Cancer and senescence are both complex transformative processes that dramatically alter many features of cell physiology and their interactions with surrounding tissues. Developing the wide range of cellular features characteristic of these conditions requires profound alterations in global gene expression patterns, which can be achieved by suppressing, activating, or uncoupling cellular gene regulatory pathways. Many genes associated with the initiation and development of tumors are regulated at the level of mRNA decay, frequently through the activity of AU-rich mRNA-destabilizing elements (AREs) located in their 3′-untranslated regions. As such, cellular factors that recognize and control the decay of ARE-containing mRNAs can influence tumorigenic or senescent phenotypes mediated by products of these transcripts. In this review, we discuss evidence showing how suppressed expression and/or activity of the ARE-binding protein tristetraprolin (TTP) can contribute to these processes. Next, we outline current findings linking TTP suppression to exacerbation of individual tumorigenic phenotypes, and the roles of specific TTP substrate mRNAs in mediating these effects. Finally, we survey potential mechanisms that cells may employ to suppress TTP expression in cancer, and propose potential diagnostic and therapeutic strategies that may exploit the relationship between TTP expression and tumor progression or senescence.

RNase-L is a mediator of type 1 interferon-induced antiviral activity that has diverse and critical cellular roles, including the regulation of cell proliferation, differentiation, senescence and apoptosis, tumorigenesis, and the control of the innate immune response. Although RNase-L was originally shown to mediate the endonucleolytic cleavage of both viral and ribosomal RNAs in response to infection, more recent evidence indicates that RNase-L also functions in the regulation of cellular mRNAs as an important mechanism by which it exerts its diverse biological functions. Despite this growing body of work, many questions remain regarding the roles of mRNAs as RNase-L substrates. This review will survey known and putative mRNA substrates of RNase-L, propose mechanisms by which it may selectively cleave these transcripts, and postulate future clinical applications.

Background The endoribonuclease RNase-L is a type-I interferon (IFN)-regulatedcomponent of the innate immune response that functions in antiviral, antibacterial and antiproliferative activities. RNase-L produces RNA agonists of RIG-I-like receptors (RLRs), sensors of cytosolic pathogen-associated RNAs that induce cytokines including IFNβ. IFNβ and RLR signaling mediate protective responses against experimental colitis and colitis-associated cancer (CAC) and contribute to gastrointestinal (GI) homeostasis. Therefore, we investigated a role for RNase-L in murine colitis and CAC and its association with RLR signaling in response to bacterial RNA. Methods Colitis was induced in wild type (WT) and RNase-L-deficient mice (RNase-L−/−) by administration of dextran sulphate sodium (DSS). CAC was induced by DSS and azoxymethane (AOM). Histological analysis and immunohistochemistry were performed on colon tissue to analyze immune cell infiltration and tissue damage following induction of colitis. Expression of cytokines was measured by qRT-PCR and ELISA. Results DSS-treated RNase-L−/− mice exhibited a significantly higher clinical score, delayed leukocyte infiltration, reduced expression of IFNβ, TNFα, IL-1β and IL-18at early times post-DSS exposure and increased mortalityas compared to WT mice. DSS/AOM-treated RNase-L−/−mice displayed an increased tumor burden. Bacterial RNA triggeredIFNβproductionin an RNase-L-dependent manner and provided a potential mechanism by whichRNase-L contributes to the GI immune response to microbiota and protects against experimental colitis and CAC. Conclusions RNase-L promotes the innate immune response to intestinal damage and ameliorates murine colitis and CAC. The RNase-L-dependent production of IFNβ stimulated by bacterial RNA may be a mechanism to protectagainst GI inflammatory disease.

Background: Serum-response factor (SRF) induces mRNAs that promote cell proliferation, whereas RNase L and tristetraprolin (TTP) degrade specific mRNAs to inhibit proliferation. Results: RNase L and TTP interact and down-regulate SRF to attenuate mitogen-induced gene expression. Conclusion: RNase L and TTP are components of a regulatory network that limits the proliferative response to mitogens. Significance: The RNase L/TTP axis represents a target to inhibit cancer cell proliferation.

The serine/threonine kinase Pim-1 directs selected signaling events that promote cell growth and survival and is overexpressed in diverse human cancers. Pim-1 expression is tightly controlled through multiple mechanisms, including regulation of mRNA turnover. In several cultured cell models, mitogenic stimulation rapidly induced and stabilized PIM1 mRNA, however, vigorous destabilization 4–6 hours later helped restore basal expression levels. Acceleration of PIM1 mRNA turnover coincided with accumulation of tristetraprolin (TTP), an mRNA-destabilizing protein that targets transcripts containing AU-rich elements. TTP binds PIM1 mRNA in cells, and suppresses its expression by accelerating mRNA decay. Reporter mRNA decay assays localized the TTP-regulated mRNA decay element to a discrete AU-rich sequence in the distal 3′-untranslated region that binds TTP. These data suggest that coordinated stimulation of TTP and PIM1 expression limits the magnitude and duration of PIM1 mRNA accumulation by accelerating its degradation as TTP protein levels increase. Consistent with this model, PIM1 and TTP mRNA levels were well correlated across selected human tissue panels, and PIM1 mRNA was induced to significantly higher levels in mitogen-stimulated fibroblasts from TTP-deficient mice. Together, these data support a model whereby induction of TTP mediates a negative feedback circuit to limit expression of selected mitogen-activated genes.