Norepinephrine induces anoikis resistance in high-grade serous ovarian cancer precursor cells

High-grade serous carcinoma (HGSC) is the most lethal gynecological malignancy in the United States. Late diagnosis and the emergence of chemoresistance have prompted studies into how the tumor microenvironment, and more recently tumor innervation, may be leveraged for HGSC prevention and interception. In addition to stess-induced sources, concentrations of the sympathetic neurotransmitter norepinephrine (NE) in the ovary increase during ovulation and after menopause. Importantly, NE exacerbates advanced HGSC progression. However, little is known about the role of NE in early disease pathogenesis. Here, we investigated the role of NE in instigating anchorage independence and micrometastasis of preneoplastic lesions from the fallopian tube epithelium (FTE) to the ovary, an essential step in HGSC onset. We found that in the presence of NE, FTE cell lines were able to survive in ultra-low-attachment (ULA) culture in a β-adrenergic receptor-dependent (β-AR-dependent) manner. Importantly, spheroid formation and cell viability conferred by treatment with physiological sources of NE were abrogated using the β-AR blocker propranolol. We have also identified that NE-mediated anoikis resistance may be attributable to downregulation of colony-stimulating factor 2. These findings provide mechanistic insight and identify targets that may be regulated by ovary-derived NE in early HGSC.

Abstract 3155: Loss of YAP1 dysregulates RhoA signaling and promotes cell invasion

While Hippo pathway signaling undoubtedly plays an important role in cancer, the role of its effector YAP1 as an oncogene or tumor suppressor is context dependent. The precise conditions that support the tumor-promoting or tumor-suppressing roles of YAP1 remain largely undefined. While YAP1 can drive oncogenic programs through its nuclear function as a transcriptional coactivator of TEAD and other transcription factors, previous findings from our lab and others suggest that loss of YAP1 function can also have tumor promoting consequences. One well-characterized role of YAP1 is that of a nuclear relay of signals triggered by mechanical forces that lead to activation of Rho GTPases. Our new studies using a combination of genetic, biochemical, and microscopy techniques provide evidence that YAP1 is not only activated by Rho, but can also regulate Rho activation and the actin cytoskeleton. Knockdown of YAP1 in MCF10A immortalized mammary epithelial cells resulted in increased lamellipodia formation in culture as seen by time-lapse microscopy, and increased protrusive, invasive activity in 3D Matrigel culture. YAP1 knockdown also induced a scattering phenotype, characterized by cell dissociation from the leading edge of a wounded monolayer. While E-cadherin protein levels were unaffected by YAP1 knockdown, adherens junction maturation at cell-cell junctions was compromised. These morphological alterations were associated with decreased levels of active RhoA, as well as a decrease in downstream myosin light chain phosphorylation. Our results indicate loss of YAP1 decreases active RhoA, leading to reduced cell-cell adhesion and increased protrusive cellular behavior. Our findings raise the possibility that YAP1 is not only a Rho-sensor, but also mediates a feedforward regulatory loop to maintain Rho-regulated cytoskeletal structures, and that loss of YAP1 through genetic deletion in tumor cells could promote invasive behavior.

Citation Format: Natalie M. Hendrick, Marcin P. Iwanicki, Carman Man-Chung Li, Duyen Amy Bui, Laura M. Selfors, Joan S. Brugge. Loss of YAP1 dysregulates RhoA signaling and promotes cell invasion [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 3155.

Corrigendum: Chaperone-mediated autophagy degrades mutant p53

In the above-mentioned article, it has come to the authors' attention that, during the preparation of Figure 5C and Supplemental Figure S2C for the final version of this article, the authors unintentionally assembled incorrect tubulin immunoblots due to similarities in the markings or names, such as FLT3 versus FT, between two similar experiments. The amended versions of these figures are shown below. Neither the quantitative determinations nor the conclusions of this article are altered. The authors apologize for these errors.

