Epigenetic inactivation of LKB1 in primary tumors associated with the Peutz-Jeghers syndrome

Comprehensive Molecular Profiling and Clinicopathological Characteristics of Gastric-Type Mucinous Carcinoma of the Uterine Cervix in Japanese Women

Gastric-type mucinous carcinoma (GAS) of the uterine cervix is the most common adenocarcinoma that develops independently of human papillomavirus infection; it is typically diagnosed at an advanced stage and has a poorer prognosis than usual-type endocervical adenocarcinoma. Few studies have examined the molecular profile of GAS, but genetic alterations in TP53 and STK11 have been repeatedly reported. We analyzed the clinicopathological characteristics and molecular profile of GAS. Fresh-frozen tissue specimens and formalin-fixed paraffin-embedded (FFPE) tissues from 13 patients with GAS treated between January 2000 and December 2020 were analyzed. We performed next-generation sequencing on eight fresh-frozen GAS specimens using the Cancer Hotspot Panel v2 (cases 1-8) and the FoundationOne companion diagnostic (F1CDx) assay on six FFPE samples (cases 8-13). Seventy-four genomic alterations were identified in 42 genes. In order of frequency, TP53, ATRX, CDKN2A, KRAS, APC, and STK11 were altered in at least three cases. Targetable genomic alterations were identified in all six patients' specimens analyzed using the F1CDx assay. GAS harbors various genomic alterations associated with sustained activation of signaling pathways or cell cycle regulation in addition to abnormalities in TP53, and precision medicine based on molecular profiling will be necessary to overcome GAS.

Epigenetic regulation in cancer

Epigenetic modifications are defined as heritable changes in gene activity that do not involve changes in the underlying DNA sequence. The oncogenic process is driven by the accumulation of alterations that impact genome's structure and function. Genetic mutations, which directly disrupt the DNA sequence, are complemented by epigenetic modifications that modulate gene expression, thereby facilitating the acquisition of malignant characteristics. Principals among these epigenetic changes are shifts in DNA methylation and histone mark patterns, which promote tumor development and metastasis. Notably, the reversible nature of epigenetic alterations, as opposed to the permanence of genetic changes, positions the epigenetic machinery as a prime target in the discovery of novel therapeutics. Our review delves into the complexities of epigenetic regulation, exploring its profound effects on tumor initiation, metastatic behavior, metabolic pathways, and the tumor microenvironment. We place a particular emphasis on the dysregulation at each level of epigenetic modulation, including but not limited to, the aberrations in enzymes responsible for DNA methylation and histone modification, subunit loss or fusions in chromatin remodeling complexes, and the disturbances in higher-order chromatin structure. Finally, we also evaluate therapeutic approaches that leverage the growing understanding of chromatin dysregulation, offering new avenues for cancer treatment.

Josephin domain containing 2 (JOSD2) promotes lung cancer by inhibiting LKB1 (Liver kinase B1) activity

Non-small cell lung cancer (NSCLC) ranks as one of the leading causes of cancer-related deaths worldwide. Despite the prominence and effectiveness of kinase-target therapies in NSCLC treatment, these drugs are suitable for and beneficial to a mere ~30% of NSCLC patients. Consequently, the need for novel strategies addressing NSCLC remains pressing. Deubiquitinases (DUBs), a group of diverse enzymes with well-defined catalytic sites that are frequently overactivated in cancers and associated with tumorigenesis and regarded as promising therapeutic targets. Nevertheless, the mechanisms by which DUBs promote NSCLC remain poorly understood. Through a global analysis of the 97 DUBs' contribution to NSCLC survival possibilities using The Cancer Genome Atlas (TCGA) database, we found that high expression of Josephin Domain-containing protein 2 (JOSD2) predicted the poor prognosis of patients. Depletion of JOSD2 significantly impeded NSCLC growth in both cell/patient-derived xenografts in vivo. Mechanically, we found that JOSD2 restricts the kinase activity of LKB1, an important tumor suppressor generally inactivated in NSCLC, by removing K6-linked polyubiquitination, an action vital for maintaining the integrity of the LKB1-STRAD-MO25 complex. Notably, we identified the first small-molecule inhibitor of JOSD2, and observed that its pharmacological inhibition significantly arrested NSCLC proliferation in vitro/in vivo. Our findings highlight the vital role of JOSD2 in hindering LKB1 activity, underscoring the therapeutic potential of targeting JOSD2 in NSCLC, especially in those with inactivated LKB1, and presenting its inhibitors as a promising strategy for NSCLC treatment.

Posttranslational regulation of liver kinase B1 (LKB1) in human cancer

Liver kinase B1 (LKB1) is a serine-threonine kinase that participates in multiple cellular and biological processes, including energy metabolism, cell polarity, cell proliferation, cell migration, and many others. LKB1 is initially identified as a germline-mutated causative gene in Peutz-Jeghers syndrome (PJS) and is commonly regarded as a tumor suppressor due to frequent inactivation in a variety of cancers. LKB1 directly binds and activates its downstream kinases including the AMP-activated protein kinase (AMPK) and AMPK-related kinases by phosphorylation, which has been intensively investigated for the past decades. An increasing number of studies has uncovered the posttranslational modifications (PTMs) of LKB1 and consequent changes in its localization, activity, and interaction with substrates. The alteration in LKB1 function as a consequence of genetic mutations and aberrant upstream signaling regulation leads to tumor development and progression. Here, we review current knowledge about the mechanism of LKB1 in cancer and the contributions of PTMs, such as phosphorylation, ubiquitination, SUMOylation, acetylation, prenylation, and others, to the regulation of LKB1 function, offering new insights into the therapeutic strategies in cancer.

Modulating Tumor Microenvironment: A Review on STK11 Immune Properties and Predictive vs Prognostic Role for Non-small-cell Lung Cancer Immunotherapy

OPINION STATEMENT

The quest for immunotherapy (IT) biomarkers is an element of highest clinical interest in both solid and hematologic tumors. In non-small-cell lung cancer (NSCLC) patients, besides PD-L1 expression evaluation with its intrinsic limitations, tissue and circulating parameters, likely portraying the tumor and its stromal/immune counterparts, have been proposed as potential predictors of IT responsiveness. STK11 mutations have been globally labeled as markers of IT resistance. After a thorough literature review, STK11 mutations condition the prognosis of NSCLC patients receiving ICI-containing regimens, implying a relevant biological and clinical significance. On the other hand, waiting for prospective and solid data, the putative negative predictive value of STK11 inactivation towards IT is sustained by less evidence. The physiologic regulation of multiple cellular pathways performed by STK11 likely explains the multifaceted modifications in tumor cells, stroma, and tumor immune microenvironment (TIME) observed in STK11 mutant lung cancer, particularly explored in the molecular subgroup of KRAS co-mutation. IT approaches available thus far in NSCLC, mainly represented by anti-PD-1/PD-L1 inhibitors, are not promising in the case of STK11 inactivation. Perceptive strategies aimed at modulating the TIME, regardless of STK11 status or specifically addressed to STK11-mutated cases, will hopefully provide valid therapeutic options to be adopted in the clinical practice.

New Scope of Targeted Therapies in Lung Carcinoma

Lung cancer (LC) is the leading cause of cancer deaths worldwide. Recent research has also shown LC as a genomic disease, causing somatic mutations in patients. Tests related to mutational analysis and genome profiles have lately expanded significantly in the genetics/genomics field of LC. This review summarizes the current knowledge about different signalling pathways of LC based on the clinical impact of molecular targets. It describes the main molecular pathways and changes involved in the development, progression, and cellular breakdown of LC and the molecular changes. This review focuses on approved and targeted experimental therapies such as immunotherapy and clinical trials that examine the different targeted approaches to treating LC. We aimto clarify the differences in the extent of various genetic mutations in several areas for LC patients. Targeted molecular therapies for LC can be continued with advanced racial differences in genetic changes, which have a significant impact on the choice of drug treatment and our understanding of the profile of drug susceptibility/resistance. The most relevant genes described in this review are EGFR, KRAS, MET, BRAF, PIK3CA, STK11, ERBB3, PTEN, and RB1. Combined research efforts in this field are required to understand the genetic difference in LC outcomes in the future.

