Simvastatin is a potential candidate drug in ovarian clear cell carcinomas

Ovarian clear cell carcinomas (OCCC) constitute a rare subtype of epithelial ovarian cancer, lacking efficient treatment options. Based on previous studies, we assessed the anti-proliferative effect of simvastatin, a Rho GTPase interfering drug, in three OCCC cell lines: JHOC-5, OVMANA and TOV-21G, and one high-grade serous ovarian cancer (HGSOC) cell line, Caov3. We used the Rho GTPase interfering drug CID-1067700 as a control. All OCCC cell lines were more sensitive to single-agent simvastatin than the HGSOC cells, while all cell lines were less sensitive to CID-1067700 than to simvastatin. Combinations of carboplatin and simvastatin were generally antagonistic. Most treatments inhibited migration, while only simvastatin and CID-1067700 also disrupted actin organization in the OCCC cell lines. All treatments induced a G1 arrest in JHOC-5 and TOV-21G cells. Treatments with simvastatin consistently reduced c-Myc protein expression in all OCCC cell lines and displayed evidence of causing both caspase-mediated apoptotic cell death and autophagic response in a cell line dependent manner. Differences between cell lines in response to the treatments were observed and such differences, including e. g. prior treatment, should be investigated further. Conclusively, simvastatin efficiently controlled OCCC proliferation and migration, thus showing potential as a candidate drug for the treatment of OCCC.

VAV2 signaling promotes regenerative proliferation in both cutaneous and head and neck squamous cell carcinoma

Regenerative proliferation capacity and poor differentiation are histological features usually linked to poor prognosis in head and neck squamous cell carcinoma (hnSCC). However, the pathways that regulate them remain ill-characterized. Here, we show that those traits can be triggered by the RHO GTPase activator VAV2 in keratinocytes present in the skin and oral mucosa. VAV2 is also required to maintain those traits in hnSCC patient-derived cells. This function, which is both catalysis- and RHO GTPase-dependent, is mediated by c-Myc- and YAP/TAZ-dependent transcriptomal programs associated with regenerative proliferation and cell undifferentiation, respectively. High levels of VAV2 transcripts and VAV2-regulated gene signatures are both associated with poor hnSCC patient prognosis. These results unveil a druggable pathway linked to the malignancy of specific SCC subtypes.

The Rho signalling pathway is frequently activated in squamous carcinomas. Here, the authors find that the Rho GEF VAV2 is over expressed in both cutaneous and head and neck squamous cell carcinomas and that at the molecular level VAV2 promotes a pro-tumorigenic stem cell-like signalling programme.

Vav proteins maintain epithelial traits in breast cancer cells using miR-200c-dependent and independent mechanisms

The bidirectional regulation of epithelial-mesenchymal transitions (EMT) is key in tumorigenesis. Rho GTPases regulate this process via canonical pathways that impinge on the stability of cell-to-cell contacts, cytoskeletal dynamics, and cell invasiveness. Here, we report that the Rho GTPase activators Vav2 and Vav3 utilize a new Rac1-dependent and miR-200c-dependent mechanism that maintains the epithelial state by limiting the abundance of the Zeb2 transcriptional repressor in breast cancer cells. In parallel, Vav proteins engage a mir-200c-independent expression prometastatic program that maintains epithelial cell traits only under 3D culture conditions. Consistent with this, the depletion of endogenous Vav proteins triggers mesenchymal features in epithelioid breast cancer cells. Conversely, the ectopic expression of an active version of Vav2 promotes mesenchymal-epithelial transitions using E-cadherin-dependent and independent mechanisms depending on the mesenchymal breast cancer cell line used. In silico analyses suggest that the negative Vav anti-EMT pathway is operative in luminal breast tumors. Gene signatures from the Vav-associated proepithelial and prometastatic programs have prognostic value in breast cancer patients.

