Diurnal change of the cold-inducible RNA-binding protein (Cirp) expression in mouse brain

Regulation of cold-inducible RNA-binding protein (CIRBP) in response to cellular stresses

Cold-inducible RNA-Binding Protein (CIRBP) is a general stress-response factor in vertebrates harboring two domains: an RNA-recognition motif and a regulatory domain rich in RG/RGG motifs. CIRBP has been described to bind mRNAs upon various stress conditions (cold, infections, UV, hypoxia …) and regulate their stability and translation. The proteins encoded by its targets are involved in key stress-responsive cellular pathways including apoptosis, inflammation, cell proliferation or translation, thus allowing their coordination. Due to its role in regulating central cellular functions, the expression of CIRBP is tightly controlled. We review here current understanding of the multiple mechanistic layers affecting CIRBP expression and function. Beyond transcriptional regulation by cold-responsive elements and the use of alternative promoters and transcription start sites, CIRBP undergoes various alternative splicing (AS) events which, depending on conditions, modulate the stability of CIRBP transcripts and/or impact the sequence of the encoded polypeptide. Typically, whilst CIRBP expression is induced in the context of hypothermia or viral infection, AS events preferentially address alternative isoforms towards mRNA degradation pathways in response to heat stress or to bacterial-secreted pore forming toxins. Post-translational modifications of CIRBP, mostly in its RGG domain, also condition CIRBP subcellular localization and access to its targets, thereby promoting or inhibiting their expression. For instance, phosphorylation and methylation events gate CIRBP nuclear to cytoplasmic translocation and control its recruitment to stress granules. Considering the therapeutic potential of modulating the expression and function of this central player in stress responses, a fine understanding of CIRBP regulation mechanisms deserves further attention.

Chronic social stress blunts core body temperature and molecular rhythms of Rbm3 and Cirbp in mouse lateral habenula

Chronic social stress in mice causes behavioural and physiological changes that result in perturbed rhythms of body temperature, activity and sleep-wake cycle. To further understand the link between mood disorders and temperature rhythmicity in mice that are resilient or susceptible to stress, we measured core body temperature (Tcore) before and after exposure to chronic social defeat stress (CSDS). We found that Tcore amplitudes of stress-resilient and susceptible mice are dampened during exposure to CSDS. However, following CSDS, resilient mice recovered temperature amplitude faster than susceptible mice. Furthermore, the interdaily stability (IS) of temperature rhythms was fragmented in stress-exposed mice during CSDS, which recovered to control levels following stress. There were minimal changes in locomotor activity after stress exposure which correlates with regular rhythmic expression of Prok2 - an output signal of the suprachiasmatic nucleus. We also determined that expression of thermosensitive genes Rbm3 and Cirbp in the lateral habenula (LHb) were blunted 1 day after CSDS. Rhythmic expression of these genes recovered 10 days later. Overall, we show that CSDS blunts Tcore and thermosensitive gene rhythms. Tcore rhythm recovery is faster in stress-resilient mice, but Rbm3 and Cirbp recovery is uniform across the phenotypes.

Chronic social stress blunts core body temperature and molecular rhythms ofRbm3andCirbpin mouse lateral habenula.. [DOI: 10.1101/2023.01.02.522528]

Chronic social stress in mice causes behavioral and physiological changes that result in perturbed rhythms of body temperature, activity and sleep-wake cycle. To further understand the link between mood disorders and temperature rhythmicity in mice that are resilient or susceptible to stress, we measured core body temperature (Tcore) before and after exposure to chronic social defeat stress (CSDS). We found that Tcore amplitudes of stress-resilient and susceptible mice are dampened during exposure to CSDS. However, following CSDS, resilient mice recovered temperature amplitude faster than susceptible mice. Furthermore, the interdaily stability (IS) of temperature rhythms was fragmented in stress-exposed mice during CSDS, which recovered to control levels following stress. There were minimal changes in locomotor activity after stress exposure which correlates with regular rhythmic expression ofProk2- an output signal of the suprachiasmatic nucleus. We also determined that expression of thermosensitive genesRbm3andCirbpin the lateral habenula (LHb) were blunted 1-day after CSDS. Rhythmic expression of these genes recovered 10 days later. Overall, we show that CSDS blunts Tcore and thermosensitive gene rhythms. Tcore rhythm recovery is faster in stress-resilient mice, butRbm3andCirbprecovery is uniform across the phenotypes.

Regulation of CIRP by genetic factors of SP1 related to cold sensitivity

Cold-inducible RNA-binding-protein (CIRP) is a cold shock protein that plays a protective role in genotoxic stress response. CIRP modulates inflammation in human diseases, inhibits cell proliferation, and protects cells from genotoxic damage during cellular stress. The mild cold responsive element and specificity protein 1 (SP1) play a role in Cirp expression at low temperatures. Although previous studies have provided insights into the immune functions of SP1 or CIRP, the mechanisms by which CIRP and SP1 me diate inflammatory responses remain largely unknown. Therefore, in the current study, we examined whether Cirp expression is affected by genetic factors related to temperature sensitivity as well as under low temperature. We performed a genome-wide association study on cold sensitivity in 2,000 participants. Fifty-six genome-wide significant trait-locus pairs were identified (p<1×10-5, false discovery rate < 0.05). Among these variants, rs1117050 and rs11170510 had a strong linkage disequilibrium (r2 > 0.8) relationship and expression quantitative trait locus-associated signals with the nearest Sp1 gene. We confirmed that the minor alleles of rs11170510 and rs58123204 were associated with increased Sp1 expression. Additionally, Sp1 overexpression led to CIRP translocation from the nucleus to the cytoplasm. CIRP protein levels increased in serum samples that had minor alleles of rs11170510 and rs58123204. Levels of various pro-inflammatory cytokines were also significantly increased in human peripheral blood mononuclear cells with minor alleles of rs11170510 and rs58123204. These results suggest that genetic factors related to cold sensitivity regulate CIRP expression and function and provide valuable insights into prediction of potential diseases through analysis of inherent genetic factors in humans.

Decreased Expression of CIRP Induced by Therapeutic Hypothermia Correlates with Reduced Early Brain Injury after Subarachnoid Hemorrhage

Early brain injury is considered to be a primary reason for the poor prognosis of patients suffering from subarachnoid hemorrhage (SAH). Due to its pro-inflammatory activity, cold-inducible RNA-binding protein (CIRP) has been implicated in the ischemic brain insult, but its possible interplay with hypothermia in SAH treatment remains to be evaluated. One-hundred and thirty-eight Sprague-Dawley rats (300–350 g males) were randomly allocated into the following groups: sham-operated (Sham); SAH; and SAH + hypothermia (SAH + H), each comprised of 46 animals. After treatments, the brain tissues of the three groups were randomly collected after 12 h, 1 d, 3 d, and 7 d, and the expression levels of the CIRP and mitochondrial apoptosis pathway-related proteins Bax, Bcl-2, caspase-9, caspase-3, and cytochrome c measured using Western blotting and real-time PCR. Brain damage was assessed by TUNEL and Nissl staining, the electron microscopy of brain tissue slices as well as functional rotarod tests. Expression of CIRP, Bax, caspase-9, caspase-3, and cytochrome c as well as reduced motor function incidence were higher in the SAH group, particularly during the first 3 d after SAH induction. Hypothermia blunted these SAH responses and apoptosis, thereby indicating reduced inflammatory signaling and less brain cell injury in the early period after SAH. Hypothermia treatment was found to effectively protect the brain tissue from early SAH injury in a rat model and its further evaluation as a therapeutic modality in SAH patients requires further study.