Dependency of human and murine LKB1-inactivated lung cancer on aberrant CRTC-CREB activation

Lung cancer with loss-of-function of the LKB1 tumor suppressor is a common aggressive subgroup with no effective therapies. LKB1-deficiency induces constitutive activation of cAMP/CREB-mediated transcription by a family of three CREB-regulated transcription coactivators (CRTC1-3). However, the significance and mechanism of CRTC activation in promoting the aggressive phenotype of LKB1-null cancer remain poorly characterized. Here, we observed overlapping CRTC expression patterns and mild growth phenotypes of individual CRTC-knockouts in lung cancer, suggesting functional redundancy of CRTC1-3. We consequently designed a dominant-negative mutant (dnCRTC) to block all three CRTCs to bind and co-activate CREB. Expression of dnCRTC efficiently inhibited the aberrantly activated cAMP/CREB-mediated oncogenic transcriptional program induced by LKB1-deficiency, and specifically blocked the growth of human and murine LKB1-inactivated lung cancer. Collectively, this study provides direct proof for an essential role of the CRTC-CREB activation in promoting the malignant phenotypes of LKB1-null lung cancer and proposes the CRTC-CREB interaction interface as a novel therapeutic target.

Metabolic reprogramming and epigenetic modifications on the path to cancer

Metabolic rewiring and epigenetic remodeling, which are closely linked and reciprocally regulate each other, are among the well-known cancer hallmarks. Recent evidence suggests that many metabolites serve as substrates or cofactors of chromatin-modifying enzymes as a consequence of the translocation or spatial regionalization of enzymes or metabolites. Various metabolic alterations and epigenetic modifications also reportedly drive immune escape or impede immunosurveillance within certain contexts, playing important roles in tumor progression. In this review, we focus on how metabolic reprogramming of tumor cells and immune cells reshapes epigenetic alterations, in particular the acetylation and methylation of histone proteins and DNA. We also discuss other eminent metabolic modifications such as, succinylation, hydroxybutyrylation, and lactylation, and update the current advances in metabolism- and epigenetic modification-based therapeutic prospects in cancer.

LKB1 Down-Modulation by miR-17 Identifies Patients With NSCLC Having Worse Prognosis Eligible for Energy-Stress-Based Treatments

INTRODUCTION

Preclinical models recently unveiled the vulnerability of LKB1/KRAS comutated NSCLC to metabolic stress-based treatments. Because miR-17 is a potential epigenetic regulator of LKB1, we hypothesized that wild-type LKB1 (LKB1^WT) NSCLC with high miR-17 expression may be sensitive to an energetic stress condition, and eligible for metabolic frailties-based therapeutic intervention.

METHODS

We took advantage of NSCLC cell lines with different combinations of KRAS mutation and LKB1 deletion and of patient-derived xenografts (PDXs) with high (LKB1^WT/miR-17 high) or low (LKB1^WT/miR-17 low) miR-17 expression. We evaluated LKB1 pathway impairment and apoptotic response to metformin. We retrospectively evaluated LKB1 and miR-17 expression levels in tissue specimens of patients with NSCLC and PDXs. In addition, a lung cancer series from The Cancer Genome Atlas data set was analyzed for miR-17 expression and potential correlation with clinical features.

RESULTS

We identified miR-17 as an epigenetic regulator of LKB1 in NSCLC and confirmed targeting of miR-17 to LKB1 3' untranslated region by luciferase reporter assay. We found that miR-17 overexpression functionally impairs the LKB1/AMPK pathway. Metformin treatment prompted apoptosis on miR-17 overexpression only in LKB1^WT cell lines, and in LKB1^WT/miR-17 high PDXs. A retrospective analysis in patients with NSCLC revealed an inverse correlation between miR-17 and LKB1 expression and highlighted a prognostic role of miR-17 expression in LKB1^WT patients, which was further confirmed by The Cancer Genome Atlas data analysis.

CONCLUSIONS

We identified miR-17 as a mediator of LKB1 expression in NSCLC tumors. This study proposes a miR-17 expression score potentially exploitable to discriminate LKB1^WT patients with NSCLC with impaired LKB1 expression and poor outcome, eligible for energy-stress-based treatments.

Hallmarks of cancer-the new testament

Diagnosis and treatment of disease demand a sound understanding of the underlying mechanisms, determining any Achilles' heel that can be targeted in effective therapies. Throughout history, this endeavour to decipher the origin and mechanism of transformation of a normal cell into cancer has led to various theories-from cancer as a curse to an understanding at the level of single-cell heterogeneity, meaning even among a single sub-type of cancer there are myriad molecular challenges to overcome. With increasing insight into cancer genetics and biology, the disease has become ever more complex to understand. The complexity of cancer as a disease was distilled into key traits by Hanahan and Weinberg in their seminal 'Hallmarks of Cancer' reviews. This lucid conceptualization of complex cancer biology is widely accepted and has helped advance cancer therapeutics by targeting the various hallmarks but, with the advancement in technologies, there is greater granularity in how we view cancer as a disease, and the additional understanding over the past decade requires us to revisit the hallmarks of cancer. Based on extensive study of the cancer research literature, we propose four novel hallmarks of cancer, namely, the ability of cells to regress from a specific specialized functional state, epigenetic changes that can affect gene expression, the role of microorganisms and neuronal signalling, to be included in the hallmark conceptualization along with evidence of various means to exploit them therapeutically.

Beyond LKB1 Mutations in Non-Small Cell Lung Cancer: Defining LKB1less Phenotype to Optimize Patient Selection and Treatment

LKB1 is frequently mutated in non-small cell lung cancer (NSCLC). LKB1-mutated NSCLCs often have a dismal prognosis and receive lower benefit from the currently available therapies. LKB1 acts as a cell emergency brake in low-energy conditions, by modulating the activity of crucial anabolic enzymes. Thus, loss of LKB1 activity leads to the enhancement of tumor cell proliferation also under conditions of energy shortage. This unrestrained growth may be exploited as an Achilles heel in NSCLC, i.e., by inhibiting mitochondrial respiration. Recently, clinical trials have started to investigate the efficacy of metabolism-based treatments in NSCLCs. To date, enrollment of patients within these trials is based on LKB1 loss of function status, defined by mutation in the gene or by complete absence of immunohistochemical staining. However, LKB1 impairment could be the consequence of epigenetic regulations that partially or completely abrogate protein expression. These epigenetic regulations result in LKB1 wild-type tumors with aggressiveness and vulnerabilities similar to those of LKB1-mutated ones. In this review, we introduced the definition of the “LKB1less phenotype”, and we summarized all currently known features linked to this status, in order to optimize selection and treatment of NSCLC patients with impaired LKB1 function.

Distinct promoter methylation patterns of LKB1 in the hamartomatous polyps of Peutz-Jeghers syndrome and its potential in gastrointestinal malignancy prediction

Background

Peutz-Jeghers Syndrome (PJS) is known as a rare inherited polyposis due to the malfunction of serine/threonine kinase gene LKB1. However, not all of PJS patients carry LKB1 germline mutation. Previous researches have observed the elevated DNA methylation level in PJS polyps. Nevertheless, the mechanism of such abnormal and its impact on PJS patients remains to be fully described.

Results

The results proved a significant increase on the methylation level of LKB1 promoter in PJS polyps compared with normal colon biopsies through bisulfite PCR followed by Sanger sequencing. Moreover, the methylation pattern in PJS polyps could be further categorized as three different scenarios: hypermethylated, hemimethylated and hypomethylated pattern. Furthermore, immunohistochemistry of DNMT1/3a/3b suggested the up-regulation of DNMT1 and 3a might participate the epigenetic alternation of LKB1 in PJS polyps. Logistic regression suggested hypomethylated LKB1 promoter in PJS polyps as a risk factor for gastrointestinal malignancies in PJS patients.

Conclusions

The promoter methylation level of LKB1 gene in PJS polyps is generally elevated compared with normal colon mucosa. Yet not all of PJS polyps carry hypermethylated LKB1 promoter. Hypomethylation in this region has linked to malignant tumors in PJS patients. Given the rarity of PJS, this work together with previous researches, have proved the importance of LKB1 promoter methylation in PJS development and prognosis.

