Expression of p68 in human colon cancer

Eukaryotic translation initiation factor 2α kinase 2 in pancreatic cancer: An approach towards managing clinical prognosis and molecular immunological characterization

Most patients with pancreatic cancer are already in the late stages of the disease when they are diagnosed, and pancreatic cancer is a deadly disease with a poor prognosis. With the advancement of research, immunotherapy has become a new focus in the treatment of tumors. To the best of our knowledge, there is currently no reliable diagnostic or prognostic marker for pancreatic cancer; therefore, the present study investigated the potential of eukaryotic translation initiation factor 2α kinase 2 (EIF2AK2) as a predictive and diagnostic marker for pancreatic cancer. Immunohistochemical staining of clinical samples independently verified that EIF2AK2 expression was significantly higher in clinically operated pancreatic cancer tissues than in adjacent pancreatic tissues., and EIF2AK2 expression and differentially expressed genes (DEGs) were identified using downloadable RNA sequencing data from The Cancer Genome Atlas and Genomic Tumor Expression Atlas. In addition, Gene Ontology/Kyoto Encyclopedia of Genes and Genomes analyses and immune cell infiltration were used for functional enrichment analysis of EIF2AK2-associated DEGs. The clinical importance of EIF2AK2 was also determined using Kaplan-Meier survival, Cox regression and time-dependent survival receiver operating characteristic curve analyses, and a predictive nomogram model was generated. Finally, the functional role of EIF2AK2 was assessed in PANC-1 cells using a short hairpin RNA-EIF2AK2 knockdown approach, including CCK-8, wound healing assay, cell cycle and apoptosis assays. The findings suggested that EIF2AK2 may have potential as a diagnostic and prognostic biomarker for patients with pancreatic cancer. Furthermore, EIF2AK2 may provide a new therapeutic target for patients with pancreatic cancer.

DDX10 promotes the proliferation and metastasis of colorectal cancer cells via splicing RPL35

Background

Colorectal cancer (CRC) has become the second deadliest cancer in the world and severely threatens human health. An increasing number of studies have focused on the role of the RNA helicase DEAD-box (DDX) family in CRC. However, the mechanism of DDX10 in CRC has not been elucidated.

Methods

In our study, we analysed the expression data of CRC samples from the Gene Expression Omnibus (GEO) and The Cancer Genome Atlas (TCGA) databases. Subsequently, we performed cytological experiments and animal experiments to explore the role of DDX10 in CRC cells. Furthermore, we performed Gene Ontology (GO)/Kyoto Encyclopedia of Genes and Genomes (KEGG) enrichment analysis and protein–protein interaction (PPI) network analyses. Finally, we predicted the interacting protein of DDX10 by LC–MS/MS and verified it by coimmunoprecipitation (Co-IP) and qPCR.

Results

In the present study, we identified that DDX10 mRNA was extremely highly expressed in CRC tissues compared with normal colon tissues in the TCGA and GEO databases. The protein expression of DDX10 was measured by immunochemistry (IHC) in 17 CRC patients. The biological roles of DDX10 were explored via cell and molecular biology experiments in vitro and in vivo and cell cycle assays. We found that DDX10 knockdown markedly reduced CRC cell proliferation, migration and invasion. Then, we constructed a PPI network with the Search Tool for the Retrieval of Interacting Genes/Proteins (STRING). GO and KEGG enrichment analysis and gene set enrichment analysis (GSEA) showed that DDX10 was closely related to RNA splicing and E2F targets. Using LC–MS/MS and Co-IP assays, we discovered that RPL35 is the interacting protein of DDX10. In addition, we hypothesize that RPL35 is related to the E2F pathway and the immune response in CRC.

Conclusions

In conclusion, provides a better understanding of the molecular mechanisms of DDX10 in CRC and provides a potential biomarker for the diagnosis and treatment of CRC.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12935-022-02478-1.

