The tumor suppressor kinase LKB1: lessons from mouse models

Liver kinase B1 (LKB1) regulates the epigenetic landscape of mouse pancreatic beta cells

Liver kinase B1 (LKB1/STK11) is an important regulator of pancreatic β-cell identity and function. Elimination of Lkb1 from the β-cell results in improved glucose-stimulated insulin secretion and is accompanied by profound changes in gene expression, including the upregulation of several neuronal genes. The mechanisms through which LKB1 controls gene expression are, at present, poorly understood. Here, we explore the impact of β cell-selective deletion of Lkb1 on chromatin accessibility in mouse pancreatic islets. To characterize the role of LKB1 in the regulation of gene expression at the transcriptional level, we combine these data with a map of islet active transcription start sites and histone marks. We demonstrate that LKB1 elimination from β-cells results in widespread changes in chromatin accessibility, correlating with changes in transcript levels. Changes occurred in hundreds of promoter and enhancer regions, many of which were close to neuronal genes. We reveal that dysregulated enhancers are enriched in binding motifs for transcription factors (TFs) important for β-cell identity, such as FOXA, MAFA or RFX6, and we identify microRNAs (miRNAs) that are regulated by LKB1 at the transcriptional level. Overall, our study provides important new insights into the epigenetic mechanisms by which LKB1 regulates β-cell identity and function.

Liver kinase B1 (LKB1) regulates the epigenetic landscape of mouse pancreatic beta cells

Liver kinase B1 (LKB1/STK11) is an important regulator of pancreatic β-cell identity and function. Elimination of Lkb1 from the β-cell results in improved glucose-stimulated insulin secretion and is accompanied by profound changes in gene expression, including the upregulation of several neuronal genes. The mechanisms through which LKB1 controls gene expression are, at present, poorly understood. Here, we explore the impact of β cell- selective deletion of Lkb1 on chromatin accessibility in mouse pancreatic islets. To characterize the role of LKB1 in the regulation of gene expression at the transcriptional level, we combine these data with a map of islet active transcription start sites and histone marks. We demonstrate that LKB1 elimination from β-cells results in widespread changes in chromatin accessibility, correlating with changes in transcript levels. Changes occurred in hundreds of promoter and enhancer regions, many of which were close to neuronal genes. We reveal that dysregulated enhancers are enriched in binding motifs for transcription factors important for β-cell identity, such as FOXA, MAFA or RFX6 and we identify microRNAs (miRNAs) that are regulated by LKB1 at the transcriptional level. Overall, our study provides important new insights into the epigenetic mechanisms by which LKB1 regulates β-cell identity and function.

Skp2: A critical molecule for ubiquitination and its role in cancer

The ubiquitin-proteasome system (UPS) is a multi-step process that serves as the primary pathway for protein degradation within cells. UPS activity also plays a crucial role in regulating various life processes, including the cell cycle, signal transduction, DNA repair, and others. The F-box protein Skp2, a crucial member of the UPS, plays a central role in the development of various diseases. Skp2 controls cancer cell growth and drug resistance by ubiquitinating modifications to a variety of proteins. This review emphasizes the multifaceted role of Skp2 in a wide range of cancers and the mechanisms involved, highlighting the potential of Skp2 as a therapeutic target in cancer. Additionally, we describe the impactful influence exerted by Skp2 in various other diseases beyond cancer.

Chrysin-phospholipid complex-based solid dispersion for improved anti-aging and neuroprotective effects in mice

The present study aimed to improve the neuroprotective effect of chrysin (CHR) by combining two formulation techniques, phospholipid (PL) complexation and solid dispersion (SD). CHR-phospholipid complex (CHR-PLC) was prepared through solvent evaporation. The molar ratio CHR/PL (1:3), which exhibited the highest complexation efficiency, was selected for the preparation of CHR-PLC loaded SD (CHR-PLC-SD) with 2-hydroxypropyl β cyclodextrin (2-HPβCD) and polyvinylpyrrolidone 8000. CHR-PLC/2-HPβCD (1:2, w/w) displayed the highest aqueous solubility of CHR (5.86 times more than that of plain CHR). CHR-SD was also prepared using 2-HPβCD for comparison. The in vitro dissolution of CHR-PLC-SD4 revealed an enhancement in the dissolution rate over CHR-PLC (1:3), CHR-SD, and plain CHR by six times. The optimum formulations and plain CHR were evaluated for their neuroprotective effect on brain aging induced by D-galactose in mice. The results demonstrated a behavioral activity elevation, an increase of AMPK, LKB1, and PGC1α brain contents as well as a reduction of AGEs, GFAP, NT-3, TNF-α, and NF-κβ brain contents when compared with those of the D-galactose control group. Thus, the developed formulations stimulated neurogenesis and mitochondrial biogenesis as well as suppressed neuroinflammation and neurodegeneration. The order of activity was as follows: CHR-PLC-SD4 > CHR-PLC (1:3) > CHR-SD > plain CHR.

Genetic variants in LKB1/AMPK/mTOR pathway are associated with clinical outcomes of chemotherapy in non-small cell lung cancer

This study was conducted to investigate the relationship between genetic variants in LKB1/AMPK/mTOR pathway and treatment outcomes of patients with non-small cell lung cancer (NSCLC) treated with chemotherapy. A total of 379 patients with NSCLC who underwent first-line paclitaxel-cisplatin chemotherapy was enrolled. The associations between 19 single nucleotide variants (SNVs) in the LKB1/AMPK/mTOR pathway and the chemotherapy response and overall survival (OS) were analyzed. Among the SNVs analyzed, AKT1 rs2494750G>C and TSC1 rs2809244C>A were associated with clinical outcomes after chemotherapy in multivariate analyses. The AKT1 rs2494750G>C was significantly associated with a better response to chemotherapy (adjusted odds ratio [aOR]: 1.92, 95% confidence interval [CI]: 1.02-3.62, p = 0.04). The TSC1 rs2809244C>A were significantly associated with better OS (adjusted hazard ratio [aHR]: 0.79, 95% CI: 0.62-0.99, p = 0.04). When stratified by tumor histology, AKT1 rs2494750G>C exhibited a significant association with the chemotherapy response only in adenocarcinoma and TSC1 rs2809244C>A was also significantly associated with OS only in adenocarcinoma. This result suggests that the AKT1 rs2494750G>C and TSC1 rs2809244 C>A may be useful for predicting the clinical outcome of first-line paclitaxel-cisplatin chemotherapy in NSCLC.

The renal inflammatory network of nephronophthisis

Renal ciliopathies are the leading cause of inherited kidney failure. In autosomal dominant polycystic kidney disease (ADPKD), mutations in the ciliary gene PKD1 lead to the induction of CCL2, which promotes macrophage infiltration in the kidney. Whether or not mutations in genes involved in other renal ciliopathies also lead to immune cells recruitment is controversial. Through the parallel analysis of patients derived material and murine models, we investigated the inflammatory components of nephronophthisis (NPH), a rare renal ciliopathy affecting children and adults. Our results show that NPH mutations lead to kidney infiltration by neutrophils, macrophages and T cells. Contrary to ADPKD, this immune cell recruitment does not rely on the induction of CCL2 in mutated cells, which is dispensable for disease progression. Through an unbiased approach, we identified a set of inflammatory cytokines that are upregulated precociously and independently of CCL2 in murine models of NPH. The majority of these transcripts is also upregulated in NPH patient renal cells at a level exceeding those found in common non-immune chronic kidney diseases. This study reveals that inflammation is a central aspect in NPH and delineates a specific set of inflammatory mediators that likely regulates immune cell recruitment in response to NPH genes mutations.

