Cold-inducible RNA-binding Protein Expression Research Articles

Cold-inducible RNA binding protein inhibits H2O2-induced apoptosis in rat cortical neurons

Objective The expression cold-inducible RNA-binding protein (CIRP) is significantly enhanced in neurons under hypothermia,but its roles remain unclear.This study aims to investigate whether the cerebral protection under hypothermia is mediated by the CIRP-mediated inhibition of neuronal apoptosis.Methods Primary rat cortical neurons were isolated,cultured,and transduced with lentiviral CIRP-RNAi.Apoptosis of the transduced neurons was induced with 100 μmol/L H2O2.The treated cells were divided into two groups,and cultured in 37℃ or 32℃ incubator respectively.Cell viability was detected by MTT colorimetric assay.Neuronal apoptosis was detected by flow cytometry after labeling the cells with Hoechst 33342 and Annexin V-FITC/PI.The protein expressions of CIRP,activated Caspase-3,and thioredoxin (TRX) were detected by Western blot.Results Under 32℃,CIRP protein was significantly induced in cortical neurons; the expression of activated Caspase-3 was decreased,while the TRX expression was increased.The rate of neuronal apoptosis was (4.5 ± 0.8) ％.Under 37 ℃,CIRP expression was evidently reduced in cortical neurons; the expression of activated caspase-3 was significantly enhanced,and TRX expression was reduced.The rate of neuronal apoptosis reaches (53.5 ± 1.7) ％ (P＜ 0.05,compared to that in 32 ℃ group).Conclusions The induction of CIRP protein in rat cortical neurons under hypothermia inhibits H2O2-induced neuronal apoptosis and thereby exerts neuroprotective effect,which forms one of the cerebral protective pathways under hypothermia. Key words: Cold-inducible RNA-binding protein; Neurons; Cerebral cortex ; Apoptosis; Hypothermia

Difference in the expression of CIRBP, RBM3 and HSP70 in the myocardium and cerebellum after death by hypothermia and carbon monoxide poisoning

We studied the expression of hypoxia-related antigens (e.g., cold-inducible antigens and apoptotic antigens) in the myocardium and the cerebellumthat were obtained from individuals after death by carbon monoxide or hypothermia. The immunohistochemistry results revealed that expression of cold-inducible RNA binding protein (CIRBP) and RNA-binding protein 3 (RBM3) may be associated with hpyothermic and the hypoxic conditions. The expression of CIRBP and RBM3 in the myocardium was different from their expression in the cerebellum, especially in the Purkinje cells. The results indicate that agonal duration influences antigen expression. In the hypothermic condition, the myocardium uses more ATP since the force of the excitation-contraction coupling of the myocardium increases by more than 400% when the experimental temperature is reduced from 35°C to 25°C. The results obtained in this study indicate that physicians should pay attention to the myocardium when cooling the patient's body to protect the brain. Key W ords: carbon monoxide death, cerebellum, CIRBP, hypothermic death, myocardium, RBM3.

Ketogenic diet and fasting induce the expression of cold-inducible RNA-binding protein with time-dependent hypothermia in the mouse liver

Cold-inducible RNA-binding protein (CIRBP) induced by cold stress modulates the molecular circadian clock in vitro. The present study examines the effect of a ketogenic diet (KD) and fasting on Cirbp expression in the mouse liver. Chronic KD administration induced time-dependent Cirbp expression with hypothermia in mice. The circadian expression of clock genes such as Bmal1 and Clock was phase-advanced and augmented in the liver of mice fed with a KD. Transient food deprivation also induced time-dependent Cirbp expression with hypothermia in mice. These findings suggest that hypothermia is involved in the increased expression of Cirbp under ketogenic or fasting conditions.

