An in vivo model of epithelial to mesenchymal transition reveals a mitogenic switch

Protein kinase D1 - A targetable mediator of pancreatic cancer development

Members of the Protein kinase D (PKD) kinase family each play important cell-specific roles in the regulation of normal pancreas functions. In pancreatic diseases PKD1 is the most widely characterized isoform with roles in pancreatitis and in induction of pancreatic cancer and its progression. PKD1 expression and activation increases in pancreatic acinar cells through macrophage secreted factors, Kirsten rat sarcoma viral oncogene homolog (KRAS) signaling, and reactive oxygen species (ROS), driving the formation of precancerous lesions. In precancerous lesions PKD1 regulates cell survival, growth, senescence, and generation of doublecortin like kinase 1 (DCLK1)-positive cancer stem cells (CSCs). Within tumors, regulation by PKD1 includes chemoresistance, apoptosis, proliferation, CSC features, and the Warburg effect. Thus, PKD1 plays a critical role throughout pancreatic disease initiation and progression.

RAB4A GTPase regulates epithelial-to-mesenchymal transition by modulating RAC1 activation

Epithelial-to-mesenchymal transition (EMT) is a critical underpinning process for cancer progression, recurrence and resistance to drug treatment. Identification of new regulators of EMT could lead to the development of effective therapies to improve the outcome of advanced cancers. In the current study we discovered, using a variety of in vitro and in vivo approaches, that RAB4A function is essential for EMT and related manifestation of stemness and invasive properties. Consistently, RAB4A suppression abolished the cancer cells' self-renewal and tumor forming ability. In terms of downstream signaling, we found that RAB4A regulation of EMT is achieved through its control of activation of the RAC1 GTPase. Introducing activated RAC1 efficiently rescued EMT gene expression, invasion and tumor formation suppressed by RAB4A knockdown in both the in vitro and in vivo cancer models. In summary, this study identifies a RAB4A-RAC1 signaling axis as a key regulatory mechanism for the process of EMT and cancer progression and suggests a potential therapeutic approach to controlling these processes.

Radiation modulates expression and related activities of c-Met protein in oral tongue squamous cell carcinoma cell lines

OBJECTIVES

c-Met, a receptor tyrosine kinase, is involved in the growth, invasion and metastasis of a variety of cancers. In a set of cell lines from several solid tumors, a five-fold increase in c-Met expression after irradiation has been reported. This study aimed to assess if c-Met is likewise abundantly expressed in oral tongue squamous cell carcinoma (OTSCC) upon exposure to irradiation, followed by a Met-induced biological response.

MATERIALS AND METHODS

Six OTSCC cell lines were exposed to gamma radiation doses of 2, 4, and 6 Gray. The changes in c-Met protein levels were assessed by western blot and flow cytometry. c-Met gene expression, cell migration, proliferation and cell cycle assays were performed as phenotypic readouts.

RESULTS

Irradiation resulted in upregulation of c.Met in all cell lines with different time kinetics. On average the cells displayed minimal c-Met expression on their surface ranging from 5 to 30% of total protein. Abrupt downregulation of c-Met surface expression occurred one hour after radiation but recovered 48 h post-radiation. Intracellularly, the highest level of expression was found on day 5 after radiation exposure. Irradiation induced aggressive invasive potential of the cells as determined in cell migration assays, particularly in cell lines with the highest c-Met expression.

CONCLUSIONS

These results provide novel insights into both intracellular and extracellular dynamics of c-Met expression profiles upon irradiation of OTSCC cells in vitro. It might also suggest that radiation enhances cell migration, indicative of invasiveness, through c-Met up-regulation, at least for certain types of OTSCC cells.

