Endometrium
Erythropoieses
Leukemia
mTOR/RICTOR is the Ser473 kinase
for Akt/PKB in 3T3-L1 adipocytes. Lycopene induces apoptosis in immortalized fibroblasts
exposed to tobacco smoke condensate through arresting cell cycle and
down-regulating cyclin D1, pAKT
and pBad. conclude
mTOR complexed to
RICTOR is the Ser473 kinase in 3T3-L1 adipocytes. Ovarian follicle development is dependent
on growth factors that stimulate cell proliferation and act as survival
factors to prevent apoptosis of follicle cells. We examined the mechanism
of the protective effect of IGF-I against Fas ligand (FasL)-induced
apoptosis of granulosa cells and its relationship
to cell proliferation. IGF-I activated both the phosphoinositide
3'-OH kinase (PI3K) and the mitogen-activated
protein kinase (MAPK) pathways. Experiments using
specific inhibitors of these pathways showed that protection by IGF-I was
mediated by the PI3K pathway and not the MAPK pathway. Recombinant
adenoviruses were used to test whether the downstream target of PI3K
activation, Akt kinase,
was required for protection against apoptosis. Expression of dominant
negative Akt (dnAkt)
prevented protection by IGF-I while expression of constitutively active Akt (myrAkt) mimicked the
effect of IGF-I. Treatment with IGF-I, or expression of myrAkt,
increased progression from G0/G1 to S phase of the cell cycle while
expression of dnAkt inhibited G0/G1 to S phase
progression and prevented the stimulatory effect of IGF-I. We tested
whether cell cycle progression was required for protection from apoptosis
using the cyclin dependent kinase-2 inhibitor roscovitine, which blocks cells at the G1/S transition.
Roscovitine prevented the protective effect of
IGF-I and myrAkt expression against apoptosis.
Therefore, activation of Akt is not sufficient to
protect granulosa cells from apoptosis in the
absence of cell cycle progression. In summary, IGF-I protects granulosa cells from apoptosis by activation of the
PI3K/Akt pathway. This protective effect can only occur when progression
from G1 to S phase of the cell cycle regulated by the PI3K/Akt pathway is
unperturbed
Hresko
RC, Mueckler
M.
Department of Cell Biology and Physiology, Washington University, School of
Medicine, St. Louis, MO 63110-1093.
The insulin-signaling pathway leading to the activation of Akt/PKB has been well-characterized except for a single
step, the phosphorylation of Akt
at Ser473. Double-stranded DNA-dependent protein kinase (DNA-PK). ataxia
telangiectasia mutated (ATM) gene product, Integrin-linked kinase (ILK),
Protein Kinase Ca (PKCa), and mammalian target of
Rapamycin (mTOR) when complexed to rapamycin
insensitive companion of mTOR (RICTOR) have all
been identified as playing a critical role in Akt-Ser473 phosphorylation. However, the apparently disparate
results reported in these studies are difficult to evaluate, given that
different stimuli and cell types were examined and that all of the
candidate proteins have never been systematically studied in a single
system. Additionally, none of these studies were performed in a classical
insulin-responsive cell-type or tissue such as muscle or fat. We therefore
examined each of these candidates in 3T3-L1 adipocytes.
In vitro kinase assays, using different subcellular fractions of 3T3-L1 adipocytes,
revealed that phosphatidylinositol 3,4,5-trisphosphate (PIP3)-stimulated Ser473 phosphorylation correlated well with the amount of
DNA-PK, mTOR, and RICTOR but did not correlate
with levels of ATM, ILK, and PKCa. PKCa was completely absent from compartments with
Ser473 phosphorylation activity. Although
purified DNA-PK could phosphorylate a peptide
derived from Akt that contains amino acid Ser473,
it could not phosphorylate full-length Akt2.
Vesicles immunoprecipitated from low-density microsomes (LDM) using antibodies directed against mTOR or RICTOR had PIP3-stimulated Ser473 activity that
was sensitive to wortmannin but not staurosporine. In contrast, immunopurified
LDM vesicles containing ILK could not phosphorylate
Akt on Ser473 in vitro. Small
interference RNA (siRNA)-knockdown of RICTOR, but
not DNA-PK, ATM, or ILK, suppressed insulin-activated Ser473 phosphorylation and to a lesser extent Thr308 phosphorylation in 3T3-L1 adipocytes.
Based on our cell-free kinase and siRNA results, we conclude mTOR
complexed to RICTOR is the Ser473 kinase in 3T3-L1 adipocytes.
Palozza
P, Sheriff A,
Serini
S, Boninsegna
A, Maggiano
N, Ranelletti
FO, Calviello
G, Cittadini
A.
There is a lot of interest in the health benefits of dietary carotenoids and on the relationship of these compounds
with smoke. In particular, it is unknown if the enhanced cancer risk
observed in smokers following beta-carotene supplementation can be also
found using other carotenoids. Here, we studied
the effects of the tomato carotenoid lycopene on molecular pathways involved in cell cycle
progression, apoptosis and survival in immortalized RAT-1 fibroblasts
exposed to cigarette smoke condensate (TAR). Lycopene
(0.5-2.0 muM) inhibited cell growth in a dose-and
time-dependent manner, by arresting cell cycle progression and by promoting
apoptosis in cells exposed to TAR. The arrest of cell cycle was independent
of p53 and of 8-OH-dG DNA damage and related to a decreased expression of cyclin D1. Moreover, the carotenoid
up-regulated apoptosis and down-regulated the phosphorylation
of AKT and Bad in cells exposed to TAR. Such an effect was associated to an
inhibition of TAR-induced expression of Cox-2 and hsp90, which is known to
maintain AKT activity. This study suggests that lycopene,
differently from beta-carotene, can exert protective effects against
cigarette smoke condensate.
PMID: 16215689 [PubMed - as supplied
PMID: 16221682 [PubMed - as supplied by
publisher]