Loss of MTSS1 results in increased metastatic potential in pancreatic cancer

Metastasis suppressor genes in clinical practice: are they druggable?

Since the identification of NM23 (now called NME1) as the first metastasis suppressor gene (MSG), a small number of other gene products and non-coding RNAs have been identified that suppress specific parameters of the metastatic cascade, yet which have little or no ability to regulate primary tumor initiation or maintenance. MSG can regulate various pathways or cell biological functions such as those controlling mitogen-activated protein kinase pathway mediators, cell-cell and cell-extracellular matrix protein adhesion, cytoskeletal architecture, G-protein-coupled receptors, apoptosis, and transcriptional complexes. One defining facet of this gene class is that their expression is typically downregulated, not mutated, in metastasis, such that any effective therapeutic intervention would involve their re-expression. This review will address the therapeutic targeting of MSG, once thought to be a daunting task only facilitated by ectopically re-expressing MSG in metastatic cells in vivo. Examples will be cited of attempts to identify actionable oncogenic pathways that might suppress the formation or progression of metastases through the re-expression of specific metastasis suppressors.

Genes with dual proto-oncogene and tumor suppressor gene activities are frequently altered by protein losses in colon cancers

Cancer genes are largely categorized into tumor suppressor gene (TSG) and proto-oncogene, but many have dual activities depending on the cellular context. In the present study, we analyzed DYRK1B, ESRP1, MTSS1, ADAMTS1, and INPP5F genes known to possess the dual activities in sporadic colon cancers (CCs). By the mutation analysis, we identified DYRK1B, ESRP1, MTSS1, ADAMTS1, and INPP5F frameshift mutations in 2, 2, 3, 3, and 1 CCs in instability-high (MSI-H) cases (1.1-3.2% of MSI-H CCs), respectively, but not microsatellite stable (MSS) cases. One CC showed regional heterogeneous mutations (RHM) of ESRP1 mutation. Immunohistochemistry identified protein expression of ESRP1, MTSS1, and ADAMTS1 in the CCs, revealing that approximately 30% of CCs lost the protein expression irrespective of the MSI status. Our study showed that dual TSG and proto-oncogene genes DYRK1B, ESRP1, MTSS1, ADAMTS1, and INPP5F harbored low incidences of inactivating mutations, but that the protein losses were frequent in CCs. Our study suggests a possibility that the dual-function genes could be altered mainly at the expression level, which might contribute to CC pathogenesis.

Downregulation of MTSS1 in acute myeloid leukemia is associated with a poor prognosis, chemotherapy resistance, and disease aggressiveness

Despite recent approval of targeted drugs for acute myeloid leukemia (AML) therapy, chemotherapy with cytosine arabinoside and anthracyclines remains an important pillar of treatment. Both primary and secondary resistance are frequent and associated with poor survival, yet the underlying molecular mechanisms are incompletely understood. In previous work, we identified genes deregulated between diagnosis and relapse of AML, corresponding to therapy naïve and resistant states, respectively. Among them was MTSS1, whose downregulation is known to enhance aggressiveness of solid tumors. Here we show that low MTSS1 expression at diagnosis was associated with a poor prognosis in AML. MTSS1 expression was regulated by promoter methylation, and reduced by cytosine arabinoside and the anthracycline daunorubicin. Experimental downregulation of MTSS1 affected the expression of numerous genes. It induced the DNA damage response kinase WEE1, and rendered human AML cell lines more resistant to cytosine arabinoside, daunorubicin, and other anti-cancer drugs. Mtss1 knockdown in murine MLL-AF9-driven AML substantially decreased disease latency, and increased leukemic burden and ex vivo chemotherapy resistance. In summary, low MTSS1 expression represents a novel factor contributing to disease aggressiveness, therapy resistance, and poor outcome in AML.