Epithelial-Mesenchymal Transition Suppresses AMPK and Sensitizes Cancer Cells to Pyroptosis under Energy Stress

Epithelial-mesenchymal transition (EMT) is implicated in tumor metastasis and therapeutic resistance. It remains a challenge to target cancer cells that have undergone EMT. The Snail family of key EMT-inducing transcription factors directly binds to and transcriptionally represses not only epithelial genes but also a myriad of additional genomic targets that may carry out significant biological functions. Therefore, we reasoned that EMT inherently causes various concomitant phenotypes, some of which may create targetable vulnerabilities for cancer treatment. In the present study, we found that Snail transcription factors bind to the promoters of multiple genes encoding subunits of the AMP-activated protein kinase (AMPK) complex, and expression of AMPK genes was markedly downregulated by EMT. Accordingly, high AMPK expression in tumors correlated with epithelial cell markers and low AMPK expression in tumors was strongly associated with adverse prognosis. AMPK is the principal sensor of cellular energy status. In response to energy stress, AMPK is activated and critically reprograms cellular metabolism to restore energy homeostasis and maintain cell survival. We showed that activation of AMPK by energy stress was severely impaired by EMT. Consequently, EMT cancer cells became hypersensitive to a variety of energy stress conditions and primarily underwent pyroptosis, a regulated form of necrotic cell death. Collectively, the study suggests that EMT impedes the activation of AMPK signaling induced by energy stress and sensitizes cancer cells to pyroptotic cell death under energy stress conditions. Therefore, while EMT promotes malignant progression, it concurrently induces collateral vulnerabilities that may be therapeutically exploited.

Platelets involved tumor cell EMT during circulation: communications and interventions

Distant spreading of metastatic tumor cells is still the leading cause of tumor death. Metastatic spreading is a complex process, in which epithelial-mesenchymal transition (EMT) is the primary and key event to promote it. Presently, extensive reviews have given insights on the occurrence of EMT at the primary tumor site that depends on invasive properties of tumor cells and the tumor-associated microenvironment. However, essential roles of circulation environment involved in tumor cell EMT is not well summarized. As a main constituent of the blood, platelet is increasingly found to work as an important activator to induce EMT. Therefore, this review aims to emphasize the novel role of platelet in EMT through signal communications between platelets and circulation tumor cells, and illustrate potent interventions aiming at their communications. It may give a complementary view of EMT in addition to the tissue microenvironment, help for better understand the hematogenous metastasis, and also illustrate theoretical and practical basis for the targeted inhibition.

Cancer-Associated Fibroblasts in the Breast Tumor Microenvironment

Years of investigation have shed light on a theory in which breast tumor epithelial cells are under the effect of the stromal microenvironment. This review aims to discuss recent findings concerning the phenotypic and functional characteristics of cancer associated fibroblasts (CAFs) and their involvement in tumor evolution, as well as their potential implications for anti-cancer therapy. In this manuscript, we reviewed that CAFs play a fundamental role in initiation, growth, invasion, and metastasis of breast cancer, and also serve as biomarkers in the clinical diagnosis, therapy, and prognosis of this disease.

RASSF10 Is a TGFβ-Target That Regulates ASPP2 and E-Cadherin Expression and Acts as Tumor Suppressor That Is Epigenetically Downregulated in Advanced Cancer

The Ras Association Domain Family (RASSF) encodes members of tumor suppressor genes which are frequently inactivated in human cancers. Here, the function and the regulation of RASSF10, that contains a RA (Ras-association) and two coiled domains, was investigated. We utilized mass spectrometry and immuno-precipitation to identify interaction partners of RASSF10. Additionally, we analyzed the up- and downstream pathways of RASSF10 that are involved in its tumor suppressive function. We report that RASSF10 binds ASPP1 (Apoptosis-stimulating protein of p53) and ASPP2 through its coiled-coils. Induction of RASSF10 leads to increased protein levels of ASPP2 and acts negatively on cell cycle progression. Interestingly, we found that RASSF10 is a target of the EMT (epithelial mesenchymal transition) driver TGFβ (Transforming growth factor beta) and that negatively associated genes of RASSF10 are significantly over-represented in an EMT gene set collection. We observed a positive correlation of RASSF10 expression and E-cadherin that prevents EMT. Depletion of RASSF10 by CRISPR/Cas9 technology induces the ability of lung cancer cells to proliferate and to invade an extracellular matrix after TGFβ treatment. Additionally, knockdown of RASSF10 or ASPP2 induced constitutive phosphorylation of SMAD2 (Smad family member 2). Moreover, we found that epigenetic reduction of RASSF10 levels correlates with tumor progression and poor survival in human cancers. Our study indicates that RASSF10 acts a TGFβ target gene and negatively regulates cell growth and invasion through ASPP2. This data suggests that epigenetic loss of RASSF10 contributes to tumorigenesis by promoting EMT induced by TGFβ.

