Functional interaction of tumor suppressor DLC1 and caveolin-1 in cancer cells

Regulation and functions of the DLC family of RhoGAP proteins: Implications for development and cancer

The DLC (Deleted in Liver Cancer) family of RhoGAP (Rho GTPase-activating) proteins has been extensively studied since the identification of the first family member nearly 30 years ago. Rho GTPase signaling is essential for various cellular processes, including cytoskeletal dynamics, cell migration, and proliferation. Members of the DLC family are key regulators of this signaling pathway, with well-established roles in development and carcinogenesis. Here, we provide a comprehensive review of research into DLC regulation and cellular functions over the last three decades. In particular, we summarize control mechanisms of DLC gene expression at both the transcriptional and post-transcriptional level. Additionally, recent advances in understanding the post-translational regulation of DLC proteins that allow for tuning of protein activity and localization are highlighted. This detailed overview will serve as resource for future studies aimed at further elucidating the complex regulatory mechanisms of DLC family proteins and exploring their potential as targets for therapeutic applications.

START domains generate paralog-specific regulons from a single network architecture

Functional divergence of transcription factors (TFs) has driven cellular and organismal complexity throughout evolution, but its mechanistic drivers remain poorly understood. Here we test for new mechanisms using CORONA (CNA) and PHABULOSA (PHB), two functionally diverged paralogs in the CLASS III HOMEODOMAIN LEUCINE ZIPPER (HD-ZIPIII) family of TFs. We show that virtually all genes bound by PHB ( ~ 99%) are also bound by CNA, ruling out occupation of distinct sets of genes as a mechanism of functional divergence. Further, genes bound and regulated by both paralogs are almost always regulated in the same direction, ruling out opposite regulation of shared targets as a mechanistic driver. Functional divergence of CNA and PHB instead results from differential usage of shared binding sites, with hundreds of uniquely regulated genes emerging from a commonly bound genetic network. Regulation of a given gene by CNA or PHB is thus a function of whether a bound site is considered 'responsive' versus 'non-responsive' by each paralog. Discrimination between responsive and non-responsive sites is controlled, at least in part, by their lipid binding START domain. This suggests a model in which HD-ZIPIII TFs use information integrated by their START domain to generate paralog-specific transcriptional outcomes from a shared network architecture. Taken together, our study identifies a mechanism of HD-ZIPIII TF paralog divergence and proposes the ubiquitously distributed START evolutionary module as a driver of functional divergence.

DLC1 promotes mechanotransductive feedback for YAP via RhoGAP-mediated focal adhesion turnover

Angiogenesis is a tightly controlled dynamic process demanding a delicate equilibrium between pro-angiogenic signals and factors that promote vascular stability. The spatiotemporal activation of the transcriptional co-factors YAP (herein referring to YAP1) and TAZ (also known WWTR1), collectively denoted YAP/TAZ, is crucial to allow for efficient collective endothelial migration in angiogenesis. The focal adhesion protein deleted-in-liver-cancer-1 (DLC1) was recently described as a transcriptional downstream target of YAP/TAZ in endothelial cells. In this study, we uncover a negative feedback loop between DLC1 expression and YAP activity during collective migration and sprouting angiogenesis. In particular, our study demonstrates that signaling via the RhoGAP domain of DLC1 reduces nuclear localization of YAP and its transcriptional activity. Moreover, the RhoGAP activity of DLC1 is essential for YAP-mediated cellular processes, including the regulation of focal adhesion turnover, traction forces, and sprouting angiogenesis. We show that DLC1 restricts intracellular cytoskeletal tension by inhibiting Rho signaling at the basal adhesion plane, consequently reducing nuclear YAP localization. Collectively, these findings underscore the significance of DLC1 expression levels and its function in mitigating intracellular tension as a pivotal mechanotransductive feedback mechanism that finely tunes YAP activity throughout the process of sprouting angiogenesis.

Research trends and hotspots on the links between caveolin and cancer: bibliometric and visual analysis from 2003 to 2022

Introduction: Extensive studies indicated that caveolin is a key regulator in multiple cellular processes. Recently, growing evidence demonstrated that caveolin is critically involved in tumor progression. Since no relevant bibliometric study has been published, we performed a bibliometric and visual analysis to depict the knowledge framework of research related to the involvement of caveolin in cancer. Methods: Relevant studies published in English during 2003-2022 were obtained from the Web of Science Core Collection database. Three programs (VOSviewer, CiteSpace, and R-bibliometrix) and the website of bibliometrics (http://bibliometric.com/) were applied to construct networks based on the analysis of countries, institutions, authors, journals, references, and keywords. Results: A total of 2,463 documents were extracted and identified. The United States had the greatest number of publications and total citations, and Thomas Jefferson University was the most productive institution. Michael P. Lisanti was the most influential scholar in this research domain. Cell Cycle was the journal with the most publications on this subject. The most local-cited document was the article titled "Caveolin-1 in oncogenic transformation, cancer, and metastasis." A comprehensive analysis has been conducted based on keywords and cited references. Initially, the research frontiers were predominantly "signal transduction", "human breast cancer," "oncogenically transformed cells," "tumor suppressor gene," and "fibroblasts." While in recent years, the research emphasis has shifted to "tumor microenvironment," "epithelial mesenchymal transition," "nanoparticles," and "stem cells." Conclusion: Taken together, our bibliometric analysis shows that caveolin continues to be of interest in cancer research. The hotspots and research frontiers have evolved from the regulation of cancer signaling, to potential targets of cancer therapy and novel techniques. These results can provide a data-based reference for the guidance of future research.

The START domain potentiates HD-ZIPIII transcriptional activity

The CLASS III HOMEODOMAIN-LEUCINE ZIPPER (HD-ZIPIII) transcription factors (TFs) were repeatedly deployed over 725 million years of evolution to regulate central developmental innovations. The START domain of this pivotal class of developmental regulators was recognized over 20 years ago, but its putative ligands and functional contributions remain unknown. Here, we demonstrate that the START domain promotes HD-ZIPIII TF homodimerization and increases transcriptional potency. Effects on transcriptional output can be ported onto heterologous TFs, consistent with principles of evolution via domain capture. We also show the START domain binds several species of phospholipids, and that mutations in conserved residues perturbing ligand binding and/or its downstream conformational readout abolish HD-ZIPIII DNA-binding competence. Our data present a model in which the START domain potentiates transcriptional activity and uses ligand-induced conformational change to render HD-ZIPIII dimers competent to bind DNA. These findings resolve a long-standing mystery in plant development and highlight the flexible and diverse regulatory potential coded within this widely distributed evolutionary module.

Diverse regulatory mechanisms of StARkin domains in land plants and mammals

The StARkin domain (derived from 'kin of steroidogenic acute regulatory protein (StAR)') is an evolutionarily conserved helix-grip-fold structure. StARkin domains possess a deep hydrophobic pocket capable of binding lipophilic ligands such as fatty acids, sterols, and isoprenoids. Dysregulation of StARkin proteins has profound effects on disease and development. In this review, we profile recent mechanistic and evolutionary studies, which highlight the remarkable diversity of regulatory mechanisms employed by the StARkin module. Although primarily focused on land plants, we also discuss select key advances in mammalian StARkin biology. The diversity of perspectives, systems, and approaches described here may be helpful to researchers characterizing poorly understood StARkin proteins.

