BRCA/Fanconi anemia pathway implicates chemoresistance to gemcitabine in biliary tract cancer

Differential operation of MLH1/MSH2 and FANCD2 crosstalk in chemotolerant bladder carcinoma: a clinical and therapeutic intervening study

We aimed to understand the crosstalk between mismatch repair (MMR) and FA-BRCA pathway in primary bladder carcinoma (BlCa) samples as well as in chemotolerant cell line. We analysed the genetic alterations of MLH1 and MSH2 (MMR-related genes) and after that we correlated it with the nuclear translocation of FANCD2 protein. Next, we evaluated this crosstalk in T24 BlCa cell line in response to doxorubicin treatment. In primary BlCa tumors, infrequent genetic deletion (17-20%) but frequent promoter methylation (28-55%) of MLH1 and MSH2 was observed, where MLH1 was significantly (p < 0.05) more methylated among the early staged samples (NMIBC). However, MSH2 was significantly more altered among the NMIBC samples, signifying the importance of MMR pathway during the early pathogenesis of the disease. Furthermore, BlCa samples with underexpressed MLH1/MSH2 protein possessed cytoplasmic FANCD2 protein; encouraging that inefficiency of MMR proteins might restrict FANCD2 nuclear translocation. Next, we analysed publicly available data in GEO2R tool where we observed that in response to chemotherapeutic drugs, expression of MLH1, MSH2 and FANCD2 were diminishing. Validating this result in doxorubicin tolerant T24 cells, we found that expression of MLH1 and MSH2 was gradually decreased with increasing dose of doxorubicin. Interestingly, FANCD2 mono-ubiquitination (L-form) was also reduced in chemotolerant T24 cells. The crosstalk between MMR and FA-BRCA pathway was substantiated in the primary BlCa tumors. Further, in response to doxorubicin, this crosstalk was found to be hampered due to under-expression of MLH1 and MSH2 gene, thereby rendering chemotolerance.

LncRNA CACClnc promotes chemoresistance of colorectal cancer by modulating alternative splicing of RAD51

Long non-coding RNAs (lncRNAs) play important roles in carcinogenesis. However, the effect of lncRNA on chemoresistance and RNA alternative splicing remains largely unknown. In this study, we identified a novel lncRNA, CACClnc, which was upregulated and associated with chemoresistance and poor prognosis in colorectal cancer (CRC). CACClnc promoted CRC resistance to chemotherapy via promoting DNA repair and enhancing homologous recombination in vitro and in vivo. Mechanistically, CACClnc specifically bound to Y-box binding protein 1 (YB1, a splicing factor) and U2AF65 (a subunit of U2AF splicing factor), promoting the interaction between YB1 and U2AF65, and then modulated alternative splicing (AS) of RAD51 mRNA, and consequently altered CRC cell biology. In addition, expression of exosomal CACClnc in peripheral plasma of CRC patients can effectively predict the chemotherapy effect of patients before treatment. Thus, measuring and targeting CACClnc and its associated pathway could yield valuable insight into clinical management and might ameliorate CRC patients' outcomes.

Improved detection of homologous recombination deficiency in Chinese patients with ovarian cancer: a novel non-exonic single-nucleotide polymorphism-based next-generation sequencing panel

As homologous recombination deficiency (HRD) is a biomarker to predict the efficiency of PARP inhibitor treatment, this study developed a non-exonic single-nucleotide polymorphism (SNP)-based targeted next-generation sequencing panel and comprehensively examined it both on standard and clinical ovarian cancer tissues. The HRD scores calculated by the panel and whole-genome sequencing were consistent, with the analysis by sequenza being the most reliable. The results on clinical samples revealed that the panel performed better in HRD analysis compared with the SNP microarray. There are several distinctions between this newly developed kit and reported HRD detection panels. First, the panel covers only 52 592 SNPs, which makes it capable of detecting genomic instability. Secondly, all the SNPs are non-exonic; as a result, the panel can be used cooperatively with any exon panel. Thirdly, all the SNPs selected have a high minor allele frequency in Chinese people, making it a better choice for HRD detection in Chinese patients. In summary, this panel shows promise as a clinical application to guide PARP inhibitors or platinum drugs used in the treatment of ovarian and other cancers.