Metabolic reprogram associated with epithelial-mesenchymal transition in tumor progression and metastasis

Epithelial-mesenchymal Transition (EMT) is a de-differentiation program that imparts tumor cells with the phenotypic and cellular plasticity required for drug resistance, metastasis, and recurrence. This dynamic and reversible events is governed by a network of EMT-transcription factors (EMT-TFs) through epigenetic regulation. Many chromatin modifying-enzymes utilize metabolic intermediates as cofactors or substrates; this suggests that EMT is subjected to the metabolic regulation. Conversely, EMT rewires metabolic program to accommodate cellular changes during EMT. Here we summarize the latest findings regarding the epigenetic regulation of EMT, and discuss the mutual interactions among metabolism, epigenetic regulation, and EMT. Finally, we provide perspectives of how this interplay contributes to cellular plasticity, which may result in the clinical manifestation of tumor heterogeneity.

The YB-1/EZH2/amphiregulin signaling axis mediates LPA-induced breast cancer cell invasion

Lysophosphatidic acid (LPA) has been known to induce epithelial-mesenchymal transition (EMT) to stimulate cancer cell invasion, and resveratrol (3,5,4'-trans-trihydroxystilbene; REV) suppresses the invasion and metastasis of various cancers. The current study aimed to identify the underlying mechanism by which LPA aggravates breast cancer cell invasion and the reversal of this phenomenon. Immunoblotting and quantitative RT-PCR analysis revealed that LPA induces amphiregulin (AREG) expression. Silencing of Y-box binding protein 1 (YB-1) or enhancer of zeste homolog 2 (EZH2) expression efficiently inhibited LPA-induced AREG expression. In addition, transfection of the cells with YB-1 siRNA abrogated LPA-induced EZH2 and AREG expression, leading to attenuation of breast cancer cell invasion. Furthermore, we observed that both REV and 5-fluorouracil (5-Fu) significantly reduce LPA-induced YB-1 phosphorylation and subsequent breast cancer invasion. Importantly, combined treatment of REV with 5-Fu showed more significant inhibition of LPA-induced breast cancer invasion compared to single treatment. Therefore, our data demonstrate that the YB-1/EZH2 signaling axis mediates LPA-induced AREG expression and breast cancer cell invasion and its inhibition by REV and 5-Fu, providing potential therapeutic targets and inhibition of breast cancer.

Regulation of tumor cell - Microenvironment interaction by the autotaxin-lysophosphatidic acid receptor axis

The lipid mediator lysophosphatidic acid (LPA) in biological fluids is primarily produced by cleavage of lysophospholipids by the lysophospholipase D enzyme Autotaxin (ATX). LPA has been identified and abundantly detected in the culture medium of various cancer cell types, tumor effusates, and ascites fluid of cancer patients. Our current understanding of the physiological role of LPA established its role in fundamental biological responses that include cell proliferation, metabolism, neuronal differentiation, angiogenesis, cell migration, hematopoiesis, inflammation, immunity, wound healing, regulation of cell excitability, and the promotion of cell survival by protecting against apoptotic death. These essential biological responses elicited by LPA are seemingly hijacked by cancer cells in many ways; transcriptional upregulation of ATX leading to increased LPA levels, enhanced expression of multiple LPA GPCR subtypes, and the downregulation of its metabolic breakdown. Recent studies have shown that overexpression of ATX and LPA GPCR can lead to malignant transformation, enhanced proliferation of cancer stem cells, increased invasion and metastasis, reprogramming of the tumor microenvironment and the metastatic niche, and development of resistance to chemo-, immuno-, and radiation-therapy of cancer. The fundamental role of LPA in cancer progression and the therapeutic inhibition of the ATX-LPA axis, although highly appealing, remains unexploited as drug development to these targets has not reached into the clinic yet. The purpose of this brief review is to highlight some unique signaling mechanisms engaged by the ATX-LPA axis and emphasize the therapeutic potential that lies in blocking the molecular targets of the LPA system.