Metastasis suppressor 1 interacts with α-actinin 4 to affect its localization and regulate formation of membrane ruffling

Membrane ruffling plays an important role in the directed cell migration and escape of tumor cells from the monolayer. Metastasis suppressor 1 (MTSS1), also known as missing in metastasis, has been implicated in cell morphology, motility, metastasis, and development. Here, the dynamic interaction proteins associated with MTSS1 and involved in membrane ruffling were determined by cross-linking and mass spectrometry analysis. We identified α-actinin 4 (ACTN4) as an interacting protein and confirmed a direct interaction between MTSS1 and ACTN4. Moreover, co-expression of MTSS1 in fibroblasts recruited cytoplasmic ACTN4 to the cell periphery, at which point ruffling became thick and rigid. In MCF-7 cells, MTSS1 knockdown did not show an obvious effect on the cell shape or the distribution of endogenous ACTN4; however, ACTN4 overexpression transformed cell morphology from an epidermal- to a fibroblast-like shape, and further MTSS1 depletion significantly increased the ratio of fibroblast cells exhibiting prominent ruffling. Furthermore, biochemical data suggested that MTSS1 cross-linking with ACTN4 induced the formation of actin fiber bundles into more organized structures in vitro. These data indicated that MTSS1 might recruit cytoplasmic ACTN4 to the cell periphery and regulate cytoskeleton dynamics to restrict its performance in membrane ruffling.

Gene expression changes contribute to stemness and therapy resistance of relapsed acute myeloid leukemia: roles of SOCS2, CALCRL, MTSS1, and KDM6A

Relapse is associated with therapy resistance and is a major cause of death in acute myeloid leukemia (AML). It is thought to result from the accretion of therapy-refractory leukemic stem cells. Genetic and transcriptional changes that are recurrently gained at relapse are likely to contribute to the increased stemness and decreased therapy responsiveness at this disease stage. Despite the recent approval of several targeted drugs, chemotherapy with cytosine arabinoside and anthracyclines is still the mainstay of AML therapy. Accordingly, a number of studies have investigated genetic and gene expression changes between diagnosis and relapse of patients subjected to such treatment. Genetic alterations recurrently acquired at relapse were identified, but were restricted to small proportions of patients, and their functional characterization is still largely pending. In contrast, the expression of a substantial number of genes was altered consistently between diagnosis and recurrence of AML. Recent studies corroborated the roles of the upregulation of SOCS2 and CALCRL and of the downregulation of MTSS1 and KDM6A in therapy resistance and/or stemness of AML. These findings spur the assumption that functional investigations of genes consistently altered at recurrence of AML have the potential to promote the development of novel targeted drugs that may help to improve the outcome of this currently often fatal disease.

UCHL3 promotes aerobic glycolysis of pancreatic cancer through upregulating LDHA expression

BACKGROUND

Aerobic glycolysis has a pivotal role in the carcinogenic process. The current understanding of the functional role and mechanism of UCHL3-related aerobic glycolysis in pancreatic cancer is far from comprehensive, therefore requires an in-depth analysis on this aspect.

METHODS

In the present research, the expressions of ubiquitin carboxyl-terminal hydrolase L3 (UCHL3), lactate dehydrogenase A (LDHA) and Forkhead box protein M1 (FOXM1) were detected by qRT-PCR, Western blot and immunohistochemistry. The effects of UCHL3 knockdown or overexpression on pancreatic cancer cells were examined by determining cell viability and colony formation. Aerobic glycolysis was assessed according to glucose uptake, lactic acid production, and lactate dehydrogenase (LDH) activity. Dual-luciferase reporter assay was performed to detect LDHA promoter activity.

RESULTS

The results showed that UCHL3 expression was significantly increased in the pancreatic cancer tissues and cells, and that knocking down UCHL3 noticeably inhibited cell viability and aerobic glycolysis. Further investigations revealed that LDHA expression was promoted by UCHL3 and could be reduced by shFOXM1, and that low-expressed LDHA partly reversed the inhibition of aerobic glycolysis induced by overexpressed UCHL3.

CONCLUSIONS

To conclude, this study demonstrates that UCHL3 plays a carcinogenic role by promoting aerobic glycolysis in pancreatic cancer, suggesting that UCHL3 may be a potential diagnostic and therapeutic target for the treatment of cancer.