P68 RNA Helicase facilitates Breast Cancer progression by promoting Proliferation and Migration via PDGFR-β/AR axis

Aberrant expression of P68 RNA helicase (p68), a prototypical member of the DEAD box family of RNA helicases, contributes to tumor development and progression. P68 tyrosine phosphorylation induced by PDGF signaling facilitates cancer metastasis by promoting EMT. In this report, we show that p68 promotes breast cancer cell EMT and cell migration by upregulation of PDGF receptor β (PDGFR-β). Knockdown of p68 in MDA-MB-231 and BT549 cells significantly decreases PDGFR-β both in mRNA and protein levels. P68 promotes EMT and cell migration in response to PDGF-BB stimulation via upregulation of PDGFR-β, suggesting that p68 enhances PDGF signaling by a positive feedback loop in cancer cells. Furthermore, our study reveals that p68 mediates the effects of PDGFR-β in regulation of androgen receptor (AR) in breast cancer cells. We demonstrate that p68 and PDGFR-β co-regulate AR expression and promote androgen-mediated proliferation in breast cancer cells. Our studies uncover an important pathway of p68-PDGFR-β axis in promoting breast cancer progression.

Targeting Protein Synthesis in Colorectal Cancer

Under physiological conditions, protein synthesis controls cell growth and survival and is strictly regulated. Deregulation of protein synthesis is a frequent event in cancer. The majority of mutations found in colorectal cancer (CRC), including alterations in the WNT pathway as well as activation of RAS/MAPK and PI3K/AKT and, subsequently, mTOR signaling, lead to deregulation of the translational machinery. Besides mutations in upstream signaling pathways, deregulation of global protein synthesis occurs through additional mechanisms including altered expression or activity of initiation and elongation factors (e.g., eIF4F, eIF2α/eIF2B, eEF2) as well as upregulation of components involved in ribosome biogenesis and factors that control the adaptation of translation in response to stress (e.g., GCN2). Therefore, influencing mechanisms that control mRNA translation may open a therapeutic window for CRC. Over the last decade, several potential therapeutic strategies targeting these alterations have been investigated and have shown promising results in cell lines, intestinal organoids, and mouse models. Despite these encouraging in vitro results, patients have not clinically benefited from those advances so far. In this review, we outline the mechanisms that lead to deregulated mRNA translation in CRC and highlight recent progress that has been made in developing therapeutic strategies that target these mechanisms for tumor therapy.

Protein kinase R and its cellular regulators in cancer: An active player or a surveillant?

Protein kinase R (PKR), originally known as an antiviral protein, senses various stresses as well as pathogen-driven double-stranded RNAs. Thereby activated PKR provokes diverse downstream events, including eIF2α phosphorylation and nuclear factor kappa-light-chain-enhancer of activated B cells activation. Consequently, PKR induces apoptosis and inflammation, both of which are highly important in cancer as much as its original antiviral role. Therefore, cellular proteins and RNAs should tightly control PKR activity. PKR and its regulators are often dysregulated in cancer and it is undoubted that such dysregulation contributes to tumorigenesis. However, PKR's precise role in cancer is still in debate, due to incomprehensible and even contradictory data. In this review, we introduce important cellular PKR regulators and discuss about their roles in cancer. Among them, we pay particular attention to nc886, a PKR repressor noncoding RNA that has been identified relatively recently, because its expression pattern in cancer can explain interesting yet obscure oncologic aspects of PKR. Based on nc886 and its regulation of PKR, we have proposed a tumor surveillance model, which reconciles contradictory data about PKR in cancer. This article is categorized under: Regulatory RNAs/RNAi/Riboswitches > Regulatory RNAs RNA Interactions with Proteins and Other Molecules > Protein-RNA Interactions: Functional Implications.

High expression of ALDOA and DDX5 are associated with poor prognosis in human colorectal cancer

Purpose

The identification of prognostic markers for colorectal cancer (CRC) is needed for clinical practice. Fructose-bisphosphate aldolase A (ALDOA) and DEAD box p68 RNA helicase (DDX5) are commonly overexpressed in cancer and correlate with tumorigenesis. However, association between expression of ALDOA and DDX5, and CRC outcome has not been reported.

Patients and methods

We used 141 formalin-fixed paraffin-embedded (FFPE) specimens collected from 105 patients with CRC treated at the Affiliated Hospital of Guilin Medical University and the People’s Hospital of Liuzhou. We performed tissue microarray based immunohistochemistry to explore expression features and prognostic value (overall survival, OS; disease-free survival, [DFS]) of ALDOA and DDX5 in CRC tissues. The prognostic values were evaluated using Kaplan–Meier analysis, and Cox regression analyses.