Mutant p53 regulates ovarian cancer transformed phenotypes through autocrine matrix deposition

High-grade serous ovarian carcinoma (HGS-OvCa) harbors p53 mutations and can originate from the epithelial cell compartment of the fallopian tube fimbriae. From this site, neoplastic cells detach, survive in the peritoneal cavity, and form cellular clusters that intercalate into the mesothelium to form ovarian and peritoneal masses. To examine the contribution of mutant p53 to phenotypic alterations associated with HGS-OvCA, we developed live-cell microscopy assays that recapitulate these early events in cultured fallopian tube nonciliated epithelial (FNE) cells. Expression of stabilizing mutant variants of p53, but not depletion of endogenous wild-type p53, in FNE cells promoted survival and cell-cell aggregation under conditions of cell detachment, leading to the formation of cell clusters with mesothelium-intercalation capacity. Mutant p53^R175H-induced phenotypes were dependent on fibronectin production, α5β1 fibronectin receptor engagement, and TWIST1 expression. These results indicate that FNE cells expressing stabilizing p53 mutants acquire anchorage independence and subsequent mesothelial intercalation capacity through a mechanism involving mesenchymal transition and matrix production. These findings provide important new insights into activities of mutant p53 in the cells of origin of HGS-OvCa.

Abstract PR12: Mutant p53 drives early events in fallopian tube tumorigenesis through mesenchyme-associated autocrine production of matrix that supports survival and mesothelial intercalation

High-grade serous ovarian cancer (HGS-OvCa) harbor p53 mutations and predominantly originates from the secretory epithelial cell compartment of the fallopian tube fimbriae. From this site, tumor cells detach, survive in the peritoneal cavity, and form cellular clusters that clear the mesothelium and expand to form peritoneal masses. To examine the contribution of mutant p53 to any of these phenotypic alterations associated with HGS-OvCA tumor progression, we developed live-cell microscopy assays that recapitulate these phenotypes and examined dynamic processes regulated by depletion of p53 or gain-of-function (GOF) mutations in p53 in cultured secretory fallopian tube epithelial cells. Expression of GOF mutant variants of p53, but not depletion of endogenous wild-type p53, promoted survival and cell-cell aggregation under conditions of cell detachment, leading to the formation of spheroids with mesothelium-clearing capacity. These phenotypes were blocked by mutant p53 reactivation and depended on the expression of the mesenchyme transcription factor TWIST1, inhibition of p63 and de novo formation of a unique cell-matrix adhesion niche supported by autocrine fibronectin production and activation of integrins in detached cells. Inhibition of fibronectin or integrin α5 in suspension blocked cell-to-cell adhesion leading to HGS-OvCa spheroid disintegration and ultimately anoikis. These results indicate the detached FTE cells-expressing GOF mutants of p53 undergo a mesenchymal transition under conditions of matrix detachment leading to autocrine production of matrix and anchorage-independent survival and proliferation, as well as mesothelial clearance activity. These findings provide important new insights into activities of mutant p53 that may play a critical role in early events in tumorigenesis of high-grade ovarian serous tumors and provide a rationale for the development of therapeutics that target ovarian cancer cells transiting through the peritoneal cavity.

This abstract is also presented as Poster B03.

Citation Format: Marcin P. Iwanicki, Hsing-Yu Chen, Ioannis Zervantonakis, Marian Novak, Taru Muranen, Tan A. Ince, Ronny Drapkin, Joan S. Brugge. Mutant p53 drives early events in fallopian tube tumorigenesis through mesenchyme-associated autocrine production of matrix that supports survival and mesothelial intercalation. [abstract]. In: Proceedings of the AACR Special Conference on Advances in Ovarian Cancer Research: Exploiting Vulnerabilities; Oct 17-20, 2015; Orlando, FL. Philadelphia (PA): AACR; Clin Cancer Res 2016;22(2 Suppl):Abstract nr PR12.