LPA-induced migration of ovarian cancer cells requires activation of ERM proteins via LPA1 and LPA2

Lysophosphatidic acid (LPA) has been implicated in the pathology of human ovarian cancer. This phospholipid elicits a wide range of cancer cell responses, such as proliferation, trans-differentiation, migration, and invasion, via various G-protein-coupled LPA receptors (LPARs). Here, we explored the cellular signaling pathway via which LPA induces migration of ovarian cancer cells. LPA induced robust phosphorylation of ezrin/radixin/moesin (ERM) proteins, which are membrane-cytoskeleton linkers, in the ovarian cancer cell line OVCAR-3. Among the LPAR subtypes expressed in these cells, LPA₁ and LPA₂, but not LPA₃, induced phosphorylation of ERM proteins at their C-termini. This phosphorylation was dependent on the Gα_12/13/RhoA pathway, but not on the Gα_q/Ca²⁺/PKC or Gα_s/adenylate cyclase/PKA pathway. The activated ERM proteins mediated cytoskeletal reorganization and formation of membrane protrusions in OVCAR-3 cells. Importantly, LPA-induced migration of OVCAR-3 cells was completely abolished not only by gene silencing of LPA₁ or LPA₂, but also by overexpression of a dominant negative ezrin mutant (ezrin-T567A). Taken together, this study demonstrates that the LPA₁/LPA₂/ERM pathway mediates LPA-induced migration of ovarian cancer cells. These findings may provide a potential therapeutic target to prevent metastatic progression of ovarian cancer.

Dynamic relocalization of NHERF1 mediates chemotactic migration of ovarian cancer cells toward lysophosphatidic acid stimulation

NHERF1/EBP50 (Na⁺/H⁺ exchanger regulating factor 1; Ezrin-binding phosphoprotein of 50 kDa) organizes stable protein complexes beneath the apical membrane of polar epithelial cells. By contrast, in cancer cells without any fixed polarity, NHERF1 often localizes in the cytoplasm. The regulation of cytoplasmic NHERF1 and its role in cancer progression remain unclear. In this study, we found that, upon lysophosphatidic acid (LPA) stimulation, cytoplasmic NHERF1 rapidly translocated to the plasma membrane, and subsequently to cortical protrusion structures, of ovarian cancer cells. This movement depended on direct binding of NHERF1 to C-terminally phosphorylated ERM proteins (cpERMs). Moreover, NHERF1 depletion downregulated cpERMs and further impaired cpERM-dependent remodeling of the cell cortex, suggesting reciprocal regulation between these proteins. The LPA-induced protein complex was highly enriched in migratory pseudopodia, whose formation was impaired by overexpression of NHERF1 truncation mutants. Consistent with this, NHERF1 depletion in various types of cancer cells abolished chemotactic cell migration toward a LPA gradient. Taken together, our findings suggest that the high dynamics of cytosolic NHERF1 provide cancer cells with a means of controlling chemotactic migration. This capacity is likely to be essential for ovarian cancer progression in tumor microenvironments containing LPA.

Epithelial-to-Pericyte Transition in Cancer

During epithelial-to-mesenchymal transition (EMT), cells lose epithelial characteristics and acquire mesenchymal properties. These two processes are genetically separable and governed by distinct transcriptional programs, rendering the EMT outputs highly heterogeneous. Our recent study shows that the mesenchymal products generated by EMT often express multiple pericyte markers, associate with and stabilize blood vessels to fuel tumor growth, thus phenotypically and functionally resembling pericytes. Therefore, some EMT events represent epithelial-to-pericyte transition (EPT). The serum response factor (SRF) plays key roles in both EMT and differentiation of pericytes, and may inherently confer the pericyte attributes on EMT cancer cells. By impacting their intratumoral location and cell surface receptor expression, EPT may enable cancer cells to receive and respond to angiocrine factors produced by the vascular niche, and develop therapy resistance.

