Cold-inducible RNA-binding protein contributes to human antigen R and cyclin E1 deregulation in breast cancer

Intracellular CIRP promotes liver regeneration via STAT3 signaling pathway activation after partial hepatectomy in mice

Cold‑inducible RNA‑binding protein (CIRP) is a cold shock protein implicated in the regulation of multiple biological processes depending on its cellular localization. However, to the best of our knowledge, the role of CIRP in liver regeneration and injury after hepatectomy has not been investigated. The present study was therefore designed to explore whether CIRP is involved in liver regeneration after hepatectomy and its specific role and underlying molecular mechanism. The overall involvement of CIRP in liver regeneration and injury after hepatectomy was evaluated in CIRP‑deficient mice. C23, an antagonist of extracellular CIRP, was used to assess the effect of extracellular CIRP on liver regeneration and injury after hepatectomy. CIRP overexpression and short hairpin RNA plasmids were transfected into HepG2 cells to study the effect of intracellular CIRP on cell proliferation. The effects of extracellular CIRP on cell proliferation and injury were determined via the use of recombinant CIRP protein to stimulate HepG2 cells in vitro. The results indicated that both hepatic and serum CIRP levels significantly increased after partial hepatectomy. Additionally, CIRP deficiency impaired liver regeneration but alleviated liver injury after partial hepatectomy in mice. C23 administration attenuated liver injury and suppressed endoplasmic reticulum (ER) stress and oxidative stress. Loss‑ and gain‑of‑function analyses in HepG2 cells indicated that an increase in intracellular CIRP promoted cell proliferation via signal transducers and activation of transcription 3 (STAT3) signaling pathway activation. Moreover, recombinant CIRP had no effect on cell proliferation or STAT3 phosphorylation but induced ER stress, which was blocked by TAK242, an inhibitor of Toll‑like receptor 4 (TLR4), in HepG2 cells. Taken together, the results of the present study demonstrated that intracellular CIRP promotes liver regeneration by activating the STAT3 pathway, whereas extracellular CIRP induces ER stress possibly via the TLR4 signaling pathway after hepatectomy.

Genomic analysis uncovers that cold-inducible RNA binding protein is associated with estrogen receptor in breast cancer

BACKGROUND

RNA-binding proteins (RBPs) perform various biological functions in humans and are associated with several diseases, including cancer. Therefore, RBPs have emerged as novel therapeutic targets. Although recent investigations have shown that RBPs have crucial functions in breast cancer (BC), detailed research is underway to determine the RBPs that are closely related to cancers.

OBJECTIVE

To provide an insight into estrogen receptor (ER) regulation by cold-inducible RNA binding protein (CIRBP) as a novel therapeutic target.

RESULTS

By analyzing the genomic data, we identified a potential RBP in BC. We found that CIRBP is highly correlated with ER function and influences clinical outcomes, such as patient survival and endocrine therapy responsiveness. In addition, CIRBP influences the proliferation of BC cells by directly binding to ER-RNA.

CONCLUSION

Our results suggest that CIRBP is a novel upstream regulator of ER and that the interplay between CIRBP and ER may be associated with the clinical relevance of BC.

Cold-Inducible RNA Binding Protein Impedes Breast Tumor Growth in the PyMT Murine Model for Breast Cancer

RNA binding proteins (RBPs) post-transcriptionally regulate gene expression by associating with regulatory sequences in the untranslated regions of mRNAs. Cold-inducible RBP (CIRP) is a stress-induced RBP that was recently shown to modulate inflammation in response to cellular stress, where it increases or decreases pro-tumorigenic (proinflammatory) cytokines in different contexts. CIRP expression is altered in several cancers, including breast cancer, but the effects of CIRP on inflammation in breast cancer is not known. Here, we investigate if CIRP alters growth and the inflammatory profile of breast tumors. Transgenic mice overexpressing CIRP in the mammary epithelium were crossed with the PyMT mouse model of breast cancer, and the effects on both early and late tumorigenesis and inflammation were assessed. The effects of CIRP knockdown were also assessed in Py2T cell grafts. Overexpression of CIRP led to decreased tumorigenesis in the PyMT mouse model. Conversely, the knockdown of CIRP in Py2T cell grafts led to increased tumor growth. Luminex cytokine assays assessed the effects on the inflammatory environment. CIRP/PyMT mammary glands/mammary tumors and serum had decreased cytokines that promote inflammation, angiogenesis, and metastasis compared to PyMT mammary glands and serum, documenting a shift towards an environment less supportive of tumorigenesis. CIRP overexpression also decreased CD4+ helper T cells and increased CD8+ cytotoxic T cells in mammary tumors. Overall, these data support a role for CIRP as a potent antitumor molecule that suppresses both local and systemic pro-tumorigenic inflammation.

RNA binding proteins (RBPs) and their role in DNA damage and radiation response in cancer

Traditionally majority of eukaryotic gene expression is influenced by transcriptional and post-transcriptional events. Alterations in the expression of proteins that act post-transcriptionally can affect cellular signaling and homeostasis. RNA binding proteins (RBPs) are a family of proteins that specifically bind to RNAs and are involved in post-transcriptional regulation of gene expression and important cellular processes such as cell differentiation and metabolism. Deregulation of RNA-RBP interactions and any changes in RBP expression or function can lead to various diseases including cancer. In cancer cells, RBPs play an important role in regulating the expression of tumor suppressors and oncoproteins involved in various cell-signaling pathways. Several RBPs such as HuR, AUF1, RBM38, LIN28, RBM24, tristetrapolin family and Musashi play critical roles in various types of cancers and their aberrant expression in cancer cells makes them an attractive therapeutic target for cancer treatment. In this review we provide an overview of i). RBPs involved in cancer progression and their mechanism of action ii). the role of RBPs, including HuR, in breast cancer progression and DNA damage response and iii). explore RBPs with emphasis on HuR as therapeutic target for breast cancer therapy.

Hu Antigen R (HuR) Protein Structure, Function and Regulation in Hepatobiliary Tumors

Simple Summary

Hepatobiliary tumors are a group of primary malignancies encompassing the liver, the intra- and extra-hepatic biliary tracts, and the gall bladder. Within the liver, hepatocellular carcinoma (HCC) is the most common type of primary cancer, which is, also, representing the third-most recurrent cause of cancer-associated death and the sixth-most prevalent type of tumor worldwide, nowadays. Although less frequent, cholangiocarcinoma (CCA) is, currently, a fatal cancer with limited therapeutic options. Here, we review the regulatory role of Hu antigen R (HuR), a ubiquitous member of the ELAV/Hu family of RNA-binding proteins (RBPs), in the pathogenesis, progression, and treatment of HCC and CCA. Overall, HuR is proposed as a valuable diagnostic and prognostic marker, as well as a therapeutic target in hepatobiliary cancers. Therefore, novel therapeutic approaches that can selectively modulate HuR function appear to be highly attractive for the clinical management of these types of tumors.

Abstract

Hu antigen R (HuR) is a 36-kDa ubiquitous member of the ELAV/Hu family of RNA-binding proteins (RBPs), which plays an important role as a post-transcriptional regulator of specific RNAs under physiological and pathological conditions, including cancer. Herein, we review HuR protein structure, function, and its regulation, as well as its implications in the pathogenesis, progression, and treatment of hepatobiliary cancers. In particular, we focus on hepatocellular carcinoma (HCC) and cholangiocarcinoma (CCA), tumors where the increased cytoplasmic localization of HuR and activity are proposed, as valuable diagnostic and prognostic markers. An overview of the main regulatory axes involving HuR, which are associated with cell proliferation, invasion, metastasis, apoptosis, and autophagy in HCC, is provided. These include the transcriptional, post-transcriptional, and post-translational modulators of HuR function, in addition to HuR target transcripts. Finally, whereas studies addressing the relevance of targeting HuR in CCA are limited, in the past few years, HuR has emerged as a potential therapeutic target in HCC. In fact, the therapeutic efficacy of some pharmacological inhibitors of HuR has been evaluated, in early experimental models of HCC. We, further, discuss the major findings and future perspectives of therapeutic approaches that specifically block HuR interactions, either with post-translational modifiers or cognate transcripts in hepatobiliary cancers.

