Plakophilin 1 in carcinogenesis.

Plakophilin 1 (PKP1) belongs to the desmosome family as an anchoring junction protein in cellular junctions. It localizes at the interface of the cell membrane and cytoplasm. Although PKP1 is a non-transmembrane protein, it may become associated with the cell membrane via transmembrane proteins such as desmocollins and desmogleins. Homozygous deletion of PKP1 results in ectodermal dysplasia-skin fragility syndrome (EDSF) and complete knockout of PKP1 in mice produces comparable symptoms to EDSF in humans, although mice do not survive more than 24 h. PKP1 is not limited to expression in desmosomal structures, but is rather widely expressed in cytoplasm and nucleus, where it assumes important cellular functions. This review will summarize distinct roles of PKP1 in the cell membrane, cytoplasm, and nucleus with an overview of relevant studies on its function in diverse types of cancer.

Spinster homolog 2 reduces malignancies of glioblastoma via PTEN/PI3K/AKT pathway.

The molecular mechanisms of glioblastoma (GBM) are unclear, and the prognosis is poor. Spinster homolog 2 (SPNS2) is reportedly involved in pathological processes such as immune response, vascular development, and cancer. However, the biological function and molecular role of SPNS2 in GBM are unclear. SPNS2 is aberrantly low expressed in glioma. Survival curves, risk scores, prognostic nomograms, and univariate and multifactorial Cox regression analyses showed that SPNS2 is an independent prognostic indicator significantly associated with glioma progression and prognosis. Cell function assays and in vivo xenograft transplantation were performed that downregulation of SPNS2 promoted GBM cell growth, migration, invasion, epithelial-mesenchymal transition (EMT), anti-apoptosis, drug resistance, and stemness, while overexpression of SPNS2 had the opposite effect. Meanwhile, the functional enrichment and signaling pathways of SPNS2 in the Cancer Genome Atlas (TCGA), Chinese Glioma Genome Atlas (CGGA), and RNA sequencing were analyzed by Gene ontology (GO), Kyoto Encyclopedia of Genes and Genomes (KEGG), and Gene set enrichment analysis (GSEA). The above results were related to the inhibition of the PTEN/PI3K/AKT pathway by SPNS2. In addition, we predicted that SPNS2 is closely associated with immune infiltration in the tumor microenvironment by four immune algorithms, ESTIMATE, TIMER, CIBERSORT, and QUANTISEQ. In particular, SPNS2 was negatively correlated with the infiltration of most immune cells, immunomodulators, and chemokines. Finally, single-cell sequencing analysis also revealed that SPNS2 was remarkably correlated with macrophages, and downregulation of SPNS2 promotes the expression of M2-like macrophages. This study provides new evidence that SPNS2 inhibits malignant progression, stemness, and immune infiltration of GBM cells through PTEN/PI3K/AKT pathway. SPNS2 may become a new diagnostic indicator and potential immunotherapeutic target for glioma.

Antipsychotic drugs induce vascular defects in hematopoietic organs.

Antipsychotic agents are clinically utilized to treat schizophrenia and other mental disorders. These drugs induce neurological and metabolic side effects, but their influence on blood vessels remains largely unknown. Here, we show that haloperidol, one of the most frequently prescribed antipsychotic agents, induces vascular defects in bone marrow. Acute haloperidol treatment results in vascular dilation that is specific to hematopoietic organs. This vessel dilation is associated with disruption of hematopoiesis and hematopoietic stem/progenitor cells (HSPCs), both of which are reversible after haloperidol withdrawal. Mechanistically, haloperidol treatment blocked the secretion of vascular endothelial growth factor A (VEGF-A) from HSPCs. Genetic blockade of VEGF-A secretion from hematopoietic cells or inhibition of VEGFR2 in endothelial cells result in similar vessel dilation in bone marrow during regeneration after irradiation and transplantation. Conversely, VEGF-A gain of function rescues the bone marrow vascular defects induced by haloperidol treatment and irradiation. Our work reveals an unknown effect of antipsychotic agents on the vasculature and hematopoiesis with potential implications for drug application in clinic.

Clinical significance of pancreatic ductal metaplasia.