The tumor suppressor activity of DLC1 requires the interaction of its START domain with Phosphatidylserine, PLCD1, and Caveolin-1

BACKGROUND

DLC1, a tumor suppressor gene that is downregulated in many cancer types by genetic and nongenetic mechanisms, encodes a protein whose RhoGAP and scaffolding activities contribute to its tumor suppressor functions. The role of the DLC1 START (StAR-related lipid transfer; DLC1-START) domain, other than its binding to Caveolin-1, is poorly understood. In other START domains, a key function is that they bind lipids, but the putative lipid ligand for DLC1-START is unknown.

METHODS

Lipid overlay assays and Phosphatidylserine (PS)-pull down assays confirmed the binding of DLC1-START to PS. Co-immunoprecipitation studies demonstrated the interaction between DLC1-START and Phospholipase C delta 1 (PLCD1) or Caveolin-1, and the contribution of PS to those interactions. Rho-GTP, cell proliferation, cell migration, and/or anchorage-independent growth assays were used to investigate the contribution of PS and PLCD1, or the implications of TCGA cancer-associated DLC1-START mutants, to DLC1 functions. Co-immunoprecipitations and PS-pull down assays were used to investigate the molecular mechanisms underlying the impaired functions of DLC1-START mutants. A structural model of DLC1-START was also built to better understand the structural implications of the cancer-associated mutations in DLC1-START.

RESULTS

We identified PS as the lipid ligand for DLC1-START and determined that DLC1-START also binds PLCD1 protein in addition to Caveolin-1. PS binding contributes to the interaction of DLC1 with Caveolin-1 and with PLCD1. The importance of these activities for tumorigenesis is supported by our analysis of 7 cancer-associated DLC1-START mutants, each of which has reduced tumor suppressor function but retains wildtype RhoGAP activity. Our structural model of DLC1-START indicates the mutants perturb different elements within the structure, which is correlated with our experimental findings that the mutants are heterogenous with regard to the deficiency of their binding properties. Some have reduced PS binding, others reduced PLCD1 and Caveolin-1 binding, and others are deficient for all of these properties.

CONCLUSION

These observations highlight the importance of DLC1-START for the tumor suppressor function of DLC1 that is RhoGAP-independent. They also expand the versatility of START domains, as DLC1-START is the first found to bind PS, which promotes the binding to other proteins.

Tumor suppressor gene DLC1: Its modifications, interactive molecules, and potential prospects for clinical cancer application

Deleted in liver cancer 1 (DLC1) is a recognized tumor suppressor gene that negatively regulates Rho family proteins by hydrolyzing the active GTP-bound state to its inactive GDP-bound state. Active Rho proteins play a positive role in tumorigenesis. Numerous in vitro and in vivo experiments have shown that DLC1 is downregulated or inactivated in various solid tumors, which may be due to the following five reasons: genomic deletion, epigenetic modification and ubiquitin-dependent proteasomal degradation may cause DLC1 underexpression; phosphorylation at the post-translation level may cause DLC1 inactivation; and failure to localize at focal adhesions (FAs) may prevent DLC1 from exerting full activity. All of the causes could be attributed to molecular binding. Experimental evidence suggests that direct or indirect targeting of DLC1 is feasible for cancer treatment. Therefore, elucidating the interaction of DLC1 with its binding partners might provide novel targeted therapies for cancer. In this review, we summarized the binding partners of DLC1 at both the gene and protein levels and expounded a variety of anticancer drugs targeting DLC1 to provide information about DLC1 as a cancer diagnostic indicator or therapeutic target.

DLC1 inhibits lung adenocarcinoma cell proliferation, migration and invasion via regulating MAPK signaling pathway

Lung adenocarcinoma (LUAD), one of the most common cancers, is a major threat to people's health due to its high mortality, and the survival of most patients suffering LUAD remains poor. This study aimed to explore the mechanism of Deleted in Liver Cancer 1 (DLC1) as a tumor suppressor underlying the occurrence and progression of LUAD. As revealed by bioinformatics analysis and qRT-PCR, DLC1 was significantly down-regulated in LUAD tumor tissue and cells. A series of cellular experiments including CCK-8, wound healing and Transwell assays were performed to detect the effect of DLC1 on the biological function of LUAD cells. It was found that overexpressing DLC1 significantly inhibited LUAD cell proliferative, migratory and invasive abilities, while knockdown of DLC1 promoted these abilities. Gene Set Enrichment Analysis (GSEA) and dual-luciferase assay were used to explore the downstream signaling pathway of DLC1, finding that DLC1 could remarkably inhibit the activity of mitogen-activated protein kinase (MAPK) signaling pathway. Western blot implemented for MAPK signaling pathway-related proteins further identified that DLC1 restrained the activation of MAPK/ERK signaling pathway. Furthermore, rescue experiments suggested that DLC1 inhibited LUAD cell proliferation and invasion by suppressing the MAPK/ERK signaling pathway. Overall, our study discussed the DLC1-dependent mechanism involved in LUAD. We found that the up-regulation of DLC1 may inhibit the malignant progression of LUAD by suppressing MAPK signaling pathway, which supports the view that DLC1 may serve as a molecular target for the targeted therapy of LUAD patients.

Multi-omics analysis identifies potential mechanisms of AURKB in mediating poor outcome of lung adenocarcinoma

Aurora kinases B (AURKB), which plays a critical role in chromosomal segmentation and mitosis, greatly promotes cell cycle progression and aggressive proliferation of cancers. So far, its role and underlying mechanisms in mediating poor outcome of lung adenocarcinoma (LUAD) remained largely unclear. Analyses on multiple omics data of lung adenocarcinoma cohort in The Cancer Genome Atlas (TCGA) were performed based on AURKB expression, and demonstrated its association with clinical characteristics and the potential of using AURKB as a biomarker in predicting patients' survival. This study found aberrant alterations of genomics and epigenetics, including up-regulation and down-regulation of oncogenic genes and tumor suppressors, pathways involved in the cell cycle, DNA repair, spliceosome, and proteasome, hypermethylation enrichments around transcriptional start sites, which are all related to AURKB expression. We further discovered the possible role of tumor suppressors DLC1 and HLF in AURKB-mediated adverse outcome of LUAD. To conclude, this study proved AURKB as a potential prognostic factor and therapeutic target for lung adenocarcinoma treatment and provide a future research direction.

The DLC-1 tumor suppressor is involved in regulating immunomodulation of human mesenchymal stromal /stem cells through interacting with the Notch1 protein

Background

Immunomodulatory activities of human mesenchymal stromal /stem cells (hMSCs) has been widely recognized as the most critical function of hMSCs for exerting its therapeutic effects. However, the detailed mechanisms responsible for regulating the immunomodulation of hMSCs still remain largely unknown. Previous studies revealed that the Notch1 protein exerted a pro-immunomodulatory function probably through interacting with the protein(s) subjective to proteasome-mediated protein degradation. The DLC-1 protein represents a well characterized tumor suppressor subjective to proteasome-mediated degradation. However, the detailed signaling pathway of Notch1 and the involvement of DLC-1 in regulating the immunomodulation of hMSCs have not been studied before.

