Elevated expression of stromal palladin predicts poor clinical outcome in renal cell carcinoma

Integrated structural model of the palladin-actin complex using XL-MS, docking, NMR, and SAXS

Palladin is an actin-binding protein that accelerates actin polymerization and is linked to the metastasis of several types of cancer. Previously, three lysine residues in an immunoglobulin-like domain of palladin have been identified as essential for actin binding. However, it is still unknown where palladin binds to F-actin. Evidence that palladin binds to the sides of actin filaments to facilitate branching is supported by our previous study showing that palladin was able to compensate for Arp2/3 in the formation of Listeria actin comet tails. Here, we used chemical crosslinking to covalently link palladin and F-actin residues based on spatial proximity. Samples were then enzymatically digested, separated by liquid chromatography, and analyzed by tandem mass spectrometry. Peptides containing the crosslinks and specific residues involved were then identified for input to the HADDOCK docking server to model the most likely binding conformation. Small-angle x-ray scattering was used to provide further insight into palladin flexibility and the binding interface, and NMR spectra identified potential interactions between palladin's Ig domains. Our final structural model of the F-actin:palladin complex revealed how palladin interacts with and stabilizes F-actin at the interface between two actin monomers. Three actin residues that were identified in this study also appear commonly in the actin-binding interface with other proteins such as myotilin, myosin, and tropomodulin. An accurate structural representation of the complex between palladin and actin extends our understanding of palladin's role in promoting cancer metastasis through the regulation of actin dynamics.

Exploring the potential role of palladin in modulating human CAF/ECM functional units

Fibroblasts, crucial for maintaining tissue homeostasis, significantly shape the tumor microenvironment (TME). In pancreatic cancer, a highly aggressive malignancy, cancer-associated fibroblast (CAF)/extracellular matrix (ECM) units dominate the TME, influencing tumor initiation, progression, and treatment responses. Palladin, an actin-associated protein, is vital for fibroblast structural integrity and activation, playing a key role in CAF/ECM functionality. Palladin interacts with cytoskeletal proteins such as alpha-actinin (α-Act) and can therefore regulate other proteins like syndecans, modulating cytoskeletal features, cell adhesion, integrin recycling, and signaling. In this review, we propose that targeting the palladin/α-Act/syndecan interaction network could modulate CAF/ECM units, potentially shifting the TME from a tumor-promoting to a tumor-suppressive state. In silico data and reported studies to suggest that stabilizing palladin-α-Act interactions, via excess palladin, influences syndecan functions; potentially modulating integrin endocytosis via syndecan engagement with protein kinase C alpha as opposed to syndecan binding to α-Act. This mechanism can then affect the distribution of active α5β1-integrin between the plasma membrane and known intracellular vesicular compartments, thereby influencing the tumor-suppressive versus tumor-promoting functions of CAF/ECM units. Understanding these interactions offers likely future therapeutic avenues for stroma normalization in pancreatic and other cancers, aiming to inhibit tumor progression and improve future treatment outcomes.

Integrated structural model of the palladin-actin complex using XL-MS, docking, NMR, and SAXS

Palladin is an actin binding protein that accelerates actin polymerization and is linked to metastasis of several types of cancer. Previously, three lysine residues in an immunoglobulin-like domain of palladin have been identified as essential for actin binding. However, it is still unknown where palladin binds to F-actin. Evidence that palladin binds to the sides of actin filaments to facilitate branching is supported by our previous study showing that palladin was able to compensate for Arp2/3 in the formation of Listeria actin comet tails. Here, we used chemical crosslinking to covalently link palladin and F-actin residues based on spatial proximity. Samples were then enzymatically digested, separated by liquid chromatography, and analyzed by tandem mass spectrometry. Peptides containing the crosslinks and specific residues involved were then identified for input to HADDOCK docking server to model the most likely binding conformation. Small angle X-ray scattering was used to provide further insight into palladin flexibility and the binding interface, and NMR spectra identified potential interactions between palladin's Ig domains. Our final structural model of the F-actin:palladin complex revealed how palladin interacts with and stabilizes F-actin at the interface between two actin monomers. Three actin residues that were identified in this study also appear commonly in the actin binding interface with other proteins such as myotilin, myosin, and tropomodulin. An accurate structural representation of the complex between palladin and actin extends our understanding of palladin's role in promoting cancer metastasis through regulation of actin dynamics.

Significance

In this study we have combined various advanced structural biology techniques to provide the first comprehensive model of the palladin-actin complex. Considering palladin's role in cancer cell metastasis, this structure could be useful in screening and developing chemotherapeutic agents that target this interaction and prevent cancer cell metastasis.

Chemokine receptors and their ligands in breast cancer: The key roles in progression and metastasis

Chemokines and their receptors are a family of chemotactic cytokines with important functions in the immune response in both health and disease. Their known physiological roles such as the regulation of leukocyte trafficking and the development of immune organs generated great interest when it was found that they were also related to the control of early and late inflammatory stages in the tumor microenvironment. In fact, in breast cancer, an imbalance in the synthesis of chemokines and/or in the expression of their receptors was attributed to be involved in the regulation of disease progression, including invasion and metastasis. Research in this area is progressing rapidly and the development of new agents based on chemokine and chemokine receptor antagonists are emerging as attractive alternative strategies. This chapter provides a snapshot of the different functions reported for chemokines and their receptors with respect to the potential to regulate breast cancer progression.

What is new in cancer-associated fibroblast biomarkers?

The tumor microenvironment is one of the important drivers of tumor development. Cancer-associated fibroblasts (CAFs) are a major component of the tumor stroma and actively participate in tumor development, invasion, metastasis, drug resistance, and other biological behaviors. CAFs are a highly heterogeneous group of cells, a reflection of the diversity of their origin, biomarkers, and functions. The diversity of CAF origin determines the complexity of CAF biomarkers, and CAF subpopulations expressing different biomarkers may play contrasting roles in tumor progression. In this review, we provide an overview of these emerging CAF biomarkers and the biological functions that they suggest, which may give a better understanding of the relationship between CAFs and tumor cells and be of great significance for breakthroughs in precision targeted therapy for tumors. Video Abstract.

