Evidence for a role of the sarcoplasmic/endoplasmic reticulum Ca(2+)-ATPase in thapsigargin and Bcl-2 induced changes in Xenopus laevis oocyte maturation.
Thapsigargin (Tg), a selective inhibitor of sarcoplasmic/endoplasmic reticulum Ca(2+)-ATPase (SERCA), causes depletion of intracellular Ca(2+) stores, hence activation of capacitative Ca(2+) entry (CCE). Incubation of Xenopus laevis oocytes with Tg resulted in an increased rate of progesterone-induced meiotic maturation. Non-mitochondrial (45)Ca(2+) uptake by SERCA-containing microsomes prepared from control wild-type oocytes microinjected with sterile water was inhibited essentially 100% by Tg. However, overexpression of Bcl-2, an oncogene known to protect against Tg-induced apoptosis in certain cell types, resulted in only 40% inhibition of microsomal (45)Ca(2+) uptake by Tg while non-inhibited (45)Ca(2+) uptake remained unchanged. Moreover Bcl-2 overexpression also protected against inhibition of CCE. I(Cl(Ca)) was similar in Bcl-2-overexpressing and control oocytes when intracellular Ca(2+) store depletion was induced by microinjection of inositol 1,4,5-trisphosphate (InsP(3)) and other means and when CCE was induced by means independent of SERCA inhibition. Our data indicate that Bcl-2 affects neither the InsP(3) receptor nor Ca(2+) entry itself. At the end of a 24-h period after progesterone addition to the medium, only 25% of Bcl-2-overexpressing oocytes had matured compared to 85% of control oocytes. Our data suggest that SERCA participates in Xenopus oocyte maturation by controlling cytosolic Ca(2+) and/or intracellular Ca(2+) stores, hence CCE. An observed progesterone-dependent protein kinase-catalysed phosphorylation of SERCA is further indication of its role in oocyte maturation.
Kobrinsky
E M
EM
Department of Physiology and Biophysics, The Mount Sinai School of Medicine of New York University, New York, NY 10029, USA.
Kirchberger
M A
MA
D000109:Acetylcholine; D000818:Animals; D001692:Biological Transport; D002118:Calcium / Q000378:metabolism*; D015220:Calcium Channels; D000252:Calcium-Transporting ATPases / Q000378:metabolism*; D002712:Chlorides / Q000378:metabolism; D004553:Electric Conductivity; D005260:Female; D053496:Inositol 1,4,5-Trisphosphate Receptors; D008861:Microsomes / Q000378:metabolism; D009866:Oogenesis / Q000187:drug effects / Q000502:physiology*; D010766:Phosphorylation; D011374:Progesterone / Q000494:pharmacology; D019253:Proto-Oncogene Proteins c-bcl-2 / Q000378:metabolism*; D018160:Receptors, Cytoplasmic and Nuclear; D012519:Sarcoplasmic Reticulum / Q000201:enzymology*; D053498:Sarcoplasmic Reticulum Calcium-Transporting ATPases; D013347:Subcellular Fractions / Q000378:metabolism; D019284:Thapsigargin / Q000494:pharmacology*; D014982:Xenopus laevis
D015220:Calcium Channels; D002712:Chlorides; D053496:Inositol 1,4,5-Trisphosphate Receptors; D019253:Proto-Oncogene Proteins c-bcl-2; D018160:Receptors, Cytoplasmic and Nuclear; D011374:Progesterone; D019284:Thapsigargin; D053498:Sarcoplasmic Reticulum Calcium-Transporting ATPases; D000252:Calcium-Transporting ATPases; D000109:Acetylcholine; D002118:Calcium