9 research outputs found
Myc Prevents Apoptosis and Enhances Endoreduplication Induced by Paclitaxel
BACKGROUND: The role of the MYC oncogene in the apoptotic pathways is not fully understood. MYC has been reported to protect cells from apoptosis activation but also to sensitize cells to apoptotic stimuli. We have previously demonstrated that the down-regulation of Myc protein activates apoptosis in melanoma cells and increases the susceptibility of cells to various antitumoral treatments. Beyond the well-known role in the G1-->S transition, MYC is also involved in the G2-M cell cycle phases regulation. METHODOLOGY/PRINCIPAL FINDINGS: In this study we have investigated how MYC could influence cell survival signalling during G2 and M phases. We used the microtubules damaging agent paclitaxel (PTX), to arrest the cells in the M phase, in a p53 mutated melanoma cell line with modulated Myc level and activity. An overexpression of Myc protein is able to increase endoreduplication favoring the survival of cells exposed to antimitotic poisoning. The PTX-induced endoreduplication is associated in Myc overexpressing cells with a reduced expression of MAD2, essential component of the molecular core of the spindle assembly checkpoint (SAC), indicating an impairment of this checkpoint. In addition, for the first time we have localized Myc protein at the spindle poles (centrosomes) during pro-metaphase in different cell lines. CONCLUSIONS: The presence of Myc at the poles during the prometaphase could be necessary for the Myc-mediated attenuation of the SAC and the subsequent induction of endoreduplication. In addition, our data strongly suggest that the use of taxane in antitumor therapeutic strategies should be rationally based on the molecular profile of the individual tumor by specifically analyzing Myc expression levels
Quantifying the Temperature Dependence of GlycineBetaine RNA Duplex Destabilization
Glycine–betaine (GB) stabilizes
folded protein structure
because of its unfavorable thermodynamic interactions with amide oxygen
and aliphatic carbon surface area exposed during protein unfolding.
However, GB can attenuate nucleic acid secondary structure stability,
although its mechanism of destabilization is not currently understood.
Here we quantify GB interactions with the surface area exposed during
thermal denaturation of nine RNA dodecamer duplexes with guanine–cytosine
(GC) contents of 17–100%. Hyperchromicity values indicate increasing
GB molality attenuates stacking. GB destabilizes higher-GC-content
RNA duplexes to a greater extent than it does low-GC-content duplexes
due to greater accumulation at the surface area exposed during unfolding.
The accumulation is very sensitive to temperature and displays characteristic
entropy–enthalpy compensation. Since the entropic contribution
to the <i>m</i>-value (used to quantify GB interaction with
the RNA solvent-accessible surface area exposed during denaturation)
is more dependent on temperature than is the enthalpic contribution,
higher-GC-content duplexes with their larger transition temperatures
are destabilized to a greater extent than low-GC-content duplexes.
The concentration of GB at the RNA surface area exposed during unfolding
relative to bulk was quantified using the solute-partitioning model.
Temperature correction predicts a GB concentration at 25 °C to
be nearly independent of GC content, indicating that GB destabilizes
all sequences equally at this temperature
l‑Proline and RNA Duplex <i>m</i>‑Value Temperature Dependence
The
temperature dependence of l-proline interactions with
the RNA dodecamer duplex surface exposed after unfolding was quantified
using thermal and isothermal titration denaturation monitored by uv-absorbance.
The <i>m</i>-value quantifying proline interactions with
the RNA duplex surface area exposed after unfolding was measured using
RNA duplexes with GC content ranging between 17 and 83%. The <i>m</i>-values from thermal denaturation decreased with increasing
GC content signifying increasingly favorable proline interactions
with the exposed RNA surface area. However, <i>m</i>-values
from isothermal titration denaturation at 25.0 °C were independent
of GC content and less negative than those from thermal denaturation.
The <i>m</i>-value from isothermal titration denaturation
for a 50% GC RNA duplex decreased (became more negative) as the temperature
increased and was in nearly exact agreement with the <i>m</i>-value from thermal denaturation. Since RNA duplex transition temperatures
increased with GC content, the more favorable proline interactions
with the high GC content duplex surface area observed from thermal
denaturation resulted from the temperature dependence of proline interactions
rather than the RNA surface chemical composition. The enthalpy contribution
to the <i>m</i>-value was positive and small (indicating
a slight increase in duplex unfolding enthalpy with proline) while
the entropic contribution to the <i>m</i>-value was positive
and increased with temperature. Our results will facilitate proline’s
use as a probe of solvent accessible surface area changes during biochemical
reactions at different reaction temperatures