Role of INSL4 Signaling in Sustaining the Growth and Viability of LKB1-Inactivated Lung Cancer

BACKGROUND

The LKB1 tumor suppressor gene is commonly inactivated in non-small cell lung carcinomas (NSCLC), a major form of lung cancer. Targeted therapies for LKB1-inactivated lung cancer are currently unavailable. Identification of critical signaling components downstream of LKB1 inactivation has the potential to uncover rational therapeutic targets. Here we investigated the role of INSL4, a member of the insulin/IGF/relaxin superfamily, in LKB1-inactivated NSCLCs.

METHODS

INSL4 expression was analyzed using global transcriptome profiling, quantitative reverse transcription PCR, western blotting, enzyme-linked immunosorbent assay, and RNA in situ hybridization in human NSCLC cell lines and tumor specimens. INSL4 gene expression and clinical data from The Cancer Genome Atlas lung adenocarcinomas (n = 515) were analyzed using log-rank and Fisher exact tests. INSL4 functions were studied using short hairpin RNA (shRNA) knockdown, overexpression, transcriptome profiling, cell growth, and survival assays in vitro and in vivo. All statistical tests were two-sided.

RESULTS

INSL4 was identified as a novel downstream target of LKB1 deficiency and its expression was induced through aberrant CRTC-CREB activation. INSL4 was highly induced in LKB1-deficient NSCLC cells (up to 543-fold) and 9 of 41 primary tumors, although undetectable in all normal tissues except the placenta. Lung adenocarcinomas from The Cancer Genome Atlas with high and low INSL4 expression (with the top 10th percentile as cutoff) showed statistically significant differences for advanced tumor stage (P < .001), lymph node metastasis (P = .001), and tumor size (P = .01). The INSL4-high group showed worse survival than the INSL4-low group (P < .001). Sustained INSL4 expression was required for the growth and viability of LKB1-inactivated NSCLC cells in vitro and in a mouse xenograft model (n = 5 mice per group). Expression profiling revealed INSL4 as a critical regulator of cell cycle, growth, and survival.

CONCLUSIONS

LKB1 deficiency induces an autocrine INSL4 signaling that critically supports the growth and survival of lung cancer cells. Therefore, aberrant INSL4 signaling is a promising therapeutic target for LKB1-deficient lung cancers.

Metabolic Dysregulations and Epigenetics: A Bidirectional Interplay that Drives Tumor Progression

Cancer has been considered, for a long time, a genetic disease where mutations in key regulatory genes drive tumor initiation, growth, metastasis, and drug resistance. Instead, the advent of high-throughput technologies has revolutionized cancer research, allowing to investigate molecular alterations at multiple levels, including genome, epigenome, transcriptome, proteome, and metabolome and showing the multifaceted aspects of this disease. The multi-omics approaches revealed an intricate molecular landscape where different cellular functions are interconnected and cooperatively contribute to shaping the malignant phenotype. Recent evidence has brought to light how metabolism and epigenetics are highly intertwined, and their aberrant crosstalk can contribute to tumorigenesis. The oncogene-driven metabolic plasticity of tumor cells supports the energetic and anabolic demands of proliferative tumor programs and secondary can alter the epigenetic landscape via modulating the production and/or the activity of epigenetic metabolites. Conversely, epigenetic mechanisms can regulate the expression of metabolic genes, thereby altering the metabolome, eliciting adaptive responses to rapidly changing environmental conditions, and sustaining malignant cell survival and progression in hostile niches. Thus, cancer cells take advantage of the epigenetics-metabolism crosstalk to acquire aggressive traits, promote cell proliferation, metastasis, and pluripotency, and shape tumor microenvironment. Understanding this bidirectional relationship is crucial to identify potential novel molecular targets for the implementation of robust anti-cancer therapeutic strategies.

Towards quantitative and multiplexed in vivo functional cancer genomics

Large-scale sequencing of human tumours has uncovered a vast array of genomic alterations. Genetically engineered mouse models recapitulate many features of human cancer and have been instrumental in assigning biological meaning to specific cancer-associated alterations. However, their time, cost and labour-intensive nature limits their broad utility; thus, the functional importance of the majority of genomic aberrations in cancer remains unknown. Recent advances have accelerated the functional interrogation of cancer-associated alterations within in vivo models. Specifically, the past few years have seen the emergence of CRISPR-Cas9-based strategies to rapidly generate increasingly complex somatic alterations and the development of multiplexed and quantitative approaches to ascertain gene function in vivo.

Promoter hypermethylation in ductal carcinoma in situ of the male breast

Ductal carcinoma in situ (DCIS) of the male breast is very rare and has hardly been studied molecularly. In males, we compared methylation status of 25 breast cancer-related genes in pure DCIS (n = 18) and invasive breast carcinoma (IBC) with adjacent DCIS (DCIS-AIC) (n = 44) using methylation-specific multiplex ligation-dependent probe amplification. Results were compared to female breast cancer (BC). There were no significant differences in methylation features between male pure DCIS, DCIS-AIC and IBC after correction for multiple comparisons. In paired analysis of IBC and adjacent DCIS, CADM1 showed a significantly higher absolute methylation percentage in DCIS (P = 0.002). In cluster analysis, two clusters stood out with respectively infrequent and frequent methylation (GATA5, KLLN, PAX6, PAX5, CDH13, MSH6 and WT1 were frequently methylated). Compared to female DCIS, methylation was in general much less common in male DCIS, especially for VHL, ESR1, CDKN2A, CD44, CHFR, BRCA2, RB1 and STK11. In contrast, THBS1 and GATA5 were more frequently methylated in male DCIS. In conclusion, there is frequent methylation of GATA5, KLLN, PAX6, PAX5, CDH13, MSH6 and WT1 in male DCIS. Since there was little change in the methylation status for the studied genes from pure male DCIS to DCIS-AIC and IBC, methylation of these seven genes is more likely to occur early in male breast carcinogenesis. Based on the current markers male DCIS seems to be an epigenetically more advanced precursor of male BC, although in comparison to its female counterpart it appears that fewer loci harbor methylation, pointing to differences between male and female breast carcinogenesis with regard to the studied loci.

Metabolic Reprogramming in Breast Cancer and Its Therapeutic Implications

Current standard-of-care (SOC) therapy for breast cancer includes targeted therapies such as endocrine therapy for estrogen receptor-alpha (ERα) positive; anti-HER2 monoclonal antibodies for human epidermal growth factor receptor-2 (HER2)-enriched; and general chemotherapy for triple negative breast cancer (TNBC) subtypes. These therapies frequently fail due to acquired or inherent resistance. Altered metabolism has been recognized as one of the major mechanisms underlying therapeutic resistance. There are several cues that dictate metabolic reprogramming that also account for the tumors’ metabolic plasticity. For metabolic therapy to be efficacious there is a need to understand the metabolic underpinnings of the different subtypes of breast cancer as well as the role the SOC treatments play in targeting the metabolic phenotype. Understanding the mechanism will allow us to identify potential therapeutic vulnerabilities. There are some very interesting questions being tackled by researchers today as they pertain to altered metabolism in breast cancer. What are the metabolic differences between the different subtypes of breast cancer? Do cancer cells have a metabolic pathway preference based on the site and stage of metastasis? How do the cell-intrinsic and -extrinsic cues dictate the metabolic phenotype? How do the nucleus and mitochondria coordinately regulate metabolism? How does sensitivity or resistance to SOC affect metabolic reprogramming and vice-versa? This review addresses these issues along with the latest updates in the field of breast cancer metabolism.