Sunitinib resistance in renal cell carcinoma: From molecular mechanisms to predictive biomarkers

Currently, renal cell carcinoma (RCC) is the most prevalent type of kidney cancer. Targeted therapy has replaced radiation therapy and chemotherapy as the main treatment option for RCC due to the lack of significant efficacy with these conventional therapeutic regimens. Sunitinib, a drug used to treat gastrointestinal tumors and renal cell carcinoma, inhibits the tyrosine kinase activity of a number of receptor tyrosine kinases, including vascular endothelial growth factor receptor (VEGFR), platelet-derived growth factor receptor (PDGFR), c-Kit, rearranged during transfection (RET) and fms-related receptor tyrosine kinase 3 (Flt3). Although sunitinib has been shown to be efficacious in the treatment of patients with advanced RCC, a significant number of patients have primary resistance to sunitinib or acquired drug resistance within the 6-15 months of therapy. Thus, in order to develop more efficacious and long-lasting treatment strategies for patients with advanced RCC, it will be crucial to ascertain how to overcome sunitinib resistance that is produced by various drug resistance mechanisms. In this review, we discuss: 1) molecular mechanisms of sunitinib resistance; 2) strategies to overcome sunitinib resistance and 3) potential predictive biomarkers of sunitinib resistance.

Palladin promotes cancer stem cell-like properties in lung cancer by activating Wnt/Β-Catenin signaling

BACKGROUND

Cancer stem cells (CSCs) are responsible for drug resistance, cancer relapse, and metastasis. Here, we report the first analysis of Palladin expression and its impacts on stem cell-like properties in lung cancer.

METHODS

Tissue microarrays were used to investigate Palladin expression and its association with prognosis. Immunofluorescence (IF), flow fluorescence assay, and Western blot were performed to detect Palladin expression in 6 NSCLC cell lines. Cell phenotypes and drug resistance were evaluated. Xenograft models were constructed to confirm the role of Palladin in vivo.

RESULTS

By using the tissue microarrays, Palladin was identified to be highly expressed in the cytoplasm, specifically in the cytomembrane of NSCLC, and its high expression is associated with poor prognosis. Palladin is widely expressed and enriched in the sphere cells. The in vitro and in vivo studies showed that Palladin promoted stem cell-like properties, including cell viability, invasion, migration, self-renewal abilities, taxol resistance, and tumorigenicity. Western blot revealed that Palladin promoted the accumulation of β-catenin and activated Wnt/β-catenin signaling. Tissue microarrays analysis further confirmed the positive correlation between Palladin and β-catenin. Wnt/β-catenin pathway inhibitor blocked the Palladin-induced enhancement of sphere-forming.

CONCLUSIONS

Palladin might act as an oncogene by promoting CSCs-like properties and tumorigenicity of NSCLC cells via the Wnt/β-catenin signaling pathway. Besides, Palladin was identified to have the potential as a cell surface marker for LCSCs identification. These findings provide a possible target for developing putative agents targeted to LCSCs.

Eribulin normalizes pancreatic cancer-associated fibroblasts by simulating selected features of TGFβ inhibition

BACKGROUND

Less than 11% of pancreatic cancer patients survive 5-years post-diagnosis. The unique biology of pancreatic cancer includes a significant expansion of its desmoplastic tumor microenvironment, wherein cancer-associated fibroblasts (CAFs) and their self-produced extracellular matrix are key components. CAF functions are both tumor-supportive and tumor-suppressive, while normal fibroblastic cells are solely tumor-suppressive. Knowing that CAF-eliminating drugs are ineffective and can accelerate cancer progression, therapies that "normalize" CAF function are highly pursued. Eribulin is a well-tolerated anti-microtubule drug used to treat a plethora of neoplasias, including advanced/metastatic cancers. Importantly, eribulin can inhibit epithelial to mesenchymal transition via a mechanism akin to blocking pathways induced by transforming growth factor-beta (TGFβ). Notably, canonical TGFβ signaling also plays a pivotal role in CAF activation, which is necessary for the development and maintenance of desmoplasia. Hence, we hypothesized that eribulin could modulate, and perhaps "normalize" CAF function.

METHODS

To test this premise, we used a well-established in vivo-mimetic fibroblastic cell-derived extracellular matrix (CDM) system and gauged the effects of eribulin on human pancreatic CAFs and cancer cells. This pathophysiologic fibroblast/matrix functional unit was also used to query eribulin effects on CDM-regulated pancreatic cancer cell survival and invasive spread.

RESULTS

Demonstrated that intact CAF CDMs modestly restricted eribulin from obstructing pancreatic cancer cell growth. Nonetheless, eribulin-treated CAFs generated CDMs that limited nutrient-deprived pancreatic cancer cell survival, similar to reported tumor-suppressive CDMs generated by TGFβ-deficient CAFs.

CONCLUSIONS

Data from this study support the central proposed premise suggesting that eribulin could be used as a CAF/matrix-normalizing drug.

A miniaturized screening platform to identify novel regulators of extracellular matrix alignment

Extracellular matrix alignment contributes to metastasis in a number of cancers and is a known prognostic stromal factor; however, the mechanisms controlling matrix organization remain unclear. Cancer-associated fibroblasts (CAF) play a critical role in this process, particularly via matrix production and modulation of key signaling pathways controlling cell adhesion and contractility. Stroma normalization, as opposed to elimination, is a highly sought strategy, and screening for drugs that effectively alter extracellular matrix (ECM) alignment is a practical way to identify novel CAF-normalizing targets that modulate ECM organization. To meet this need, we developed a novel high-throughput screening platform in which fibroblast-derived matrices were produced in 384-well plates, imaged with automated confocal microscopy, and analyzed using a customized MATLAB script. This platform is a technical advance because it miniaturizes the assay, eliminates costly and time-consuming experimental steps, and streamlines data acquisition and analysis to enable high-throughput screening applications. As a proof of concept, this platform was used to screen a kinase inhibitor library to identify modulators of matrix alignment. A number of novel potential regulators were identified, including several receptor tyrosine kinases (c-MET, tropomyosin receptor kinase 1 (NTRK1), HER2/ERBB2) and the serine/threonine kinases protein kinase A, C, and G (PKA, PKC, and PKG). The expression of these regulators was analyzed in publicly available patient datasets to examine the association between stromal gene expression and patient outcomes.

PALLD mutation in a European family conveys a stromal predisposition for familial pancreatic cancer

BACKGROUNDPancreatic cancer is one of the deadliest cancers, with low long-term survival rates. Despite recent advances in treatment, it is important to identify and screen high-risk individuals for cancer prevention. Familial pancreatic cancer (FPC) accounts for 4%-10% of pancreatic cancers. Several germline mutations are related to an increased risk and might offer screening and therapy options. In this study, we aimed to identity of a susceptibility gene in a family with FPC.METHODSWhole exome sequencing and PCR confirmation was performed on the surgical specimen and peripheral blood of an index patient and her sister in a family with high incidence of pancreatic cancer, to identify somatic and germline mutations associated with familial pancreatic cancer. Compartment-specific gene expression data and immunohistochemistry were also queried.RESULTSThe identical germline mutation of the PALLD gene (NM_001166108.1:c.G154A:p.D52N) was detected in the index patient with pancreatic cancer and the tumor tissue of her sister. Whole genome sequencing showed similar somatic mutation patterns between the 2 sisters. Apart from the PALLD mutation, commonly mutated genes that characterize pancreatic ductal adenocarcinoma were found in both tumor samples. However, the 2 patients harbored different somatic KRAS mutations (G12D and G12V). Healthy siblings did not have the PALLD mutation, indicating a disease-specific impact. Compartment-specific gene expression data and IHC showed expression in cancer-associated fibroblasts (CAFs).CONCLUSIONWe identified a germline mutation of the palladin (PALLD) gene in 2 siblings in Europe, affected by familial pancreatic cancer, with a significant overexpression in CAFs, suggesting that stromal palladin could play a role in the development, maintenance, and/or progression of pancreatic cancer.FUNDINGDFG SFB 1321.