Pancreatic ductal metaplasia (PDM) is the stepwise replacement of differentiated somatic cells with ductal or ductal-like cells in the pancreas. PDM is usually triggered by cellular and environmental insults. PDM development may involve all cell lineages of the pancreas, and acinar cells with the highest plasticity are the major source of PDM. Pancreatic progenitor cells are also involved as cells of origin or transitional intermediates. PDM is heterogeneous at the histological, cellular, and molecular levels and only certain subsets of PDM develop further into pancreatic intraepithelial neoplasia (PanIN) and then pancreatic ductal adenocarcinoma (PDAC). The formation and evolution of PDM is regulated at the cellular and molecular levels through a complex network of signaling pathways. The key molecular mechanisms that drive PDM formation and its progression into PanIN/PDAC remain unclear, but represent key targets for reversing or inhibiting PDM. Alternatively, PDM could be a source of pancreas regeneration, including both exocrine and endocrine components. Cellular aging and apoptosis are obstacles to PDM-to-PanIN progression or pancreas regeneration. Functional identification of the cellular and molecular events driving senescence and apoptosis in PDM and its progression would help not only to restrict the development of PDM into PanIN/PDAC, but may also facilitate pancreatic regeneration. This review systematically assesses recent advances in the understanding of PDM physiology and pathology, with a focus on its implications for enhancing regeneration and prevention of cancer. © 2022 The Pathological Society of Great Britain and Ireland.

Nucleolar protein treacle ribosome biogenesis factor 1 maintains gastric cancer cell proliferation by regulating R-loop associated DNA replication stress.

BACKGROUND AND AIM: Gastric cancer (GC) is a common malignant neoplasm in the gastrointestinal tract, accounting for high mortality globally. Treacle ribosome biogenesis factor 1 (TCOF1) is a nucleolar protein, which has been reported to be implicated in the pathogenesis of Treacher Collins syndrome and the development of several types of human cancer. However, the role of TCOF1 in GC is not known. METHODS: Immunohistochemistry was carried out to determine TCOF1 expression in GC tissues. Immunofluorescence, co-IP, and DNA fiber assays were conducted to investigate the function of TCOF1 in GC-derived BGC-823 and SGC-7901 cell lines. RESULTS: TCOF1 expression was aberrantly increased in GC tissues compared with adjacent normal tissues. In addition, we found that TCOF1 left the nucleolus and localized to R-loops (DNA/RNA hybrids) during S phase in GC cells. Furthermore, TCOF1 interacted with DDX5 and suppressed R-loop levels. Knockdown of TCOF1 led to increased nucleoplasmic R-loops specifically during S phase, which restrained DNA replication and cell proliferation. Overexpression of R-loop eraser RNaseH1 rescued the DNA synthesis defects and decreased DNA damage caused by TCOF1 depletion. CONCLUSION: These findings demonstrate a novel role of TCOF1 in maintaining GC cell proliferation by alleviating R-loop associated DNA replication stress.

Coupled liquid biopsy and bioinformatics for pancreatic cancer early detection and precision prognostication.

Early detection and diagnosis are the key to successful clinical management of pancreatic cancer and improve the patient outcome. However, due to the absence of early symptoms and the aggressiveness of pancreatic cancer, its 5-year survival rate remains below 5 %. Compared to tissue samples, liquid biopsies are of particular interest in clinical settings with respect to minimal invasiveness, repeated sampling, complete representation of the entire or multi-site tumor bulks. The potential of liquid biopsies in pancreatic cancer has been demonstrated by many studies which prove that liquid biopsies are able to detect early emergency of pancreatic cancer cells, residual disease, and recurrence. More interestingly, they show potential to delineate the heterogeneity, spatial and temporal, of pancreatic cancer. However, the performance of liquid biopsies for the diagnosis varies largely across different studies depending of the technique employed and also the type and stage of the tumor. One approach to improve the detect performance of liquid biopsies is to intensively inspect circulome and to define integrated biomarkers which simultaneously profile circulating tumor cells and DNA, extracellular vesicles, and circulating DNA, or cell free DNA and proteins. Moreover, the diagnostic validity and accuracy of liquid biopsies still need to be comprehensively demonstrated and validated.

Methylation of RNA N6-methyladenosine in modulation of cytokine responses and tumorigenesis.

Among myriads of distinct chemical modification in RNAs, the dynamic, reversible and fine-tuned methylation of N6-methyladenosine (m6A) is the most prevalent modification in eukaryotic mRNAs. This RNA mark is generated by proteins that act as m6A writers and can be reversed by proteins that act as m6A erasers. The RNA m6A modification is also mediated by another group of proteins capable of recognizing m6A that act as m6A readers. The m6A modification exerts direct control over the RNA metabolism including mRNA processing, mRNA exporting, translation initiation, mRNA stability and the biogenesis of long-non-coding RNA (LncRNA), thereby can influence various aspects of cell function. Evidently, m6A is intimately associated with cancer development and progression such as self-renewal capacity of cancer stem cells, proliferation, apoptosis and therapeutic resistance, and immune response. In this review, we will discuss the regulation and function of m6A, the various functions ascribed to these proteins and the emerging concepts that impact our knowledge of these proteins and their roles in the epitranscriptome. Conceivably, m6A may play pivotal roles in cytokine and immune response and carcinogenesis.