GLI1-targeting drugs induce replication stress and homologous recombination deficiency and synergize with PARP-targeted therapies in triple negative breast cancer cells

Triple negative breast cancer (TNBC), an aggressive and highly metastatic subtype of breast cancer. Glioma-associated oncogene 1 (GLI1) is a transcription factor and effector of the Hedgehog (Hh) signaling pathway, and is predictive of poor survival for TNBC patients. A nanostring DNA Damage Response (DDR) mRNA panel was used to identify GLI1-induced regulation of DDR genes. Western blots, immunohistochemistry and immunofluorescence were used to evaluate protein expression. Colony assays and mammosphere formation assays were utilized to assess survival of cancer cells. Flow cytometry analyses were employed to evaluate changes in the cell cycle profile, and DNA fiber assays were used to analyze alterations in replication dynamics in TNBC cells. The UALCAN portal and Ensemble programs were used for computational analysis of TCGA data. CompuSyn software was used to calculate combination index (CI) values to assess synergism in drug combination experiments. Inhibition of GLI1 in TNBC cells transcriptionally downregulate expression of FANCD2 and its foci formation, and causes a homologous recombination repair (HR) deficiency. As HR-deficient cancer cells are sensitive to PARP-targeted therapies, we evaluated a combination of the GLI1 inhibitor, GANT61, and a PARP inhibitor (olaparib) in TNBC cells. Combination of GANT61 and olaparib elevated DNA damage levels and these drug combinations caused synergistic lethality to TNBC cells. Aberrantly activated GLI1 regulates HR-mediated DNA repair by transcriptionally regulating FANCD2 to overcome chemotherapy-induced replication stress and DNA damage, and it contributes to resistance of TNBC cells to therapeutics.

Calreticulin: a potential diagnostic and therapeutic biomarker in gallbladder cancer

Recent studies suggested that calreticulin (CRT) has an important role in the progression of various types of cancer. Our previous study suggested that CRT was upregulated and acted as an oncogene in hepatocellular carcinoma. However, the role of CRT in gallbladder cancer (GBC) remains unclear. The expression level of CRT was upregulated in GBC tissues in comparison with adjacent non-tumor tissues and chronic cholecystitis tissues. Moreover, CRT expression was found to be correlated with the tumor size. Knockdown of CRT inhibited cell proliferation, induced apoptosis, arrested cell cycle and resulted in decreased resistance to gemcitabine, which was mediated by the inactivation of the PI3K/Akt pathway. Collectively, the present results suggested a potential role of CRT in GBC progression and provided novel insights into the mechanism underlying the CRT-mediated chemosensitivity in GBC cells.

Comparison of Prognostic Value of Red Cell-Related Parameters of Biliary Tract Cancer After Surgical Resection and Integration of a Prognostic Nomogram: A Retrospective Study

INTRODUCTION

Biliary tract cancer (BTC) comprises infrequently occurring neoplasms with poor prognoses. Red blood cell-related parameters are commonly reported prognostic factors. We aimed to compare and evaluate the clinical value of red blood cell-related parameters and develop a prognostic nomogram.

METHODS

The analysis involved 418 patients with BTC who underwent surgery from December 2003 to April 2017. Patients were divided into training and validation cohorts. Red blood cell-related parameters were compared using Kaplan-Meier analysis, the area under receiver-operating characteristic curve (AUC), and C-index. Predictive abilities were evaluated using Cox regression. We developed a nomogram incorporating superior parameters verified using calibration curves, internal validation, and subgroup analysis. The nomogram was compared with the tumour-node-metastasis staging system through ROC, C-index, and Kaplan-Meier analysis.

RESULTS

A combined parameter comprising haemoglobin, albumin, lymphocytes, and platelets (HALP), which was superior to other red blood cell-related parameters, indicated a high risk of worse overall survival when low. Univariate analysis revealed that HALP together with other clinical characteristics was associated with overall survival. Multivariate analysis revealed that HALP, tumour-node-metastasis staging, and operative outcome were independent predictors of poor overall survival. Internal validation proved the predictive value of the nomogram. Additional statistical analyses established the advantages of the nomogram vs. tumour-node-metastasis staging.

CONCLUSION

HALP was a superior red blood cell-related parameter and an independent predictor of prognosis. Our nomogram based on HALP, tumour-node-metastasis staging, and operative outcome is a promising model for predicting overall survival.

