Lkb1 and Pten synergise to suppress mTOR-mediated tumorigenesis and epithelial-mesenchymal transition in the mouse bladder

Zonula Occludens Proteins Signaling in Inflammation and Tumorigenesis

Tight junction (TJ) is the barrier of epithelial and endothelial cells to maintain paracellular substrate transport and cell polarity. As one of the TJ cytoplasmic adaptor proteins adjacent to cell membrane, zonula occludens (ZO) proteins are responsible for connecting transmembrane TJ proteins and cytoplasmic cytoskeleton, providing a binding platform for transmembrane TJ proteins to maintain the barrier function. In addition to the basic structural function, ZO proteins play important roles in signal regulation such as cell proliferation and motility, the latter including cell migration, invasion and metastasis, to influence embryonic development, tissue homeostasis, damage repair, inflammation, tumorigenesis, and cancer progression. In this review, we will focus on the signal regulating function of ZO proteins in inflammation and tumorigenesis, and discuss the limitations of previous research and future challenges in ZO protein research.

Inhibition of β-Catenin Activity Abolishes LKB1 Loss-Driven Pancreatic Cystadenoma in Mice

Pancreatic cancer (PC) is the seventh leading cause of cancer death worldwide, and remains one of our most recalcitrant and dismal diseases. In contrast to many other malignancies, there has not been a significant improvement in patient survival over the past decade. Despite advances in our understanding of the genetic alterations associated with this disease, an incomplete understanding of the underlying biology and lack of suitable animal models have hampered efforts to develop more effective therapies. LKB1 is a tumor suppressor that functions as a primary upstream kinase of adenine monophosphate-activated protein kinase (AMPK), which is an important mediator in the regulation of cell growth and epithelial polarity pathways. LKB1 is mutated in a significant number of Peutz–Jeghers syndrome (PJS) patients and in a small proportion of sporadic cancers, including PC; however, little is known about how LKB1 loss contributes to PC development. Here, we report that a reduction in Wnt/β-catenin activity is associated with LKB1 tumor-suppressive properties in PC. Remarkably, in vivo functional analyses of β-catenin in the Pdx-1-Cre LKB1^L/L β-catenin^L/L mouse model compared to LKB1 loss-driven cystadenoma demonstrate that the loss of β-catenin impairs cystadenoma development in the pancreas of Pdx-1Cre LKB1^L/L mice and dramatically restores the normal development and functions of the pancreas. This study further determined the in vivo and in vitro therapeutic efficacy of the β-catenin inhibitor FH535 in suppressing LKB1 loss-driven cystadenoma and reducing PC progression that delineates the potential roles of Wnt/β-catenin signaling in PC harboring LKB1 deficiency.

LKB1 and cancer: The dual role of metabolic regulation

Liver kinase B1 (LKB1) is an essential serine/threonine kinase frequently associated with Peutz-Jeghers syndrome (PJS). In this review, we provide an overview of the role of LKB1 in conferring protection to cancer cells against metabolic stress and promoting cancer cell survival and invasion. This carcinogenic effect contradicts the previous conclusion that LKB1 is a tumor suppressor gene. Here we try to explain the contradictory effect of LKB1 on cancer from a metabolic perspective. Upon deletion of LKB1, cancer cells experience increased energy as well as oxidative stress, thereby causing genomic instability. Meanwhile, mutated LKB1 cooperates with other metabolic regulatory genes to promote metabolic reprogramming that subsequently facilitates adaptation to strong metabolic stress, resulting in development of a more aggressive malignant phenotype. We aim to specifically discuss the contradictory role of LKB1 in cancer by reviewing the mechanism of LKB1 with an emphasis on metabolic stress and metabolic reprogramming.

PTEN: What we know of the function and regulation of this onco-suppressor factor in bladder cancer?

Bladder cancer accounts for high morbidity and mortality around the world and its incidence rate is suggested to be higher in following years. A number of factors involve in bladder cancer development such as lifestyle and drugs. However, it appears that genetic factors play a significant role in bladder cancer development and progression. Phosphatase and tensin homolog (PTEN) is a cancer-related transcription factor that is corelated with reduced proliferation and invasion of cancer cells by negatively targeting PI3K/Akt/mTOR signaling pathway. In the present review, we aimed to explore the role of PTEN in bladder cancer cells and how upstream modulators affect PTEN in this life-threatening disorder. Down-regulation of PTEN is associated with poor prognosis, chemoresistance and progression of cancer cells. Besides, microRNAs, long non-coding RNAs, circular RNAs and other molecular pathways such as NF-kB are able to target PTEN in bladder cancer cells. Notably, anti-tumor drugs such as kaempferol, β-elemene and sorafenib upregulate the expression of PTEN to exert their inhibitory effects on bladder cancer cells.

mTOR in Lung Neoplasms

With the discovery of rapamycin 45 years ago, studies in the mechanistic target of rapamycin (mTOR) field started 2 decades before the identification of the mTOR kinase. Over the years, studies revealed that the mTOR signaling is a master regulator of homeostasis and integrates a variety of environmental signals to regulate cell growth, proliferation, and metabolism. Deregulation of mTOR signaling, particularly hyperactivation, frequently occurs in human tumors. Recent advances in molecular profiling have identified mutations or amplification of certain genes coding proteins involved in the mTOR pathway (eg, PIK3CA, PTEN, STK11, and RICTOR) as the most common reasons contributing to mTOR hyperactivation. These genetic alterations of the mTOR pathway are frequently observed in lung neoplasms and may serve as a target for personalized therapy. mTOR inhibitor monotherapy has met limited clinical success so far; however, rational drug combinations are promising to improve efficacy and overcome acquired resistance. A better understanding of mTOR signaling may have the potential to help translation of mTOR pathway inhibitors into the clinical setting.

LKB1 deficiency promotes proliferation and invasion of glioblastoma through activation of mTOR and focal adhesion kinase signaling pathways

Liver kinase B1 (LKB1), a serine/threonine kinase, is frequently inactivated in several types of human cancers. To date, inactivation of LKB1 tumor suppressor has rarely been reported in glioblastoma. In this study, we investigated LKB1 status, biological significance, and therapeutic implications in glioblastoma. Loss of LKB1 immunostaining was identified in 8.6% (5/58), while decrease of LKB1 immunostaining was found in 29.3% (17/58) of glioblastoma tissues. Notably, mining TCGA database of LKB1 expression in glioblastoma revealed that lower mRNA level of LKB1 was associated with shorter survival in glioblastoma. We found that knockdown of LKB1 significantly promoted in vitro proliferation, adhesion, invasion, and metformin-induced apoptosis, and simultaneously enhanced activation of ERK and mammalian-target of rapamycin (mTOR) signaling pathways in LKB1-compenent U87 and T98 glioblastoma cells. Moreover, global transcriptional profiling revealed that adhesion and cytoskeletal proteins such as Vinculin, Talin and signaling pathways including focal adhesion kinase (FAK), extracellular martrix (ECM) receptor interaction, and cellular motility were significantly enriched in U87 and T98 glioblastoma cells upon LKB1 knockdown. Additionally, we demonstrated that the enhanced activation of FAK by LKB1 knockdown was dependent on differentially expressed cytoskeletal proteins in these glioblastoma cells. Importantly, we further found that mTOR1 inhibitor rapamycin dominantly inhibited in vitro cellular proliferation, while FAK inhibitor PF-573288 drastically decreased invasion of LKB1-attenuated glioblastoma cells. Therefore, downregulation of LKB1 may contribute to the pathogenesis and malignancy of glioblastoma and may have potential implications for stratification and treatment of glioblastoma patients.