FAK phosphorylation by ERK primes ras-induced tyrosine dephosphorylation of FAK mediated by PIN1 and PTP-PEST.

Activated Ras has been found in many types of cancer. However, the mechanism underlying Ras-promoted tumor metastasis remains unclear. We demonstrate here that activated Ras induces tyrosine dephosphorylation and inhibition of FAK mediated by the Ras downstream Fgd1-Cdc42-PAK1-MEK-ERK signaling cascade. ERK phosphorylates FAK S910 and recruits PIN1 and PTP-PEST, which colocalize with FAK at the lamellipodia of migrating cells. PIN1 binding and prolyl isomerization of FAK cause PTP-PEST to interact with and dephosphorylate FAK Y397. Inhibition of FAK mediated by this signal relay promotes Ras-induced cell migration, invasion, and metastasis. These findings uncover the importance of sequential modification of FAK-by serine phosphorylation, isomerization, and tyrosine dephosphorylation--in the regulation of FAK activity and, thereby, in Ras-related tumor metastasis.

Forkhead Box M1 Is Essential for Nuclear Localization of Glioma-associated Oncogene Homolog 1 in Glioblastoma Multiforme Cells by Promoting Importin-7 Expression.

The transcription factors glioma-associated oncogene homolog 1 (GLI1), a primary marker of Hedgehog pathway activation, and Forkhead box M1 (FOXM1) are aberrantly activated in a wide range of malignancies, including glioma. However, the mechanism of nuclear localization of GLI1 and whether FOXM1 regulates the Hedgehog signaling pathway are poorly understood. Here we found that FOXM1 promotes nuclear import of GLI1 in glioblastoma multiforme cells and thus increases the expression of its target genes. Conversely, knockdown of FOXM1 expression with FOXM1 siRNA abrogated its nuclear import and inhibited the expression of its target genes. Also, genetic deletion of FOXM1 in mouse embryonic fibroblasts abolished nuclear localization of GLI1. We observed that FOXM1 directly binds to the importin-7 (IPO7) promoter and increases its promoter activity. IPO7 interacted with GLI1, leading to enhanced nuclear import of GLI1. Depletion of IPO7 by IPO7 siRNA reduced nuclear accumulation of GLI1. In addition, FOXM1 induced nuclear import of GLI1 by promoting IPO7 expression. Moreover, the FOXM1/IPO7/GLI1 axis promoted cell proliferation, migration, and invasion in vitro. Finally, expression of FOXM1 was markedly correlated with that of GLI1 in human glioblastoma specimens. These data suggest that FOXM1 and GLI1 form a positive feedback loop that contributes to glioblastoma development. Furthermore, our study revealed a mechanism that controls nuclear import of GLI1 in glioblastoma multiforme cells.

FOXM1 and its oncogenic signaling in pancreatic cancer pathogenesis.

Pancreatic cancer is a devastating disease with an overall 5-year survival rate less than 5%. Multiple signaling pathways are implicated in the pathogenesis of pancreatic cancer, such as Wnt/ß-catenin, Notch, Hedgehog, hypoxia-inducible factor, signal transducer and activator of transcription, specificity proteins/Krüppel-like factors, and Forkhead box (FOX). Recently, increasing evidence has demonstrated that the transcription factor FOXM1 plays important roles in the initiation, progression, and metastasis of a variety of human tumors, including pancreatic cancer. In this review, we focus on the current understanding of the molecular pathogenesis of pancreatic cancer with a special focus on the function and regulation of FOXM1 and rationale for FOXM1 as a novel molecular target for pancreatic cancer prevention and treatment.

PKM2 regulates neural invasion of and predicts poor prognosis for human hilar cholangiocarcinoma.