Identification of a novel enhancer that binds Sp1 and contributes to induction of cold-inducible RNA-binding protein (cirp) expression in mammalian cells

BackgroundThere are a growing number of reports on the sub-physiological temperature culturing of mammalian cells for increased recombinant protein yields. However, the effect varies and the reasons for the enhancement are not fully elucidated. Expression of cold-inducible RNA-binding protein (cirp, also called cirbp or hnRNP A18) is known to be induced in response to mild, but not severe, hypothermia in mammalian cells. To clarify the molecular mechanism underlying the induction and to exploit this to improve the productivity of recombinant proteins, we tried to identify the regulatory sequence(s) in the 5′ flanking region of the mouse cirp gene.ResultsBy transiently transfecting HEK293 cells with plasmids expressing chloramphenicol acetyltransferase as a reporter, we found that the cirp 5′ flanking region octanucleotide 5′-TCCCCGCC-3′ is a mild-cold responsive element (MCRE). When 3 copies of MCRE were placed upstream of the CMV promoter and used in transient transfection, reporter gene expression was increased 3- to 7-fold at 32°C relative to 37°C in various cell lines including HEK293, U-2 OS, NIH/3T3, BALB/3T3 and CHO-K1 cells. In stable transfectants, MCRE also enhanced the reporter gene expression at 32°C, although more copy numbers of MCRE were necessary. Sp1 transcription factor bound to MCRE in vitro. Immunohistochemistry and chromatin immunoprecipitation assays demonstrated that more Sp1, but not Sp3, was localized in the nucleus to bind to the cirp regulatory region containing MCRE at 32°C than 37°C. Overexpression of Sp1 protein increased the expression of endogenous Cirp as well as a reporter gene driven by the 5′ flanking region of the cirp gene, and down-regulation of Sp1 had the opposite effect. Mutations within the MCRE sequence in the 5′ flanking region abolished the effects of Sp1 on the reporter gene expression both at 37°C and 32°C.ConclusionsCold-induced, as well as constitutive, expression of cirp is dependent, at least partly, on MCRE and Sp1. The present novel enhancer permits conditional high-level gene expression at moderately low culture temperatures and could be utilized to increase the yield of recombinant proteins in mammalian cells.

Downregulation of cold-inducible RNA-binding protein activates mitogen-activated protein kinases and impairs spermatogenic function in mouse testes

Cold-inducible RNA-binding protein (CIRP) is an RNA-binding protein that is expressed in normal testes and downregulated after heat stress caused by cryptorchidism, varicocele or environmental temperatures. The purpose of this study was to investigate the functions of CIRP in the testes. We employed RNAi technique to knock down the expression of CIRP in the testes, and performed haematoxylin and eosin staining to evaluate morphological changes following knockdown. Germ cell apoptosis was examined by terminal deoxynucleotidal transferase-mediated dUTP nick end labelling (TUNEL) assay, and mitogen-activated protein kinase (MAPK) signalling pathways were investigated by Western blotting to determine the possible mechanism of apoptosis. We found that using siRNA is a feasible and reliable method for knocking down gene expression in the testes. Compared to controls, the mean seminiferous tubule diameter (MSTD) and the thickness of the germ cell layers decreased following siRNA treatment, whereas the percentage of apoptotic seminiferous tubules increased. The p44/p42, p38 and SAPK/JNK MAPK pathways were activated after downregulation of CIRP. In conclusion, we discovered that downregulation of CIRP resulted in increased germ cell apoptosis, possibly via the activation of the p44/p42, p38 and SAPK/JNK MAPK pathways.

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 48h, 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 48h. 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 48h 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.