The effects of UCP2 on autophagy through the AMPK signaling pathway in septic cardiomyopathy and the underlying mechanism

Background

Mitochondrial dysfunction plays an important role in the development of septic cardiomyopathy. This study aimed to reveal the protective role of uncoupling protein 2 (UCP2) in mitochondria through AMP-activated protein kinase (AMPK) on autophagy during septic cardiomyopathy.

Methods

UCP2 knockout mice via a cecal ligation and puncture (CLP) model and the H9C2 cardiomyocyte cell line in response to lipopolysaccharide (LPS) in vitro were used to study the effect. The myocardial morphological alterations, indicators of mitochondrial injury and levels of autophagy-associated proteins (pAMPK, pmTOR, pULK1, pTSC2, Beclin-1, and LC3-I/II) were assessed. In addition, the mechanism of the interaction between UCP2 and AMPK was further studied through gain- and loss-of-function studies.

Results

Compared with the wild-type mice, the UCP2 knockout mice exhibited more severe cardiomyocyte injury after CLP, and the AMPK agonist AICAR protected against such injury. Consistent with this result, silencing UCP2 augmented the LPS-induced pathological damage and mitochondrial injury in the H9C2 cells, limited the upregulation of autophagy proteins and reduced AMPK phosphorylation. AICAR protected the cells from morphological changes and mitochondrial membrane potential loss and promoted autophagy. The silencing and overexpression of UCP2 led to correlated changes in the AMPK upstream kinases pLKB1 and CAMKK2.

Conclusions

UCP2 exerts cardioprotective effects on mitochondrial dysfunction during sepsis via the action of AMPK on autophagy.

Autophagy compensates for Lkb1 loss to maintain adult mice homeostasis and survival

Liver kinase B1 (LKB1), also known as serine/threonine kinase 11 (STK11) is the major energy sensor for cells to respond to metabolic stress. Autophagy degrades and recycles proteins, macromolecules, and organelles for cells to survive starvation. To assess the role and cross-talk between autophagy and Lkb1 in normal tissue homeostasis, we generated genetically engineered mouse models where we can conditionally delete Stk11 and autophagy essential gene, Atg7, respectively or simultaneously, throughout the adult mice. We found that Lkb1 was essential for the survival of adult mice, and autophagy activation could temporarily compensate for the acute loss of Lkb1 and extend mouse life span. We further found that acute deletion of Lkb1 in adult mice led to impaired intestinal barrier function, hypoglycemia, and abnormal serum metabolism, which was partly rescued by the Lkb1 loss-induced autophagy upregulation via inhibiting p53 induction. Taken together, we demonstrated that autophagy and Lkb1 work synergistically to maintain adult mouse homeostasis and survival.

Tobacco chemical-induced mouse lung adenocarcinoma cell lines pin the prolactin orthologue proliferin as a lung tumour promoter

Lung adenocarcinoma (LADC) is the leading cause of cancer death worldwide. Nevertheless, syngeneic mouse models of the disease are sparse, and cell lines suitable for transplantable and immunocompetent mouse models of LADC remain unmet needs. We established multiple mouse LADC cell lines by repeatedly exposing two mouse strains (FVB, Balb/c) to the tobacco carcinogens urethane or diethylnitrosamine and by culturing out the resulting lung tumours for prolonged periods of time. Characterization of the resulting cell lines (n = 7) showed that they were immortal and phenotypically stable in vitro, and oncogenic, metastatic and lethal in vivo. The primary tumours that gave rise to the cell lines, as well as secondary tumours generated by transplantation of the cell lines, displayed typical LADC features, such as glandular architecture and mucin and thyroid transcription factor 1 expression. Moreover, these cells exhibited marked molecular similarity with human smokers' LADC, including carcinogen-specific Kras point mutations (KrasQ61R in urethane- and KrasQ61H in diethylnitrosamine-triggered cell lines) and Trp53 deletions and displayed stemness features. Interestingly, all cell lines overexpressed proliferin, a murine prolactin orthologue, which functioned as a lung tumour promoter. Furthermore, prolactin was overexpressed and portended poor prognosis in human LADC. In conclusion, we report the first LADC cell lines derived from mice exposed to tobacco carcinogens. These cells closely resemble human LADC and provide a valuable tool for the functional investigation of the pathobiology of the disease.

LKB1 as a Gatekeeper of Hepatocyte Proliferation and Genomic Integrity during Liver Regeneration

Liver kinase B1 (LKB1) is involved in several biological processes and is a key regulator of hepatic metabolism and polarity. Here, we demonstrate that the master kinase LKB1 plays a dual role in liver regeneration, independently of its major target, AMP-activated protein kinase (AMPK). We found that the loss of hepatic Lkb1 expression promoted hepatocyte proliferation acceleration independently of metabolic/energetic balance. LKB1 regulates G₀/G₁ progression, specifically by controlling epidermal growth factor receptor (EGFR) signaling. Furthermore, later in regeneration, LKB1 controls mitotic fidelity. The deletion of Lkb1 results in major alterations to mitotic spindle formation along the polarity axis. Thus, LKB1 deficiency alters ploidy profile at late stages of regeneration. Our findings highlight the dual role of LKB1 in liver regeneration, as a guardian of hepatocyte proliferation and genomic integrity.

An expression quantitative trait locus variant for LKB1 gene predicts the clinical outcomes of chemotherapy in patients with non-small cell lung cancer

BACKGROUND

We conducted this study to identify regulatory variants in cancer-related pathway genes which can predict clinical outcomes of chemotherapy in advanced NSCLC, using a comprehensive list of regulatory SNPs prioritized by RegulomeDB.

METHODS

A total of 509 potentially functional SNPs in cancer-related pathway genes were evaluated. The SNPs were analyzed in a discovery set (n = 198), and an independent validation set (n = 181). The associations of the SNPs with chemotherapy response and overall survival (OS) were analyzed.

RESULTS

In the discovery set, 95 SNPs were significantly associated with clinical outcomes. Among the 95 SNPs, only rs10414193A > G in the intronic region of ARID3A, an eQTL for LKB1, was consistently associated with chemotherapy response and OS in the validation set. In combined analysis, the rs10414193A > G was significantly associated with worse response to chemotherapy (adjusted odds ratio = 0.63, 95% CI = 0.47-0.85, P = 0.002), and with worse OS (adjusted hazard ratio = 1.25, 95% CI = 1.08-1.45, P = 0.004). Luciferase assay showed a significantly higher LKB1 promoter activity associated with rs10414193G allele compared with rs10414193A allele (P = 0.0009).

CONCLUSIONS

Our results suggest that rs10414193A > G may be useful for the prediction of clinical outcomes of chemotherapy in advanced NSCLC.

