The expression of the cytoskeletal focal adhesion protein paxillin in breast cancer correlates with HER2 overexpression and may help predict response to chemotherapy: a retrospective immunohistochemical study

Paxillin Promotes Breast Tumor Collective Cell Invasion through Maintenance of Adherens Junction Integrity

Distant organ metastasis is linked to poor prognosis during cancer progression. The expression level of the focal adhesion adapter protein paxillin varies among different human cancers, but its role in tumor progression is unclear. Herein, we utilize a newly generated PyMT mammary tumor mouse model with conditional paxillin ablation in breast tumor epithelial cells, combined with in vitro 3D tumor organoids invasion analysis and 2D calcium switch assays, to assess the roles for paxillin in breast tumor cell invasion. Paxillin had little effect on primary tumor initiation and growth but is critical for the formation of distant lung metastasis. In paxillin-depleted 3D tumor organoids, collective cell invasion was substantially perturbed. Two-dimensional cell culture revealed paxillin-dependent stabilization of adherens junctions (AJ). Mechanistically, paxillin is required for AJ assembly through facilitating E-cadherin endocytosis and recycling and HDAC6-mediated microtubule acetylation. Furthermore, Rho GTPase activity analysis and rescue experiments with a RhoA activator or Rac1 inhibitor suggest paxillin is potentially regulating the E-cadherin-dependent junction integrity and contractility through control of the balance of RhoA and Rac1 activities. Together, these data highlight new roles for paxillin in the regulation of cell-cell adhesion and collective tumor cell migration to promote the formation of distance organ metastases. [Media: see text] [Media: see text] [Media: see text] [Media: see text] [Media: see text] [Media: see text] [Media: see text] [Media: see text].

Molecular Basis of LH Action on Breast Cancer Cell Migration and Invasion via Kinase and Scaffold Proteins

Breast cancer (BC) is a major public health problem affecting women worldwide. Approximately 80% of diagnosed cases are hormone-dependent breast cancers. These hormones are known to stimulate tumor development and progression. In this setting, tentative evidence suggests that luteinizing hormone (LH) may also play a role in tumors. In BC cells that express functional LH receptors (LHR), this hormone regulates cell migration and invasion by controlling several kinases that activate actin cytoskeletal proteins. In this article, we show that LH induces phosphorylation of paxillin and its translocation toward the plasmatic membrane, where focal adhesion complexes are assembled. This process is triggered via a rapid extra-gonadal LHR signaling to Src/FAK/paxillin, which results in the phosphorylation/activation of the nucleation promoter factors cortactin and N-WASP. As a consequence, Arp2/3 complexes induce actin polymerization, essential to promote cell adhesion, migration, and invasion, thus enhancing metastatic spread of tumoral cells. Our findings provide relevant information about how gonadotrophins exert their action in BC. This information helps us understand the extragonadal effects of LH on BC metastasis. It may provide new perspectives for therapeutic treatment, especially for women with high serum levels of gonadotrophins.

MiR-216b regulates the tumorigenesis of gastric cancer by targeting PXN

BACKGROUND

Accumulating evidence has demonstrated that microRNAs (miRNAs) are associated with tumorigenesis. miR-216b can play a vital role in the genesis and development of gastric cancer (GC), and its molecular mechanisms require further elucidation.

METHODS

The biological effects of miR-216b in GC cells were investigated by MTT, transwell assays, and cell cycle. Western blot and luciferase assay were performed to demonstrate the direct binding of miR-216b on PXN 3'UTR. Furthermore, MTT, colony formation assays, transwell assays, and flow cytometry analysis, as well as xenograft mice model, were used to measure the effects of miR-216b-PXN on GC cell proliferation, migration, and invasion indicated by in vitro and in vivo.

