Background: Malignant pleural mesothelioma (MPM) is an aggressive asbestosrelated
cancer that develops via mesothelial cell transformation. At present there
are no effective therapies for MPM. Great efforts have been made in finding
specific markers/mechanisms for MPM onset, including studies into microRNAs
and adenosine receptors (ARs). Recent studies have shown the differential
expression of mature microRNAs in several human cancers, suggesting their
potential role as oncogenes or tumor suppressor genes, and the involvement of
ARs in the regulation of cell death and proliferation.
Methods: In this study, we investigated miRNAs profile and the expression of
A3ARs in MPM. MiRNAs profile was investigated in 5 HMCs (human normal
pleural mesothelial short term cell cultures) and 5 MPMs, with microarray
approach. These results were confirmed by Real Time quantitative RT-PCR and
western blotting. ARs were analyzed by using RT-PCR, western blotting and
saturation binding assays. HMC were treated with crocidolite asbestos which is the
principal risk factor of MM. The role of A3ARs on these cellular models,
evaluating cAMP production, Akt phosphorylation and NF-kB activation was
investigated. The dual effect of A3AR stimulation on healthy and cancer cell
growth was studied by means of proliferation, apoptosis and cytotoxicity assays.
Results: A comparative analysis of miRNA expression in MPM and HMCs was
carried out. Microarray profiling showed different miRNA expression between
MPM and HMCs. Specifically, 13 miRNAs (17-5p, 18a, 19b, 20a, 20b, 25, 92,
106a, 106b), members of the oncomiRNA miR 17-92 and its paralogs were markedly dysregulated. Besides, in our investigation, additional miRNAs, such as
miR-7, miR-182, miR-214 and miR-497 were found to be dysregulated in MPM.
A3AR was up-regulated by 2.5 fold (P<0.01) in MMP when compared with HMP.
Stimulation of A3ARs decreases proliferation and exerts cytotoxic and proapoptotic
effect on MMC and on HMC exposed to asbestos and TNF-�, but not in
HMC with an involvement of the de-regulation of Akt/NF-kB cell survival
pathway.
Conclusion: These data are in agreement with results which have previously been
reported on dysregulated miRNAs for other solid human tumors. Moreover, in our
investigation, additional miRNAs were found to be dysregulated in MPM.
Interestingly, gene products which regulate the cell cycle are targets and predicted
targets for these miRNAs. Our data suggest that specific miRNAs and A3ARs
could be key players in MPM development/progression. In addition, some of these
miRNAs may represent MPM markers and potential targets for new therapeutic
approaches. Besides, our data suggest that A3AR could represent a
pharmacological target to prevent tumor development after asbestos exposure and
to treat full blown MPM