Relevance of epithelial-to-pericyte transition in cancer

The relevance of epithelial-to-mesenchymal transition (EMT) in cancer is still under debate. Recently, we reported that EMT bestows key pericyte properties on cancer cells and may thus represent epithelial-to-pericyte transition (EPT). Carcinoma cells undergo EPT to stabilize blood vessels and fuel primary tumor growth. Association of EPT cancer cells with vascular niches may also promote resistance to therapy.

Epithelial-to-mesenchymal transition confers pericyte properties on cancer cells

Carcinoma cells can acquire increased motility and invasiveness through epithelial-to-mesenchymal transition (EMT). However, the significance of EMT in cancer metastasis has been controversial, and the exact fates and functions of EMT cancer cells in vivo remain inadequately understood. Here, we tracked epithelial cancer cells that underwent inducible or spontaneous EMT in various tumor transplantation models. Unlike epithelial cells, the majority of EMT cancer cells were specifically located in the perivascular space and closely associated with blood vessels. EMT markedly activated multiple pericyte markers in carcinoma cells, in particular PDGFR-β and N-cadherin, which enabled EMT cells to be chemoattracted towards and physically interact with endothelium. In tumor xenografts generated from carcinoma cells that were prone to spontaneous EMT, a substantial fraction of the pericytes associated with tumor vasculature were derived from EMT cancer cells. Depletion of such EMT cells in transplanted tumors diminished pericyte coverage, impaired vascular integrity, and attenuated tumor growth. These findings suggest that EMT confers key pericyte attributes on cancer cells. The resulting EMT cells phenotypically and functionally resemble pericytes and are indispensable for vascular stabilization and sustained tumor growth. This study thus proposes a previously unrecognized role for EMT in cancer.

Neuromedin U is upregulated by Snail at early stages of EMT in HT29 colon cancer cells

BACKGROUND

The epithelial-mesenchymal transition (EMT) is considered a core process that facilitates the escape of cancer cells from the primary tumor site. The transcription factor Snail was identified as a key regulator of EMT; however, the cascade of regulatory events leading to metastasis remains unknown and new predictive markers of the process are awaited.

METHODS

Gene expressions were analysed using real-time PCR, protein level by Western immunoblotting and confocal imaging. The motility of the cells was examined using time-lapse microscopy. Affymetrix GeneChip Human Genome U133 Plus 2.0 analysis was performed to identify transcriptomic changes upon Snail. Snail silencing was performed using siRNA nucleofection. NMU detection was performed by ELISA.

RESULTS

HT29 cells overexpressing Snail showed changed morphology, functions and transcriptomic profile indicating EMT induction. Changes in expression of 324 genes previously correlated with cell motility were observed. Neuromedin U was the second highest upregulated gene in HT29-Snail cells. This increase was validated by real-time PCR. Additionally elevated NMU protein was detected by ELISA in cell media.

CONCLUSIONS

These results show that Snail in HT29 cells regulates early phenotype conversion towards an intermediate epithelial state. We provided the first evidence that neuromedin U is associated with Snail regulatory function of metastatic induction in colon cancer cells.

GENERAL SIGNIFICANCE

We described the global, early transcriptomic changes induced through Snail in HT29 colon cancer cells and suggested NMU involvement in this process.