RNA-binding proteins and post-transcriptional regulation in lens biology and cataract: Mediating spatiotemporal expression of key factors that control the cell cycle, transcription, cytoskeleton and transparency

Development of the ocular lens - a transparent tissue capable of sustaining frequent shape changes for optimal focusing power - pushes the boundaries of what cells can achieve using the molecular toolkit encoded by their genomes. The mammalian lens contains broadly two types of cells, the anteriorly located monolayer of epithelial cells which, at the equatorial region of the lens, initiate differentiation into fiber cells that contribute to the bulk of the tissue. This differentiation program involves massive upregulation of select fiber cell-expressed RNAs and their subsequent translation into high amounts of proteins, such as crystallins. But intriguingly, fiber cells achieve this while also simultaneously undergoing significant morphological changes such as elongation - involving about 1000-fold length-wise increase - and migration, which requires modulation of cytoskeletal and cell adhesion factors. Adding further to the challenges, these molecular and cellular events have to be coordinated as fiber cells progress toward loss of their nuclei and organelles, which irreversibly compromises their potential for harnessing genetically hardwired information. A long-standing question is how processes downstream of signaling and transcription, which may also participate in feedback regulation, contribute toward orchestrating these cellular differentiation events in the lens. It is now becoming clear from findings over the past decade that post-transcriptional gene expression regulatory mechanisms are critical in controlling cellular proteomes and coordinating key processes in lens development and fiber cell differentiation. Indeed, RNA-binding proteins (RBPs) such as Caprin2, Celf1, Rbm24 and Tdrd7 have now been described in mediating post-transcriptional control over key factors (e.g. Actn2, Cdkn1a (p21Cip1), Cdkn1b (p27Kip1), various crystallins, Dnase2b, Hspb1, Pax6, Prox1, Sox2) that are variously involved in cell cycle, transcription, cytoskeleton maintenance and differentiation in the lens. Furthermore, deficiencies of these RBPs have been shown to result in various eye and lens defects and/or cataract. Because fiber cell differentiation in the lens occurs throughout life, the underlying regulatory mechanisms operational in development are expected to also be recruited for the maintenance of transparency in aged lenses. Indeed, in support of this, TDRD7 and CAPRIN2 loci have been linked to age-related cataract in humans. Here, I will review the role of key RBPs in the lens and their importance in understanding the pathology of lens defects. I will discuss advances in RBP-based gene expression control, in general, and the important challenges that need to be addressed in the lens to define the mechanisms that determine the epithelial and fiber cell proteome. Finally, I will also discuss in detail several key future directions including the application of bioinformatics approaches such as iSyTE to study RBP-based post-transcriptional gene expression control in the aging lens and in the context of age-related cataract.

Cold-inducible RNA-binding protein regulates cyclin B1 against spermatogenesis arrest caused by heat stress

BACKGROUND

Spermatogenesis arrest and spermatogenic cell apoptosis occur in the testes of heat-stressed mice. Although heat stress-induced spermatogenic cell apoptosis is due to the decreased expression of cold-inducible RNA-binding protein (CIRBP), it remains unclear whether spermatogenesis arrest is also affected by CIRBP. Additionally, the specific mechanism by which CIRBP regulates spermatogenic cell apoptosis or inhibits spermatogenesis remains to be elucidated.

OBJECTIVES

To investigate the mechanism by which CIRBP contributes to heat stress-induced testicular spermatogenesis arrest.

MATERIALS AND METHODS

Target mRNAs downstream of CIRBP in testicular tissue of BALB/c mice, exposed or not to heat stress, were sequenced. Sequencing data were subjected to bioinformatics analysis to identify key mRNAs and pathways associated with heat stress-induced spermatogenic damage. The link between CIRBP and its target mRNA Ccnb1 (cyclin B1) was verified by western blotting, flow cytometry, and RNA pulldown assays, and the ability of CIRBP to inhibit germ cell cycle arrest by regulating cyclin B1 expression was investigated in a mouse spermatocyte cell line (GC-2spd).

RESULTS

Changes in mRNA expression downstream of CIRBP were mainly associated with the cell cycle and RNA binding, transport and splicing. Cyclin B1 was found to regulate the G2/M transition during the first meiotic division of spermatogenic cells. Further, CIRBP was shown to bind directly to the 3'-untranslated region of Ccnb1 mRNA and was associated with cyclin B1-induced inhibition of spermatogenesis arrest.

DISCUSSION AND CONCLUSION

In conclusion, our results provide strong evidence that CIRBP may exert its key function in heat stress-induced testicular spermatogenic cell injury partly by regulating the expression of Ccnb1, the product of which inhibits spermatogenesis arrest.

Controversial roles of cold‑inducible RNA‑binding protein in human cancer (Review)

Cold‑inducible RNA‑binding protein (CIRBP) is a cold‑shock protein comprised of an RNA‑binding motif that is induced by several stressors, such as cold shock, UV radiation, nutrient deprivation, reactive oxygen species and hypoxia. CIRBP can modulate post‑transcriptional regulation of target mRNA, which is required to control DNA repair, circadian rhythms, cell growth, telomere integrity and cardiac physiology. In addition, the crucial function of CIRBP in various human diseases, including cancers and inflammatory disease, has been reported. Although CIRBP is primarily considered to be an oncogene, it may also serve a role in tumor suppression. In the present study, the controversial roles of CIRBP in various human cancers is summarized, with a focus on the interconnectivity between CIRBP and its target mRNAs involved in tumorigenesis. CIRBP may represent an important prognostic marker and therapeutic target for cancer therapy.

Stress Granules Involved in Formation, Progression and Metastasis of Cancer: A Scoping Review

The assembly of stress granules (SGs) is a well-known cellular strategy for reducing stress-related damage and promoting cell survival. SGs have become important players in human health, in addition to their fundamental role in the stress response. The critical role of SGs in cancer cells in formation, progression, and metastasis makes sense. Recent researchers have found that several SG components play a role in tumorigenesis and cancer metastasis via tumor-associated signaling pathways and other mechanisms. Gene-ontology analysis revealed the role of these protein components in the structure of SGs. Involvement in the translation process, regulation of mRNA stability, and action in both the cytoplasm and nucleus are among the main features of SG proteins. The present scoping review aimed to consider all studies on the effect of SGs on cancer formation, proliferation, and metastasis and performed based on a six-stage methodology structure and the PRISMA guideline. A systematic search of seven databases for qualified articles was conducted before July 2021. Publications were screened, and quantitative and qualitative analysis was performed on the extracted data. Go analysis was performed on seventy-one SGs protein components. Remarkably G3BP1, TIA1, TIAR, and YB1 have the largest share among the proteins considered in the studies. Altogether, this scoping review tries to demonstrate and provide a comprehensive summary of the role of SGs in the formation, progression, and metastasis of cancer by reviewing all studies.

CIRBP Knockdown Attenuates Tumourigenesis and Improves the Chemosensitivity of Pancreatic Cancer via the Downregulation of DYRK1B

Pancreatic ductal adenocarcinoma (PDAC) is one of the most lethal malignancies worldwide with very limited treatment options. Cold-inducible RNA binding protein (CIRBP) plays promoting roles in several types of cancers, but its function remains unclear in PDAC. Here, we found that the expression of CIRBP was upregulated in PDAC tumor tissues and was significantly associated with poor prognosis. Knockdown of CIRBP in PANC-1 and SW1990 cells inhibited proliferation, migration and invasion in vitro and suppressed tumor growth in vivo. Moreover, CIRBP knockdown enhanced the antitumour effects of gemcitabine treatment in PANC-1 and SW1990 cells, whereas CIRBP overexpression exerted the opposite effects. Mechanistically, CIRBP promoted PDAC malignancy and chemoresistance via upregulation of dual-specificity tyrosine-Y-phosphorylation regulated kinase 1B (DYRK1B). Indeed, knockdown of CIRBP sensitized pancreatic tumors to gemcitabine treatment by diminishing DYRK1B expression and increasing the ratio of ERK/p38 activity. Our findings suggest that CIRBP overexpression facilitates PDAC progression and gemcitabine resistance by upregulating DYRK1B expression and inhibiting the ERK/p38 signaling pathway, highlighting CIRBP as a potential new therapeutic target for PDAC.

