Prosurvival function of the cellular apoptosis susceptibility/importin-α1 transport cycle is repressed by p53 in liver cancer

Oxeiptosis core genes and their multi-omics analysis in hepatocellular carcinoma

Oxeiptosis is a recently discovered caspase-independent, non-inflammatory programmed cell death modality. Current studies suggest that oxeiptosis has crucial effects on biological processes in a variety of diseases. However, the mechanism of oxeiptosis in hepatocellular carcinoma (HCC) remains unclear and no relevant studies have been published. Therefore, this study is intended to investigate the mechanism and prognostic role of oxeiptosis-related genes in HCC. We explored the mechanisms and molecular phenotypes underlying the role of oxeiptosis in HCC through multi-omics analysis. Firstly, we obtained RNA-sequencing and clinical data from public database and divided the samples into trial and validation cohorts in subsequent analyses. We then screened oxeiptosis core genes (OCGs) and screened prognosis-related genes. Based on different molecular markers, we identified the molecular phenotypes of HCC, and the potential OCGs molecular mechanisms were explored. Subsequently, we construct a prognostic prediction system for HCC. Finally, we analyzed the tumor microenvironment and the immune escape phenomenon. We screened a total of 69 OCGs, most of which were prognostic risk factors for HCC. A majority of OCGs were enriched in cell cycle regulation and mitotic processes, which were related to both tumor cell proliferation and death. We identified 2 different molecular typing options with significant differences in prognosis, function, and signaling pathway enrichment between different molecular subtypes. The prognostic prediction model combined with molecular phenotypes and had a good predictive effect. Finally, we found CD4 + T-cell exhaustion in samples with specific molecular phenotypes. Through multi-omics analysis of OCGs, we not only revealed the possible molecular mechanisms of OCGs in HCC but also provided a prognostic prediction system for clinical application through molecular typing and risk scoring model. Meanwhile, we found immune escape mechanisms in HCC.

Novel roles of karyopherin subunit alpha 2 in hepatocellular carcinoma

Hepatocellular carcinoma is the most common type of liver cancer and associated with a high fatality rate. This disease poses a major threat to human health worldwide. A considerable number of genetic and epigenetic factors are involved in the development of hepatocellular carcinoma. However, the molecular mechanism underlying the progression of hepatocellular carcinoma remains unclear. Karyopherin subunit alpha 2 (KPNA2), also termed importin α1, is a member of the nuclear transporter family. In recent years, KPNA2 has been gradually linked to the nuclear transport pathway for a variety of tumor-associated proteins. Furthermore, it promotes tumor development by participating in various pathophysiological processes such as cell proliferation, apoptosis, immune response, and viral infection. In hepatocellular carcinoma, it has been found that KPNA2 expression is significantly higher in liver cancer tissues versus paracancerous tissues. Moreover, it has been identified as a marker of poor prognosis and early recurrence in patients with hepatocellular carcinoma. Nevertheless, the role of KPNA2 in the development of hepatocellular carcinoma remains to be determined. This review summarizes the current knowledge on the pathogenesis and role of KPNA2 in hepatocellular carcinoma, and provides new directions and strategies for the diagnosis, treatment, and prediction of prognosis of this disease.

Bisphenol A replacement chemicals, BPF and BPS, induce protumorigenic changes in human mammary gland organoid morphology and proteome

SignificanceBisphenol A (BPA), found in many plastic products, has weak estrogenic effects that can be harmful to human health. Thus, structurally related replacements-bisphenol S (BPS) and bisphenol F (BPF)-are coming into wider use with very few data about their biological activities. Here, we compared the effects of BPA, BPS, and BPF on human mammary organoids established from normal breast tissue. BPS disrupted organoid architecture and induced supernumerary branching. At a proteomic level, the bisphenols altered the abundance of common targets and those that were unique to each compound. The latter included proteins linked to tumor-promoting processes. These data highlighted the importance of testing the human health effects of replacements that are structurally related to chemicals of concern.