Cold-inducible RNA binding protein inhibits H2O2-induced apoptosis in rat cortical neurons

Objective: The expression cold-inducible RNA-binding protein (CIRP) is significantly enhanced in neurons under hypothermia, but its roles remain unclear. This study aims to investigate whether the cerebral protection under hypothermia is mediated by the CIRP-mediated inhibition of neuronal apoptosis. Methods: Primary rat cortical neurons were isolated, cultured, and transduced with lentiviral CIRP-RNAi. Apoptosis of the transduced neurons was induced with 100μmol/L H2O2, the treated cells were divided into two groups, and cultured in 37°C or 32°C incubator respectively. Cell viability was detected by MTT colorimetric assay. Neuronal apoptosis was detected by flow cytometry after labeling the cells with Hoechst 33342 and Annexin V-FITC/PI. The protein expressions of CIRP, activated caspase-3, and thioredoxin (TRX) were detected by Western blot. Results: Under 32°C, CIRP protein is significantly induced in cortical neurons; the expression of activated caspase-3 decreases, while the TRX expression increases. The rate of neuronal apoptosis is 4.5±0.8%. Under 37°C, CIRP expression is evidently reduced in cortical neurons; the expression of activated caspase-3 is significantly enhanced with reduced level of TRX expression. The rate of neuronal apoptosis reaches 53.5±1.7% (P<0.05, compared to that in 32°C group). Conclusions: The induction of CIRP protein in rat cortical neurons under hypothermia inhibits H2O2-induced neuronal apoptosis and thereby exerts neuroprotective effect, which forms one of the cerebral protective pathways under hypothermia.

Effects of Cold Stimulation with Different Intensities on Expression of CIRP in Heart,Brain,Testis and Lung Tissues of Wistar Rats

In order to investegate the changes of cold inducible RNA-binding protein(CIRP) expression in heart,lung,brain and testis,healthy Wistar rats were treated by cold stimulation with different intensities.Totally 100 Wistar rats were divided into control group,acute cold stimulation group and chronic cold stimulation group.The control group was raised under normal ambient temperature(20 ℃ ± 1 ℃),acute cold stimulation group was subject to cold stress under different temperature(-10 ℃±1 ℃,-4 ℃±1 ℃,0 ℃±1 ℃,4 ℃±1 ℃) for different time(3 h,6 h,12 h and 24 h),respectively,and the chronic cold stimulation group was subject to cold stress under 10 ℃ ± 1 ℃ for 1 weak,2 weak and 3 weak.Methods of SYBR green I real time PCR and Western-blot were used to qualify the levels of CIRP expression.The results indicated that CIRP in four tissues of rats existed the basic expression level under normal condition;CIRP was expressed at all time after cold stimulation,but the expression levels were different in different tissues;after acute cold stimulation,the expression level of CIRP mRNA in hearts,brains and testes of rats increased in 0~6 h and peaked at 6 h then started to decline,while in lungs the change tendency was opposite to the former;after chronic cold stimulation,the expression levels of CIRP increased in hearts,brains and testes,while decreased in lungs,but the difference was not significant among different groups.Therefore,it can be concluded that the expression of CIRP in hearts,lungs,brains and testes of healthy Wistar rats is regular,although there is tissue specificity.

Moderate low temperature preserves the stemness of neural stem cells and suppresses apoptosis of the cells via activation of the cold-inducible RNA binding protein

We hypothesized that one of the mechanisms underlying the protection of brain injury by therapeutic hypothermia is associated with preservation of neural stem cells. We investigated effects of moderate low temperature and the contribution of a cold-inducible molecule for the stemness of neural stem cells. The MEB5 mouse neural stem cell line was cultured in the presence or absence of EGF, and apoptosis, mRNA expression, and immunocytochemistry of the differentiation markers nestin and GFAP were evaluated at 37 or 32°C. We investigated the contribution of the cold-inducible RNA binding protein (CIRP) on apoptosis and differentiation of MEB5 cells at 32°C. EGF deprivation increased the number of apoptotic cells, decreased expression of nestin, and increased expression of GFAP. The moderate low temperature prevented apoptosis and decreases in expression of GFAP in MEB5 by EGF deprivation. The moderate low temperature significantly increased expression of CIRP. siRNA against CIRP significantly increased the apoptotic cell population of MEB5 cells via EGF deprivation at 32°C. These findings suggest that moderate low temperature preserved stemness of neural stem cells and prevented cell apoptosis via the stimulation of CIRP, and one of the mechanisms of rescue of brain injury by the moderate hypothermia is associated with preservation of neural stem cells.