Rapamycin enhances growth inhibition on urothelial carcinoma cells through LKB1 deficiency-mediated mitochondrial dysregulation

Rapamycin, a mammalian target of rapamycin (mTOR) inhibitor, has significant potential for application in the treatment of urothelial carcinoma (URCa) of the bladder. Previous studies have shown that regulation of the AMP-activated serine/threonine protein kinase (AMPK)-mTOR signaling pathway enhances apoptosis by inducing autophagy or mitophagy in bladder cancer. Alteration of liver kinase B1 (LKB1)-AMPK signaling leads to mitochondrial dysfunction and the accumulation of autophagy-related proteins as a result of mitophagy, resulting in enhanced cell sensitivity to drug treatments. Therefore, we hypothesized that LKB1 deficiency in URCa cells could lead to increased sensitivity to rapamycin by inducing mitochondrial defect-mediated mitophagy. To test this, we established stable LKBI-knockdown URCa cells and analyzed the effects of rapamycin on their growth. Rapamycin enhanced growth inhibition and apoptosis in stable LKB1-knockdown URCa cells and in a xenograft mouse model. In spite of the stable downregulation of LKB1 expression, rapamycin induced AMPK activation in URCa cells, causing loss of the mitochondrial membrane potential, ATP depletion, and ROS accumulation, indicating an alteration of mitochondrial biogenesis. Our findings suggest that the absence of LKB1 can be targeted to induce dysregulated mitochondrial biogenesis by rapamycin treatment in the design of novel therapeutic strategies for bladder cancer.

LKB1 loss cooperating with BRAF V600E promotes melanoma cell invasion and migration by up-regulation MMP-2 via PI3K/Akt/mTOR pathway

The serine/threonine kinase LKB1, act as a tumor suppressor, has been reported in several sporadic cancers. However, how the loss of LKB1 promotes melanoma invasion and metastasis remains incompletely understood. In this study, we inactivated LKB1expression by RNA interference in BRAF mutation and wild type melanoma cells respectively. We found LKB1 inactivation cooperate with BRAF V600E lead to melanoma cells more aggressive by a series of experiments including wound scratch test, Transwell assay. While single alteration, either LKB1 loss or BRAF V600E, fails to enhance melanoma cells invasion ability. Mechanistically, LKB1 loss synergism with BRAF V600E resulted in the activation of the PI3K/Akt/mTOR signaling pathway and significant up-regulation expression of MMP-2. In addition, LKB1 expression in human melanoma tissues was negatively associated with MMP-2 expression in the presence of BRAF V600E. Thus, our findings indicate a probable explanation on LKB1 function as a tumor suppressor in melanoma and a new therapeutic strategy for melanoma by targeting on BRAF and LKB1 together.

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.

The regulatory role of aberrant Phosphatase and Tensin Homologue and Liver Kinase B1 on AKT/mTOR/c-Myc axis in pancreatic neuroendocrine tumors

Pancreatic neuroendocrine tumor (pNET) is an uncommon type of pancreatic neoplasm. Low Phosphatase and Tensin Homologue (PTEN) expression and activation of the mechanistic target of rapamycin (mTOR) pathway have been noted in pNETs, and the former is associated with poor survival in pNET patients. Based on the results of the RADIANT-3 study, everolimus, an oral mTOR inhibitor, has been approved to treat advanced pNETs. However, the exact regulatory mechanism for the mTOR pathway in pNETs remains largely unknown. PTEN and liver kinase B1 (LKB1) are well-known for their regulatory role in the mTOR pathway. We evaluated the expression of PTEN and LKB1 in 21 pNET patients, and low PTEN and LKB1 expression levels were noted in 48% and 24% of the patients, respectively. Loss of PTEN and LKB1 synergistically promoted cell proliferation of pNET, attenuated the sensitivity of cells to mTOR inhibitors and enhanced c-Myc expression, which back-regulated PTEN, AKT, mTOR and its downstream effectors. For pNET cells with low expression levels of PTEN and LKB1, silencing the expression of c-Myc by shRNA reduced their proliferative rate, while adding either c-Myc inhibitor or AMP-activated protein kinase activator reversed their resistance to mTOR inhibitors in vitro and in vivo. Furthermore, high c-Myc expression was subsequently identified in 81% of pNETs, suggesting that up-regulation of c-Myc expression in pNETs may occur through PTEN/LKB1-dependent and PTEN/LKB1-independent regulation. The results delineated the regulation of PTEN and LKB1 on the AKT/mTOR/c-Myc axis and suggested that both c-Myc and mTOR are potential therapeutic targets for pNET.

Crosstalk of LKB1- and PTEN-regulated signals in liver morphogenesis and tumor development

Liver kinase B 1 (LKB1 or STK11) and phosphatase and tensin homologue deleted on chromosome 10 (PTEN) are two tumor suppressors that regulate the mammalian target of rapamycin signaling pathway. Deletion studies show that loss of either Lkb1 (Lkb^+/–) or Pten (Pten^loxP/loxP; Alb‐Cre⁺) leads to liver injury and development of hepatocarcinoma. In this study, we investigated the crosstalk of LKB1 and PTEN loss during tumorigenesis and liver development. We show that haplo‐insufficiency of Lkb1 in the liver leads to advanced tumor development in Pten‐null mice (Pten^loxP/loxP; Lkb^loxP/+; Alb‐Cre⁺). Our analysis shows that LKB1 and PTEN interact with each other in their regulation of fatty acid synthase as well as p21 expression. The combined loss of LKB1 and PTEN (Pten^loxP/loxP; Lkb^loxP/loxP; Alb‐Cre⁺) also leads to the inability to form zonal structures in the liver. The lack of metabolic zonal structures is consistent with the inability of the livers to store glycogen as well as elevated plasma bilirubin and alanine aminotransferase, indicative of liver dysfunction. These structural and functional defects are associated with cytoplasm distribution of a canalicular membrane protein multidrug resistant protein 2, which is responsible for clearing bilirubin. This observed regulation of multidrug resistant protein 2 by LKB1 likely contributes to the lack of cellular polarity and the early lethality phenotype associated with the homozygous loss of Lkb1 alone or in combination with Pten. Finally, Pten deletion does not rescue the precocious ductal plate formation reported for Lkb1‐deleted livers. Conclusion: Our study dissected the functional and molecular crosstalk of PTEN and LKB1 and elucidated key molecular targets for such interactions. (Hepatology Communications 2017;1:153‐167)

Kavalactone yangonin induces autophagy and sensitizes bladder cancer cells to flavokawain A and docetaxel via inhibition of the mTOR pathway