HELLS Is Negatively Regulated by Wild-Type P53 in Liver Cancer by a Mechanism Involving P21 and FOXM1

Simple Summary

The tumor suppressor protein P53 is a major player in preventing liver cancer development and progression. In this study we could show that P53 negatively regulates the expression of Helicase, lymphoid specific (HELLS), previously described as an important pro-tumorigenic epigenetic regulator in hepatocarcinogenesis. The regulatory mechanism included induction of the P53 target gene P21 (CDKN1A) resulting in repression of HELLS via downregulation of the transcription factor Forkhead Box Protein M1 (FOXM1). Our in vitro and in vivo findings indicate an important additional aspect of the tumor suppressive function of P53 in liver cancer linked to epigenetic regulation.

Abstract

The major tumor suppressor P53 (TP53) acts primarily as a transcription factor by activating or repressing subsets of its numerous target genes, resulting in different cellular outcomes (e.g., cell cycle arrest, apoptosis and senescence). P53-dependent gene regulation is linked to several aspects of chromatin remodeling; however, regulation of chromatin-modifying enzymes by P53 is poorly understood in hepatocarcinogenesis. Herein, we identified Helicase, lymphoid specific (HELLS), a major epigenetic regulator in liver cancer, as a strong and selective P53 repression target within the SNF2-like helicase family. The underlying regulatory mechanism involved P53-dependent induction of P21 (CDKN1A), leading to repression of Forkhead Box Protein M1 (FOXM1) that in turn resulted in downregulation of HELLS expression. Supporting our in vitro data, we found higher expression of HELLS in murine HCCs arising in a Trp53−/− background compared to Trp53+/+ HCCs as well as a strong and highly significant correlation between HELLS and FOXM1 expression in different HCC patient cohorts. Our data suggest that functional or mutational inactivation of P53 substantially contributes to overexpression of HELLS in HCC patients and indicates a previously unstudied aspect of P53′s ability to suppress liver cancer formation.

Multiomics-based analyses of KPNA2 highlight its multiple potentials in hepatocellular carcinoma

Dysregulation and prognostic roles of Karyopherin α2 (KPNA2) were reported in many malignancies including hepatocellular carcinoma (HCC). A multi-omics analysis of KPNA2 is needed to gain a deeper understanding of its multilevel molecular characteristics and provide novel clues for HCC diagnosis, prognosis, and target therapy. Herein multi-omic alterations of KPNA2 were analyzed at genetic, epigenetic, transcript, and protein levels with evaluation of their relevance with clinicopathological features of HCC by integrative analyses. The significant correlations of KPNA2 expression with its gene copy number variation (CNV) and methylation status were shown through Spearman correlation analyses. With Cox regression, Kaplan-Meier survival, and receiver operating characteristic (ROC) analyses, based on the factors of KPNA2 CNV, methylation, expression, and tumor stage, risk models for HCC overall survival (OS) and disease-free survival (DFS) were constructed which could discriminate the 1-year, 3-year, and 5-year OS/DFS status effectively. With Microenvironment Cell Populations-counter (MCP-counter), the immune infiltrations of HCC samples were evaluated and their associations with KPNA2 were shown. KPNA2 expression in liver was found to be influenced by low fat diet and presented significant correlations with fatty acid metabolism and fatty acid synthase activity in HCC. KPNA2 was detected lowered in HCC patient's plasma by enzyme linked immunosorbent assay (ELISA), consistent with its translocation to nuclei of HCC cells. In conclusion, KPNA2 multilevel dysregulation in HCC and its correlations with immune infiltration and the fatty acid metabolism pathway indicated its multiple roles in HCC. The clinicopathological significance of KPNA2 was highlighted through the in-depth analyses at multilevels.

KPNA2 promotes renal cell carcinoma proliferation and metastasis via NPM

Karyopherin α2 (KPNA2), involved in nucleocytoplasmic transport, has been reported to be up‐regulated in tumorigenesis. However, comprehensive studies of KPNA2 functions in renal cell carcinoma (RCC) are still lacking. In this study, we aim to investigate the roles of KPNA2 in kidney tumour development. Our results showed that down‐regulation of KPNA2 inhibited the proliferation and invasion of kidney tumour cell cells in vitro, while the cell cycle arrest and cellular apoptosis were induced once KPNA2 was silenced. Repression of KPNA2 was proved to be efficient to repress tumorigenesis and development of kidney tumour in in nude mice. Furthermore, one related participator, NPM, was identified based on Co‐IP/MS and bioinformatics analyses. The up‐regulation of NPM attenuates the efficiency of knockdown KPNA2. These results indicated that KPNA2 may regulate NPM to play a crucial role for kidney tumour development.