LKB1, Salt-Inducible Kinases, and MEF2C Are Linked Dependencies in Acute Myeloid Leukemia

The lineage-specific transcription factor (TF) MEF2C is often deregulated in leukemia. However, strategies to target this TF have yet to be identified. Here, we used a domain-focused CRISPR screen to reveal an essential role for LKB1 and its Salt-Inducible Kinase effectors (SIK3, in a partially redundant manner with SIK2) to maintain MEF2C function in acute myeloid leukemia (AML). A key phosphorylation substrate of SIK3 in this context is HDAC4, a repressive cofactor of MEF2C. Consequently, targeting of LKB1 or SIK3 diminishes histone acetylation at MEF2C-bound enhancers and deprives leukemia cells of the output of this essential TF. We also found that MEF2C-dependent leukemias are sensitive to on-target chemical inhibition of SIK activity. This study reveals a chemical strategy to block MEF2C function in AML, highlighting how an oncogenic TF can be disabled by targeting of upstream kinases.

Intestinal Epithelial Cell-Derived LKB1 Suppresses Colitogenic Microbiota

Dysregulation of the immune barrier function of the intestinal epithelium can often result in dysbiosis. In this study we report a novel role of intestinal epithelial cell (IEC)-derived liver kinase B1 (LKB1) in suppressing colitogenic microbiota. IEC-specific deletion of LKB1 (LKB1^ΔIEC) resulted in an increased susceptibility to dextran sodium sulfate (DSS)-induced colitis and a definitive shift in the composition of the microbial population in the mouse intestine. Importantly, transfer of the microbiota from LKB1^ΔIEC mice was sufficient to confer increased susceptibility to DSS-induced colitis in wild-type recipient mice. Collectively, the data indicate that LKB1 deficiency in intestinal epithelial cells nurtures the outgrowth of colitogenic bacteria in the commensal community. In addition, LKB1 deficiency in the intestinal epithelium reduced the production of IL-18 and antimicrobial peptides in the colon. Administration of exogenous IL-18 restored the expression of antimicrobial peptides, corrected the outgrowth of several bacterial genera, and rescued the LKB1^ΔIEC mice from increased sensitivity to DSS challenge. Taken together, our study reveals an important function of LKB1 in IECs for suppressing colitogenic microbiota by IL-18 expression.

Stromal Lkb1 deficiency leads to gastrointestinal tumorigenesis involving the IL-11-JAK/STAT3 pathway

Germline mutations in the gene encoding tumor suppressor kinase LKB1 lead to gastrointestinal tumorigenesis in Peutz-Jeghers syndrome (PJS) patients and mouse models; however, the cell types and signaling pathways underlying tumor formation are unknown. Here, we demonstrated that mesenchymal progenitor- or stromal fibroblast-specific deletion of Lkb1 results in fully penetrant polyposis in mice. Lineage tracing and immunohistochemical analyses revealed clonal expansion of Lkb1-deficient myofibroblast-like cell foci in the tumor stroma. Loss of Lkb1 in stromal cells was associated with induction of an inflammatory program including IL-11 production and activation of the JAK/STAT3 pathway in tumor epithelia concomitant with proliferation. Importantly, treatment of LKB1-defcient mice with the JAK1/2 inhibitor ruxolitinib dramatically decreased polyposis. These data indicate that IL-11-mediated induction of JAK/STAT3 is critical in gastrointestinal tumorigenesis following Lkb1 mutations and suggest that targeting this pathway has therapeutic potential in Peutz-Jeghers syndrome.

AMPK: guardian of metabolism and mitochondrial homeostasis

Cells constantly adapt their metabolism to meet their energy needs and respond to nutrient availability. Eukaryotes have evolved a very sophisticated system to sense low cellular ATP levels via the serine/threonine kinase AMP-activated protein kinase (AMPK) complex. Under conditions of low energy, AMPK phosphorylates specific enzymes and growth control nodes to increase ATP generation and decrease ATP consumption. In the past decade, the discovery of numerous new AMPK substrates has led to a more complete understanding of the minimal number of steps required to reprogramme cellular metabolism from anabolism to catabolism. This energy switch controls cell growth and several other cellular processes, including lipid and glucose metabolism and autophagy. Recent studies have revealed that one ancestral function of AMPK is to promote mitochondrial health, and multiple newly discovered targets of AMPK are involved in various aspects of mitochondrial homeostasis, including mitophagy. This Review discusses how AMPK functions as a central mediator of the cellular response to energetic stress and mitochondrial insults and coordinates multiple features of autophagy and mitochondrial biology.

LKB1 pro-oncogenic activity triggers cell survival in circulating tumor cells

During intravasation, circulating tumor cells (CTCs) detach from the epithelium of origin and begin the epithelial‐to‐mesenchymal transition (EMT) process, where they lose epithelial features and pass through the endothelium to enter circulation. Although detachment from the extracellular matrix is a strong source of metabolic stress, which induces anoikis, CTCs can survive. Recently, the tumor suppressor liver kinase B1 (LKB1) has gained attention for its role as a proto‐oncogene in restoring the correct ATP/AMP ratio during metabolic stress. The aim of this study was to assess LKB1 expression in epithelial‐negative CTCs isolated from patients with metastatic breast cancer and to characterize its possible association with EMT and stemness features. Transcriptome analysis of EpCAM‐negative CTCs indicated that over 25% of patients showed enhanced LKB1 levels, while almost 20% of patients showed enhanced levels of an EMT transcription factor known as ZEB1. Transcriptome and immunofluorescence analyses showed that patients with enhanced LKB1 were correspondingly ZEB1 negative, suggesting complementary activity for the two proteins. Only ZEB1 was significantly associated with cancer stem cell (CSC) markers. Neither LKB1 nor ZEB1 upregulation showed a correlation with clinical outcome, while enhanced levels of stemness‐associated CD44 correlated with a lower progression‐free and overall survival. Ex vivo models showed that MDA‐MB‐231, a mesenchymal tumor cell line, grew in suspension only if LKB1 was upregulated, but the MCF‐7 epithelial cell line lost its ability to generate spheroids and colonies when LKB1 was inhibited, supporting the idea that LKB1 might be necessary for CTCs to overcome the absence of the extracellular matrix during the early phases of intravasation. If these preliminary results are confirmed, LKB1 will become a novel therapeutic target for eradicating metastasis‐initiating CTCs from patients with primary breast cancer.

Prediction of phosphorylation sites based on Krawtchouk image moments

Protein phosphorylation is one of the most pervasive post-translational modifications and regulates diverse cellular processes in organisms. Under the catalysis of protein kinases, protein phosphorylation usually occurred in the residues serine (S), threonine (T), or tyrosine (Y). In this contribution, we proposed a novel scheme (named KMPhos) for the theoretical prediction of protein phosphorylation sites. First, the numerical matrix was obtained from a protein sequence fragment by replacing the characters of the residues with the chemical descriptors of amino acid molecules to approximately describe the chemical environment of the protein fragment, which was turned to the grayscale image. Then the Krawtchouk image moments were calculated and used to establish the support vector machine models. The accuracies of 10-fold cross validation for the obtained models on the training set are up to 89.7%, 88.6%, and 90.1% for the residues S, Y, and T, respectively. For the independent test set, the prediction accuracies are up to 90.7% (S), 87.8% (T), and 89.3% (Y). The results of ROC and other evaluations are also satisfactory. Compared with several specialized prediction tools, KMPhos provided the higher accuracy and reliability. An available KMPhos package is provided and can be used directly for phosphorylation sites prediction.