Effects of hypothermia and cerebral ischemia on cold-inducible RNA-binding protein mRNA expression in rat brain

CIRP (cold-inducible RNA-binding protein) mRNA is highly expressed in hypothermic conditions in mammalian cells, and the relationship between CIRP and neuroprotection for cerebral ischemia under hypothermia has been focused upon. At present, however, the expression characteristics of CIRP under hypothermia and cerebral ischemia in vivo are not clearly elucidated. In this study, CIRP mRNA expression in various regions of rat brain was examined by reverse transcriptase polymerase chain reaction (RT-PCR). CIRP expression levels were found to be similar in the hippocampus and cortex. Real-time quantitative PCR analysis revealed increasing CIRP mRNA expression in the cortex during the 24-h observation period following treatment with hypothermia or cerebral ischemia, with a greater increase in the hypothermia group. When cerebral ischemia was induced following hypothermia, CIRP mRNA expression in the cortex again showed a significant increasing tendency, but ischemia delayed the appearance of this increase. To reveal the relationship between CIRP and energy metabolism in the rat brain, lactate and pyruvate concentrations in the cortex of the rats treated with hypothermia, ischemia and ischemia after hypothermia were determined by spectrophotometric assay, and levels of phosphofructokinas-1 (PFK-1), the major regulatory enzyme of the glycolytic pathway, in the rat cortex in the three groups was also analyzed by Western blot. Using linear correlation, lactate and pyruvate concentrations, and PFK-1 levels, were each analyzed in the three groups in association with CIRP mRNA expression levels. The analysis did not reveal any correlation between the three metabolic parameters and CIRP mRNA expression induced by hypothermia, suggesting that while playing a role in neuroprotection under hypothermia, CIRP does not affect cerebral energy metabolism.

Cold‐inducible RNA binding protein modulates proliferation in the mouse mammary epithelium

Cold‐inducible RNA binding protein (CIRP) is upregulated in response to cellular stress, either facilitating or repressing translation of its mRNA targets. We showed that CIRP is upregulated in all breast cancer cell lines examined, while others have shown CIRP overexpression in primary breast tumors. In the MCF‐7 breast cancer cell line, CIRP upregulates the expression of another stress‐induced RNA binding protein, HuR, as well as the cell cycle regulator cyclin E1. Both HuR and cyclin E1 are also overexpressed in breast cancer, with higher expression correlating with a poor prognosis. In order to determine the in vivo function of CIRP in the breast epithelium, we produced a transgenic mouse expressing CIRP in the mammary epithelium under control of the mouse mammary tumor virus (MMTV) regulatory sequences. Real‐time RT‐PCR showed maximal expression of the transgene in the pregnant mouse at gestation day 16, and a second peak of expression after birth, at lactation day 14. Immunohistochemistry for the proliferation marker Ki‐67 showed decreased proliferation in the mammary epithelium of CIRP transgenic mice compared to wild type littermates at gestation day 16 (45% CIRP vs. 56% wild type, p=0.05) and lactation day 1 (7% CIRP vs. 25% wild type, p=0.0068). These results suggest that CIRP negatively regulates proliferation in the intact mammary gland. We are currently examining effects of CIRP expression on apoptosis in the involuting mammary gland. This work was supported by a grant from the National Cancer Institute‐National Institutes of Health to RSH (R01CA095898).

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.

