Suppression of lung cancer cell invasion by LKB1 is due to the downregulation of tissue factor and vascular endothelial growth factor, partly dependent on SP1

Hotspots and trends in liver kinase B1 research: A bibliometric analysis

Introduction

In the past 22 years, a large number of publications have reported that liver kinase B1 (LKB1) can regulate a variety of cellular processes and play an important role in many diseases. However, there is no systematic bibliometric analysis on the publications of LKB1 to reveal the research hotspots and future direction.

Methods

Publications were retrieved from the Web of Science Core Collection (WoSCC), Scopus, and PubMed databases. CiteSpace and VOSviewer were used to analysis the top countries, institutions, authors, source journals, discipline categories, references, and keywords.

Results

In the past 22 years, the number of LKB1 publications has increased gradually by year. The country, institution, author, journals that have published the most articles and cited the most frequently were the United States, Harvard University, Prof. Benoit Viollet, Journal of Biochemistry and Plos One. The focused research hotspot was the molecular functions of LKB1. The emerging hotspots and future trends are the clinical studies about LKB1 and co-mutated genes as biomarkers in tumors, especially in lung adenocarcinoma.

Conclusions

Our research could provide knowledge base, frontiers, emerging hotspots and future trends associated with LKB1 for researchers in this field, and contribute to finding potential cooperation possibilities.

PTPN6 promotes chemosensitivity of colorectal cancer cells via inhibiting the SP1/MAPK signalling pathway

The abnormal expression of protein tyrosine phosphatase nonreceptor type 6 (PTPN6) has been proved to be associated with the progression of colorectal cancer. However, its role in chemosensitivity and related molecular mechanism have not been clarified. It has been reported that PTPN6 was down-regulated in colorectal cancer cells compared with the normal colorectal cells. To evaluate the effects of PTPN6 on the proliferation and survival of colorectal cancer cells, PTPN6 was overexpressed in colorectal cancer cells in the present study. We found that cell proliferation and viability were both decreased after overexpression of PTPN6. The IC50 of 5-Fu against colorectal cells was also declined in PTPN6 transfected cells. And further, we verified that PTPN6 could down-regulate the expression of P-gp and MRP-1. Moreover, SP1 was the target protein of PTPN6 predicated by ChIPBase software and confirmed through Co-immunoprecipitation assay and it was negatively regulated by PTPN6. To further verify the effect of SP1 on chemoresistance, SP1 was overexpressed. SP1 overexpression enhanced the drug-resistance to 5-Fu and abrogated the effects of PTPN6 upregulation on 5-Fu resistance. All the above changes were associated with the down-regulation of proteins related to MAPK signalling pathway, such as phosphorylation of extracellular regulated protein kinases (ERK) and p38. In summary, PTPN6 promoted chemosensitivity of colorectal cancer cells by targeting SP1 and inhibiting the activation of MAPK signalling pathway. SIGNIFICANCE OF THE STUDY: It has been demonstrated that the abnormal expression of PTPN6 was related to the progression of colorectal cancer. However, the chemosensitivity of PTPN6 and its molecular mechanisms were still unclear. Here, we identified that PTPN6 was down-regulated in colorectal cancer cells. Moreover, PTPN6 overexpression not only reduced cell proliferation and viability, but decreased the resistance of colorectal cells to 5-Fu. In our research, we found that the SP1 was the target protein of PTPN6 and it was negatively regulated by PTPN6. In addition, SP1 could increase the resistance of colorectal cells to 5-Fu. Molecular mechanism studies have shown that PTPN6 promoted the chemosensitivity of colorectal cancer cells by inhibiting the activation of MAPK signalling pathway.

HPV16 E6/E7 upregulate hTERC mRNA and gene amplification levels by relieving the effect of LKB1 on Sp1 phosphorylation in lung cancer cells

Background:

There is an immediate need for research on the mechanism underlying telomerase activation and overexpression.

Materials & Methods:

A total of 174 patients with lung cancer (n = 106) and benign lung disease (n = 68) were recruited for the current study. The mRNA expression levels of E6, E7, LKB1, Sp1, and hTERC in brushing cells were detected by quantitative reverse transcriptase polymerase chain reaction (qRT-PCR), and hTERC amplification was also detected by fluorescence in situ hybridization (FISH). To investigate the potential mechanism, bidirectional genetic manipulation was performed in well-established lung cancer cell lines.