GSTZ1 expression and chloride concentrations modulate sensitivity of cancer cells to dichloroacetate

Dichloroacetate (DCA), commonly used to treat metabolic disorders, is under investigation as an anti-cancer therapy due to its ability to reverse the Warburg effect and induce apoptosis in tumor cells. While DCA's mechanism of action is well-studied, other factors that influence its potential as a cancer treatment have not been thoroughly investigated. Here we show that expression of glutathione transferase zeta 1 (GSTZ1), the enzyme responsible for conversion of DCA to its inactive metabolite, glyoxylate, is downregulated in liver cancer and upregulated in some breast cancers, leading to abnormal expression of the protein. The cellular concentration of chloride, an ion that influences the stability of GSTZ1 in the presence of DCA, was also found to be abnormal in tumors, with consistently higher concentrations in hepatocellular carcinoma than in surrounding non-tumor tissue. Finally, results from experiments employing two- and three-dimensional cultures of HepG2 cells, parental and transduced to express GSTZ1, demonstrate that high levels of GSTZ1 expression confers resistance to the effect of high concentrations of DCA on cell viability. These results may have important clinical implications in determining intratumoral metabolism of DCA and, consequently, appropriate oral dosing.

Regulation of metastatic ability and drug resistance in pulmonary adenocarcinoma by matrix rigidity via activating c-Met and EGFR

Lung fibrosis is a poor prognostic factor for pulmonary adenocarcinoma, and the effect of a rigid microenvironment on cancer behavior is unclear. We cultured A549 cells on matrices of 0.2, 2, and 25 kPa to mimic the rigidities of normal lung parenchyma, progressive fibrotic change, and lung fibrosis, respectively. Lung tissue from patients with pulmonary adenocarcinoma was used to confirm the in vitro findings. Increased matrix rigidity promoted cell proliferation and upregulated the epidermal growth factor receptor (EGFR), hepatocyte growth factor receptor (c-Met), and Snail expression in A549 cells. A549 cells became more resistant to the EGFR inhibitor (Erlotinib) and c-Met inhibitor (PHA-665752) when matrix rigidity increased; however, a high concentration of PHA-665752 reversed the rigidity-induced morphological pleomorphism. In human lung tissue, expression of type I collagen was more consistent with clinical fibrosis than the expression of alpha-smooth muscle antibody was. c-Met- and Snail-expressing tumor cells, rather than EGFR-experssing cells, were localized with lung parenchyma rich in type I collagen. Our findings suggest that c-Met causes the rigidity-induced biophysical reaction in pulmonary adenocarcinoma. Treatment targeting both EGFR and c-Met should be considered for patients with lung fibrosis and who are abundant type I collagen expression in the tumor mass.

Alteration of angiogenesis in Helicobacter heilmannii-induced mucosa-associated lymphoid tissue lymphoma: interaction with c-Met and hepatocyte growth factor

BACKGROUND AND AIM

The hepatocyte growth factor (HGF)/c-Met pathway has attracted attention in the formation of malignant tumors, as HGF secreted from the microcirculatory components as well as residing macrophages has been suggested to act on the c-Met receptors of cancer cells to decrease apoptosis and increase proliferation, invasion, and metastasis. The present study was undertaken to elucidate the interaction of the gastric, hepatic, and pulmonary mucosa-associated lymphoid tissue (MALT) lymphoma induced by Helicobacter heilmannii infection with c-Met and HGF.

METHODS

C57BL/6 female mice, infected with H. heilmannii for 3 months were used. The localization of the HGF, c-Met, and HGF activator immunoreactivities was observed by the indirect immunohistochemical methods. In addition, the effect of c-Met antibody and c-Met inhibitor, PHA-665752, was also investigated.

RESULTS

c-Met immunoreactivity was found in the lymphocytes composing the MALT lymphoma, and HGF immunoreactivity was recognized mostly in the endothelial cells and macrophages in the MALT lymphoma. HGFA was localized on mesenchymal cells other than the lymphocytes. The administration of the antibody against c-Met or the c-Met inhibitor to the infected mice induced the significant suppression of hepatic and pulmonary MALT lymphoma, while the gastric MALT lymphoma showed only a tendency to decrease in size, while the active caspase 3 positive cells markedly decreased in the gastric, hepatic, and pulmonary MALT lymphoma after the treatment with the c-Met antibody or the c-Met antagonist.