Hypoxia causes mitochondrial dysfunction and brain memory disorder in a manner mediated by the reduction of Cirbp

Environmental hypoxic hazard has increasingly become a global public health issue, with impelling evidences supporting the relation between hypoxia and cognitive disorders. As a potent stressor, hypoxia causes mitochondrial dysfunction with insufficient energy production, thus the formation of brain memory disorder. Yet, the underlying molecular mechanism/s against hypoxia induced injury have yet to be identified. Here, we report that cold inducible RNA binding protein (Cirbp) attenuates hypoxia induced insufficient energy production and oxidative stress. Further analyses show that Cirbp sustains protein levels of respiratory chain complexes II (SDHB) and IV (MT-CO1), and directly binds the 3'UTR of Atp5g3 to control mitochondrial homeostasis and ATP biogenesis upon hypoxic stress. Altogether, our data establish Cirbp as a critical protective factor against hypoxic health hazard and provide novel insights into its latent regulation network.

Rearing temperature conditions (constant vs. thermocycle) affect daily rhythms of thermal tolerance and sensing in zebrafish

In the wild, the environment does not remain constant, but periodically oscillates so that temperature rises in the daytime and drops at night, which generates a daily thermocycle. The effects of thermocycles on thermal tolerance have been previously described in fish. However, the impact of thermocycles on daytime-dependent thermal responses and daily rhythms of temperature tolerance and sensing expression mechanisms remain poorly understood. This study investigates the effects of two rearing conditions: constant (26 °C, C) versus a daily thermocycle (28 °C in the daytime; 24 °C at night, T) on the thermal tolerance response in zebrafish. Thermal tolerance (mortality) was assessed in 4dpf (days post fertilization) zebrafish larvae after acute heat shock (39 °C for 1 h) at two time points: middle of the light phase (ML) or middle of the dark phase (MD). Thermal stress responses were evaluated in adult zebrafish after a 37 °C challenge for 1 h at ML or MD to examine the expression of the heat-shock protein (HSP) (hsp70, hsp90ab1, grp94, hsp90aa1, hspb1, hsp47, cirbp) and transient receptor potential (TRP) channels (trpv4, trpm4a, trpm2, trpa1b) in the brain. Finally, the daily rhythms of gene expression of HSPs and TRPs were measured every 4 h for 24 h. The results revealed the larval mortality rates and the expression induction of most HSPs in adult zebrafish brain reached the highest values in fish reared under constant temperature and subjected to thermal shock at MD. The expression of most HSPs and TRPs was mainly synchronized to the light/dark (LD) cycle, regardless of the temperature regime. Most HSPs involved in hyperthermic challenges displayed diurnal rhythms with their acrophases in phase with warm-sensing thermoTRPs acrophases. The cold-sensing trpa1b peaked in the second half of the light period and slightly shifted toward the dark phase anticipating the acrophase of cirpb, which is involved in hypothermic challenges. These findings indicated that: a) thermal shocks are best tolerated in the daytime; b) the implementation of daily thermocycles during larval development reduces mortality and stress-cellular expression of HSPs to an acute thermal stress at MD; c) daily rhythms need to be considered when discussing physiological responses of thermal sensing and thermotolerance in zebrafish.

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.

The regulation of circadian clock by tumor necrosis factor alpha

All organisms display circadian rhythms which are under the control of the circadian clock located in the hypothalamus at the suprachiasmatic nucleus, (SCN). The circadian rhythms allow individuals to adjust their physiological activities and daily behavior for the diurnal changes in the living environment. To achieve these, all metabolic processes are aligned with the sleep/wake and fasting/feeding cycles. Subtle changes of daily behavior or food intake can result in misalignment of circadian rhythms. This can cause development of variety of metabolic diseases and even cancer. Although light plays a pivotal role for the activation of the master clock in SCN, the peripheral secondary clocks (or non-SCN), such as melatonin, growth hormone (GH), insulin, adiponectin and Ghrelin also are important in maintaining the circadian rhythms in the brain and peripheral organs. In recent years, growing body of evidence strongly suggest that CA²⁺ signaling, tumor necrosis factor alpha (TNFα) and transforming growth factor beta (TGFβ) also play very important roles in the regulation of circadian rhythms by regulating the transcription of the clock genes.

A New Vision for Therapeutic Hypothermia in the Era of Targeted Temperature Management: A Speculative Synthesis

Three decades of animal studies have reproducibly shown that hypothermia is profoundly cerebroprotective during or after a central nervous system (CNS) insult. The success of hypothermia in preclinical acute brain injury has not only fostered continued interest in research on the classic secondary injury mechanisms that are prevented or blunted by hypothermia but has also sparked a surge of new interest in elucidating beneficial signaling molecules that are increased by cooling. Ironically, while research into cold-induced neuroprotection is enjoying newfound interest in chronic neurodegenerative disease, conversely, the scope of the utility of therapeutic hypothermia (TH) across the field of acute brain injury is somewhat controversial and remains to be fully defined. This has led to the era of Targeted Temperature Management, which emphasizes a wider range of temperatures (33–36°C) showing benefit in acute brain injury. In this comprehensive review, we focus on our current understandings of the novel neuroprotective mechanisms activated by TH, and discuss the critical importance of developmental age germane to its clinical efficacy. We review emerging data on four cold stress hormones and three cold shock proteins that have generated new interest in hypothermia in the field of CNS injury, to create a framework for new frontiers in TH research. We make the case that further elucidation of novel cold responsive pathways might lead to major breakthroughs in the treatment of acute brain injury, chronic neurological diseases, and have broad potential implications for medicines of the distant future, including scenarios such as the prevention of adverse effects of long-duration spaceflight, among others. Finally, we introduce several new phrases that readily summarize the essence of the major concepts outlined by this review—namely, Ultramild Hypothermia, the “Responsivity of Cold Stress Pathways,” and “Hypothermia in a Syringe.”

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.