Gene expression profiling of cultured mouse testis fragments treated with ethinylestradiol

The assessment of xenobiotic-induced testicular toxicity is important in drug development. Nonetheless, in vitro models to test drugs and chemicals that may cause testicular toxicity are lacking, requiring the continued use of animal models for those studies. We previously evaluated an in vitro mouse testis organ culture system using ethinylestradiol (EE), a well-studied testicular toxicant, and demonstrated a dose-dependent relationship between adverse effects to germ cell differentiation and increasing EE concentrations. However, we terminated that study after 20 days of culture due to oxygen deficiency during germ cell differentiation. Therefore, in the current study, we aimed to identify gene(s) with potential for supporting the histopathological evaluations of testicular toxicity using in vitro testis organ culture system. We cultured testis fragments obtained from mice at postnatal day (PND) 5 in α-Minimal Essential Medium containing 40 mg/mL AlbuMAX^™ I and treated them with 0.01 or 1 nM EE on day 1 of culture. On day 20, we collected testis fragments for RNA sequencing analysis and quantitative polymerase chain reaction (qPCR). We found that phospholipase C, zeta 1 and testis-specific serine kinase 4 genes, that are involved in spermatogenesis and predominantly expressed in the testis, were significantly reduced in testis fragments treated with the highest concentration of EE. Also, cytochrome P450, family 26, subfamily b, polypeptide 1 (Cyp26b1) and interleukin 16 (Il16) were up-regulated in the highest EE-treated groups. Further studies are needed to confirm the variations of these gene expression using other testicular toxicants.

The transcribed pseudogene RPSAP52 enhances the oncofetal HMGA2-IGF2BP2-RAS axis through LIN28B-dependent and independent let-7 inhibition

One largely unknown question in cell biology is the discrimination between inconsequential and functional transcriptional events with relevant regulatory functions. Here, we find that the oncofetal HMGA2 gene is aberrantly reexpressed in many tumor types together with its antisense transcribed pseudogene RPSAP52. RPSAP52 is abundantly present in the cytoplasm, where it interacts with the RNA binding protein IGF2BP2/IMP2, facilitating its binding to mRNA targets, promoting their translation by mediating their recruitment on polysomes and enhancing proliferative and self-renewal pathways. Notably, downregulation of RPSAP52 impairs the balance between the oncogene LIN28B and the tumor suppressor let-7 family of miRNAs, inhibits cellular proliferation and migration in vitro and slows down tumor growth in vivo. In addition, high levels of RPSAP52 in patient samples associate with a worse prognosis in sarcomas. Overall, we reveal the roles of a transcribed pseudogene that may display properties of an oncofetal master regulator in human cancers.

MicroRNA-182-5p Modulates Oral Squamous Cell Carcinoma Migration and Invasion Via Targeting MTSS1 Gene

Oral squamous cell carcinoma (OSCC) characterized with invasive growth, local metastasis and later stage diagnosis was a common malignancy in head and neck region. The aim of this study was to explore the relationship between miR-182-5p and OSCC, which will contribute to find potential biomarker for OSCC metastasis. MiR-182-5p expression level was detected by the quantitative real-time PCR (qRT-PCR). Cell migration and invasion ability were examined by scratch and transwell assay. Loss-of function together with luciferase reporter assay were used to verify the miR-182-5p modulated OSCC cells migration and metastasis was mediated by MTSS1. The expression of MTSS1 protein was examined by western blotting. MiR-182-5p up-regulated in OSCC, was involved in the migration and invasion of OSCC and the increased miR-182-5p expression was correlated with lower OSCC differentiation grade, higher T and N stage. Bioinformatics analysis predicted MTSS1 gene was a potential target of miR-182-5p. Following co-transfection, qRT-PCR, luciferase activities assay and western blotting confirmed that MTSS1 gene was a direct target of miR-182-5p and silence of MTSS1 could reverse the effects of miR-182-5p on OSCC migration and invasion. MiR-182-5p was up-regulated in OSCC and the ability of miR-182-5p to promote MTSS1 repression may precipitate in the OSCC through bypassing cell migration and invasion control.