Genomic profiling reveals high frequency of DNA repair genetic aberrations in gallbladder cancer

DNA repair gene aberrations (GAs) occur in several cancers, may be prognostic and are actionable. We investigated the frequency of DNA repair GAs in gallbladder cancer (GBC), association with tumor mutational burden (TMB), microsatellite instability (MSI), programmed cell death protein 1 (PD-1), and its ligand (PD-L1) expression. Comprehensive genomic profiling (CGP) of 760 GBC was performed. We investigated GAs in 19 DNA repair genes including direct DNA repair genes (ATM, ATR, BRCA1, BRCA2, FANCA, FANCD2, MLH1, MSH2, MSH6, PALB2, POLD1, POLE, PRKDC, and RAD50) and caretaker genes (BAP1, CDK12, MLL3, TP53, and BLM) and classified patients into 3 groups based on TMB level: low (< 5.5 mutations/Mb), intermediate (5.5-19.5 mutations/Mb), and high (≥ 19.5 mutations/Mb). We assessed MSI status and PD-1 & PD-L1 expression. 658 (86.6%) had at least 1 actionable GA. Direct DNA repair gene GAs were identified in 109 patients (14.2%), while 476 (62.6%) had GAs in caretaker genes. Both direct and caretaker DNA repair GAs were significantly associated with high TMB (P = 0.0005 and 0.0001, respectively). Tumor PD-L1 expression was positive in 119 (15.6%), with 17 (2.2%) being moderate or high. DNA repair GAs are relatively frequent in GBC and associated with coexisting actionable mutations and a high TMB.

The forkhead box M1 (FOXM1) expression and antitumor effect of FOXM1 inhibition in malignant rhabdoid tumor

PURPOSE

Malignant rhabdoid tumor (MRT) is a rare, highly aggressive sarcoma with an uncertain cell of origin. Despite the existing standard of intensive multimodal therapy, the prognosis of patients with MRT is very poor. Novel antitumor agents are needed for MRT patients. Forkhead box transcription factor 1 (FOXM1) is overexpressed and is correlated with the pathogenesis in several human malignancies. In this study, we identified the clinicopathological and prognostic values of the expression of FOXM1 and its roles in the progression of MRT.

METHODS

We investigated the FOXM1 expression levels and their clinical significance in 23 MRT specimens using immunohistochemistry and performed clinicopathologic and prognostic analyses. We also demonstrated correlations between the downregulation of FOXM1 and oncological characteristics using small interfering RNA (siRNA) and FOXM1 inhibitor in MRT cell lines.

RESULTS

Histopathological analyses revealed that primary renal MRTs showed significantly low FOXM1 protein expression levels (p = 0.032); however, there were no significant differences in other clinicopathological characteristics or the survival rate. FOXM1 siRNA and FOXM1 inhibitor (thiostrepton) successfully downregulated the mRNA and protein expression of FOXM1 in vitro and the downregulation of FOXM1 inhibited cell proliferation, drug resistance to chemotherapeutic agents, migration, invasion, and caused the cell cycle arrest and apoptosis of MRT cell lines. A cDNA microarray analysis showed that FOXM1 regulated FANCD2 and NBS1, which are key genes for DNA damage repair.

CONCLUSION

This study demonstrates that FOXM1 may serve as a promising therapeutic target for MRT.

Heterogeneity of Treg/Th17 According to Cancer Progression and Modification in Biliary Tract Cancers via Self-Producing Cytokines

BACKGROUND/AIM

We previously demonstrated that inflammatory cytokine interleukin-6 (IL-6) was produced during cancer progression, worked together with transforming growth factor-beta 1 (TGF-β1), and induced the epithelial-mesenchymal transition (EMT) with chemo-resistance against gemcitabine (GR) at the invasion front of biliary tract cancers (BTCs). However, the significance of cytokine-induced T cell accumulation at the tumor microenvironment in biliary tract cancer (BTC) is not well understood. Because these cytokines (IL-6 and TGF-β1) are able to differentiate naïve T cells into Foxp3-expressing T cells (Tregs) and/or IL-17-producing T helper 17 (Th17) cells, we investigated the relationship between heterogeneous, cancer-producing cytokines and T cell differentiation.