Results:

Our results indicated that the mRNA expression levels of E6, E7, Sp1, and hTERC and the amplification level of hTERC were significantly increased in the malignant group compared with those of the benign group (p < 0.01). Conversely, the mRNA expression level of LKB1 was significantly decreased in the malignant group (p < 0.01). The correlation between E6, E7, Sp1, and hTERC expression was positive but was negative with LKB1 (p < 0.01). Our results also showed that HPV16 E6/E7 downregulated the expression of LKB1 at both the protein and mRNA levels. The loss of LKB1 upregulated Sp1 expression, and also promoted Sp1 activity. Sp1 further upregulated hTERC at the mRNA and gene amplification levels. Thus, we proposed a HPV–LKB1–Sp1–hTERC axis of E6/E7 upregulation of hTERC expression.

Conclusion:

We demonstrated for the first time that E6 and E7 promoted hTERC mRNA expression and the amplification of hTERC by relieving the effect of LKB1 on the phosphorylation of Sp1. Sp1 further activated hTERC by directly binding to the promoter regions of hTERC.

Understanding the Role of the Transcription Factor Sp1 in Ovarian Cancer: from Theory to Practice

Ovarian cancer (OC) is one of the deadliest cancers among women contributing to high risk of mortality, mainly owing to delayed detection. There is no specific biomarker for its detection in early stages. However, recent findings show that over-expression of specificity protein 1 (Sp1) is involved in many OC cases. The ubiquitous transcription of Sp1 apparently mediates the maintenance of normal and cancerous biological processes such as cell growth, differentiation, angiogenesis, apoptosis, cellular reprogramming and tumorigenesis. Sp1 exerts its effects on cellular genes containing putative GC-rich Sp1-binding site in their promoters. A better understanding of the mechanisms underlying Sp1 transcription factor (TF) regulation and functions in OC tumorigenesis could help identify novel prognostic markers, to target cancer stem cells (CSCs) by following cellular reprogramming and enable the development of novel therapies for future generations. In this review, we address the structure, function, and biology of Sp1 in normal and cancer cells, underpinning the involvement of Sp1 in OC tumorigenesis. In addition, we have highlighted the influence of Sp1 TF in cellular reprogramming of iPSCs and how it plays a role in controlling CSCs. This review highlights the drugs targeting Sp1 and their action on cancer cells. In conclusion, we predict that research in this direction will be highly beneficial for OC treatment, and chemotherapeutic drugs targeting Sp1 will emerge as a promising therapy for OC.

Simultaneous interference of SP1 and HIF1α retarding the proliferation, migration, and invasion of human microvascular endothelial cells (HMEC-1) under hypoxia

OBJECTIVE

To investigate the regulation of special protein 1 (SP1) and hypoxia-inducible factor-1α (HIF1α) on human microvascular endothelial cells (HMEC-1) under hypoxic conditions.

METHODS

The expression of SP1 and HIF1α under normoxia and hypoxic conditions were assessed by Western blot. SP1 and HIF1α were knocked down by small interfering RNA (siRNA) under hypoxic conditions. The proliferation, migration, and invasion of HMEC-1 were measured by cell counting kit 8, 5-ethynyl-2'-deoxyuridine and Transwell coculture system. Western blot analysis and Immunofluorescence were carried out to study the mechanisms of simultaneously inhibiting the adenosine triphosphatase (CD39), 5'-nucleotidase (CD73), adenosine, and vascular endothelial growth factor (VEGF). We compared the inhibitory effects between groups concurrently interfering SP1, HIF-1α, and ranibizumab under hypoxic conditions.

RESULTS

Under hypoxic conditions, the protein expression of SP1 and HIF1α was increased in HMEC-1, contrarily, SP1 siRNA and HIF1α siRNA downregulated the expression. Simultaneous inhibition of SP1 and HIF1α demonstrated a much greater restraint of proliferation, migration, and invasion characteristics on HMEC-1 than respectively knocking down SP1 or HIF1α and anti-VEGF drugs (0.5 mg/mL ranibizumab) (siRNA and the VEGF inhibitor were applied separately in different groups). Meanwhile, simultaneous inhibition of SP1 and HIF1α effectively reduced the expression of CD39, CD73, adenosine, and VEGF on HMEC-1 under hypoxic conditions.

CONCLUSIONS

Our study demonstrated that both SP1 and HIF1α played important roles in HMEC-1 under hypoxia condition. Simultaneous inhibition of SP1 and HIF1α effectively decreased the activity of HMEC-1 under hypoxic conditions through the CD39-CD73-adenosine and VEGF angiogenesis pathways. Our study may provide a new approach to the treatment of retinal neovascular diseases.