RESULTS

Our results showed that miR-216b acted as a tumor suppressor in GC progression. miR-216b overexpression suppressed GC cell proliferation, migration, and invasion in vitro. Luciferase reporter assays identified paxillin (PXN) as a novel target gene of miR-216b. PXN overexpression could partially rescue miR-216b-induced the inhibitory effects in GC cells. Besides, overexpression of miR-216b contributed to the activation of PI3K/AKT signaling via partly regulating PXN in GC cells.

CONCLUSIONS

The above results showed that miR-216b could offer a novel therapeutic avenue by targeting PXN in GC.

FAK, paxillin, and PI3K in ameloblastoma and adenomatoid odontogenic tumor

OBJECTIVE

Integrins function to bind cells to extracellular matrix in tissues, which triggers downstream signaling cascades that are important in cell survival, proliferation, cytokine activation, and cytoskeleton reorganization. These processes also play significant roles in neoplasms. This work aimed to investigate the pattern of expression of FAK, paxillin, and PI3K in ameloblastoma and adenomatoid odontogenic tumor (AOT).

MATERIALS AND METHODS

Immunohistochemistry was used to study FAK, paxillin, and PI3K in 45 ameloblastomas (32 conventional, 12 unicystic, and 1 peripheral types), 7 AOTs, and two developing human teeth.

RESULTS

Weak expression of FAK was seen in all AOT cases, while ameloblastoma had varying expression patterns, mostly strong to weak. The pattern of expression of paxillin and PI3K was relatively similar in both tumor types. In the dental germ, FAK and paxillin stained all the enamel organ components, while PI3K stained strongly the inner enamel epithelium. Stromal expression of FAK was not found to be useful in differentiating between tumors or tumor classes.

CONCLUSION

The expression of the proteins in the enamel organ suggests that their signaling may be important in odontogenesis. While some ameloblastomas strongly expressed FAK, all cases of AOT had weak signals suggesting low presence and phosphorylating activity of FAK in the latter.

CLINICAL RELEVANCE

A subset of FAK-positive ameloblastoma (as well as their malignant or metastasizing counterparts) which may have relatively aggressive behavior may be candidates for drug targeting of FAK as an additional management option.

Targeting Cell Adhesion Molecules via Carbonate Apatite-Mediated Delivery of Specific siRNAs to Breast Cancer Cells In Vitro and In Vivo

While several treatment strategies are applied to cure breast cancer, it still remains one of the leading causes of female deaths worldwide. Since chemotherapeutic drugs have severe side effects and are responsible for development of drug resistance in cancer cells, gene therapy is now considered as one of the promising options to address the current treatment limitations. Identification of the over-expressed genes accounting for constitutive activation of certain pathways, and their subsequent knockdown with specific small interfering RNAs (siRNAs), could be a powerful tool in inhibiting proliferation and survival of cancer cells. In this study, we delivered siRNAs against mRNA transcripts of over-regulated cell adhesion molecules such as catenin alpha 1 (CTNNA1), catenin beta 1 (CTNNB1), talin-1 (TLN1), vinculin (VCL), paxillin (PXN), and actinin-1 (ACTN1) in human (MCF-7 and MDA-MB-231) and murine (4T1) cell lines as well as in the murine female Balb/c mice model. In order to overcome the barriers of cell permeability and nuclease-mediated degradation, the pH-sensitive carbonate apatite (CA) nanocarrier was used as a delivery vehicle. While targeting CTNNA1, CTNNB1, TLN1, VCL, PXN, and ACTN1 resulted in a reduction of cell viability in MCF-7 and MDA-MB-231 cells, delivery of all these siRNAs via carbonate apatite (CA) nanoparticles successfully reduced the cell viability in 4T1 cells. In 4T1 cells, delivery of CTNNA1, CTNNB1, TLN1, VCL, PXN, and ACTN1 siRNAs with CA caused significant reduction in phosphorylated and total AKT levels. Furthermore, reduced band intensity was observed for phosphorylated and total MAPK upon transfection of 4T1 cells with CTNNA1, CTNNB1, and VCL siRNAs. Intravenous delivery of CTNNA1 siRNA with CA nanoparticles significantly reduced tumor volume in the initial phase of the study, while siRNAs targeting CTNNB1, TLN1, VCL, PXN, and ACTN1 genes significantly decreased the tumor burden at all time points. The tumor weights at the end of the treatments were also notably smaller compared to CA. This successfully demonstrates that targeting these dysregulated genes via RNAi and by using a suitable delivery vehicle such as CA could serve as a promising therapeutic treatment modality for breast cancers.