DTNA promotes HBV-induced hepatocellular carcinoma progression by activating STAT3 and regulating TGFβ1 and P53 signaling

OBJECTIVE

Hepatitis B virus (HBV) infection causes liver fibrosis, cirrhosis and hepatocellular carcinoma (HCC) development, but the underlying mechanism remains poorly understood. This study aimed to investigate the roles and molecular mechanisms of Dystrobrevin-α (DTNA) in HBV-induced liver cirrhosis and HCC pathogenesis.

METHODS

DTNA expression was bioinformatically analyzed using the GEO database. DTNA expression was silenced by transfection with shRNAs. Cell proliferation and apoptosis were evaluated by MTT and flow cytometry respectively. The expression of genes in mRNA or protein levels was assessed by quantitative RT-PCR and western blotting. The interaction between proteins was predicted with the String and GCBI online softwares, and then confirmed by co-immunoprecipitation. Animal models were established by injecting nude mice with AVV8-HBV1.3 vector.

RESULTS

Bioinformatics analysis showed a significantly increase in DTNA expression in HBV-positive liver cirrhosis and HCC patients. HBV infection caused a significantly increase in DTNA expression in HCC cell lines HepAD38 and HepG2.2.15. DTNA knockdown suppressed proliferation and promoted apoptosis of HBV-infected HepAD38 and HepG2.2.15 cells. HBV induced elevated expression of fibrosis-related genes Collagen II and TGFβ1 in LO-2 cells, which were suppressed by DTNA knockdown. DTNA directly binded with STAT3 protein to promote STAT3 phosphorylation and TGFβ1 expression and repress P53 expression in HBV-infected HepAD38 and LO-2 cells. The DTNA/STAT3 axis was activated during HBV-induced fibrosis, cirrhosis and HCC development in mouse model.

CONCLUSION

DTNA binds with and further activates STAT3 to induce TGFβ1 expression and repress P53 expression, thus promoting HBV-induced liver fibrosis, cirrhosis and hepatocellular carcinoma progression.

The emerging roles of KPNA2 in cancer

Karyopherin α2 (KPNA2, also known as importinα-1), a member of the nuclear transporter family, is involved in the nucleocytoplasmic transport pathway of a variety of tumor-associated proteins. Recent studies have found that KPNA2 is overexpressed in various cancers, which is associated with poor prognosis. In addition, it has been shown to promote tumor formation and progression by participating in cell differentiation, proliferation, apoptosis, immune response, and viral infection. It is indicated that KPNA2 also plays an important role in the diagnosis, treatment and prognosis of tumors. Herein, we provide an overview of the function and mechanism of KPNA2 in cancer and the prospects in the diagnosis and treatment of cancer. In the future, KPNA2 provides new ideas for the early diagnosis of malignant tumors, the development of molecularly targeted drugs, and prognosis evaluation.

Karyopherin α2-dependent import of E2F1 and TFDP1 maintains protumorigenic stathmin expression in liver cancer

Background

Members of the karyopherin superfamily serve as nuclear transport receptors/adaptor proteins and provide exchange of macromolecules between the nucleo- and cytoplasm. Emerging evidence suggests a subset of karyopherins to be dysregulated in hepatocarcinogenesis including karyopherin-α2 (KPNA2). However, the functional and regulatory role of KPNA2 in liver cancer remains incompletely understood.

Methods

Quantitative proteomics (LC-MS/MS, ~ 1750 proteins in total) was used to study changes in global protein abundance upon siRNA-mediated KPNA2 knockdown in HCC cells. Functional and mechanistic analyses included colony formation and 2D migration assays, co-immunoprecipitation (CoIP), chromatin immunoprecipitation (ChIP), qRT-PCR, immmunblotting, and subcellular fractionation. In vitro results were correlated with data derived from a murine HCC model and HCC patient samples (3 cohorts, n > 600 in total).

Results

The proteomic approach revealed the pro-tumorigenic, microtubule (MT) interacting protein stathmin (STMN1) among the most downregulated proteins upon KPNA2 depletion in HCC cells. We further observed that KPNA2 knockdown leads to reduced tumor cell migration and colony formation of HCC cells, which could be phenocopied by direct knockdown of stathmin. As the underlying regulatory mechanism, we uncovered E2F1 and TFDP1 as transport substrates of KPNA2 being retained in the cytoplasm upon KPNA2 ablation, thereby resulting in reduced STMN1 expression. Finally, murine and human HCC data indicate significant correlations of STMN1 expression with E2F1/TFPD1 and with KPNA2 expression and their association with poor prognosis in HCC patients.