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.

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.

Specific deletion of LKB1/Stk11 in the Müllerian duct mesenchyme drives hyperplasia of the periurethral stroma and tumorigenesis in male mice

Nearly all older men will experience lower urinary tract symptoms associated with benign prostatic hyperplasia (BPH), the etiology of which is not well understood. We have generated Stk11^CKO mice by conditional deletion of the liver kinase B1 (LKB1) tumor suppressor gene, Stk11 (serine threonine kinase 11), in the fetal Müllerian duct mesenchyme (MDM), the caudal remnant of which is thought to be assimilated by the urogenital sinus primordial mesenchyme in males during fetal development. We show that MDM cells contribute to the postnatal stromal cells at the dorsal aspect of the prostatic urethra by lineage tracing. The Stk11^CKO mice develop prostatic hyperplasia with bladder outlet obstruction, most likely because of stromal expansion. The stromal areas from prostates of Stk11^CKO mice, with or without significant expansion, were estrogen receptor positive, which is consistent with both MD mesenchyme-derived cells and the purported importance of estrogen receptors in BPH development and/or progression. In some cases, stromal hyperplasia was admixed with epithelial metaplasia, sometimes with keratin pearls, consistent with squamous cell carcinomas. Mice with conditional deletion of both Stk11 and Pten developed similar features as the Stk11^CKO mice, but at a highly accelerated rate, often within the first few months after birth. Western blot analyses showed that the loss of LKB1 and phosphatase and tensin homolog deleted on chromosome 10 (PTEN) induces activation of the phospho-5' adenosine monophosphate-activated protein kinase and phospho-AKT serine/threonine kinase 1 signaling pathways, as well as increased total and active β-catenin. These results suggest that activation of these signaling pathways can induce hyperplasia of the MD stroma, which could play a significant role in the etiology of human BPH.

Peutz-Jeghers Syndrome: Pathobiology, Pathologic Manifestations, and Suggestions for Recommending Genetic Testing in Pathology Reports

Peutz-Jeghers syndrome (PJS), in most cases, is attributed to mutation in STK11/LKB1 and is clinically characterized by gastrointestinal hamartomatous polyposis, mucocutaneous pigmentation, and predisposition to certain neoplasms. There are currently no recommended gynecologic screening or clinical surveillance guidelines beyond those recommended for the general population; however, cervical cytology samples must be examined with a high level of suspicion for cervical adenocarcinoma. It is considered prudent to note the established association with PJS and recommend referral for genetic counseling. Complete surgical excision after a diagnosis of atypical lobular endocervical glandular hyperplasia is recommended.

LKB1 deletion causes early changes in atrial channel expression and electrophysiology prior to atrial fibrillation

AIMS

Liver kinase B1 (LKB1) is a protein kinase that activates the metabolic regulator AMP-activated protein kinase (AMPK) and other related kinases. Deletion of LKB1 in mice leads to cardiomyopathy and atrial fibrillation (AF). However, the specific role of the LKB1 pathway in early atrial biology remains unknown. Thus, we investigated whether LKB1 deletion altered atrial channel expression and electrophysiological function in a cardiomyocyte-specific knockout mouse model.

METHODS AND RESULTS

We performed a systematic comparison of αMHC-Cre LKB1(fl/fl) and littermate LKB1(fl/fl) male mice. This included analysis of gene expression, histology, and echocardiography, as well as cellular and tissue-level electrophysiology using patch-clamp recordings in vitro, optical mapping ex vivo, and ECG recordings in vivo. At postnatal day 1, atrial depolarization was prolonged, and Nav1.5 and Cx40 expression were markedly down-regulated in MHC-Cre LKB1(fl/fl) mice. Inward sodium current density was significantly decreased in MHC-Cre LKB1(fl/fl) neonatal atrial myocytes. Subsequently, additional alterations in atrial channel expression, atrial fibrosis, and spontaneous onset of AF developed by 2 weeks of age. In adult mice, abnormalities of interatrial conduction and bi-atrial electrical coupling were observed, likely promoting the perpetuation of AF. Mice with AMPK-inactivated hearts demonstrated modest overlap in channel expression with MHC-Cre LKB1(fl/fl) hearts, but retained normal structure, electrophysiological function and contractility.

CONCLUSIONS

Deletion of LKB1 causes early defects in atrial channel expression, action potential generation and conduction, which precede widespread atrial remodelling, fibrosis and AF. LKB1 is critical for normal atrial growth and electrophysiological function.

Isoflurane suppresses the self-renewal of normal mouse neural stem cells in a p53-dependent manner by activating the Lkb1-p53-p21 signalling pathway

Isoflurane is widely used in anaesthesia for surgical operations. However, whether it elicits unwanted side effects, particularly in neuronal cells, remains to be fully elucidated. The Lkb1-p53-p21 signalling pathway is able to modulate neuronal self-renewal and proliferation. Furthermore, the suppression of Lkb1-dependent p21 induction leads to apoptosis. In the present study, whether Lkb1-p53-p21 signalling is involved in the response to isoflurane was investigated. A comparison of mouse primary, wild-type neural stem cells (WT NSCs) with the p53^−/− NSC cell line, NE-4C, revealed that isoflurane inhibited proliferation in a dose-, a time- and a p53-dependent manner. However, flow cytometric analysis revealed that the concentration of isoflurane which caused 50% inhibition (the IC₅₀ value) induced cell cycle arrest in WT NSCs. Furthermore, the protein expression levels of LKB1, p53 and p21 were increased, although those of nestin and survivin decreased, following treatment of WT NSCs with isoflurane. On the other hand, isoflurane induced the phosphorylation of Ser15 in p53 in WT NSCs, which was associated with p53 binding to the p21 promoter, and consequentially, the transcriptional activation of p21. All these events were abrogated in NE-4C cells. Taken together, the present study has demonstrated that isoflurane suppresses the self-renewal of normal mouse NSCs by activating the Lkb1-p53-p21 signalling pathway.

LKB1 loss promotes endometrial cancer progression via CCL2-dependent macrophage recruitment

Endometrial cancer is the most common gynecologic malignancy and the fourth most common malignancy in women. For most patients in whom the disease is confined to the uterus, treatment results in successful remission; however, there are no curative treatments for tumors that have progressed beyond the uterus. The serine/threonine kinase LKB1 has been identified as a potent suppressor of uterine cancer, but the biological modes of action of LKB1 in this context remain incompletely understood. Here, we have shown that LKB1 suppresses tumor progression by altering gene expression in the tumor microenvironment. We determined that LKB1 inactivation results in abnormal, cell-autonomous production of the inflammatory cytokine chemokine (C-C motif) ligand 2 (CCL2) within tumors, which leads to increased recruitment of macrophages with prominent tumor-promoting activities. Inactivation of Ccl2 in an Lkb1-driven mouse model of endometrial cancer slowed tumor progression and increased survival. In human primary endometrial cancers, loss of LKB1 protein was strongly associated with increased CCL2 expression by tumor cells as well as increased macrophage density in the tumor microenvironment. These data demonstrate that CCL2 is a potent effector of LKB1 loss in endometrial cancer, creating potential avenues for therapeutic opportunities.