Methods

The transfection with cDNA or siRNA into hMSCs assisted by co-culture of hMSCs with peripheral blood mononuclear cells and small molecule inhibitors of signaling proteins, followed by immunoprecipitation, Western blotting, RT-PCR, and flowcytometry, were employed to characterize the Notch1 signaling, to identify DLC-1 as a candidate proteasome-targeted protein, and to characterize DLC-1 signaling pathway and its interaction with the Notch1 signaling, in the regulation of immunomodulation of hMSCs, specifically, the inhibition of pro-inflammatory CD4⁺-Th1 lymphocytes, and the release of immunomodulatory molecule IDO1.

Statistical analysis

One-way ANOVA was utilized as a statistical tool to analyze the data presented as means ± SEM of at least three separate experiments.

Results

The present study revealed that the Notch1-Hey1 axis, but not the Notch1-Hes1 axis, was likely responsible for mediating the pro-immunomodulatory function of the Notch1 signaling. The DLC-1 protein was found subjective to proteasome-mediated protein degradation mediated by the DDB1 and FBXW5 E3 ligases and served as an inhibitor of the immunomodulation of hMSCs through inhibiting Rock1, but not Rock2, downstream the DLC-1 signaling. The Notch1 signaling in the Notch1-Hey1 pathway and the DLC-1 signaling in the DLC-1-Rock1-FBXW5 pathway exhibited a mutual exclusion interaction in the regulation of immunomodulation of hMSCs.

Conclusions

The present study uncovers a novel function of DLC-1 tumor suppressor in regulating the immunomodulation of hMSCs. It also proposes a novel mutual exclusion mechanism between the DLC-1 signaling and the Notch1 signaling that is possibly responsible for fine-tuning the immunomodulation of hMSCs with different clinical implications in hMSCs therapy.

Supplementary Information

Supplementary information accompanies this paper at 10.1186/s12885-020-07542-5.

Identifying Cancer-Relevant Mutations in the DLC START Domain Using Evolutionary and Structure-Function Analyses

Rho GTPase signaling promotes proliferation, invasion, and metastasis in a broad spectrum of cancers. Rho GTPase activity is regulated by the deleted in liver cancer (DLC) family of bona fide tumor suppressors which directly inactivate Rho GTPases by stimulating GTP hydrolysis. In addition to a RhoGAP domain, DLC proteins contain a StAR-related lipid transfer (START) domain. START domains in other organisms bind hydrophobic small molecules and can regulate interacting partners or co-occurring domains through a variety of mechanisms. In the case of DLC proteins, their START domain appears to contribute to tumor suppressive activity. However, the nature of this START-directed mechanism, as well as the identities of relevant functional residues, remain virtually unknown. Using the Catalogue of Somatic Mutations in Cancer (COSMIC) dataset and evolutionary and structure-function analyses, we identify several conserved residues likely to be required for START-directed regulation of DLC-1 and DLC-2 tumor-suppressive capabilities. This pan-cancer analysis shows that conserved residues of both START domains are highly overrepresented in cancer cells from a wide range tissues. Interestingly, in DLC-1 and DLC-2, three of these residues form multiple interactions at the tertiary structural level. Furthermore, mutation of any of these residues is predicted to disrupt interactions and thus destabilize the START domain. As such, these mutations would not have emerged from traditional hotspot scans of COSMIC. We propose that evolutionary and structure-function analyses are an underutilized strategy which could be used to unmask cancer-relevant mutations within COSMIC. Our data also suggest DLC-1 and DLC-2 as high-priority candidates for development of novel therapeutics that target their START domain.

Cancer-Associated Point Mutations in the DLC1 Tumor Suppressor and Other Rho-GAPs Occur Frequently and Are Associated with Decreased Function

In advanced cancer, the RHOA GTPase is often active together with reduced expression of genes encoding Rho-specific GTPase-accelerating proteins (Rho-GAP), which negatively regulate RHOA and related GTPases. Here we used the The Cancer Genome Atlas dataset to examine 12 tumor types (including colon, breast, prostate, pancreas, lung adenocarcinoma, and squamous cell carcinoma) for the frequency of codon mutations of 10 Rho-GAP and experimentally tested biochemical and biological consequences for cancer-associated mutants that arose in the DLC1 tumor suppressor gene. DLC1 was the Rho-GAP gene mutated most frequently, with 5%-8% of tumors in five of the tumor types evaluated having DLC1 missense mutations. Furthermore, 20%-26% of the tumors in four of these five tumor types harbored missense mutations in at least one of the 10 Rho-GAPs. Experimental analysis of the DLC1 mutants indicated 7 of 9 mutants whose lesions were located in the Rho-GAP domain were deficient for Rho-GAP activity and for suppressing cell migration and anchorage-independent growth. Analysis of a DLC1 linker region mutant and a START domain mutant showed each was deficient for suppressing migration and growth in agar, but their Rho-GAP activity was similar to that of wild-type DLC1. Compared with the wild-type, the linker region mutant bound 14-3-3 proteins less efficiently, while the START domain mutant displayed reduced binding to Caveolin-1. Thus, mutation of Rho-GAP genes occurs frequently in some cancer types and the majority of cancer-associated DLC1 mutants evaluated were deficient biologically, with various mechanisms contributing to their reduced activity. SIGNIFICANCE: These findings indicate that point mutation of Rho-GAP genes is unexpectedly frequent in several cancer types, with DLC1 mutants exhibiting reduced function by various mechanisms.

The START-domain proteins in intracellular lipid transport and beyond

The Steroidogenic Acute Regulatory Protein-related Lipid Transfer (START) domain is a ~210 amino acid sequence that folds into an α/β helix-grip structure forming a hydrophobic pocket for lipid binding. The helix-grip fold structure defines a large superfamily of proteins, and this review focuses on the mammalian START domain family members that include single START domain proteins with identified ligands, and larger multi-domain proteins that may have novel roles in metabolism. Much of our understanding of the mammalian START domain proteins in lipid transport and changes in metabolism has advanced through studies using knockout mouse models, although for some of these proteins the identity and/or physiological role of ligand binding remains unknown. The findings that helped define START domain lipid-binding specificity, lipid transport, and changes in metabolism are presented to highlight that fundamental questions remain regarding the biological function(s) for START domain-containing proteins.

Multifaceted Roles of Caveolin-1 in Lung Cancer: A New Investigation Focused on Tumor Occurrence, Development and Therapy

Lung cancer is one of the most common and malignant cancers with extremely high morbidity and mortality in both males and females. Although traditional lung cancer treatments are fast progressing, there are still limitations. Caveolin-1 (Cav-1), a main component of caveolae, participates in multiple cellular events such as immune responses, endocytosis, membrane trafficking, cellular signaling and cancer progression. It has been found tightly associated with lung cancer cell proliferation, migration, apoptosis resistance and drug resistance. In addition to this, multiple bioactive molecules have been confirmed to target Cav-1 to carry on their anti-tumor functions in lung cancers. Cav-1 can also be a predictor for lung cancer patients’ prognosis. In this review, we have summarized the valuable research on Cav-1 and lung cancer in recent years and discussed the multifaceted roles of Cav-1 on lung cancer occurrence, development and therapy, hoping to provide new insights into lung cancer treatment.

Combination of dihydroartemisinin and resveratrol effectively inhibits cancer cell migrationviaregulation of the DLC1/TCTP/Cdc42 pathway

Mechanism of DHA combined with RES in inhibition of cancer cell migration by DLC1/TCTP/Cdc42 signaling.