Conclusion

Our data suggest that KPNA2 regulates STMN1 by import of E2F1/TFDP1 and thereby provide a novel link between nuclear transport and MT-interacting proteins in HCC with functional and prognostic significance.

Prognostic roles of the transcriptional expression of exportins in hepatocellular carcinoma

Aims: A large number of studies have suggested that exportins (XPOs) play a pivotal role in human cancers. In the present study, we analyzed XPO mRNA expression in cancer tissues and explored their prognostic value in hepatocellular carcinoma (HCC).Methods: Transcriptional and survival data related to XPO expression in HCC patients were obtained through the ONCOMINE and UALCAN databases. Survival analysis plots were drawn with Gene Expression Profiling Interactive Analysis (GEPIA). Sequence alteration data for XPOs were obtained from The Cancer Genome Atlas (TCGA) database and c-BioPortal. Gene functional enrichment analyses were performed with Database for Annotation, Visualization and Integrated Discovery (DAVID).Results: Compared with normal liver tissues, significant XPO mRNA overexpression was observed in HCC cancer tissues. There was a trend of higher XPO expression in more advanced clinical stages and lower differentiated pathological grades of HCC. In HCC patients, high expression of XPO1, CSE1L, XPOT, XPO4/5/6 was related to poor overall survival (OS), and XPO1, CSE1L and XPO5/6 were correlated with poor disease-free survival (DFS). The main genetic alterations in XPOs involved mRNA up-regulation, DNA amplification and deletion. General XPO mutations were remarkably associated with worse OS and mostly affected the pathways of RNA transport and oocyte meiosis.Conclusion: High expression of XPOs was associated with a poor prognosis in HCC patients. XPOs may be exploited as good prognostic biomarkers for survival in HCC patients.

Nucleoporin Nup155 is part of the p53 network in liver cancer

Cancer-relevant signalling pathways rely on bidirectional nucleocytoplasmic transport events through the nuclear pore complex (NPC). However, mechanisms by which individual NPC components (Nups) participate in the regulation of these pathways remain poorly understood. We discover by integrating large scale proteomics, polysome fractionation and a focused RNAi approach that Nup155 controls mRNA translation of p21 (CDKN1A), a key mediator of the p53 response. The underlying mechanism involves transcriptional regulation of the putative tRNA and rRNA methyltransferase FTSJ1 by Nup155. Furthermore, we observe that Nup155 and FTSJ1 are p53 repression targets and accordingly find a correlation between the p53 status, Nup155 and FTSJ1 expression in murine and human hepatocellular carcinoma. Our data suggest an unanticipated regulatory network linking translational control by and repression of a structural NPC component modulating the p53 pathway through its effectors.

The nuclear pore complex (NPC) is known to regulate p53 signaling and this has mainly been linked to peripheral NPC subunits. Here the authors show that Nup155 from the NPC inner ring regulates the p53 pathway by controlling p21 translation while also being a target of p53-mediated repression.

Upregulated KPNA2 promotes hepatocellular carcinoma progression and indicates prognostic significance across human cancer types

Hepatocellular carcinoma (HCC) is one of the most aggressive cancers worldwide. Identification of the molecular mechanisms underlying the development and progression of HCC is particularly important. Here, we demonstrated the expression pattern, clinical significance, and function of Karyopherin α2 (KPNA2) in HCC. The expression of KPNA2 was upregulated in tumor tissue and negatively associated with the survival time, and a significant correlation between KPNA2 expression and aggressive clinical characteristics was established. Both in vitro and in vivo experiments demonstrated that knockdown of KPNA2 reduced migration and proliferation capacities of HCC cells, while over-expression of KPNA2 increased these malignant characteristics. The analysis of the Cancer Genome Atlas cohorts also reveals that high-KPNA2 expression is associated with poor outcome in multiple cancer types. In addition, gene sets enrichment analysis exhibited cell cycle and DNA replication as the top altered pathways in the high-KPNA2 expression group in HCC and other two cancer types. Overall, this study identified KPNA2 as a potential diagnostic and prognostic biomarker in HCC and other neoplasms, probably by regulating cell cycle and DNA replication.