The Chemosensory Function of Primary Cilia Regulates Cholangiocyte Migration, Invasion, and Tumor Growth

Cholangiocytes, the epithelial cells lining the biliary tree in the liver, express primary cilia that can detect several kinds of environmental signals and then transmit this information into the cell. We have reported that cilia are significantly reduced in cholangiocarcinoma (CCA) and that the experimental deciliation of normal cells induces a malignant-like phenotype with increased proliferation, anchorage-independent growth, invasion, and migration. Here, we tested the hypothesis that the chemosensory function of cholangiocyte primary cilia acts as a mechanism for tumor suppression. We found that in the presence of extracellular nucleotides cilia-dependent chemosensation of the nucleotides inhibited migration and invasion in normal ciliated cholangiocytes through a P2Y11 receptor and liver kinase B1 (LKB1)-phosphatase and tensin homolog-AKT-dependent mechanism. In contrast, in normal deciliated cholangiocytes and CCA cells, the nucleotides induced the opposite effects, i.e., increased migration and invasion. As activation of LKB1 through a cilia-dependent mechanism was required for the nucleotide-mediated inhibitory effects on migration and invasion, we attempted to activate LKB1 directly, independent of ciliary expression, using the compound hesperidin methyl chalcone (HMC). We found that HMC induced activation of LKB1 in both ciliated and deciliated cells in vitro, resulting in the inhibition of migration and proliferation. Furthermore, using a rat syngeneic orthotopic CCA model, we found that HMC inhibited tumor growth in vivo. Conclusion: These findings highlight the importance of the chemosensory function of primary cilia for the control of migration and invasion and suggest that, by directly activating LKB1 and bypassing the need for primary cilia, it is possible to emulate this chemosensory function in CCA cells; these data warrant further studies evaluating the possibility of using HMC as therapy for CCA.

Impact of liver kinase B1 on p53 and survivin and its correlation with prognosis in gastric cancer

Background

Liver kinase B1 (LKB1) is a newly discovered tumor suppressor gene that plays a role in apoptosis induction. However, the precise impact of LKB1 expression on gastric cancer (GC) progression and its correlation with survivin and p53 in GC have not yet been elucidated.

Purpose

The aim of this study was to explore the significance of LKB1 expression and its correlation with p53 and survivin in GC.

Patients and methods

In this study, LKB1 expression was detected in GC and adjacent paracancerous tissues from 150 patients through immunohistochemical (IHC) staining. The relationship between LKB1 expression and clinical pathological factors in GC was analyzed, alongside its correlation with p53 and survivin expression.

Results

LKB1 expression was reduced in GC tissues compared with adjacent paracancerous tissues (P=0.001). In patients with GC, lower LKB1 expression was associated with greater invasion depth (P=0.013), higher pTNM stage (P=0.009), and lymph node metastasis (P=0.029). Furthermore, LKB1 expression in GC was inversely associated with p53 (r=-0.181, P=0.027) and survivin expression (r=-0.198, P=0.015). Kaplan-Meier analysis indicated that the expression of LKB1, p53 and survivin, as well as tumor differentiation, invasion, and pTNM and lymph node metastasis were all associated with overall survival (OS) (all P<0.05). Finally, multivariate analysis showed that LKB1 expression [hazard ratio (HR): 0.605 (0.414-0.882), P=0.009], p53 expression [hazard ratio (HR): 1.840 (1.232-2.750), P=0.003], and survivin expression [hazard ratio (HR): 1.561 (1.039-2.345), P=0.032] were all independent prognostic factors for patients with GC.

Conclusion

Our study suggests that LKB1 expression is reduced in GC, negatively correlated with p53 and survivin expression, and plays an important role in predicting invasion and metastasis of GC.