Upregulation of DLC-1 inhibits pancreatic cancer progression: Studies with clinical samples and a pancreatic cancer model

Deleted in liver cancer 1 (DLC-1) serves a vital role in the progression of multiple cancers, including those of the pancreas. Numerous studies have aimed to reveal the anti-cancer mechanisms of the DLC-1 gene, though few have focused on its impact on the development of pancreatic cancer. Using clinical pancreatic cancer samples and pancreatic cancer cell lines, the present study aimed to reveal the role of DLC-1 in this disease. The expression levels of DLC-1 were determined in pancreatic cancer and adjacent normal tissues from patients with pancreatic cancer, indicating a decreased expression level of DLC-1 in cancerous tissues. Using the pancreatic cancer cell line SW1990, the effect of DLC overexpression on cell proliferation, invasive capacity and the cell cycle and were assessed. Using a mouse tumor model, the tumor-progression capacity of transfected and untransfected SW1990 cells was investigated, indicating that DLC-1 transfection reduced the capacity for tumor progression. Thus, the present study indicated that the overexpression of DLC-1 inhibited the proliferation and reduced the invasive capacity of SW1990 cells both in vitro and in vivo, and that it may have significant inhibitory effects on the development of pancreatic cancer.

TFAP2C increases cell proliferation by downregulating GADD45B and PMAIP1 in non-small cell lung cancer cells

Background

Non-small cell lung cancer (NSCLC) is one of the leading causes of death in the world. NSCLC diagnosed at an early stage can be highly curable with a positive prognosis, but biomarker limitations make it difficult to diagnose lung cancer at an early stage. To identify biomarkers for lung cancer development, we previously focused on the oncogenic roles of transcription factor TFAP2C in lung cancers and revealed the molecular mechanism of several oncogenes in lung tumorigenesis based on TFAP2C-related microarray analysis.

Results

In this study, we analyzed microarray data to identify tumor suppressor genes and nine genes downregulated by TFAP2C were screened. Among the nine genes, we focused on growth arrest and DNA-damage-inducible beta (GADD45B) and phorbol-12-myristate-13-acetate-induced protein 1 (PMAIP1) as representative TFAP2C-regulated tumor suppressor genes. It was observed that overexpressed TFAP2C resulted in inhibition of GADD45B and PMAIP1 expressions at both the mRNA and protein levels in NSCLC cells. In addition, downregulation of GADD45B and PMAIP1 by TFAP2C promoted cell proliferation and cell motility, which are closely associated with NSCLC tumorigenesis.

Conclusion

This study indicates that GADD45B and PMAIP1 could be promising tumor suppressors for NSCLC and might be useful as prognostic markers for use in NSCLC therapy.

Electronic supplementary material

The online version of this article (10.1186/s40659-019-0244-5) contains supplementary material, which is available to authorized users.

High expression of DLC family proteins predicts better prognosis and inhibits tumor progression in NSCLC

The incidence of primary lung cancer (PLC) is increasing and is becoming a leading cause of cancer‑associated mortality worldwide. Non‑small cell lung cancer (NSCLC) accounts for ~80% of PLC cases and has the worst prognosis among malignant tumors. Deleted in liver cancer (DLC) proteins belong to the RhoGTPase‑activating protein family and are considered to be tumor suppressor genes. However, the role of the proteins, particularly DLC2 and DLC3, in NSCLC, has not been fully elucidated. The present study investigated the expression levels and prognostic values of DLCs in NSCLC using The Cancer Genome Atlas, the Genotype‑Tissue Expression project and Kaplan‑Meier plotter datasets. The current study demonstrated that the three DLCs were downregulated in NSCLC. High expression levels of DLC1 and DLC2 were associated with an improved survival in NSCLC. Additionally, the effects of DLCs on the proliferation and apoptosis of the lung cancer cell line A‑549 were investigated in vitro using a Cell Counting Kit‑8 assay and flow cytometry analysis. DLC2 and DLC3 overexpression inhibited proliferation and induced apoptosis in A549 cells. To the best of our knowledge, the current study was the first to investigate the expression level and prognostic values of DLC2 and DLC3 in NSCLC. The results indicated that DLC1 DLC2 and DLC3 serve specific roles in the occurrence and development of NSCLC, and may be considered as potential prognostic indicators in NSCLC.

Effects of DLC1 Deficiency on Endothelial Cell Contact Growth Inhibition and Angiosarcoma Progression

Background

Deleted in Liver Cancer 1 (DLC1) is a tumor suppressor gene frequently deleted in cancer. However, DLC1 is not known to be deleted in angiosarcoma, an aggressive malignancy of endothelial cell derivation. Additionally, the physiologic functions of DLC1 protein in endothelial cells are poorly defined.

Methods

We investigated the effects of shRNA-induced DLC1 depletion in endothelial cells. Cell growth was measured by 3H thymidine incorporation, IncuCyte imaging, and population doublings; cell death by cell cycle analysis; gene expression by Affimetrix arrays and quantitative polymerase chain reaction; NF-κB activity by reporter assays; and protein levels by immunoblotting and immunofluorescence staining. We tested Tanespimycin/17-AAG and Fasudil treatment in groups of nine to 10 mice bearing ISOS-1 angiosarcoma. All statistical tests were two-sided.

Results

We discovered that DLC1 is a critical regulator of cell contact inhibition of proliferation in endothelial cells, promoting statistically significant (P < .001) cell death when cells are confluent (mean [SD] % viability: control DLC1 = 15.6 [19.3]; shDLC1 = 73.4 [13.1]). This prosurvival phenotype of DLC1-depleted confluent endothelial cells is attributable to a statistically significant and sustained increase of NF-κB activity (day 5, P = .001; day 8, P = .03) associated with increased tumor necrosis factor alpha-induced protein 3 (TNFAIP3/A20) signaling. Consistently, we found that DLC1 is statistically significantly reduced (P < .001 in 5 of 6) and TNFAIP3/A20 is statistically significantly increased (P < .001 in 2 of 3 and P = 0.02 in 1 of 3) in human angiosarcoma compared with normal adjacent endothelium. Treatment with the NF-κB inhibitor Tanespimycin/17-AAG statistically significantly reduced angiosarcoma tumor growth in mice (treatment tumor weight vs control, 0.50 [0.19] g vs 0.91 [0.21] g, P = .001 experiment 1; 0.66 [0.26] g vs 1.10 [0.31] g, P = .01 experiment 2).

Conclusions

These results identify DLC1 as a previously unrecognized regulator of endothelial cell contact inhibition of proliferation that is depleted in angiosarcoma and support NF-κB targeting for the treatment of angiosarcoma where DLC1 is lost.

Downregulation of STARD8 in gastric cancer and its involvement in gastric cancer progression

Objective

Rho-GTPases play a pivotal role in a wide variety of signal transduction pathways and are associated with a great number of human carcinomas. STARD8, which is a Rho-GTPase-activating protein, has been proposed as a tumor suppressor gene, but its role in gastric cancer remains elusive. In this study, we investigate the expression of STARD8 in gastric cancer and its association with gastric cancer progression.