CONCLUSIONS

HGF and c-Met pathway were suggested to contribute to the lymphomagenesis in the MALT lymphoma after H. heilmannii infection.

Aberrant expression and potential therapeutic target of lysophosphatidic acid receptor 3 in triple-negative breast cancers

Triple receptor-negative breast cancers (TNBCs) generally have poor prognoses because of the loss of therapeutic targets. As lysophosphatidic acid (LPA) receptor signaling has been shown to affect breast cancer initiation and progression, we try to evaluate the potential roles of LPA receptors in TNBCs. We examined mRNA and protein expressions of LPA receptors 1-3, using quantitative real-time PCR and immunohistochemical analyses in normal (n = 37), benign disease (n = 55), and breast cancer tissues (n = 82). Carcinomas expressed higher levels of LPA₂ and LPA₃ mRNAs (0.17 ± 0.070 and 0.05 ± 0.023, respectively) than did normal breast tissue (0.13 ± 0.072 and 0.02 ± 0.002, respectively). Enhanced immunohistochemical staining for LPA₂ and LPA₃ protein was also consistently observed in carcinomas. The LPA₃ overexpression was associated with lymph node metastases, and absence of estrogen receptor, progesterone receptors, and human epidermal growth factor receptor 2 expression. TNBC tissues and cell lines showed the highest LPA₃ expression compared with luminal-type A and B breast cancers. Suppression of LPA₃ by shRNA did not influence cell growth in breast cancer cells. However, the migration and invasion of TNBC cells were significantly inhibited by LPA₃-shRNA or inhibitor, which had no or less effect on normal and non-TNBC breast cells. In conclusion, our data indicated that the expression of LPA receptor 3 was increased in human TNBCs and is associated with tumor metastatic ability, and this implies that LPA₃ is a potential therapeutic target for the treatment of TNBCs.

Overexpression of c-Met increases the tumor invasion of human prostate LNCaP cancer cells in vitro and in vivo

c-Met is a transmembrane tyrosine kinase receptor that may be activated by hepatocyte growth factor, an inducer of epithelial-mesenchymal transition (EMT), to regulate the associated downstream gene expression. This process is critical to cell migration in normal and pathological conditions. In the present study, the function of c-Met in the process of EMT was investigated in prostate cancer. Initially, a c-Met stable expression cell line was constructed using EMT- and c-Met-negative LNCaP prostate cancer cells. Following the identification of c-Met in the transfected cells, the changes in EMT, phosphatidylinositol 3-kinase (PI3K) and extracellular signal-regulated kinase pathway biomarkers were determined by western blot analysis. MTT, soft agar and Transwell assays, and xenograft studies were used to investigate the effects of c-Met on the proliferation, migration and tumorigenicity of LNCaP cells. The results of the present study revealed downregulation of E-cadherin and upregulation of vimentin in LNCaP-Met cells. The results demonstrated that c-Met enhanced proliferation, migration and tumorigenicity capacity when compared with LNCaP and LNCaP-pcDNA3.1 cells. Furthermore, these EMT-like changes were mediated via the PI3K and mitogen-activated protein kinase signaling pathways. The present study clearly demonstrates a crucial function for c-Met in EMT development in prostate cancer. c-Met-targeted treatment may be an effective adjuvant therapy for improving survival rates in patients with prostate cancer.

Signaling mechanisms that suppress the cytostatic actions of rapamycin

While rapamycin and the "rapalogs" Everolimus and Temsirolimus have been approved for clinical use in the treatment of a number of forms of cancer, they have not met overarching success. Some tumors are largely refractory to rapamycin treatment, with some even undergoing an increase in growth rates. However the mechanisms by which this occurs are largely unknown. The results presented here reveal novel cell-signaling mechanisms that may lead to this resistance. The absence of TGFβ signaling results in resistance to rapamycin. Additionally, we observed that treatment of some cancer cell lines with rapamycin and its analogs not only potentiates mitogenic signaling and proliferation induced by HGF, but also stimulates the pro-survival kinase Akt. Together, the data show that the effectiveness of rapamycin treatment can be influenced by a number of factors and bring to light potential biomarkers for the prediction of responsiveness to treatment, and suggest combination therapies to optimize rapalog anticancer efficacy.