Consumption of kava (Piper methysticum Forst) has been linked to reduced cancer risk in the South Pacific Islands. Kavalactones are major bioactive components in kava root extracts, which have recently demonstrated anti-cancer activities. However, molecular mechanisms of kavalactones' anti-cancer action remain largely unknown. We have identified two kavalactones, yangonin and 5′ 6'-dehydrokawain, as potent inducers of autophagic cell death in bladder cancer cells. The effect of yangonin inducing autophagy is associated with increased expression of beclin and ATG5. In addition, yangonin increases the expression of LKB1 and decreases the phosphorylation of Akt, PRAS40, rpS6, p70S6K and 4E-BP1, leading to increased binding of 4E-BP1 to m7 GTP. The growth inhibitory effects of yangonin were attenuated inTSC1 or LKB1 knockout mouse embryonic fibroblasts, suggesting that TSC1 and LKB1 expression may contribute to optimal growth inhibition by yangonin. Furthermore, yangonin reduces the viability of bladder cancer cell lines derived from different stages of human bladder cancer, and acts synergistically with apoptosis-inducing agents such as docetaxel and flavokawain A. Our results support a novel anti-bladder cancer mechanism by yangonin and further studies are needed to assess the potential use of yangonin for bladder cancer prevention and treatment

E-cadherin downregulation sensitizes PTEN-mutant tumors to PI3Kβ silencing

Alterations in phosphatidylinositol 3-kinase (PI3K) and in PTEN (phosphatase and tensin homolog), the negative regulator of the PI3K pathway, are found in nearly half of human tumors. As PI3Kβ, the main isoform activated in PTEN-mutant tumors, has kinase-dependent and -independent activities, we compared the effects of depleting vs. drug-inhibiting PI3Kβ kinase activity in a collection of diverse tumor types and in a set of bladder carcinoma cell lines grown as xenografts in mice. PI3Kβ depletion (by intratumor injection of PIK3CB siRNA) induced apoptosis and triggered regression of PTEN-mutant tumors more efficiently than PI3Kβ inhibition. A small proportion of these tumors was resistant to PI3Kβ downregulation; we analyzed what determined resistance in these cases. Using add-back experiments, we show that both PTEN mutation and low E-cadherin expression are necessary for PI3Kβ dependence. In bladder carcinoma, loss of E-cadherin expression coincides with N-cadherin upregulation. We found that PI3Kβ associated with N-cadherin and that PIK3CB depletion selectively disrupted N-cadherin cell adhesions in PTEN-mutant bladder carcinoma. These results support the use of PIK3CB interfering RNA as a therapeutic approach for high-risk bladder cancers that show E-cadherin loss and express mutant PTEN.

AMPKα Is Suppressed in Bladder Cancer through Macrophage-Mediated Mechanisms

Bladder cancer presents as either low- or high-grade disease, each with distinct mutational profiles; however, both display prominent mTORC1 activation. One major negative regulator of mTORC1 is AMPK, which is a critical metabolic regulator that suppresses cellular growth in response to metabolic stress by negatively regulating mTORC1. Alterations in the activation and protein levels of AMPK have been reported in breast, gastric, and hepatocellular carcinoma. To investigate whether AMPK suppression is responsible for mTOR activation in bladder cancer, the levels of AMPKα were quantified in a cohort of primary human bladder cancers and adjacent nontumor tissues. The levels of p-AMPKα, AMPKα1, AMPKα2, and total AMPKα were significantly suppressed in both low- and high-grade disease when compared with nontumor tissue. To elucidate the AMPKα suppression mechanism, we focused on inflammation, particularly tumor-infiltrating macrophages, due to their reported role in regulating AMPK expression. Treatment of HTB2 cancer cells with varying doses of differentiated U937 macrophage conditioned medium (CM) demonstrated a dose-dependent reduction of AMPKα protein. Additionally, macrophage CM treatment of HTB2 and HT1376 bladder cells for various times also reduced AMPKα protein but not mRNA levels. Direct TNFα treatment also suppressed AMPKα at the protein but not RNA level. Finally, staining of the human cohort for CD68, a macrophage marker, revealed that CD68+ cell counts correlated with reduced AMPKα levels. In summary, these data demonstrate the potential role for inflammation and inflammatory cytokines in regulating the levels of AMPKα and promoting mTORC1 activation in bladder cancer.

AMPKα2 Regulates Bladder Cancer Growth through SKP2-Mediated Degradation of p27

AMP-activated protein kinase (AMPK) is the central metabolic regulator of the cell and controls energy consumption based upon nutrient availability. Due to its role in energy regulation, AMPK has been implicated as a barrier for cancer progression and is suppressed in multiple cancers. To examine whether AMPK regulates bladder cancer cell growth, HTB2 and HT1376 bladder cells were treated with an AMPK activator, 5-aminoimidazole-4-carboxamide ribonucleotide (AICAR). AICAR treatment reduced proliferation and induced the expression of p27^Kip1 (CDKN1B), which was mediated through an mTOR-dependent mechanism. Interestingly, AMPKα2 knockdown resulted in reduced p27 levels, whereas AMPKα1 suppression did not. To further determine the exact mechanism by which AMPKa2 regulates p27, HTB2 and HT1376 cells were transduced with an shRNA targeting AMPKα2. Stable knockdown of AMPKα2 resulted in increased proliferation and decreased p27 protein. The reduced p27 protein was determined to be dependent upon SKP2. Additionally, loss of AMPKα2 in a xenograft and a chemical carcinogen model of bladder cancer resulted in larger tumors with less p27 protein and high SKP2 levels. Consistent with the regulation observed in the bladder cancer model systems, a comprehensive survey of human primary bladder cancer clinical specimens revealed low levels of AMPKα2 and p27 and high levels of SKP2.

IMPLICATIONS

These results highlight the contribution of AMPKα2 as a mechanism for controlling bladder cancer growth by regulating proliferation through mTOR suppression and induction of p27 protein levels, thus indicating how AMPKα2 loss may contribute to tumorigenesis. Mol Cancer Res; 14(12); 1182-94. ©2016 AACR.

Homeostatic Signaling by Cell-Cell Junctions and Its Dysregulation during Cancer Progression

The transition of sessile epithelial cells to a migratory, mesenchymal phenotype is essential for metazoan development and tissue repair, but this program is exploited by tumor cells in order to escape the confines of the primary organ site, evade immunosurveillance, and resist chemo-radiation. In addition, epithelial-to-mesenchymal transition (EMT) confers stem-like properties that increase efficiency of colonization of distant organs. This review evaluates the role of cell–cell junctions in suppressing EMT and maintaining a quiescent epithelium. We discuss the conflicting data on junctional signaling in cancer and recent developments that resolve some of these conflicts. We focus on evidence from breast cancer, but include other organ sites where appropriate. Current and potential strategies for inhibition of EMT are discussed.

Energy sensing and cancer: LKB1 function and lessons learnt from Peutz-Jeghers syndrome

We describe in this review increasing evidence that loss of LKB1 kinase in Peutz-Jeghers syndrome (PJS) derails the existing natural balance between cell survival and tumour growth suppression. LKB1 deletion can plunge cells into an energy/oxidative stress-induced crisis which leads to the activation of alternative and often carcinogenic pathways to maintain cellular energy levels. It therefore appears that although LKB1 deficiency can suppress oncogenic transformation in the short term, it can ultimately lead to more progressed and malignant phenotypes by driving abnormal cell differentiation, genomic instability and increased tumour heterogeneity.

