Integrin alpha 3 beta 1 participates in the phagocytosis of extracellular matrix molecules by human breast cancer cells

Galectin-8 inhibition and functions in immune response and tumor biology

Galectins are among organisms' most abundantly expressed lectins (carbohydrate-binding proteins) that specifically bind β-galactosides. They act not only outside the cell, where they bind to extracellular matrix glycans, but also inside the cell, where they have a significant impact on signaling pathways. Galectin-8 is a galectin family protein encoded by the LGALS8 gene. Its role is evident in both T- and B-cell immunity and in the innate immune response, where it acts directly on dendritic cells and induces some pro-inflammatory cytokines. Galectin-8 also plays an important role in the defense against bacterial and viral infections. It is known to promote antibacterial autophagy by recognizing and binding glycans present on the vacuolar membrane, thus acting as a danger receptor. The most important role of galectin-8 is the regulation of cancer growth, metastasis, tumor progression, and tumor cell survival. Importantly, the expression of galectins is typically higher in tumor tissues than in noncancerous tissues. In this review article, we focus on galectin-8 and its function in immune response, microbial infections, and cancer. Given all of these functions of galectin-8, we emphasize the importance of developing new and selective galectin-8 inhibitors and report the current status of their development.

The long-loop recycling (LLR) of synaptic components as a question of economics

The pre- and post-synaptic compartments contain a variety of molecules that are known to recycle between the plasma membrane and intracellular organelles. The recycling steps have been amply described in functional terms, with, for example, synaptic vesicle recycling being essential for neurotransmitter release, and postsynaptic receptor recycling being a fundamental feature of synaptic plasticity. However, synaptic protein recycling may also serve a more prosaic role, simply ensuring the repeated use of specific components, thereby minimizing the energy expenditure on the synthesis of synaptic proteins. This type of process has been recently described for components of the extracellular matrix, which undergo long-loop recycling (LLR), to and from the cell body. Here we suggest that the energy-saving recycling of synaptic components may be more widespread than is generally acknowledged, potentially playing a role in both synaptic vesicle protein usage and postsynaptic receptor metabolism.

Discovery and Targeting of a Noncanonical Mechanism of Sarcoma Resistance to ADI-PEG20 Mediated by the Microenvironment

PURPOSE

Many cancers lack argininosuccinate synthetase 1 (ASS1), the rate-limiting enzyme of arginine biosynthesis. This deficiency causes arginine auxotrophy, targetable by extracellular arginine-degrading enzymes such as ADI-PEG20. Long-term tumor resistance has thus far been attributed solely to ASS1 reexpression. This study examines the role of ASS1 silencing on tumor growth and initiation and identifies a noncanonical mechanism of resistance, aiming to improve clinical responses to ADI-PEG20.

EXPERIMENTAL DESIGN

Tumor initiation and growth rates were measured for a spontaneous Ass1 knockout (KO) murine sarcoma model. Tumor cell lines were generated, and resistance to arginine deprivation therapy was studied in vitro and in vivo.

RESULTS

Conditional Ass1 KO affected neither tumor initiation nor growth rates in a sarcoma model, contradicting the prevalent idea that ASS1 silencing confers a proliferative advantage. Ass1 KO cells grew robustly through arginine starvation in vivo, while ADI-PEG20 remained completely lethal in vitro, evidence that pointed toward a novel mechanism of resistance mediated by the microenvironment. Coculture with Ass1-competent fibroblasts rescued growth through macropinocytosis of vesicles and/or cell fragments, followed by recycling of protein-bound arginine through autophagy/lysosomal degradation. Inhibition of either macropinocytosis or autophagy/lysosomal degradation abrogated this growth support effect in vitro and in vivo.

CONCLUSIONS

Noncanonical, ASS1-independent tumor resistance to ADI-PEG20 is driven by the microenvironment. This mechanism can be targeted by either the macropinocytosis inhibitor imipramine or the autophagy inhibitor chloroquine. These safe, widely available drugs should be added to current clinical trials to overcome microenvironmental arginine support of tumors and improve patient outcomes.

Collagen Remodeling along Cancer Progression Providing a Novel Opportunity for Cancer Diagnosis and Treatment

The extracellular matrix (ECM) is a significant factor in cancer progression. Collagens, as the main component of the ECM, are greatly remodeled alongside cancer development. More and more studies have confirmed that collagens changed from a barrier to providing assistance in cancer development. In this course, collagens cause remodeling alongside cancer progression, which in turn, promotes cancer development. The interaction between collagens and tumor cells is complex with biochemical and mechanical signals intervention through activating diverse signal pathways. As the mechanism gradually clears, it becomes a new target to find opportunities to diagnose and treat cancer. In this review, we investigated the process of collagen remodeling in cancer progression and discussed the interaction between collagens and cancer cells. Several typical effects associated with collagens were highlighted in the review, such as fibrillation in precancerous lesions, enhancing ECM stiffness, promoting angiogenesis, and guiding invasion. Then, the values of cancer diagnosis and prognosis were focused on. It is worth noting that several generated fragments in serum were reported to be able to be biomarkers for cancer diagnosis and prognosis, which is beneficial for clinic detection. At a glance, a variety of reported biomarkers were summarized. Many collagen-associated targets and drugs have been reported for cancer treatment in recent years. The new targets and related drugs were discussed in the review. The mass data were collected and classified by mechanism. Overall, the interaction of collagens and tumor cells is complicated, in which the mechanisms are not completely clear. A lot of collagen-associated biomarkers are excavated for cancer diagnosis. However, new therapeutic targets and related drugs are almost in clinical trials, with merely a few in clinical applications. So, more efforts are needed in collagens-associated studies and drug development for cancer research and treatment.