HOTAIR contributes to cell proliferation and metastasis of cervical cancer via targetting miR-23b/MAPK1 axis

The long non-coding RNA (lncRNA) HOX transcript antisense RNA (HOTAIR) has been found to be overexpressed in many human malignancies and involved in tumor progression and metastasis. Although the downstream target through which HOTAIR modulates tumor metastasis is not well-known, evidence suggests that miR-23b might be involved in this event. In the present study, the expressions of HOTAIR and miR-23b were detected by real-time PCR in 33 paired cervical cancer tissue samples and cervical cell lines. The effects of HOTAIR on the expressions of miR-23b and mitogen-activated protein kinase 1 (MAPK1) were studied by overexpression and RNAi approaches. We found that HOTAIR expression was significantly increased in cervical cancer cells and tissues. In contrast, the expression of miR-23b was obviously decreased. We further demonstrated that HOTAIR knockdown promoted apoptosis and inhibited cell proliferation and invasion in vitro and in vivo. Moreover, our data indicated that HOTAIR may competitively bind miR-23b and modulate the expression of MAPK1 indirectly in cervical cancer cells. Taken together, our study has identified a novel pathway through which HOTAIR exerts its oncogenic role, and provided a molecular basis for potential applications of HOTAIR in the prognosis and treatment of cervical cancer.

SP1 promotes tumor angiogenesis and invasion by activating VEGF expression in an acquired trastuzumab‑resistant ovarian cancer model

Ovarian cancer is one of the most common gynecologic cancers and the leading cause of mortality in women worldwide. HER2/neu is overexpressed in various types of cancers and is most commonly associated with decreased survival. Trastuzumab is a humanized anti-HER2 monoclonal antibody for the treatment of HER2-positive breast cancers. However, primary and/or acquired resistance occurs in up to 62% patients during the first year of treatment. Vascular endothelial growth factor (VEGF) is a well‑known angiogenesis factor involved in many physiological and pathological processes. Its significance has been implicated in promoting tumor growth and metastasis via angiogenesis. In the present study, we demonstrated that the upregulation of SP1 enhanced expression of VEGF promoting the angiogenesis and migration of trastuzumab-resistant ovarian cancer cell line SKOV3-T. Our in vitro and in vivo results both gave evidence that the SP1-VEGF axis was responsible for the enhanced malignancy, angiogenesis and migration in the acquired trastuzumab-resistant ovarian cancer cell model.

Long-term persistent infection of HPV 16 E6 up-regulate SP1 and hTERT by inhibiting LKB1 in lung cancer cells

HPV 16 E6 upregulates hTERT expression in lung cancer cells. However, the underlying molecular mechanism is unclear. In this paper, E6, LKB1, SP1, and hTERT mRNA expression levels were detected in brushing cells of patients with lung cancer (n = 106) and with benign lung disease (n = 68) by qRT-PCR. The mRNA expression levels of E6, SP1, and hTERT were significantly increased in the malignant group compared with the benign group (P < 0.01). Conversely, the mRNA expression level of LKB1 was significantly decreased in the malignant group (P < 0.01). Furthermore, the correlation between E6, Sp1, hTERT, and LKB1 was performed, our results indicated that E6, Sp1, and hTERT with positive, but LKB1 with negative correlation (P < 0.01). To investigate the potential relationship between these genes, using double directional genetic manipulation, we showed that overexpression of E6 in H1299 cells down-regulated LKB1 mRNA and protein expression but up-regulated SP1 and hTERT as well as the transcriptional activity of Sp1. In contrast, knockdown of E6 in A549 cells by short-interference RNAs (siRNAs) up-regulated LKB1 expression, but down-regulated SP1 and hTERT expression as well as Sp1 activity. LKB1 loss upregulated both SP1 and hTERT at the protein and mRNA level as well as SP1 activity. To verify that the role of E6 on hTERT was mediated by SP1, siRNA knockdown of SP1 was performed on both H1299 and A549 cell lines. Inhibition of SP1 downregulated hTERT expression. Our results indicate that HPV16 E6 indirectly upregulated the expression of hTERT by inhibition of LBK1 expression and upregulation of Sp1 expression, thus suggesting a HPV-LKB1-SP1-hTERT axis for the tumorigenesis of lung cancer. Our study also provides new evidence to support the critical role of SP1 and LKB1 in the pathogenesis of HPV-related lung cancer, and suggests novel therapeutic targets.