Inhibition of epithelial-mesenchymal transition in bladder cancer cells via modulation of mTOR signalling

Mounting evidence suggests that signalling cross-talk plays a significant role in the regulation of epithelial-mesenchymal transition (EMT) in cancer cells. However, the complex network regulating the EMT in different cancer types has not been fully described yet which affects the development of novel therapeutic strategies. In the present study, we investigated the signalling pathways involved in EMT of bladder cancer cells and demonstrated the effects of two novel agents in the regulation of EMT. Myrtucommulone-A (MC-A) and thymoquinone (TQ) have been shown to possess anti-cancer properties. However, their targets in the regulation of cancer cell behavior are not well defined. Here, we defined the effects of two putative anti-cancer agents on bladder cancer cell migration and their possible intracellular targets in the regulation of EMT. Our results suggest that MC-A or TQ treatment affected N-cadherin, Snail, Slug, and β-catenin expressions and effectively attenuated mTOR activity. The downstream components in mTOR signalling were also affected. MC-A treatment resulted in the concomitant inhibition of extracellular matrix-regulated protein kinases 1 and 2 (ERK 1/2), p38 mitogen-activated protein kinase (MAPK) and Src activity. On the other hand, TQ treatment increased Src activity while exerting no effect on ERK 1/2 or p38 MAPK activity. Given the stronger inhibition of EMT-related markers in MC-A-treated samples, we concluded that this effect might be due to collective inhibition of multiple signalling pathways which result in a decrease in their cross-talk in bladder cancer cells. Overall, the data in this study proposes novel action mechanisms for MC-A or TQ in bladder cancer cells and highlights the potential use of these active compounds in the regulation of EMT.

Advances in intravesical therapy for urinary tract disorders

INTRODUCTION

Intravesical therapy is a valuable option in the clinical management of urinary tract disorders such as interstitial cystitis/ painful bladder syndrome (IC/PBS) and refractory overactive bladder. This review will cover the latest advances in this field using polymer and liposomes as delivery platform for drugs, protein and nucleic acids.

AREAS COVERED

This review summarizes the significance of intravesical therapy for lower urinary tract disorders. The recent advancement of liposomes as a drug delivery platform for botulinum toxin, tacrolimus and small interfering RNA is discussed. The importance of polymers forming indwelling devices and hydrogels are also discussed, where all preparations improved efficacy parameters in rodent models. Clinical experience of treating IC/PBS with indwelling devices and liposomes are summarized and preclinical evidence about the downregulation of target gene expression in rodent bladder with liposomes complexed with siRNA is also reviewed.

EXPERT OPINION

There have been several advances in the field of intravesical therapy for improving clinical outcomes. One of the most promising research avenues is the repurposing of drugs, given previously by other routes of administration, such as tacrolimus. Intravesical therapy also opens up novel therapeutic targets with improved efficacy and safety for underactive bladder.

Role of the LKB1/AMPK pathway in tumor invasion and metastasis of cancer cells (Review)

Liver kinase B1 (LKB1), also known as serine/threo-nine kinase 11 (STK11), is a tumor suppressor that is inactivated in Peutz-Jeghers familial cancer syndrome. LKB1 phosphorylates and activates AMP-activated protein kinase (AMPK), which negatively regulates cancer cell proliferation and metabolism. However, recent evidence demonstrates that the LKB1/AMPK pathway is involved in the process of tumor invasion and migration, which is an important hallmark of carcinoma progression to higher pathological grades of malignancy. This review focuses on the function of the LKB1/AMPK pathway in the invasion and migration of cancer cells and provides an overview of therapeutic strategies aimed at this pathway in malignant tumors.

Induction of epithelial-mesenchymal transition via activation of epidermal growth factor receptor contributes to sunitinib resistance in human renal cell carcinoma cell lines

Sunitinib is widely used for treating renal cell carcinoma (RCC). However, some patients do not respond to treatment with this drug. We aimed to study the association between sunitinib sensitivity and epithelial-mesenchymal transition (EMT) regulation via epidermal growth factor receptor (EGFR) signaling, which is a mechanism of resistance to anticancer drugs. Three RCC cell lines (786-O, ACHN, and Caki-1) were used, and then we evaluated cell viability, EMT regulatory proteins, and signal transduction with sunitinib treatment. Cell viability of 786-O cells was maintained after treatment with sunitinib. After treatment with sunitinib, EGFR phosphorylation increased in 786-O cells, resulting in an increase in the phosphorylation of extracellular signal-regulated kinase, nuclear translocation of β-catenin, and expression of mesenchymal markers. These results suggest that sunitinib induced EMT via activation of EGFR in 786-O cells, but not in ACHN and Caki-1 cells. Caki-1/SN cells, a resistant cell line generated by continuous exposure to sunitinib, displayed increased phosphorylation of EGFR. Cell viability in the presence of sunitinib was decreased by erlotinib, as the selective inhibitor of EGFR, treatment in 786-O and Caki-1/SN cells. Similarly, erlotinib suppressed sunitinib-induced EGFR activation and upregulated mesenchymal markers. Thus, we postulate that resistance to sunitinib in RCC may be associated with EMT caused by activation of EGFR.

1-Methyl-D-tryptophan potentiates TGF-β-induced epithelial-mesenchymal transition in T24 human bladder cancer cells

Immune escape and metastasis are the hallmarks of several types of cancer including bladder cancer. One of the mechanisms involved in these processes has been linked to indoleamine 2,3-dioxygenase (IDO). Although IDO is classically recognized for its immunomodulatory property, it has presented nonimmunological effects in some tumors. TGF-β1 is believed to contribute to carcinoma development by modulating immunossupressive molecules, including IDO. In addition, TGF-β1 induces the epithelial-mesenchymal transition (EMT), which is a critical step in the tumor invasiveness and metastasis. We investigated the role of MT and IDO modulation in the induction of EMT by TGF-β1 in T24 human bladder carcinoma cells. When T24 cells were incubated with the IDO inhibitor (MT, 1-methyl-D-tryptophan), with TGF-β1, and with MT+TGF-β1, a significant decrease of IDO expression and activity was observed. In addition, downregulation of e-cadherin and upregulation of n-cadherin and EMT transcription factors were induced by the treatments, confirming the induction of EMT. siRNA-mediated knockdown of IDO decreased e-cadherin expression, but had no effect on EMT transcription factors. In the scratch-wound assay, the heightened migration process was intensified when the cells were incubated with MT+TGF-β1. These effects were associated with a robust inhibition of Akt activation. After inoculation of T24 cells under the kidney capsule of Balb/c nude, the cells were positive for IDO in the center of the cell infiltrate, being negative in the periphery, where EMT is high. In conclusion, inhibition of IDO by TGF-β1 and MT is associated with EMT in T24 human bladder carcinoma cells. MT has potentiating effect in TGF-β1-induced EMT, independently of IDO. This nonimmunological effect of MT should be considered if IDO is the target to avoid immune escape in bladder cancer.

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.