Regulators of the RAS-ERK pathway as therapeutic targets in thyroid cancer

Thyroid cancer is mostly an ERK-driven carcinoma, as up to 70% of thyroid carcinomas are caused by mutations that activate the RAS/ERK mitogenic signaling pathway. The incidence of thyroid cancer has been steadily increasing for the last four decades; yet, there is still no effective treatment for advanced thyroid carcinomas. Current research efforts are focused on impairing ERK signaling with small-molecule inhibitors, mainly at the level of BRAF and MEK. However, despite initial promising results in animal models, the clinical success of these inhibitors has been limited by the emergence of tumor resistance and relapse. The RAS/ERK pathway is an extremely complex signaling cascade with multiple points of control, offering many potential therapeutic targets: from the modulatory proteins regulating the activation state of RAS proteins to the scaffolding proteins of the pathway that provide spatial specificity to the signals, and finally, the negative feedbacks and phosphatases responsible for inactivating the pathway. The aim of this review is to give an overview of the biology of RAS/ERK regulators in human cancer highlighting relevant information on thyroid cancer and future areas of research.

FAK and paxillin, two potential targets in pancreatic cancer

Pancreatic ductal adenocarcinoma (PDAC) is a devastating cancer in large part due to late diagnosis and a lack of effective screening tests. In spite of recent progress in imaging, surgery and new therapeutic options for pancreatic cancer, the overall five-year survival still remains unacceptably low. Numerous studies have shown that focal adhesion kinase (FAK) is activated in many cancers including PDAC and promotes cancer progression and metastasis. Paxillin, an intracellular adaptor protein that plays a key role in cytoskeletal organization, connects integrins to FAK and plays a key role in assembly and disassembly of focal adhesions. Here, we have reviewed evidence in support of FAK as a potential therapeutic target and summarized related combinatorial therapies.

Paxillin: a crossroad in pathological cell migration

Paxilllin is a multifunctional and multidomain focal adhesion adapter protein which serves an important scaffolding role at focal adhesions by recruiting structural and signaling molecules involved in cell movement and migration, when phosphorylated on specific Tyr and Ser residues. Upon integrin engagement with extracellular matrix, paxillin is phosphorylated at Tyr31, Tyr118, Ser188, and Ser190, activating numerous signaling cascades which promote cell migration, indicating that the regulation of adhesion dynamics is under the control of a complex display of signaling mechanisms. Among them, paxillin disassembly from focal adhesions induced by extracellular regulated kinase (ERK)-mediated phosphorylation of serines 106, 231, and 290 as well as the binding of the phosphatase PEST to paxillin have been shown to play a key role in cell migration. Paxillin also coordinates the spatiotemporal activation of signaling molecules, including Cdc42, Rac1, and RhoA GTPases, by recruiting GEFs, GAPs, and GITs to focal adhesions. As a major participant in the regulation of cell movement, paxillin plays distinct roles in specific tissues and developmental stages and is involved in immune response, epithelial morphogenesis, and embryonic development. Importantly, paxillin is also an essential player in pathological conditions including oxidative stress, inflammation, endothelial cell barrier dysfunction, and cancer development and metastasis.