Inhibition of Karyopherin beta 1 suppresses prostate cancer growth

Prostate cancer (PCa) initiation and progression requires activation of numerous oncogenic signaling pathways. Nuclear-cytoplasmic transport of oncogenic factors is mediated by Karyopherin proteins during cell transformation. However, the role of nuclear transporter proteins in PCa progression has not been well defined. Here, we report that the KPNB1, a key member of Karyopherin beta subunits, is highly expressed in advanced prostate cancers. Further study showed that targeting KPNB1 suppressed the proliferation of prostate cancer cells. The knockdown of KPNB1 reduced nuclear translocation of c-Myc, the expression of downstream cell cycle modulators, and phosphorylation of regulator of chromatin condensation 1 (RCC1), a key protein for spindle assembly during mitosis. Meanwhile, CHIP assay demonstrated the binding of c-Myc to KPNB1 promoter region, which indicated a positive feedback regulation of KPNB1 expression mediated by the c-Myc. In addition, NF-κB subunit p50 translocation to nuclei was blocked by KPNB1 inhibition, which led to an increase in apoptosis and a decrease in tumor sphere formation of PCa cells. Furthermore, subcutaneous xenograft tumor models with a stable knockdown of KPNB1 in C42B PCa cells validated that the inhibition of KPNB1 could suppress the growth of prostate tumor in vivo. Moreover, the intravenously administration of importazole, a specific inhibitor for KPNB1, effectively reduced PCa tumor size and weight in mice inoculated with PC3 PCa cells. In summary, our data established the functional link between KPNB1 and PCa prone c-Myc, NF-kB, and cell cycle modulators. More importantly, inhibition of KPNB1 could be a new therapeutic target for PCa treatment.

CSE1L participates in regulating cell mitosis in human seminoma

Objectives

CSE1L has been reported to be highly expressed in various tumours. Testicular germ cell tumours are common among young males, and seminoma is the major type. However, whether CSE1L has functions in the seminoma is unclear.

Materials and methods

The expression of CSE1L was detected by immunohistochemistry in seminoma tissues and non‐tumour normal testis tissues from patients. CSE1L distribution during cell mitosis was determined by immunofluorescent staining with CSE1L, α‐tubulin and γ‐tubulin antibodies. The effects of Cse1L knockdown on cell proliferation and cell cycle progression were determined by Cell Counting Kit‐8 assay, flow cytometry, PH3 staining and bromodeoxyuridine incorporation assay.

Results

CSE1L was significantly enriched in the seminoma tissue compared with the non‐tumour normal testis tissue. CSE1L also co‐localized with α‐tubulin in the cells with a potential to divide. In the seminoma cell line TCam‐2, CSE1L was associated with the spindles and the centrosomes during cell division. The knockdown of CSE1L in TCam‐2 cells attenuated the cells’ proliferative capacity. Cell cycle assay revealed that the CSE1L‐deficient cells were mainly arrested in the G0/G1 phase and moderately delayed in the G2/M phase. The proportion of cells with multipolar spindle and abnormal spindle geometry was obviously increased by CSE1L expression silencing in the TCam‐2 cells.

Conclusions

Overall, these findings showed that CSE1L plays a pivotal role in maintaining cell proliferation and cell division in seminomas.

Spatial Tissue Proteomics Quantifies Inter- and Intratumor Heterogeneity in Hepatocellular Carcinoma (HCC)

The interpatient variability of tumor proteomes has been investigated on a large scale but many tumors display also intratumoral heterogeneity regarding morphological and genetic features. It remains largely unknown to what extent the local proteome of tumors intrinsically differs. Here, we used hepatocellular carcinoma as a model system to quantify both inter- and intratumor heterogeneity across human patient specimens with spatial resolution. We defined proteomic features that distinguish neoplastic from the directly adjacent nonneoplastic tissue, such as decreased abundance of NADH dehydrogenase complex I. We then demonstrated the existence of intratumoral variations in protein abundance that re-occur across different patient samples, and affect clinically relevant proteins, even in the absence of obvious morphological differences or genetic alterations. Our work demonstrates the suitability and the benefits of using mass spectrometry-based proteomics to analyze diagnostic tumor specimens with spatial resolution. Data are available via ProteomeXchange with identifier PXD007052.