Isoprenaline induces epithelial-mesenchymal transition in gastric cancer cells

The emerging role of stress-related signaling in regulating cancer development and progression has been recognized. However, whether stress serves as a mechanism to promote gastric cancer metastasis is not clear. Here, we show that the β2-AR agonist, isoprenaline, upregulates expression levels of CD44 and CD44v8-10 in gastric cancer cells. CD44, a cancer stem cell-related marker, is expressed at high levels in gastric cancer tissues, which strongly correlates with the occurrence of epithelial-mesenchymal transition (EMT)-associated phenotypes both in vivo and in vitro. Combined with experimental observations in two human gastric cancer cell lines, we found that β2-AR signaling can initiate EMT. It led to an increased expression of mesenchymal markers, such as α-SMA, vimentin, and snail at mRNA and protein levels, and conversely a decrease in epithelial markers, E-cadherin and β-catenin. Isoprenaline stimulation of β2-AR receptors activates the downstream target STAT3, which functions as a positive regulator and mediated the phenotypic switch toward a mesenchymal cell type in gastric cancer cells. Our data provide a mechanistic understanding of the complex signaling cascades involving stress-related hormones and their effects on EMT. In light of our observations, pharmacological interventions targeting β2-AR-STAT3 signaling can potentially be used to ameliorate stress-associated influences on gastric cancer development and progression.

Modelling bladder cancer in mice: opportunities and challenges

The prognosis and treatment of bladder cancer have improved little in the past 20 years. Bladder cancer remains a debilitating and often fatal disease, and is among the most costly cancers to treat. The generation of informative mouse models has the potential to improve our understanding of bladder cancer progression, as well as to affect its diagnosis and treatment. However, relatively few mouse models of bladder cancer have been described, and in particular, few that develop invasive cancer phenotypes. This Review focuses on opportunities for improving the landscape of mouse models of bladder cancer.

Targeted inhibition of mTORC2 prevents osteosarcoma cell migration and promotes apoptosis

Dysregulation of mammalian target of rapamycin (mTOR) signaling often occurs in many human malignant diseases, making it a potential target in the treatment of cancer. However, the effects of specifically targeted inhibition of mammalian target of rapamycin complex 2 (mTORC2) on osteosarcoma have not been reported. Three types of osteosarcoma cell lines (MG63/U2OS/Saos-2) were used in this study. Inhibition of mTORC2 was carried out by mTOR inhibitor PP242 and targeted siRNA. The anti-migration effect was evaluated through wound healing and Transwell assays. Osteosarcoma cells were either treated independently by inhibition of mTORC2 or in combination with cisplatin, and apoptosis was evaluated by staining with propidium iodide; PARP and caspase 7 expression levels were evaluated. Targeting of mTORC2 either by kinase inhibitor or rictor knockdown promoted cisplatin-induced apoptosis, but inhibition of mTORC1 either by rapamycin or raptor knockdown did not promote cisplatin-induced apoptosis. Furthermore, inhibition of mTORC2 but not mTORC1 effectively prevented osteosarcoma cell migration. These results suggest that agents that inhibit mTORC2 have advantages over mTORC1 inhibitors in the treatment of osteosarcoma. The present study provides a strong rationale for testing the use of mTORC1/2 inhibitors or the combination of mTORC1/2 inhibitors and cisplatin in the treatment of osteosarcoma.

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.

The regulatory roles of phosphatases in cancer

The relevance of potentially reversible post-translational modifications required for controlling cellular processes in cancer is one of the most thriving arenas of cellular and molecular biology. Any alteration in the balanced equilibrium between kinases and phosphatases may result in development and progression of various diseases, including different types of cancer, though phosphatases are relatively under-studied. Loss of phosphatases such as PTEN (phosphatase and tensin homologue deleted on chromosome 10), a known tumour suppressor, across tumour types lends credence to the development of phosphatidylinositol 3-kinase inhibitors alongside the use of phosphatase expression as a biomarker, though phase 3 trial data are lacking. In this review, we give an updated report on phosphatase dysregulation linked to organ-specific malignancies.

Cancer Stem Cells and Epithelial-to-Mesenchymal Transition (EMT)-Phenotypic Cells: Are They Cousins or Twins?

Cancer stem cells (CSCs) are cells within a tumor that possess the capacity to self-renew and maintain tumor-initiating capacity through differentiation into the heterogeneous lineages of cancer cells that comprise the whole tumor. These tumor-initiating cells could provide a resource for cells that cause tumor recurrence after therapy. Although the cell origin of CSCs remains to be fully elucidated, mounting evidence has demonstrated that Epithelial-to-Mesenchymal Transition (EMT), induced by different factors, is associated with tumor aggressiveness and metastasis and these cells share molecular characteristics with CSCs, and thus are often called cancer stem-like cells or tumor-initiating cells. The acquisition of an EMT phenotype is a critical process for switching early stage carcinomas into invasive malignancies, which is often associated with the loss of epithelial differentiation and gain of mesenchymal phenotype. Recent studies have demonstrated that EMT plays a critical role not only in tumor metastasis but also in tumor recurrence and that it is tightly linked with the biology of cancer stem-like cells or cancer-initiating cells. Here we will succinctly summarize the state-of-our-knowledge regarding the molecular similarities between cancer stem-like cells or CSCs and EMT-phenotypic cells that are associated with tumor aggressiveness focusing on solid tumors.

Loss of LKB1 and PTEN tumor suppressor genes in the ovarian surface epithelium induces papillary serous ovarian cancer

Epithelial ovarian cancer presents mostly with serous, endometrioid or mucinous histology but is treated as a single disease. The development of histotype-specific therapy has been challenging because of the relative lack of studies attributing disrupted pathways to a distinct histotype differentiation. mTOR activation is frequently associated with poor prognosis in serous ovarian cancer, which is the most common and most deadly histotype. However, the mechanisms dysregulating mTOR in the pathogenesis of ovarian cancer are unknown. We detected copy number loss and correlated lower expression levels of LKB1, TSC1, TSC2 and PTEN tumor suppressor genes for upstream regulators of mTOR activity in up to 80% in primary ovarian serous tumor databases, with LKB1 allelic loss-predominant. Reduced LKB1 protein was usually associated with increased mTOR activity in both serous ovarian cancer cell lines and primary tumors. Conditional deletion of Lkb1 in murine ovarian surface epithelial (OSE) cells caused papillary hyperplasia and shedding but not tumors. Simultaneous deletion of Lkb1 and Pten, however, led to development of high-grade ovarian serous histotype tumors with 100% penetrance that expressed WT1, ERα, PAX8, TP53 and cytokeratin 8, typical markers used in the differential diagnosis of serous ovarian cancer. Neither hysterectomy nor salpingectomy interfered with progression of ovarian tumorigenesis, suggesting that neither uterine nor Fallopian tube epithelial cells were contributing to tumorigenesis. These results implicate LKB1 loss in the OSE in the pathogenesis of serous ovarian cancer and provide a compelling rationale for investigating the therapeutic potential of targeting LKB1 signaling in patients with this deadly disease.

Regulation of blood-testis barrier (BTB) dynamics during spermatogenesis via the "Yin" and "Yang" effects of mammalian target of rapamycin complex 1 (mTORC1) and mTORC2

In mammalian testes, haploid spermatozoa are formed from diploid spermatogonia during spermatogenesis, which is a complicated cellular process. While these cellular events were reported in the 1960s and 1970s, the underlying molecular mechanism(s) that regulates these events remained unexplored until the past ∼10 years. For instance, adhesion proteins were shown to be integrated components at the Sertoli cell-cell interface and/or the Sertoli-spermatid interface in the late 1980s. But only until recently, studies have demonstrated that some of the adhesion proteins serve as the platform for signal transduction that regulates cell adhesion. In this chapter, a brief summary and critical discussion are provided on the latest findings regarding these cell-adhesion proteins in the testis and their relationship to spermatogenesis. Moreover, antagonistic effects of two mammalian target of rapamycin (mTOR) complexes, known as mTORC1 and mTORC2, on cell-adhesion function in the testis are discussed. Finally, a hypothetic model is presented to depict how these two mTOR-signaling complexes having the "yin" and "yang" antagonistic effects on the Sertoli cell tight junction (TJ)-permeability barrier can maintain the blood-testis barrier (BTB) integrity during the epithelial cycle while preleptotene spermatocytes are crossing the BTB.