CIRBP promotes ferroptosis by interacting with ELAVL1 and activating ferritinophagy during renal ischaemia-reperfusion injury

Renal ischaemia-reperfusion (IR) is a major cause of acute kidney injury (AKI). Cold-inducible RNA-binding protein (CIRBP) may contribute to AKI because its deficiency protects against renal IR injury in a mechanism believed to involve ferroptosis. We aimed to investigate whether ferroptosis is associated with CIRBP-mediated renal damage. The differential expression of CIRBP was examined in tubular epithelial (HK2) cells during hypoxia-reoxygenation (HR) or in response to erastin, an inducer of ferroptosis. CIRBP expression was increased in response to HR or erastin in HK2 cells but the silencing of CIRBP inhibited HR and erastin-induced ferroptosis together with ferritinophagy. We discovered an interaction between CIRBP and ELAVL1 using STRING software, which was verified through co-immunoprecipitation and fluorescence colocalization assays. We found that ELAVL1 is a critical regulator in the activation of ferritinophagy and the promotion of ferroptosis. HR or erastin also induced the expression of ELAVL1. An autophagy inhibitor (hydroxychloroquine) or si-ELAVL1 transfection reversed CIRBP-enhanced ferritinophagy activation and ferroptosis in HK2 cells under HR. Injection of anti-CIRBP antibody into a mouse model of IR inhibited ferroptosis and decreased renal IR injury in vivo. In summary, our results provide evidence that ferritinophagy-mediated ferroptosis could be responsible for CIRBP-enhanced renal IR injury.

Absence of Cold-Inducible RNA-Binding Protein (CIRP) Promotes Angiogenesis and Regeneration of Ischemic Tissue by Inducing M2-Like Macrophage Polarization

Cold-inducible RNA-binding protein (CIRP) is an intracellular RNA-chaperone and extracellular promoter of inflammation, which is increasingly expressed and released under conditions of hypoxia and cold stress. The functional relevance of CIRP for angiogenesis and regeneration of ischemic muscle tissue has never been investigated and is the topic of the present study. We investigated the role of CIRP employing CIRP deficient mice along with a hindlimb model of ischemia-induced angiogenesis. 1 and 7 days after femoral artery ligation or sham operation, gastrocnemius muscles of CIRP-deficient and wildtype mice were isolated and processed for (immuno-) histological analyses. CIRP deficient mice showed decreased ischemic tissue damage as evidenced by Hematoxylin and Eosin staining, whereas angiogenesis was enhanced as demonstrated by increased capillary/muscle fiber ratio and number of proliferating endothelial (CD31⁺/BrdU⁺) cells on day 7 after surgery. Moreover, CIRP deficiency resulted in a reduction of total leukocyte count (CD45⁺), neutrophils (myeloperoxidase, MPO⁺), neutrophil extracellular traps (NETs) (MPO⁺/CitH3⁺), and inflammatory M1-like polarized macrophages (CD68⁺/MRC1^-), whereas the number of tissue regenerating M2-like polarized macrophages (CD68⁺/MRC1^-) was increased in ischemic tissue samples. In summary, we show that the absence of CIRP ameliorates angiogenesis and regeneration of ischemic muscle tissue, most likely by influencing macrophage polarization in direction to regenerative M2-like macrophages.

Cold-inducible RNA binding protein promotes breast cancer cell malignancy by regulating Cystatin C levels

Cold-inducible RNA binding protein (CIRBP) is a stress-responsive protein that promotes cancer development and inflammation. Critical to most CIRBP functions is its capacity to bind and posttranscriptionally modulate mRNA. However, a transcriptome-wide analysis of CIRBP mRNA targets in cancer has not yet been performed. Here, we use an ex vivo breast cancer model to identify CIRBP targets and mechanisms. We find that CIRBP transcript levels correlate with breast cancer subtype and are an indicator of luminal A/B prognosis. Accordingly, overexpression of CIRBP in nontumoral MCF-10A cells promotes cell growth and clonogenicity, while depletion of CIRBP from luminal A MCF-7 cells has opposite effects. We use RNA immunoprecipitation followed by high-throughput sequencing (RIP-seq) to identify a set of 204 high confident CIRBP targets in MCF-7 cells. About 10% of these showed complementary changes after CIRBP manipulation in MCF-10A and MCF-7 cells, and were highly interconnected with known breast cancer genes. To test the potential of CIRBP-mediated regulation of these targets in breast cancer development, we focused on Cystatin C (CST3), one of the most highly interconnected genes, encoding a protein that displays tumor suppressive capacities. CST3 depletion restored the effects of CIRBP depletion in MCF-7 cells, indicating that CIRBP functions, at least in part, by down-regulating CST3 levels. Our data provide a resource of CIRBP targets in breast cancer, and identify CST3 as a novel downstream mediator of CIRBP function.

Moderate Hypothermia Effectively Alleviates Acetaminophen-Induced Liver Injury With Prolonged Action Beyond Cooling

Acetaminophen (APAP) overdose accounts for the highest incidence of acute liver failure, despite the availability of an antidote i.e. N-acetylcysteine. This calls for alternative strategies to manage APAP-induced liver injury (AILI). Therapeutic hypothermia has been explored in past studies for hepatoprotection, but these phenomenal reports lack clarification of its optimal window for application, and mechanistic effects in specific AILI. Hence, we conducted an in vitro study with transforming growth factor-α transgenic mouse hepatocytes cell line, TAMH, and human liver hepatocytes cell line, L-02, where cells were conditioned with deep (25°C) or moderate (32°C) hypothermia before, during or after APAP toxicity. Cell viability was evaluated as a hallmark of cytoprotection, along with cell death. Simultaneously, cold shock proteins (CSPs) and heat shock proteins expressions were monitored; key liver functions including drug-metabolizing ability and hepatic clearance were also investigated. Herein, we demonstrated significant hepatoprotection with 24-hour moderate hypothermic conditioning during AILI and this effect sustained for at least 24 hours of rewarming. Such liver preservation was associated with a CSP—RNA-binding motif protein 3 (RBM3) as its knockdown promptly abolished the cytoprotective effects of hypothermia. With mild and reversible liver perturbations, hypothermic therapy appears promising and its RBM3 involvement deserves future exploration.

Cold-inducible RNA-binding protein Cirp, but not Rbm3, may regulate transcript processing and protection in tissues of the hibernating ground squirrel

RNA-binding proteins (RBPs) have important roles in transcription, pre-mRNA processing/transport, mRNA degradation, translation, and non-coding RNA processing, among others. RBPs that are expressed in response to cold stress, such as Cirp and Rbm3, could regulate RNA stability and translation in hibernating mammals that reduce their body temperatures from 37 °C to as low as 0-5 °C during torpor bouts. RBPs including Cirp, Rbm3, and stress-inducible HuR translocate from the nucleus to stabilize mRNAs in the cytoplasm, and thereby could regulate which mRNA transcripts are protected from degradation and are translated, versus stored, for future protein synthesis or degraded by nucleases during cell stress associated with metabolic rate depression. This is the first study to explore the transcriptional/translational regulation, and subcellular localization of cold-inducible RBPs in a model hibernator, the 13-lined ground squirrel (Ictidomys tridecemlineatus). Cirp protein levels were upregulated in liver, skeletal muscle, and brown adipose tissue throughout the torpor-arousal cycle whereas Rbm3 protein levels stayed constant or decreased, suggesting an important role for Cirp, but likely not Rbm3, in the hibernator stress response. Increased cytoplasmic localization of Cirp in liver and muscle and HuR in liver during torpor, but no changes in the relative levels of Rbm3 in the cytoplasm, emphasizes a role for Cirp and possibly HuR in regulating mRNA processing during torpor. This study informs our understanding of the natural adaptations that extreme animals use in the face of stress, and highlight natural stress response mediators that could be used to bolster cryoprotection of human organs donated for transplant.