Materials and methods

One normal gastric mucosa cell line for example GES1 and six human gastric cancer cell lines such as AGS, MGC803, MKN45, SGC7901, HGC27 and BGC823 were utilized to analyze STARD8 mRNA and protein levels by reverse transcription polymerase chain reaction (RT-PCR) and Western blot. A total of 70 paired gastric tissues including corresponding nonmalignant gastric tissues and cancer tissues were utilized to analyze the protein expression of STARD8 using immunohistochemistry, and the correlation between STARD8 level and clinicopathological features was also evaluated.

Results

STARD8 was found to be downregulated in primary gastric cancer cells and tissues compared with the normal gastric mucosa cell line, GES1, and corresponding nonmalignant gastric tissues, while its decreased expression was significantly associated with TNM stage, lymph node metastasis and differentiation (p<0.05).

Conclusion

There is significantly decreased expression of STARD8 in gastric cancer cells and tissues, and its expression may contribute to gastric tumorigenesis.

Mutations in six nephrosis genes delineate a pathogenic pathway amenable to treatment

No efficient treatment exists for nephrotic syndrome (NS), a frequent cause of chronic kidney disease. Here we show mutations in six different genes (MAGI2, TNS2, DLC1, CDK20, ITSN1, ITSN2) as causing NS in 17 families with partially treatment-sensitive NS (pTSNS). These proteins interact and we delineate their roles in Rho-like small GTPase (RLSG) activity, and demonstrate deficiency for mutants of pTSNS patients. We find that CDK20 regulates DLC1. Knockdown of MAGI2, DLC1, or CDK20 in cultured podocytes reduces migration rate. Treatment with dexamethasone abolishes RhoA activation by knockdown of DLC1 or CDK20 indicating that steroid treatment in patients with pTSNS and mutations in these genes is mediated by this RLSG module. Furthermore, we discover ITSN1 and ITSN2 as podocytic guanine nucleotide exchange factors for Cdc42. We generate Itsn2-L knockout mice that recapitulate the mild NS phenotype. We, thus, define a functional network of RhoA regulation, thereby revealing potential therapeutic targets.

DLC1 is the principal biologically-relevant down-regulated DLC family member in several cancers

The RHO family of RAS-related GTPases in tumors may be activated by reduced levels of RHO GTPase accelerating proteins (GAPs). One common mechanism is decreased expression of one or more members of the Deleted in Liver Cancer (DLC) family of Rho-GAPs, which comprises three closely related genes (DLC1, DLC2, and DLC3) that are down-regulated in a wide range of malignancies. Here we have studied their comparative biological activity in cultured cells and used publicly available datasets to examine their mRNA expression patterns in normal and cancer tissues, and to explore their relationship to cancer phenotypes and survival outcomes. In The Cancer Genome Atlas (TCGA) database, DLC1 expression predominated in normal lung, breast, and liver, but not in colorectum. Conversely, reduced DLC1 expression predominated in lung squamous cell carcinoma (LSC), lung adenocarcinoma (LAD), breast cancer, and hepatocellular carcinoma (HCC), but not in colorectal cancer. Reduced DLC1 expression was frequently associated with promoter methylation in LSC and LAD, while DLC1 copy number loss was frequent in HCC. DLC1 expression was higher in TCGA LAD patients who remained cancer-free, while low DLC1 had a poorer prognosis than low DLC2 or low DLC3 in a more completely annotated database. The poorest prognosis was associated with low expression of both DLC1 and DLC2 (P < 0.0001). In cultured cells, the three genes induced a similar reduction of Rho-GTP and cell migration. We conclude that DLC1 is the predominant family member expressed in several normal tissues, and its expression is preferentially reduced in common cancers at these sites.

IGF2-derived miR-483 mediated oncofunction by suppressing DLC-1 and associated with colorectal cancer

Emerging evidence indicates that IGF2 plays an important role in various human malignancies, including colorectal cancer (CRC). Hsa-miR-483 is located within intron 7 of the IGF2 locus. However, the mechanism by which increased IGF2 induces carcinogenesis remains largely elusive. DLC-1 has been identified as a candidate tumor suppressor. In this study, we aimed at investigating whether miR-483 transcription is IGF2-dependent, identifying the functional target of miR-483, and evaluating whether tissue and serum miR-483-3p or miR-483-5p levels are associated with CRC. Our results showed that sequences upstream miR-483 had undetectable promoter activity and levels of IGF2, miR-483-3p, and miR-483-5p were synchronously increased in CRC tissues. Positive correlations between IGF2 and miR-483-3p (r=0.4984, ***p<0.0001), and between IGF2 and miR-483-5p (r=0.6659, ***p<0.0001) expression were found. In addition, patients with CRC had a significantly higher serum miR-483-5p level (*p<0.05) compared to normal controls. DLC-1 expression was decreased in colorectal cancer tissues and diminished through transient transfection with miR-483-3p. Our results suggest that IGF2 may exert its oncofunction, at least partly, through its parasitic miR-483 which suppressed DLC-1 in CRC cells. Thus, miR-483 might serve as a new target for therapy and a potential biomarker for the detection of colorectal cancer.

Resveratrol inhibits age-dependent spontaneous tumorigenesis by SIRT1-mediated post-translational modulations in the annual fish Nothobranchius guentheri

Resveratrol, SIRT1 activator, inhibits carcinogenesis predominantly performed in transgenic animal models, orthotopic cancers of nude mice or different cancer cell lines, but its effects during process of spontaneous tumors using vertebrate models remain untested. Spontaneous liver neoplasm is an age-related disease and is inhibited by resveratrol in the annual fish Nothobranchius guentheri, which indicates that the fish can act as an excellent model to study spontaneous tumorigenesis. Totally, 175 fish were fed with resveratrol and another 175 fish for controls. Treated fish were fed with resveratrol (25 μg/fish/day) from sexual maturity (4-month-old) until they were sacrificed at 6-, 9- and 12-month-old. Immunoblot, immunohistochemistry and co-immunoprecipitation were employed to investigate the underlying mechanisms that resveratrol inhibited age-dependent spontaneous tumorigenesis in the fish. Results showed that resveratrol increased protein level of SIRT1 and alleviated age-associated tumorigenesis in liver. With SIRT1 up-regulation, resveratrol reduced proliferation by deacetylating K-Ras and inactivating K-Ras/PI3K/AKT pathway; and promoted apoptosis through deacetylation and dephosphorylation of FoxOs, up-regulation of DLC1 and interaction between SIRT1 and DLC1, and dephosphorylation of DLC1 in spontaneous neoplasms. We established a novel short-lived fish model for understanding the molecular mechanisms of drugs on age-dependent spontaneous tumorigenesis.

Liquid formulation containing doxorubicin-loaded lipid-core nanocapsules: Cytotoxicity in human breast cancer cell line and in vitro uptake mechanism

Cancer is a major public health problem in the world, being breast cancer the most frequent cancer affecting women. Despite advances in detection and treatment, mortality rates remain high. Therefore, new approaches for breast cancer treatments are necessary. In this study, our objective was to develop a liquid formulation containing doxorubicin-loaded lipid-core nanocapsules (DOX-LNC), to evaluate the in vitro antiproliferative activity and to determine the nanocapsules uptake by MCF-7 cells. Lipid-core nanocapsules (LNC), blank formulation, and DOX-LNC, proposed treatment, were prepared by self-assembling using the solvent displacement method. Hydrodynamic mean diameters (z-average) were respectively 191±31nm and 230±23nm presenting narrow size distributions. Drug content was 0.102±0.029mgmL^-1 with an encapsulation efficiency higher than 90%. Formulations were applied to semiconfluent MCF-7 cells. After 24h, LNC showed no cytotoxicity, while DOX-LNC showed an IC₅₀ of 4.49 micromolar. After 72h of incubation, DOX-LNC showed an IC₅₀ of 1.60 micromolar demonstrating a sustained effect. The nanocapsules were internalized by endocytosis mediated by caveolin and by fluid phase endocytosis, which are active transport mechanisms. In conclusion, the liquid formulation containing DOX-LNC showed to be a promising product for the breast cancer treatment opening new avenues for further in vivo studies.