Cellular apoptosis susceptibility (CAS) is linked to integrin β1 and required for tumor cell migration and invasion in hepatocellular carcinoma (HCC)

Importins and exportins represent an integral part of the nucleocytoplasmic transport machinery with fundamental importance for eukaryotic cell function. A variety of malignancies including hepatocellular carcinoma (HCC) show de-regulation of nuclear transport factors such as overexpression of the exportin Cellular Apoptosis Susceptibility (CAS). The functional implications of CAS in hepatocarcinogenesis remain, however, poorly understood. Here we integrated proteomics, transcriptomics and functional assays with patient data to further characterize the role of CAS in HCC. By analyzing ∼ 1700 proteins using quantitative mass spectrometry in HCC cells we found that CAS depletion by RNAi leads to de-regulation of integrins, particularly down-regulation of integrin β1. Consistent with this finding, CAS knockdown resulted in substantially reduced migration and invasion of HCC cell lines as analyzed by 2D ‘scratch’ and invasion chamber assays, respectively. Supporting the potential in vivo relevance, high expression levels of CAS in HCC tissue samples were associated with macroangioinvasion and poorer patient outcome. Our data suggest a previously unanticipated link between CAS and integrin signaling which correlates with an aggressive HCC phenotype.

Alterations of the nuclear transport system in hepatocellular carcinoma - New basis for therapeutic strategies

Hepatocellular carcinoma (HCC) is among the most prevalent human malignancies worldwide with rising incidence in industrialised countries, few therapeutic options and poor prognosis. To expand and improve therapeutic strategies, identification of drug targets involved in several liver cancer-related pathways is crucial. Virtually all signal transduction cascades cross the nuclear envelope and therefore require components of the nuclear transport system (NTS), including nuclear transport receptors (e.g. importins and exportins) and the nuclear pore complex. Accordingly, members of the NTS represent promising targets for therapeutic intervention. Selective inhibitors of nuclear export have already entered clinical trials for various malignancies. Herein, we review the current knowledge regarding alterations of the NTS and their potential for targeted therapy in HCC.

Multiplexed Thiol Reactivity Profiling for Target Discovery of Electrophilic Natural Products

Electrophilic groups, such as Michael acceptors, expoxides, are common motifs in natural products (NPs). Electrophilic NPs can act through covalent modification of cysteinyl thiols on functional proteins, and exhibit potent cytotoxicity and anti-inflammatory/cancer activities. Here we describe a new chemoproteomic strategy, termed multiplexed thiol reactivity profiling (MTRP), and its use in target discovery of electrophilic NPs. We demonstrate the utility of MTRP by identifying cellular targets of gambogic acid, an electrophilic NP that is currently under evaluation in clinical trials as anticancer agent. Moreover, MTRP enables simultaneous comparison of seven structurally diversified α,β-unsaturated γ-lactones, which provides insights into the relative proteomic reactivity and target preference of diverse structural scaffolds coupled to a common electrophilic motif and reveals various potential druggable targets with liganded cysteines. We anticipate that this new method for thiol reactivity profiling in a multiplexed manner will find broad application in redox biology and drug discovery.

Increased expression of importin-β, exportin-5 and nuclear transportable proteins in Alzheimer's disease aids anatomic pathologists in its diagnosis

Understanding the metabolic profile of neurons with the hyperphosphorylated tau protein characteristic of Alzheimer's disease is essential to unraveling new potential therapies and diagnostics for the surgical pathologist. We stratified 75 brain tissues from Alzheimer's disease into hyperphosphorylated tau positive or negative and did co-expression analyses and qRTPCR for importin-β and exportin-5 plus several bcl2 family members and compared the data to controls, Down's dementia and Parkinson's disease. There was a significant increase in the expression of importin-β and exportin-5 in Alzheimer's disease relative to the three other categories (each p value<0.0001) where each protein co-localized with hyperphosphorylated tau. Both apoptotic and anti-apoptotic proteins were each significantly increased in Alzheimer's disease relative to the three other groups. Neurons with hyperphosphorylated tau in Alzheimer's disease have the profile of metabolically active cells including increased exportin-5 and importin-β mRNA and proteins which indicates that immunohistochemistry testing of these proteins may aid the surgical pathologist in making a definitive diagnosis.