A cold-inducible RNA-binding protein (CIRP)-derived peptide attenuates inflammation and organ injury in septic mice

Cold-inducible RNA-binding protein (CIRP) is a novel sepsis inflammatory mediator and C23 is a putative CIRP competitive inhibitor. Therefore, we hypothesized that C23 can ameliorate sepsis-associated injury to the lungs and kidneys. First, we confirmed that C23 dose-dependently inhibited TNF-α release, IκBα degradation, and NF-κB nuclear translocation in macrophages stimulated with CIRP. Next, we observed that male C57BL/6 mice treated with C23 (8 mg/kg BW) at 2 h after cecal ligation and puncture (CLP) had lower serum levels of LDH, ALT, IL-6, TNF-α, and IL-1β (reduced by ≥39%) at 20 h after CLP compared with mice treated with vehicle. C23-treated mice also had improved lung histology, less TUNEL-positive cells, lower serum levels of creatinine (34%) and BUN (26%), and lower kidney expression of NGAL (50%) and KIM-1 (86%). C23-treated mice also had reduced lung and kidney levels of IL-6, TNF-α, and IL-1β. E-selectin and ICAM-1 mRNA was significantly lower in C23-treated mice. The 10-day survival after CLP of vehicle-treated mice was 55%, while that of C23-treated mice was 85%. In summary, C23 decreased systemic, lung, and kidney injury and inflammation, and improved the survival rate after CLP, suggesting that it may be developed as a new treatment for sepsis.

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.

Attenuation of hemorrhage-associated lung injury by adjuvant treatment with C23, an oligopeptide derived from cold-inducible RNA-binding protein

BACKGROUND

Hemorrhagic shock (HS) is an important cause of mortality. HS is associated with an elevated incidence of acute lung injury and acute respiratory distress syndrome, significantly contributing to HS morbidity and mortality. Cold-inducible RNA-binding protein (CIRP) is released into the circulation during HS and can cause lung injury. C23 is a CIRP-derived oligopeptide that binds with high affinity to the CIRP receptor and inhibits CIRP-induced phagocyte secretion of TNF-α. This study was designed to determine whether C23 is able to attenuate HS-associated lung injury.

METHODS

C57BL/6 mice were subjected to controlled hemorrhage leading to a mean arterial pressure of 25 ± 3 mm Hg for 90 minutes. Mice were then volume-resuscitated for 30 minutes with normal saline solution alone (vehicle) or plus adjuvant treatment with C23 (8 mg/kg BW). At 4.5 hours after resuscitation, the blood and lungs were harvested.

RESULTS

Serum levels of organ injury markers lactate dehydrogenase, aspartate aminotransferase were significantly elevated in hemorrhaged mice receiving vehicle and were reduced by 51.3% and 52.2% in mice adjuvantly treated with C23, respectively. Similarly, lung mRNA levels of IL-1β, TNF-α, and IL-6, and lung myeloperoxidase activity were elevated after HS and reduced by 66.1%, 54.4%, 69.7%, and 24.3%, respectively, in mice treated with C23. Adjuvant treatment with C23 also decreased the lung histology score by 33.9%, lung extravasation of albumin carrying Evans blue dye by 36.8%, and the protein level of intercellular adhesion molecule-1, and indicator of vascular endothelial cell activation, by 40.3%.

CONCLUSION

Together, these results indicate that adjuvant treatment with the CIRP-derived oligopeptide C23 is able to improve lung inflammation and vascular endothelial activation secondary to HS, lending support to the development of CIRP-targeting adjuvant treatments to minimize lung injury after HS.

Cold Inducible RNA Binding Protein Is Involved in Chronic Hypoxia Induced Neuron Apoptosis by Down-Regulating HIF-1α Expression and Regulated By microRNA-23a

Background: Neuron apoptosis mediated by hypoxia inducible factor 1α (HIF-1α) in hippocampus is one of the most important factors accounting for the chronic hypobaric hypoxia induced cognitive impairment. As a neuroprotective molecule that is up-regulated in response to various environmental stress, CIRBP was reported to crosstalk with HIF-1α under cellular stress. However, its function under chronic hypobaric hypoxia remains unknown. Objective: In this study, we tried to identify the role of CIRBP in HIF-1α mediated neuron apoptosis under chronic hypobaric hypoxia and find a possible method to maintain its potential neuroprotective in long-term high altitude environmental exposure. Methods: We established a chronic hypobaric hypoxia rat model as well as a tissue culture model where SH-SY5Y cells were exposed to 1% hypoxia. Based on these models, we measured the expressions of HIF-1α and CIRBP under hypoxia exposure and examined the apoptosis of neurons by TUNEL immunofluorescence staining and western blot analysis of apoptosis related proteins. In addition, by establishing HIF-1α shRNA and pEGFP-CIRBP plasmid transfected cells, we confirmed the role of HIF-1α in chronic hypoxia induced neuron apoptosis and identified the influence of CIRBP over-expression upon HIF-1α and neuron apoptosis in the process of exposure. Furthermore, we measured the expression of the reported hypoxia related miRNAs in both models and the influence of miRNAs' over-expression/knock-down upon CIRBP in the process of HIF-1α mediated neuron apoptosis. Results: HIF-1α expression as well as neuron apoptosis was significantly elevated by chronic hypobaric hypoxia both in vivo and in vitro. CIRBP was induced in the early stage of exposure (3d/7d); however as the exposure was prolonged (21d), CIRBP level of the hypoxia group became significantly lower than that of control. In addition, HIF-1α knockdown significantly decreased neuron apoptosis under hypoxia, suggesting HIF-1α may be pro-apoptotic in the process of exposure. CIRBP over-expression significantly suppressed HIF-1α up-regulation in hypoxia and inhibited HIF-1α mediated neuron apoptosis. Interestingly, miR-23a was also induced by hypoxia exposure and showed the same changing tendency with CIRBP (increasing in 3d/7d, decreasing in 21d). In addition, over-expressing miR-23a up-regulated CIRBP, down-regulated HIF-1α and attenuated neuron apoptosis. Conclusion: Cold inducible RNA binding protein is involved in chronic hypoxia induced neuron apoptosis by down-regulating HIF-1α expression, and MiR-23a may be an important tool to maintain CIRBP level and function.

Posttranscriptional mechanisms controlling diurnal gene expression cycles by body temperature rhythms

In mammals, body temperature oscillates in a daily fashion around a set point of 36°C-37°C. These fluctuations are controlled by the circadian master clock residing in the brain's suprachiasmatic nucleus and, despite their small amplitudes, contribute to the diurnal expression of genes throughout the organism. By focusing on the mechanisms underlying the temperature-dependent accumulation of the cold-inducible RNA-binding protein CIRBP - a factor involved in the tuning of amplitude and phase in circadian clocks of peripheral tissues - we have recently identified a novel mechanism governing temperature-dependent gene expression. This mechanism involves the differential spicing efficiency of primary RNA transcripts under different temperature conditions and thereby determines the fraction of Cirbp pre-mRNA processed into mature mRNA. A genome-wide transcriptome analysis revealed that this mechanism affects the output of hundreds of genes. Here we discuss our findings and future directions toward the identification of specific factors and parameters governing temperature-sensitive splicing efficacy.