Fluctuation of ROS regulates proliferation and mediates inhibition of migration by reducing the interaction between DLC1 and CAV-1 in breast cancer cells

The aim of our present study was to elucidate the effects of up-regulation and down-regulation of intracellular reactive oxygen species (ROS) level on proliferation, migration, and related molecular mechanism. Breast cancer cells were treated by catalase or H₂O₂. MTT, colony formation assay, and Hoechst/PI staining were used to evaluate proliferation and apoptosis. The level of intracellular ROS was measured by dichlorodihydrofluorescein diacetate probes. The ability of migration was detected by wound healing. Western blotting and coimmunoprecipitation (co-IP) were used to determine the expression of DLC1 and CAV-1 and their interaction. Our data indicated that up-regulation of intracellular ROS induced by H₂O₂ significantly inhibited proliferation and induced apoptosis accompanying G1 cell cycle arrest and elevated expression of p53. For cell migration, either up-regulation or down-regulation of ROS induced migration inhibition with reduction of interaction between DLC1 and CAV-1. Our results suggested that up-regulation of intracellular ROS inhibited proliferation by promoting expression of p53 and induced G1 cycle arrest and apoptosis. Fluctuation of ROS inhibited migration through reducing the interaction between DLC1 and CAV-1.

Caveolin-1, a stress-related oncotarget, in drug resistance

Caveolin-1 (Cav-1) is both a tumor suppressor and an oncoprotein. Cav-1 overexpression was frequently confirmed in advanced cancer stages and positively associated with ABC transporters, cancer stem cell populations, aerobic glycolysis activity and autophagy. Cav-1 was tied to various stresses including radiotherapy, fluid shear and oxidative stresses and ultraviolet exposure, and interacted with stress signals such as AMP-activated protein kinase. Finally, a Cav-1 fluctuation model during cancer development is provided and Cav-1 is suggested to be a stress signal and cytoprotective. Loss of Cav-1 may increase susceptibility to oncogenic events. However, research to explore the underlying molecular network between Cav-1 and stress signals is warranted.

Dlc1 interaction with non-muscle myosin heavy chain II-A (Myh9) and Rac1 activation

The Deleted in liver cancer 1 (Dlc1) gene codes for a Rho GTPase-activating protein that also acts as a tumour suppressor gene. Several studies have consistently found that overexpression leads to excessive cell elongation, cytoskeleton changes and subsequent cell death. However, none of these studies have been able to satisfactorily explain the Dlc1-induced cell morphological phenotypes and the function of the different Dlc1 isoforms. Therefore, we have studied the interacting proteins associated with the three major Dlc1 transcriptional isoforms using a mass spectrometric approach in Dlc1 overexpressing cells. We have found and validated novel interacting partners in constitutive Dlc1-expressing cells. Our study has shown that Dlc1 interacts with non-muscle myosin heavy chain II-A (Myh9), plectin and spectrin proteins in different multiprotein complexes. Overexpression of Dlc1 led to increased phosphorylation of Myh9 protein and activation of Rac1 GTPase. These data support a role for Dlc1 in induced cell elongation morphology and provide some molecular targets for further analysis of this phenotype.

Caveolin-1 promotes tumor growth and metastasis via autophagy inhibition in hepatocellular carcinoma

BACKGROUND

Caveolin-1 is a member of the caveolae family of membrane proteins. Although some researchers have investigated the function of Caveolin-1 in hepatocellular carcinoma, the mechanism of Caveolin-1 action and its prognostic value in hepatocellular carcinoma remain unclear.

METHODS

Caveolin-1 expression was measured in hepatocellular carcinoma cell lines and tissues using quantitative reverse transcription-polymerase chain reaction, western blot, and immunofluorescence assays. In in vitro experiments, Caveolin-1 was depleted using a short hairpin RNA lentiviral vector, and tumor cell behavior was analyzed. The effect of Caveolin-1 on hepatocellular carcinoma cell autophagy was investigated. Prognostic value of Caveolin-1 was analyzed by immunohistochemistry in two cohorts that included a total of 721 hepatocellular carcinoma patients.

RESULTS

We found that Caveolin-1 was overexpressed in highly metastatic hepatocellular carcinoma cell lines and tumor tissues. Moreover, Caveolin-1 promoted hepatocellular carcinoma cell proliferation, migration, and angiogenesis and inhibited autophagy. Finally, Caveolin-1 expression in hepatocellular carcinoma tissues was inversely correlated with patient overall survival and time to recurrence.

CONCLUSION

Our data obtained from cell lines suggest an oncogenic role for Caveolin-1 in hepatocellular carcinoma, Caveolin-1 contributed to hepatocellular carcinoma cell autophagy deficiency. Furthermore, Caveolin-1 may function as a novel prognostic indicator for hepatocellular carcinoma patients after curative resection, and combination of targeted therapy aimed at Caveolin-1 and autophagy modulation may represent an effective way to treat hepatocellular carcinoma.

The Deleted in Liver Cancer 1 (Dlc1) tumor suppressor is haploinsufficient for mammary gland development and epithelial cell polarity

BACKGROUND

Deleted in Liver Cancer 1 (Dlc1) is a tumor suppressor gene, which maps to human chromosome 8p21-22 and is found frequently deleted in many cancers including breast cancer. The promoter of the remaining allele is often found methylated. The Dlc1 gene encodes a RhoGAP protein that regulates cell proliferation, migration and inhibits cell growth and invasion when restored in Dlc1 deficient tumor cell lines. This study focuses on determining the role of Dlc1 in normal mammary gland development and epithelial cell polarity in a Dlc1 gene trapped (gt) mouse.

METHODS

Mammary gland whole mount preparations from 10-week virgin heterozygous Dlc1(gt/+) gene-trapped mice were compared with age-matched wild type (WT) controls. Hematoxylin-Eosin (H&E) and Masson's Trichrome staining of histological sections were carried out. Mammary glands from Dlc1(gt/+) mice and WT controls were enzymatically digested with collagenase and dispase and then cultured overnight to deplete hematopoietic and endothelial cells. The single cell suspensions were then cultured in Matrigel for 12 days. To knockdown Dlc1 expression, primary WT mammary epithelial cells were infected with short hairpin (sh) RNA expressing lentivirus or with a scrambled shRNA control.