Cancer stem cells and fibroblast niche cross talk in an in-vitro oral dysplasia model

Understanding the cellular interactions during oral carcinogenesis has the potential to identify novel prognostic and therapeutic targets. This study aimed at investigating the cancer stem cell (CSC)-fibroblast niche interactions using in-vitro dysplastic cell line models developed from different stages of 4NQO-induced oral carcinogenic mice model. The spontaneously transformed epithelial cells (DysMSCTR6, 14 and 16) were developed from three time points (mild/moderate/severe), while two fibroblast cell lines (FibroMSCTR12, 16) were developed from moderate and severe dysplastic tissue. The epithelial (Epcam+/Ck+) and the fibroblast cell lines (Vimentin+/α-SMA+/Ck-) were authenticated and assessment of cells representing progressive grades of dysplastic severity indicated a significant increase in dysplastic marker profile (P < 0.05). Evaluation of the CSC characteristics showed that an increase in expression of Cd133, Cd44, Aldh1a1, Notch1, and Sox2 was accompanied by an increase in migratory (P > 0.05) and colony formation capacity (P > 0.005). Targeting Notch1 (GSI inhibitor PZ0187; 30 μM), showed a significant reduction in cell proliferation capacity (P < 0.05) and in the dysplastic marker profile. Further, Notch1 inhibition resulted in down regulation of Cd133 and Aldh1a 1 (P < 0.05) and a complete abrogation of colony formation ability (P < 0.0001). The effect of niche interactions evaluated using FibroMSCTR12-conditioned media studies, revealed an enrichment of ALDH1A1+ cells (P < 0.05), induction of spheroid formation ability (P < 0.0001) and increased proliferation capacity (3.7 fold; P < 0.005). Although PZ0187 reduced cell viability by ∼40%, was unable to abrogate the conditioned-media induced increase in proliferation capacity completely. This study reports a Notch-1 dependent enrichment of CSC properties during dysplastic progression and a Notch-1 independent dysplastic cell-fibroblast interaction during oral carcinogenesis.

Metastasis suppressor protein 1 regulated by PTEN suppresses invasion, migration, and EMT of gastric carcinoma by inactivating PI3K/AKT signaling

Epithelial-mesenchymal transition (EMT) is a crucial event for cancer progression and metastasis. Metastasis suppressor protein 1 (MTSS1) is a metastasis suppressor in several cancers. In this study, we elucidated the potential physiological function of MTSS1 in the invasion and migration of gastric cancer (GC), and its distinct role in EMT and subsequently determined the potential molecular mechanism. We observed that MTSS1 expression was downregulated in GC tissues and several GC cell lines (SGC-7901, MGC-803, MKN-28, MKN-45, and BGC-823). Importantly, forced expression of MTSS1 drastically diminished the cell viability in both SGC-7901 and MKN-45 cells. Moreover, overexpression of MTSS1 attenuated the invasion ability of these two cell lines. In addition to the invasive capability, introduction of MTSS1 led to a loss of migratory potential. Furthermore, augmentation of MTSS1 exhibited the typical EMT phenotype switch, accompanied by enhanced the expression of vimentin and N-cadherin and reduced E-cadherin expression. Interestingly, MTSS1 also repressed transforming growth factor beta 1 (TGF-β1)-induced EMT. Our mechanistic investigations revealed that MTSS1 was positively regulated by the phosphatase and tensin homolog (PTEN), and it functioned as a tumor suppressor, possibly by inactivating the phosphoinositide 3-kinase (PI3K)/v-akt murine thymoma viral oncogene (AKT) pathway in GC cells. Collectively, our data provide insight into an important role for MTSS1 in suppressing tumor cell invasion, migration and EMT, which indicates that MTSS1 may act as a prospective prognostic biological marker and a promising therapeutic target for GC.