Results

ALDOA and DDX5 were highly expressed in CRC tissues and liver metastatic CRC tissues compared with normal glandular epithelium tissues (all p<0.05). Interestingly, primary CRC tissues highly expressing ALDOA or DDX5 had poor outcome (p<0.0001 for both OS and DFS for ALDOA; p=0.001 for OS; and p=0.011 for DFS for DDX5) compared with patients who had low expression of those proteins. Furthermore, multivariate Cox analysis showed that ALDOA/DDX5 combination was an independent risk factor for OS and ALDOA was an independent risk factor for DFS.

Conclusion

High levels of ALDOA and DDX5 contribute to the aggressiveness and poor prognosis of CRC. ALDOA/DDX5 expression could be a biomarkers for the prognosis of CRC.

Hepatitis B Virus-Associated Hepatocellular Carcinoma and Hepatic Cancer Stem Cells

Chronic Hepatitis B Virus (HBV) infection is linked to hepatocellular carcinoma (HCC) pathogenesis. Despite the availability of a HBV vaccine, current treatments for HCC are inadequate. Globally, 257 million people are chronic HBV carriers, and children born from HBV-infected mothers become chronic carriers, destined to develop liver cancer. Thus, new therapeutic approaches are needed to target essential pathways involved in HCC pathogenesis. Accumulating evidence supports existence of hepatic cancer stem cells (hCSCs), which contribute to chemotherapy resistance and cancer recurrence after treatment or surgery. Understanding how hCSCs form will enable development of therapeutic strategies to prevent their formation. Recent studies have identified an epigenetic mechanism involving the downregulation of the chromatin modifying Polycomb Repressive Complex 2 (PRC2) during HBV infection, which results in re-expression of hCSC marker genes in infected hepatocytes and HBV-associated liver tumors. However, the genesis of hCSCs requires, in addition to the expression of hCSC markers cellular changes, rewiring of metabolism, cell survival, escape from programmed cell death, and immune evasion. How these changes occur in chronically HBV-infected hepatocytes is not yet understood. In this review, we will present the basics about HBV infection and hepatocarcinogenesis. Next, we will discuss studies describing the mutational landscape of liver cancers and how epigenetic mechanisms likely orchestrate cellular reprograming of hepatocytes to enable formation of hCSCs.

P68 RNA helicase as a molecular target for cancer therapy

The DEAD-box family of RNA helicase is known to be required in virtually all cellular processes involving RNA, and p68 is a prototypic one of the family. Reports have indicated that in addition to ATPase and RNA helicase ability, p68 can also function as a co-activator for transcription factors such as estrogen receptor alpha, tumor suppressor p53 and beta-catenin. More than that, post-translational modification of p68 including phosphorylation, acetylation, sumoylation, and ubiquitylation can regulate the coactivation effect. Furthermore, aberrant expression of p68 in cancers highlights that p68 plays an important role for tumorgenesis and development. In this review, we briefly introduce the function and modulation of p68 in cancer cells, and put forward envisagement about future study about p68.

Prognostic significance of combinations of RNA-dependent protein kinase and EphA2 biomarkers for NSCLC

INTRODUCTION

RNA-dependent protein kinase (PKR) is an independent prognostic variable in patients with non-small-cell lung cancer (NSCLC). In the current study, we investigated the correlation between PKR and 25 other biomarkers for NSCLC, identified the markers that could further improve the prognostic significance of PKR and elucidated the mechanisms of interaction between these markers and PKR.

METHODS

Tissue microarray samples obtained from 218 patients with lung cancer were stained with an anti-PKR antibody and antibodies against 25 biomarkers. Immunohistochemical expression was scored and used for Kaplan-Meier survival analysis. The interaction between PKR and EphA2 in NSCLC cell lines was examined.

RESULTS

We found that PKR was associated with EphA2 and that the prognostic information regarding NSCLC provided by the combination of PKR and EphA2 (P/E) was significantly more accurate than that provided by either marker alone. The 5-year overall survival rate in patients with PKR/EphA2 (20%) was significantly lower than that of patients with PKR/EphA2 (74%), patients with PKR/EphA2 (55%), and patients with PKR/EphA2 (55%) (p < 0.0001). We also found that the PKR:EphA2 (P/E) ratio was significantly associated with prognosis (p < 0.0001). Univariate and multivariate Cox analyses revealed that this P/E combination or ratio was an independent predictor of overall survival. In addition, induction of PKR expression reduced EphA2 protein expression levels in NSCLC cell lines.

CONCLUSIONS

PKR/EphA2 is a significant predictor of prognosis for NSCLC. PKR/EphA2 may be a promising approach to improving screening efficiency and predicting prognosis in patients with NSCLC.