METHODS

In total, 127 curative resected specimens from patients with BTCs at Osaka University Hospital between 2000 and 2012 were evaluated for IL-6, TGF-β1, Tregs, and Th17 cells by immunohistochemistry. The ability of BTC-GR cells to undergo T cell differentiation was investigated in vitro.

RESULTS

Tregs accumulated at the tumor center and Th17 cells accumulated at the invasion front during cancer progression and/or metastasis; each signaled poor prognosis. Treg accumulation was related to TGF-β1 expression by cancer cells, and Th17 cell accumulation was related to IL-6 expression by cancer cells, in resected specimens; this was confirmed in vitro. Compared with parent cells, GR cells produced IL-6 but not TGF-β1 in a time-dependent manner, had EMT features, and induced T cell differentiation to Th17 cells but not Tregs.

CONCLUSION

Cytokines produced by cancer cells (IL-6 and TGF-β1) induced heterogeneity of Tregs and Th17 cells in the tumor microenvironment, supporting progression of BTC.

Subcellular localization of FANCD2 is associated with survival in ovarian carcinoma

Objective: Ovarian cancer is a leading cause of death from gynecological cancers. Late diagnosis and resistance to therapy results in mortality and effective screening is required for early diagnosis and better treatments. Expression of the Fanconi Anemia complementation group D2 protein (FANCD2) is reduced in ovarian surface epithelial cells (OSE) in patients with ovarian cancer. FANCD2 has been studied for its role in DNA repair; however multiple studies have suggested that FANCD2 has a role outside the nucleus. We sought to determine whether subcellular localization of FANCD2 correlates with patient outcome in ovarian cancer.

Methods: We examined the subcellular localization of FANCD2 in primary OSE cells from consenting patients with ovarian cancer or a normal ovary. Ovarian tissue microarray was stained with anti-FANCD2 antibody by immunohistochemistry and the correlation of FANCD2 localization with patient outcomes was assessed. FANCD2 binding partners were identified by immunoprecipitation of cytoplasmic FANCD2.

Results: Nuclear and cytoplasmic localization of FANCD2 was observed in OSEs from both normal and ovarian cancer patients. Patients with cytoplasmic localization of FANCD2 (cFANCD2) experienced significantly longer median survival time (50 months), versus patients without cytoplasmic localization of FANCD2 (38 months; p < 0.05). Cytoplasmic FANCD2 was found to bind proteins involved in the innate immune system, cellular response to heat stress, amyloid fiber formation and estrogen mediated signaling.

Conclusions: Our results suggest that the presence of cytoplasmic FANCD2 modulates FANCD2 activity resulting in better survival outcome in ovarian cancer patients.

DNA damage response and resistance of cancer stem cells

The cancer stem cell (CSC) model defines tumors as hierarchically organized entities, containing a small population of tumorigenic CSC, or tumour-initiating cells, placed at the apex of this hierarchy. These cells may share common qualities with chemo- and radio-resistant cancer cells and contribute to self-renewal activities resulting in tumour formation, maintenance, growth and metastasis. Yet, it remains obscure what self-defense mechanisms are utilized by these cells against the chemotherapeutic drugs or radiotherapy. Recently, attention has been focused on the pivotal role of the DNA damage response (DDR) in tumorigenesis. In line with this note, an increased DDR that prevents CSC and chemoresistant cells from genotoxic pressure of chemotherapeutic drugs or radiation may be responsible for cancer metastasis. In this review, we focus on the current knowledge concerning the role of DDR in CSC and resistant cancer cells and describe the existing opportunities of re-sensitizing such cells to modulate therapeutic treatment effects.

Establishment and Characterization of a New Intrahepatic Cholangiocarcinoma Cell Line Resistant to Gemcitabine