[Molecular pathology of lung cancer. State of the art 2014]

Lung cancer is the most frequent cause of cancer-related death in Germany in men and women alike. While in the last decades a classification of epithelial lung tumors into non-small cell and small cell lung cancer was clearly sufficient from the therapeutic viewpoint, the dawn of the era of personalized medicine together with tremendous developments in the field of high throughput technologies have led to a molecular individualization of these tumors and, even more important, to a molecularly defined individualization of tumor therapy. This development resulted in the definition of a wide array of molecularly divergent tumor families. In this article we will give an overview on relevant molecular alterations in non-small cell lung cancers, comprising adenocarcinomas, squamous cell carcinomas and large cell carcinomas and also small cell carcinomas and carcinoids. Besides some similarities data gathered in the last few years specifically highlighted the immense diversity of molecular alterations that might underlie tumorigenesis of lung neoplasms. The knowledge on how to detect these alterations is of utmost importance in pathology, as treatment decisions are increasingly based on their presence or absence, putting molecular pathology in the central focus of the novel era of personalized medicine in oncology.

Targeting LKB1 in cancer - exposing and exploiting vulnerabilities

The LKB1 tumour suppressor is a serine/threonine kinase that functions as master regulator of cell growth, metabolism, survival and polarity. LKB1 is frequently mutated in human cancers and research spanning the last two decades have begun decoding the cellular pathways deregulated following LKB1 inactivation. This work has led to the identification of vulnerabilities present in LKB1-deficient tumour cells. Pre-clinical studies have now identified therapeutic strategies targeting this subset of tumours that promise to benefit this large patient population harbouring LKB1 mutations. Here, we review the current efforts that are underway to translate pre-clinical discovery of therapeutic strategies targeting LKB1 mutant cancers into clinical practice.

Fyn-phosphorylated PIKE-A binds and inhibits AMPK signaling, blocking its tumor suppressive activity

The AMP-activated protein kinase, a key regulator of energy homeostasis, has a critical role in metabolic disorders and cancers. AMPK is mainly regulated by cellular AMP and phosphorylation by upstream kinases. Here, we show that PIKE-A binds to AMPK and blocks its tumor suppressive actions, which are mediated by tyrosine kinase Fyn. PIKE-A directly interacts with AMPK catalytic alpha subunit and impairs T172 phosphorylation, leading to repression of its kinase activity on the downstream targets. Mutation of Fyn phosphorylation sites on PIKE-A, depletion of Fyn, or pharmacological inhibition of Fyn blunts the association between PIKE-A and AMPK, resulting in loss of its inhibitory effect on AMPK. Cell proliferation and oncogenic assays demonstrate that PIKE-A antagonizes tumor suppressive actions of AMPK. In human glioblastoma samples, PIKE-A expression inversely correlates with the p-AMPK levels, supporting that PIKE-A negatively regulates AMPK activity in cancers. Thus, our findings provide additional layer of molecular regulation of the AMPK signaling pathway in cancer progression.

Tripterygium glycosides induce premature ovarian failure in rats by promoting p53 phosphorylation and activating the serine/threonine kinase 11-p53-p21 signaling pathway

Premature ovarian failure (POF) is a typical pathological disease of the reproductive system in aging females. Infection, inflammation, immune abnormalities, genetic mutation, radiotherapy and chemotherapy can cause POF. Tripterygium glycosides (TGs) are a component extracted from the Chinese herb Tripterygium wilfordii Hook. f., also known as Huangteng. Although TGs have been used to treat various diseases, drug resistance and toxicity can affect patients. The aim of the present study was to investigate the mechanism of TG-induced POF in rats. The rats were treated with different concentrations of TG, and pathology assays showed that the TG-induced POF was predominantly composed of interstitial cells in a fibrous matrix with a reduced number of follicles at each stage and an increased number of collapsed oocytes. Furthermore, reverse transcription-quantitative polymerase chain reaction (PCR) and immunohistochemistry assays indicated that the expression levels of serine/threonine kinase 11 (Stk11), p53 p21 and activated caspase-3 were elevated significantly in the TG-treated groups. Serine 15 phosphorylation of p53 was also enhanced significantly in the TG-treated groups. In addition, a chromatin immunoprecipitation-PCR assay revealed that the TGs induced p53 activation and enhanced the transcription of p21. In conclusion, TGs induce apoptosis and necrosis in rat ovarian tissues, as well as POF, via p53 phosphorylation and activation of the Stk11-p53-p21 signaling pathway.

Skp2-dependent ubiquitination and activation of LKB1 is essential for cancer cell survival under energy stress

LKB1 is activated by forming a heterotrimeric complex with STRAD and MO25. Recent studies suggest that LKB1 has pro-oncogenic functions, besides acting as a tumor suppressor. How the LKB1 activity is maintained and how LKB1 regulates cancer development are largely unclear. Here we show that K63-linked LKB1 polyubiquitination by Skp2-SCF ubiquitin ligase is critical for LKB1 activation by maintaining LKB1-STRAD-MO25 complex integrity. We further demonstrate that oncogenic Ras acts upstream of Skp2 to promote LKB1 polyubiquitination by activating Skp2-SCF ubiquitin ligase. Moreover, Skp2-mediated LKB1 polyubiquitination is required for energy-stress-induced cell survival. We also detected overexpression of Skp2 and LKB1 in late-stage hepatocellular carcinoma (HCC), and their overexpression predicts poor survival outcomes. Finally, we show that Skp2-mediated LKB1 polyubiquitination is important for HCC tumor growth in vivo. Our study provides new insights into the upstream regulation of LKB1 activation and suggests a potential target, the Ras/Skp2/LKB1 axis, for cancer therapy.

AMPK as a potential anticancer target - friend or foe?

Adenosine monophosphate-activated protein kinase (AMPK) is a key player in maintaining energy homeostasis in response to metabolic stress. Beyond diabetes and metabolic syndrome, there is a growing interest in the therapeutic exploitation of the AMPK pathway in cancer treatment in light of its unique ability to regulate cancer cell proliferation through the reprogramming of cell metabolism. Although many studies support the tumor-suppressive role of AMPK, emerging evidence suggests that the metabolic checkpoint function of AMPK might be overridden by stress or oncogenic signals so that tumor cells use AMPK activation as a survival strategy to gain growth advantage. These findings underscore the complexity in the cellular function of AMPK in maintaining energy homeostasis under physiological versus pathological conditions. Thus, this review aims to provide an overview of recent findings on the functional interplay of AMPK with different cell metabolic and signaling effectors, particularly histone deacetylases, in mediating downstream tumor suppressive or promoting mechanisms in different cell systems. Although AMPK activation inhibits tumor growth by targeting multiple signaling pathways relevant to tumorigenesis, under certain cellular contexts or certain stages of tumor development, AMPK might act as a protective response to metabolic stresses, such as nutrient deprivation, low oxygen, and low pH, or as downstream effectors of oncogenic proteins, including androgen receptor, hypoxia-inducible factor-1α, c-Src, and MYC. Thus, investigations to define at which stage(s) of tumorigenesis and cancer progression or for which genetic aberrations AMPK inhibition might represent a more relevant strategy than AMPK activation for cancer treatment are clearly warranted.

