Lkb1 and Pten Synergise to Suppress mTOR-Mediated Tumorigenesis and Epithelial-Mesenchymal Transition in the Mouse Bladder

The AKT/PI3K/mTOR pathway is frequently altered in a range of human tumours, including bladder cancer. Here we report the phenotype of mice characterised by deletion of two key players in mTOR regulation, Pten and Lkb1, in a range of tissues including the mouse urothelium. Despite widespread recombination within the range of epithelial tissues, the primary phenotype we observe is the rapid onset of bladder tumorigenesis, with median onset of approximately 100 days. Single deletion of either Pten or Lkb1 had no effect on bladder cell proliferation or tumour formation. However, simultaneous deletion of Lkb1 and Pten led to an upregulation of the mTOR pathway and the hypoxia marker GLUT1, increased bladder epithelial cell proliferation and ultimately tumorigenesis. Bladder tissue also exhibited characteristic features of epithelial-mesenchymal transition, with loss of the epithelial markers E-cadherin and the tight junction protein ZO-1, and increases in the mesenchymal marker vimentin as well as nuclear localization of epithelial-mesenchymal transition (EMT) regulator Snail. We show that these effects were all dependent upon mTOR activity, as rapamycin treatment blocked both EMT and tumorigenesis. Our data therefore establish clear synergy between Lkb1 and Pten in controlling the mTOR pathway within bladder epithelium, and show that loss of this control leads to the disturbance of epithelial structure, EMT and ultimately tumorigenesis

Post-translational regulation contributes to the loss of LKB1 expression through SIRT1 deacetylase in osteosarcomas

background: The most prevalent form of bone cancer is osteosarcoma (OS), which is associated with poor prognosis in case of metastases formation. Mice harbouring liver kinase B1 (LKB1+/−) develop osteoblastoma-like tumours. Therefore, we asked whether loss of LKB1 gene has a role in the pathogenesis of human OS. methods: Osteosarcomas (n=259) were screened for LKB1 and sirtuin 1 (SIRT1) protein expression using immunohistochemistry and western blot. Those cases were also screened for LKB1 genetic alterations by next-generation sequencing, Sanger sequencing, restriction fragment length polymorphism and fluorescence in situ hybridisation approaches. We studied LKB1 protein degradation through SIRT1 expression. MicroRNA expression investigations were also conducted to identify the microRNAs involved in the SIRT1/LKB1 pathway. results: Forty-one per cent (106 out of 259) OS had lost LKB1 protein expression with no evident genetic anomalies. We obtained evidence that SIRT1 impairs LKB1 protein stability, and that SIRT1 depletion leads to accumulation of LKB1 in OS cell lines resulting in growth arrest. Further investigations revealed the role of miR-204 in the regulation of SIRT1 expression, which impairs LKB1 stability. conclusions: We demonstrated the involvement of sequential regulation of miR-204/SIRT1/LKB1 in OS cases and showed a mechanism for the loss of expression of LKB1 tumour suppressor in this malignancy

Epithelial cell polarity: a major gatekeeper against cancer?

The correct establishment and maintenance of cell polarity are crucial for normal cell physiology and tissue homeostasis. Conversely, loss of cell polarity, tissue disorganisation and excessive cell growth are hallmarks of cancer. In this review, we focus on identifying the stages of tumoural development that are affected by the loss or deregulation of epithelial cell polarity. Asymmetric division has recently emerged as a major regulatory mechanism that controls stem cell numbers and differentiation. Links between cell polarity and asymmetric cell division in the context of cancer will be examined. Apical–basal polarity and cell–cell adhesion are tightly interconnected. Hence, how loss of cell polarity in epithelial cells may promote epithelial mesenchymal transition and metastasis will also be discussed. Altogether, we present the argument that loss of epithelial cell polarity may have an important role in both the initiation of tumourigenesis and in later stages of tumour development, favouring the progression of tumours from benign to malignancy

Intestinal renin-angiotensin system is stimulated after deletion of Lkb1

Background and aims LKB1 is a serine-threonine kinase, mutation of which can lead to the development of multiple benign intestinal hamartomas (Peutz-Jeghers syndrome). In this study, the authors investigate the mechanisms underlying this phenotype by exploring the transcriptional changes associated with Lkb1 deletion in intestinal epithelium. Methods The authors used mice with Lkb1 deleted in the intestinal epithelium using a Cyp1a1-specific inducible Cre recombinase and used Affymetrix (Santa Clara, California, USA) microarray analysis to examine the transcriptional changes occurring immediately after Lkb1 loss. The authors also generated crypt-villus organoid culture to analyse Lkb1 role in intestinal responses to exogenous stimuli. Results Affymetrix analysis identified the most significant change to be in Ren1 expression, a gene encoding a protease involved in angiotensinogen processing. Lkb1 deletion also enhanced ACE expression and subsequently angiotensin II (AngII) production in the mouse intestine. Intestinal apoptosis induced by Lkb1 deficiency was suppressed by ACE inhibitor captopril. Lkb1-deficient intestinal epithelium showed dynamic changes in AngII receptor type 1, suggesting a possible compensatory response to elevated AngII levels. A similar reduction in epithelial AngII receptor type 1 was also observed in human Peutz-Jeghers syndrome tumours contrasting with high expression of the receptor in the tumour stroma. Mechanistically, the authors showed two pieces of data that position Lkb1 in renin expression regulation, and they implied the importance of Lkb1 in linking cell responses with nutrient levels. First, the authors showed that Lkb1 deletion in isolated epithelial organoid culture resulted in renin upregulation only when the organoids were challenged with external cues such as AngII; second, that renin upregulation was dependent upon the MEK/ERK pathway in a circadian fashion and corresponded to active feeding time when nutrient levels were high. Conclusions Taken together, these data reveal a novel role for Lkb1 in regulation of the gastrointestinal renineangiotensin system

Ridaforolimus as a single agent in advanced endometrial cancer: results of a single-arm, phase 2 trial

BACKGROUND: This open-label, multicentre, phase 2 trial evaluated the efficacy and tolerability of the mammalian target of rapamycin inhibitor ridaforolimus in women with advanced endometrial cancer. METHODS: Women with measurable recurrent or persistent endometrial cancer and documented disease progression were treated with ridaforolimus 12.5 mg intravenously once daily for 5 consecutive days every 2 weeks in a 4-week cycle. The primary end point was clinical benefit response, defined as an objective response or prolonged stable disease of 16 weeks or more. RESULTS: In all, 45 patients were treated with single-agent ridaforolimus. Clinical benefit was achieved by 13 patients (29%), including 5 (11%) with confirmed partial responses and 8 (18%) with prolonged stable disease. All patients with clinical benefit response received ridaforolimus for more than 4 months. In this heavily pretreated population, the 6-month progression-free survival was 18%. Ridaforolimus was generally well tolerated: adverse events were predictable and manageable, consistent with prior studies in other malignancies. Overall, the most common adverse events were diarrhoea (58%) and mouth sores (56%); most common grade 3 or higher adverse events were anaemia (27%) and hyperglycaemia (11%). CONCLUSION: Single-agent ridaforolimus has antitumor activity and acceptable tolerability in advanced endometrial cancer patients. Further clinical evaluation of ridaforolimus is warranted