Selective Killing of Melanoma Cells With Non-Thermal Atmospheric Pressure Plasma and p-FAK Antibody Conjugated Gold Nanoparticles

Melanomas are fast growing high-mortality tumors, and specific treatments for melanomas are needed. Melanoma cells overexpress focal adhesion kinase (FAK) compared to normal keratinocytes, and we sought to exploit this difference to create a selectively lethal therapy. We combined gold nanoparticles (GNP) with antibodies targeting phosphorylated FAK (p-FAK). These conjugates (p-FAK-GNP) entered G361 melanoma cells and bound p-FAK. Treatment with p-FAK-GNP decreased the viability of G361 cells in a time dependent manner by inducing apoptosis. To maximize the preferential killing of G361 cells, non-thermal atmospheric pressure plasma was used to stimulate the GNP within p-FAK-GNP. Combined treatment with plasma and p-FAK-GNP showed much higher lethality against G361 cells than HaCaT keratinocyte cells. The p-FAK-GNP induced apoptosis over 48 hours in G361 cells, whereas plasma and p-FAK-GNP killed G361 cells immediately. This study demonstrates that combining plasma with p-FAK-GNP results in selective lethality against human melanoma cells.

Overexpression of Paxillin Correlates with Tumor Progression and Predicts Poor Survival in Glioblastoma

AIMS

To explore the prognostic and clinicopathological features of glioma with Paxillin (PXN) expression based on a large number of samples.

METHODS

RNA sequencing data of 325 glioma samples from Chinese Glioma Genome Atlas (CGGA) database were obtained as discovery set. Three additional datasets were further obtained as validation sets. The protein expression pattern of PXN in glioma was measured by IHC. Kaplan-Meier survival and multivariate Cox analysis were used to estimate the survival distributions. Moreover, the functional annotation of PXN was also analyzed.

RESULTS

In the discovery set, PXN overexpression was significantly associated with high-grade glioma as well as the higher mortality in survival analysis (log-rank test, P < 0.01). The results of the other validation datasets showed similar findings. PXN also served as an independent prognostic biomarker in glioblastoma patients. Functional assays showed that PXN contributed to glioma cell proliferation and invasion.

CONCLUSION

PXN plays as an oncogene in glioma progression and suggests a new potential biotarget for therapy.

Overlapping nongenomic and genomic actions of thyroid hormone and steroids

The genomic actions of thyroid hormone and steroids depend upon primary interactions of the hormones with their specific nuclear receptor proteins. Formation of nuclear co-activator or co-repressor complexes involving the liganded receptors subsequently result in transcriptional events-either activation or suppression-at genes that are specific targets of thyroid hormone or steroids. Nongenomic actions of thyroid hormone and steroids are in contrast initiated at binding sites on the plasma membrane or in cytoplasm or organelles and do not primarily require formation of intranuclear receptor protein-hormone complexes. Importantly, hormonal actions that begin nongenomically outside the nucleus often culminate in changes in nuclear transcriptional events that are regulated by both traditional intranuclear receptors as well as other nuclear transcription factors. In the case of thyroid hormone, the extranuclear receptor can be the classical "nuclear" thyroid receptor (TR), a TR isoform, or integrin αvβ3. In the case of steroid hormones, the membrane receptor is usually, but not always, the classical "nuclear" steroid receptor. This concept defines the paradigm of overlapping nongenomic and genomic hormone mechanisms of action. Here we review some examples of how extranuclear signaling by thyroid hormone and by estrogens and androgens modulates intranuclear hormone signaling to regulate a number of vital biological processes both in normal physiology and in cancer progression. We also point out that nongenomic actions of thyroid hormone may mimic effects of estrogen in certain tumors.

Leupaxin is expressed in mammary carcinoma and acts as a transcriptional activator of the estrogen receptor α

