PLATELET-DERIVED GROWTH-FACTOR (PDGF)-INDUCED CA2-LINE AND IN TRANSFORMED OLIGODENDROCYTES EXPRESSING THE BETA-PDGF RECEPTOR( SIGNALING IN THE CG4 OLIGODENDROGLIAL CELL)

Ca2+ signaling induced by platelet-derived growth factor (PDGF) was in vestigated in the oligodendroglial cell lines CG4 and CEINGE clone 3, using fura-2 microfluorimetry and video imaging. CEINGE cia cells, imm ortalized with polyoma middle T antigen, were found to uniformly expre ss the polyoma middle T antigen protein as well as 2',3'-cyclic nucleo tide 3'-phosphodiesterase, a specific marker for oligodendroglia. PDGF -BB induced both oscillatory and non-oscillatory Ca2+ responses in CEI NGE c13 cells as well as in CG4 cells, grown either as O-2A progenitor s or differentiated oligodendrocytes However, in CG4 cells the percent age of oscillatory Ca2+ responses was higher than that observed in CEI NGE c13 cells. In contrast, oscillatory Ca2+ responses were not observ ed in PC-12 cells transfected with beta-PDGF receptor (PDGFR) or in NI H 3T3 fibroblasts, CG4 cells expressed only the alpha-PDGFR, whereas C EINGE c13 cells expressed both alpha and beta isoforms. When CEINGE c1 3 cells were exposed to PDGF-AA, which binds only to the alpha-PDGFR, the percentage of oscillatory Ca2+ responses was higher than that obse rved after PDGF-BB stimulation We previously reported that block of th e enzyme sphingosine kinase, and a consequent increase in intracellula r sphingosine levels in CEINGE c13 cells caused an increase in the per centage of oscillatory Ca2+ responses induced by PDGF-BB. However, in CG4 cells block of sphingosine kinase did not increase the oscillatory Ca2+ response elicted by PDGF-BB, although the addition of exogenous sphinogosine induced an oscillatory Ca2+ response in 77% of cells stud ied. We hypothesize that the alpha-PDGFR is less effective than the be ta-PDGFR in stimulating the activity of sphinogosine kinase. The resul ts also suggest that alpha- and beta-PDGFRs may differently regulate s phingolipid metabolism.