Abstract
Intravenous application of high‐dose ascorbate is used in complementary palliative medicine to treat cancer patients. Pharmacological doses of ascorbate in the mM range induce cytotoxicity ...in cancer cells mediated by reactive oxygen species (
ROS
), namely hydrogen peroxide and ascorbyl radicals. However, little is known about intrinsic or extrinsic factors modulating this ascorbate‐mediated cytotoxicity. Under normoxia and hypoxia, ascorbate
IC
50
values were determined on the
NCI
60 cancer cells. The cell cycle, the influence of cobalt chloride‐induced hypoxia‐inducible factor‐1α (
HIF
‐1α) and the glucose transporter 1 (
GLUT
‐1) expression (a pro‐survival
HIF
‐1α‐downstream‐target) were analysed after ascorbate exposure under normoxic and hypoxic conditions. The amount of ascorbyl radicals increased with rising serum concentrations. Hypoxia (0.1%
O
2
) globally increased the
IC
50
of ascorbate in the 60 cancer cell lines from 4.5 ± 3.6 mM to 10.1 ± 5.9 mM (2.2‐fold increase,
P
< 0.001, Mann–Whitney
t
‐test), thus inducing cellular resistance towards ascorbate. This ascorbate resistance depended on
HIF
‐1α‐signalling, but did not correlate with cell line‐specific expression of the ascorbate transporter
GLUT
‐1. However, under normoxic and hypoxic conditions, ascorbate treatment at the individual
IC
50
reduced the expression of
GLUT
‐1 in the cancer cells. Our data show a
ROS
‐induced,
HIF
‐1α‐ and
O
2
‐dependent cytotoxicity of ascorbate on 60 different cancer cells. This suggests that for clinical application, cancer patients should additionally be oxygenized to increase the cytotoxic efficacy of ascorbate.
Beta-catenin plays an important role in embryogenesis and carcinogenesis by controlling either cadherin-mediated cell adhesion or transcriptional activation of target gene expression. In many types ...of cancers nuclear translocation of beta-catenin has been observed. Our data indicate that during melanoma progression an increased dependency on the transcriptional function of beta-catenin takes place. Blockade of beta-catenin in metastatic melanoma cell lines efficiently induces apoptosis, inhibits proliferation, migration and invasion in monolayer and 3-dimensional skin reconstructs and decreases chemoresistance. In addition, subcutaneous melanoma growth in SCID mice was almost completely inhibited by an inducible beta-catenin knockdown. In contrast, the survival of benign melanocytes and primary melanoma cell lines was less affected by beta-catenin depletion. However, enhanced expression of beta-catenin in primary melanoma cell lines increased invasive capacity in vitro and tumor growth in the SCID mouse model. These data suggest that beta-catenin is an essential survival factor for metastatic melanoma cells, whereas it is dispensable for the survival of benign melanocytes and primary, non-invasive melanoma cells. Furthermore, beta-catenin increases tumorigenicity of primary melanoma cell lines. The differential requirements for beta-catenin signaling in aggressive melanoma versus benign melanocytic cells make beta-catenin a possible new target in melanoma therapy.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
Sacrococcygeal teratomas (SCTs) are benign tumours of the newborn with absolute indication for surgery directly after birth. We recently described the presence of stem cells positive for the stem ...cell markers nanog and Oct4 in SCTs. Here we report the isolation of three stem cell lines from three different SCTs. Cells were propagated in mesenchymal or in embryonic stem cell medium. Non-clonal homogeneous stem cell lines were obtained after two to three passages and characterized in vitro by immunocytochemistry, RT-PCR, western blot, FACS analysis, and metaphase spreads. The differentiation potential was tested in vitro and in vivo. The isolated cell lines, which we refer to as human sacrococcygeal teratoma stem cells (hSctSCs), express nanog, Oct4 and stella, and are negative for malignancy markers alpha-fetoprotein and carcinoembryonic antigen. They can be induced in vitro to express neuronal, osteogenic, and chondrogenic traits. After grafting in vivo, spontaneous integration into the neural crest of the chick embryo and teratoma formation in the nude mouse were obtained. Our results indicate that SCTs are derived from remnants of the epiblast-derived primitive streak, which in the human embryo normally regresses but forms teratomas in children affected with SCT. The hSctSCs therefore may be comparable to mouse epiblast-derived stem cells (EpiSCs) and share characteristic features with human embryonic stem (hES) cells. Thus, SCT tissue obtained after surgery appears to be a novel source for the generation of human stem cells without the ethical implications associated with hES cells.
Casein kinase 1 alpha (CK1alpha) is a multifunctional Ser/Thr kinase that phosphorylates several substrates. Among those is beta-catenin, an important player in cell adhesion and Wnt signaling. ...Phosphorylation of beta-catenin by CK1alpha at Ser45 is the priming reaction for the proteasomal degradation of beta-catenin. Interestingly, aside from this role in beta-catenin degradation, very little is known about the expression and functional role of CK1alpha in tumor cells. Here, we show that CK1alpha expression in different tumor types is either strongly suppressed or completely lost during tumor progression and that CK1alpha is a key factor determining beta-catenin stability and transcriptional activity in tumor cells. CK1alpha reexpression in metastatic melanoma cells reduces growth in vitro and metastasis formation in vivo, and induces cell cycle arrest and apoptosis, whereas suppression of CK1alpha in primary melanoma cells induces invasive tumor growth. Inactivation of CK1alpha promotes tumor progression by regulating a switch in beta-catenin-mediated signaling. These results show that melanoma cells developed an efficient new mechanism to activate the beta-catenin signaling pathway and define CK1alpha as a novel tumor suppressor.
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