Extracellular CIRP induces macrophage endotoxin tolerance through IL-6R-mediated STAT3 activation

Extracellular cold-inducible RNA-binding protein (eCIRP) is a damage-associated molecular pattern, whose effect on macrophages is not entirely elucidated. Here we identified that eCIRP promotes macrophage endotoxin tolerance. Septic mice had higher serum levels of eCIRP; this was associated with a reduced ex vivo immune response of their splenocytes to LPS. Pretreatment of macrophages with recombinant murine CIRP (rmCIRP) resulted in a tolerance to LPS stimulation as demonstrated by a reduction of TNF-α production. We found that eCIRP increased phosphorylated STAT3 (p-STAT3) in macrophages. A STAT3 inhibitor, Stattic, rescued macrophages from rmCIRP-induced tolerance by restoring the release of TNF-α in response to LPS stimulation. We discovered strong binding affinity between eCIRP and IL-6 receptor (IL-6R) as revealed by Biacore, fluorescence resonance energy transfer (FRET), and their colocalization in macrophages by immunostaining assays. Blockade of IL-6R with its neutralizing Ab inhibited eCIRP-induced p-STAT3 and restored LPS-stimulated TNF-α release in macrophages. Incubation of macrophages with rmCIRP skewed them toward an M2 phenotype, while treatment with anti-IL-6R Ab prevented rmCIRP-induced M2 polarization. Thus, we have demonstrated that eCIRP activates p-STAT3 via a novel receptor, IL-6R, to promote macrophage endotoxin tolerance. Targeting eCIRP appears to be a new therapeutic option to correct immune tolerance in sepsis.

Loss of Cirbp expression is correlated with the malignant progression and poor prognosis in nasopharyngeal carcinoma

Purpose: The correlation of cold-inducible RNA-binding protein (Cirbp) expression with clinicopathological features including patient prognosis in nasopharyngeal carcinoma (NPC) was investigated.

Methods: The expression of Cirbp in NPC cell lines and tissue specimens was examined by qRT-PCR or immunohistochemistry (IHC).

Results: Immunohistochemistry (IHC) results showed that high Cirbp expression was detected in 61 of 61 non-cancerous nasopharyngeal squamous epithelial biopsies, whereas the significantly reduced expression of Cirbp was observed in NPC specimens. In addition, IHC assay for Cirbp protein illustrated that the cells of 177 NPC samples and nasopharyngeal squamous epithlial cells displayed strong signals in nuclei and faint signals in cytoplasm, whereas Cirbp protein is mainly detected in the cell’s cytoplasm in many other cancers. More importantly, TNM classification displayed that the low expression of Cirbp was more frequently observed in T3-T4, N2-N3, M1 and III-IV NPC biopsies, and undifferentiated carcinoma (UDC) than T1-T2, N0-N1, M0 and I-II tumors, and differentiated nonkeratinizing carcinoma (DNKC), suggesting that Cirbp loss is a key molecular event in advanced cases of NPC. Kaplan–Meier survival analysis indicated that NPC patients showing lower Cirbp expression had a significantly shorter overall survival time than those with high Cirbp expression. Multivariate analysis suggested that the level of Cirbp expression was an independent prognostic indicator for NPC survival. Finally, we revealed a significant positive association between Cirbp expression and E-cadherin, and a notable negative correlation between Cirbp expression and Ki67 labeling index in NPC biopsies.

Conclusion: Collectively, these findings demonstrate that loss of Cirbp expression is correlated with malignant progression and poor prognosis in NPC.

Cold-inducible RNA-binding protein (CIRP) induces translation of the cell-cycle inhibitor p27Kip1

The CDK inhibitor p27^Kip1 plays a central role in controlling cell proliferation and cell-cycle exit. p27^Kip1 protein levels oscillate during cell-cycle progression and are regulated by mitogen or anti-proliferative signaling. The abundance of the protein is frequently determined by post-transcriptional mechanisms including ubiquitin-mediated proteolysis and translational control. Here, we report that the cold-inducible RNA-binding protein (CIRP) selectively binds to the 5′ untranslated region of the p27^Kip1 mRNA. CIRP is induced, modified and relocalized in response to various stress stimuli and can regulate cell survival and cell proliferation particularly during stress. Binding of CIRP to the 5′UTR of the p27^Kip1 mRNA significantly enhanced reporter translation. In cells exposed to mild hypothermia, the induction of CIRP correlated with increased translation of a p27^Kip1 5′UTR reporter and with the accumulation of p27^Kip1 protein. shRNA-mediated CIRP knockdown could prevent the induction of translation. We found that p27^Kip1 is central for the decreased proliferation at lower temperature, since p27^Kip1 KO mouse embryonic fibroblasts (MEFs) hardly increased their doubling time in hypothermic conditions, whereas wild-type MEFs significantly delayed proliferation in response to cold stress. This suggests that the CIRP-dependent p27^Kip1 upregulation during mild hypothermia contributes to the cold shock-induced inhibition of cell proliferation.

Extracellular CIRP (eCIRP) and inflammation

Cold-inducible RNA-binding protein (CIRP) was discovered 2 decades ago while studying the mechanism of cold stress adaptation in mammals. Since then, the role of intracellular CIRP (iCIRP) as a stress-response protein has been extensively studied. Recently, extracellular CIRP (eCIRP) was discovered to also have an important role, acting as a damage-associated molecular pattern, raising critical implications for the pathobiology of inflammatory diseases. During hemorrhagic shock and sepsis, inflammation triggers the translocation of CIRP from the nucleus to the cytosol and its release to the extracellular space. eCIRP then induces inflammatory responses in macrophages, neutrophils, lymphocytes, and dendritic cells. eCIRP also induces endoplasmic reticulum stress and pyroptosis in endothelial cells by activating the NF-κB and inflammasome pathways, and necroptosis in macrophages via mitochondrial DNA damage. eCIRP works through the TLR4-MD2 receptors. Studies with CIRP-/- mice reveal protection against inflammation, implicating eCIRP to be a novel drug target. Anti-CIRP Ab or CIRP-derived small peptide may have effective therapeutic potentials in sepsis, acute lung injury, and organ ischemia/reperfusion injuries. The current review focuses on the pathobiology of eCIRP by emphasizing on signal transduction machineries, leading to discovering novel therapeutic interventions targeting eCIRP in various inflammatory diseases.

The MAPK Pathway-Based Drug Therapeutic Targets in Pituitary Adenomas

Mitogen-activated protein kinases (MAPKs) include ERK, p38, and JNK MAPK subfamilies, which are crucial regulators of cellular physiology, cell pathology, and many diseases including cancers. For the MAPK signaling system in pituitary adenomas (PAs), the activation of ERK signaling is generally thought to promote cell proliferation and growth; whereas the activations of p38 and JNK signaling are generally thought to promote cell apoptosis. The role of MAPK in treatment of PAs is demonstrated through the effects of currently used medications such as somatostatin analogs such as SOM230 and OCT, dopamine agonists such as cabergoline and bromocriptine, and retinoic acid which inhibit the MAPK pathway. Further, there are potential novel therapies based on putative molecular targets of the MAPK pathway, including 18beta-glycyrrhetinic acid (GA), dopamine-somatostatin chimeric compound (BIM-23A760), ursolic acid (UA), fulvestrant, Raf kinase inhibitory protein (RKIP), epidermal growth factor pathway substrate number 8 (Eps8), transmembrane protein with EGF-like and two follistatin-like domains (TMEFF2), cold inducible RNA-binding protein (CIRP), miR-16, and mammaliansterile-20-like kinase (MST4). The combined use of ERK inhibitor (e.g., SOM230, OCT, or dopamine) plus p38 activator (e.g., cabergoline, bromocriptine, and fulvestrant) and/or JNK activator (e.g., UA), or the development of single drug (e.g., BIM-23A760) to target both ERK and p38 or JNK pathways, might produce better anti-tumor effects on PAs. This article reviews the advances in understanding the role of MAPK signaling in pituitary tumorigenesis, and the MAPK pathway-based potential therapeutic drugs for PAs.