Intrahepatic cholangiocarcinoma (ICC) is one of the most lethal liver cancers. Late diagnosis and chemotherapy resistance contribute to the scarce outfit and poor survival. Resistance mechanisms are still poorly understood. Here, we established a Gemcitabine (GEM) resistant model, the MT-CHC01R1.5 cell line, obtained by a GEM gradual exposure (up to 1.5 µM) of the sensitive counterpart, MT-CHC01. GEM resistance was irreversible, even at high doses. The in vitro and in vivo growth was slower than MT-CHC01, and no differences were highlighted in terms of migration and invasion. Drug prediction analysis suggested that Paclitaxel and Doxycycline might overcome GEM resistance. Indeed, in vitro MT-CHC01R1.5 growth was reduced by Paclitaxel and Doxycycline. Importantly, Doxycycline pretreatment at very low doses restored GEM sensitivity. To assess molecular mechanisms underlying the acquisition of GEM resistance, a detailed analysis of the transcriptome in MT-CHC01R1.5 cells versus the corresponding parental counterpart was performed. Transcriptomic analysis showed that most up-regulated genes were involved in cell cycle regulation and in the DNA related process, while most down-regulated genes were involved in the response to stimuli, xenobiotic metabolism, and angiogenesis. Furthermore, additional panels of drug resistance and epithelial to mesenchymal transition genes (n = 168) were tested by qRT-PCR and the expression of 20 genes was affected. Next, based on a comparison between qRT-PCR and microarray data, a list of up-regulated genes in MT-CHC01R1.5 was selected and further confirmed in a primary cell culture obtained from an ICC patient resistant to GEM. In conclusion, we characterized a new GEM resistance ICC model that could be exploited either to study alternative mechanisms of resistance or to explore new therapies.

Reactive Oxygen Species-Mediated Autophagy Defines the Fate of Cancer Stem Cells

Significance: A fraction of tumorigenic cells, also known as tumor initiating or cancer stem cells (CSCs), is thought to drive tumor growth, metastasis, and chemoresistance. However, little is known regarding mechanisms that convey relevant pathways contributing to their self-renewal, proliferation, and differentiation abilities. Recent Advances: Recent works on CSCs provide evidence on the role of redox disruption and regulation of autophagic flux. This has been linked to increased DNA repair capacity and chemoresistance. Critical Issues: The current review summarizes the most recent studies assessing the role of redox homeostasis, autophagy, and chemoresistance in CSCs, including some novel findings on microRNAs and their role in horizontal transfer within cancer cell populations. Future Directions: Rational anticancer therapy and prevention should rely on the fact that cancer is a redox disease with the CSCs being the apex modulated by redox-mediated autophagy. Antioxid. Redox Signal. 28, 1066-1079.

AMP-activated protein kinase is involved in the activation of the Fanconi anemia/BRCA pathway in response to DNA interstrand crosslinks

Fanconi anemia complementation group (FANC) proteins constitute the Fanconi Anemia (FA)/BRCA pathway that is activated in response to DNA interstrand crosslinks (ICLs). We previously performed yeast two-hybrid screening to identify novel FANC-interacting proteins and discovered that the alpha subunit of AMP-activated protein kinase (AMPKα1) was a candidate binding partner of the FANCG protein, which is a component of the FA nuclear core complex. We confirmed the interaction between AMPKα and both FANCG using co-immunoprecipitation experiments. Additionally, we showed that AMPKα interacted with FANCA, another component of the FA nuclear core complex. AMPKα knockdown in U2OS cells decreased FANCD2 monoubiquitination and nuclear foci formation upon mitomycin C-induced ICLs. Furthermore, AMPKα knockdown enhanced cellular sensitivity to MMC. MMC treatment resulted in an increase in AMPKα phosphorylation/activation, indicating AMPK is involved in the cellular response to ICLs. FANCA was phosphorylated by AMPK at S347 and phosphorylation increased with MMC treatment. MMC-induced FANCD2 monoubiquitination and nuclear foci formation were compromised in a U2OS cell line that stably overexpressed the S347A mutant form of FANCA compared to wild-type FANCA-overexpressing cells, indicating a requirement for FANCA phosphorylation at S347 for proper activation of the FA/BRCA pathway. Our data suggest AMPK is involved in the activation of the FA/BRCA pathway.

Biliary tract cancer stem cells - translational options and challenges

Management of biliary tract cancer remains challenging. Tumors show high recurrence rates and therapeutic resistance, leading to dismal prognosis and short survival. The cancer stem cell model states that a tumor is a heterogeneous conglomerate of cells, in which a certain subpopulation of cells - the cancer stem cells - possesses stem cell properties. Cancer stem cells have high clinical relevance due to their potential contributions to development, progression and aggressiveness as well as recurrence and metastasis of malignant tumors. Consequently, reliable identification of as well as pharmacological intervention with cancer stem cells is an intensively investigated and promising research field. The involvement of cancer stem cells in biliary tract cancer is likely as a number of studies demonstrated their existence and the obvious clinical relevance of several established cancer stem cell markers in biliary tract cancer models and tissues. In the present article, we review and discuss the currently available literature addressing the role of putative cancer stem cells in biliary tract cancer as well as the connection between known contributors of biliary tract tumorigenesis such as oncogenic signaling pathways, micro-RNAs and the tumor microenvironment with cancer stem cells.