RESULTS

Dlc1(gt/+) mice showed anomalies in the mammary gland that included increased ductal branching and deformities in terminal end buds and branch points. Compared to the WT controls, Masson's Trichrome staining showed a thickened stromal layer with increased collagen deposition in mammary glands from Dlc1(gt/+) mice. Dlc1(gt/+) primary mammary epithelial cells formed increased solid acinar spheres in contrast with WT and scrambled shRNA control cells, which mostly formed hollow acinar structures when plated in 3D Matrigel cultures. These solid acinar structures were similar to the acinar structures formed when Dlc1 gene expression was knocked down in WT mammary cells by shRNA lentiviral transduction. The solid acinar structures were not due to a defect in apoptosis as determined by a lack of detectible cleaved caspase 3 antibody staining. Primary mammary cells from Dlc1(gt/+) mice showed increased RhoA activity compared with WT cells.

CONCLUSIONS

The results illustrate that decreased Dlc1 expression can disrupt the normal cell polarization and mammary ductal branching. Altogether this study suggests that Dlc1 plays a role in maintaining normal mammary epithelial cell polarity and that Dlc1 is haploinsufficient.

Pathogenic mechanisms of lung adenocarcinoma in smokers and non-smokers determined by gene expression interrogation

Cigarette smoking is the leading risk factor for lung cancer, which accounts for the highest number of cancer-related mortalities worldwide in men and women. Individuals with a history of smoking are 15-30 times more likely to develop lung cancer compared with those who do not smoke. However, our understanding of the underlying molecular mechanisms that contribute to lung tumorigenesis in smokers versus non-smokers remains incomplete. In order to investigate such mechanisms, the present study aimed to systemically interrogate microarray datasets from tumor biopsies and matching normal tissues from stage I and II lung adenocarcinoma patients who had never smoked or were current smokers. The gene expression analysis identified 422 (99 upregulated and 323 downregulated) and 534 (174 upregulated and 360 downregulated) differentially-expressed genes from the never-smokers and current smokers, respectively, and the two groups shared 277 genes that exhibited similar trends of alteration. These genes encode regulators that are involved in a variety of cellular functions, including collagen metabolism and homeostasis of caveolae plasma membranes. Gene Ontology and Kyoto Encyclopedia of Genes and Genomes characterization indicated that biological pathways, including extracellular matrix-receptor interaction and cell migration and proliferation, were all affected in the lung cancer patients regardless of the smoking status. However, smoking induced a unique gene expression pattern characterized by upregulation of cell cycle regulators (CDK1, CCNB1 and CDC20), as well as significantly affected biological networks, including p53 signaling pathways. Taken together, these findings suggest novel mechanistic insights, and provide an improved understanding of the smoking-induced molecular alterations that contribute to the pathogenesis of lung adenocarcinoma.

GAP-independent functions of DLC1 in metastasis

Metastases are responsible for most cancer-related deaths. One of the hallmarks of metastatic cells is increased motility and migration through extracellular matrixes. These processes rely on specific small GTPases, in particular those of the Rho family. Deleted in liver cancer-1 (DLC1) is a tumor suppressor that bears a RhoGAP activity. This protein is lost in most cancers, allowing malignant cells to proliferate and disseminate in a Rho-dependent manner. However, DLC1 is also a scaffold protein involved in alternative pathways leading to tumor and metastasis suppressor activities. Recently, substantial information has been gathered on these mechanisms and this review is aiming at describing the potential and known alternative GAP-independent mechanisms allowing DLC1 to impair migration, invasion, and metastasis formation.

Rho regulation: DLC proteins in space and time

Rho GTPases function as molecular switches that connect changes of the external environment to intracellular signaling pathways. They are active at various subcellular sites and require fast and tight regulation to fulfill their role as transducers of extracellular stimuli. New imaging technologies visualizing the active states of Rho proteins in living cells elucidated the necessity of precise spatiotemporal activation of the GTPases. The local regulation of Rho proteins is coordinated by the interaction with different guanine nucleotide exchange factors (GEFs) and GTPase-activating proteins (GAPs) that turn on and off GTPase signaling to downstream effectors. GEFs and GAPs thus serve as critical signaling nodes that specify the amplitude and duration of a particular Rho signaling pathway. Despite their importance in Rho regulation, the molecular aspects underlying the spatiotemporal control of the regulators themselves are still largely elusive. In this review we will focus on the Deleted in Liver Cancer (DLC) family of RhoGAP proteins and summarize the evidence gathered over the past years revealing their different subcellular localizations that might account for isoform-specific functions. We will also highlight the importance of their tightly controlled expression in the context of neoplastic transformation.

Deleted in liver cancer-1 (DLC1): an emerging metastasis suppressor gene

While significant progress continues to be made in the early detection and therapeutic management of primary tumors, the incidence of metastatic disease remains the major cause of mortality. Accordingly, the development of novel effective therapies that can ameliorate dissemination and secondary tumor growth are a clinical priority. The identification of genetic and functional alterations in cancer cells that affect factors implicated in the metastatic process is critical for designing preventive and therapeutic strategies. Evidence implicating the protein deleted in liver cancer-1 (DLC1), a Rho GTPase activator, in metastasis has accumulated to a point where DLC1 may be considered as a metastasis suppressor gene. This review presents evidence supporting an anti-metastatic role for DLC1 in several human cancers and discusses the mechanisms contributing to its inhibitory effects. In addition, promising opportunities for therapeutic interventions based on DLC1 function and downstream pathways involved in the metastatic process are considered.

Epidermal growth factor activates the Rho GTPase-activating protein (GAP) Deleted in Liver Cancer 1 via focal adhesion kinase and protein phosphatase 2A

Deleted in Liver Cancer 1 (DLC1) is a RHO GTPase-activating protein (GAP) that negatively regulates RHO. Through its GAP activity, it modulates the actin cytoskeleton network and focal adhesion dynamics, ultimately leading to suppression of cell invasion and metastasis. Despite its presence in various structural and signaling components, little is known about how the activity of DLC1 is regulated at focal adhesions. Here we show that EGF stimulation activates the GAP activity of DLC1 through a concerted mechanism involving DLC1 phosphorylation by MEK/ERK and its subsequent dephosphorylation by protein phosphatase 2A (PP2A) and inhibition of focal adhesion kinase by MEK/ERK to allow the binding between DLC1 and PP2A. Phosphoproteomics and mutation studies revealed that threonine 301 and serine 308 on DLC1, known previously to be mutated in certain cancers, are required for DLC1-PP2A interaction and the subsequent activation of DLC1 upon their dephosphorylation. The intricate interplay of this "MEK/ERK-focal adhesion kinase-DLC1-PP2A" quartet provides a novel checkpoint in the spatiotemporal control of cell spreading and cell motility.

Cooperation of DLC1 and CDK6 affects breast cancer clinical outcome

Low DLC1 expression is found to frequently co-occur with aberrant expression of cell cycle genes including CDK6 in human lung and colon cancer. Here, we explore the influence of the synergistic effect of DLC1 and CDK6 on human breast cancer survival at the genetic, transcriptional, and translational levels. We found that high DLC1 and low CDK6 expression are associated with good prognosis. The DLC1 intronic SNP rs561681 is found to fit a recessive model, complying with the tumor suppressive role of DLC1. The heterozygote of the DLC1 SNP is found to increase the hazard when the CDK6 intronic SNP rs3731343 is rare homozygous, and it becomes protective when rs3731343 is common homozygous. We propose that DLC1 expression is the lowest in patients harboring the rare homozygote of rs561681 and functional DLC1 is the lowest when rs561681 is heterozygous and rs3731343 is rare homozygous. We are the first to report such synergistic effects of DLC1 and CDK6 on breast cancer survival at the transcriptional level, the overdominant model fitted by the SNP pair, and the dominant negative effect at the translational level. These findings link the germline genetic polymorphisms and synergistic effect of DLC1 and CDK6 with breast cancer progression, which provide the basis for experimentally elucidating the mechanisms driving differential tumor progression and avail in tailoring the clinical treatments for such patients based on their genetic susceptibility.