Overexpression of CIRP may reduce testicular damage induced by cryptorchidism

To investigate the protective effect of overexpression of cold-inducible RNA-binding protein (CIRP) on testicular damage induced by cryptorchidism. Male BALB/c mice were made surgically cryptorchid and CIRP gene was transferred into the cryptorchid testis by in vivo electroporation. Seven or ten days after electroporation, the expression of CIRP, p53 and Fas mRNA and protein were analyzed by reverse-transcription polymerase chain reaction (RT-PCR) and immunoblotting, respectively. Meanwhile, Histopathological changes were observed by light microscope, and flow cytometry was used to detect testicular cell apoptosis. Testicular weights after transfection with pVAX1-CIRP or pVAX1 were 0.083+/-0.005 g and 0.065+/-0.004 g, respectively, on day 7(P < 0.05) and 0.078+/-0.004 g and 0.052+/-0.007 g, on day 10 (P < 0.05). Testicular cell apoptosis after transfection with pVAX1-CIRP or pVAX1 were 9.8+/-1.1 % and 20.7+/-1.3 %, respectively, on day 7 (P < 0.01) and 10.4+/-0.9 % and 27.5+/-1.2 %, on day 10 (P < 0.01). In addition, the expression of CIRP mRNA and protein in the testes transfected with pVAX1-CIRP were both increased (P < 0.05) at each indicated time point. Meanwhile, the expression of p53 was decreased on day 7 (P < 0.05) and Fas was decreased on day 10(P < 0.05). Overexpression of CIRP may reduce testicular damage induced by cryptorchidism by down-regulating the levels of p53 and Fas.

Artificial cold exposure induced stroke in renovascular hypertensive rats and its association with cold-inducible RNA binding protein mRNA expression in brain tissue and blood pressure

Background High incidence of stroke at interchange period of autumn and winter was demonstrated by epidemiological survey, and the specific causes should be further investigated. Objective To investigate the influence of artificial cold exposure on the incidence of stroke in renovascular hypertensive rats (RHR), and analyze the association with blood pressure and cold-inducible RNA binding protein (CIRP) mRNA expression in brain tissue. Design A completely randomized grouping design, a randomized control animal trial. Settings Lab of Neurology, the First Affiliated Hospital of Sun Yat-sen University; Department of Chemistry, Open laboratory of Chemical Biology, Institute of Molecular Technology for Drug Discovery and Synthesis, University of Hong Kong. Materials Male SD rats ( n = 460), weighing 80–100 g were obtained from Guangdong Province Health Animal Unit. A modified RXZ-300A intelligent artificial climate cabinet (Ningbo Jiangnan Instrument Co., Ltd., China). Methods The experiment were processed in the Lab of Neurology, the First Affiliated Hospital of Sun Yat-sen University and the Open Laboratory of Chemical Biology, Institute of Molecular Technology for Drug Discovery and Synthesis, University of Hong Kong from October 2004 to November 2005. Rats ( n = 400) were operated to establish 2-kidney 2-clip RHR model as described previously. The sham-operated rats ( n = 60) served as normotensive controls. Eight weeks later, 300 of RHR were randomly selected according to their systolic blood pressure (SBP) and divided into 3 sub-groups ( n = 100 per group): mild hypertensive group (SBP of 160–200 mm Hg), moderate hypertensive group (SBP of 200–220 mm Hg) and severe hypertensive group (SBP > 220 mm Hg). Each group was further divided into two groups ( n = 50) under ACE and non-ACE. Normal sham-operated SD rats ( n = 60), SBP < 140 mm Hg, were randomly divided into two groups: Sham-operated control group ( n = 30) under ACE and non-ACE. To establish the ACE and non-ACE treatment, rats were housed individually in artificial climate cabinet, and ACE was designed as three cycles of 12-hour light of 22 °C (7:00–19:00) and 12-hour dark of 4 °C(19:00–7:00). The non-ACE group was kept at 22 °C throughout the experiment. Main outcome measures Blood Pressure changes were measured and stroke symptom were observed; Expression of the CIRP were examined by reverse transcription-polymerase chain reaction. Results Finally 360 rats were involved in the analysis of results. ▪ Incidence of stroke: The incidence of stroke in 2k2c RHR was significantly higher after a three-day intermittent (12-hour) ACE (29.3%) as compared with that in non-ACE (17.3%) ( P < 0.05). Furthermore, the severe hypertensive 2k2c RHR (BP > 220 mm Hg) was found to have much higher incidence of stroke (66%, 33/50) than the mild (8%, 4/50) and moderate (18%) hypertensive 2k2c RHR. ▪ CIRP mRNA in brain tissue: ACE treatment stimulated the mRNA expression of CIRP in non-stroke 2k2c RHR but not in stroke 2k2c RHR ( P < 0.05). Conclusion High blood pressure and low expression of CIRP are associated with ACE induced stroke.