Late DNA Damage Mediated by Homologous Recombination Repair Results in Radiosensitization with Gemcitabine

Gemcitabine (dFdCyd) shows broad antitumor activity in solid tumors in chemotherapeutic regimens or when combined with ionizing radiation (radiosensitization). While it is known that mismatches in DNA are necessary for dFdCyd radiosensitization, the critical event resulting in radiosensitization has not been identified. Here we hypothesized that late DNA damage (≥24 h after drug washout/irradiation) is a causal event in radiosensitization by dFdCyd, and that homologous recombination repair (HRR) is required for this late DNA damage. Using γ-H2AX as a measurement of DNA damage in MCF-7 breast cancer cells, we demonstrate that 10 or 80 nM dFdCyd alone produced significantly more late DNA damage compared to that observed within 4 h after treatment. The combination of dFdCyd treatment followed by irradiation did not produce a consistent increase in DNA damage in the first 4 h after treatment, however, there was a synergistic increase 24-48 h later relative to treatment with dFdCyd or radiation alone. RNAi suppression of the essential HRR protein, XRCC3, significantly decreased both radiosensitization and late DNA damage. Furthermore, inhibition of HRR with the Rad51 inhibitor B02 prevented radiosensitization when added after, but not during, treatment with dFdCyd and radiation. To our knowledge, this is the first published study to show that radiosensitization with dFdCyd results from a synergistic increase in DNA damage at 24-48 h after drug and radiation treatment, and that this damage and radiosensitization require HRR. These results suggest that tumors that overexpress HRR will be more vulnerable to chemoradiotherapy, and treatments that increase HRR and/or mismatches in DNA will enhance dFdCyd radiosensitization.

A Histone Deacetylase Inhibitor Suppresses Epithelial-Mesenchymal Transition and Attenuates Chemoresistance in Biliary Tract Cancer

Epithelial-mesenchymal transition (EMT) is involved in the characteristics of malignancy, such as invasion, metastasis, and chemoresistance. In biliary tract cancer (BTC), EMT is induced by transforming growth factor-beta 1 (TGF-β1). The EMT is reversible; therefore, it is conceivable that it could be related to some epigenetic changes. We focused on histone deacetylase (HDAC) inhibitors as regulators of TGF-β1 signaling, and investigated their effect on EMT and chemoresistance. We employed four BTC cell lines (MzChA-1, gemcitabine-resistant MzChA-1, TFK-1, and gemcitabine-resistant TFK-1) and used vorinostat as the HDAC inhibitor. The relative mRNA expression of an epithelial marker (CDH1) and mesenchymal markers (CDH2, vimentin, SNAI1) were measured by qRT-PCR to evaluate factors associated with EMT. MTT (3-(4,5-Dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide) assay was performed to evaluate the chemoresistance of each cell line. In addition, NOD/SCID mice were used to evaluate the effect of vorinostat in vivo. In the parent MzChA-1 and TFK-1 cell lines, TGF-β1 induced EMT and chemoresistance; while vorinostat inhibited the EMT and chemoresistance induced by TGF-β1. In gemcitabine-resistant cell lines that highly expressed TGF-β1, vorinostat inhibited EMT and attenuated chemoresistance. We showed that vorinostat inhibits nuclear translocation of SMAD4 which is a signaling factor of TGF-β1, and this is one of the mechanisms by which vorinostat regulates EMT. We also showed that vorinostat attenuates the binding affinity of SMAD4 to the CDH1-related transcription factors SNAI1, SNAI2, ZEB1, ZEB2, and TWIST. Furthermore, combination therapy with vorinostat and gemcitabine improved survival time in the mice xenografted with gemcitabine resistant MzChA-1 cells. In conclusion, vorinostat regulated TGF-β1-induced EMT and chemoresistance through inhibition of SMAD4 nuclear translocation.