Palladin isoforms 3 and 4 regulate cancer-associated fibroblast pro-tumor functions in pancreatic ductal adenocarcinoma

Pancreatic Ductal Adenocarcinoma (PDAC) has a five-year survival under 10%. Treatment is compromised due to a fibrotic-like stromal remodeling process, known as desmoplasia, which limits therapeutic perfusion, supports tumor progression, and establishes an immunosuppressive microenvironment. These processes are driven by cancer-associated fibroblasts (CAFs), functionally activated through transforming growth factor beta1 (TGFβ1). CAFs produce a topographically aligned extracellular matrix (ECM) that correlates with reduced overall survival. Paradoxically, ablation of CAF populations results in a more aggressive disease, suggesting CAFs can also restrain PDAC progression. Thus, unraveling the mechanism(s) underlying CAF functions could lead to therapies that reinstate the tumor-suppressive features of the pancreatic stroma. CAF activation involves the f-actin organizing protein palladin. CAFs express two palladin isoforms (iso3 and iso4) which are up-regulated in response to TGFβ1. However, the roles of iso3 and iso4 in CAF functions remain elusive. Using a CAF-derived ECM model, we uncovered that iso3/iso4 are required to sustain TGFβ1-dependent CAF activation, secrete immunosuppressive cytokines, and produce a pro-tumoral ECM. Findings demonstrate a novel role for CAF palladin and suggest that iso3/iso4 regulate both redundant and specific tumor-supportive desmoplastic functions. This study highlights the therapeutic potential of targeting CAFs to restore fibroblastic anti-tumor activity in the pancreatic microenvironment.

The Adhesome Network: Key Components Shaping the Tumour Stroma

Beyond the conventional perception of solid tumours as mere masses of cancer cells, advanced cancer research focuses on the complex contributions of tumour-associated host cells that are known as "tumour microenvironment" (TME). It has been long appreciated that the tumour stroma, composed mainly of blood vessels, cancer-associated fibroblasts and immune cells, together with the extracellular matrix (ECM), define the tumour architecture and influence cancer cell properties. Besides soluble cues, that mediate the crosstalk between tumour and stroma cells, cell adhesion to ECM arises as a crucial determinant in cancer progression. In this review, we discuss how adhesome, the intracellular protein network formed at cell adhesions, regulate the TME and control malignancy. The role of adhesome extends beyond the physical attachment of cells to ECM and the regulation of cytoskeletal remodelling and acts as a signalling and mechanosensing hub, orchestrating cellular responses that shape the tumour milieu.

CD38 in cancer-associated fibroblasts promotes pro-tumoral activity

Primary and metastatic melanoma progression are supported by a local microenvironment comprising, inter alia, of cancer-associated fibroblasts (CAFs). We previously reported in orthotropic/syngeneic mouse models that the stromal ectoenzyme CD38 participates in melanoma growth and metastasis. The results presented here suggest that CD38 is a novel regulator of CAFs' pro-tumorigenic functions. Orthotopic co-implantation of CD38 deficient fibroblasts and B16F10 melanoma cells limited tumor size, compared with CD38-expressing fibroblasts. Intrinsically, CAF-CD38 promoted migration of primary fibroblasts toward melanoma cells. Further, in vitro paracrine effects of CAF-CD38 fostered tumor cell migration and invasion as well as endothelial cell tube formation. Mechanistically, we report that CAF-CD38 drives the protein expression of an angiogenic/pro-metastatic signature, which includes VEGF-A, FGF-2, CXCL-12, MMP-9, and HGF. Data suggest that CAF-CD38 fosters tumorigenesis by enabling the production of pro-tumoral factors that promote cell invasion, migration, and angiogenesis.

Expression of palladin is associated with disease progression in metastatic high-grade serous carcinoma

OBJECTIVE

To analyse the expression and clinical role of the actin-associated molecule palladin in serous effusions.

METHODS

PALLD mRNA expression was analysed by quantitative reverse transcription polymerase chain reaction in 83 high-grade serous carcinoma (HGSC) effusions. Fifteen malignant mesothelioma (MM) effusions and 18 surgical HGSC specimens from the ovary were studied for comparative purposes. Palladin protein expression by immunohistochemistry was analysed in another series consisting of 261 HGSC effusions.

RESULTS

PALLD mRNA was significantly overexpressed in HGSC compared to MM effusions (P < .001). Palladin expression by immunohistochemistry was found in HGSC cells in 106/261 (41%) effusions, most commonly focally (<5% of cells). PALLD expression was additionally higher in ovarian HGSC specimens compared to HGSC effusions (P < .001). However, immunohistochemistry showed only stromal expression of this protein in surgical specimens. PALLD mRNA expression in HGSC effusions was unrelated to clinicopathological parameters, chemotherapy response or survival. Palladin protein expression was higher in post-chemotherapy, mainly disease recurrence, specimens compared to chemo-naïve effusions tapped at diagnosis (P = .018), although it was unrelated to other clinicopathological parameters or survival.

CONCLUSION

PALLD mRNA is overexpressed in HGSC compared to MM effusions, and its protein product is overexpressed in post-chemotherapy compared to pre-chemotherapy HGSC effusions, suggesting upregulation along tumour progression. The presence of this molecule in HGSC effusions, at the mRNA or the protein level, is unrelated to disease outcome.

Cancer associated fibroblast: Mediators of tumorigenesis

It is well accepted that the tumor microenvironment plays a pivotal role in cancer onset, development, and progression. The majority of clinical interventions are designed to target either cancer or stroma cells. These emphases have been directed by one of two prevailing theories in the field, the Somatic Mutation Theory and the Tissue Organization Field Theory, which represent two seemingly opposing concepts. This review proposes that the two theories are mutually inclusive and should be concurrently considered for cancer treatments. Specifically, this review discusses the dynamic and reciprocal processes between stromal cells and extracellular matrices, using pancreatic cancer as an example, to demonstrate the inclusivity of the theories. Furthermore, this review highlights the functions of cancer associated fibroblasts, which represent the major stromal cell type, as important mediators of the known cancer hallmarks that the two theories attempt to explain.