Down-regulation of cold-inducible RNA-binding protein does not improve hypothermic growth of Chinese hamster ovary cells producing erythropoietin

Discovery of the cold-inducible RNA-binding protein (CIRP) in mouse fibroblasts suggests that growth suppression at hypothermic conditions is due to an active response by the cell rather than due to passive thermal effects. To determine the effect of down-regulated CIRP expression on cell growth and erythropoietin (EPO) production in recombinant Chinese hamster ovary (rCHO) cells at low culture temperature, stable CHO cell clones with reduced CIRP expression level were established by transfecting (rCHO) cells with the CIRP siRNA vector with a target sequence of TCGTCCTTCCATGGCTGTA. For comparison of the degree of specific growth rate ( μ) reduction at low culture temperature, three CIRP-reduced clones with different μ and three control clones transfected with null vector were cultivated at two different temperatures, 32 °C and 37 °C. Unlike mouse fibroblasts, alleviation of hypothermic growth arrest of rCHO cells by CIRP down-regulation was insignificant, as shown by statistical analysis using the t-test ( P<0.18, n=3). The ratios of μ at 32 °C to μ at 37 °C of CIRP-reduced clones and control clones were 0.29±0.03 and 0.25±0.03 on an average, respectively. Furthermore, it was also found that overexpression of CIRP did not inhibit rCHO cell growth significantly at 37 °C. Taken together, the data obtained show that down-regulation of only CIRP in rCHO cells, unlike mouse fibroblasts, is not sufficient to recover growth arrest at low-temperature culture (32 °C).

Adaptation of Chinese hamster ovary cells to low culture temperature: Cell growth and recombinant protein production

Recombinant Chinese hamster ovary (rCHO) cells producing erythropoietin (EPO) and rCHO cells producing follicle-stimulating hormone (FSH) showed a significant increase in specific productivity (q) when grown at 32 degrees C compared to 37 degrees C. However, low culture temperature suppressed cell growth, and therefore, did not increase volumetric productivity as much as q. In an attempt to increase the volumetric productivity through improvement of hypothermic growth, EPO producing rCHO (CHO-EPO) cells and FSH producing rCHO (CHO-FSH) cells were adapted at 32 degrees C in a repeated batch mode using spinner flasks. Cell growth of both CHO-EPO and CHO-FSH gradually improved during adaptation at 32 degrees C. Specific growth rates of CHO-EPO and CHO-FSH cells at 32 degrees C, through adaptation, were increased by 73% and 20%, respectively. During adaptation at 32 degrees C, mRNA levels of cold-inducible RNA-binding protein (CIRP) of both rCHO cell lines did not change significantly, suggesting that CIRP expression may not be the only cause for growth suppression at low culture temperature. Unlike cell growth, the recombinant protein production of both rCHO cell lines was not increased during adaptation due to decreased specific productivities. The specific EPO productivity and specific FSH productivity were decreased by 49% and 22%, respectively. Southern blot analyses showed that the decreased specific productivities were not due to the loss of foreign gene copies. Taken together, improvement of hypothermic cell growth by adaptation does not appear to be applicable for enhanced recombinant protein production, since specific productivity decreases during adaptation to the low culture temperature.

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.

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°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°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 H 2O 2 on the cold stress protein CIRP expression in rat neuronal cells

Expression of CIRP (cold-inducible RNA-binding protein) is inducible at 32°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°C, the CIRP mRNA level was increased. The presence of H 2O 2 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.