Leupaxin belongs to the group of paxillin proteins and was reported to play a major role in the invasion and migration of prostate cancer cells. In the present study we were able to show by using a cDNA cancer profiling array that leupaxin is upregulated in breast and endometrial cancer, whereas downregulation of leupaxin was observed in lung cancer. In addition, immunohistochemical studies using a leupaxin-specific antibody on human breast cancer specimens (n=127) revealed that leupaxin is expressed mainly in invasive ductal carcinomas and ductal carcinoma in situ (40 and 49% respectively), and only in a minority of lobular mammary carcinomas. To further investigate the role of leupaxin in the progression of breast cancer the expression of leupaxin was analysed in six breast cancer cell lines. The estrogen receptor α (ERα)-positive HCC70 and the ERα-negative MDA-MB-231 cells showed leupaxin expression on the RNA and protein level. Leupaxin localizes in these mammary carcinoma cells at focal adhesion sites and shuttles between membrane and nucleus via its LD4 motif as major nuclear export signal. Interaction partners of leupaxin in the nucleus represent the estrogen receptors ERα and ERβ. Both ERα and ERβ bind to the LIM domains of leupaxin via their AF-1/DNA binding domains. Furthermore, leupaxin is able to induce transcriptional activity of ERα independent of the presence of estradiol. The specific downregulation of leupaxin expression using siRNAs in mammary carcinoma cells resulted in reduced migratory capability and diminished invasiveness whereas no effect on proliferation was observed. Collectively, these results show that leupaxin has particular influence on the progression and invasion of breast cancer cells and may therefore represent an interesting candidate protein for diagnosis and therapeutic interventions.

c-Jun N-Terminal Kinases Mediate a Wide Range of Targets in the Metastatic Cascade

Disseminated cancer cells rely on intricate interactions among diverse cell types in the tumor-associated stroma, vasculature, and immune system for survival and growth. Ubiquitous expression of c-Jun N-terminal kinase (jnk) genes in various cell types permits their control of metastasis. In early stages of metastasis, JNKs affect tumor-associated inflammation and angiogenesis as well as tumor cell migration and intravasation. Within the tumor stroma, JNKs are essential for the release of growth factors that promote epithelial-to-mesenchymal transition (EMT) in tumor cells. JNK3, the least ubiquitous isoform, facilitates angiogenesis by increasing endothelial cell migration. Importantly, JNK expression in tumor cells integrates stromal signals to promote tumor cell invasion. However, JNK isoforms differentially regulate migration toward the endothelial barrier. Once tumor cells enter the bloodstream, JNKs increase circulating tumor cell (CTC) survival and homing to tissues. By promoting fibrosis, JNKs improve CTC attachment to the endothelium. Once anchored, JNKs stimulate EMT to facilitate tumor cell extravasation and enhance the secretion of endothelial barrier disrupters. Tumor cells attract barrier-disrupting macrophages by JNK-dependent transcription of macrophage chemoattractant molecules. In the secondary tissue, JNKs are instrumental in the premetastatic niche and stimulate tumor cell proliferation. JNK expression in cancer cells stimulates tissue-remodeling macrophages to improve tumor colonization. However, in T-cells, JNKs alter cytokine production that increases tumor surveillance and inhibits the recruitment of tissue-remodeling macrophages. Therapeutically targeting JNKs for metastatic disease is attractive considering their promotion of metastasis; however, specific JNK tools are needed to determine their definitive actions within the context of the entire metastatic cascade.

Paxillin controls endothelial cell migration and tumor angiogenesis by altering neuropilin 2 expression

Although a number of growth factors and receptors are known to control tumor angiogenesis, relatively little is known about the mechanism by which these factors influence the directional endothelial cell migration required for cancer microvessel formation. Recently, it has been shown that the focal adhesion protein paxillin is required for directional migration of fibroblasts in vitro. Here, we show that paxillin knockdown enhances endothelial cell migration in vitro and stimulates angiogenesis during normal development and in response to tumor angiogenic factors in vivo. Paxillin produces these effects by decreasing expression of neuropilin 2 (NRP2). Moreover, soluble factors secreted by tumors that stimulate vascular ingrowth, including vascular endothelial growth factor (VEGF), also decrease endothelial cell expression of paxillin and NRP2, and overexpression of NRP2 reverses these effects. These results suggest that the VEGF-paxillin-NRP2 pathway could represent a new therapeutic target for cancer and other angiogenesis-related diseases.