Engineering clinically-relevant human fibroblastic cell-derived extracellular matrices

Three-dimensional (3D) culturing models, replicating in vivo tissue microenvironments that incorporate native extracellular matrix (ECM), have revolutionized the cell biology field. Fibroblastic cells generate lattices of interstitial ECM proteins. Cell interactions with ECMs and with molecules sequestered/stored within these are crucial for tissue development and homeostasis maintenance. Hence, ECMs provide cells with biochemical and biomechanical cues to support and locally control cell function. Further, dynamic changes in ECMs, and in cell-ECM interactions, partake in growth, development, and temporary occurrences such as acute wound healing. Notably, dysregulation in ECMs and fibroblasts could be important triggers and modulators of pathological events such as developmental defects, and diseases associated with fibrosis and chronic inflammation such as cancer. Studying the type of fibroblastic cells producing these matrices and how alterations to these cells enable changes in ECMs are of paramount importance. This chapter provides a step-by-step method for producing multilayered (e.g., 3D) fibroblastic cell-derived matrices (fCDM). Methods also include means to assess ECM topography and other cellular traits, indicative of fibroblastic functional statuses, like naïve/normal vs. inflammatory and/or myofibroblastic. For these, protocols include indications for isolating normal and diseased fibroblasts (i.e., cancer-associated fibroblasts known as CAFs). Protocols also include means for conducting microscopy assessments, querying whether fibroblasts present with fCDM-dependent normal or CAF phenotypes. These are supported by discrete semi-quantitative digital imaging analyses, providing some imaging processing advice. Additionally, protocols include descriptions for effective fCDM decellularization, which renders cellular debris-free patho/physiological in vivo-like scaffolds, suitable as 3D substrates for subsequent cell culturing.

The role of cancer-associated fibroblasts in renal cell carcinoma. An example of tumor modulation through tumor/non-tumor cell interactions

Cancer-associated fibroblasts (CAF) are a cellular compartment of the tumor microenvironment (TME) with critical roles in tumor development. Fibroblast activation protein-α (FAP) is one of the proteins expressed by CAF and its immunohistochemical detection in routine practice is associated with tumor aggressiveness and shorter patient survival. For these reasons, FAP seems a good prognostic marker in many malignant neoplasms, including renal cell carcinoma (RCC). The start point of this Perspective paper is to review the role of CAF in the modulation of renal cell carcinoma evolution. In this sense, CAF have demonstrated to develop important protumor and/or antitumor activities. This apparent paradox suggests that some type of temporally or spatially-related specialization is present in this cellular compartment during tumor evolution. The end point is to remark that tumor/non-tumor cell interactions, in particular the symbiotic tumor/CAF connections, are permanent and ever-changing crucial phenomena along tumor lifetime. Interestingly, these interactions may be responsible of many therapeutic failures.

Resistance to Systemic Therapies in Clear Cell Renal Cell Carcinoma: Mechanisms and Management Strategies

Renal cell carcinoma (RCC) is the most common form of kidney cancer. It is categorized into various subtypes, with clear cell RCC (ccRCC) representing about 85% of all RCC tumors. The lack of sensitivity to chemotherapy and radiation therapy prompted research efforts into novel treatment options. The development of targeted therapeutics, including multi-targeted tyrosine kinase inhibitors (TKI) and mTOR inhibitors, has been a major breakthrough in ccRCC therapy. More recently, other therapeutic strategies, including immune checkpoint inhibitors, have emerged as effective treatment options against advanced ccRCC. Furthermore, recent advances in disease biology, tumor microenvironment, and mechanisms of resistance formed the basis for attempts to combine targeted therapies with newer generation immunotherapies to take advantage of possible synergy. This review focuses on the current status of basic, translational, and clinical studies on mechanisms of resistance to systemic therapies in ccRCC. Mol Cancer Ther; 17(7); 1355-64. ©2018 AACR.

Overexpression of COL5A1 promotes tumor progression and metastasis and correlates with poor survival of patients with clear cell renal cell carcinoma

Background and aims

COL5A1 has been identified to be involved in metastasis of clear cell renal cell carcinoma (ccRCC) by bioinformatic analysis. This study aimed to investigate COL5A1 expression and its clinical significance in ccRCC. The function of COL5A1 in ccRCC was further investigated.

Methods

COL5A1 expression was examined in 256 ccRCC tissues and paired adjacent normal renal tissues by immunohistochemistry and real-time quantitative PCR. The clinical significance of COL5A1 expression was evaluated. Downregulation of COL5A1 was achieved using siRNA. The effects of COL5A1 silencing on cell proliferation, apoptosis, migration, invasion in vitro, and tumor growth in vivo were investigated.

Results

COL5A1 expression was upregulated in the majority of the ccRCC tissues at both protein and mRNA levels. COL5A1 expression was significantly correlated with tumor diameter, tumor stage, tumor grade, distant metastasis, recurrence, necrosis, and sarcomatoid (all P<0.05). COL5A1 expression was also significantly associated with overall survival of ccRCC patients (HR 1.876; P=0.027) and recurrence-free survival of localized ccRCC patients (HR 4.751; P<0.001). The accuracy of TNM, University of California Los Angeles Integrated Staging System, and Mayo clinic stage, size, grade, and necrosis prognostic models was improved when COL5A1 expression was added.

Conclusion

COL5A1 knockdown significantly inhibited cell proliferation, induced cell apoptosis, inhibited cell migration and invasion in vitro, and inhibited tumor growth in vivo. Therefore, COL5A1 may be a novel prognostic biomarker and a promising therapeutic target for ccRCC.

Intratumoral stromal morphometry predicts disease recurrence but not response to 5-fluorouracil-results from the QUASAR trial of colorectal cancer

AIMS

The biological importance of tumour-associated stroma is becoming increasingly apparent, but its clinical utility remains ill-defined. For stage II/Dukes B colorectal cancer (CRC), clinical biomarkers are urgently required to direct therapeutic options. We report here prognostic/predictive analyses, and molecular associations, of stromal morphometric quantification in the Quick and Simple and Reliable (QUASAR) trial of CRC.

METHODS AND RESULTS

Relative proportions of tumour epithelium (PoT) or stroma (PoS) were morphometrically quantified on digitised haematoxylin and eosin (H&E) sections derived from 1800 patients enrolled in QUASAR, which randomised 3239 (91% stage II) CRC patients between adjuvant fluorouracil/folinic acid (FUFA) chemotherapy and observation. The prognostic and predictive values of PoT/PoS measurements were determined by the use of stratified log-rank analyses. A high proportion of tumour stroma (≥50%) was associated with an increased recurrence risk: 31.3% (143/457) recurrence for ≥50% versus 21.9% (294/1343) for <50% [rate ratio (RR) 1.62; 95% confidence interval (CI) 1.30-2.02; P < 0.0001]. Of patients with stromal proportions of ≥65%, 40% (46/115) had recurrent disease within 10 years. The adverse prognostic effect of a high stromal proportion was independent of established prognostic variables, and was maintained in stage II/Dukes B patients (RR 1.62; 95% CI 1.26-2.08; P = 0.0002). KRAS mutation in the presence of a high stromal proportion augmented recurrence risk (RR 2.93; 95% CI 1.87-4.59; P = 0.0005). Stromal morphometry did not predict response to FUFA chemotherapy.

