Staphylococcus aureus
is a Gram-positive bacterial pathogen of global concern and a leading cause of bacterial infections worldwide. Asymptomatic carriage of
S
.
aureus
on the skin and in the anterior nares is common and recognized as a predisposing factor to invasive infection. Transition of
S
.
aureus
from the carriage state to that of invasive infection is often accompanied by a temperature upshift from approximately 33°C to 37°C. Such a temperature shift is known in other pathogens to influence gene expression, often resulting in increased production of factors that promote survival or virulence within the host. One mechanism by which bacteria modulate gene expression in response to temperature is by the regulatory activity of RNA-based thermosensors,
cis-
acting riboregulators that control translation efficiency. This study was designed to identify and characterize RNA-based thermosensors in
S
.
aureus
. Initially predicted by
in silico
analyses of the
S
.
aureus
USA300 genome, reporter-based gene expression analyses and site-specific mutagenesis were performed to demonstrate the presence of a functional thermosensor within the 5’ UTR of
cidA
, a gene implicated in biofilm formation and survival of the pathogen. The nucleic sequence composing the identified thermosensor are sufficient to confer temperature-dependent post-transcriptional regulation, and activity is predictably altered by the introduction of site-specific mutations designed to stabilize or destabilize the structure within the identified thermosensor. The identified regulator is functional in both the native bacterial host
S
.
aureus
and in the distally related species
Escherichia coli
, suggesting that its regulatory activity is independent of host-specific factors. Interestingly, unlike the majority of bacterial RNA-based thermosensors characterized to date, the
cidA
thermosensor facilitates increased target gene expression at lower temperatures. In addition to the characterization of the first RNA-based thermosensor in the significant pathogen
S
.
aureus
, it highlights the diversity of function within this important class of ribo-regulators.
Aim:
The clinical application of cisplatin is limited by severe side effects associated with high applied
doses. The synergistic effect of a combination treatment of a low dose of cisplatin with the natural alkaloid
α-solanine on human hepatocellular carcinoma cells was evaluated.
Methods:
HepG2 cells were exposed to low doses of α-solanine and cisplatin, either independently or in combination.
The efficiency of this treatment modality was evaluated by investigating cell growth inhibition, cell
cycle arrest, and apoptosis enhancement.
Results:
α-solanine synergistically potentiated the effect of cisplatin on cell growth inhibition and significantly
induced apoptosis. This synergistic effect was mediated by inducing cell cycle arrest at the G2/M phase, enhancing
DNA fragmentation and increasing apoptosis through the activation of caspase 3/7 and/or elevating the
expression of the death receptors DR4 and DR5. The induced apoptosis from this combination treatment was
also mediated by reducing the expression of the anti-apoptotic mediators Bcl-2 and survivin, as well as by
modulating the miR-21 expression.
Conclusion:
Our study provides strong evidence that a combination treatment of low doses of α-solanine and
cisplatin exerts a synergistic anticancer effect and provides an effective treatment strategy against hepatocellular
carcinoma.
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