Abstract
Protein inhibitor of activated STAT3 (PIAS3) is an endogenous suppressor of signal transducer and activator of transcription 3 (STAT3) signaling. By directly interacting with phosphorylated STAT3, PIAS3 can block the downstream transcriptional activity of STAT3, which is hyper‐activated in various cancers. We previously reported that in malignant mesothelioma (MM), low PIAS3 expression is associated with increased STAT3 activation and correlates with poor patient survival, yet the regulatory mechanism(s) governing PIAS3 expression in MM remain unclear. Here, we demonstrate that PIAS3 protein expression does not correlate with its mRNA level in MM cell lines, indicating that PIAS3 expression is regulated at a post‐transcriptional level. Inhibition of proteasomal degradation with MG132 (10 μm) or bortezomib (1 μm), alone and in combination, did not increase PIAS3 protein levels; furthermore, inhibition of protein synthesis by cycloheximide treatment did not decrease PIAS3 levels within 48 h, suggesting that PIAS3 expression is not actively regulated at a post‐translational level. To determine whether miRNA (miRs) can translationally regulate PIAS3 expression, we combined miR microarray analysis with bioinformatic screening to identify candidate miRs, in MM cell lines with low PIAS3 expression, followed by luciferase reporter assays to validate miR regulation of the PIAS3 3′UTR. We identified miR‐18a as a suppressor of PIAS3 expression that is upregulated in MM cells and whose inhibition can increase PIAS3 expression and suppress STAT3 activity. Moreover, we showed that miR‐18a inhibition can decrease MM cell viability and that its expression is negatively correlated with MM patient survival. Taken together, these results suggest that targeting miR‐18a may have therapeutic benefit in MM.
Highlights
Protein inhibitor of activated signal transducer and activator of transcription 3 (STAT3) (PIAS3) was originally identified as a major negative regulator of STAT3 activity (Chung et al, 1997)
Protein inhibitor of activated STAT3 (PIAS3) protein expression does not correlate with PIAS3 messenger RNA (mRNA) levels
We found that PIAS3 protein is markedly downregulated in three MM cell lines, 211H, H2052, and H2452, compared to H28 MM cells and A549 cells (Fig. 1A)
Summary
PIAS3 (protein inhibitor of activated STAT3) was originally identified as a major negative regulator of STAT3 (signal transducer and activator of transcription 3) activity (Chung et al, 1997). STAT3 is a key transcriptional regulator of diverse cellular activities, including proliferation, differentiation, metabolism, and apoptosis. When stimulated by its upstream activators, that is, growth factors and cytokines, Abbreviations 30UTR, 30 untranslated region; miR, microRNA; MM, malignance mesothelioma; PIAS3, protein inhibitor of activated STAT3; STAT3, signal transducer and activator of transcription 3.
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Disclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.