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.

Temperature regulates splicing efficiency of the cold-inducible RNA-binding protein gene Cirbp

Gotic et al. show that the temperature-dependent accumulation of cold-inducible RNA-binding protein (Cirbp) mRNA is controlled primarily by the regulation of splicing efficiency. As revealed by genome-wide “approach-to-steady-state” kinetics, this post-transcriptional mechanism is widespread in the temperature-dependent control of gene expression.

In mammals, body temperature fluctuates diurnally around a mean value of 36°C–37°C. Despite the small differences between minimal and maximal values, body temperature rhythms can drive robust cycles in gene expression in cultured cells and, likely, animals. Here we studied the mechanisms responsible for the temperature-dependent expression of cold-inducible RNA-binding protein (CIRBP). In NIH3T3 fibroblasts exposed to simulated mouse body temperature cycles, Cirbp mRNA oscillates about threefold in abundance, as it does in mouse livers. This daily mRNA accumulation cycle is directly controlled by temperature oscillations and does not depend on the cells’ circadian clocks. Here we show that the temperature-dependent accumulation of Cirbp mRNA is controlled primarily by the regulation of splicing efficiency, defined as the fraction of Cirbp pre-mRNA processed into mature mRNA. As revealed by genome-wide “approach to steady-state” kinetics, this post-transcriptional mechanism is widespread in the temperature-dependent control of gene expression.

Cold-inducible RNA-binding protein mediates cold air inducible airway mucin production through TLR4/NF-κB signaling pathway

Mucus overproduction is an important feature in patients with chronic inflammatory airway diseases and cold air stimulation has been shown to be associated with the severity of these diseases. However, the regulatory mechanisms that mediate excessive mucin production under cold stress remain elusive. Recently, the cold-inducible RNA-binding protein (CIRP) has been shown to be markedly induced after exposure to cold air. In this study, we sought to explore the expression of CIRP within bronchial biopsy specimens, the effect on mucin5AC (MUC5AC) production in chronic inflammatory airway diseases and the potential signaling pathways involved in cold air stimulation process. We found that CIRP protein expression was significantly increased in patients with COPD and in mice treated with cold air. Moreover, cold air stimulation induced MUC5AC expression in wild-type mice but not in CIRP(-/-) mice. In vitro, cold air stress significantly elevated the transcriptional and protein expression levels of MUC5AC in human bronchial epithelial cells. CIRP, toll-like receptor 4 (TLR4) and phosphorylated NF-κB p65 (p-p65) increased significantly in response to cold stress and CIRP siRNA, TLR4 - neutralizing Ab and a specific inhibitor of NF-κB could attenuated cold stress inducible MUC5AC expression. In addition, CIRP siRNA could hindered the expression levels of TLR4 and p-p65 both induced by cold stress. Taken together, these results suggest that airway epithelial cells constitutively express CIRP in vitro and in vivo. CIRP is responsible for cold-inducible MUC5AC expression by activating TLR4/NF-κB signaling pathway.

Involvement of Cold Inducible RNA-Binding Protein in Severe Hypoxia-Induced Growth Arrest of Neural Stem Cells In Vitro

Neonatal hypoxia is the leading cause of brain damage with birth complications. Many studies have reported proliferation-promoting effect of mild hypoxia on neural stem cells (NSCs). However, how severe hypoxia influences the behavior of NSCs has been poorly explored. In the present study, we investigated the effects of 5, 3, and 1 % oxygen exposure on NSCs in vitro. MTT, neurosphere assay, and 5-ethynyl-2′-deoxyuridine (EdU) incorporation revealed a quick growth arrest of C17.2 cells and primary NSCs induced by 1 % oxygen exposure. Cell cycle analysis showed that this hypoxia exposure caused a significant increase of cells in G0/G1 phase and decrease of cells in S phase that is associated with decrease of Cyclin D1. Interestingly, the expression of cold inducible RNA-binding protein (CIRBP), a cold responsive gene reacting to multiple cellular stresses, was decreased in parallel with the 1 % oxygen-induced proliferation inhibition. Forced expression of CIRBP under hypoxia could restore the proliferation of NSCs, as showed by EdU incorporation and cell cycle analysis. Furthermore, the expression of Cyclin D1 under hypoxia was also restored by CIRBP overexpression. Taken together, these data suggested a growth-suppressing effect of severe hypoxia on NSCs and, for the first time, revealed a novel role of CIRBP in hypoxia-induced cell cycle arrest, suggesting that modulating CIRBP may be utilized for preventing hypoxia-induced neonatal brain injury.

Cold-inducible RNA-binding protein plays a central role in the pathogenesis of abdominal aortic aneurysm in a murine experimental model

BACKGROUND

Cold-inducible RNA-binding protein (CIRP) is a recently identified proinflammatory cytokine. We hypothesize that CIRP is involved in the progression of abdominal aortic aneurysms (AAA) and that anti-CIRP treatment could inhibit this progression.

METHODS

We investigated CIRP expression in the sera and aneurysmal tissues of human AAA patients and elastase-induced AAA rats. To further examine the role of CIRP in the development of AAA, anti-CIRP antibody (1 mg/kg) or nonimmunized control immunoglobulin (Ig)G (1 mg/kg) was injected via the caudal vein in the experimental AAA model. To further investigate the underlying mechanisms, RAW 267.4 cells were stimulated with recombinant murine CIRP (rmCIRP).

RESULTS

In human AAA tissue, CIRP exhibited a 5.6-fold and 93% increase in mRNA and protein expression, respectively. In a rat AAA model, CIRP was upregulated significantly in a time-dependent manner in the serum and AAA tissue. The anti-CIRP antibody treatment significantly suppressed the dilation of experimental AAA. Simultaneously, inhibition of CIRP significantly attenuated the expression of matrix metalloproteinase (MMP)-2, MMP-9, tumor necrosis factor-α, and monocyte chemoattractant protein-1, and the number of CD68-positive macrophages in the experimental AAA tissue. In vitro, rmCIRP significantly increased MMP-9 messenger RNA expression in a dose-dependent manner by 1.2-fold, 2.9-fold, and 5.5-fold, respectively. Simultaneously, rmCIRP promoted RAW 264.7 cell migration, with an approximately 2.7-fold increase in the number of migrated cells.

CONCLUSION

Our findings demonstrate that CIRP mediates experimental AAA development by promoting the inflammatory response and inducing MMP-9 expression, demonstrating its potential as a novel target for inhibiting the progression of AAA.