Dynamics of p14ARF and Focal Adhesion Kinase-Mediated Autophagy in Cancer

It has been widely shown that the focal adhesion kinase (FAK) is involved in nearly every aspect of cancer, from invasion to metastasis to epithelial–mesenchymal transition and maintenance of cancer stem cells. FAK has been shown to interact with p14ARF (alternative reading frame)—a well-established tumor suppressor—and functions in the negative regulation of cancer through both p53-dependent and -independent pathways. Interestingly, both FAK and ARF (human and mouse counterpart) proteins, as well as p53, are involved in autophagy—a process of “self-digestion”—whose main function is the recycling of cellular components and quality control of proteins and organelles. In the last years, an unexpected role of p14ARF in the survival of cancer cells has been underlined in different cellular contexts, suggesting a novel pro-oncogenic function of this protein. In this review, the mechanisms whereby ARF and FAK control autophagy are presented, as well as the role of autophagy in cell migration and spreading. Integrated investigation of these cell functions is extremely important to understand the mechanism of the basis of cell transformation and migration and thus cancer development.

Characterization of Novel Molecular Mechanisms Favoring Rac1 Membrane Translocation

The Rac1 GTPase plays key roles in cytoskeletal organization, cell motility and a variety of physiological and disease-linked responses. Wild type Rac1 signaling entails dissociation of the GTPase from cytosolic Rac1-Rho GDP dissociation inhibitor (GDI) complexes, translocation to membranes, activation by exchange factors, effector binding, and activation of downstream signaling cascades. Out of those steps, membrane translocation is the less understood. Using transfections of a expression cDNA library in cells expressing a Rac1 bioreporter, we previously identified a cytoskeletal feedback loop nucleated by the F-actin binding protein coronin 1A (Coro1A) that promotes Rac1 translocation to the plasma membrane by facilitating the Pak-dependent dissociation of Rac1-Rho GDI complexes. This screening identified other potential regulators of this process, including WDR26, basigin, and TMEM8A. Here, we show that WDR26 promotes Rac1 translocation following a Coro1A-like and Coro1A-dependent mechanism. By contrast, basigin and TMEM8A stabilize Rac1 at the plasma membrane by inhibiting the internalization of caveolin-rich membrane subdomains. This latter pathway is F-actin-dependent but Coro1A-, Pak- and Rho GDI-independent.

The P-Rex1/Rac signaling pathway as a point of convergence for HER/ErbB receptor and GPCR responses

Guanine nucleotide Exchange Factors (GEFs) are responsible for mediating GDP/GTP exchange for specific small G proteins, such as Rac. There has been substantial evidence for the involvement of Rac-GEFs in the control of cancer cell migration and metastatic progression. We have previously established that the Rac-GEF P-Rex1 is a mediator of actin cytoskeleton rearrangements and cell motility in breast cancer cells downstream of HER/ErbB receptors and the G-Protein Coupled Receptor (GPCR) CXCR4. P-Rex1 is highly expressed in luminal A and B breast cancer compared to normal mammary tissue, whereas expression is very low in basal breast cancer, and its expression correlates with the appearance of metastasis in patients. Here, we discuss the involvement of P-Rex1 as an effector of oncogenic/metastatic receptors in breast cancer and underscore its relevance in the convergence of receptor-triggered motile signals. In addition, we provide an overview of our recent findings describing a cross-talk between HER/ErbB receptors and CXCR4, and how this impacts on the activation of P-Rex1/Rac1 signaling, as well as highlight challenges that lie ahead. We propose a model in which P-Rex1 acts as a crucial node for the integration of upstream inputs from HER/ErbB receptors and CXCR4 in luminal breast cancer cells.

Subtype-specific overexpression of the Rac-GEF P-REX1 in breast cancer is associated with promoter hypomethylation

Introduction

The Rac-GEF P-REX1 is a key mediator of ErbB signaling in breast cancer recently implicated in mammary tumorigenesis and metastatic dissemination. Although P-REX1 is essentially undetectable in normal human mammary epithelial tissue, this Rac-GEF is markedly upregulated in human breast carcinomas, particularly of the luminal subtype. The mechanisms underlying P-REX1 upregulation in breast cancer are unknown. Toward the goal of dissecting the mechanistic basis of P-REX1 overexpression in breast cancer, in this study we focused on the analysis of methylation of the PREX1 gene promoter.

Methods

To determine the methylation status of the PREX1 promoter region, we used bisulfite genomic sequencing and pyrosequencing approaches. Re-expression studies in cell lines were carried out by treatment of breast cancer cells with the demethylating agent 5-aza-2′-deoxycitidine. PREX1 gene methylation in different human breast cancer subtypes was analyzed from the TCGA database.