MTSS1 and SCAMP1 cooperate to prevent invasion in breast cancer

Cell-cell adhesions constitute the structural "glue" that retains cells together and contributes to tissue organisation and physiological function. The integrity of these structures is regulated by extracellular and intracellular signals and pathways that act on the functional units of cell adhesion such as the cell adhesion molecules/adhesion receptors, the extracellular matrix (ECM) proteins and the cytoplasmic plaque/peripheral membrane proteins. In advanced cancer, these regulatory pathways are dysregulated and lead to cell-cell adhesion disassembly, increased invasion and metastasis. The Metastasis suppressor protein 1 (MTSS1) plays a key role in the maintenance of cell-cell adhesions and its loss correlates with tumour progression in a variety of cancers. However, the mechanisms that regulate its function are not well-known. Using a system biology approach, we unravelled potential interacting partners of MTSS1. We found that the secretory carrier-associated membrane protein 1 (SCAMP1), a molecule involved in post-Golgi recycling pathways and in endosome cell membrane recycling, enhances Mtss1 anti-invasive function in HER2+/ER-/PR- breast cancer, by promoting its protein trafficking leading to elevated levels of RAC1-GTP and increased cell-cell adhesions. This was clinically tested in HER2 breast cancer tissue and shown that loss of MTSS1 and SCAMP1 correlates with reduced disease-specific survival. In summary, we provide evidence of the cooperative roles of MTSS1 and SCAMP1 in preventing HER2+/ER-/PR- breast cancer invasion and we show that the loss of Mtss1 and Scamp1 results in a more aggressive cancer cell phenotype.

Metastasis suppressor 1 (MTSS1) expression is associated with reduced in-vivo metastasis and enhanced patient survival in lung adenocarcinoma

Metastasis suppressor 1 (MTSS1) has been shown to be a metastasis suppressor in a number of cancers. However, its role in lung adenocarcinoma is largely unknown. To evaluate the significance of MTSS1 expression on lung adenocarcinoma metastatic properties, the gain or loss of MTSS1 in in vivo and in vitro experiments were employed. Using an in vivo orthotopic mouse xenograft model mimicking human disease progression, stable overexpression of MTSS1 in lung adenocarcinoma cells resulted in a significant decrease in metastatic burden. Stable overexpression of MTSS1 in NCI-H1299 decreased in vitro lung adenocarcinoma invasion and migration while knockdown of MTSS1 in A549 resulted in a significant increase in cell invasion and migration. Using The Cancer Genome Atlas dataset of over 500 patient lung adenocarcinoma specimens, we demonstrated a 20% increase in 5-year survival associated with preserved intratumoral MTSS expression. MTSS1 expression in lung adenocarcinoma is associated with decreased metastatic burden, as assessed by an in vivo orthotopic model, and correlates with a 20% survival advantage at 5 years following diagnosis. In vitro data suggests MTSS1 regulates lung adenocarcinoma through augmentation of cell invasion and migration.

PTEN-Dependent Stabilization of MTSS1 Inhibits Metastatic Phenotype in Pancreatic Ductal Adenocarcinoma

Pancreatic ductal adenocarcinoma (PDAC) presents at metastatic stage in over 50% of patients. With a survival rate of just 2.7% for patients presenting with distant disease, it is imperative to uncover novel mechanisms capable of suppressing metastasis in PDAC. Previously, we reported that the loss of metastasis suppressor protein 1 (MTSS1) in PDAC cells results in significant increase in cellular migration and invasion. Conversely, we also found that overexpressing MTSS1 in metastatic PDAC cell lines corresponds with not only decreased metastatic phenotype, but also greater overall survival. While it is known that MTSS1 is downregulated in late-stage PDAC, the mechanism behind that loss has not yet been elucidated. Here, we build off our previous findings to present a novel regulatory mechanism for the stabilization of MTSS1 via the tumor suppressor protein phosphatase and tensin homolog (PTEN). We show that PTEN loss in PDAC cells results in a decrease in MTSS1 expression and increased metastatic potential. Additionally, we demonstrate that PTEN forms a complex with MTSS1 in order to stabilize and protect it from proteasomal degradation. Finally, we show that the inflammatory tumor microenvironment, which makes up over 90% of PDAC tumor bulk, is capable of downregulating PTEN expression through secretion of miRNA-23b, potentially uncovering a novel extrinsic mechanism of MTSS1 regulation. Collectively, these data offer new insight into the role and regulation of MTSS1in suppressing tumor cell invasion and migration and help shed light as to what molecular mechanisms could be leading to early cell dissemination in PDAC.