The Mechanism of CIRP in Regulation of STAT3 Phosphorylation and Bag-1/S Expression Upon UVB Radiation

Cold-inducible RNA binding protein (CIRP) is a stress-inducible protein, which could be activated by various cellular stresses, such as hypothermia, hypoxia and UV irradiation. Our previous study indicated that UVB radiation (3 mJ cm^-2 ) induces CIRP expression, which promotes keratinocytes growth, survival and eventually transformation via activation of STAT3-Bag-1/S signaling cascade. However, the mechanism(s) of CIRP in regulating p-STAT3 activation and Bag-1/S expression have not been fully elucidated. In this study, we demonstrate that repeated exposure of UVB radiation (3 mJ cm^-2 ) or overexpression of CIRP could lead to an elevation of the phosphorylation of Janus kinase (JAK) family proteins (JAK2 and JAK3) in HaCaT cells. The increased phosphorylation of the JAKs correlates to an increased phosphorylation of STAT3 (p-STAT3) in the cells; inhibiting JAKs using JAK inhibitor I lead to a reduction of STAT3 phosphorylation and Bag-1/S expression in wild type HaCaT and CIRP stably transfected HaCaT cells with or without UVB exposure. Furthermore, our data indicated that inhibiting the downstream factor of CIRP, NF-κB, using BAY 11-7085 could also decrease the p-STAT3. These results lead us to propose that CIRP mediates the activation of STAT3-Bag-1/S signaling cascade via activating the JAKs and NF-κB signaling pathways.

V-ATPase-dependent repression of androgen receptor in prostate cancer cells

Prostate Cancer (PCa) is the most commonly diagnosed cancer and the third leading cause of death for men in the United States. Suppression of androgen receptor (AR) expression is a desirable mechanism to manage PCa. Our studies showed that AR expression was reduced in LAPC4 and LNCaP PCa cell lines treated with nanomolar concentrations of the V-ATPase inhibitor concanamycin A (CCA). This treatment decreased PSA mRNA levels, indicative of reduced AR activity. V-ATPase-dependent repression of AR expression was linked to defective endo-lysosomal pH regulation and reduced AR expression at the transcriptional level. CCA treatment increased the protein level and nuclear localization of the alpha subunit of the transcription factor HIF-1 (HIF-1α) in PCa cells via decreased hydroxylation and degradation of HIF-1α. The addition of iron (III) citrate restored HIF-1α hydroxylation and decreased total HIF-1α levels in PCa cells treated with CCA. Moreover, iron treatment partially rescued CCA-mediated AR repression. Dimethyloxalylglycine (DMOG), which prevents HIF-1α degradation independently of V-ATPase, also decreased AR levels, supporting our hypothesis that HIF-1α serves as a downstream mediator in the V-ATPase-AR axis. We propose a new V-ATPase-dependent mechanism to inhibit androgen receptor expression in prostate cancer cells involving defective endosomal trafficking of iron and the inhibition of HIF-1 α-subunit turnover.

Expression of cold-inducible RNA-binding protein (CIRP) in renal cell carcinoma and the effect of CIRP downregulation cell proliferation and chemosensitivity to gemcitabine

The aim of the present study was to investigate the expression of cold-inducible RNA-binding protein (CIRP) in renal cell carcinoma (RCC) and to determine the effects of downregulation of CIRP on cell proliferation and chemosensitivity to gemcitabine. The expression of CIRP was detected by western blot analysis, quantitative polymerase chain reaction and immunohistochemistry (IHC) in 17 RCC and peri-cancerous tissue samples. Subsequently, the RCC 786-0 cell line was selected in order to investigate the function of CIRP using RNA interference (RNAi) technology, which was able to inhibit the expression of CIRP in vitro. Furthermore, the chemosensitivity to gemcitabine of each group [CIRP small interfering RNA (siCIRP), negative control small interfering RNA (siNC) and blank control] was compared. There were marked differences between the RCC and peri-cancerous tissues. IHC demonstrated that the CIRP expression in 13/17 (76.50%) tumor samples was markedly positive compared with that in the peri-cancerous tissues and the most common pathological type was clear cell RCC (92.30%). This observation was further confirmed through western blot analysis of protein expression levels. CIRP downregulation by RNAi in the RCC 786-0 cell line significantly decreased RCC proliferation. Additionally, when RNAi was coupled with gemcitabine treatment, there was a significant increase in apoptosis in the siCIRP group. CIRP was overexpressed in RCC tissues and in the 786-0 cell line. Downregulation of CIRP by siRNA inhibited the proliferation of the 786-0 cell line and enhanced the chemosensitivity of the cells to gemcitabine. Therefore, CIRP downregulation may provide a novel pathway for the treatment of metastatic RCC.

Cold-inducible RNA binding protein in cancer and inflammation

RNA binding proteins (RBPs) play key roles in RNA dynamics, including subcellular localization, translational efficiency and metabolism. Cold-inducible RNA binding protein (CIRP) is a stress-induced protein that was initially described as a DNA damage-induced transcript (A18 hnRNP), as well as a cold-shock domain containing cold-stress response protein (CIRBP) that alters the translational efficiency of its target messenger RNAs (mRNAs). This review summarizes recent work on the roles of CIRP in the context of inflammation and cancer. The function of CIRP in cancer appeared to be solely driven though its functions as an RBP that targeted cancer-associated mRNAs, but it is increasingly clear that CIRP also modulates inflammation. Several recent studies highlight roles for CIRP in immune responses, ranging from sepsis to wound healing and tumor-promoting inflammation. While modulating inflammation is an established role for RBPs that target cytokine mRNAs, CIRP appears to modulate inflammation by several different mechanisms. CIRP has been found in serum, where it binds the TLR4-MD2 complex, acting as a Damage-associated molecular pattern (DAMP). CIRP activates the NF-κB pathway, increasing phosphorylation of Iκκ and IκBα, and stabilizes mRNAs encoding pro-inflammatory cytokines. While CIRP promotes higher levels of pro-inflammatory cytokines in certain cancers, it also decreases inflammation to accelerate wound healing. This dichotomy suggests that the influence of CIRP on inflammation is context dependent and highlights the importance of detailing the mechanisms by which CIRP modulates inflammation. WIREs RNA 2018, 9:e1462. doi: 10.1002/wrna.1462 This article is categorized under: RNA in Disease and Development > RNA in Disease RNA Interactions with Proteins and Other Molecules > Protein-RNA Interactions: Functional Implications.

Recent progress in the research of cold-inducible RNA-binding protein

Cold-inducible RNA-binding protein (CIRP) is a cold-shock protein which can be induced after exposure to a moderate cold-shock in different species ranging from amphibians to humans. Expression of CIRP can also be regulated by hypoxia, UV radiation, glucose deprivation, heat stress and H₂O₂, suggesting that CIRP is a general stress-response protein. In response to stress, CIRP can migrate from the nucleus to the cytoplasm and regulate mRNA stability through its binding site on the 3'-UTR of its targeted mRNAs. Through the regulation of its targets, CIRP has been implicated in multiple cellular process such as cell proliferation, cell survival, circadian modulation, telomere maintenance and tumor formation and progression. In addition, CIRP can also exert its functions by directly interacting with intracellular signaling proteins. Moreover, CIRP can be secreted out of cells. Extracellular CIRP functions as a damage-associated molecular pattern to promote inflammatory responses and plays an important role in both acute and chronic inflammatory diseases. Here, we summarize novel findings of CIRP investigation and hope to provide insights into the role of CIRP in cell biology and diseases.

