Calcium/Calmodulin and Calmodulin Kinase II
Stimulate Hyperactivation in Demembranated
Bovine Sperm. The polo-like kinase Plx1 prevents
premature inactivation of the APC(Fizzy)-dependent
pathway in the early Xenopus cell cycle. IGF-1 protects cardiac myocytes from hyperosmotic stress-induced apoptosis via CREB.
Ignotz GG, Suarez SS.
Department of Biomedical Sciences,
Hyperactivated motility is observed among sperm
in the mammalian oviduct near the time of ovulation. It is characterized by
high-amplitude, asymmetrical flagellar beating
and assists sperm in penetrating the cumulus oophorus
and zona pellucida.
Elevated intracellular Ca(2+) is required for the
initiation of hyperactivated motility, suggesting
that calmodulin (CALM) and Ca(2+)/CALM-stimulated
pathways are involved. A demembranated sperm
model was used to investigate the role of CALM in promoting hyperactivation. Ejaculated bovine sperm were demembranated and immobilized by brief exposure to
Triton X-100. Motility was restored by addition of reactivation medium
containing MgATP and Ca(2+),
and hyperactivation was observed as free Ca(2+)
was increased from 50 nM to 1 muM.
However, when 2.5 mM Ca(2+)
was added to the demembranation medium to extract
flagellar CALM, motility was not reactivated
unless exogenous CALM was readded. The inclusion
of anti-CALM IgG in the reactivation medium
reduced the proportion hyperactivated in 1 muM Ca(2+) to 5%. Neither
control IgG, the CALM antagonist W-7, nor a
peptide directed against the CALM-binding domain of myosin light chain kinase (MYLK2) inhibited hyperactivation.
However, when sperm were reactivated in the presence of CALM kinase II (CAMK2) inhibiting peptides, hyperactivation was reduced by 75%. Furthermore,
an inhibitor of CAMK2, KN-93, inhibited hyperactivation
without impairing normal motility of intact sperm. CALM and CAMK2
were immunolocalized to the acrosomal
region and flagellum. These results indicate that hyperactivation
is stimulated by a Ca(2+)/CALM pathway involving
CAMK2.
PMID: 15878888 [PubMed - in process
Brassac
T, Castro A, Lorca
T, Le Peuch C, Doree
M, Labbe
JC, Galas S.
Centre de Recherches de Biochimie Macromoleculaire,
CNRS UPR 1086,
Members of the polo-like family of protein kinases
have been involved in the control of APC (anaphase-promoting complex)
during the cell cycle, yet how they activate APC is not understood in any
detail. In Xenopus oocytes,
Ca2+-dependent degradation of cyclin B associated
with release from arrest at second meiotic metaphase was demonstrated to
require the polo-like kinase Plx1. The aim of the
present study was to examine, beyond Ca2+-dependent resumption of meiosis,
the possible role of Plx1 in the control of cyclin
degradation during the early mitotic cell cycle. Plx1 was found to be
dispensable for MPF to turn on the cyclin
degradation machinery. However, it is required to prevent premature
inactivation of the APC-dependent proteolytic
pathway. Microcystin suppresses the requirement
for Plx1 in both Ca2+-dependent exit from meiosis, associated with
degradation of both cyclin B and A downstream of
CaMK2 activation, and prevention of premature APC(Fizzy)
inactivation in the early mitotic cell cycle. These results are consistent
with the view that Plx1 antagonizes an unidentified microcystin-sensitive
phosphatase that inactivates APC(Fizzy).
Maldonado C,
Cea
P, Adasme
T, Collao
A, Diaz-Araya G,
Chiong
M, Lavandero
S.
Departamento de Bioquimica
y Biologia Molecular, Facultad
de Ciencias Quimicas y Farmaceuticas, Universidad de Chile, Santiago, Chile;
Centro FONDAP Estudios Moleculares
de la Celula, Universidad de Chile, Santiago,
Chile.
Hyperosmotic stress stimulates a rapid and
pronounced apoptosis in cardiac myocytes which is
attenuated by insulin-like growth factor-1 (IGF-1). Because in these cells
IGF-1 induces intracellular Ca(2+) increase, we
assessed whether the cyclic AMP response element-binding protein (CREB) is
activated by IGF-1 through Ca(2+)-dependent signalling
pathways. In cultured cardiac myocytes, IGF-1
induced phosphorylation (6.5+/-1.0-fold at 5min),
nuclear translocation (30min post-stimulus) and DNA binding activity of
CREB. IGF-1-induced CREB phosphorylation was
mediated by MEK1/ERK, PI3-K, p38-MAPK, as well as Ca(2+)/calmodulin kinase and calcineurin. Exposure of cardiac myocytes
to hyperosmotic stress (sorbitol
600mOsm) decreased IGF-1-induced CREB activation Moreover,
overexpression of a dominant negative CREB
abolished the anti-apoptotic effects of IGF-1. Our results suggest that
IGF-1 activates CREB through a complex signalling
pathway, and this transcription factor plays an important role in the
anti-apoptotic action of IGF-1 in cultured cardiac myocytes.
PMID: 16168389 [PubMed - as supplied by publisher]