Loss of stromal caveolin-1 expression: a novel tumor microenvironment biomarker that can predict poor clinical outcomes for pancreatic cancer

AIMS

Cancer development and progression is not only associated with the tumor cell proliferation but also depends on the interaction between tumor cells and the stromal microenvironment. A new understanding of the role of the tumor microenvironment suggests that the loss of stromal caveolin-1 (Cav-1) as a key regulator may become a potential therapy target. This study aims to elucidate whether stromal Cav-1 expression in pancreatic cancer can be a strong prognosis biomarker.

METHODS

Tissue samples from 45 pancreatic cancer patients were studied. Parenchyma and stroma were separated and purified using laser capture microdissection. Stromal Cav-1 expression was measured from pancreatic cancer, paraneoplastic, and normal tissue using immunohistochemistry. We analyzed the correlation of stromal Cav-1 expression with clinicopathologic features and prognostic indicators, such as tumor marker HER-2/neu gene.

RESULTS

Specimens from six patients (13.3%) showed high levels of stromal Cav-1 staining, those from eight patients (17.8%) showed a lower, intermediate level of staining, whereas those from 31 patients (68.9%) showed an absence of staining. Cav-1 expression in cancer-associated fibroblasts was lower than that in paracancer-associated and in normal fibroblasts. Stromal Cav-1 loss was associated with TNM stage (P = 0.018), lymph node metastasis (P = 0.014), distant metastasis (P = 0.027), and HER-2/neu amplification (P = 0.007). The relationships of age, sex, histological grade, and tumor size with stromal Cav-1 expression were not significant (P>0.05). A negative correlation was found between circulating tumor cells and stromal Cav-1 expression (P<0.05).

CONCLUSION

The loss of stromal Cav-1 in pancreatic cancer was an independent prognostic indicator, thus suggesting that stromal Cav-1 may be an effective therapeutic target for patients with pancreatic cancer.

Endocytosis and cancer

Endocytosis entails selective packaging of cell-surface proteins, such as receptors for cytokines and adhesion components, in cytoplasmic vesicles (endosomes). The series of sorting events that determines the fate of internalized proteins, either degradation in lysosomes or recycling back to the plasma membrane, relies on intrinsic sequence motifs, posttranslational modifications (e.g., phosphorylation and ubiquitination), and transient assemblies of both Rab GTPases and phosphoinositide-binding proteins. This multicomponent process is enhanced and skewed in cancer cells; we review mechanisms enabling both major drivers of cancer, p53 and Ras, to bias recycling of integrins and receptor tyrosine kinases (RTKs). Likewise, cadherins and other junctional proteins of cancer cells are constantly removed from the cell surface, thereby disrupting tissue polarity and instigating motile phenotypes. Mutant forms of RTKs able to evade Cbl-mediated ubiquitination, along with overexpression of the wild-type forms and a variety of defective feedback regulatory loops, are frequently detected in tumors. Finally, we describe pharmacological attempts to harness the peculiar endocytic system of cancer, in favor of effective patient treatment.

DLC1 as a regulator of proliferation, invasion, cell cycle, and apoptosis in cutaneous squamous cell carcinoma

Increasing evidence has demonstrated that the tumor suppressor gene deleted in liver cancer-1 (DLC1) is tightly implicated in the development and progression of tumors and is verified to be downregulated in a variety of tumors. However, the roles and precise molecular mechanisms of DLC1 in cutaneous squamous cell carcinoma (cutaneous SCC) remain to be elucidated. In the present study, we confirmed the reduced level in cutaneous SCC tissues and cells, and DLC1 mRNA relative level in cutaneous SCC tissues with lymph node metastasis (0.801 ± 0.079) was markedly lower than those without lymph node metastasis (1.245 ± 0.071) (P < 0.0001). Importantly, the survival rates of patients with low DLC1 level were lower than those with high DLC1 level (P = 0.0051). Further investigation revealed that DLC1 overexpression inhibited proliferation and arrested cell cycle at G0/G1 phase in A431 cells, which may be tightly associated with upregulation of p21 protein and downregulation of cyclin D1 and cdk2 proteins. Moreover, the decreases of FAK and p-FAK as well as the increase of E-cadherin level mediated by elevated DLC1 level suppressed invasion in A431 cells. Additionally, DLC1 overexpression induced apoptosis coupled with elevations of Bax level and caspase-3 activity and decrease of Bcl-2 level in A431 cells. Taken altogether, our data presented herein suggest that DLC1 plays a pivotal role in the development and progression of cutaneous SCC, which may be in part achieved by regulating the signaling pathway related to proliferation, invasion, cell cycle, and apoptosis in cutaneous SCC cells.

In vitro and in vivo effects of geranylgeranyltransferase I inhibitor P61A6 on non-small cell lung cancer cells

Background

Lung cancer is the leading cause of cancer-related mortality. Therapies against non-small cell lung cancer (NSCLC) are particularly needed, as this type of cancer is relatively insensitive to chemotherapy and radiation therapy. We recently identified GGTI compounds that are designed to block geranylgeranylation and membrane association of signaling proteins including the Rho family G-proteins. One of the GGTIs is P61A6 which inhibits proliferation of human cancer cells, causes cell cycle effects with G1 accumulation and exhibits tumor-suppressing effects with human pancreatic cancer xenografts. In this paper, we investigated effects of P61A6 on non-small cell lung cancer (NSCLC) cells in vitro and in vivo.

Methods

Three non-small cell lung cancer cell lines were used to test the ability of P61A6 to inhibit cell proliferation. Further characterization involved analyses of geranylgeranylation, membrane association and activation of RhoA, and anchorage-dependent and –independent growth, as well as cell cycle effects and examination of cell cycle regulators. We also generated stable cells expressing RhoA-F, which bypasses the geranylgeranylation requirement of wild type RhoA, and examined whether the proliferation inhibition by P61A6 is suppressed in these cells. Tumor xenografts of NSCLC cells growing in nude mice were also used to test P61A6’s tumor-suppressing ability.

Results

P61A6 was shown to inhibit proliferation of NSCLC lines H358, H23 and H1507. Detailed analysis of P61A6 effects on H358 cells showed that P61A6 inhibited geranylgeranylation, membrane association of RhoA and caused G1 accumulation associated with decreased cyclin D1/2. The effects of P61A6 to inhibit proliferation could mainly be ascribed to RhoA, as expression of the RhoA-F geranylgeranylation bypass mutant rendered the cells resistant to inhibition by P61A6. We also found that P61A6 treatment of H358 tumor xenografts growing in nude mice reduced their growth as well as the membrane association of RhoA in the tumors.

Conclusion

Thus, P61A6 inhibits proliferation of NSCLC cells and causes G1 accumulation associated with decreased cyclin D1/2. The result with the RhoA-F mutant suggests that the effect of P61A6 to inhibit proliferation is mainly through the inhibition of RhoA. P61A6 also shows efficacy to inhibit growth of xenograft tumor.