Results

We found that the human PREX1 gene promoter has a CpG island located between -1.2 kb and +1.4 kb, and that DNA methylation in this region inversely correlates with P-REX1 expression in human breast cancer cell lines. A comprehensive analysis of human breast cancer cell lines and tumors revealed significant hypomethylation of the PREX1 promoter in ER-positive, luminal subtype, whereas hypermethylation occurs in basal-like breast cancer. Treatment of normal MCF-10A or basal-like cancer cells, MDA-MB-231 with the demethylating agent 5-aza-2′-deoxycitidine in combination with the histone deacetylase inhibitor trichostatin A restores P-REX1 levels to those observed in luminal breast cancer cell lines, suggesting that aberrant expression of P-REX1 in luminal breast cancer is a consequence of PREX1 promoter demethylation. Unlike PREX1, the pro-metastatic Rho/Rac-GEF, VAV3, is not regulated by methylation. Notably, PREX1 gene promoter hypomethylation is a prognostic marker of poor patient survival.

Conclusions

Our study identified for the first time gene promoter hypomethylation as a distinctive subtype-specific mechanism for controlling the expression of a key regulator of Rac-mediated motility and metastasis in breast cancer.

Electronic supplementary material

The online version of this article (doi:10.1186/s13058-014-0441-7) contains supplementary material, which is available to authorized users.

How cells explore shape space: a quantitative statistical perspective of cellular morphogenesis

Through statistical analysis of datasets describing single cell shape following systematic gene depletion, we have found that the morphological landscapes explored by cells are composed of a small number of attractor states. We propose that the topology of these landscapes is in large part determined by cell-intrinsic factors, such as biophysical constraints on cytoskeletal organization, and reflects different stable signaling and/or transcriptional states. Cell-extrinsic factors act to determine how cells explore these landscapes, and the topology of the landscapes themselves. Informational stimuli primarily drive transitions between stable states by engaging signaling networks, while mechanical stimuli tune, or even radically alter, the topology of these landscapes. As environments fluctuate, the topology of morphological landscapes explored by cells dynamically adapts to these fluctuations. Finally we hypothesize how complex cellular and tissue morphologies can be generated from a limited number of simple cell shapes.

Contribution of the R-Ras2 GTP-binding protein to primary breast tumorigenesis and late-stage metastatic disease

R-Ras2 is a transforming GTPase that shares downstream effectors with Ras subfamily proteins. However, little information exists about the function of this protein in tumorigenesis and its signalling overlap with classical Ras GTPases. Here we show, by combining loss- and gain-of-function studies in breast cancer cells, mammary epithelial cells and mouse models, that endogenous R-Ras2 has a role in both primary breast tumorigenesis and the late metastatic steps of cancer cells in the lung parenchyma. R-Ras2 drives tumorigenesis in a phosphatidylinostiol-3 kinase (PI3K)-dependent and signalling autonomous manner. By contrast, its prometastatic role requires other priming oncogenic signals and the engagement of several downstream elements. R-Ras2 function is required even in cancer cells exhibiting constitutive activation of classical Ras proteins, indicating that these GTPases are not functionally redundant. Our results also suggest that application of long-term R-Ras2 therapies will result in the development of compensatory mechanisms in breast tumours.

Development of EHop-016: a small molecule inhibitor of Rac

The Rac inhibitor EHop-016 was developed as a compound with the potential to inhibit cancer metastasis. Inhibition of the first step of metastasis, migration, is an important strategy for metastasis prevention. The small GTPase Rac acts as a pivotal binary switch that is turned "on" by guanine nucleotide exchange factors (GEFs) via a myriad of cell surface receptors, to regulate cancer cell migration, survival, and proliferation. Unlike the related GTPase Ras, Racs are not usually mutated, but overexpressed or overactivated in cancer. Therefore, a rational Rac inhibitor should block the activation of Rac by its upstream effectors, GEFs, and the Rac inhibitor NSC23766 was developed using this rationale. However, this compound is ineffective at inhibiting the elevated Rac activity of metastatic breast cancer cells. Therefore, a panel of small molecule compounds were derived from NSC23766 and screened for Rac activity inhibition in metastatic cancer cells. EHop-016 was identified as a compound that blocks the interaction of Rac with the GEF Vav in metastatic human breast cancer cells with an IC50 of ~1μM. At higher concentrations (10μM), EHop-016 inhibits the related Rho GTPase Cdc42, but not Rho, and also reduces cell viability. Moreover, EHop-016 inhibits the activation of the Rac downstream effector p21-activated kinase, extension of motile actin-based structures, and cell migration. Future goals are to develop EHop-016 as a therapeutic to inhibit cancer metastasis, either individually or in combination with current anticancer compounds. The next generation of EHop-016-based Rac inhibitors is also being developed.