Constitutive BRCA1 Promoter Hypermethylation Can Be a Predisposing Event in Isolated Early-Onset Breast Cancer

Early age at onset of breast cancer (eoBC) is suggestive of an increased genetic risk. Although genetic testing is offered to all eoBC-affected women, in isolated cases the detection rate of pathogenic variants is <10%. This study aimed at assessing the role of constitutive promoter methylation at BC-associated loci as an underlying predisposing event in women with eoBC and negative family history. Promoter methylation at 12 loci was assessed by the MassARRAY technology in blood from 154 BRCA1/2 negative patients with eoBC and negative family history, and 60 healthy controls. Hypermethylation was determined, within each promoter, by comparing the patient’s mean methylation value with thresholds based on one-sided 95% bootstrap confidence interval of the controls’ mean. Three patients had hypermethylated results, two at BRCA1 and one at RAD51C. Analyses on tumor tissue from the patient exceeding the highest threshold at BRCA1 revealed a mean methylation >60% and loss of heterozygosity at chromosome 17q. The patient hypermethylated at RAD51C showed low methylation in the tumor sample, ruling out a role for methylation-induced silencing in tumor development. In isolated eoBC patients, BRCA1 constitutive promoter methylation may be a predisposing event. Further studies are required to define the impact of methylation changes occurring at BC-predisposing genes and their role in tumorigenesis.

Expression of STK11 gene and its promoter activity in MCF control and cancer cells

Serine/threonine kinase gene (STK11) is identified as tumor suppressor gene whose mutation can lead to Peutz-Jeghers syndrome (PJS). STK11 is emerging as a multifunctional protein, it activates 14 different AMP-activated protein kinase (AMPK) family members, important in the regulation of cell polarity, cell cycle arrest, energy and hemostasis. Present study was designed to evaluate STK11 mRNA expression in MCF-7 cancer and MCF-10 normal breast cells lines. mRNA expression was studied by real-time PCR. Further, human STK11 promoter construct was fused to a luciferase reporter and transfected into both MCF-7 and MCF-10 cells to identify the promoter activity in these cells. STK11 mRNA was found significantly higher in MCF-7 compared to MCF-10 cells (p value < 0.0005) indicating its role in the onset of breast cancer. Interestingly, it was found that the promoter activity of STK11 gene in MCF-7 cells was also significantly higher when compared to MCF-10 cells (p value < 0.005). Positive correlation was observed in promoter activity and gene expression (p = 0.048, r2 = 0.587). This study for the first time relates the altered STK11 gene expression in breast cancer cells with altered promoter activity. The present finding may shed light on the new therapeutic approaches against breast cancer by targeting gene or its promoter.

Metformin and berberine, two versatile drugs in treatment of common metabolic diseases

Metformin has been used as a glucose lowering drug for several centuries and is now a first-line drug for type 2 diabetes mellitus (T2DM). Since the discovery that it activates AMP-activated protein kinase (AMPK) and reduces risk of cancer, metformin has drawn great attentions. Another drug, berberine, extracted from berberis vulgaris L. (root), was an ancient herbal medicine in treating diarrhea. Ongoing experimental and clinical studies have illuminated great potential of berberine in regulation of glucose and lipid homeostasis, cancer growth and inflammation. Furthermore, the lipid lowering effect of berberine is comparable to those conventional lipid drugs but with low toxicity. Therefore, it is right time to transform beneficial effects of berberine into therapeutic practice. Metformin and berberine share many features in actions despite different structure and both could be excellent drugs in treating T2DM, obesity, cardiac diseases, tumour, as well as inflammation. Since these disorders are often connected and comprise common pathogenic factors that could be targeted by the two drugs, understanding their actions can give us rationale for expansion of their clinical uses.

LKB1 as a Tumor Suppressor in Uterine Cancer: Mouse Models and Translational Studies

The LKB1 tumor suppressor was identified in 1998 as the gene mutated in the Peutz-Jeghers Syndrome (PJS), a hereditary cancer predisposition characterized by gastrointestinal polyposis and a high incidence of cancers, particularly carcinomas, at a variety of anatomic sites including the gastrointestinal tract, lung, and female reproductive tract. Women with PJS have a high incidence of carcinomas of the uterine corpus (endometrium) and cervix. The LKB1 gene is also somatically mutated in human cancers arising at these sites. Work in mouse models has highlighted the potency of LKB1 as an endometrial tumor suppressor and its distinctive roles in driving invasive and metastatic growth. These in vivo models represent tractable experimental systems for the discovery of underlying biological principles and molecular processes regulated by LKB1 in the context of tumorigenesis and also serve as useful preclinical model systems for experimental therapeutics. Here we review LKB1's known roles in mTOR signaling, metabolism, and cell polarity, with an emphasis on human pathology and mouse models relevant to uterine carcinogenesis, including cancers of the uterine corpus and cervix.

Role of CPS1 in Cell Growth, Metabolism and Prognosis in LKB1-Inactivated Lung Adenocarcinoma

Background

Liver kinase B1 ( LKB1 ) is a tumor suppressor in lung adenocarcinoma (LADC). We investigated the proteomic profiles of 45 LADC cell lines with and without LKB1 inactivation. Carbamoyl phosphate synthetase 1 (CPS1), the first rate-limiting mitochondrial enzyme in the urea cycle, was distinctively overexpressed in LKB1-inactivated LADC cell lines. We therefore assessed the role of CPS1 and its clinical relevance in LKB1-inactivated LADC.

Methods

Mass spectrometric profiling of proteome and metabolome and function of CPS1 were analyzed in LADC cell lines. CPS1 and LKB1 expression in tumors from 305 LADC and 160 lung squamous cell carcinoma patients was evaluated by immunohistochemistry. Kaplan-Meier and Cox regression analyses were applied to assess the association between overall survival and CPS1 and LKB1 expression. All statistical tests were two-sided.

Results

CPS1 knockdown reduced cell growth, decreased metabolite levels associated with nucleic acid biosynthesis pathway, and contributed an additive effect when combined with gemcitabine, pemetrexed, or CHK1 inhibitor AZD7762. Tissue microarray analysis revealed that CPS1 was expressed in 65.7% of LKB1-negative LADC, and only 5.0% of LKB1-positive LADC. CPS1 expression showed statistically significant association with poor overall survival in LADC (hazard ratio = 3.03, 95% confidence interval = 1.74 to 5.25, P < .001).

Conclusions

Our findings suggest functional relevance of CPS1 in LKB1-inactivated LADC and association with worse outcome of LADC. CPS1 is a promising therapeutic target in combination with other chemotherapy agents, as well as a prognostic biomarker, enabling a personalized approach to treatment of LADC.

Methylation of STK11 promoter is a risk factor for tumor stage and survival in clear cell renal cell carcinoma

Inactivation of tumor suppressor gene serine-threonine kinase 11 (STK11) in clear cell renal cell carcinoma (ccRCC) has been demonstrated; however, the mechanism of this inactivation remains to be investigated. To investigate whether epigenetic alteration plays a role in the inactivation of STK11 in RCC, the present study aimed to investigate the methylation status of the STK11 promoter and its association with tumor stage and survival in ccRCC patients. Paraffin-embedded specimens were obtained from 42 ccRCC patients. The specimens were analyzed for the methylation status of the STK11 promoter CpG island using methylation-specific polymerase chain reaction. Survival, tumor-node-metastasis (TNM)/American Joint Committee on Cancer (AJCC) stages, and hematological parameters were compared between patients with unmethylated (U), partially methylated (P) and methylated (M) STK11 promoter. Among the 42 patients, there were 12 (28.6%), 18 (42.9%) and 12 (28.6%) patients in the M, P and U groups, respectively. The methylation status of the STK11 promoter was associated with T, N and AJCC stages in RCC. Survival analysis showed that the M group had a significantly shorter survival time compared with the P and U groups. These findings suggested that methylation of the STK11 promoter in RCC is a not rare event, and it may have an important role in the pathogenesis of RCC and be a risk factor for the prognosis of RCC.