BACKGROUND: The therapeutic and prognostic value of the glycolytic enzymes hexokinase, phosphofructokinase, and pyruvate kinase (PK) has been implicated in a variety of cancers, while their roles in treatment of and prognosis for hilar cholangiocarcinoma (HC) remain unclear. In this study, we determined the expression of PKM2 in and its impact on biology and clinical outcome of human HC. METHODS: The regulation and function of PKM2 in HC pathogenesis was evaluated using human tissues, molecular and cell biology, and animal models, and its prognostic significance was determined according to its impact on patient survival. RESULTS: We found that expression of hexokinase 1 and the M2 splice isoform of PK (PKM2) was upregulated in HC tissues and that this expression correlated with tumor recurrence and outcome. PKM2 expression was increased in HC cases with chronic cholangitis as demonstrated by isobaric tags for relative and absolute quantification. High PKM2 expression was highly correlated with high syndecan 2 (SDC2) expression and neural invasion. PKM2 downregulation led to a decrease in SDC2 expression. Treatment with metformin markedly suppressed PKM2 and SDC2 expression at both the transcriptional and posttranscriptional levels and inhibited HC cell proliferation and tumor growth. CONCLUSIONS: PKM2 regulates neural invasion of HC cells at least in part via regulation of SDC2. Inhibition of PKM2 and SDC2 expression contributes to the therapeutic effect of metformin on HC. Therefore, PKM2 is an independent prognostic factor and potential therapeutic target for human HC.

Down-regulation of microRNA-494 via loss of SMAD4 increases FOXM1 and ß-catenin signaling in pancreatic ductal adenocarcinoma cells.

BACKGROUND & AIMS: Dysregulation of ß-catenin and the transcriptional activator FOXM1 mediate oncogenesis, but it is not clear how these proteins become dysregulated in tumors that do not typically carry mutations in adenomatous polyposis coli (APC) or ß-catenin, such as pancreatic ductal adenocarcinomas (PDACs). We searched for microRNAs that regulate levels of FOXM1 in PDAC cells and samples from patients. METHODS: We identified microRNAs that affect levels of FOXM1 in PDACs using bioinformatic, genetic, and pharmacologic approaches. We altered expression of the microRNA-494 (miR-494) in PDAC cell lines (AsPC-1 and PANC-1) and examined the effects on FOXM1 and ß-catenin signaling and cell proliferation and colony formation. The cells were injected into immunocompromised mice and growth of xenograft tumors and liver metastases were measured. We performed immunohistochemical analyses of 10 paired PDAC and nontumor pancreatic tissue samples collected from untreated patients during surgery. RESULTS: We identified miR-494 as a negative regulator of FOXM1 levels in PDAC cells, and found that levels of this microRNA were reduced in PDAC specimens, compared with nontumor tissues. Loss of response of PDAC cells to transforming growth factor ß, owing to SMAD4 deficiency, reduced expression of miR-494. Transgenic expression of miR-494 in PDAC cells produced the same effects as reducing expression of FOXM1 or blocking nuclear translocation of ß-catenin, reducing cell proliferation, migration, and invasion, and increasing their sensitivity to gemcitabine. Reduced expression of miR-494 correlated with PDAC metastasis and reduced survival times of patients. CONCLUSIONS: Loss of SMAD4 in PDAC cells leads to reduced levels of miR-494, increased levels of FOXM1, and nuclear localization of ß-catenin. miR-494 might be developed as a prognostic marker for patients with PDAC or a therapeutic target.

Cingulin family: Structure, function and clinical significance.

Cingulin and its paralog paracingulin are vital components of the apical junctional complex in vertebrate epithelial and endothelial cells. They are both found in tight junctions (TJ), and paracingulin is also detectable in adherens junctions (AJ) as TJ cytoplasmic plaque proteins. Cingulin and paracingulin interact with other proteins to perform functions. They interact with cytoskeletal proteins, modulate the activity of small GTPases, such as RhoA and Rac1, and regulate gene expression. In addition, cingulin and paracingulin regulate barrier function and many pathological processes, including inflammation and tumorigenesis. In this review, we summarize the discovery and structure, expression and subcellular distribution, and molecular interactions of cingulin family proteins and discuss their role in development, physiology, and pathological processes.

Unveiling the role of interleukin-6 in pancreatic cancer occurrence and progression.

Pancreatic cancer is difficult to diagnose early and progresses rapidly. Researchers have found that a cytokine called Interleukin-6 (IL-6) is involved in the entire course of pancreatic cancer, promoting its occurrence and development. From the earliest stages of pancreatic intraepithelial neoplasia to the invasion and metastasis of pancreatic cancer cells and the appearance of tumor cachexia, IL-6 drives oncogenic signal transduction pathways and immune escape that accelerate disease progression. IL-6 is considered a biomarker for pancreatic cancer diagnosis and prognosis, as well as a potential target for treatment. IL-6 antibodies are currently being explored as a hot topic in oncology. This article aims to systematically explain how IL-6 induces the deterioration of normal pancreatic cells, with the goal of finding a breakthrough in pancreatic cancer diagnosis and treatment.