Mesenchymal gene program-expressing ovarian cancer spheroids exhibit enhanced mesothelial clearance

Metastatic dissemination of ovarian tumors involves the invasion of tumor cell clusters into the mesothelial cell lining of peritoneal cavity organs; however, the tumor-specific factors that allow ovarian cancer cells to spread are unclear. We used an in vitro assay that models the initial step of ovarian cancer metastasis, clearance of the mesothelial cell layer, to examine the clearance ability of a large panel of both established and primary ovarian tumor cells. Comparison of the gene and protein expression profiles of clearance-competent and clearance-incompetent cells revealed that mesenchymal genes are enriched in tumor populations that display strong clearance activity, while epithelial genes are enriched in those with weak or undetectable activity. Overexpression of transcription factors SNAI1, TWIST1, and ZEB1, which regulate the epithelial-to-mesenchymal transition (EMT), promoted mesothelial clearance in cell lines with weak activity, while knockdown of the EMT-regulatory transcription factors TWIST1 and ZEB1 attenuated mesothelial clearance in ovarian cancer cell lines with strong activity. These findings provide important insights into the mechanisms associated with metastatic progression of ovarian cancer and suggest that inhibiting pathways that drive mesenchymal programs may suppress tumor cell invasion of peritoneal tissues.

Gene expression signature of normal cell-of-origin predicts ovarian tumor outcomes

The potential role of the cell-of-origin in determining the tumor phenotype has been raised, but not adequately examined. We hypothesized that distinct cells-of-origin may play a role in determining ovarian tumor phenotype and outcome. Here we describe a new cell culture medium for in vitro culture of paired normal human ovarian (OV) and fallopian tube (FT) epithelial cells from donors without cancer. While these cells have been cultured individually for short periods of time, to our knowledge this is the first long-term culture of both cell types from the same donors. Through analysis of the gene expression profiles of the cultured OV/FT cells we identified a normal cell-of-origin gene signature that classified primary ovarian cancers into OV-like and FT-like subgroups; this classification correlated with significant differences in clinical outcomes. The identification of a prognostically significant gene expression signature derived solely from normal untransformed cells is consistent with the hypothesis that the normal cell-of-origin may be a source of ovarian tumor heterogeneity and the associated differences in tumor outcome.

Chaperone-mediated autophagy degrades mutant p53

Missense mutations in the gene TP53, which encodes p53, one of the most important tumor suppressors, are common in human cancers. Accumulated mutant p53 proteins are known to actively contribute to tumor development and metastasis. Thus, promoting the removal of mutant p53 proteins in cancer cells may have therapeutic significance. Here we investigated the mechanisms that govern the turnover of mutant p53 in nonproliferating tumor cells using a combination of pharmacological and genetic approaches. We show that suppression of macroautophagy by multiple means promotes the degradation of mutant p53 through chaperone-mediated autophagy in a lysosome-dependent fashion. In addition, depletion of mutant p53 expression due to macroautophagy inhibition sensitizes the death of dormant cancer cells under nonproliferating conditions. Taken together, our results delineate a novel strategy for killing tumor cells that depend on mutant p53 expression by the activation of chaperone-mediated autophagy and potential pharmacological means to reduce the levels of accumulated mutant p53 without the restriction of mutant p53 conformation in quiescent tumor cells.

Abstract A7: Targeting mutant p53 and cell-cell adhesion in ovarian cancer

One of the most important challenges in the ovarian cancer research is to identify new molecular pathways that can be targeted to kill ovarian cancer cells. High-grade serous ovarian cancer (HGS-OvCa) cells survive, proliferate, and assemble into multicellular clusters that have a capacity to disseminate within the peritoneum. Therefore, it is important to identify specific molecular mechanisms that can be targeted to block survival, growth, and assembly of ovarian cancer multicellular clusters that metastasize within peritoneum. High-grade ovarian tumors originate from the fallopian tube epithelium (FTE) and almost all have mutations in theTP53 gene. The contribution of various mutant p53 proteins (m-p53) to ovarian cancer and whether targeting mutant p53 –dependent molecular mechanisms in ovarian cancer is poorly understood and of clinical significance. We have developed new methodologies and used them to identify m-p53-dependent pathways that support HGS-OvCa survival, proliferation and assembly of multicellular aggregates under condition mimicking peritoneal suspension. To determine whether mutations in TP53 contribute to the ability of HGS-OvCa cells to survive, proliferate, and assemble into multicellular clusters we introduced different variants of mutant p53 (m-p53) into normal human non-transformed FTE cells. We found that expression of m-p53 variants (R175H; R249S; R273H) in FTE cells promoted survival, growth, and assembly of multicellular clusters under conditions mimicking peritoneal suspension. Interestingly m-p53-driven phenotypes were not induced by the loss of p53 expression; and more importantly, these phenotypes were blocked by the reactivation of p53 pathway with small molecule inhibitor NSC319726. We further found that m-p53 induced phenotypes were dependent on the expression of integrin β 1 (ITGB1). The evidence that activated ITGB1 is enriched at cell's surface of precursors of HGS-OvCa within the fallopian tube and HGS-OvCa isolated from ovarian cancer patients highlighted the relevance of these findings to ovarian cancer. We hypothesize that mutant p53 supports survival, growth, and assembly of multicellular HGS-OvCa clusters through mechanisms in which ITGB1 plays a critical role. Our data indicate that observed phenotypes are the consequence of the m-p53 gain of function mechanisms that are amenable to therapeutic inhibitions and targeting m-p53 in HGS-OvCa might be of clinical significance.