The role of PKR/eIF2α signaling pathway in prognosis of non-small cell lung cancer

BACKGROUND

In this study, we investigated whether PKR protein expression is correlated with mRNA levels and also evaluated molecular biomarkers that are associated with PKR, such as phosphorylated PKR (p-PKR) and phosphorylated eIF2α (p-eIF2α).

METHODOLOGY AND FINDINGS

We determined the levels of PKR protein expression and mRNA in 36 fresh primary lung tumor tissues by using Western blot analysis and real-time reverse-transcriptase PCR (RT-PCR), respectively. We used tissue microarrays for immunohistochemical evaluation of the expression of p-PKR and p-eIF2α proteins. We demonstrated that PKR mRNA levels are significantly correlated with PKR protein levels (Spearman's rho = 0.55, p<0.001), suggesting that PKR protein levels in tumor samples are regulated by PKR mRNA. We also observed that the patients with high p-PKR or p-eIF2α expression had a significantly longer median survival than those with little or no p-PKR or p-eIF2α expression (p = 0.03 and p = 0.032, respectively). We further evaluated the prognostic effect of combined expression of p-PKR plus PKR and p-eIF2α plus PKR and found that both combinations were strong independent prognostic markers for overall patient survival on stage I and all stage patients.

CONCLUSIONS

Our findings suggest that PKR protein expression may controlled by transcription level. Combined expression levels of PKR and p-PKR or p-eIF2α can be new markers for predicting the prognosis of patients with NSCLC.

Prognostic significance of RNA-dependent protein kinase on non-small cell lung cancer patients

PURPOSE

The role of RNA-dependent protein kinase (PKR) in antiviral defense mechanisms and in cellular differentiation, growth, and apoptosis is well known, but the role of PKR in human lung cancer remains poorly understood. To explore the role of PKR in human lung cancer, we evaluated the expression of PKR in tissue microarray (TMA) specimens from both non-small cell lung cancer (NSCLC) and normal human bronchial epithelium tissue.

EXPERIMENTAL DESIGN

TMA samples (TMA-1) from 231 lung cancers were stained with PKR antibody and validated on TMA-2 from 224 lung cancers. Immunohistochemical expression score was quantified by three pathologists independently. Survival probability was computed by the Kaplan-Meier method.

RESULTS

The NSCLC cells showed lower levels of PKR expression than normal bronchial epithelium cells did. We also found a significant association between lower levels of PKR expression and lymph node metastasis. We found that loss of PKR expression is correlated with a more aggressive behavior, and that a high PKR expression predicts a subgroup of patients with a favorable outcome. Univariate and multivariate Cox proportional hazards regression models showed that a lower level of PKR expression was significantly associated with shorter survival in NSCLC patients. We further validated and confirmed PKR to be a powerful prognostic factor in TMA-2 lung cancer (hazard ratio, 0.22; P < 0.0001).

CONCLUSIONS

Our findings first indicate that PKR expression is an independent prognostic variable in NSCLC patients.

Functional expression of double-stranded RNA-dependent protein kinase in rat intestinal epithelial cells

Intestinal epithelial cells (IECs) are exposed to external environment, microbial and viral products, and serve as essential barriers to antigens. Recent studies have shown that IECs express Toll-like receptors (TLRs) and respond to microbial components. The antimicrobial and antiviral barriers consist of many molecules including TLRs. To investigate the further component of this barrier in intestine, we examined the expression of double-stranded RNA-dependent protein kinase (PKR). PKR is a player in the cellular antiviral response and phosphorylates alpha-subunit of the eukaryotic translation initiation factor 2 (eIF-2alpha) to block protein synthesis and induces apoptosis. In this study, we showed that the expression of PKR was restricted to the cytoplasm of absorptive epithelial cells in the intestine of adult rat. We also demonstrated that PKR was expressed in the cultured rat intestinal epithelial cells (IEC-6). The level of PKR protein expression and the activity of alkaline phosphatase (ALP) increased in the cultured IEC-6 cells in a time-dependent manner. Inhibition of PKR by the 2-aminopurine treatment decreased ALP activity in the IEC-6 cells. Treatment of IEC-6 cells with synthetic double-stranded RNA (dsRNA) induced cell death in a dose-dependent manner. The addition of hydrocortisone also provoked suppression of PKR expression and ALP activity. This modulation might be mediated by signal transducers and activators of transcription-1 (STAT-1) protein. We concluded that PKR is expressed in IECs as potent barriers to antigens and is a possible modulator of the differentiation of rat IECs.