MicroRNA-17 promotes normal ovarian cancer cells to cancer stem cells development via suppression of the LKB1-p53-p21/WAF1 pathway

The mechanism underlying the development of human ovarian cancer is poorly understood. The liver kinase protein, LKB1, is hypothesized to play a pivotal role in tumor cell proliferation and invasion capacity through regulation of p53 and p21/WAF1 expression. Previous studies suggest LKB1 may, in turn, be regulated by microRNA-17. Here, we examined the role of miR-17 in the expression of LKB1 and the downstream effects on proliferation and invasion capacity of normal ovarian cancer cells (OCCs) and ovarian stem cells. In this study, both the mRNA and protein expression levels of LKB1, p53, and p21 decreased in OCCs following transfection with a miR-17 expression plasmid. MiR-17 expression affected cell cycle regulation and stimulated the proliferation and invasion capacity of OCCs in vitro. ChIP assays indicated that the binding efficiency of p53 to the p21/WAF1 gene promoter was much lower in miR-17 transfected OCCs than in OCCs transfected with a mutated miR-17. Co-immunoprecipitation and western blotting showed significantly lower levels of p53 and p53 Ser15-pho in the miR-17 transfected OCCs as compared to the mutant miR-17 transfected OCCs. Xenograft experiments confirmed that suppression of tumor growth in vivo occurred in the absence of functional miR-17. These findings suggest that mature miR-17 expression may have an important role in the pathogenesis of human ovarian tumors through its interference with the LKB1-p53-p21/WAF1 pathway expression by epigenetic modification. These findings are of potential importance in the identification of novel therapeutic targets in human ovarian cancer.

LKB1 and AMPK regulate synaptic remodeling in old age

Age-related decreases in neural function result in part from alterations in synapses. To identify molecular defects that lead to such changes, we focused on the outer retina, in which synapses are markedly altered in old rodents and humans. We found that the serine/threonine kinase LKB1 and one of its substrates, AMPK, regulate this process. In old mice, synaptic remodeling was accompanied by specific decreases in the levels of total LKB1 and active (phosphorylated) AMPK. In the absence of either kinase, young adult mice developed retinal defects similar to those that occurred in old wild-type animals. LKB1 and AMPK function in rod photoreceptors where their loss leads to aberrant axonal retraction, the extension of postsynaptic dendrites and the formation of ectopic synapses. Conversely, increasing AMPK activity genetically or pharmacologically attenuates and may reverse age-related synaptic alterations. Together, these results identify molecular determinants of age-related synaptic remodeling and suggest strategies for attenuating these changes.

An AMPK-independent signaling pathway downstream of the LKB1 tumor suppressor controls Snail1 and metastatic potential

The serine/threonine kinase LKB1 is a tumor suppressor whose loss is associated with increased metastatic potential. In an effort to define biochemical signatures of metastasis associated with LKB1 loss, we discovered that the epithelial-to-mesenchymal transition transcription factor Snail1 was uniquely upregulated upon LKB1 deficiency across cell types. The ability of LKB1 to suppress Snail1 levels was independent of AMPK but required the related kinases MARK1 and MARK4. In a screen for substrates of these kinases involved in Snail regulation, we identified the scaffolding protein DIXDC1. Similar to loss of LKB1, DIXDC1 depletion results in upregulation of Snail1 in a FAK-dependent manner, leading to increased cell invasion. MARK1 phosphorylation of DIXDC1 is required for its localization to focal adhesions and ability to suppress metastasis in mice. DIXDC1 is frequently downregulated in human cancers, which correlates with poor survival. This study defines an AMPK-independent phosphorylation cascade essential for LKB1-dependent control of metastatic behavior.

Antagonistic role of natural compounds in mTOR-mediated metabolic reprogramming

Cells reprogram their metabolism very early during carcinogenesis; this event is critical for the establishment of other cancer hallmarks. Many oncogenes and tumor suppressor genes control metabolism by interplaying with the existing nutrient-sensing intracellular pathways. Mammalian target of rapamycin, mTOR, is emerging as a collector and sorter of a metabolic network controlling upstream and downstream modulation of these same genes. Natural compounds represent a source of anti-cancer molecules with chemopreventive and therapeutic properties. This review describes selected pathways and genes orchestrating the metabolic reprogramming and discusses the potential of natural compounds to target oncogenic metabolic aberrations.

Connexin36 contributes to INS-1E cells survival through modulation of cytokine-induced oxidative stress, ER stress and AMPK activity

Cell-to-cell communication mediated by gap junctions made of Connexin36 (Cx36) contributes to pancreatic β-cell function. We have recently demonstrated that Cx36 also supports β-cell survival by a still unclear mechanism. Using specific Cx36 siRNAs or adenoviral vectors, we now show that Cx36 downregulation promotes apoptosis in INS-1E cells exposed to the pro-inflammatory cytokines (IL-1β, TNF-α and IFN-γ) involved at the onset of type 1 diabetes, whereas Cx36 overexpression protects against this effect. Cx36 overexpression also protects INS-1E cells against endoplasmic reticulum (ER) stress-mediated apoptosis, and alleviates the cytokine-induced production of reactive oxygen species, the depletion of the ER Ca(2+) stores, the CHOP overexpression and the degradation of the anti-apoptotic protein Bcl-2 and Mcl-1. We further show that cytokines activate the AMP-dependent protein kinase (AMPK) in a NO-dependent and ER-stress-dependent manner and that AMPK inhibits Cx36 expression. Altogether, the data suggest that Cx36 is involved in Ca(2+) homeostasis within the ER and that Cx36 expression is downregulated following ER stress and subsequent AMPK activation. As a result, cytokine-induced Cx36 downregulation elicits a positive feedback loop that amplifies ER stress and AMPK activation, leading to further Cx36 downregulation. The data reveal that Cx36 plays a central role in the oxidative stress and ER stress induced by cytokines and the subsequent regulation of AMPK activity, which in turn controls Cx36 expression and mitochondria-dependent apoptosis of insulin-producing cells.

Functional proteomics characterization of residual triple-negative breast cancer after standard neoadjuvant chemotherapy

BACKGROUND

In this study, we used functional proteomics to determine the molecular characteristics of residual triple receptor-negative breast cancer (TNBC) patients after neoadjuvant systemic chemotherapy (NCT) and their relationship with patient outcomes in order to identify potential targets for therapy.