Citation Format: Marcin P. Iwanicki, Marian Novak, Ioannis K. Zervantonakis, Tan A. Ince, Ronny Drapkin, Joan S. Brugge. Targeting mutant p53 and cell-cell adhesion in ovarian cancer. [abstract]. In: Proceedings of the AACR Special Conference on Advances in Ovarian Cancer Research: From Concept to Clinic; Sep 18-21, 2013; Miami, FL. Philadelphia (PA): AACR; Clin Cancer Res 2013;19(19 Suppl):Abstract nr A7.

The reorientation of cell nucleus promotes the establishment of front-rear polarity in migrating fibroblasts

The establishment of cell polarity is an essential step in the process of cell migration. This process requires precise spatiotemporal coordination of signaling pathways that in most cells create the typical asymmetrical profile of a polarized cell with nucleus located at the cell rear and the microtubule organizing center (MTOC) positioned between the nucleus and the leading edge. During cell polarization, nucleus rearward positioning promotes correct microtubule organizing center localization and thus the establishment of front-rear polarity and directional migration. We found that cell polarization and directional migration require also the reorientation of the nucleus. Nuclear reorientation is manifested as temporally restricted nuclear rotation that aligns the nuclear axis with the axis of cell migration. We also found that nuclear reorientation requires physical connection between the nucleus and cytoskeleton mediated by the LINC (linker of nucleoskeleton and cytoskeleton) complex. Nuclear reorientation is controlled by coordinated activity of lysophosphatidic acid (LPA)-mediated activation of GTPase Rho and the activation of integrin, FAK (focal adhesion kinase), Src, and p190RhoGAP signaling pathway. Integrin signaling is spatially induced at the leading edge as FAK and p190RhoGAP are predominantly activated or localized at this location. We suggest that integrin activation within lamellipodia defines cell front, and subsequent FAK, Src, and p190RhoGAP signaling represents the polarity signal that induces reorientation of the nucleus and thus promotes the establishment of front-rear polarity.

Emerging role for nuclear rotation and orientation in cell migration

Nucleus movement, positioning, and orientation is precisely specified and actively regulated within cells, and it plays a critical role in many cellular and developmental processes. Mutation of proteins that regulate the nucleus anchoring and movement lead to diverse pathologies, laminopathies in particular, suggesting that the nucleus correct positioning and movement is essential for proper cellular function. In motile cells that polarize toward the direction of migration, the nucleus undergoes controlled rotation promoting the alignment of the nucleus with the axis of migration. Such spatial organization of the cell appears to be optimal for the cell migration. Nuclear reorientation requires the cytoskeleton to be anchored to the nuclear envelope, which exerts pulling or pushing torque on the nucleus. Here we discuss the possible molecular mechanisms regulating the nuclear rotation and reorientation and the significance of this type of nuclear movement for cell migration.

Ovarian cancer spheroids use myosin-generated force to clear the mesothelium

Dissemination of ovarian tumors involves the implantation of cancer spheroids into the mesothelial monolayer on the walls of peritoneal and pleural cavity organs. Biopsies of tumors attached to peritoneal organs show that mesothelial cells are not present under tumor masses. We have developed a live, image-based in vitro model in which interactions between tumor spheroids and mesothelial cells can be monitored in real time to provide spatial and temporal understanding of mesothelial clearance. Here we provide evidence that ovarian cancer spheroids utilize integrin- and talin- dependent activation of myosin and traction force to promote mesothelial cells displacement from underneath a tumor cell spheroid. These results suggest that ovarian tumor cell clusters gain access to the sub-mesothelial environment by exerting force on the mesothelial cells lining target organs, driving migration and clearance of the mesothelial cells.