The mechanism of CIRP in inhibition of keratinocytes growth arrest and apoptosis following low dose UVB radiation

UV induces CIRP expression and subsequent Stat3 activation, but the biological function and mechanism of CIRP and Stat3 in mediating UVB-induced skin carcinogenesis have not been fully elucidated. In this study, we demonstrate that CIRP is elevated in all tested melanoma and non-melanoma skin cancer cell lines; and the expression of CIRP is upregulated in keratinocytes after being irradiated with relatively low dose (<5 mJ/cm² ), but not high dose (50 mJ/cm² ), UVB acutely and chronically. The increased expression of CIRP, either induced by UVB or through overexpression, leads to resistance of keratinocytes to UVB-induced growth arrest and death; and reduced expression of CIRP by RNA knockdown sensitizes keratinocyte cells to the low dose UVB radiation. We also demonstrated that CIRP expression is required for the low dose UVB-induced Tyr705-phosphorylation, but not total amount, of Stat3. The p-Stat3 level is correlated with the expression levels of cyclin D1 and VEGF, two known downstream cell growth regulators of Stat3, as well as Bag-1/S, an apoptosis regulator. Inhibition of Stat3 DNA-binding activity by S3I-201 leads to a reduction of the p-Stat3 and Bag-1/S along with growth and survival of keratinocytes post-UVB; and the effect of S3I-201 on the UVB-irradiated cells can be partially inhibited by overexpression of CIRP or Bag-1/S. Furthermore, the overexpression of Bag-1/S can totally inhibit UVB-induced PARP cleavage and caspase 3 activation. The results presented above led us to propose that CIRP-p(705)Stat3 cascade promotes cell proliferation and survival post-UVB via upregulating the expression of cyclin D1 and Bag-1/S, respectively. Published 2017. This article is a U.S. Government work and is in the public domain in the USA.

Cold inducible RNA binding protein upregulation in pituitary corticotroph adenoma induces corticotroph cell proliferation via Erk signaling pathway

Cushing's disease is caused by pituitary corticotroph adenoma, and the pathogenesis of it has remained obscure. Here, we showed that cold inducible RNA binding protein (CIRP) was markedly elevated in corticotroph tumors. Forced overexpression of CIRP in murine AtT20 pituitary corticotroph cell line increased corticotroph precursor hormone proopiomelanocortin (POMC) transcription, ACTH secretion and cellular proliferation. In vivo, CIRP overexpression promotes murine corticotroph tumor growth and enhances ACTH production. Mechanistically, we show that CIRP could promote AtT20 cells proliferation by inducing cyclinD1 and decreasing p27 expression via Erk1/2 signaling pathway. Clinically, CIRP overexpression is significantly correlated with Cushing's disease recurrence. CIRP appears to play a critical tumorigenesis function in Cushing's disease and its expression might be a useful biomarker for tumor recurrence.

Cold-inducible RNA binding protein in mouse mammary gland development

RNA binding proteins (RBPs) regulate gene expression by controlling mRNA export, translation, and stability. When altered, some RBPs allow cancer cells to grow, survive, and metastasize. Cold-inducible RNA binding protein (CIRP) is overexpressed in a subset of breast cancers, induces proliferation in breast cancer cell lines, and inhibits apoptosis. Although studies have begun to examine the role of CIRP in breast and other cancers, its role in normal breast development has not been assessed. We generated a transgenic mouse model overexpressing human CIRP in the mammary epithelium to ask if it plays a role in mammary gland development. Effects of CIRP overexpression on mammary gland morphology, cell proliferation, and apoptosis were studied from puberty through pregnancy, lactation and weaning. There were no gross effects on mammary gland morphology as shown by whole mounts. Immunohistochemistry for the proliferation marker Ki67 showed decreased proliferation during the lactational switch (the transition from pregnancy to lactation) in mammary glands from CIRP transgenic mice. Two markers of apoptosis showed that the transgene did not affect apoptosis during mammary gland involution. These results suggest a potential in vivo function in suppressing proliferation during a specific developmental transition.

Current Evidence and Future Perspectives on HuR and Breast Cancer Development, Prognosis, and Treatment

Hu-antigen R (HuR) is an RNA-binding posttranscriptional regulator that belongs to the Hu/ELAV family. HuR expression levels are modulated by a variety of proteins, microRNAs, chemical compounds, or the microenvironment, and in turn, HuR affects mRNA stability and translation of various genes implicated in breast cancer formation, progression, metastasis, and treatment. The aim of the present review is to critically summarize the role of HuR in breast cancer development and its potential as a prognosticator and a therapeutic target. In this aspect, all the existing English literature concerning HuR expression and function in breast cancer cell lines, in vivo animal models, and clinical studies is critically presented and summarized. HuR modulates many genes implicated in biological processes crucial for breast cancer formation, growth, and metastasis, whereas the link between HuR and these processes has been demonstrated directly in vitro and in vivo. Additionally, clinical studies reveal that HuR is associated with more aggressive forms of breast cancer and is a putative prognosticator for patients' survival. All the above indicate HuR as a promising drug target for cancer therapy; nevertheless, additional studies are required to fully understand its potential and determine against which types of breast cancer and at which stage of the disease a therapeutic agent targeting HuR would be more effective.

Cold-inducible proteins CIRP and RBM3, a unique couple with activities far beyond the cold

Cold-inducible RNA-binding protein (CIRP) and RNA-binding motif protein 3 (RBM3) are two evolutionarily conserved RNA-binding proteins that are transcriptionally upregulated in response to low temperature. Featuring an RNA-recognition motif (RRM) and an arginine-glycine-rich (RGG) domain, these proteins display many similarities and specific disparities in the regulation of numerous molecular and cellular events. The resistance to serum withdrawal, endoplasmic reticulum stress, or other harsh conditions conferred by RBM3 has led to its reputation as a survival gene. Once CIRP protein is released from cells, it appears to bolster inflammation, contributing to poor prognosis in septic patients. A variety of human tumor specimens have been analyzed for CIRP and RBM3 expression. Surprisingly, RBM3 expression was primarily found to be positively associated with the survival of chemotherapy-treated patients, while CIRP expression was inversely linked to patient survival. In this comprehensive review, we summarize the evolutionary conservation of CIRP and RBM3 across species as well as their molecular interactions, cellular functions, and roles in diverse physiological and pathological processes, including circadian rhythm, inflammation, neural plasticity, stem cell properties, and cancer development.

Cold-inducible RNA-binding protein mediates airway inflammation and mucus hypersecretion through a post-transcriptional regulatory mechanism under cold stress

Acute or chronic cold exposure exacerbates chronic inflammatory airway diseases, such as chronic obstructive pulmonary disease (COPD) and asthma. Cold-inducible RNA-binding protein (CIRP) is a cold-shock protein and is induced by various environmental stressors, such as hypothermia and hypoxia. In this study, we showed that CIRP gene and protein levels were significantly increased in patients with COPD and in rats with chronic airway inflammation compared with healthy subjects. Similarly, inflammatory cytokine production and MUC5AC secretion were up-regulated in rats following cigarette smoke inhalation. Cold temperature-induced CIRP overexpression and translocation were shown to be dependent on arginine methylation in vitro. CIRP overexpression promoted stress granule (SG) assembly. In the cytoplasm, the stability of pro-inflammatory cytokine mRNAs was increased through specific interactions between CIRP and mediator mRNA 3'-UTRs; these interactions increased the mRNA translation, resulting in MUC5AC overproduction in response to cold stress. Conversely, CIRP silencing and a methyltransferase inhibitor (adenosine dialdehyde) promoted cytokine mRNA degradation and inhibited the inflammatory response and mucus hypersecretion. These findings indicate that cold temperature can induce an airway inflammatory response and excess mucus production via a CIRP-mediated increase in mRNA stability and protein translation.