CONCLUSIONS

Simple digital morphometry applied to a single representative H&E section identifies CRC patients with a >50% higher risk of disease recurrence. This technique can reliably partition patients into subpopulations with different risks of tumour recurrence in a simple and cost-effective manner. Further prospective validation is warranted.

Matrix-regulated integrin αvβ5 maintains α5β1-dependent desmoplastic traits prognostic of neoplastic recurrence

Desmoplasia, a fibrotic mass including cancer-associated fibroblasts (CAFs) and self-sustaining extracellular matrix (D-ECM), is a puzzling feature of pancreatic ductal adenocarcinoma (PDACs). Conflicting studies have identified tumor-restricting and tumor-promoting roles of PDAC-associated desmoplasia, suggesting that individual CAF/D-ECM protein constituents have distinguishable tumorigenic and tumor-repressive functions. Using 3D culture of normal pancreatic versus PDAC-associated human fibroblasts, we identified a CAF/D-ECM phenotype that correlates with improved patient outcomes, and that includes CAFs enriched in plasma membrane-localized, active α₅β₁-integrin. Mechanistically, we established that TGFβ is required for D-ECM production but dispensable for D-ECM-induced naïve fibroblast-to-CAF activation, which depends on α_vβ₅-integrin redistribution of pFAK-independent active α₅β₁-integrin to assorted endosomes. Importantly, the development of a simultaneous multi-channel immunofluorescence approach and new algorithms for computational batch-analysis and their application to a human PDAC panel, indicated that stromal localization and levels of active SMAD2/3 and α₅β₁-integrin distinguish patient-protective from patient-detrimental desmoplasia and foretell tumor recurrences, suggesting a useful new prognostic tool.

DOI:http://dx.doi.org/10.7554/eLife.20600.001

Tumors are not entirely made out of cancerous cells. They contain many other components – referred to as tumor stroma – that may either encourage or hinder the tumor’s growth. Tumor stroma includes non-cancerous cells and a framework of fibrous sugary proteins, called the extracellular matrix, which surround and signal to cells while providing physical support.

In the most common and aggressive form of pancreatic cancer, the stroma often makes up the majority of the tumor’s mass. Sometimes the stroma of these pancreatic tumors can protect the cancer cells from anti-cancer drugs. Researchers have therefore been interested in finding out exactly which aspects of the tumor stroma shield and support cancer cells, and which impede their growth and progression. Answering these questions could make it possible to develop new drugs that will change a tumor-supporting stroma into one that hinders the tumor’s growth and spread.

The most abundant cells in the stroma of pancreatic tumors are called cancer-associated fibroblasts. Healthy specialized fibroblasts – known as pancreatic stellate cells – help to build and maintain the ‘normal’ extracellular matrix and so these cells normally restrict a tumor’s development. However, cancer cells can adapt healthy fibroblasts into cancer-associated fibroblasts, which produce an altered extracellular matrix that could allow the tumor to grow.

Franco-Barraza et al. have now compared healthy and cancer-associated fibroblasts from patients’ pancreatic tumors. One of the main differences between these two cell types was the location of the activated form of a molecule called α₅β₁-integrin. Healthy fibroblasts, in a normal extracellular matrix, have active α₅β₁-integrin on the surface of the cell. However, a number of tumor-promoting signals, including some from the altered extracellular matrix, could force the active α₅β₁-integrins to relocate inside the fibroblasts instead. In further experiments, where the activated integrin was retained at the cell surface, the fibroblasts were able to resist the influence of the cancer-associated extracellular matrix. Then again, if the active α₅β₁-integrins were directed inside the cells, healthy cells turned into cancer-associated fibroblasts.

With this information in hand, Franco-Barraza et al. examined tumor samples from over a hundred pancreatic cancer patients using a new microscopy-based technique that distinguishes cancer cells from stroma cells. The analysis confirmed the pattern observed in the laboratory: those patients who appeared to produce more normal extracellular matrix and have active α₅β₁-integrin localized mostly to the surface of the cells survived longer without the cancer returning than those patients who lacked these stroma traits. Samples from patients with kidney cancer also showed similar results and, as before, an altered extracellular matrix was linked to a worse outcome of the disease.

Together these findings suggest that if future studies uncover ways to relocate or maintain active α₅β₁-integrin to the cell surface of fibroblasts they could lead to new treatments to restrict the growth of tumors in cancer patients.

DOI:http://dx.doi.org/10.7554/eLife.20600.002

Local microRNA delivery targets Palladin and prevents metastatic breast cancer

Metastasis is the primary cause for mortality in breast cancer. MicroRNAs, gene expression master regulators, constitute an attractive candidate to control metastasis. Here we show that breast cancer metastasis can be prevented by miR-96 or miR-182 treatment, and decipher the mechanism of action. We found that miR-96/miR-182 downregulate Palladin protein levels, thereby reducing breast cancer cell migration and invasion. A common SNP, rs1071738, at the miR-96/miR-182-binding site within the Palladin 3'-UTR abolishes miRNA:mRNA binding, thus diminishing Palladin regulation by these miRNAs. Regulation is successfully restored by applying complimentary miRNAs. A hydrogel-embedded, gold-nanoparticle-based delivery vehicle provides efficient local, selective, and sustained release of miR-96/miR-182, markedly suppressing metastasis in a breast cancer mouse model. Combined delivery of the miRNAs with a chemotherapy drug, cisplatin, enables significant primary tumour shrinkage and metastasis prevention. Our data corroborate the role of miRNAs in metastasis, and suggest miR-96/miR-182 delivery as a potential anti-metastatic drug.

Preparation of Extracellular Matrices Produced by Cultured and Primary Fibroblasts

Fibroblasts secrete and organize extracellular matrix (ECM), which provides structural support for their adhesion, migration, and tissue organization, besides regulating cellular functions such as growth and survival. Cell-to-matrix interactions are vital for vertebrate development. Disorders in these processes have been associated with fibrosis, developmental malformations, cancer, and other diseases. This unit describes a method for preparing a three-dimensional matrix derived from fibroblastic cells; the matrix is three-dimensional, cell and debris free, and attached to a two-dimensional culture surface. Cell adhesion and spreading are normal on these matrices. This matrix can also be compressed into a two-dimensional matrix and solubilized to study the matrix biochemically. © 2016 by John Wiley & Sons, Inc.