Altered energy intake and the amplitude of the body temperature rhythm are associated with changes in phase, but not amplitude, of clock gene expression in the rat suprachiasmatic nucleus in vivo

Circadian rhythms in mammals are driven by a central clock in the suprachiasmatic nucleus (SCN). In vitro, temperature cycles within the physiological range can act as potent entraining cues for biological clocks. We altered the body temperature (Tc) rhythm in rats by manipulating energy intake (EI) to determine whether EI-induced changes in Tc oscillations are associated with changes in SCN clock gene rhythms in vivo. Male Wistar rats (n = 16 per diet) were maintained on either an ad libitum diet (CON), a high energy cafeteria diet (CAF), or a calorie restricted diet (CR), and Tc was recorded every 30 min for 6-7 weeks. SCN tissue was harvested from rats at zeitgeber time (ZT) 0, ZT6, ZT12, or ZT18. Expression of the clock genes Bmal1, Per2, Cry1, and Rev-erbα, the heat shock transcription factor Hsf1, and the heat shock protein Hsp90aa1, were determined using qPCR. The circadian profile of gene expression for each gene was characterized using cosinor analysis. Compared to the CON rats, the amplitude of Tc was decreased in CAF rats by 0.1 °C (p < 0.001), and increased in CR rats by 0.3 °C (p < 0.001). The amplitude of Hsp90aa1 expression was lowest in CAF rats and highest in CR rats (p = 0.045), but the amplitude of all of the clock genes and Hsf1 were unaffected by diet (p > 0.25). Compared to CON, phase advances of the Tc, Bmal1, and Per2 rhythms were observed with CR feeding (p < 0.05), but CAF feeding elicited no significant changes in phase. The present results indicate that in vivo, the SCN is largely resistant to entrainment by EI-induced changes in the Tc rhythm, although some phase entrainment may occur.

A deficiency in cold-inducible RNA-binding protein accelerates the inflammation phase and improves wound healing

Chronic or non-healing wounds are a major concern in clinical practice and these wounds are mostly associated with diabetes, and venous and pressure ulcers. Wound healing is a complex process involving overlapping phases and the primary phase in this complex cascade is the inflammatory state. While inflammation is necessary for wound healing, a prolonged inflammatory phase leads to impaired healing. Cold-inducible RNA-binding protein (CIRP) belongs to a family of cold-shock proteins that are expressed in high levels under stress conditions. Recently, we demonstrated that a deficiency in CIRP led to decreased inflammation and mortality in an experimental model of hemorrhagic shock. Thus, we hypothesized that a deficiency in CIRP would accelerate the inflammatory phase and lead to an improvement in cutaneous wound healing. In this study, to examine this hypothesis, a full-thickness wound was created on the dorsum of wild-type (WT) and CIRP-/- mice. The wound size was measured every other day for 14 days. The wound area was significantly decreased in the CIRP-/- mice by day 9 and continued to decrease until day 14 compared to the WT mice. In a separate cohort, mice were sacrificed on days 3 and 7 after wounding and the skin tissues were harvested for histological analysis and RNA measurements. On day 3, the mRNA expression of tumor necrossis factor (TNF)-α in the skin tissues was increased by 16-fold in the WT mice, whereas these levels were increased by 65-fold in the CIRP-/- mice. Of note on day 7, while the levels of TNF-α remained high in the WT mice, these levels were significantly decreased in the CIRP-/- mice. The histological analysis of the wounded skin tissue indicated an improvement as early as day 3 in the CIRP-/- mice, whereas in the WT mice, infiltrated immune cells were still present on day 7. On day 7 in the CIRP-/- mice, Gr-1 expression was low and CD31 expression was high, whereas in the WT mice, Gr-1 expression was high and CD31 expression was low, indicating that the CIRP-/- mice have already moved into the angiogenesis and tissue formation phase, whereas the WT mice were still in the inflammatory state. These data collectively suggest that a deficiency in CIRP accelerates the wound healing process.

Mild hypothermia inhibits differentiation of human embryonic and induced pluripotent stem cells

Culture of pluripotent stem cells at 35°C strikingly reduces unwanted spontaneous differentiation during hESC and iPSC maintenance compared with 37°C. Growth at 35°C did not affect expression of pluripotency mRNAs nor induce expression of cold-inducible genes. Colony size was somewhat reduced at 35°C. Thus, growth at 35°C is a convenient, simple method to reduce the labor of removing spontaneously differentiated colonies when maintaining pluripotent cells.

Molecular characterization of RNA binding motif protein 3 (RBM3) gene from Pashmina goat

Pashmina goat inhabits the high altitude cold arid desert of Ladakh, India. This goat is known for its finest and costliest under fiber. Though the under fiber may be a part of its complex thermoregulation mechanism, the genetics of its adaptability under cold conditions is not known. As an attempt to understand its adaptive genetics, and the role of RNA-binding proteins at the cellular response, this study was conducted to characterize the RBM3 gene in Pashmina goat and its expression during hypothermia. The ORF of Pashmina RBM3 gene was 273 bp. Phylogenetic analysis revealed that Pashmina RBM3 is closely related to Bos taurus RBM3. Pashmina RBM3 was characterized by comparative modeling studies. The final 3-D model contained two α-helices and four β-sheets. qRT-PCR data showed that Pashmina RBM3 gene expression was significantly higher (P < 0.05) at moderate (30 °C) hypothermic stress conditions as compared with deep (15 °C) hypothermia.

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.

Cold-inducible RNA-binding protein mediates neuroinflammation in cerebral ischemia

BACKGROUND

Neuroinflammation is a key cascade after cerebral ischemia. Excessive production of proinflammatory mediators in ischemia exacerbates brain injury. Cold-inducible RNA-binding protein (CIRP) is a newly discovered proinflammatory mediator that can be released into the circulation during hemorrhage or septic shock. Here, we examine the involvement of CIRP in brain injury during ischemic stroke.

METHODS

Stroke was induced by middle cerebral artery occlusion (MCAO). In vitro hypoxia was conducted in a hypoxia chamber containing 1% oxygen. CIRP and tumor necrosis factor-α (TNF-α) levels were assessed by RT-PCR and Western blot analysis.

RESULTS

CIRP is elevated along with an upregulation of TNF-α expression in mouse brain after MCAO. In CIRP-deficient mice, the brain infarct volume, induction of TNF-α, and activation of microglia are markedly reduced after MCAO. Using microglial BV2 cells, we demonstrate that hypoxia induces the expression, translocation, and release of CIRP, which is associated with an increase of TNF-α levels. Addition of recombinant murine (rm) CIRP directly induces TNF-α release from BV2 cells and such induction is inhibited by neutralizing antisera to CIRP. Moreover, rmCIRP activates the NF-κB signaling pathway in BV2 cells. The conditioned medium from BV2 cells exposed to hypoxia triggers the apoptotic cascade by increasing caspase activity and decreasing Bcl-2 expression in neural SH-SY5Y cells, which is inhibited by antisera to CIRP.