Cold-inducible RNA-binding protein promotes epithelial-mesenchymal transition by activating ERK and p38 pathways

Transforming growth factor-β1 (TGF-β1), a potent inducer of epithelial-to-mesenchymal transition (EMT), upregulates the cold-inducible RNA-binding protein (CIRP). The link between CIRP and EMT, however, remains unknown. To determine the role of CIRP in EMT, we performed CIRP knockdown and overexpression experiments in in vitro TGF-β1-induced EMT models. We found that CIRP overexpression promoted the downregulation of epithelial markers and the upregulation of mesenchymal markers after TGF-β1 treatment for EMT induction. It also promoted cell migration and invasion, key features of EMT. In contrast, CIRP knockdown inhibited the downregulation of epithelial markers and the upregulation of mesenchymal markers after TGF-β1 treatment for EMT induction. In addition, it also inhibited cell migration and invasion. Furthermore, we demonstrated that the RNA-recognition motif in CIRP is essential for the role of CIRP in EMT. At the downstream level, CIRP knockdown downregulated Snail, key transcriptional regulator of EMT, while CIRP overexpression upregulated it. We found out that the link between CIRP and Snail is mediated by ERK and p38 pathways. EMT is a critical component of carcinoma metastasis and invasion. As demonstrated in this study, the biological role of CIRP in EMT may explain why CIRP overexpression has been associated with a bad prognosis in cancer patients.

Hallmarks of cancer and AU-rich elements

Post‐transcriptional control of gene expression is aberrant in cancer cells. Sustained stabilization and enhanced translation of specific mRNAs are features of tumor cells. AU‐rich elements (AREs), cis‐acting mRNA decay determinants, play a major role in the posttranscriptional regulation of many genes involved in cancer processes. This review discusses the role of aberrant ARE‐mediated posttranscriptional processes in each of the hallmarks of cancer, including sustained cellular growth, resistance to apoptosis, angiogenesis, invasion, and metastasis. WIREs RNA 2017, 8:e1368. doi: 10.1002/wrna.1368

For further resources related to this article, please visit the WIREs website.

RNA-binding proteins in eye development and disease: implication of conserved RNA granule components

The molecular biology of metazoan eye development is an area of intense investigation. These efforts have led to the surprising recognition that although insect and vertebrate eyes have dramatically different structures, the orthologs or family members of several conserved transcription and signaling regulators such as Pax6, Six3, Prox1, and Bmp4 are commonly required for their development. In contrast, our understanding of posttranscriptional regulation in eye development and disease, particularly regarding the function of RNA-binding proteins (RBPs), is limited. We examine the present knowledge of RBPs in eye development in the insect model Drosophila as well as several vertebrate models such as fish, frog, chicken, and mouse. Interestingly, of the 42 RBPs that have been investigated for their expression or function in vertebrate eye development, 24 (~60%) are recognized in eukaryotic cells as components of RNA granules such as processing bodies, stress granules, or other specialized ribonucleoprotein (RNP) complexes. We discuss the distinct developmental and cellular events that may necessitate potential RBP/RNA granule-associated RNA regulon models to facilitate posttranscriptional control of gene expression in eye morphogenesis. In support of these hypotheses, three RBPs and RNP/RNA granule components Tdrd7, Caprin2, and Stau2 are linked to ocular developmental defects such as congenital cataract, Peters anomaly, and microphthalmia in human patients or animal models. We conclude by discussing the utility of interdisciplinary approaches such as the bioinformatics tool iSyTE (integrated Systems Tool for Eye gene discovery) to prioritize RBPs for deriving posttranscriptional regulatory networks in eye development and disease. WIREs RNA 2016, 7:527-557. doi: 10.1002/wrna.1355 For further resources related to this article, please visit the WIREs website.

Cold-inducible RNA-binding protein CIRP/hnRNP A18 regulates telomerase activity in a temperature-dependent manner

The telomerase is responsible for adding telomeric repeats to chromosomal ends and consists of the reverse transcriptase TERT and the RNA subunit TERC. The expression and activity of the telomerase are tightly regulated, and aberrant activation of the telomerase has been observed in >85% of human cancers. To better understand telomerase regulation, we performed immunoprecipitations coupled with mass spectrometry (IP-MS) and identified cold inducible RNA-binding protein (CIRP or hnRNP A18) as a telomerase-interacting factor. We have found that CIRP is necessary to maintain telomerase activities at both 32°C and 37°C. Furthermore, inhibition of CIRP by CRISPR-Cas9 or siRNA knockdown led to reduced telomerase activities and shortened telomere length, suggesting an important role of CIRP in telomere maintenance. We also provide evidence here that CIRP associates with the active telomerase complex through direct binding of TERC and regulates Cajal body localization of the telomerase. In addition, CIRP regulates the level of TERT mRNAs. At the lower temperature, TERT mRNA is upregulated in a CIRP-dependent manner to compensate for reduced telomerase activities. Taken together, these findings highlight the dual roles that CIRP plays in regulating TERT and TERC, and reveal a new class of telomerase modulators in response to hypothermia conditions.

Environmental stress induces trinucleotide repeat mutagenesis in human cells

The dynamic mutability of microsatellite repeats is implicated in the modification of gene function and disease phenotype. Studies of the enhanced instability of long trinucleotide repeats (TNRs)-the cause of multiple human diseases-have revealed a remarkable complexity of mutagenic mechanisms. Here, we show that cold, heat, hypoxic, and oxidative stresses induce mutagenesis of a long CAG repeat tract in human cells. We show that stress-response factors mediate the stress-induced mutagenesis (SIM) of CAG repeats. We show further that SIM of CAG repeats does not involve mismatch repair, nucleotide excision repair, or transcription, processes that are known to promote TNR mutagenesis in other pathways of instability. Instead, we find that these stresses stimulate DNA rereplication, increasing the proportion of cells with >4 C-value (C) DNA content. Knockdown of the replication origin-licensing factor CDT1 eliminates both stress-induced rereplication and CAG repeat mutagenesis. In addition, direct induction of rereplication in the absence of stress also increases the proportion of cells with >4C DNA content and promotes repeat mutagenesis. Thus, environmental stress triggers a unique pathway for TNR mutagenesis that likely is mediated by DNA rereplication. This pathway may impact normal cells as they encounter stresses in their environment or during development or abnormal cells as they evolve metastatic potential.

Cloning, expression, and purification of cold inducible RNA-binding protein and its neuroprotective mechanism of action

BACKGROUND

Cold-inducible RNA-binding protein (CIRP) is induced in response to hypothermia, where it exerts neuroprotective effects. Our preliminary studies revealed that it inhibits H2O2-induced apoptosis in rat neurons. In the current study, we report effective expression and purification approaches for the synthesis of CIRP, and assess its potential protective effects against oxidative stress.

METHODS

CIRP-encoding was expressed using the prokaryotic expression system pGEX-4T-1, and SP-Sepharose and Sephacryl S-200 columns were used to purify rCIRP. To mimic ischemia/reperfusion injury-associated oxidative stress, neuro2a cells (N2a) were pre-treated with rCIRP for 2h, followed by hydrogen peroxide (H2O2 60 μmol/ml) for 24h. Cell viability was then quantified using an MTT assay. In addition, western blotting was performed to measure the cell cycle related signal transduction pathways.

RESULTS

N2a cells exhibited decreased viability following H2O2 treatment, whereas rCIRP significantly improved viability following H2O2 treatment. CIRP also accelerated cell cycle progression from S to G2/M phase in cultured mouse neuroblastoma cells. In addition, CIRP increased levels of p-ERK and p-Akt, and also re-activated the cell cycle-related protein cyclin D1 and c-Myc. These results suggest that CIRP activated the Akt and ERK signal transduction pathways in N2a cells.

CONCLUSIONS

Our findings suggest that CIRP could exert protective effects against oxidative stress, and that it might be a novel neuroprotective agent.

Protein overexpression of CIRP and TLR4 in oral squamous cell carcinoma: an immunohistochemical and clinical correlation analysis

Oral squamous cell carcinoma (OSCC) is the most common head and neck malignancy. Here, we evaluated the expression of cold-inducible RNA-binding protein (CIRP) and toll-like receptors 4 (TLR4) in OSCC tissues with immunohistochemistry. Using biostatistical methods designed to assess the impact of the expression of CIRP and TLR4 on the prognosis of patients with OSCC and relate that expression to the clinicopathological characteristics of these patients. For the first time, we demonstrated that the expression of CIRP and TLR4 was increased in OSCC and that high levels of CIRP or TLR4 expression were associated with a short survival rate. In addition, we were surprised to find that the levels of expression of CIRP and TLR4 were very similar. The goal of this study was to evaluate whether these two genes may provide clues as to the regulatory mechanisms of OSCC, serve as prognostic markers and establish a new direction for further studies of these biological mechanisms.

