maintained for up to 30 min. Interestingly, LbetaT2 cells, which represent a later stage of gonadotroph development lacked this pAkt response to BMP-2. Despite reported effects of BMP-2 on proliferation of other cell types and the crucial role of PI3 kinase in cell survival, we observed no significant effects of BMP-2 on proliferation of either gonadotroph cell type.
These studies demonstrate differential expression of isoforms of BMPR mRNA and protein in gonadotroph cells of different developmental origin and differential regulation of the Akt signal transduction pathway. These differences may reflect different functions of BMP-2 during pituitary gonadotroph development.
This study was supported by the BBSRC.
03 - 05 Nov 2003
Society for Endocrinology