PATIENTS AND METHODS

Protein was extracted from 54 residual TNBCs, and 76 proteins related to breast cancer signaling were measured by reverse phase protein arrays (RPPAs). Univariable and multivariable Cox proportional hazard models were fitted for each protein. Survival outcomes were estimated by the Kaplan-Meier product limit method. Training and cross validation were carried out. The coefficients estimated from the multivariable Cox model were used to calculate a risk score (RS) for each sample.

RESULTS

Multivariable analysis using the top 25 proteins from univariable analysis at a false discovery rate (FDR) of 0.3 showed that AKT, IGFBP2, LKB1, S6 and Stathmin were predictors of recurrence-free survival (RFS). The cross-validation model was reproducible. The RS model calculated based on the multivariable analysis was -1.1086 × AKT + 0.2501 × IGFBP2 - 0.6745 × LKB1+1.0692 × S6 + 1.4086 × stathmin with a corresponding area under the curve, AUC = 0.856. The RS was an independent predictor of RFS (HR = 3.28, 95%CI = 2.07-5.20, P < 0.001).

CONCLUSIONS

We found a five-protein model that independently predicted RFS risk in patients with residual TNBC disease. The PI3 K pathway may represent potential therapeutic targets in this resistant disease.

Genetic and epigenetic alterations of the LKB1 gene and their associations with mutations in TP53 and EGFR pathway genes in Korean non-small cell lung cancers

INTRODUCTION

Liver kinase 1 (LKB1) plays a critical barrier role in lung tumorigenesis by controlling initiation, differentiation and metastasis. We searched for genetic and epigenetic alterations of the LKB1 gene in Korean non-small cell lung cancers (NSCLCs) and correlated the results with clinicopathological features. We also investigated the relationship between genetic and epigenetic alterations of LKB1 and mutations in the TP53 gene and epidermal growth factor receptor (EGFR) pathway genes.

METHODS

A total of 159 NSCLCs were analyzed for loss of heterozygosity (LOH) at microsatellite loci D19S886, and D19S878. Mutations and methylation status of LKB1 were examined by direct sequencing and a methylation-specific polymerase chain reaction, respectively.

RESULTS

A somatic mutation was found in one of the 159 tumors. LOH and promoter methylation was detected in 19.5% (31/159) and 13.2% (21/159) of the tumors, respectively. Four of the 159 tumors had concomitant LOH and methylation of LKB1. In total, 30.2% of the 159 NSCLCs harbored LKB1 LOH or promoter methylation, which were correlated with down-regulation of gene expression. LKB1 LOH was more frequent in males, smokers, and tumors with a TP53 mutation than in females, never-smokers, and tumors without a TP53 mutation, respectively. However, no significant correlation between LKB1 alterations and mutations in EGFR pathway genes was found.

CONCLUSION

These results suggest that the prevalence of LKB1 genetic and epigenetic alterations in NSCLCs vary depending on patient ethnicity. Our results show that LKB1 alterations often occur simultaneously with mutations in EGFR pathway genes.

AMPK: a contextual oncogene or tumor suppressor?

The AMP-activated protein kinase (AMPK) functions to monitor and maintain energy homeostasis at the cellular and organism level. AMPK was perceived historically primarily as a component of the LKB1/STK11 tumor suppressor (LKB1 mutations cause the Peutz-Jegher cancer predisposition syndrome) cascade upstream of the TSC1/2/mTOR pathway and thus likely to be a tumor suppressor. However, AMPK has recently been shown to promote cancer cell survival in the face of extrinsic and intrinsic stressors including bioenergetic, growth factor, and oncogene stress compatible with studies showing that AMPK is required for oncogenic transformation. Thus, whether AMPK acts as a bona fide tumor suppressor or a contextual oncogene and, of particular importance, whether AMPK should be targeted for activation or inhibition during cancer therapy, is controversial and requires clarification. We aim to initiate discussions of these critical questions by reviewing the role of AMPK with an emphasis on cancer cell adaptation to microenvironment stress and therapeutic intervention.

Functional aspects of primary cilia in signaling, cell cycle and tumorigenesis

Dysfunctional cilia underlie a broad range of cellular and tissue phenotypes and can eventually result in the development of ciliopathies: pathologically diverse diseases that range from clinically mild to highly complex and severe multi-organ failure syndromes incompatible with neonatal life. Given that virtually all cells of the human body have the capacity to generate cilia, it is likely that clinical manifestations attributed to ciliary dysfunction will increase in the years to come. Disputed but nevertheless enigmatic is the notion that at least a subset of tumor phenotypes fit within the ciliopathy disease spectrum and that cilia loss may be required for tumor progression. Contending for the centrosome renders ciliation and cell division mutually exclusive; a regulated tipping of balance promotes either process. The mechanisms involved, however, are complex. If the hypothesis that tumorigenesis results from dysfunctional cilia is true, then why do the classic ciliopathies only show limited hyperplasia at best? Although disassembly of the cilium is a prerequisite for cell proliferation, it does not intrinsically drive tumorigenesis per se. Alternatively, we will explore the emerging evidence suggesting that some tumors depend on ciliary signaling. After reviewing the structure, genesis and signaling of cilia, the various ciliopathy syndromes and their genetics, we discuss the current debate of tumorigenesis as a ciliopathy spectrum defect, and describe recent advances in this fascinating field.

Expression of key members of classical Wnt signal pathway in Peutz-Jeghers syndrome

AIM: To detect the expression of E-cadherin (E-Cad), β-catenin (β-Cat), matrix metalloproteinase-7 (MMP-7), c-Myc and Cyclin D1 proteins in Peutz-Jeghers syndrome (PJS).

METHODS: Immunohistochemistry was used to detect the protein expression of E-Cad, β-Cat, MMP-7, C-Myc and Cyclin D1 in 40 cases of PJS, 20 cases of colorectal cancer and 20 cases of normal colorectal mucosa. The clinical data for the included patients were analyzed retrospectively.

RESULTS: The positive rates of E-Cad and β-Cat expression on the membrane, β-Cat expression in the nucleus, and MMP-7, c-Myc and Cyclin D1 expression differed significantly among the normal mucosa group, PJS group and colorectal cancer group. In the PJS group, the expression of E-Cad and β-Cat on the membrane increased with the increase in patient age or polyp size, and the expression of β-Cat in the nucleus and the expression of MMP-7, c-Myc and Cyclin D1 increased with the increase in polyp size. The expression of E-Cad and β-Cat on the membrane had a negative correlation with that of β-Cat in the nucleus and the expression of MMP-7, c-Myc and Cyclin D1 in PJS.

CONCLUSION: The aberrant activation of classical Wnt pathway and the epithelial- mesenchymal transition mediated by Wnt signalling may play an important role in the tumorigenesis and development of PJS. This may correlate with the crosstalk with the LKB1/mTOR pathway.

Inhibition of the mitochondrial Hsp90 chaperone network: a novel, efficient treatment strategy for cancer?