Pancreatic stellate cells and the interleukin family: Linking fibrosis and immunity to pancreatic ductal adenocarcinoma (Review).

Pancreatic ductal adenocarcinoma (PDAC) is an extremely aggressive form of cancer with a low survival rate. A successful treatment strategy should not be limited to targeting cancer cells alone, but should adopt a more comprehensive approach, taking into account other influential factors. These include the extracellular matrix (ECM) and immune microenvironment, both of which are integral components of the tumor microenvironment. The present review describes the roles of pancreatic stellate cells, differentiated cancer­associated fibroblasts and the interleukin family, either independently or in combination, in the progression of precursor lesions in pancreatic intraepithelial neoplasia and PDAC. These elements contribute to ECM deposition and immunosuppression in PDAC. Therapeutic strategies that integrate interleukin and/or stromal blockade for PDAC immunomodulation and fibrogenesis have yielded inconsistent results. A deeper comprehension of the intricate interplay between fibrosis, and immune responses could pave the way for more effective treatment targets, by elucidating the mechanisms and causes of ECM fibrosis during PDAC progression.

Down-regulation of microRNA-23a promotes pancreatic ductal adenocarcinoma initiation and progression by up-regulation of FOXM1 expression.

Transcriptional factor Forkhead box M1 (FOXM1) plays an important role in pancreatic ductal adenocarcinoma (PDAC) development and progression. The molecular mechanisms underlying its dysregulation remain unclear. We identified and functionally validated the microRNAs (miRNAs) that critically regulate FOXM1 expression in PDAC. The expression levels of miRNA-23a (miR-23a-3p and -5p) were altered in PDAC cell lines and their effects on FOXM1 signaling and cell proliferation and migration and tumorigenesis were examined in vitro and in vivo using mouse PDAC models. Compared with non-tumor pancreatic tissues, PDAC tissues and cell lines exhibited significantly reduced levels of miR-23a expression. Reduced miR-23a expression and concomitant increase in FOXM1 expression were also observed in acinar-to-ductal metaplasia and pancreatic intraepithelial neoplasia, the major premalignant lesions of PDAC. Transgenic expression of miR-23a reduced the expression of FOXM1 and suppressed cell proliferation and migration in PDAC cells, whereas the inhibitors of miR-23a did the opposite. Loss or reduced levels of miR-23a increased the levels of FOXM1 expression, while increased expression of FOXM1 down-regulated miR-23a expression, suggesting that miR-23a and FOXM1 were mutual negative regulators of their expression in PDAC cells. Therefore, the miR-23a/FOXM1 signaling axis is important in PDAC initiation and progression and could serve as an interventional or therapeutic target for patients with early or late stages of PDAC.

Roles of PPAR activation in cancer therapeutic resistance: Implications for combination therapy and drug development.

Therapeutic resistance is a major obstacle to successful treatment or effective containment of cancer. Peroxisome proliferator-activated receptors (PPARs) play an essential role in regulating energy homeostasis and determining cell fate. Despite of the pleiotropic roles of PPARs in cancer, numerous studies have suggested their intricate relationship with therapeutic resistance in cancer. In this review, we provided an overview of the roles of excessively activated PPARs in promoting resistance to modern anti-cancer treatments, including chemotherapy, radiotherapy, targeted therapy, and immunotherapy. The mechanisms through which activated PPARs contribute to therapeutic resistance in most cases include metabolic reprogramming, anti-oxidant defense, anti-apoptosis signaling, proliferation-promoting pathways, and induction of an immunosuppressive tumor microenvironment. In addition, we discussed the mechanisms through which activated PPARs lead to multidrug resistance in cancer, including drug efflux, epithelial-to-mesenchymal transition, and acquisition and maintenance of the cancer stem cell phenotype. Preliminary studies investigating the effect of combination therapies with PPAR antagonists have suggested the potential of these antagonists in reversing resistance and facilitating sustained cancer management. These findings will provide a valuable reference for further research on and clinical translation of PPAR-targeting treatment strategies.

WNK1 Interaction with KEAP1 Promotes NRF2 Stabilization to Enhance the Oxidative Stress Response in Hepatocellular Carcinoma.