Prognostic significance of LKB1 promoter methylation in cutaneous malignant melanoma

Liver kinase B1 (LKB1) loss is a common occurrence in various types of human cancer, and promoter methylation has been hypothesized to be a major mechanism of LKB1 inactivation. The association between LKB1 gene promoter methylation status and tumor progression in cutaneous malignant melanoma (CMM) remains unknown. In the present study, the methylation status of the LKB1 promoter region was examined in 57 human cutaneous malignant melanomas and 50 benign skin lesion controls by methylation-specific polymerase chain reaction. Consequently, 12 (12/57) melanoma tissues exhibited LKB1 promoter methylation, while only 2 (2/50) benign lesions presented with LKB1 hypermethylation. The frequency of LKB1 promoter methylation in melanoma was significantly increased compared with the benign controls (P<0.05). Additional statistical analysis demonstrated that hypermethylation of the LKB1 gene was correlated with Breslow's thickness, presence of ulceration and American Joint Committee on Cancer stage (P<0.05). Additionally, Kaplan-Meier analysis revealed that LKB1 hypermethylation was significantly associated with poorer survival (P<0.01). Multivariate COX regression analysis indicated that LKB1 promoter methylation was an independent prognostic factor for overall survival in patients with melanoma.

Interplay between epigenetics and metabolism in oncogenesis: mechanisms and therapeutic approaches

Epigenetic and metabolic alterations in cancer cells are highly intertwined. Oncogene-driven metabolic rewiring modifies the epigenetic landscape via modulating the activities of DNA and histone modification enzymes at the metabolite level. Conversely, epigenetic mechanisms regulate the expression of metabolic genes, thereby altering the metabolome. Epigenetic-metabolomic interplay has a critical role in tumourigenesis by coordinately sustaining cell proliferation, metastasis and pluripotency. Understanding the link between epigenetics and metabolism could unravel novel molecular targets, whose intervention may lead to improvements in cancer treatment. In this review, we summarized the recent discoveries linking epigenetics and metabolism and their underlying roles in tumorigenesis; and highlighted the promising molecular targets, with an update on the development of small molecule or biologic inhibitors against these abnormalities in cancer.

cAMP/CREB-regulated LINC00473 marks LKB1-inactivated lung cancer and mediates tumor growth

The LKB1 tumor suppressor gene is frequently mutated and inactivated in non-small cell lung cancer (NSCLC). Loss of LKB1 promotes cancer progression and influences therapeutic responses in preclinical studies; however, specific targeted therapies for lung cancer with LKB1 inactivation are currently unavailable. Here, we have identified a long noncoding RNA (lncRNA) signature that is associated with the loss of LKB1 function. We discovered that LINC00473 is consistently the most highly induced gene in LKB1-inactivated human primary NSCLC samples and derived cell lines. Elevated LINC00473 expression correlated with poor prognosis, and sustained LINC00473 expression was required for the growth and survival of LKB1-inactivated NSCLC cells. Mechanistically, LINC00473 was induced by LKB1 inactivation and subsequent cyclic AMP-responsive element-binding protein (CREB)/CREB-regulated transcription coactivator (CRTC) activation. We determined that LINC00473 is a nuclear lncRNA and interacts with NONO, a component of the cAMP signaling pathway, thereby facilitating CRTC/CREB-mediated transcription. Collectively, our study demonstrates that LINC00473 expression potentially serves as a robust biomarker for tumor LKB1 functional status that can be integrated into clinical trials for patient selection and treatment evaluation, and implicates LINC00473 as a therapeutic target for LKB1-inactivated NSCLC.

Gene-set Analysis with CGI Information for Differential DNA Methylation Profiling

DNA methylation is a well-established epigenetic biomarker for many diseases. Studying the relationships among a group of genes and their methylations may help to unravel the etiology of diseases. Since CpG-islands (CGIs) play a crucial role in the regulation of transcription during methylation, including them in the analysis may provide further information in understanding the pathogenesis of cancers. Such CGI information, however, has usually been overlooked in existing gene-set analyses. Here we aimed to include both pathway information and CGI status to rank competing gene-sets and identify among them the genes most likely contributing to DNA methylation changes. To accomplish this, we devised a Bayesian model for matched case-control studies with parameters for CGI status and pathway associations, while incorporating intra-gene-set information. Three cancer studies with candidate pathways were analyzed to illustrate this approach. The strength of association for each candidate pathway and the influence of each gene were evaluated. Results show that, based on probabilities, the importance of pathways and genes can be determined. The findings confirm that some of these genes are cancer-related and may hold the potential to be targeted in drug development.

Aberrant gene methylation in non-neoplastic mucosa as a predictive marker of ulcerative colitis-associated CRC

BACKGROUND PROMOTER: hypermethylation plays a major role in cancer through transcriptional silencing of critical genes. The aim of our study is to evaluate the methylation status of these genes in the colonic mucosa without dysplasia or adenocarcinoma at the different steps of sporadic and UC-related carcinogenesis and to investigate the possible role of genomic methylation as a marker of CRC.

RESULTS

The expression of Dnmts 1 and 3A was significantly increased in UC-related carcinogenesis compared to non inflammatory colorectal carcinogenesis. In non-neoplastic colonic mucosa, the number of methylated genes resulted significantly higher in patients with CRC and in those with UC-related CRC compared to the HC and UC patients and patients with dysplastic lesion of the colon. The number of methylated genes in non-neoplastic colonic mucosa predicted the presence of CRC with good accuracy either in non inflammatory and inflammatory related CRC.

METHODS

Colonic mucosal samples were collected from healthy subjects (HC) (n = 30) and from patients with ulcerative colitis (UC) (n = 29), UC and dysplasia (n = 14), UC and cancer (n = 10), dysplastic adenoma (n = 14), and colon adenocarcinoma (n = 10). DNA methyltransferases-1, -3a, -3b, mRNA expression were quantified by real time qRT-PCR. The methylation status of CDH13, APC, MLH1, MGMT1 and RUNX3 gene promoters was assessed by methylation-specific PCR.

CONCLUSIONS

Methylation status of APC, CDH13, MGMT, MLH1 and RUNX3 in the non-neoplastic mucosa may be used as a marker of CRC: these preliminary results could allow for the adjustment of a patient's surveillance interval and to select UC patients who should undergo intensive surveillance.

A Sensitive NanoString-Based Assay to Score STK11 (LKB1) Pathway Disruption in Lung Adenocarcinoma

INTRODUCTION

Serine/threonine kinase 11 gene (STK11), better known as liver kinase β1, is a tumor suppressor that is commonly mutated in lung adenocarcinoma (LUAD). Previous work has shown that mutational inactivation of the STK11 pathway may serve as a predictive biomarker for cancer treatments, including phenformin and cyclooxygenase-2 inhibition. Although immunohistochemical (IHC) staining and diagnostic sequencing are used to measure STK11 pathway disruption, there are serious limitations to these methods, thus emphasizing the importance of validating a clinically useful assay.

METHODS

An initial STK11 mutation mRNA signature was generated using cell line data and refined using three large, independent patient databases. The signature was validated as a classifier using The Cancer Genome Atlas (TCGA) LUAD cohort as well as a 442-patient LUAD cohort developed at Moffitt. Finally, the signature was adapted to a NanoString-based format and validated using RNA samples isolated from formalin-fixed, paraffin-embedded tissue blocks corresponding to a cohort of 150 patients with LUAD. For comparison, STK11 IHC staining was also performed.

RESULTS

The STK11 signature was found to correlate with null mutations identified by exon sequencing in multiple cohorts using both microarray and NanoString formats. Although there was a statistically significant correlation between reduced STK11 protein expression by IHC staining and mutation status, the NanoString-based assay showed superior overall performance, with a -0.1588 improvement in area under the curve in receiver-operator characteristic curve analysis (p < 0.012).

CONCLUSION

The described NanoString-based STK11 assay is a sensitive biomarker to study emerging therapeutic modalities in clinical trials.

Stem cell dynamics and pretumor progression in the intestinal tract

Colorectal carcinogenesis is a process that follows a stepwise cascade that goes from the normal to an invisible pretumor stage ultimately leading to grossly visible tumor progression. During pretumor progression, an increasing accumulation of genetic alterations occurs, by definition without visible manifestations. It is generally thought that stem cells in the crypt base are responsible for this initiation of colorectal cancer progression because they are the origin of the differentiated epithelial cells that occupy the crypt. Furthermore, they are characterized by a long life span that enables them to acquire these cumulative mutations. Recent studies visualized the dynamics of stem cells both in vitro and in vivo. Translating this work into clinical applications will contribute to the evaluation of patients' predisposition for colorectal carcinogenesis and may help in the design of preventive measures for high-risk groups. In this review, we outline the progress made in the research into tracing stem cell dynamics. Further, we highlight the importance and potential clinical value of tracing stem cell dynamics in pretumor progression.