Stromal dynamic reciprocity in cancer: intricacies of fibroblastic-ECM interactions

Stromal dynamic reciprocity (SDR) consists of the biophysical and biochemical interplay between connective tissue elements that regulate and maintain organ homeostasis. In epithelial cancers, chronic alterations of SDR result in the once tumor-restrictive stroma evolving into a 'new' tumor-permissive environment. This altered stroma, known as desmoplasia, is initiated and maintained by cancer associated fibroblasts (CAFs) that remodel the extracellular matrix (ECM). Desmoplasia fuels a vicious cycle of stromal dissemination enriching both CAFs and desmoplastic ECM. Targeting specific drivers of desmoplasia, such as CAFs, either enhances or halts tumor growth and progression. These conflicting effects suggest that stromal interactions are not fully understood. This review highlights known fibroblastic-ECM interactions in an effort to encourage therapies that will restore cancer-restrictive stromal cues.

Palladin mediates stiffness-induced fibroblast activation in the tumor microenvironment

Mechanical properties of the tumor microenvironment have emerged as key factors in tumor progression. It has been proposed that increased tissue stiffness can transform stromal fibroblasts into carcinoma-associated fibroblasts. However, it is unclear whether the three to five times increase in stiffness seen in tumor-adjacent stroma is sufficient for fibroblast activation. In this study we developed a three-dimensional (3D) hydrogel model with precisely tunable stiffness and show that a physiologically relevant increase in stiffness is sufficient to lead to fibroblast activation. We found that soluble factors including CC-motif chemokine ligand (CCL) chemokines and fibronectin are necessary for this activation, and the combination of C-C chemokine receptor type 4 (CCR4) chemokine receptors and β1 and β3 integrins are necessary to transduce these chemomechanical signals. We then show that these chemomechanical signals lead to the gene expression changes associated with fibroblast activation via a network of intracellular signaling pathways that include focal adhesion kinase (FAK) and phosphoinositide 3-kinase (PI3K). Finally, we identify the actin-associated protein palladin as a key node in these signaling pathways that result in fibroblast activation.

Stromal Palladin Expression Is an Independent Prognostic Factor in Pancreatic Ductal Adenocarcinoma

It has been clear that cancer-associated fibroblasts (CAFs) in the tumor microenvironment play an important role in pancreatic ductal adenocarcinoma (PDAC) progression. However, how CAFs relate to the patients' prognosis and the effects of chemoradiation therapy (CRT) has not been fully investigated. Tissue microarrays (TMAs) representing 167 resected PDACs without preoperative treatment were used for immunohistochemical studies (IHC) of palladin, α-smooth muscle actin (SMA), and podoplanin. Correlations between the expression levels of these markers and clinicopathological findings were analyzed statistically. Whole sections of surgical specimens from PDACs with and without preoperative CRT, designated as the chemotherapy-first group (CF, n = 19) and the surgery-first group (SF, n = 21), respectively, were also analyzed by IHC. In TMAs, the disease-specific survival rate (DSS) at 5 years for all 167 cases was 23.1%. Seventy cases (41.9%) were positive for palladin and had significantly lower DSS (p = 0.0430). α-SMA and podoplanin were positive in 167 cases (100%) and 131 cases (78.4%), respectively, and they were not significantly associated with DSS. On multivariable analysis, palladin expression was an independent poor prognostic factor (p = 0.0243, risk ratio 1.60). In the whole section study, palladin positivity was significantly lower (p = 0.0037) in the CF group (5/19) with a significantly better DSS (p = 0.0144) than in the SF group (16/22), suggesting that stromal palladin expression is a surrogate indicator of the treatment effect after chemoradiation therapy.

Twist1-induced activation of human fibroblasts promotes matrix stiffness by upregulating palladin and collagen α1(VI)

The transcription factor Twist1 is involved in the epithelial-mesenchymal transition and contributes to cancer metastasis through mostly unknown mechanisms. In colorectal cancer, Twist1 expression is mainly restricted to the tumor stroma. We found that human fibroblast cell lines stably transfected with Twist1 acquired characteristics of activated cancer-associated fibroblasts (CAFs), such as hyperproliferation, an increased ability to migrate and an alignment of the actin cytoskeleton. Further, Twist1-activated fibroblasts promoted increased matrix stiffness. Using quantitative proteomics, we identified palladin and collagen α1(VI) as two major mediators of the Twist1 effects in fibroblast cell lines. Co-immunoprecipitation studies indicated that palladin and Twist1 interact within the nucleus, suggesting that palladin could act as a transcription regulator. Palladin was found to be more relevant for the cellular biomechanical properties, orientation and polarity, and collagen α1(VI) for the migration and invasion capacity, of Twist1-activated fibroblasts. Both palladin and collagen α1(VI) were observed to be overexpressed in colorectal CAFs and to be associated with poor colorectal cancer patient survival and relapse prediction. Our results demonstrate that Twist1-expressing fibroblasts mimic the properties of CAFs present at the tumor invasive front, which likely explains the prometastatic activities of Twist1. Twist1 appears to require both palladin and collagen α1(VI) as downstream effectors for its prometastatic effects, which could be future therapeutic targets in cancer metastasis.

Capturing relevant extracellular matrices for investigating cell migration

Much progress in understanding cell migration has been determined by using classic two-dimensional (2D) tissue culture platforms. However, increasingly, it is appreciated that certain properties of cell migration in vivo are not represented by strictly 2D assays. There is much interest in creating relevant three-dimensional (3D) culture environments and engineered platforms to better represent features of the extracellular matrix and stromal microenvironment that are not captured in 2D platforms. Important to this goal is a solid understanding of the features of the extracellular matrix—composition, stiffness, topography, and alignment—in different tissues and disease states and the development of means to capture these features

Palladin expression is a conserved characteristic of the desmoplastic tumor microenvironment and contributes to altered gene expression

The stroma surrounding solid tumors contributes in complex ways to tumor progression. Cancer-associated fibroblasts (CAFs) are the predominant cell type in the tumor stroma. Previous studies have shown that the actin-binding protein palladin is highly expressed in the stroma of pancreas tumors, but the interpretation of these results is complicated by the fact that palladin exists as multiple isoforms. In the current study, the expression and localization of palladin isoform 4 was examined in normal specimens and adenocarcinomas of human pancreas, lung, colon, and stomach samples. Immunohistochemistry with isoform-selective antibodies revealed that expression of palladin isoform 4 was higher in adenocarcinomas versus normal tissues, and highest in CAFs. Immunohistochemistry staining revealed that palladin was present in both the cytoplasm and the nucleus of CAFs, and this was confirmed using immunofluorescence staining and subcellular fractionation of a pancreatic CAF cell line. To investigate the functional significance of nuclear palladin, RNA Seq analysis of palladin knockdown CAFs versus control CAFs was performed, and the results showed that palladin regulates the expression of genes involved in the biosynthesis and assembly of collagen, and organization of the extracellular matrix. These results suggested that palladin isoform 4 may play a conserved role in establishing the phenotype of CAFs in multiple tumor types.