In vitro mesothelial clearance assay that models the early steps of ovarian cancer metastasis

Ovarian cancer is the fifth leading cause of cancer related deaths in the United States(1). Despite a positive initial response to therapies, 70 to 90 percent of women with ovarian cancer develop new metastases, and the recurrence is often fatal(2). It is, therefore, necessary to understand how secondary metastases arise in order to develop better treatments for intermediate and late stage ovarian cancer. Ovarian cancer metastasis occurs when malignant cells detach from the primary tumor site and disseminate throughout the peritoneal cavity. The disseminated cells can form multicellular clusters, or spheroids, that will either remain unattached, or implant onto organs within the peritoneal cavity(3) (Figure 1, Movie 1). All of the organs within the peritoneal cavity are lined with a single, continuous, layer of mesothelial cells(4-6) (Figure 2). However, mesothelial cells are absent from underneath peritoneal tumor masses, as revealed by electron micrograph studies of excised human tumor tissue sections(3,5-7) (Figure 2). This suggests that mesothelial cells are excluded from underneath the tumor mass by an unknown process. Previous in vitro experiments demonstrated that primary ovarian cancer cells attach more efficiently to extracellular matrix than to mesothelial cells(8), and more recent studies showed that primary peritoneal mesothelial cells actually provide a barrier to ovarian cancer cell adhesion and invasion (as compared to adhesion and invasion on substrates that were not covered with mesothelial cells)(9,10). This would suggest that mesothelial cells act as a barrier against ovarian cancer metastasis. The cellular and molecular mechanisms by which ovarian cancer cells breach this barrier, and exclude the mesothelium have, until recently, remained unknown. Here we describe the methodology for an in vitro assay that models the interaction between ovarian cancer cell spheroids and mesothelial cells in vivo (Figure 3, Movie 2). Our protocol was adapted from previously described methods for analyzing ovarian tumor cell interactions with mesothelial monolayers(8-16), and was first described in a report showing that ovarian tumor cells utilize an integrin -dependent activation of myosin and traction force to promote the exclusion of the mesothelial cells from under a tumor spheroid(17). This model takes advantage of time-lapse fluorescence microscopy to monitor the two cell populations in real time, providing spatial and temporal information on the interaction. The ovarian cancer cells express red fluorescent protein (RFP) while the mesothelial cells express green fluorescent protein (GFP). RFP-expressing ovarian cancer cell spheroids attach to the GFP-expressing mesothelial monolayer. The spheroids spread, invade, and force the mesothelial cells aside creating a hole in the monolayer. This hole is visualized as the negative space (black) in the GFP image. The area of the hole can then be measured to quantitatively analyze differences in clearance activity between control and experimental populations of ovarian cancer and/ or mesothelial cells. This assay requires only a small number of ovarian cancer cells (100 cells per spheroid X 20-30 spheroids per condition), so it is feasible to perform this assay using precious primary tumor cell samples. Furthermore, this assay can be easily adapted for high throughput screening.

Inhibition of PI3K/mTOR leads to adaptive resistance in matrix-attached cancer cells

The PI3K/mTOR-pathway is the most commonly dysregulated pathway in epithelial cancers and represents an important target for cancer therapeutics. Here, we show that dual inhibition of PI3K/mTOR in ovarian cancer-spheroids leads to death of inner matrix-deprived cells, whereas matrix-attached cells are resistant. This matrix-associated resistance is mediated by drug-induced upregulation of cellular survival programs that involve both FOXO-regulated transcription and cap-independent translation. Inhibition of any one of several upregulated proteins, including Bcl-2, EGFR, or IGF1R, abrogates resistance to PI3K/mTOR inhibition. These results demonstrate that acute adaptive responses to PI3K/mTOR inhibition in matrix-attached cells resemble well-conserved stress responses to nutrient and growth factor deprivation. Bypass of this resistance mechanism through rational design of drug combinations could significantly enhance PI3K-targeted drug efficacy.