Research has shown that cancer cells exhibit multiple deregulated pathways, involving proliferation, migration and cell death. Heat-shock-proteins have evolved as "central regulators" and are implicated in the modulation of these pathways and in organelle-specific signaling. In this instance, heat-shock-proteins (Hsps) assist cancer cells in the maturation of proteins. Hsp90 is of particular interest because its enzymatic ATPase activity is elevated in malignant cells as compared to non-neoplastic counterparts. Consistent with its high-activity in cancer cells, Hsp90 stabilizes a considerable number of proteins being instrumental in carcinogenesis and the maintenance and growth of highly malignant cancers. Among its distribution Hsp90 is also localized within mitochondria of neoplastic cells of various origin, interacting with another chaperone, TRAP1 (Tumor necrosis factor type 1 receptor-associated protein or Heat-shock-protein 75) to antagonize the cell death promoting properties of the matrix protein, Cyclophilin-D. Several preclinical studies, including in vivo studies in both orthotopic and genetic animal models, have confirmed that targeting mitochondrial Hsp90 may be a novel efficient treatment method for highly recalcitrant tumors. This review summarizes the most recent findings of mitochondrial Hsp90 signaling and its potential implications for cancer therapy.

Somatic mutations of STK11 gene in human papillomavirus positive and negative penile cancer

BACKGROUND

Human papillomavirus (HPV) infection accounts for about 40-50% of all cases of penile carcinoma suggesting that other factors, including host genetic status, are involved in neoplastic transformation. In this perspective, STK11 gene, which has been found frequently mutated in HPV-related cervical carcinoma, has been analyzed in HPV-positive and HPV-negative invasive penile cancers to establish its mutational status and the possible correlation of HPV infection with specific genetic alterations.

METHODS

Genomic DNAs extracted from 26 cases of penile squamous cell carcinoma were analyzed for genetic alterations in the exons 1 to 9 of STK11 gene by quantitative real-time PCR. Ratios of potentially deleted and non-deleted exons were indicative of specific loss of STK11 coding regions. DNA samples of 5 cancer cases were subjected to standard PCR amplification of STK11 exons 1 to 9 and analyzed for somatic mutations by direct nucleotide sequencing analysis.

RESULTS

Heterozygous deletions of STK11 exon 1 and 2 were identified in 2 out of 14 HPV-positive (14.3%) and 1 out of 12 HPV-negative cases (8.3%). Complete nucleotide sequencing analysis of exons 1 to 9 showed a single nucleotide change upstream the exon 2 coding region in 1 out of 5 penile carcinoma samples.

CONCLUSIONS

The present results suggest that single nucleotide mutations and/or deletions of STK11 gene are rare events in penile cancer. Moreover, no significant association was observed between STK11 alterations and HPV infection in these tumors.

Lkb1 takes different paths to morphogenesis

Study uses chemical genetics and embryonic explants to reveal kinase’s tissue-specific functions.

Stromal liver kinase B1 [STK11] signaling loss induces oviductal adenomas and endometrial cancer by activating mammalian Target of Rapamycin Complex 1

Germline mutations of the Liver Kinase b1 (LKB1/STK11) tumor suppressor gene have been linked to Peutz-Jeghers Syndrome (PJS), an autosomal-dominant, cancer-prone disorder in which patients develop neoplasms in several organs, including the oviduct, ovary, and cervix. We have conditionally deleted Lkb1 in Müllerian duct mesenchyme-derived cells of the female reproductive tract and observed expansion of the stromal compartment and hyperplasia and/or neoplasia of adjacent epithelial cells throughout the reproductive tract with paratubal cysts and adenomyomas in oviducts and, eventually, endometrial cancer. Examination of the proliferation marker phospho-histone H3 and mammalian Target Of Rapamycin Complex 1 (mTORC1) pathway members revealed increased proliferation and mTORC1 activation in stromal cells of both the oviduct and uterus. Treatment with rapamycin, an inhibitor of mTORC1 activity, decreased tumor burden in adult Lkb1 mutant mice. Deletion of the genes for Tuberous Sclerosis 1 (Tsc1) or Tsc2, regulators of mTORC1 that are downstream of LKB1 signaling, in the oviductal and uterine stroma phenocopies some of the defects observed in Lkb1 mutant mice, confirming that dysregulated mTORC1 activation in the Lkb1-deleted stroma contributes to the phenotype. Loss of PTEN, an upstream regulator of mTORC1 signaling, along with Lkb1 deletion significantly increased tumor burden in uteri and induced tumorigenesis in the cervix and vagina. These studies show that LKB1/TSC1/TSC2/mTORC1 signaling in mesenchymal cells is important for the maintenance of epithelial integrity and suppression of carcinogenesis in adjacent epithelial cells. Because similar changes in the stromal population are also observed in human oviductal/ovarian adenoma and endometrial adenocarcinoma patients, we predict that dysregulated mTORC1 activity by upstream mechanisms similar to those described in these model systems contributes to the pathogenesis of these human diseases.

Peutz-Jeghers Syndrome patients have autosomal dominant mutations in the LKB1/STK11 gene and are prone to developing cancer, predominantly in the intestinal tract but also in other tissues, including the reproductive tracts and gonads. To elucidate the mechanisms disrupted by the loss of LKB1 in the reproductive tract, we have developed a mouse model with deletion of Lkb1 specifically in stromal cells of gynecologic tissues. These mice show stromal cell expansion and develop oviductal adenomas and endometrial cancer. Deletion of either Tsc1 or Tsc2 genes, which are mutated in patients with Tuberous Sclerosis Complex and whose protein products are indirect downstream targets of LKB1 signaling, resulted in some of the same defects observed in Lkb1 mutant mice. Activation of mammalian Target Of Rapamycin Complex 1 (mTORC1), a common effector of disrupted LKB1, TSC1, and TSC2 signaling, was observed in all mutant tissues examined, suggesting that uninhibited mTORC1 activity is necessary for the phenotypes. Suppression of mTORC1 signaling by rapamycin reduced tumor burden in Lkb1 mutant mice, confirming the link between dysregulation of mTORC1 to development of the Lkb1 mutant phenotype and suggesting that therapeutic targeting of LKB1/TSC1/TSC2/mTORC1 signaling would benefit human Peutz-Jeghers Syndrome and Tuberous Sclerosis patients with reproductive tract disease.

Prediction of functional phosphorylation sites by incorporating evolutionary information

Protein phosphorylation is a ubiquitous protein post-translational modification, which plays an important role in cellular signaling systems underlying various physiological and pathological processes. Current in silico methods mainly focused on the prediction of phosphorylation sites, but rare methods considered whether a phosphorylation site is functional or not. Since functional phosphorylation sites are more valuable for further experimental research and a proportion of phosphorylation sites have no direct functional effects, the prediction of functional phosphorylation sites is quite necessary for this research area. Previous studies have shown that functional phosphorylation sites are more conserved than non-functional phosphorylation sites in evolution. Thus, in our method, we developed a web server by integrating existing phosphorylation site prediction methods, as well as both absolute and relative evolutionary conservation scores to predict the most likely functional phosphorylation sites. Using our method, we predicted the most likely functional sites of the human, rat and mouse proteomes and built a database for the predicted sites. By the analysis of overall prediction results, we demonstrated that protein phosphorylation plays an important role in all the enriched KEGG pathways. By the analysis of protein-specific prediction results, we demonstrated the usefulness of our method for individual protein studies. Our method would help to characterize the most likely functional phosphorylation sites for further studies in this research area.