Additive effects of eukaryotic co‑expression plasmid carrying GRIM‑19 and LKB1 genes on breast cancer in vitro and in vivo

Gene associated with retinoid‑interferon‑induced mortality 19 (GRIM‑19) and the liver kinase B1 (LKB1) gene, two types of tumor suppressor gene, have been demonstrated to have important roles in breast carcinogenesis. The present study developed a dual expression plasmid that co‑expressed GRIM‑19 and LKB1, and evaluated the combined effects of the two genes against breast cancer in vitro and in vivo. Transfection with a plasmid for the simultaneous expression of GRIM‑19 and LKB1 (pGRIM19‑LKB1) into MCF‑7 breast cancer cells significantly inhibited the proliferation, colony formation, migration and invasion compared with the effects of transfection with either pGRIM‑19 or pLKB1 alone. Furthermore, transfection with pGRIM19‑LKB1 induced enhanced levels of apoptosis and cell cycle arrest at G0/G1 stage in MCF7 cells compared to the effects of pGRIM‑19 or pLKB1 alone. An in vivo experiment using an MCF‑7 xenograft tumor model demonstrated that intravenous injection of pGRIM19‑LKB1 had an enhanced effect on tumor growth inhibition compared to that of pGRIM‑19 or pLKB1 alone. In conclusion the findings of the present study suggested that transfection with eukaryotic plasmid for the simultaneous expression of GRIM‑19 and LKB1 more effectively suppressed the growth of breast cancer in vitro and in vivo, and may therefore have therapeutic potential for the treatment of human breast cancer.

Induced pluripotent stem cell technology for dissecting the cancer epigenome

Cancer arises through the accumulation of both genetic and epigenetic alterations. Although the causal role of genetic mutations on cancer development has been established in vivo, similar evidence for epigenetic alterations is limited. Moreover, mutual interactions between genetic mutations and epigenetic alterations remain unclear. Cellular reprogramming technology can be used to actively modify the epigenome without affecting the underlying genomic sequences. Here we introduce recent studies that have utilized this property for cancer research. We propose that just as it has potential for regenerative medicine and disease modeling, cell reprogramming could also be a powerful tool for dissecting the role of the cancer epigenome in the development and maintenance of cancer cells.

Update on the roles of liver kinase B1 in pancreatic cancer

Germline mutations of the liver kinase B1 (STK11/LKB1) gene which encodes a serine/threonine kinase is responsible for Peutz-Jeghers syndrome. There are 14 AMP-activated protein kinase (AMPK)-related kinases in pathways downstream of LKB1, which are involved in many physiological and pathological processes such as regulation of energy metabolism, cell polarity and apoptosis in cells. LKB1 gene mutation has been investigated extensively in a variety of cancers, including pancreatic cancer. Pancreatic cancer is commonly recognized as a disease with extremely poor prognosis. Therefore, a full understanding of its molecular pathology is critical. This review aims to elucidate the structure, distribution, and function of LKB1, and the relationship with pancreatic cancer. In addition, we also point out that in some scenarios, LKB1 may play a role as a tumor protector.

The negative regulators of Wnt pathway-DACH1, DKK1, and WIF1 are methylated in oral and oropharyngeal cancer and WIF1 methylation predicts shorter survival

The deregulation of Wnt signaling has recently emerged as one of the drivers of head and neck cancers. This is frequently related to the methylation of several antagonists of this pathway. This study aimed at the assessment of the profile of methylation of Wnt pathway antagonists and the determination of the prognostic value of the methylation of selected genes in oral carcinomas. The methylation of DACH1, DKK1, LKB1, PPP2R2B, RUNX3, SFRP2, and WIF-1 was analyzed in 16 oral squamous cell carcinoma cell lines using the methylation-specific polymerase chain reaction. The methylation of selected genes was further analyzed in tumor sections from 43 primary oral carcinoma patients. The analysis of oral carcinoma cell lines showed very frequent methylation of SFRP2 and WIF-1 and also a less frequent methylation of DACH1 and DKK1. On the other hand, RUNX3 was methylated only in one cell line, while LKB1 and PPP2R2B were not methylated in any of the cell lines. The biallelic methylation of DKK1 correlated with the low level of expression of this gene. Further evaluation of the methylation of DACH1, DKK1, and WIF1 in a clinical patient group confirmed the frequent methylation of WIF1 and intermediate or low frequency of methylation of DACH1 or DKK1, respectively. Importantly, the methylation of WIF-1 correlated with shorter survival in oral cancer patients. Overall, the methylation of the antagonists of Wnt pathway is frequently detected in oral squamous cell carcinomas. The methylation of WIF1 may be considered a prognostic marker in oral cancers.

LKB1 Loss induces characteristic patterns of gene expression in human tumors associated with NRF2 activation and attenuation of PI3K-AKT

Introduction:

Inactivation of serine/threonine kinase 11 (STK11 or LKB1) is common in lung cancer, and understanding the pathways and phenotypes altered as a consequence will aid the development of targeted therapeutic strategies. Gene and protein expressions in a murine model of v-Ki-ras2 Kirsten rat sarcoma viral oncogene homolog (Kras)-mutant lung cancer have been studied to gain insight into the biology of these tumors. However, the molecular consequences of LKB1 loss in human lung cancer have not been fully characterized.

Methods:

We studied gene expression profiles associated with LKB1 loss in resected lung adenocarcinomas, non–small-cell lung cancer cell lines, and murine tumors. The biological significance of dysregulated genes was interpreted using gene set enrichment and transcription factor analyses and also by integration with somatic mutations and proteomic data.

Results:

Loss of LKB1 is associated with consistent gene expression changes in resected human lung cancers and cell lines that differ substantially from the mouse model. Our analysis implicates novel biological features associated with LKB1 loss, including altered mitochondrial metabolism, activation of the nuclear respiratory factor 2 (NRF2) transcription factor by kelch-like ECH-associated protein 1 (KEAP1) mutations, and attenuation of the phosphatidylinositiol 3-kinase and v-akt murine thymoma viral oncogene homolog (PI3K/AKT) pathway. Furthermore, we derived a 16-gene classifier that accurately predicts LKB1 mutations and loss by nonmutational mechanisms. In vitro, transduction of LKB1 into LKB1-mutant cell lines results in attenuation of this signature.

Conclusion:

Loss of LKB1 defines a subset of lung adenocarcinomas associated with characteristic molecular phenotypes and distinctive gene expression features. Studying these effects may improve our understanding of the biology of these tumors and lead to the identification of targeted treatment strategies.

Synergistic effects of eukaryotic co-expression plasmid-based STAT3-specific siRNA and LKB1 on ovarian cancer in vitro and in vivo

The signal transducer and activator of transcription 3 (STAT3) are ideal targets for ovarian cancer. Previous studies showed that downregulation of STAT3 using specific short hairpin RNAs (shRNA) can significantly reduce ovarian tumor growth. However, RNA interference does not fully ablate target gene expression due to idiosyncrasies associated with shRNAs and their targets. To enhance the therapeutic efficacy of STAT3-specific shRNA, we employed a combinatorial expression of STAT3-specific shRNA and liver kinase B1 (LKB1), a tumor suppressor. Thus, the LKB1 coding sequences and STAT3-specific shRNAs were constructed in a eukaryotic co-expression plasmid pCDNA3.1, and then transfected into ovarian cancer cells to evaluate the synergistic effects of this combination on anticancer activity and explore the relevant molecular mechanisms. Co-expression of STAT3‑specific siRNA and LKB1 (pSi-STAT3-LKB1) synergistically inhibited ovarian cancer cell growth, invasion and migration, induced cell apoptosis and arrested the cell cycle in vitro when compared with monotherapy. The results showed that the co-expression of plasmid pSi-STAT3-LKB1 inserted subcutaneously into ovarian tumor xenograft resulted in more significant inhibition of tumor growth. Further study showed that the synergistic anti-ovarian cancer effects of the co-expression of STAT3-specific siRNA and LKB1 may be associated with the upregulation of p-p53, p21 and downregulation of survivin, BCL-2 and cyclin D1. Results of the present study suggested that combined therapy with eukaryotic co-expression of the plasmid‑carrying STAT3-specific siRNA and LKB1 is a novel and efficient treatment strategy for human ovarian cancer.

