| Abstrakt: |
Prostaglandin F2α(PGF2α) receptors are G-protein-coupled receptors consisting of two alternative mRNA splice variants, named FPAand FPB. As compared with the FPAisoform, the FPBisoform lacks the last 46 amino acids of the carboxyl terminus and, therefore, represents a truncated version of the FPA. We recently found (Pierce, K. L., Fujino, H., Srinivasan, D., and Regan, J. W. (1999)J. Biol. Chem.274, 35944–35949) that stimulation of both isoforms with PGF2αleads to activation of a Rho signaling pathway, resulting in tyrosine phosphorylation of p125 focal adhesion kinase, formation of actin stress fibers, and cell rounding. Although the activation of Rho and subsequent cell rounding occur at a similar rate for both isoforms, we now report that following the removal of PGF2αthe reversal of cell rounding is much slower for cells expressing the FPBisoform as compared with the FPAisoform. Thus, in HEK-293 cells that stably express the FPAisoform, the reversal of cell rounding appears to be complete after 1 h, whereas for FPB-expressing cells there is essentially no reversal even after 2 h. Similarly, the disappearance of stress fibers and dephosphorylation of p125 focal adhesion kinase following removal of agonist are much slower in FPB-expressing cells than in FPA-expressing cells. The mechanism of this differential reversal appears to involve a difference in receptor resensitization following the removal of agonist. Based upon whole cell radioligand binding, agonist-induced stimulation of inositol phosphate formation, and mobilization of intracellular Ca2+, the FPBisoform resensitizes more slowly than the FPAisoform. These findings suggest that the carboxyl terminus of the FPAis critical for resensitization and that the slower resensitization of the FPBisoform leads to prolonged signaling. This differential signaling distinguishes the FPAand FPBreceptor isoforms and could be important toward understanding the physiological actions of PGF2α. |