Phosphorylation of P-Rex1 at serine 1169 participates in IGF-1R signaling in breast cancer cells

Former reports demonstrated that P-Rex, a Rac guanine nucleotide exchange factor (GEF), participated in signaling upon activation of the ErbB receptor tyrosine kinases (RTKs). Activation of ErbB receptors turned on a phosphorylation/dephosphorylation cycle of P-Rex in which stimulation of serine(1169) phosphorylation played a critical role in the activation of this GEF. This precedent raised the important question of whether this P-Rex1 activation mechanism was restricted to ErbB receptors or could represent a general signaling event shared by several RTKs. To explore that possibility the effect of activation of distinct RTKs on the phosphorylation of P-Rex1 at serine(1169) was analyzed. Here we report that IGF-1 and FGF receptors activate serine(1169) phosphorylation of P-Rex1. P-Rex1 phosphorylation was required for IGF-1-induced up-regulation of Rac activity and cell proliferation. Moreover, IGF-1-induced adhesion was impaired in MCF7 breast cancer cells by knocking down P-Rex1. These results demonstrate that phosphorylation P-Rex1 at S(1169) represents a mechanism of activation of P-Rex1 common to multiple RTKs. We suggest that P-Rex proteins may act as novel and important transducers of pro-oncogenic signals that emanate from RTKs, and could even participate in other biological responses, such as metabolic control, which are not strictly related to the proliferation effects of RTKs.

Molecular pathways: P-Rex in cancer

P-Rex proteins are Rho/Rac guanine nucleotide exchange factors that participate in the regulation of several cancer-related cellular functions such as proliferation, motility, and invasion. Expectedly, a significant portion of these actions of P-Rex proteins must be related to their Rac regulatory properties. In addition, P-Rex proteins control signaling by the phosphoinositide 3-kinase (PI3K) route by interacting with PTEN and mTOR. The interaction with PTEN inhibits its phosphatase activity, leading to AKT activation. The interaction with mTOR may be important in nutrient-stimulated Rac activation and migration. In humans, several studies have implicated P-Rex proteins in the pathophysiology of various neoplasias. Thus, overexpression of P-Rex proteins has been linked to poor patient outcome in breast cancer and may facilitate metastatic dissemination of prostate cancer cells. In addition, whole-genome sequencing described P-Rex2 as a significantly mutated gene in melanoma. Furthermore, expression in melanocytes of mutated forms of P-Rex2 found in patients with melanoma showed the protumorigenic role of these P-Rex mutations in melanoma genesis. These findings open interesting opportunities for P-Rex targeting in cancer. Moreover, the implication of P-Rex partner proteins such as Rac, mTOR, or PTEN in cancer has opened the possibility of acting on P-Rex to restrict protumorigenic signaling through these pathways.

Emerging molecular targets in melanoma invasion and metastasis

Metastatic cutaneous melanoma accounts for the majority of skin cancer deaths due to its aggressiveness and high resistance to current therapies. To efficiently metastasize, invasive melanoma cells need to change their cytoskeletal organization and alter contacts with the extracellular matrix and the surrounding stromal cells. Melanoma cells can use different migratory strategies depending on varying environments to exit the primary tumour mass and invade surrounding and later distant tissues. In this review, we have focused on tumour cell plasticity or the interconvertibility that melanoma cells have as one of the factors that contribute to melanoma metastasis. This has been an area of very intense research in the last 5 yr yielding a vast number of findings. We have therefore reviewed all the possible clinical opportunities that this new knowledge offers to both stratify and treat cutaneous malignant melanoma patients.