Evidence for a role of the sarcoplasmic/endoplasmic reticulum Ca2+-ATPase in thapsigargin and Bcl-2 induced changes in Xenopus laevis oocyte maturation
Em. Kobrinsky et Ma. Kirchberger, Evidence for a role of the sarcoplasmic/endoplasmic reticulum Ca2+-ATPase in thapsigargin and Bcl-2 induced changes in Xenopus laevis oocyte maturation, ONCOGENE, 20(8), 2001, pp. 933-941
Thapsigargin (Tg), a selective inhibitor of sarcoplasmic/ endoplasmic retic
ulum Ca2+-ATPase (SERCA), causes depiction of intracellular Ca2+ stores, he
nce activation of capacitative Ca2+ entry (CCE). Incubation of Xenopus laev
is oocytes with Tg resulted in an increased rate of progesterone-induced me
iotic maturation. Non-mitochondrial Ca-45(2+) uptake by SERCA-containing mi
crosomes 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 ce
ll types, resulted in only 40% inhibition of microsomal Ca-45(2+) uptake by
Tg while non-inhibited Ca-45(2+) uptake remained unchanged, Moreover Bcl-2
overexpression also protected against inhibition of CCE. I-Cl(Ca) was simi
lar in Bcl-2-overexpressing and control oocytes when intracellular Ca2+ sto
re 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 Ca2+ entry itself. At the end of a 24-h period after progester
one addition to the medium, only 25% of Bcl-2-overexpressing oocytes had ma
tured compared to 85% of control oocytes. Our data suggest that SERCA parti
cipates in Xenopus oocyte maturation by controlling cytosolic Ca2+ and/or i
ntracellular Ca2+ stores, hence CCE. An observed progesterone-dependent pro
tein kinase-catalysed phosphorylation of SERCA is further indication of its
role in oocyte maturation.