Proteomic Analysis Reveals GMP Synthetase as p53 Repression Target in Liver Cancer

Disruption of the tumor-suppressive p53 network is a key event in human malignancies, including primary liver cancer. In response to different types of stress, p53 mediates several antiproliferative cellular outcomes, such as cell cycle arrest, apoptosis, and senescence, by activation or repression of its target genes. Metabolic alterations initiating or being part of the p53 response have become an actively studied research area in the p53 field, with several aspects that still remain to be elucidated. Herein, we identified GMP synthetase (GMPS), a key enzyme of de novo purine biosynthesis, as an important p53 repression target using a large-scale proteomics approach. This p53-mediated repression of GMPS could be validated by immunoblotting in Sk-Hep1, HepG2, and HuH6 cells. Moreover, we found GMPS transcriptionally repressed in a p21-dependent manner and its repression maintained in the context of p53-mediated cellular senescence. More important, direct knockdown of GMPS by RNA interference resulted in reduced cell viability and was sufficient to trigger cellular senescence. Finally, by comparing murine hepatocellular carcinomas, which developed in p53 wild-type (^+/+) versus p53 null (^-/-) mice, we observed higher GMPS expression in the latter, supporting the in vivo relevance of our findings. We conclude that repression of GMPS by p53 through p21 is a functionally relevant part of the p53-mediated senescence program limiting tumor cell growth in liver cancer.

Targeting nuclear transporters in cancer: Diagnostic, prognostic and therapeutic potential

The Karyopherin superfamily is a major class of soluble transport receptors consisting of both import and export proteins. The trafficking of proteins involved in transcription, cell signalling and cell cycle regulation among other functions across the nuclear membrane is essential for normal cellular functioning. However, in cancer cells, the altered expression or localization of nuclear transporters as well as the disruption of endogenous nuclear transport inhibitors are some ways in which the Karyopherin proteins are dysregulated. The value of nuclear transporters in the diagnosis, prognosis and treatment of cancer is currently being elucidated with recent studies highlighting their potential as biomarkers and therapeutic targets.

Oncogenic role of p21 in hepatocarcinogenesis suggests a new treatment strategy

A well-known tumor suppressor, p21, acts paradoxically by promoting tumor growth in some cellular conditions. These conflicting functions have been demonstrated in association with the HBx gene and in hepatocarcinogenesis. The molecular behavior of p21 depends on its subcellular localization. Nuclear p21 may inhibit cell proliferation and be proapoptotic, while cytoplasmic p21 may have oncogenic and anti-apoptotic functions. Because most typical tumor suppressive proteins also have different effects according to subcellular localization, elucidating the regulatory mechanisms underlying nucleo-cytoplasmic transport of these proteins would be significant and may lead to a new strategy for anti-hepatocellular carcinoma (HCC) therapy. Chromosome region maintenance 1 (CRM1) is a major nuclear export receptor involved in transport of tumor suppressors from nucleus to cytoplasm. Expression of CRM1 is enhanced in a variety of malignancies and in vitro studies have shown the efficacy of specific inhibition of CRM1 against cancer cell lines. Interestingly, interferon may keep p21 in the nucleus; this is one of the mechanisms of its anti-hepatocarcinogenic function. Here we review the oncogenic property of p21, which depends on its subcellular localization, and discuss the rationale underlying a new strategy for HCC treatment and prevention.

Nuclear Pore Complexes and Nucleocytoplasmic Transport: From Structure to Function to Disease

Nucleocytoplasmic transport is an essential cellular activity and occurs via nuclear pore complexes (NPCs) that reside in the double membrane of the nuclear envelope. Significant progress has been made during the past few years in unravelling the ultrastructural organization of NPCs and their constituents, the nucleoporins, by cryo-electron tomography and X-ray crystallography. Mass spectrometry and genomic approaches have provided deeper insight into the specific regulation and fine tuning of individual nuclear transport pathways. Recent research has also focused on the roles nucleoporins play in health and disease, some of which go beyond nucleocytoplasmic transport. Here we review emerging results aimed at understanding NPC architecture and nucleocytoplasmic transport at the atomic level, elucidating the specific function individual nucleoporins play in nuclear trafficking, and finally lighting up the contribution of nucleoporins and nuclear transport receptors in human diseases, such as cancer and certain genetic disorders.