Genome-Wide Loss of Heterozygosity and DNA Copy Number Aberration in HPV-Negative Oral Squamous Cell Carcinoma and Their Associations with Disease-Specific Survival

Oral squamous cell cancer of the oral cavity and oropharynx (OSCC) is associated with high case-fatality. For reasons that are largely unknown, patients with the same clinical and pathologic staging have heterogeneous response to treatment and different probability of recurrence and survival, with patients with Human Papillomavirus (HPV)-positive oropharyngeal tumors having the most favorable survival. To gain insight into the complexity of OSCC and to identify potential chromosomal changes that may be associated with OSCC mortality, we used Affymtrix 6.0 SNP arrays to examine paired DNA from peripheral blood and tumor cell populations isolated by laser capture microdissection to assess genome-wide loss of heterozygosity (LOH) and DNA copy number aberration (CNA) and their associations with risk factors, tumor characteristics, and oral cancer-specific mortality among 75 patients with HPV-negative OSCC. We found a highly heterogeneous and complex genomic landscape of HPV-negative tumors, and identified regions in 4q, 8p, 9p and 11q that seem to play an important role in oral cancer biology and survival from this disease. If confirmed, these findings could assist in designing personalized treatment or in the creation of models to predict survival in patients with HPV-negative OSCC.

Priming cancer cells for drug resistance: role of the fibroblast niche

Conventional and targeted chemotherapies remain integral strategies to treat solid tumors. Despite the large number of anti-cancer drugs available, chemotherapy does not completely eradicate disease. Disease recurrence and the growth of drug resistant tumors remain significant problems in anti-cancer treatment. To develop more effective treatment strategies, it is important to understand the underlying cellular and molecular mechanisms of drug resistance. It is generally accepted that cancer cells do not function alone, but evolve through interactions with the surrounding tumor microenvironment. As key cellular components of the tumor microenvironment, fibroblasts regulate the growth and progression of many solid tumors. Emerging studies demonstrate that fibroblasts secrete a multitude of factors that enable cancer cells to become drug resistant. This review will explore how fibroblast secretion of soluble factors act on cancer cells to enhance cancer cell survival and cancer stem cell renewal, contributing to the development of drug resistant cancer.

Miniaturized pre-clinical cancer models as research and diagnostic tools

Cancer is one of the most common causes of death worldwide. Consequently, important resources are directed towards bettering treatments and outcomes. Cancer is difficult to treat due to its heterogeneity, plasticity and frequent drug resistance. New treatment strategies should strive for personalized approaches. These should target neoplastic and/or activated microenvironmental heterogeneity and plasticity without triggering resistance and spare host cells. In this review, the putative use of increasingly physiologically relevant microfabricated cell-culturing systems intended for drug development is discussed. There are two main reasons for the use of miniaturized systems. First, scaling down model size allows for high control of microenvironmental cues enabling more predictive outcomes. Second, miniaturization reduces reagent consumption, thus facilitating combinatorial approaches with little effort and enables the application of scarce materials, such as patient-derived samples. This review aims to give an overview of the state-of-the-art of such systems while predicting their application in cancer drug development.

The wound healing, chronic fibrosis, and cancer progression triad

For decades tumors have been recognized as "wounds that do not heal." Besides the commonalities that tumors and wounded tissues share, the process of wound healing also portrays similar characteristics with chronic fibrosis. In this review, we suggest a tight interrelationship, which is governed as a concurrence of cellular and microenvironmental reactivity among wound healing, chronic fibrosis, and cancer development/progression (i.e., the WHFC triad). It is clear that the same cell types, as well as soluble and matrix elements that drive wound healing (including regeneration) via distinct signaling pathways, also fuel chronic fibrosis and tumor progression. Hence, here we review the relationship between fibrosis and cancer through the lens of wound healing.

TGF-beta in CAF-mediated tumor growth and metastasis

TGF-beta signaling is one of the major pathways controlling cell and tissue behavior not only in homeostasis but also in disease. During tumorigenesis TGF-beta orchestrated processes are key due to its dual role as tumor suppressor and tumor promoter. Important functions of this pathway have been described in a context-dependent manner both in epithelial cancer cells and in the tumor microenvironment during tumor progression. Carcinoma-associated fibroblasts (CAFs) are one of the most abundant stromal cell types in virtually all solid tumors. CAFs favor malignant progression by providing cancer cells with proliferative, migratory, survival and invasive capacities. A complex network of signaling pathways underlying their tumor-promoting properties is beginning to take shape. In this review, we examine current evidence on the emerging mechanisms involving TGF-beta in CAF-mediated cancer progression, and discuss their potential as therapeutic targets.

Palladin promotes invasion of pancreatic cancer cells by enhancing invadopodia formation in cancer-associated fibroblasts

The stromal compartment surrounding epithelial-derived pancreatic tumors is thought to have a key role in the aggressive phenotype of this malignancy. Emerging evidence suggests that cancer-associated fibroblasts (CAFs), the most abundant cells in the stroma of pancreatic tumors, contribute to the tumor's invasion, metastasis and resistance to therapy, but the precise molecular mechanisms that regulate CAFs behavior are poorly understood. In this study, we utilized immortalized human pancreatic CAFs to investigate molecular pathways that control the matrix-remodeling and invasion-promoting activity of CAFs. We showed previously that palladin, an actin-associated protein, is expressed at high levels in CAFs of pancreatic tumors and other solid tumors, and also in an immortalized line of human CAFs. In this study, we found that short-term exposure of CAFs to phorbol esters reduced the number of stress fibers and triggered the appearance of individual invadopodia and invadopodial rosettes in CAFs. Molecular analysis of invadopodia revealed that their composition resembled that of similar structures (that is, invadopodia and podosomes) described in other cell types. Pharmacological inhibition and small interfering RNA knockdown experiments demonstrated that protein kinase C, the small GTPase Cdc42 and palladin were necessary for the efficient assembly of invadopodia by CAFs. In addition, GTPase activity assays showed that palladin contributes to the activation of Cdc42. In mouse xenograft experiments using a mixture of CAFs and tumor cells, palladin expression in CAFs promoted the rapid growth and metastasis of human pancreatic tumor cells. Overall, these results indicate that high levels of palladin expression in CAFs enhance their ability to remodel the extracellular matrix by regulating the activity of Cdc42, which in turn promotes the assembly of matrix-degrading invadopodia in CAFs and tumor cell invasion. Together, these results identify a novel molecular signaling pathway that may provide new molecular targets for the inhibition of pancreatic cancer metastasis.