Paxillin and steroid signaling: from frog to human

Paxillin is a well-characterized cytoplasmic adaptor protein that is known to play important roles in cytoskeletal rearrangement, cell adhesion, and cell motility. In addition to its structural functions, paxillin has more recently been shown to function as a regulator of cell division-mediating steroid-triggered meiosis in oocytes as well as steroid- and growth factor-induced proliferation in prostate and breast cancer. Paxillin mediates these processes through a conserved pathway that involves both extranuclear (nongenomic) and nuclear (genomic) steroid signaling, as well as both cytoplasmic and nuclear kinase signaling. In fact, paxillin appears to serve as a critical liaison between extranuclear and nuclear signaling in response to multiple stimuli, making it a fascinating molecule to study when trying to determine how growth signals from the membrane lead to important proliferative changes in the nucleus. This chapter outlines recent advances in understanding how paxillin regulates both steroid and growth factor signaling, focusing on the conserved nature of its actions from a frog germ cell to a human cancer cell.

Paxillin expression is closely linked to the pathogenesis, progression and prognosis of gastric carcinomas

Paxillin encodes a focal adhesion-associated protein and is involved in the progression and aggressive phenotypes of malignancies through its interactions with the actin cytoskeleton and key signal transduction oncogenes. The present study aimed to investigate the clinicopathological and prognostic significance of paxillin in gastric cancer. The expression of paxillin was evaluated using tissue microarrays of gastric adjacent non-cancerous mucosa, adenoma and carcinoma specimens by immunohistochemistry. Paxillin expression was compared against clinicopathological parameters and the survival time of the patients. Paxillin was highly expressed in gastric adenoma compared with that in non-neoplastic mucosa and carcinoma (P<0.05). Paxillin expression was lower in the younger carcinoma patients compared with that in the elder carcinoma patients (P<0.05). Paxillin expression was negatively correlated with tumor size, depth of invasion and lymph node metastasis, but not with patient gender, lymphatic or venous invasion, or TNM staging (P>0.05). Higher paxillin expression was observed in intestinal-type compared with diffuse-type carcinoma (P<0.05). Kaplan-Meier analysis indicated a positive association between paxillin expression and cumulative survival rate in all, advanced and intestinal-type carcinoma patients (P<0.05). Multivariate analysis using the Cox proportional hazards model indicated that patient age, depth of invasion, lymphatic invasion, lymph node metastasis, TNM staging and Lauren classification were independent prognostic factors for all gastric carcinomas (P<0.05). Aberrant paxillin expression may be involved in the growth, invasion, metastasis and differentiation of gastric carcinoma. Altered paxillin expression may, therefore, be employed as an indicator of pathobiological behaviors and prognosis of gastric carcinomas.

Identification of a breast cancer susceptibility locus at 4q31.22 using a genome-wide association study paradigm

More than 40 single nucleotide polymorphisms (SNPs) for breast cancer susceptibility were identified by genome-wide association studies (GWASs). However, additional SNPs likely contribute to breast cancer susceptibility and overall genetic risk, prompting this investigation for additional variants. Six putative breast cancer susceptibility SNPs identified in a two-stage GWAS that we reported earlier were replicated in a follow-up stage 3 study using an independent set of breast cancer cases and controls from Canada, with an overall cumulative sample size of 7,219 subjects across all three stages. The study design also encompassed the 11 variants from GWASs previously reported by various consortia between the years 2007–2009 to (i) enable comparisons of effect sizes, and (ii) identify putative prognostic variants across studies. All SNP associations reported with breast cancer were also adjusted for body mass index (BMI). We report a strong association with 4q31.22-rs1429142 (combined per allele odds ratio and 95% confidence interval = 1.28 [1.17–1.41] and P_combined = 1.5×10⁻⁷), when adjusted for BMI. Ten of the 11 breast cancer susceptibility loci reported by consortia also showed associations in our predominantly Caucasian study population, and the associations were independent of BMI; four FGFR2 SNPs and TNRC9-rs3803662 were among the most notable associations. Since the original report by Garcia-Closas et al. 2008, this is the second study to confirm the association of 8q24.21-rs13281615 with breast cancer outcomes.