Data Mining for Gene Networks Relevant to Poor Prognosis in Lung Cancer via Backward-Chaining Rule Induction

We use Backward Chaining Rule Induction (BCRI), a novel data mining method for hypothesizing causative mechanisms, to mine lung cancer gene expression array data for mechanisms that could impact survival. Initially, a supervised learning system is used to generate a prediction model in the form of “IF <conditions> THEN <outcome>” style rules. Next, each antecedent (i.e. an IF condition) of a previously discovered rule becomes the outcome class for subsequent application of supervised rule induction. This step is repeated until a termination condition is satisfied. “Chains” of rules are created by working backward from an initial condition (e.g. survival status). Through this iterative process of “backward chaining,” BCRI searches for rules that describe plausible gene interactions for subsequent validation. Thus, BCRI is a semi-supervised approach that constrains the search through the vast space of plausible causal mechanisms by using a top-level outcome to kick-start the process. We demonstrate the general BCRI task sequence, how to implement it, the validation process, and how BCRI-rules discovered from lung cancer microarray data can be combined with prior knowledge to generate hypotheses about functional genomics.

Expression of double-stranded RNA-activated protein kinase in small-size peripheral adenocarcinoma of the lung

The authors investigated the protein expression of double-stranded RNA-activated protein kinase (PKR), which was identified by using a previous cDNA microarray study, to discover PKR's correlations with several pathological parameters and to elucidate its role in neoplastic transformation and progression of lung adenocarcinomas. Immunohistochemistry for PKR was performed and a semiquantitative scoring method was calculated based on staining intensity and percentage of immunoreactive tumor cells (high vs low) for one bronchioloalveolar carcinoma (BAC), 16 adenocarcinomas consisting of BAC and invasive carcinoma (mixed) and 21 invasive adenocarcinomas without BAC (invasive). The BAC had high-grade expression and the mixed type tended to more frequently show high-grade expression than the invasive type (P = 0.028). There were no significant associations with age, tumor size, lymph node metastasis, lymphovascular invasion or the pathological stage. The Kaplan-Meier survival curves demonstrated that the patients with high-grade PKR expression had significantly shorter survival periods than those patients with low-grade PKR expression (P = 0.018). These results do not support the concept of PKR as a tumor suppressor in small-size peripheral adenocarcinomas of the lung.

Expression of double-stranded RNA-activated protein kinase (PKR) and its prognostic significance in lymph node negative rectal cancer

OBJECTIVE

The interferon-induced, double-stranded RNA-activated, protein kinase (PKR) is a key regulator of translational initiation, and plays an important role in the regulation of cell proliferation, apoptosis and transformation. The aim of this study was to evaluate the prognostic significance of PKR in lymph node negative rectal cancer.

METHODS

Forty-three patients with stage II rectal carcinoma who underwent potentially curative resection followed by post-operative adjuvant chemoradiation and 5-fluorouracil-based chemotherapy were investigated immunohistochemically using the monoclonal antibody TJ4C4. Overall scores for PKR expression were calculated based on staining intensity and immunoreactive tumor cell fraction. Clinical information, including tumor grade, carcinoembryonic antigen (CEA), disease-free survival (DFS) and overall survival (OS) was evaluated and compared with the degree of PKR expression.

RESULTS

The median follow-up duration was 53.2 months, and median patient age was 55 years (range 33-73). No relationships were found between PKR score and age, sex, tumor grade or CEA level; however, smaller tumors (< or =5 cm) were associated with high PKR score (P = 0.025). When patients were subdivided into two groups based on the PKR score, the relapse rate was lower for those with a high PKR score (7.4 versus 43.8%, P = 0.008), and a significant difference was found between these two groups in terms of 5 year DFS (92.6 versus 55.6%, P = 0.0072) and 5 year OS (92.6 versus 57.7%, P = 0.0459). Other clinicopathologic variables were not related to clinical outcome.

CONCLUSION

PKR expression levels were associated with disease recurrence, DFS and OS in lymph node negative rectal cancer patients.