LKB1 is a central regulator of tumor initiation and pro-growth metabolism in ErbB2-mediated breast cancer

Background

Germline and somatic mutations in STK11, the gene encoding the serine/threonine kinase LKB1, are strongly associated with tumorigenesis. While loss of LKB1 expression has been linked to breast cancer, the mechanistic role of LKB1 in regulating breast cancer development, metastasis, and tumor metabolism has remained unclear.

Methods

We have generated and analyzed transgenic mice expressing ErbB2 in the mammary epithelium of LKB1 wild-type or LKB1-deficient mice. We have also utilized ErbB2-expressing breast cancer cells in which LKB1 levels have been reduced using shRNA approaches. These transgenic and xenograft models were characterized for the effects of LKB1 loss on tumor initiation, growth, metastasis and tumor cell metabolism.

Results

We demonstrate that loss of LKB1 promotes tumor initiation and induces a characteristic shift to aerobic glycolysis (‘Warburg effect’) in a model of ErbB2-mediated breast cancer. LKB1-deficient breast cancer cells display enhanced early tumor growth coupled with increased cell migratory and invasive properties in vitro. We show that ErbB2-positive tumors deficient for LKB1 display a pro-growth molecular and phenotypic signature characterized by elevated Akt/mTOR signaling, increased glycolytic metabolism, as well as increased bioenergetic markers both in vitro and in vivo. We also demonstrate that mTOR contributes to the metabolic reprogramming of LKB1-deficient breast cancer, and is required to drive glycolytic metabolism in these tumors; however, LKB1-deficient breast cancer cells display reduced metabolic flexibility and increased apoptosis in response to metabolic perturbations.

Conclusions

Together, our data suggest that LKB1 functions as a tumor suppressor in breast cancer. Loss of LKB1 collaborates with activated ErbB2 signaling to drive breast tumorigenesis and pro-growth metabolism in the resulting tumors.

Unravelling the connection between metabolism and tumorigenesis through studies of the liver kinase B1 tumour suppressor

The liver kinase B1 (LKB1) tumour suppressor functions as a master regulator of growth, metabolism and survival in cells, which is frequently mutated in sporadic human non-small cell lung and cervical cancers. LKB1 functions as a key upstream activator of the AMP-activated protein kinase (AMPK), a central metabolic switch found in all eukaryotes that govern glucose and lipid metabolism and autophagy in response to alterations in nutrients and intracellular energy levels. The LKB1/AMPK signalling pathway suppresses mammalian target of rapamycin complex 1 (mTORC1), an essential regulator of cell growth in all eukaryotes that is deregulated in a majority of human cancers. LKB1 inactivation in cancer leads to both tumorigenesis and metabolic deregulation through the AMPK and mTORC1-signalling axis and there remain critical challenges to elucidate the direct role LKB1 inactivation plays in driving aberrant metabolism and tumour growth. This review addresses past and current efforts to delineate the molecular mechanisms fueling metabolic deregulation and tumorigenesis following LKB1 inactivation as well as translational promise of therapeutic strategies aimed at targeting LKB1-deficient tumors.

MicroRNA-antagonism regulates breast cancer stemness and metastasis via TET-family-dependent chromatin remodeling

Tumor cells metastasize to distant organs through genetic and epigenetic alterations, including changes in microRNA (miR) expression. Here we find miR-22 triggers epithelial-mesenchymal transition (EMT), enhances invasiveness and promotes metastasis in mouse xenografts. In a conditional mammary gland-specific transgenic (TG) mouse model, we show that miR-22 enhances mammary gland side-branching, expands the stem cell compartment, and promotes tumor development. Critically, miR-22 promotes aggressive metastatic disease in MMTV-miR-22 TG mice, as well as compound MMTV-neu or -PyVT-miR-22 TG mice. We demonstrate that miR-22 exerts its metastatic potential by silencing antimetastatic miR-200 through direct targeting of the TET (Ten eleven translocation) family of methylcytosine dioxygenases, thereby inhibiting demethylation of the mir-200 promoter. Finally, we show that miR-22 overexpression correlates with poor clinical outcomes and silencing of the TET-miR-200 axis in patients. Taken together, our findings implicate miR-22 as a crucial epigenetic modifier and promoter of EMT and breast cancer stemness toward metastasis.

Dysregulation of mTOR activity through LKB1 inactivation

Mammalian target of rapamycin (mTOR) is aberrantly activated in many cancer types, and two rapamycin derivatives are currently approved by the Food and Drug Administration (FDA) of the United States for treating renal cell carcinoma. Mechanistically, mTOR is hyperactivated in human cancers either due to the genetic activation of its upstream activating signaling pathways or the genetic inactivation of its negative regulators. The tumor suppressor liver kinase B1 (LKB1), also known as serine/threonine kinase 11 (STK11), is involved in cell polarity, cell detachment and adhesion, tumor metastasis, and energetic stress response. A key role of LKB1 is to negatively regulate the activity of mTOR complex 1 (mTORC1). This review summarizes the molecular basis of this negative interaction and recent research progress in this area.

In vivo NCL targeting affects breast cancer aggressiveness through miRNA regulation

Numerous studies have described the altered expression and the causal role of microRNAs (miRNAs) in human cancer. However, to date, efforts to modulate miRNA levels for therapeutic purposes have been challenging to implement. Here we find that nucleolin (NCL), a major nucleolar protein, posttranscriptionally regulates the expression of a specific subset of miRNAs, including miR-21, miR-221, miR-222, and miR-103, that are causally involved in breast cancer initiation, progression, and drug resistance. We also show that NCL is commonly overexpressed in human breast tumors and that its expression correlates with that of NCL-dependent miRNAs. Finally, inhibition of NCL using guanosine-rich aptamers reduces the levels of NCL-dependent miRNAs and their target genes, thus reducing breast cancer cell aggressiveness both in vitro and in vivo. These findings illuminate a path to novel therapeutic approaches based on NCL-targeting aptamers for the modulation of miRNA expression in the treatment of breast cancer.

Integrin-binding protein nischarin interacts with tumor suppressor liver kinase B1 (LKB1) to regulate cell migration of breast epithelial cells

Biallelic inactivation of LKB1, a serine/threonine kinase, has been detected in 30% of lung adenocarcinomas, and inhibition of breast tumor growth has been demonstrated. We have identified the tumor suppressor, Nischarin, as a novel binding partner of LKB1. Our mapping analysis shows that the N terminus of Nischarin interacts with amino acids 44-436 of LKB1. Time lapse microscopy and Transwell migration data show that the absence of both Nischarin and LKB1 from an invasive breast cancer cell line (MDA-MB-231) enhances migration as measured by increased distance and speed of migrating cells. Our data suggest that this is a result of elevated PAK1 and LIMK1 phosphorylation. Moreover, the absence of Nischarin and LKB1 increased tumor growth in vivo. Consistent with this, the percentage of S phase cells was increased, as demonstrated by flow cytometry and enhanced cyclin D1. The absence of Nischarin and LKB1 also led to a dramatic increase in the formation of lung metastases. Our studies, for the first time, demonstrate functional interaction between LKB1 and Nischarin to inhibit cell migration and breast tumor progression. Mechanistically, we show that these two proteins together regulate PAK-LIMK-Cofilin and cyclin D1/CDK4 pathways.