Loss of LKB1 in high-grade endometrial carcinoma: LKB1 is a novel transcriptional target of p53

BACKGROUND

Liver kinase B1 (LKB1) is a serine/threonine kinase that functions as a tumor suppressor and regulates cell polarity, proliferation, and metabolism. Mutations in LKB1 are associated with Peutz-Jeghers syndrome as well as sporadic cervical and lung cancers. Although LKB1-null mice develop invasive endometrial cancers, the role and regulation of LKB1 in the pathogenesis of human endometrial cancer are not well defined and are the focus of these studies.

METHODS

LKB1 protein and messenger RNA (mRNA) expression levels were evaluated in high-grade and low-grade endometrioid endometrial cancer (EEC) and cell lines by reverse transcriptase-polymerase chain reaction analysis, Western blot analysis, and immunohistochemistry. Mutational and promoter analyses of the LKB1 gene (serine/threonine kinase 11 [STK11]) were performed to identify the mechanisms that contribute to the loss of LKB1 in high-grade EEC.

RESULTS

Analysis of the LKB1 gene in low-grade and high-grade EECs revealed no genetic mutations, suggesting that alterations in LKB1 transcription may be responsible for LKB1 protein loss in high-grade EEC. Analysis of the LKB1 promoter revealed 4 putative tumor protein 53 (p53) binding sites. Quantitative chromatin immunoprecipitation demonstrated that p53 bound directly to 1 of these sites and increased LKB1 promoter activity 140-fold. LKB1 promoter activity, mRNA, and protein levels were suppressed after silencing of p53 with small interfering RNA and were elevated in cells that overexpressed p53. Levels of p53 mRNA and protein expression were decreased in high-grade EEC and were positively correlated with LKB1 protein levels (Spearman correlation, r=0.601; P<.001).

CONCLUSIONS

LKB1 is a direct transcriptional target of p53. The loss of wild-type p53 in high-grade EEC may contribute to the LKB1 loss observed in these more aggressive tumors.

Recent progress on liver kinase B1 (LKB1): expression, regulation, downstream signaling and cancer suppressive function

Liver kinase B1 (LKB1), known as a serine/threonine kinase, has been identified as a critical cancer suppressor in many cancer cells. It is a master upstream kinase of 13 AMP-activated protein kinase (AMPK)-related protein kinases, and possesses versatile biological functions. LKB1 gene is mutated in many cancers, and its protein can form different protein complexes with different cellular localizations in various cell types. The expression of LKB1 can be regulated through epigenetic modification, transcriptional regulation and post-translational modification. LKB1 dowcnstream pathways mainly include AMPK, microtubule affinity regulating kinase (MARK), salt-inducible kinase (SIK), sucrose non-fermenting protein-related kinase (SNRK) and brain selective kinase (BRSK) signalings, etc. This review, therefore, mainly discusses recent studies about the expression, regulation, downstream signaling and cancer suppressive function of LKB1, which can be helpful for better understanding of this molecular and its significance in cancers.

LKB1 Tumor Suppressor: Therapeutic Opportunities Knock when LKB1 Is Inactivated

LKB1 is commonly thought of as a tumor suppressor gene because its hereditary mutation is responsible for a cancer syndrome, and somatic inactivation of LKB1 is found in non-small cell lung cancer, melanoma, and cervical cancers. However, unlike other tumor suppressors whose main function is to either suppress cell proliferation or promote cell death, one of the functions of LKB1-regulated AMPK signaling is to suppress cell proliferation in order to promote cell survival under energetic stress conditions. This unique, pro-survival function of LKB1 has led to the discovery of reagents, such as phenformin, that specifically exploit the vulnerability of LKB1-null cells in their defect in sensing energetic stress. Such targeted agents represent a novel treatment strategy because they induce cell killing when LKB1 is absent. This review article summarizes various vulnerabilities of LKB1-mutant cells that have been reported in the literature and discusses the potential of using existing or developing novel reagents to target cancer cells with defective LKB1.

Alterations of LKB1 and KRAS and risk of brain metastasis: comprehensive characterization by mutation analysis, copy number, and gene expression in non-small-cell lung carcinoma

BACKGROUND

Brain metastases are one of the most malignant complications of lung cancer and constitute a significant cause of cancer related morbidity and mortality worldwide. Recent years of investigation suggested a role of LKB1 in NSCLC development and progression, in synergy with KRAS alteration. In this study, we systematically analyzed how LKB1 and KRAS alteration, measured by mutation, gene expression (GE) and copy number (CN), are associated with brain metastasis in NSCLC.

MATERIALS AND METHODS

Patients treated at University of North Carolina Hospital from 1990 to 2009 with NSCLC provided frozen, surgically extracted tumors for analysis. GE was measured using Agilent 44,000 custom-designed arrays, CN was assessed by Affymetrix GeneChip Human Mapping 250K Sty Array or the Genome-Wide Human SNP Array 6.0 and gene mutation was detected using ABI sequencing. Integrated analysis was conducted to assess the relationship between these genetic markers and brain metastasis. A model was proposed for brain metastasis prediction using these genetic measurements.

RESULTS

17 of the 174 patients developed brain metastasis. LKB1 wild type tumors had significantly higher LKB1 CN (p<0.001) and GE (p=0.002) than the LKB1 mutant group. KRAS wild type tumors had significantly lower KRAS GE (p<0.001) and lower CN, although the latter failed to be significant (p=0.295). Lower LKB1 CN (p=0.039) and KRAS mutation (p=0.007) were significantly associated with more brain metastasis. The predictive model based on nodal (N) stage, patient age, LKB1 CN and KRAS mutation had a good prediction accuracy, with area under the ROC curve of 0.832 (p<0.001).

CONCLUSION

LKB1 CN in combination with KRAS mutation predicted brain metastasis in NSCLC.

The transcriptional responsiveness of LKB1 to STAT-mediated signaling is differentially modulated by prolactin in human breast cancer cells

Background

Liver kinase 1 (LKB1) is an important multi-tasking protein linked with metabolic signaling, also controlling polarity and cytoskeletal rearrangements in diverse cell types including cancer cells. Prolactin (PRL) and Signal transducer and activator of transcription (STAT) proteins have been associated with breast cancer progression. The current investigation examines the effect of PRL and STAT-mediated signaling on the transcriptional regulation of LKB1 expression in human breast cancer cells.

Methods

MDA-MB-231, MCF-7, and T47D human breast cancer cells, and CHO-K1 cells transiently expressing the PRL receptor (long form), were treated with 100 ng/ml of PRL for 24 hours. A LKB1 promoter-luciferase construct and its truncations were used to assess transcriptional changes in response to specific siRNAs or inhibitors targeting Janus activated kinase 2 (JAK2), STAT3, and STAT5A. Real-time PCR and Western blotting were applied to quantify changes in mRNA and protein levels. Electrophoretic mobility shift (EMSA) and chromatin immunoprecipitation (ChIP) assays were used to examine STAT3 and STAT5A binding to the LKB1 promoter.

Results

Consistent with increases in mRNA, the LKB1 promoter was up-regulated by PRL in MDA-MB-231 cells, a response that was lost upon distal promoter truncation. A putative GAS element that could provide a STAT binding site mapped to this region, and its mutation decreased PRL-responsiveness. PRL-mediated increases in promoter activity required signaling through STAT3 and STAT5A, also involving JAK2. Both STATs imparted basally repressive effects in MDA-MB-231 cells. PRL increased in vivo binding of STAT3, and more definitively, STAT5A, to the LKB1 promoter region containing the GAS site. In T47D cells, PRL down-regulated LKB1 transcriptional activity, an effect that was reversed upon culture in phenol red-free media. Interleukin 6, a cytokine activating STAT signaling in diverse cell types, also increased LKB1 mRNA levels and promoter activity in MDA-MB-231 cells.