CONCLUSION

Extracellular CIRP is a detrimental factor in stimulating inflammation to cause neuronal damage in cerebral ischemia.

GENERAL SIGNIFICANCE

Development of an anti-CIRP therapy may benefit patients with brain ischemia.

Tumor necrosis factor and transforming growth factor β regulate clock genes by controlling the expression of the cold inducible RNA-binding protein (CIRBP)

The circadian clock drives the rhythmic expression of a broad array of genes that orchestrate metabolism, sleep wake behavior, and the immune response. Clock genes are transcriptional regulators engaged in the generation of circadian rhythms. The cold inducible RNA-binding protein (CIRBP) guarantees high amplitude expression of clock. The cytokines TNF and TGFβ impair the expression of clock genes, namely the period genes and the proline- and acidic amino acid-rich basic leucine zipper (PAR-bZip) clock-controlled genes. Here, we show that TNF and TGFβ impair the expression of Cirbp in fibroblasts and neuronal cells. IL-1β, IL-6, IFNα, and IFNγ do not exert such effects. Depletion of Cirbp is found to increase the susceptibility of cells to the TNF-mediated inhibition of high amplitude expression of clock genes and modulates the TNF-induced cytokine response. Our findings reveal a new mechanism of cytokine-regulated expression of clock genes.

Cold-inducible RNA-binding protein (CIRP) triggers inflammatory responses in hemorrhagic shock and sepsis

Excessive production of proinflammatory mediators is observed in patients undergoing hemorrhagic and septic shock. Here, we report the detection of cold-inducible RNA-binding protein (CIRP) in the blood of surgical ICU individuals. In animal models of hemorrhage and sepsis, CIRP is up-regulated in several organs and released into the circulation. Under hypoxic stresses, CIRP in macrophages is translocated from the nucleus to the cytosol and actively released. Recombinant CIRP stimulates TNF-α and HMGB1 release in macrophages as well as induces inflammatory responses and causes tissue injury in animals. Antisera to CIRP attenuate shock-induced inflammation, tissue injury, and lethality. Extracellular CIRP's activity is mediated through the TLR4/MD2 complex. Surface plasmon resonance analysis indicates that CIRP binds to the TLR4/MD2 complex as well as to individual TLR4 and MD2. The human CIRP amino-acid segment 106-125 binds to MD2 with high affinity. Collectively, CIRP is a new proinflammatory mediator of shock.

Effects of moderate and deep hypothermia on RNA-binding proteins RBM3 and CIRP expressions in murine hippocampal brain slices

Therapeutic hypothermia has emerged as an effective neuroprotective therapy for cardiac arrest survivors. There are a number of purported mechanisms for therapeutic hypothermia, but the exact mechanism still remains to be elucidated. Although hypothermia generally down-regulates protein synthesis and metabolism in mammalian cells, a small subset of homologous (>70%) cold-shock proteins (RNA-binding motif protein 3, RBM3 and cold-inducible RNA-binding protein, CIRP) are induced under these conditions. In addition, RBM3 up-regulation in neuronal cells has recently been implicated in hypothermia-induced neuroprotection. Therefore, we compared the effects of moderate (33.5°C) and deep (17°C) hypothermia with normothermia (37°C) on the regulation of RBM3 and CIRP expressions in murine organotypic hippocampal slice cultures (OHSC), hippocampal neuronal cells (HT-22), and microglia cells (BV-2). Moderate hypothermia resulted in significant up-regulation of both RBM3 and CIRP mRNA in murine OHSC, but deep hyporthermia did not. RBM3 protein regulation was also significantly up-regulated by 33.5°C, but no significant up-regulation of CIRP protein was observed in the OHSC. Additionally, OHSC exposed to 17°C for 24h were positive for Propidium Iodide (PI) immunostaining, indicating the onset of cell death. Similarly, RBM3 gene expression in a HT-22 neuronal cells mono-culture and direct co-culture of HT-22 neuronal cells with BV-2 microglia cells were also up-regulated at 33.5°C but only in the co-culture at 17°C. No significant up-regulation of RBM3 nor CIRP gene expression were observed in a BV-2 mono-culture at either temperature. We observed that RBM3 mRNA and protein expressions in murine OHSC, as well as in mono-culture of HT-22 neuronal cells and direct co-culture of HT-22 neuronal cells with BV-2 microglia cells were significantly up-regulated by exposure to moderate hypothermia. These findings further support the implication of RBM3 as a potential effector for hypothermia-induced neuroprotection.

Mild hypothermia facilitates the expression of cold-inducible RNA-binding protein and heat shock protein 70.1 in mouse brain

An appropriate thermal control system is essential for maintaining brain homeostasis. Hypothermia is a decrease in core body temperature that occurs when the thermoregulatory responses of homeothermic animals are impaired by environmental and situational influences, such as cold ambience and anesthesia. In recent years, hypothermia has been used for medical treatment, i.e., therapeutic hypothermia, for patients with stroke, traumatic brain injury, and heart surgery. However, the target molecules acting during hypothermia have not been identified. To understand the molecular mechanisms, we generated a mouse model of mild hypothermia (1°C-2°C below normal), and analyzed the expression of several genes. After mice were exposed to cold for 24 and 48 h, their rectal temperature reached 33°C-35°C. Then, using real-time quantitative PCR, we analyzed the mRNA expression levels of c-fos, cold-inducible RNA-binding protein (CIRP), heat shock protein (hsp) 70.1, oxytocin, and representative inflammatory cytokines, i.e., tumor necrosis factor (TNF)-α and interleukin (IL)-6 in target organs. Importantly, we found that the expression levels of CIRP and hsp70.1 were elevated in the olfactory bulb within 48 h. In the hypothalamus, CIRP expression levels increased and were followed by an increase in hsp70.1 expression. Meanwhile, TNF-α and IL-6 expression decreased gradually over 24 and 48 h in the olfactory bulb and hypothalamus. These specific expression profiles, i.e., enhanced CIRP and hsp70.1 expression and depressed cytokine expression, suggest that they could regulate apoptosis related to the cytokine signaling.

Spotlight on post-transcriptional control in the circadian system

An endogenous timing mechanism, the circadian clock, causes rhythmic expression of a considerable fraction of the genome of most organisms to optimally align physiology and behavior with their environment. Circadian clocks are self-sustained oscillators primarily based on transcriptional feedback loops and post-translational modification of clock proteins. It is increasingly becoming clear that regulation at the RNA level strongly impacts the cellular circadian transcriptome and proteome as well as the oscillator mechanism itself. This review focuses on posttranscriptional events, discussing RNA-binding proteins that, by influencing the timing of pre-mRNA splicing, polyadenylation and RNA decay, shape rhythmic expression profiles. Furthermore, recent findings on the contribution of microRNAs to orchestrating circadian rhythms are summarized.