Epithelial-to-mesenchymal transition rewires the molecular path to PI3K-dependent proliferation

Tumors showing evidence of epithelial-to-mesenchymal transition (EMT) have been associated with metastasis, drug resistance, and poor prognosis. Heterogeneity along the EMT spectrum is observed between and within tumors. To develop effective therapeutics, a mechanistic understanding of how EMT affects the molecular requirements for proliferation is needed. We found that although cells use phosphoinositide 3-kinase (PI3K) for proliferation in both the epithelial and mesenchymal states, EMT rewires the mechanism of PI3K pathway activation. In epithelial cells, autocrine ERBB3 activation maintains PI3K signaling, whereas after EMT, downregulation of ERBB3 disrupts autocrine signaling to PI3K. Loss of ERBB3 leads to reduced serum-independent proliferation after EMT that can be rescued through reactivation of PI3K by enhanced signaling from p110α, ERBB3 reexpression, or growth factor stimulation. In vivo, we demonstrate that PIK3CA expression is upregulated in mesenchymal tumors with low levels of ERBB3. This study defines how ERBB3 downregulation after EMT affects PI3K-dependent proliferation.

SIGNIFICANCE

This study describes a mechanism through which EMT transition alters the proliferative potential of cells by modulating ERBB3 expression. Furthermore, it demonstrates the potential for multiple molecular routes to drive proliferation in different cell states, illustrating how changes in EMT status can rewire signaling upstream of cell proliferation.

Lysophosphatidic acid (LPA) signalling in cell migration and cancer invasion: a focussed review and analysis of LPA receptor gene expression on the basis of more than 1700 cancer microarrays

Lysophosphatidic acid (LPA) is a ubiquitously present signalling molecule involved in diverse cellular processes such as cell migration, proliferation and differentiation. LPA acts as an autocrine and/or paracrine signalling molecule via different G-protein-coupled LPA receptors (LPARs) that trigger a broad range of intracellular signalling cascades, especially the RHOA pathway. Mounting evidence suggests a crucial role of the LPA/LPAR-axis in cancer cell metastasis and promising studies are underway to investigate the therapeutic potential of LPAR-antagonists. This review summarises current knowledge on how LPA promotes cytoskeletal remodelling to enhance the migratory and invasive properties of cells, which may ultimately contribute to cancer metastasis. Furthermore, we provide comprehensive transcriptome analyses of published microarrays of more than 350 normal tissues and more than 1700 malignant tissues to define the expression signatures of LPARs and the LPA-generating enzymes autotaxin (ATX) and lipase member 1 (LIPI). These analyses demonstrate that ATX is highly expressed in a variety of carcinomas and sarcomas, whereas LIPI is almost exclusively overexpressed in highly aggressive Ewing's sarcomas, which underscores the potential contribution of LPA in metastatic disease. In addition, these analyses show that different cancer entities display distinct expression signatures of LPARs that distinguish them from one another. Finally, we discuss current approaches to specifically target the LPA/LPAR circuits in experimental cancer therapy.

Modulation of c-Met signaling and cellular sensitivity to radiation: potential implications for therapy

The c-Met/hepatocyte growth factor receptor and its family members are known to promote cancer cell migration and invasion. Signaling within and beyond this pathway contributes to the systemic spread of metastases through induction of the epithelial-mesenchymal transition, a process also implicated in mediating resistance to current anticancer therapies, including radiation. Induction of c-Met has also been observed after irradiation, suggesting that c-Met participates in radiation-induced disease progression through the epithelial-mesenchymal transition. Therefore, c-Met inhibition is an attractive target for potentially mitigating radiation resistance. This article summarizes key findings regarding crosstalk between radiotherapy and c-Met and discusses studies performed to date in which c-Met inhibition was used as a strategy to increase cellular radiosensitivity.