Palladin regulation of the actin structures needed for cancer invasion

Cell migration and invasion involve the formation of cell adhesion structures as well as the dynamic and spatial regulation of the cytoskeleton. The adhesive structures known as podosomes and invadopodia share a common role in cell motility, adhesion, and invasion, and form when the plasma membrane of motile cells undergoes highly regulated protrusions. Palladin, a molecular scaffold, co-localizes with actin-rich structures where it plays a role in their assembly and maintenance in a wide variety of cell lines. Palladin regulates actin cytoskeleton organization as well as cell adhesion formation. Moreover, palladin contributes to the invasive nature of cancer metastatic cells by regulating invadopodia formation. Palladin seems to regulate podosome and invodopodia formation through Rho GTPases, which are known as key players in coordinating the cellular responses required for cell migration and metastasis.

Arousal of cancer-associated stromal fibroblasts: palladin-activated fibroblasts promote tumor invasion

Cancer-associated fibroblasts (CAF), comprised of activated fibroblasts or myofibroblasts, are found in stroma surrounding solid tumors; these myofibroblasts promote invasion and metastasis of cancer cells. Activation of stromal fibroblasts into myofibroblasts is induced by expression of cystoskeleton protein, palladin, at early stages in tumorigenesis and increases with neoplastic progression. Expression of palladin in fibroblasts is triggered by paracrine signaling from adjacent k-ras-expressing epithelial cells. Three-dimensional co-cultures of palladin-expressing fibroblasts and pancreatic cancer cells reveals that the activated fibroblasts lead the invasion by creating tunnels through the extracellular matrix through which the cancer cells follow. Invasive tunneling occurs as a result of the development of invadopodia-like cellular protrusions in the palladin-activated fibroblasts and the addition of a wounding/inflammatory trigger. Abrogation of palladin reduces the invasive capacity of these cells. CAF also play a role in cancer resistance and immuno-privilege, making the targeting of activators of these cells of interest for oncologists.

Controlled breast cancer microarrays for the deconvolution of cellular multilayering and density effects upon drug responses

Background

Increasing evidence shows that the cancer microenvironment affects both tumorigenesis and the response of cancer to drug treatment. Therefore in vitro models that selectively reflect characteristics of the in vivo environment are greatly needed. Current methods allow us to screen the effect of extrinsic parameters such as matrix composition and to model the complex and three-dimensional (3D) cancer environment. However, 3D models that reflect characteristics of the in vivo environment are typically too complex and do not allow the separation of discrete extrinsic parameters.

Methodology/Principal Findings

In this study we used a poly(ethylene glycol) (PEG) hydrogel-based microwell array to model breast cancer cell behavior in multilayer cell clusters that allows a rigorous control of the environment. The innovative array fabrication enables different matrix proteins to be integrated into the bottom surface of microwells. Thereby, extrinsic parameters including dimensionality, type of matrix coating and the extent of cell-cell adhesion could be independently studied. Our results suggest that cell to matrix interactions and increased cell-cell adhesion, at high cell density, induce independent effects on the response to Taxol in multilayer breast cancer cell clusters. In addition, comparing the levels of apoptosis and proliferation revealed that drug resistance mediated by cell-cell adhesion can be related to altered cell cycle regulation. Conversely, the matrix-dependent response to Taxol did not correlate with proliferation changes suggesting that cell death inhibition may be responsible for this effect.

Conclusions/Significance

The application of the PEG hydrogel platform provided novel insight into the independent role of extrinsic parameters controlling drug response. The presented platform may not only become a useful tool for basic research related to the role of the cancer microenvironment but could also serve as a complementary platform for in vitro drug development.

The mesenchymal tumor microenvironment: a drug-resistant niche

Drug and radiation resistance represent a challenge for most anticancer therapies. Diverse experimental approaches have provided evidence that the tumor-associated microenvironment constitutes both a protective shell that impedes drug or radiation access and a permissive or promotive microenvironment that encourages a nurturing cancer (i.e., cancer stem cell) niche where tumor cells overcome treatment- and cancer-induced stresses. Better understanding of the effects of the tumor microenvironment on cancer cells before, during and immediately after chemo- or radiotherapy is imperative to design new therapies aimed at targeting this tumor-protective niche. This review summarizes some of the known mesenchymal stromal effects that account for drug resistance, the main signal transduction pathways associated with this resistance and the therapeutic efforts directed to increase the success of current therapies. Special emphasis is given to environment-mediated drug resistance in general and to cell adhesion-mediated drug resistance in particular.

Arousal of cancer-associated stroma: overexpression of palladin activates fibroblasts to promote tumor invasion

Background

Cancer-associated fibroblasts, comprised of activated fibroblasts or myofibroblasts, are found in the stroma surrounding solid tumors. These myofibroblasts promote invasion and metastasis of cancer cells. Mechanisms regulating the activation of the fibroblasts and the initiation of invasive tumorigenesis are of great interest. Upregulation of the cytoskeletal protein, palladin, has been detected in the stromal myofibroblasts surrounding many solid cancers and in expression screens for genes involved in invasion. Using a pancreatic cancer model, we investigated the functional consequence of overexpression of exogenous palladin in normal fibroblasts in vitro and its effect on the early stages of tumor invasion.

Principal Findings

Palladin expression in stromal fibroblasts occurs very early in tumorigenesis. In vivo, concordant expression of palladin and the myofibroblast marker, alpha smooth muscle actin (α-SMA), occurs early at the dysplastic stages in peri-tumoral stroma and progressively increases in pancreatic tumorigenesis. In vitro introduction of exogenous 90 kD palladin into normal human dermal fibroblasts (HDFs) induces activation of stromal fibroblasts into myofibroblasts as marked by induction of α-SMA and vimentin, and through the physical change of cell morphology. Moreover, palladin expression in the fibroblasts enhances cellular migration, invasion through the extracellular matrix, and creation of tunnels through which cancer cells can follow. The fibroblast invasion and creation of tunnels results from the development of invadopodia-like cellular protrusions which express invadopodia proteins and proteolytic enzymes. Palladin expression in fibroblasts is triggered by the co-culture of normal fibroblasts with k-ras-expressing epithelial cells.

Conclusions

Overall, palladin expression can impart myofibroblast properties, in turn promoting the invasive potential of these peri-tumoral cells with invadopodia-driven degradation of extracellular matrix. Palladin expression in fibroblasts can be triggered by k-ras expression in adjacent epithelial cells. This data supports a model whereby palladin-activated fibroblasts facilitate stromal-dependent metastasis and outgrowth of tumorigenic epithelium.