Cytoplasmic HuR expression correlates with P-gp, HER-2 positivity, and poor outcome in breast cancer

HuR is an ubiquitously expressed RNA-binding protein that stabilizes messenger RNA and regulates translation. This protein has been shown to play an important role in carcinogenesis and cancer progression. P-glycoprotein (P-gp) is the product of the multidrug resistance 1 gene, and the overexpression of P-gp induces multidrug resistance and represents a major obstacle in cancer chemotherapy. The purpose of this study was to determine the expression of HuR and P-gp in human breast cancer tissues and analyze the relationship between HuR or P-gp expression and the clinical-pathological variables and patient outcomes. Immunohistochemistry was used to determine HuR and P-gp expression in 82 human breast cancer tissues and 20 matched adjacent noncancerous tissues. Additionally, 16 benign breast tumor samples were used as controls. The overexpression of cytoplasmic HuR was found in breast cancer but not in the matched adjacent noncancerous tissues or benign breast tumors. The expression levels of cytoplasmic HuR were significantly associated with increased age, high nuclear grade, and the positive expression of the ER, PR, and HER-2/neu. HuR was also associated with the expression of P-gp protein. Furthermore, univariate analysis indicates that patients with high expression levels of cytoplasmic HuR or P-gp had significantly reduced survival compared to patients with low expression levels. A multivariate analysis showed that age at diagnosis, nuclear grade, and cytoplasmic HuR positivity were independent indicators for disease-free survival and overall survival in patients with breast cancer. In conclusion, cytoplasmic HuR expression detected by immunohistochemical staining is a negative prognostic indicator for survival in patients with breast cancer.

NF-κB-dependent role for cold-inducible RNA binding protein in regulating interleukin 1β

The cold inducible RNA binding protein (CIRBP) responds to a wide array of cellular stresses, including short wavelength ultraviolet light (UVC), at the transcriptional and post-translational level. CIRBP can bind the 3'untranslated region of specific transcripts to stabilize them and facilitate their transport to ribosomes for translation. Here we used RNA interference and oligonucleotide microarrays to identify potential downstream targets of CIRBP induced in response to UVC. Twenty eight transcripts were statistically increased in response to UVC and these exhibited a typical UVC response. Only 5 of the 28 UVC-induced transcripts exhibited a CIRBP-dependent pattern of expression. Surprisingly, 3 of the 5 transcripts (IL1B, IL8 and TNFAIP6) encoded proteins important in inflammation with IL-1β apparently contributing to IL8 and TNFAIP6 expression in an autocrine fashion. UVC-induced IL1B expression could be inhibited by pharmacological inhibition of NFκB suggesting that CIRBP was affecting NF-κB signaling as opposed to IL1B mRNA stability directly. Bacterial lipopolysaccharide (LPS) was used as an activator of NF-κB to further study the potential link between CIRBP and NFκB. Transfection of siRNAs against CIRBP reduced the extent of the LPS-induced phosphorylation of IκBα, NF-κB DNA binding activity and IL-1β expression. The present work firmly establishes a novel link between CIRBP and NF-κB signaling in response to agents with diverse modes of action. These results have potential implications for disease states associated with inflammation.

Application of DNA microarray technology to gerontological studies

Gene expression patterns change dramatically in aging and age-related events. The DNA microarray is now recognized as a useful device in molecular biology and widely used to identify the molecular mechanisms of aging and the biological effects of drugs for therapeutic purpose in age-related diseases. Recently, numerous technological advantages have led to the evolution of DNA microarrays and microarray-based techniques, revealing the genomic modification and all transcriptional activity. Here, we show the step-by-step methods currently used in our lab to handling the oligonucleotide microarray and miRNA microarray. Moreover, we introduce the protocols of ribonucleoprotein [RNP] immunoprecipitation followed by microarray analysis (RIP-chip) which reveal the target mRNA of age-related RNA-binding proteins.

Cold-inducible RNA-binding protein modulates circadian gene expression posttranscriptionally

In mammalian tissues, circadian gene expression can be driven by local oscillators or systemic signals controlled by the master pacemaker in the suprachiasmatic nucleus. We show that simulated body temperature cycles, but not peripheral oscillators, controlled the rhythmic expression of cold-inducible RNA-binding protein (CIRP) in cultured fibroblasts. In turn, loss-of-function experiments indicated that CIRP was required for high-amplitude circadian gene expression. The transcriptome-wide identification of CIRP-bound RNAs by a biotin-streptavidin-based cross-linking and immunoprecipitation (CLIP) procedure revealed several transcripts encoding circadian oscillator proteins, including CLOCK. Moreover, CLOCK accumulation was strongly reduced in CIRP-depleted fibroblasts. Because ectopic expression of CLOCK improved circadian gene expression in these cells, we surmise that CIRP confers robustness to circadian oscillators through regulation of CLOCK expression.

The cyclins: a family of widely expressed tumor antigens?

Continuous cell division is a hallmark of cancer and cell-cycle regulators therefore represent relevant target molecules for tumor therapy. Among these targets the cyclins are of particular interest as they are overexpressed in various tumor entities with little expression in normal tissue. Here we review evidence that these molecules are recognized by the immune system, summarize why cyclins A, B and D in particular appear to be interesting targets for active and passive immunotherapy, and discuss whether the entire family could be an interesting novel class of tumor antigens for cancer treatment and prevention.

Posttranscriptional regulation of cancer traits by HuR

Cancer-related gene expression programs are strongly influenced by posttranscriptional mechanisms. The RNA-binding protein HuR is highly abundant in many cancers. Numerous HuR-regulated mRNAs encode proteins implicated in carcinogenesis. Here, we review the collections of HuR target mRNAs that encode proteins responsible for implementing five major cancer traits. By interacting with specific mRNA subsets, HuR enhances the levels of proteins that (1) promote cell proliferation, (2) increase cell survival, (3) elevate local angiogenesis, (4) help the cancer cell evade immune recognition, and (5) facilitate cancer cell invasion and metastasis. We propose that HuR exerts a tumorigenic function by enabling these cancer phenotypes. We discuss evidence that links HuR to several specific cancers and suggests its potential usefulness in cancer diagnosis, prognosis, and therapy.

Three-dimensional collagen represses cyclin E1 via β1 integrin in invasive breast cancer cells

The behavior of breast epithelial cells is influenced by their microenvironment which includes stromal cells and extracellular matrix (ECM). During cancer progression, the tissue microenvironment fails to control proliferation and differentiation, resulting in uncontrolled growth and invasion. Upon invasion, the ECM encountered by breast cancer cells changes from primarily laminin and collagen IV to primarily collagen I. We show here that culturing invasive breast cancer cells in 3-dimensional (3D) collagen I inhibits proliferation through direct regulation of cyclin E1, a G(1)/S regulator that is overexpressed in breast cancer. When the breast cancer cell line MDA-MB-231 was cultured within 3D collagen I gels, the G(1)/S transition was inhibited as compared to cells cultured on conventional 2D collagen or plastic dishes. Cells in 3D collagen downregulated cyclin E1 protein and mRNA, with no change in cyclin D1 level. Cyclin D1 was primarily cytoplasmic in 3D cultures, and this was accompanied by decreased phosphorylation of Rb, a nuclear target for both cyclin E1- and cyclin D1-associated kinases. Positive regulators of cyclin E1 expression, the transcription factor c-Myc and cold-inducible RNA binding protein (CIRP), were decreased in 3D collagen cultures, while the collagen I receptor β1 integrin was greatly increased. Inhibition of β1 integrin function rescued proliferation and cyclin E1 expression as well as c-Myc expression and Rb phosphorylation, but cyclin D1 remained cytoplasmic. We conclude that cyclin E1 is repressed independent of effects on cyclin D1 in a 3D collagen environment and dependent on β1 integrin interaction with collagen I, reducing proliferation of invasive breast cancer cells.