Identification of prognostic gene signatures of glioblastoma: a study based on TCGA data analysis

BACKGROUND

The Cancer Genome Atlas (TCGA) project is a large-scale effort with the goal of identifying novel molecular aberrations in glioblastoma (GBM).

METHODS

Here, we describe an in-depth analysis of gene expression data and copy number aberration (CNA) data to classify GBMs into prognostic groups to determine correlates of subtypes that may be biologically significant.

RESULTS

To identify predictive survival models, we searched TCGA in 173 patients and identified 42 probe sets (P = .0005) that could be used to divide the tumor samples into 3 groups and showed a significantly (P = .0006) improved overall survival. Kaplan-Meier plots showed that the median survival of group 3 was markedly longer (127 weeks) than that of groups 1 and 2 (47 and 52 weeks, respectively). We then validated the 42 probe sets to stratify the patients according to survival in other public GBM gene expression datasets (eg, GSE4290 dataset). An overall analysis of the gene expression and copy number aberration using a multivariate Cox regression model showed that the 42 probe sets had a significant (P < .018) prognostic value independent of other variables.

CONCLUSIONS

By integrating multidimensional genomic data from TCGA, we identified a specific survival model in a new prognostic group of GBM and suggest that molecular stratification of patients with GBM into homogeneous subgroups may provide opportunities for the development of new treatment modalities.

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.

Regulation of actin dynamics and protein trafficking during spermatogenesis--insights into a complex process

In the mammalian testis, extensive restructuring takes place across the seminiferous epithelium at the Sertoli-Sertoli and Sertoli-germ cell interface during the epithelial cycle of spermatogenesis, which is important to facilitate changes in the cell shape and morphology of developing germ cells. However, precise communications also take place at the cell junctions to coordinate the discrete events pertinent to spermatogenesis, namely spermatogonial renewal via mitosis, cell cycle progression and meiosis, spermiogenesis and spermiation. It is obvious that these cellular events are intimately related to the underlying actin-based cytoskeleton which is being used by different cell junctions for their attachment. However, little is known on the biology and regulation of this cytoskeleton, in particular its possible involvement in endocytic vesicle-mediated trafficking during spermatogenesis, which in turn affects cell adhesive function and communication at the cell-cell interface. Studies in other epithelia in recent years have shed insightful information on the intimate involvement of actin dynamics and protein trafficking in regulating cell adhesion and communications. The goal of this critical review is to provide an updated assessment of the latest findings in the field on how these complex processes are being regulated during spermatogenesis. We also provide a working model based on the latest findings in the field including our laboratory to provide our thoughts on an apparent complicated subject, which also serves as the framework for investigators in the field. It is obvious that this model will be rapidly updated when more data are available in future years.

Targeting LKB1 signaling in cancer

The serine/threonine kinase LKB1 is a master kinase involved in cellular responses such as energy metabolism, cell polarity and cell growth. LKB1 regulates these crucial cellular responses mainly via AMPK/mTOR signaling. Germ-line mutations in LKB1 are associated with the predisposition of the Peutz-Jeghers syndrome in which patients develop gastrointestinal hamartomas and have an enormously increased risk for developing gastrointestinal, breast and gynecological cancers. In addition, somatic inactivation of LKB1 has been associated with sporadic cancers such as lung cancer. The exact mechanisms of LKB1-mediated tumor suppression remain so far unidentified; however, the inability to activate AMPK and the resulting mTOR hyperactivation has been detected in PJS-associated lesions. Therefore, targeting LKB1 in cancer is now mainly focusing on the activation of AMPK and inactivation of mTOR. Preclinical in vitro and in vivo studies show encouraging results regarding these approaches, which have even progressed to the initiation of a few clinical trials. In this review, we describe the functions, regulation and downstream signaling of LKB1, and its role in hereditary and sporadic cancers. In addition, we provide an overview of several AMPK activators, mTOR inhibitors and additional mechanisms to target LKB1 signaling, and describe the effect of these compounds on cancer cells. Overall, we will explain the current strategies attempting to find a way of treating LKB1-associated cancer.

Deficiency in metabolic regulators PPARγ and PTEN cooperates to drive keratinizing squamous metaplasia in novel models of human tissue regeneration

Hindgut-derived endoderm can differentiate into rectal, prostatic, and bladder phenotypes. Stromal-epithelial interactions are crucial for this development; however, the precise mechanisms by which epithelium responds to stromal cues remain unknown. We have previously reported ectopic expression of peroxisome proliferator-activated receptor-γ2 (PPARγ2) increased androgen receptor expression and promoted differentiation of mouse prostate epithelium. PPARγ is also implicated in urothelial differentiation. Herein we demonstrate that knockdown of PPARγ2 in benign human prostate epithelial cells (BHPrEs) promotes urothelial transdifferentiation. Furthermore, in vitro and in vivo heterotypic tissue regeneration models with embryonic bladder mesenchyme promoted urothelial differentiation of PPARγ2-deficient BHPrE cells, and deficiency of both PPARγ isoforms 1 and 2 arrested differentiation. Because PTEN deficiency is cooperative in urothelial pathogenesis, we engineered BHPrE cells with combined knockdown of PPARγ and PTEN and performed heterotypic recombination experiments using embryonic bladder mesenchyme. Whereas PTEN deficiency alone induced latent squamous differentiation in BHPrE cells, combined PPARγ and PTEN deficiency accelerated the development of keratinizing squamous metaplasia (KSM). We further confirmed via immunohistochemistry that gene expression changes in metaplastic recombinants reflected human urothelium undergoing KSM. In summary, these data suggest that PPARγ isoform expression provides a molecular basis for observations that adult human epithelium can be transdifferentiated on the basis of heterotypic mesenchymal induction. These data also implicate PPARγ and PTEN inactivation in the development of KSM.