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

The cell cycle regulator cyclin E1 is aberrantly expressed in a variety of human cancers. In breast cancer, elevated cyclin E1 correlates with poor outcome, as do high cytoplasmic levels of the stress-induced RNA-binding protein human antigen R (HuR). We showed previously that increased cytoplasmic HuR elevates cyclin E1 in MCF-7 breast cancer cells by stabilizing its mRNA. We show here that cold-inducible RNA-binding protein (CIRP) co-regulates cyclin E1 with HuR in breast cancer cells. CIRP had been shown to interact with HuR in Xenopus laevis oocytes and to be decreased in endometrial cancer. To investigate if human CIRP and HuR co-regulate cyclin E1, HuR and CIRP levels were altered in MCF-7 cells and effects on cyclin E1 assessed. Altering HuR expression resulted in a reciprocal change in CIRP expression, while altering CIRP expression resulted in corresponding changes in HuR and cyclin E1 expression. CIRP and HuR co-precipitated in the presence of RNA and CIRP enhanced HuR binding to the cyclin E1 mRNA and increased cyclin E1 mRNA stability. CIRP co-localized with HuR predominantly in the nucleus, but also in discrete cytoplasmic foci identified as stress granules (SGs). CIRP overexpression increased the number of HuR-containing SGs, while its knockdown decreased them. Our results suggest that CIRP positively regulates HuR, ultimately resulting in increased protein synthesis of at least one of its targets.

Cold-inducible RNA binding protein (CIRP) expression is modulated by alternative mRNAs

Cold-inducible RNA binding protein (CIRP) is a mammalian protein whose expression is up-regulated in response to mild hypothermia. Although the exact function of this protein is currently unknown, it is thought to function as an RNA chaperone, facilitating mRNA translation upon the perception of cold stress. In this study we have identified and characterized the major CIRP 5'-untranslated region (5'-UTR) transcripts in mouse embryonic fibroblast NIH-3T3 cells. We show that the 5'-UTR of CIRP, a protein highly homologous to the cold-shock protein Rbm3, is much shorter than the previously published 5' leader sequence of Rbm3. In addition, three major CIRP transcripts with different transcription start sites are generated, with the levels of each of these transcripts being regulated in response to time and temperature. The major transcript generated at 37 degrees C does not encode for the full-length CIRP open reading frame, while the two major transcripts at 32 degrees C do. Further, the longest transcript detected at 32 degrees C shows a discrete expression and stability profile under mild hypothermic conditions and exhibits internal ribosome entry segment (IRES)-like activity. The IRES-like activity is not responsive to conditions of mild hypothermia or hypoxia, but the levels and stability of the transcript harboring the putative IRES are increased at 32 degrees C. We discuss the emerging transcriptional and translational mechanisms by which CIRP expression appears to be controlled and the role that the 5'-UTR plays in the modulation of CIRP expression.

Cold-inducible RNA-binding protein bypasses replicative senescence in primary cells through extracellular signal-regulated kinase 1 and 2 activation

Embryonic stem cells are immortalized cells whose proliferation rate is comparable to that of carcinogenic cells. To study the expression of embryonic stem cell genes in primary cells, genetic screening was performed by infecting mouse embryonic fibroblasts (MEFs) with a cDNA library from embryonic stem cells. Cold-inducible RNA-binding protein (CIRP) was identified due to its ability to bypass replicative senescence in primary cells. CIRP enhanced extracellular signal-regulated kinase 1 and 2 (ERK1/2) phosphorylation, and treatment with an MEK inhibitor decreased the proliferation caused by CIRP. In contrast to CIRP upregulation, CIRP downregulation decreased cell proliferation and resulted in inhibition of phosphorylated ERK1/2 inhibition. This is the first evidence that ERK1/2 activation, through the same mechanism as that described for a Val12 mutant K-ras to induce premature senescence, is able to bypass senescence in the absence of p16(INK4a), p21(WAF1), and p19(ARF) upregulation. Moreover, these results show that CIRP functions by stimulating general protein synthesis with the involvement of the S6 and 4E-BP1 proteins. The overall effect is an increase in kinase activity of the cyclin D1-CDK4 complex, which is in accordance with the proliferative capacity of CIRP MEFs. Interestingly, CIRP mRNA and protein were upregulated in a subgroup of cancer patients, a finding that may be of relevance for cancer research.

Two isoforms of the cold-inducible mRNA-binding protein RBM3 localize to dendrites and promote translation

A diverse set of mRNA-binding proteins (BPs) regulate local translation in neurons. However, little is known about the role(s) played by a family of cold-inducible, glycine-rich mRNA-BPs. Unlike neuronal mRNA-BPs characterized thus far, these proteins are induced by hypothermia and are comprised of one RNA recognition motif and an adjacent arginine- and glycine-rich domain. We studied the expression and function of the RNA-binding motif protein 3 (RBM3), a member of this family, in neurons. RBM3 was expressed in multiple brain regions, with the highest levels in cerebellum and olfactory bulb. In dissociated neurons, RBM3 was observed in nuclei and in a heterogeneous population of granules within dendrites. In sucrose gradient assays, RBM3 cofractionated with heavy mRNA granules and multiple components of the translation machinery. Two alternatively spliced RBM3 isoforms that differed by a single arginine residue were identified in neurons; both were post-translationally modified. The variant lacking the spliced arginine exhibited a higher dendritic localization and was the only isoform present in astrocytes. When overexpressed in neuronal cell lines, RBM3 isoforms-enhanced global translation, the formation of active polysomes, and the activation of initiation factors. These data suggest that RBM3 plays a distinctive role in enhancing translation in neurons.

System-driven and oscillator-dependent circadian transcription in mice with a conditionally active liver clock

The mammalian circadian timing system consists of a master pacemaker in neurons of the suprachiasmatic nucleus (SCN) and clocks of a similar molecular makeup in most peripheral body cells. Peripheral oscillators are self-sustained and cell autonomous, but they have to be synchronized by the SCN to ensure phase coherence within the organism. In principle, the rhythmic expression of genes in peripheral organs could thus be driven not only by local oscillators, but also by circadian systemic signals. To discriminate between these mechanisms, we engineered a mouse strain with a conditionally active liver clock, in which REV-ERBalpha represses the transcription of the essential core clock gene Bmal1 in a doxycycline-dependent manner. We examined circadian liver gene expression genome-wide in mice in which hepatocyte oscillators were either running or arrested, and found that the rhythmic transcription of most genes depended on functional hepatocyte clocks. However, we discovered 31 genes, including the core clock gene mPer2, whose expression oscillated robustly irrespective of whether the liver clock was running or not. By contrast, in liver explants cultured in vitro, circadian cycles of mPer2::luciferase bioluminescence could only be observed when hepatocyte oscillators were operational. Hence, the circadian cycles observed in the liver of intact animals without functional hepatocyte oscillators were likely generated by systemic signals. The finding that rhythmic mPer2 expression can be driven by both systemic cues and local oscillators suggests a plausible mechanism for the phase entrainment of subsidiary clocks in peripheral organs.