Cellular oxidative stress plays a key role in the development and progression of hepatocellular carcinoma (HCC). A better understanding of the processes that regulate reactive oxygen species (ROS) homeostasis could uncover improved strategies for treating HCC. Here, we identified WNK1 as an antioxidative factor and therapeutic target in HCC. In human HCC, WNK1 expression was increased and correlated with poor patient prognosis. WNK1 knockdown significantly inhibited cell proliferation and xenograft tumor growth. Mechanistically, WNK1 competed with NRF2 for binding to the partial Kelch domain of KEAP1, reducing NRF2 ubiquitination and promoting NRF2 accumulation and nuclear translocation to increase antioxidant response. WNK1 silencing increased H2O2-induced apoptosis and inhibited cell growth by elevating reactive oxygen species (ROS) levels, which could be rescued by treatment with the antioxidant N-acetylcysteine (NAC) and NRF2 activator tert-butylhydroquinone (tBHQ). Liver-specific WNK1 knockout mouse models of HCC substantiated that WNK1 promoted HCC development by regulating ROS levels. WNK463, an inhibitor of the WNK kinase family, suppressed HCC progression and altered the redox status. These findings suggest that WNK1 plays a critical role in HCC development and progression and that the WNK1-oxidative stress axis may be a promising therapeutic target for HCC.

The roles of FOXM1 in pancreatic stem cells and carcinogenesis.

Pancreatic ductal adenocarcinoma (PDAC) has one of the poorest prognoses among all cancers. Over the past several decades, investigators have made great advances in the research of PDAC pathogenesis. Importantly, identification of pancreatic cancer stem cells (PCSCs) in pancreatic cancer cases has increased our understanding of PDAC biology and therapy. PCSCs are responsible for pancreatic tumorigenesis and tumor progression via a number of mechanisms, including extensive proliferation, self-renewal, high tumorigenic ability, high propensity for invasiveness and metastasis, and resistance to conventional treatment. Furthermore, emerging evidence suggests that PCSCs are involved in the malignant transformation of pancreatic intraepithelial neoplasia. The molecular mechanisms that control PCSCs are related to alterations of various signaling pathways, for instance, Hedgehog, Notch, Wnt, B-cell-specific Moloney murine leukemia virus insertion site 1, phosphoinositide 3-kinase/AKT, and Nodal/Activin. Also, authors have reported that the proliferation-specific transcriptional factor Forkhead box protein M1 is involved in PCSC self-renewal and proliferation. In this review, we describe the current knowledge about the signaling pathways related to PCSCs and the early stages of PDAC development, highlighting the pivotal roles of Forkhead box protein M1 in PCSCs and their impacts on the development and progression of pancreatic intraepithelial neoplasia.

Dysregulated Krüppel-like factor 4 and vitamin D receptor signaling contribute to progression of hepatocellular carcinoma.

BACKGROUND & AIMS: Krüppel-like factor 4 (KLF4) is a transcription factor and putative tumor suppressor. However, little is known about its effects in hepatocellular carcinogenesis. We investigated the clinical significance, biologic effects, and mechanisms of dysregulated KLF4 signaling. METHODS: We performed microarray analysis of hepatocellular carcinoma (HCC) tissues. We used molecular biology analyses and animal models to evaluate activation and function of KLF4-vitamin D receptor (VDR) pathway. RESULTS: Expression of KLF4 protein was decreased or lost in primary HCC samples, in particular, lymph node metastases, compared with normal liver tissues. Loss of KLF4 from primary tumors was significantly associated with reduced survival time and was identified as a prognostic marker. Most human HCC cell lines had losses or substantial decreases in levels of KLF4. Exogenous expression of KLF4 in HCC cells upregulated expression of mesenchymal-epithelial transition (MET) and inhibited their migration, invasion, and proliferation in vitro. When these cells were injected into mice, tumors grew more slowly and metastasis was inhibited, compared with HCC cells that did not express KLF4. VDR is a direct transcriptional target of KLF4; we identified 2 sites in the VDR promoter that bound specifically to KLF4. Increased expression of VDR sensitized tumor cells to the inhibitory effects of vitamin D. CONCLUSIONS: KLF4 binds to the promoter of VDR to regulate its expression; levels of KLF4 are reduced and levels of VDR are increased in HCC cell lines and primary tumor samples. Expression of KLF4 in HCC cells sensitizes them to the anti-proliferative effects of VD3. This pathway might be manipulated to prevent or treat liver cancer.