Mutant p53 drives invasion by promoting integrin recycling

p53 is a tumor suppressor protein whose function is frequently lost in cancers through missense mutations within the Tp53 gene. This results in the expression of point-mutated p53 proteins that have both lost wild-type tumor suppressor activity and show gain of functions that contribute to transformation and metastasis. Here, we show that mutant p53 expression can promote invasion, loss of directionality of migration, and metastatic behavior. These activities of p53 reflect enhanced integrin and epidermal growth factor receptor (EGFR) trafficking, which depends on Rab-coupling protein (RCP) and results in constitutive activation of EGFR/integrin signaling. We provide evidence that mutant p53 promotes cell invasion via the inhibition of TAp63, and simultaneous loss of p53 and TAp63 recapitulates the phenotype of mutant p53 in cells. These findings open the possibility that blocking alpha5/beta1-integrin and/or the EGF receptor will have therapeutic benefit in mutant p53-expressing cancers.

Transcriptional regulation of metastatic [Id]entity by KLF17

A novel in vivo screening approach has identified KLF17 as a key metastasis suppressor gene that acts through regulation of Id1 transcription factor-dependent induction of the epithelial-to-mesenchymal transition.

FAK, PDZ-RhoGEF and ROCKII cooperate to regulate adhesion movement and trailing-edge retraction in fibroblasts

A key step in cell migration is the dynamic formation and disassembly of adhesions at the front and the concomitant movement and release of adhesions in the rear of the cell. Fibroblasts maintained in the absence of serum have stable adhesions within the rear of the cell and exhibit reduced trailing-edge retraction resulting in an elongated cell phenotype. Addition of lysophosphatidic acid (LPA) induced the movement of adhesions and retraction of the trailing edge, thus mimicking tail retraction in a migrating cell. Focal adhesion kinase (FAK), guanine nucleotide exchange factors (GEF) for Rho and the Rho effector Rho kinase II (ROCKII) are crucial for the regulation of adhesion movement and trailing-edge retraction. Downregulation of FAK by small interfering RNAs or small hairpin RNAs blocked LPA-induced adhesion movement and restoration of cell shape. This phenotype was rescued by the ectopic expression of PDZ-RhoGEF or a RhoA-effector-domain mutant that activates ROCK. Knockdown of PDZ-RhoGEF or ROCKII inhibited LPA-induced trailing-edge retraction and adhesion movement. Moreover, overexpressed PDZ-RhoGEF co-immunoprecipitated with FAK and localized to FAK-containing adhesions. These studies support a model in which FAK and PDZ-RhoGEF cooperate to induce Rho/ROCKII-dependent focal adhesion movement and trailing-edge retraction in response to LPA.

RACK1 targets the extracellular signal-regulated kinase/mitogen-activated protein kinase pathway to link integrin engagement with focal adhesion disassembly and cell motility

The extracellular signal-regulated kinase (ERK) cascade is activated in response to a multitude of extracellular signals and converts these signals into a variety of specific biological responses, including cell differentiation, cell movement, cell division, and apoptosis. The specificity of the biological response is likely to be controlled in large measure by the localization of signaling, thus enabling ERK activity to be directed towards specific targets. Here we show that the RACK1 scaffold protein functions specifically in integrin-mediated activation of the mitogen-activated protein kinase/ERK cascade and targets active ERK to focal adhesions. We found that RACK1 associated with the core kinases of the ERK pathway, Raf, MEK, and ERK, and that attenuation of RACK1 expression resulted in a decrease in ERK activity in response to adhesion but not in response to growth factors. RACK1 silencing also caused a reduction of active ERK in focal adhesions, an increase in focal adhesion length, a decreased rate of focal adhesion disassembly, and decreased motility. Our data further suggest that focal adhesion kinase is an upstream activator of the RACK1/ERK pathway. We suggest that RACK1 tethers the ERK pathway core kinases and channels signals from upstream activation by integrins to downstream targets at focal adhesions.