Expression of claudin, paxillin and FRA-1 in non-nodular breast lesions in association with microcalcifications

CONTEXT AND OBJECTIVE

The possible role of adhesion molecules in early breast carcinogenesis has been shown in the literature. We aimed to analyze early adhesion imbalances in non-nodular breast lesions and their association with precursor lesions, in order to ascertain whether these alterations exist and contribute towards early carcinogenesis.

DESIGN AND SETTING

Retrospective cross-sectional study based on medical records at a private radiological clinic in São Paulo, Brazil.

METHODS

We retrospectively reviewed the medical records of all consecutive women attended between August 2006 and July 2007 who presented mammographic evidence of breast microcalcifications classified as Breast Imaging Reporting and Data System Atlas (BI-RADS) type 4. These women underwent stereotaxic biopsy. Clinical, radiological and pathological data were collected, and immunohistochemical assays searched for claudin, paxillin, FRA-1 and HER-2.

RESULTS

Over this period, 127 patients were evaluated. Previous BI-RADS diagnoses showed that 69 cases were in category 4A, 47 in 4B and 11 in 4C. Morphological assessment showed benign entities in 86.5%. Most of the benign lesions showed preserved claudin expression, associated with paxillin (P < 0.001). Paxillin and HER-2 expressions were correlated. FRA-1 expression was also strongly associated with HER-2 expression (P < 0.001).

CONCLUSIONS

Although already present in smaller amounts, imbalance of adhesion molecules is not necessarily prevalent in non-nodular breast lesions. Since FRA-1 expression reached statistically significant correlations with radiological and morphological diagnoses and HER-2 status, it may have a predictive role in this setting.

Diverse roles for the paxillin family of proteins in cancer

The paxillin family of intracellular scaffold proteins includes paxillin, Hic-5, and leupaxin, and all have been identified as key regulators of the cellular migration machinery in both 2- and 3-dimensional microenvironments. Herein, we provide insight into the roles of these proteins during tumorigenesis and metastasis, highlighting their functions in cancer initiation as well as tumor cell dissemination and survival. Furthermore, we speculate on the potential of paxillin family proteins as both future prognostic and therapeutic targets.

Paxillin mediates sensing of physical cues and regulates directional cell motility by controlling lamellipodia positioning

Physical interactions between cells and the extracellular matrix (ECM) guide directional migration by spatially controlling where cells form focal adhesions (FAs), which in turn regulate the extension of motile processes. Here we show that physical control of directional migration requires the FA scaffold protein paxillin. Using single-cell sized ECM islands to constrain cell shape, we found that fibroblasts cultured on square islands preferentially activated Rac and extended lamellipodia from corner, rather than side regions after 30 min stimulation with PDGF, but that cells lacking paxillin failed to restrict Rac activity to corners and formed small lamellipodia along their entire peripheries. This spatial preference was preceded by non-spatially constrained formation of both dorsal and lateral membrane ruffles from 5-10 min. Expression of paxillin N-terminal (paxN) or C-terminal (paxC) truncation mutants produced opposite, but complementary, effects on lamellipodia formation. Surprisingly, pax-/- and paxN cells also formed more circular dorsal ruffles (CDRs) than pax+ cells, while paxC cells formed fewer CDRs and extended larger lamellipodia even in the absence of PDGF. In a two-dimensional (2D) wound assay, pax-/- cells migrated at similar speeds to controls but lost directional persistence. Directional motility was rescued by expressing full-length paxillin or the N-terminus alone, but paxN cells migrated more slowly. In contrast, pax-/- and paxN cells exhibited increased migration in a three-dimensional (3D) invasion assay, with paxN cells invading Matrigel even in the absence of PDGF. These studies indicate that paxillin integrates physical and chemical motility signals by spatially constraining where cells will form motile processes, and thereby regulates directional migration both in 2D and 3D. These findings also suggest that CDRs may correspond to invasive protrusions that drive cell migration through 3D extracellular matrices.