The role of translation in neoplastic transformation from a pathologist's point of view

Increased cell proliferation, which is a hallmark of aggressive malignant neoplasms, requires a general increase in protein synthesis and a specific increase in the synthesis of replication-promoting proteins. Transient increase in the general protein synthesis rate, as well as preferential translation of specific mRNAs coding for growth promoting proteins (e.g. cyclin D1), takes place during normal mitogenic response. A number of extensively studied growth signal transduction pathways (Ras, PI3K, MAPK, mTOR-dependent pathways) activate the function and expression of various components of the translational machinery. In abnormal situations, constitutive activation of signal transduction pathways (e.g. oncogenic activation of Ras or Myc) leads to continuous upregulation of key elements of translational machinery. On the other hand, tumor suppressor genes (p53, pRb) downregulate ribosomal and tRNA synthesis, and their inactivation results in uncontrolled production of these translational components. During recent years, a significant effort has been dedicated to determining whether expression of translation factors is increased in human tumors using clinical biopsy specimens. The results of these studies indicate that expression of particular translation initiation factors is not always increased in human neoplasms. The pattern of expression is characteristic for a particular tumor type. For example, eIF-4E is usually increased in bronchioloalveolar carcinomas but not in squamous cell carcinomas of the lung. Interestingly, in certain highly proliferative and aggressive neoplasms (e.g. squamous cell carcinoma of the lung, melanoma), the expression of eIF-4E is barely detectable. These findings suggest that mechanisms for increasing general protein synthesis in various neoplasms differ significantly. Finally, the possibility of qualitative alterations in the translational machinery, rather than a simple increase in the activity of its components, is discussed along with the possibility of targeting those qualitative differences for tumor therapy.

Genetically Targeted Cancer Therapy

The is a double-stranded RNA-activated protein kinase (PKR) has been largely investigated for its key role in viral host defense. Although best characterized by its function in mediating the antiviral and antiproliferative effects of interferon (IFN), PKR is also implicated in transcriptional regulation, cell differentiation, signal transduction, and tumor suppression. However, recent findings identifying PKR as an important effector of apoptosis have led to an increased interest in PKR modulation as an antitumor strategy. PKR can either be up-regulated through direct induction by the transcription factor E2F-1, or it can be activated through direct protein-protein interactions with the melanoma differentiation-associated gene-7 (MDA7, IL-24). Additionally, the intracellular formation of double-stranded RNA by transfection with antisense RNA complementary to tumor-specific RNA sequences can induce PKR activation and apoptosis selective to these tumor cells. The growing application of viral vector-based gene therapies and oncolytic, replicating viruses that must elude viral defense in order to be effective, has also drawn attention to PKR. Oncolytic viruses, like the attenuated herpes simplex virus R3616, the vesicular stomatitis virus, or reovirus, specifically replicate in tumor cells only because the viral host defense in the permissive cells is suppressed. In this article we review the role of PKR as an effector of apoptosis and a target for tumor treatment strategies and discuss the potential of PKR-modifying agents to treat patients with cancer. Targeted gene therapy against cancer can be approached by activation of PKR with the down-regulation of protein synthesis and induction of apoptosis, or by suppression of PKR with the propagation of oncolytic virus. Since the PKR pathway can be modified by many routes, antitumor therapies combining oncolytic virus, gene therapies, and chemotherapy with PKR modifiers are likely to emerge in the near future as therapeutic options in the treatment of patients with cancer.

Expression of double-stranded RNA-activated protein kinase in keratinocytes and keratinocytic neoplasia

Double-stranded RNA-activated protein kinase (PKR) is a interferon-induced protein initially known for its inhibitory effects on cellular and viral protein synthesis. In recent studies, PKR has been shown to be an important participant in a broad array of cellular processes, including signal transduction, differentiation, apoptosis, cell growth, and tumorigenesis. The expression of PKR in normal human keratinocytes (NHEK) was examined, and its expression in several skin lesions was compared immunohistochemically with that of proliferating cell nuclear antigen (PCNA). Expression of PKR mRNA was detected in NHEK without IFNgamma treatment; the level of PKR mRNA increased with IFNgamma treatment for two hours. Immunoblot analysis revealed that the monoclonal anti-PKR antibody reacted specifically with a 68kDa PKR protein in extracts from NHEK. Immunohistochemistry revealed that PKR protein was expressed in normal epidermis and mucosa. PKR expression was not restricted only to suprabasal cells but was also observed in basal cells positive for PCNA. In psoriatic plaques, PKR expression was lower in basal and parabasal keratinocytes and comparable in suprabasal keratinocytes to the levels in normal skin. PKR was partially detected in atypical cells in non-invasive keratinocytic neoplasia but was completely absent from undifferentiated tumor cells of squamous cell carcinoma. The present study demonstrated that PKR protein is constitutively expressed in epidermal and epithelial keratinocytes of normal skin and mucosa and indicated that a loss of PKR is not associated with the malignant transformation itself but with the increased cell proliferative activity and the altered differentiation of keratinocytes.