HPV16 E6/E7 upregulates HIF-2α and VEGF by inhibiting LKB1 in lung cancer cells

Long-term persistent infection of HPV16 E6/E7 is frequently associated with lung cancers, especially in non-smokers and in Asians. However, molecular mechanisms of HPV16 E6/E7 induction of lung cancer are not fully understood. Using bi-directional genetic manipulation and four well-established lung cancer cell lines, we showed HPV16 E6/E7 downregulated expression of liver kinase B1 at both protein and messenger RNA levels; liver kinase B1 downregulated hypoxia-inducible factor 2α at protein level but not at messenger RNA level, and hypoxia-inducible factor 2α upregulated vascular endothelial growth factor at both protein and messenger RNA levels. This is the first study to show hypoxia-inducible factor 2α as a downstream effector of liver kinase B1 in lung cancer cells. Our results indicate that HPV16 E6/E7 indirectly upregulated the expression of vascular endothelial growth factor by inhibition of liver kinase B1 expression and upregulation of hypoxia-inducible factor 2α expression, thus propose a human papillomavirus-liver kinase B1-hypoxia-inducible factor 2α-vascular endothelial growth factor axis for the tumorigenesis of lung cancer. Our study also provides new evidence to support the critical role of liver kinase B1 in the pathogenesis of human papillomavirus-related lung cancer and suggests novel therapeutic targets.

Deletion of endothelial cell-specific liver kinase B1 increases angiogenesis and tumor growth via vascular endothelial growth factor

Liver kinase B1 (LKB1) is a serine/threonine protein kinase ubiquitously expressed in mammalian cells. It was first identified in Peutz-Jeghers syndrome as a tumor suppressor gene. Whether endothelial LKB1 regulates angiogenesis and tumor growth is unknown. In this study, we generated endothelial cell-specific LKB1-knockout (LKB1^endo−/−) mice by crossbreeding vascular endothelial-cadherin-Cre mice with LKB1^flox/flox mice. Vascular endothelial growth factor (VEGF) level was highly co-stained in endothelial cells but not macrophages in LKB1^endo−/− mice. Consistently, LKB1^endo−/− mouse tissues including the lung, skin, kidney, and liver showed increased vascular permeability. Tumors implanted in LKB1^endo−/− mice but not macrophage-specific LKB1-knockout mice grew faster and showed enhanced vascular permeability and increased angiogenesis as compared with those implanted in wild-type mice. Injection of VEGF-neutralizing antibody but not the isotype-matched control antibody decreased endothelial-cell angiogenesis and tumor growth in vivo. Furthermore, LKB1 deletion enhanced mouse retinal and cell angiogenesis, and knockdown of VEGF by small-interfering RNA decreased endothelial cell proliferation and migration. Re-expression of LKB1 or knockdown of VEGF receptor 2 decreased the over-proliferation and -migration observed in LKB1^endo−/− cells. Mechanistically, LKB1 could bind to the VEGF transcription factor, specificity protein 1 (Sp1), which then inhibited the binding of Sp1 to the VEGF promoter to reduce VEGF expression. Endothelial LKB1 may regulate endothelial angiogenesis and tumor growth by modulating Sp1-mediated VEGF expression.

Integrative genomic analyses of a novel cytokine, interleukin-34 and its potential role in cancer prediction

Interleukin-34 (IL-34) is a novel cytokine, which is composed of 222 amino acids and forms homodimers. It binds to the macrophage colony-stimulating factor (M-CSF) receptor and plays an important role in innate immunity and inflammatory processes. In the present study, we identified the completed IL-34 gene in 25 various mammalian genomes and found that IL-34 existed in all types of vertebrates, including fish, amphibians, birds and mammals. These species have a similar 7 exon/6 intron gene organization. The phylogenetic tree indicated that the IL-34 gene from the primate lineage, rodent lineage and teleost lineage form a species-specific cluster. It was found mammalian that IL-34 was under positive selection pressure with the identified positively selected site, 196Val. Fifty-five functionally relevant single nucleotide polymorphisms (SNPs), including 32 SNPs causing missense mutations, 3 exonic splicing enhancer SNPs and 20 SNPs causing nonsense mutations were identified from 2,141 available SNPs in the human IL-34 gene. IL-34 was expressed in various types of cancer, including blood, brain, breast, colorectal, eye, head and neck, lung, ovarian and skin cancer. A total of 5 out of 40 tests (1 blood cancer, 1 brain cancer, 1 colorectal cancer and 2 lung cancer) revealed an association between IL-34 gene expression and cancer prognosis. It was found that the association between the expression of IL-34 and cancer prognosis varied in different types of cancer, even in the same types of cancer from different databases. This suggests that the function of IL-34 in these tumors may be multidimensional. The upstream transcription factor 1 (USF1), regulatory factor X-1 (RFX1), the Sp1 transcription factor 1, POU class 3 homeobox 2 (POU3F2) and forkhead box L1 (FOXL1) regulatory transcription factor binding sites were identified in the IL-34 gene upstream (promoter) region, which may be involved in the effects of IL-34 in tumors.