Isoform-specific induction of nuclear free calcium oscillations by platelet-derived growth factor.
Confocal laser scanning microscopy was used to analyze alterations in nuclear free calcium (Ca2+n) levels induced by platelet-derived growth factor (PDGF) isoforms in BALB/c3T3 fibroblasts loaded with the calcium-sensitive fluorescent indicator Fluo-3. Both AA-PDGF and BB-PDGF caused a transient increase in Ca2+n. Analysis of PDGF-induced Ca2+n alterations as a function of time revealed that BB-PDGF stimulation resulted in the generation of Ca2+n oscillations that diminished over time. The frequency of BB-PDGF-stimulated oscillations was modulated by extracellular Ca2+ and could not be mimicked by increasing intracellular inositol 1,4,5-trisphosphate levels in the absence of growth factor stimulation. Caffeine alone had no effect on Ca2+n levels, but exposure of cells to caffeine after BB-PDGF stimulation augmented Ca2+n oscillations, either by increasing the frequency or reinitiating preexisting oscillations. The genesis of these oscillations in Ca2+n appears to be in the region just outside of the nucleus, as perinuclear cytoplasmic free calcium (Ca2+i) increased just prior to Ca2+n. In contrast, AA-PDGF stimulation resulted in the generation of one or two irregular, transient Ca2+n spikes. Caffeine pretreatment followed by AA-PDGF stimulation resulted in Ca2+n oscillations very similar to those produced by BB-PDGF alone. Additionally, the AA-PDGF and BB-PDGF isoforms appeared to modulate distinct pools of cellular Ca2+, as BB-PDGF was still capable of inducing Ca2+n oscillations subsequent to prior induction of oscillations by AA-PDGF/caffeine. These PDGF isoform-specific changes in nuclear free Ca2+ could serve as a mechanism by which isoform-specific cellular signaling pathways may be manifested by the growth factors.
Diliberto
P A
PA
Department of Cell Biology and Anatomy, School of Medicine, University of North Carolina, Chapel Hill 27599.
Krishna
S
S
Kwon
S
S
Herman
B
B
D016475:3T3 Cells; D000818:Animals; D002110:Caffeine / Q000494:pharmacology; D002118:Calcium / Q000378:metabolism*; D002467:Cell Nucleus / Q000378:metabolism; D003593:Cytoplasm / Q000378:metabolism; D015544:Inositol 1,4,5-Trisphosphate / Q000494:pharmacology; D051379:Mice; D010982:Platelet-Derived Growth Factor / Q000737:chemistry / Q000494:pharmacology*
D010982:Platelet-Derived Growth Factor; D002110:Caffeine; D015544:Inositol 1,4,5-Trisphosphate; D002118:Calcium