Conclusions

LKB1 is differentially regulated by PRL at the level of transcription in representative human breast cancer cells. Its promoter is targeted by STAT proteins, and the cellular estrogen receptor status may affect PRL-responsiveness. The hormonal and possibly cytokine-mediated control of LKB1 expression is particularly relevant in aggressive breast cancer cells, potentially promoting survival under energetically unfavorable conditions.

LKB1 loss at transcriptional level promotes tumor malignancy and poor patient outcomes in colorectal cancer

BACKGROUND

Liver kinase B1 (LKB1) loss by gene mutation, loss of heterozygosity, and promoter methylation rarely occurs in colorectal cancer. We wondered whether LKB1 loss could be deregulated at the transcriptional level to promote tumor progression and poor outcome in colorectal cancer.

METHODS

Mechanistic studies were performed in two each of p53 wild-type (HCT116, LoVo) and p53-mutated (SW480, HT29) colon cancer cells to explore whether LKB1 loss could be deregulated by NKX2-1-mediated p53 pathway. LKB1 and NK2 homeobox 1 (NKX2-1) expressions in colorectal tumors were determined by immunohistochemistry, and the prognostic value of both molecules was assessed by Kaplan-Meier test and Cox regression model.

RESULTS

Mechanistically, LKB1 loss at the transcriptional level due to alteration of the NKX2-1-mediated p53 pathway promotes invasiveness in colon cancer cells. The cell invasiveness induced by LKB1 loss was nearly suppressed by mammalian target of rapamycin (mTOR) inhibitor (rapamycin and everolimus) and mTOR/AKT dual inhibitor Palomid 529 (P529). Among patients, low LKB1 tumors exhibited shorter overall survival (OS) and relapse-free survival periods than high LKB1 tumors. The highest hazard ratio value for OS and relapse-free survival was observed in wild-type p53 with low LKB1/low NKX2-1 tumors and in mutated p53 with low LKB1/high NKX2-1 tumors when wild-type p53 with high LKB1/high NKX2-1 and mutated p53 with high LKB1/low NKX2-1 tumors were used as references.

CONCLUSIONS

LKB1 loss at the transcriptional level via alteration of the NKX2-1/p53 axis promotes cell invasion, consequently resulting in poor outcome in colorectal cancer patients.

Expression and transcriptional profiling of the LKB1 tumor suppressor in cervical cancer cells

OBJECTIVES

To characterize the biological activities of LKB1, examine LKB1 protein expression and identify LKB1-regulated genes that may serve as therapeutic targets in cervical cancer.

METHODS

Proliferation of cervical cancer HeLa cells expressing LKB1 was examined. LKB1 expression in normal cervical tissues and cervical cancers was assessed by immunohistochemistry. Gene expression profiles of cervical cancer HeLa cells stably expressing LKB1 were analyzed by microarray. Differentially expressed genes were analyzed using Gene Ontology (GO) terms and the Kyoto Encyclopedia of Genes and Genomes (KEGG) PATHWAY database. Quantitative RT-PCR was used to validate the microarray data. The expression of lipid phosphatase inositol polyphosphate 4-phosphatase type II (INPP4B) was confirmed by western blotting.

RESULTS

Expression of LKB1 inhibited HeLa cell proliferation, activated AMPK and was lost in more than 50% of cervical carcinomas. More than 200 genes were differentially expressed between HeLa cells with and without LKB1. Bioinformatics analysis with GO annotation indicated that LKB1 plays a role in receiving diverse stimuli and converting them into molecular signals. KEGG PATHWAY analysis showed that 8 pathways were significantly regulated. These include arginine and proline metabolism and inositol phosphate metabolism. The differential expression of 7 randomly selected genes was confirmed by quantitative RT-PCR. Furthermore, the steady-state level of INPP4B protein was up-regulated in LKB1-overexpressing cells.

CONCLUSIONS

This study establishes LKB1 as an important tumor suppressor in cervical cancer and sheds light on a novel signaling pathway regulated by LKB1.

Frequent hypermethylation of WNT pathway genes in laryngeal squamous cell carcinomas

BACKGROUND

Aberrations in the function of the WNT signaling pathway have been recently implicated in the pathogenesis of head and neck cancer, and the hypermethylation of several WNT cascade inhibitors were shown to be useful in disease prognosis. However, the extent of deregulation of WNT pathway by DNA hypermethylation has not been studied in detail in laryngeal cancer so far. The aim of this study was to establish the frequency of methylation of WNT pathway negative regulators in laryngeal squamous cell carcinomas and evaluate its prognostic significance.

METHODS

Twenty-six laryngeal squamous cell carcinoma cell lines and samples obtained from twenty-eight primary laryngeal carcinoma patients were analyzed. The methylation status of DKK1, LKB1, PPP2R2B, RUNX3, SFRP1, SFRP2, and WIF-1 was assessed using the methylation-specific polymerase chain reaction.

RESULTS

Frequent hypermethylation of DKK1, PPP2R2B, SFRP1, SFRP2, and WIF-1 was detected, and a high methylation index was usually observed. Half of the cell lines analyzed and seventy percent of primary laryngeal carcinoma cases were characterized by the methylation of at least four genes. The hypermethylation of PPP2R2B or WIF-1 was associated with longer survival in laryngeal carcinoma cell lines. Moreover, the concurrent methylation of PPP2R2B and SFRP1 differentiated primary from recurrent laryngeal carcinoma cell lines.

CONCLUSIONS

Frequent hypermethylation of WNT pathway negative regulators is observed in laryngeal squamous cell carcinomas. The possible prognostic significance of the methylation of DKK1, PPP2R2B, and SFRP1 needs to be evaluated in further prospective studies.

Decreased expression of LKB1 correlates with poor prognosis in hepatocellular carcinoma patients undergoing hepatectomy

AIM

To study any correlation of LKB1 expression with prognosis in hepatocellular carcinoma (HCC) cases.

METHODS

A total of 70 HCC patients and 20 primary intrahepatic stone patients in the first affiliated hospital of Wenzhou Medical College were enrolled in this study. LKB1 expression was detected by immunohistochemistry. Patients were followed-up and prognostic factors were evaluated.

RESULT

LKB1 expression was decreased in the HCC samples. Loss of LKB1 expression in HCC was significantly related to histologic grade (P=0.010), vascular invasion (P=0.025) and TMN stage (P=0.011). Patients showing negative LKB1 expression had a significantly shorter disease-free and overall survival than those with positive expression (P = 0.001, P=0.000, respectively). Multivariate Cox regression analysis indicated that LKB1 expression level was an independent factor of survival (P = 0.033).

CONCLUSION

HCC patients with decreased expression LKB1 have a poor prognosis. The loss of LKB1 expression is correlated with a lower survival rate.

Breaking the epithelial polarity barrier in cancer: the strange case of LKB1/PAR-4

The PAR clan of polarity regulating genes was initially discovered in a genetic screen searching for genes involved in asymmetric cell divisions in the Caenorhabditis elegans embryo. Today, investigations in worms, flies and mammals have established PAR proteins as conserved and fundamental regulators of animal cell polarization in a broad range of biological phenomena requiring cellular asymmetries. The human homologue of invertebrate PAR-4, a serine-threonine kinase LKB1/STK11, has caught attention as a gene behind Peutz-Jeghers polyposis syndrome and as a bona fide tumour suppressor gene commonly mutated in sporadic cancer. LKB1 functions as a master regulator of AMP-activated protein kinase (AMPK) and 12 other kinases referred to as the AMPK-related kinases, including four human homologues of PAR-1. The role of LKB1 as part of the energy sensing LKB1-AMPK module has been intensively studied, whereas the polarity function of LKB1, in the context of homoeostasis or cancer, has gained less attention. Here, we focus on the PAR-4 identity of LKB1, discussing the weight of evidence indicating a role for LKB1 in regulation of cell polarity and epithelial integrity across species and highlight recent investigations providing new insight into the old question: does the PAR-4 identity of LKB1 matter in cancer?