Targeting carbonic anhydrase IX depletes breast cancer stem cells within the hypoxic niche

The sub-population of tumor cells termed 'cancer stem cells' (CSCs) possess the capability to generate tumors, undergo epithelial-mesenchymal transition (EMT) and are implicated in metastasis, making treatments to specifically target CSCs an attractive therapeutic strategy. Tumor hypoxia plays a key role in regulating EMT and cancer stem cell function. Carbonic anhydrase IX (CAIX) is a hypoxia-inducible protein that regulates cellular pH to promote cancer cell survival and invasion in hypoxic microenvironments and is a biomarker of poor prognosis for breast cancer metastasis and survival. Here, we demonstrate that inhibition of CAIX expression or activity with novel small-molecule inhibitors in breast cancer cell lines, or in primary metastatic breast cancer cells, results in the inhibition of breast CSC expansion in hypoxia. We identify the mTORC1 axis as a critical pathway downstream of CAIX in the regulation of cancer stem cell function. CAIX is also required for expression of EMT markers and regulators, as well as drivers of 'stemness', such as Notch1 and Jagged1 in isolated CSCs. In addition, treatment of mice bearing orthotopic breast tumors with CAIX-specific small-molecule inhibitors results in significant depletion of CSCs within these tumors. Furthermore, combination treatment with paclitaxel results in enhanced tumor growth delay and eradication of lung metastases. These data demonstrate that CAIX is a critical mediator of the expansion of breast CSCs in hypoxic niches by sustaining the mesenchymal and 'stemness' phenotypes of these cells, making CAIX an important therapeutic target for selectively depleting breast CSCs.

rpS6 Regulates blood-testis barrier dynamics by affecting F-actin organization and protein recruitment

During spermatogenesis, preleptotene spermatocytes residing near the basement membrane of the seminiferous tubule must traverse the blood-testis barrier (BTB) at stage VIII-IX of the epithelial cycle to continue their development in the adluminal compartment. Unlike other blood-tissue barriers (e.g. the blood-brain barrier) that are created by the endothelial tight junction (TJ) barrier of capillaries, the BTB is created by specialized junctions between Sertoli cells in which TJ coexists with basal ectoplasmic specialization (basal ES, a testis-specific adherens junction). The basal ES is typified by the presence of tightly packed actin filament bundles sandwiched between cisternae of endoplasmic reticulum and the apposing plasma membranes of Sertoli cells. These actin filament bundles also confer unusual adhesive strength to the BTB. Yet the mechanisms by which these filamentous actin (F-actin) networks are regulated from the bundled to the debundled state to facilitate the transit of spermatocytes remain elusive. Herein, we provide evidence that ribosomal protein S6 (rpS6), the downstream signaling molecule of the mammalian target of rapamycin complex 1 (mTORC1) pathway, is a major regulator of F-actin organization and adhesion protein recruitment at the BTB. rpS6 is restrictively and spatiotemporally activated at the BTB during the epithelial cycle. An activation of rpS6 led to a disruption of the Sertoli cell TJ barrier and BTB integrity. Its silencing in vitro or in vivo by using small interfering RNA duplexes or short hairpin RNA was found to promote the Sertoli cell TJ permeability barrier by the recruitment of adhesion proteins (e.g. claudin-11 and occludin) to the BTB. Thus, rpS6 in the mTORC1 pathway regulates BTB restructuring via its effects on the F-actin organization and protein recruitment at the BTB.

Immunohistochemical expression of mTOR negatively correlates with PTEN expression in gastric carcinoma

The phosphoinositide-3 kinase (PI3K)-AKT-mammalian target of rapamycin (mTOR) pathway is a cellular pathway involved in cell growth, tumorigenesis and cell invasion which is frequently activated in various types of cancer. The downstream effector of the pathway is mTOR which is important in cellular growth and homeostasis and aberrant activation of mTOR has been reported in several types of cancer. The tumor suppressor gene phosphatase and tensin homolog (PTEN) is essential in this pathway for inhibiting tumor invasion and metastasis. However, the involvement of mTOR and PTEN in the progression of human gastric cancer remains to be identified. Immunohistochemical staining was performed to detect the expression of mTOR and PTEN in paraffin-embedded gastric tissue sections obtained from 33 patients with gastric cancer and 30 normal controls. The expressed mTOR was mainly distributed in the cytoplasm, while PTEN was mainly localized to the nucleus. By considering negative mTOR expression with positive PTEN expression as one group and negative PTEN expression with positive mTOR expression as the other, significant statistical differences were observed in various categories, including histological types and metastatic and clinical pathology stages, between the 2 groups (P<0.01 or 0.05). The results indicated that the expression levels of mTOR and PTEN were negatively correlated in the PI3K-AKT-mTOR signaling pathway. Combined detection of mTOR and PTEN expression may be used to evaluate the degree of malignancy in gastric cancer and may be a useful marker for the early diagnosis of gastric cancer.

Novel tumor subgroups of urothelial carcinoma of the bladder defined by integrated genomic analysis

PURPOSE

There is a need for improved subclassification of urothelial carcinoma (UC) at diagnosis. A major aim of this study was to search for novel genomic subgroups.

EXPERIMENTAL DESIGN

We assessed 160 tumors for genome-wide copy number alterations and mutation in genes implicated in UC. These comprised all tumor grades and stages and included 49 high-grade stage T1 (T1G3) tumors.

RESULTS

Our findings point to the existence of genomic subclasses of the "gold-standard" grade/stage groups. The T1G3 tumors separated into 3 major subgroups that differed with respect to the type and number of copy number events and to FGFR3 and TP53 mutation status. We also identified novel regions of copy number alteration, uncovered relationships between molecular events, and elucidated relationships between molecular events and clinico-pathologic features. FGFR3 mutant tumors were more chromosomally stable than their wild-type counterparts and a mutually exclusive relationship between FGFR3 mutation and overrepresentation of 8q was observed in non-muscle-invasive tumors. In muscle-invasive (MI) tumors, metastasis was positively associated with losses of regions on 10q (including PTEN), 16q and 22q, and gains on 10p, 11q, 12p, 19p, and 19q. Concomitant copy number alterations positively associated with TP53 mutation in MI tumors were losses on 16p, 2q, 4q, 11p, 10q, 13q, 14q, 16q, and 19p, and gains on 1p, 8q, 10q, and 12q. Significant complexity was revealed in events affecting chromosome 9.

CONCLUSIONS

These findings may lead to improved biologic understanding and the development of prognostic biomarkers. Novel regions of copy number alteration may reveal potential therapeutic targets.

Upregulation of SATB1 promotes tumor growth and metastasis in liver cancer

BACKGROUND

Special AT-rich binding protein-1 (SATB1) reprograms chromatin organization and transcription profiles to promote tumour growth and metastasis.

AIMS

This study aimed to confirm the effects of SATB1 on the growth and metastasis of liver cancer and its specific regulation mechanism.

METHODS

SATB1 expression was evaluated in human hepatoma tissue, adjacent noncancerous tissue and seven kinds of liver cancer cell lines. Cell cycle, cell proliferation, apoptosis and epithelial-mesenchymal transition (EMT) was investigated after enhanced or silenced expression of SATB1. The regulatory action of SATB1 on the expression of genes that are known to regulate cell cycle progression, apoptosis and EMT and the specific apoptotic pathway on which it acts were further analysed. Nude mice that received subcutaneous implantation were used to study the effects of SATB1 on tumour growth in vivo.

RESULTS

Our data show that the high expression of SATB1 was observed in the human hepatocellular carcinoma tissue (26/45) and liver cancer cell lines with high metastatic potential. SATB1 upregulated CDK4 and downregulated p16 (INK) (4A) to promote cell cycle progression and cell proliferation and prevented apoptosis by inhibiting the FADD-caspase-8-caspase-3 death receptor-mediated apoptosis pathway. SATB1 also induced EMT concomitant with increased expression of Snail1, Slug, Twist and vimentin and decreased expression of E-cadherin, tight junction protein ZO-1 and desmoplakin. SATB1 promoted the growth of tumour in vivo.

CONCLUSION

These data suggest that the SATB1 gene may play an important role in the development and progression of liver cancer by regulation of genes related to cell cycle progression, apoptosis and EMT.