Control and regulation of the cellular responses to cold shock: the responses in yeast and mammalian systems

Although the cold-shock response has now been studied in a number of different organisms for several decades, it is only in the last few years that we have begun to understand the molecular mechanisms that govern adaptation to cold stress. Notably, all organisms from prokaryotes to plants and higher eukaryotes respond to cold shock in a comparatively similar manner. The general response of cells to cold stress is the elite and rapid overexpression of a small group of proteins, the so-called CSPs (cold-shock proteins). The most well characterized CSP is CspA, the major CSP expressed in Escherichia coli upon temperature downshift. More recently, a number of reports have shown that exposing yeast or mammalian cells to sub-physiological temperatures (<30 or <37 degrees C respectively) invokes a co-ordinated cellular response involving modulation of transcription, translation, metabolism, the cell cycle and the cell cytoskeleton. In the present review, we summarize the regulation and role of cold-shock genes and proteins in the adaptive response upon decreased temperature with particular reference to yeast and in vitro cultured mammalian cells. Finally, we present an integrated model for the co-ordinated responses required to maintain the viability and integrity of mammalian cells upon mild hypothermic cold shock.

Xenopus Cold-inducible RNA-binding Protein 2 Interacts with ElrA, the Xenopus Homolog of HuR, and Inhibits Deadenylation of Specific mRNAs

Xenopus cold-inducible RNA-binding protein 2 (xCIRP2) is a major cytoplasmic RNA-binding protein in oocytes. In this study, we identify another RNA-binding protein ElrA, the Xenopus homolog of HuR, as an interacting protein of xCIRP2 by yeast two-hybrid screening. As ElrA stabilizes the RNA body in the in vitro mRNA stability system, we examine the role of xCIRP2 in the stabilization of mRNA and find that xCIRP2 inhibits deadenylation of AU-rich element-containing mRNA. These results suggest that xCIRP2 and ElrA may be involved in the regulation of mRNA stability at different steps. By immunoprecipitation with anti-xCIRP2 antibody, we find that xCIRP2 interacts with several mRNAs including mRNA encoding the centrosomal kinase Nek2B in oocytes. xCIRP2 also inhibits deadenylation of the mRNA substrate containing the 3'-untranslated region of Nek2B mRNA in the in vitro system. Our results suggest that xCIRP2 associates with specific mRNAs and can regulate the length of poly(A) tail in Xenopus oocytes.

Expression of cold-inducible RNA-binding protein in the normal endometrium, endometrial hyperplasia, and endometrial carcinoma

Cold-inducible RNA-binding protein (CIRP), an 18-kD protein in the mouse and human, is induced by lowering the temperature of cultured cells. CIRP is possibly a cell cycle regulator because its overexpression results in prolongation of G1 phase in vitro. We investigated the immunohistochemical expression of CIRP in 39 endometrial carcinomas, 12 endometrial hyperplasias, and 27 normal endometria using polyclonal antibody against CIRP and confirmed by Western blot analysis. CIRP was localized in the nuclei of glandular, stromal, and endothelial cells. The intensity of CIRP expression in glandular cells during the menstrual cycle was inversely proportional to its proliferative (Ki-67) activity, whereas it remained unchanged in stromal and vascular endothelial cells. The intensity of CIRP expression in hyperplastic glands was variable, whereas CIRP expression was absent or markedly reduced in most of the endometrial carcinomas. These results suggest that CIRP may participate in the cell cycle regulation of normal endometrium and the loss of its expression may be involved in endometrial carcinogenesis.

Maternal cold inducible RNA binding protein is required for embryonic kidney formation in Xenopus laevis

We cloned a major isoform of Xenopus homologue of cold inducible RNA binding protein (CIRP), XCIRP-1. XCIRP-1 was neither cold inducible nor essential for cell division during early embryonic development. Suppression of XCIRP-1 dose dependently produced tailbuds with deformations of the brain and internal organs. The defects were XCIRP-1 specific as they could be rescued by sense transcript. Suppression of XCIRP-1 also disrupted the morphogenetic migration of the C3 blastomeres (lineaged to become the embryonic kidney, the pronephros). In animal cap explants, depletion of XCIRP-1 inhibited activin/retinoic acid induced expressions of pronephros related Xlim-1 and WT1 genes. These results suggest that XCIRP-1 is required for the specification and morphogenetic lineage migration of the pronephros.

Cloning and characterization of amphibian cold inducible RNA-binding protein

Gene expression of cold inducible RNA-binding protein (CIRP) was examined in the frog. In Xenopus laevis, expression of CIRP (XCIRP) was observed in both brain and liver at 24 degrees C. Circadian expression of XCIRP was observed in brain. Expression of XCIRP in brain was induced by cold treatment and gradually decreased to the control level at 24 degrees C, but no significant changes were observed in liver. Employing the sequence of murine CIRP, bullfrog (Rana catesbeiana) CIRP gene was cloned. The bullfrog CIRP gene, designated BFCIRP, was 706 bp in length and encoded a putative protein of 164 amino acid residues. The deduced protein contained one consensus sequence of RNA-binding domain (CS-RBD) and a glycine rich domain (GRD). The amino acid sequence of BFCIRP was 78.4% identical to XCIRP. Expression of BFCIRP in brain was stronger in winter than that in summer. These findings suggest that BFCIRP expression in brain may link to hibernation.

Effects of ischemia and H2O2 on the cold stress protein CIRP expression in rat neuronal cells

Expression of CIRP (cold-inducible RNA-binding protein) is inducible at 32 degrees C in cultured fibroblasts. Because ischemia is known to induce expression of heat shock proteins, its effect on the CIRP expression was examined using the rat transient forebrain ischemia model. The isolated rat CIRP cDNA encoded amino acids 100% identical in its sequence to mouse CIRP. Northern blot analysis revealed that the CIRP transcripts were ubiquitously expressed in various tissues. In situ hybridization histochemistry of normal rat brain revealed the expression of CIRP in neurons in the hippocampus and the cerebral cortex among others. In the hippocampus of postischemic rats, CIRP mRNA level decreased from 3-6 h after the onset of reperfusion, while it did not change in the cerebral cortex. When PC12 pheochromocytoma cells were cultured at 32 degrees C, the CIRP mRNA level was increased. The presence of H2O2 in the culture media inhibited dose dependently this induction as well as constitutive expression, suggesting that the effect of brain ischemia on CIRP expression is related to generation of reactive oxygen species. Further studies are necessary to clarify the roles played by cold shock proteins in the hypothermic therapy of brain damages.