β1-integrins signaling and mammary tumor progression in transgenic mouse models: implications for human breast cancer

Consistent with their essential role in cell adhesion to the extracellular matrix, integrins and their associated signaling pathways have been shown to be involved in cell proliferation, migration, invasion and survival, processes required in both tumorigenesis and metastasis. β1-integrins represent the predominantly expressed integrins in mammary epithelial cells and have been proven crucial for mammary gland development and differentiation. Here we provide an overview of the studies that have used transgenic mouse models of mammary tumorigenesis to establish β1-integrin as a critical mediator of breast cancer progression and thereby as a potential therapeutic target for the development of new anticancer strategies.

Paxillin expression and amplification in early lung lesions of high-risk patients, lung adenocarcinoma and metastatic disease

Background

Paxillin is a modular protein that localises to cell adhesion sites where it facilitates bidirectional communication between the intracellular actin cytoskeleton and the extracellular matrix. These complex and dynamic interactions are essential for cell adhesion, cell migration and cell survival. The authors have previously demonstrated that paxillin is overexpressed in lung cancer tissues and identified somatic paxillin mutations in 9% of lung cancers. A murine in vivo xenograft model of the most common paxillin mutation (A127T) showed increased cell proliferation and invasive tumour growth, establishing an important role for paxillin in the development of lung cancer.

Methods

The authors analysed 279 bronchoscopy-aided biopsy specimens from 92 high-risk patients. Adenocarcinoma with bronchioloalveolar features and pure bronchioloalveolar carcinoma (BAC) were analysed with fluorescence in situ hybridisation (FISH) and immunohistochemistry (IHC).

Results

Paxillin is overexpressed in premalignant areas of hyperplasia, squamous metaplasia and goblet cell metaplasia, as well as dysplastic lesions and carcinoma in high-risk patients. Concordance between increased paxillin gene copy number and paxillin overexpression was observed in cases of adenocarcinoma eusomic for chromosome 12.

Conclusions

Paxillin overexpression occurs during the earliest stages of lung cancer development. FISH and IHC analysis of lung adenocarcinoma suggests that relatively small-scale genomic rearrangements of chromosome 12 are associated with paxillin overexpression in lung adenocarcinoma.

Proteomics and cancer epidemiology

Profiling of differentially expressed proteins is perhaps the most important and useful approach in developing tools for risk assessment in a population, diagnostic screening, and therapeutics. Proteomic markers have potential for identifying individuals at high risk of developing cancer; however, these markers have not been extensively used in cancer epidemiologic studies. Several markers have to be clinically validated. In this chapter, methods used in proteomic analysis of clinical samples, challenges in the proteomics and cancer epidemiology, and their potential solutions are discussed.

Increased expression of paxillin is found in human oesophageal squamous cell carcinoma: a tissue microarray study

Oesophageal cancer is one of the most common cancers worldwide. Currently, the tumour, node, metastasis (TNM) staging system is the primary method for determining its extent and prognosis, however, data suggest this system does not predict prognosis accurately. Research has, therefore, concentrated on searching for specific biomarkers. Paxillin has been shown to play an important role in controlling cell spread and migration. Its over-expression is considered to correlate with the prognosis of some types of cancers, however, the relationship between paxillin expression and clinical outcome in oesophageal cancer has not been investigated. This study determined the expression of paxillin by immunohistochemistry on the tissue microarray of 100 oesophageal squamous cell cancer patients followed up for a mean of 55 months. Paxillin was over-expressed in tumours in 27/100 cases, compared with 6/100 cases for adjacent non-tumoural cells. No correlation occurred between expression of paxillin and overall patient survival, hence paxillin is not an effective prognostic marker in these patients.