Neoplastic progression in melanoma and colon cancer is associated with increased expression and activity of the interferon-inducible protein kinase, PKR

The interferon-inducible, double-stranded RNA (dsRNA)-activated protein kinase, PKR, plays key roles in regulation of cell growth and differentiation, and has been postulated as a tumor suppressor. Downstream effectors of PKR include the translation initiation factor, eIF2alpha, and the transcription factor, NF-kappaB. We found elevated levels of PKR protein, dsRNA-dependent PKR autophosphorylation activity, and phosphorylated eIF2alpha in melanoma cells compared to nontransformed melanocytes in culture. Treatment with interferon-alpha2b further induced PKR expression and activity. Immunohistochemical analysis of primary melanomas demonstrated minimal PKR immunoreactivity, but melanoma lymph node metastases expressed a high level of PKR protein. Furthermore, analysis of colon cancer specimens revealed that transformation from normal mucosa to adenomas and carcinomas was coincident with an increase in PKR expression. These data do not support the concept of PKR as a classic tumor suppressor but instead suggest that PKR upregulation occurs at defined steps in cancer progression, probably as a cellular response to neoplasia.

Double-stranded RNA-dependent protein kinase, PKR, down-regulates CDC2/cyclin B1 and induces apoptosis in non-transformed but not in v-mos transformed cells

The interferon (IFN)-induced, double stranded RNA (dsRNA)-activated serine/threonine kinase, PKR, is a potent negative regulator of cell growth when overexpressed in yeast or mammalian cells. Paradoxically, while it can function as a tumor suppressor and inducer of apoptosis, it is overexpressed in a variety of human cancers. To resolve this enigma, we established cell-lines that overexpress PKR in non-transformed and in v-mos transformed CHO cells. Overexpression of PKR suppressed the proliferation of CHO cells by inducing a transient G0/G1 arrest, followed by a delayed G2/M arrest, which attenuated cell cycle progression. These effects were accompanied by early induction of p21/WAF-1 and delayed downregulation of CDC2 and cyclin B1. Induction of proapoptotic activity of the ectopic PKR paralleled the onset of G2/M arrest in CHO cells. However, while transiently inducing p21/WAF-1, PKR did not impose G2/M arrest or apoptosis in v-mos-transformed cells, nor was CDC2 or cyclin B1 down-regulated in those cells. These findings link the proapoptotic activity of PKR to the arrest of cell cycle at the G2/M phase. Consequently, the apoptotic activity of PKR could be counter-acted by an oncogene-like v-mos that overrides the G2/M arrest induced by PKR.

Levels, phosphorylation status and cellular localization of translational factor eIF2 in gastrointestinal carcinomas

The level of expression and the phosphorylation status of the alpha subunit of initiation factor 2 (eIF2alpha) protein have been determined by comparing samples from human stomach, colon and sigma-rectum carcinomas with normal tissue from the same patients. The unphosphorylated and phosphorylated levels of cytoplasmic eIF2alpha, as well as the percentage of phosphorylated factor over the total, were significantly higher in stomach, colon and sigma-rectum tumours compared with normal tissue. The expression of this factor was also studied by using immunocytochemical methods, where redistribution towards the nucleus in tumour cells as compared with normal tissue was observed. Our results support a likely implication of eIF2alpha in gastrointestinal cancer.

PKR, apoptosis and cancer

The double-stranded (ds) RNA-regulated serine/threonine protein kinase, PKR, is an interferon-inducible enzyme of widespread occurrence in mammalian cells. PKR is activated by dsRNA via a mechanism involving autophosphorylation. Once activated, the enzyme phosphorylates the alpha-subunit of protein synthesis initiation factor eIF2, thereby inhibiting translation. Accumulating data suggest that PKR has additional substrates, and that the kinase may also regulate gene transcription and signal transduction pathways. Although PKR plays an important role in mediating the antiviral effects of interferons, PKR is also implicated in regulating cell proliferation in uninfected cells and may have a tumor suppressor function under normal conditions. Studies of human malignancies and tumor cell lines suggest that, in general, patients bearing tumors with a higher PKR content have a more favorable prognosis. However, in human breast carcinoma cells, dysregulation of PKR may be associated with the establishment or maintenance of the transformed state.

Abnormal levels and minimal activity of the dsRNA-activated protein kinase, PKR, in breast carcinoma cells

The interferon induced, dsRNA-activated, protein kinase, PKR, is a key regulator of translational initiation, playing an important role in the regulation of cell proliferation, apoptosis and transformation. PKR levels correlate inversely with proliferative activity in several human tumor systems. This inverse relationship breaks down in human invasive ductal breast carcinomas which exhibit high levels of PKR (Haines et al., Tumor Biol. 17 (1996) 5-12). Consistent with the data from human tumors, the levels of PKR in several breast carcinoma cell lines, MCF7, T47D, BT20, MDAMB231 and MDAMB468, are paradoxically high compared to those found in the normal breast cell lines MCF10A and Hs578Bst. The activity of affinity- or immuno-purified PKR from MCF7, T47D, and BT20 cells appears to be severely attenuated, as judged by its ability to autophosphorylate, or phosphorylate eIF2 alpha. Furthermore, the activity of the kinase from breast carcinoma cells is refractory to stimulation by dsRNA or heparin. However, PKR from breast carcinoma cells remains functional with respect to its ability to bind dsRNA. The activity of PKR from MCF10A cells is reduced by prior incubation with extracts from MCF7 cells, suggesting that MCF7 extracts contain a transdominant inhibitor of PKR. Deregulation of PKR may therefore provide a mechanism for the development or maintenance of a transformed phenotype of human breast carcinomas, mimicking the effects of manipulation of PKR or eIF2 activity observed in experimental systems. Thus, breast carcinomas may provide the first indication of a role for PKR in the pathogenesis of a naturally occurring human cancer.

Translational control: the cancer connection

There is now a growing body of evidence which suggests links between the regulation of protein synthesis and the disruption of cell behaviour that typifies cancer. This directed issue of the International Journal of Biochemistry and Cell Biology presents several review articles of relevance to this field. The topics covered include the significance of the regulation and overexpression of polypeptide chain initiation factors for cell transformation and malignancy, the role of mRNA structure in the control of synthesis of key growth regulatory proteins, the actions of the eIF2 alpha-specific protein kinase PKR in the control cell growth and apoptosis, and the involvement of the elongation factor eEF1 in oncogenesis. The purpose of this article is to give an overview of the field and to indicate where we may expect developments to occur in the next few years.

Expression of p68 protein kinase and its prognostic significance during IFN-alpha therapy in patients with carcinoid tumours

The aim of this study was to evaluate the antiproliferative effects of interferon alpha (IFN-alpha) on neuroendocrine differentiated cell lines and, retrospectively, to assess the prognostic significance of p68 protein kinase (PKR) induction in neuroendocrine gut and pancreatic tumour patients. Archive specimens from 56 patients were studied, 43 before IFN-alpha and 56 during therapy. The tissues were immunostained for p68 protein kinase (PKR) using the monoclonal antibody (MAb) TJ4C4. A significant increase in immunostaining after treatment with IFN-alpha compared with before treatment (3.47 +/- 0.12 versus 2.72 +/- 0.15, P < 0.001) was noted. The p68 score was significantly increased after treatment only in patients with stable disease before = 2.71 +/- 0.19, after = 3.40 +/- 0.14 (P < 0.001) or an objective response before 3.13 +/- 0.22, after = 4.00 +/- 0.24 (P < 0.05) but not in those with progressive disease (before = 2.32 +/- 0.24, after 2.86 +/- 0.26, NS). A low p68 score (< 3.0) during treatment was a predictor of shorter duration of response and overall survival (P = 0.0062 and P < 0.0001, respectively). Furthermore, IFN-alpha showed a significant antiproliferative effect (by [3H]thymidine incorporation) on two carcinoid tumour cell lines in a dose-dependent manner which correlated with a dose-dependent induction of p68 mRNA and protein expression (by Northern and Western blot analysis). We conclude that IFN-alpha can effectively inhibit the in vitro growth of carcinoid tumor cell lines and upregulates the expression of p68 at both mRNA and protein levels in carcinoid tumours. The induction of p68 could be a prognostic indicator of response in patients with carcinoid tumours during IFN-alpha treatment.