Recurrence of Papillary Thyroid Cancer: A Systematic Appraisal of Risk Factors

CONTEXT

Thyroid cancer recurrence is associated with increased mortality and adverse outcomes. Recurrence risk is currently predicted using clinical tools, often restaging patients after treatment. Detailed understanding of recurrence risk at disease onset could lead to personalized and improved patient care.

OBJECTIVE

We aimed to perform a comprehensive bioinformatic and experimental analysis of 3 levels of genetic change (mRNA, microRNA, and somatic mutation) apparent in recurrent tumors and construct a new combinatorial prognostic risk model.

METHODS

We analyzed The Cancer Genome Atlas data (TCGA) to identify differentially expressed genes (mRNA/microRNA) in 46 recurrent vs 455 nonrecurrent thyroid tumors. Two exonic mutational pipelines were used to identify somatic mutations. Functional gene analysis was performed in cell-based assays in multiple thyroid cell lines. The prognostic value of genes was evaluated with TCGA datasets.

RESULTS

We identified 128 new potential biomarkers associated with recurrence, including 40 mRNAs, 39 miRNAs, and 59 genetic variants. Among differentially expressed genes, modulation of FN1, ITGα3, and MET had a significant impact on thyroid cancer cell migration. Similarly, ablation of miR-486 and miR-1179 significantly increased migration of TPC-1 and SW1736 cells. We further utilized genes with a validated functional role and identified a 5-gene risk score classifier as an independent predictor of thyroid cancer recurrence.

CONCLUSION

Our newly proposed risk model based on combinatorial mRNA and microRNA expression has potential clinical utility as a prognostic indicator of recurrence. These findings should facilitate earlier prediction of recurrence with implications for improving patient outcome by tailoring treatment to disease risk and increasing posttreatment surveillance.

Extracellular Matrix Recycling as a Novel Plasticity Mechanism With a Potential Role in Disease

The extracellular matrix (ECM) stabilizes neural circuits and synapses in the healthy brain, while also retaining the ability to be remodeled, to allow synapses to be plastic. A well-described mechanism for ECM remodeling is through the regulated secretion of proteolytic enzymes at the synapse, together with the synthesis of new ECM molecules. The importance of this process is evidenced by the large number of brain disorders that are associated with a dysregulation of ECM-cleaving protease activity. While most of the brain ECM molecules are indeed stable for remarkable time periods, evidence in other cell types, as cancer cells, suggests that at least a proportion of the ECM molecules may be endocytosed regularly, and could even be recycled back to the ECM. In this review, we discuss the involvement of such a mechanism in the brain, under physiological activity conditions and in relation to synapse and brain disease.

The Synaptic Extracellular Matrix: Long-Lived, Stable, and Still Remarkably Dynamic

In the adult brain, synapses are tightly enwrapped by lattices of the extracellular matrix that consist of extremely long-lived molecules. These lattices are deemed to stabilize synapses, restrict the reorganization of their transmission machinery, and prevent them from undergoing structural or morphological changes. At the same time, they are expected to retain some degree of flexibility to permit occasional events of synaptic plasticity. The recent understanding that structural changes to synapses are significantly more frequent than previously assumed (occurring even on a timescale of minutes) has called for a mechanism that allows continual and energy-efficient remodeling of the extracellular matrix (ECM) at synapses. Here, we review recent evidence for such a process based on the constitutive recycling of synaptic ECM molecules. We discuss the key characteristics of this mechanism, focusing on its roles in mediating synaptic transmission and plasticity, and speculate on additional potential functions in neuronal signaling.

DDR1 associates with TRPV4 in cell-matrix adhesions to enable calcium-regulated myosin activity and collagen compaction

Tissue fibrosis manifests as excessive deposition of compacted, highly aligned collagen fibrils, which interfere with organ structure and function. Cells in collagen-rich lesions often exhibit marked overexpression of discoidin domain receptor 1 (DDR1), which is linked to increased collagen compaction through the association of DDR1 with the Ca²⁺ -dependent nonmuscle myosin IIA (NMIIA). We examined the functional relationship between DDR1 and the transient receptor potential vanilloid type 4 (TRPV4) channel, a Ca²⁺ -permeable ion channel that is implicated in collagen compaction. Fibroblasts expressing high levels of DDR1 were used to model cells in lesions with collagen compaction. In these cells, the expression of the β1 integrin was deleted to simplify studies of DDR1 function. Compared with DDR1 wild-type cells, high DDR1 expression was associated with increased Ca²⁺ influx through TRPV4, enrichment of TRPV4 in collagen adhesions, and enhanced contractile activity mediated by NMIIA. At cell adhesion sites to collagen, DDR1 associated with TRPV4, which enhanced DDR1-mediated collagen alignment and compaction. We conclude that DDR1 regulates Ca²⁺ influx through the TRPV4 channel to promote critical, DDR1-mediated processes that are important in lesions with collagen compaction and alignment.

Phagocytic Integrins: Activation and Signaling

Phagocytic integrins are endowed with the ability to engulf and dispose of particles of different natures. Evolutionarily conserved from worms to humans, they are involved in pathogen elimination and apoptotic and tumoral cell clearance. Research in the field of integrin-mediated phagocytosis has shed light on the molecular events controlling integrin activation and their effector functions. However, there are still some aspects of the regulation of the phagocytic process that need to be clarified. Here, we have revised the molecular events controlling phagocytic integrin activation and the downstream signaling driving particle engulfment, and we have focused particularly on α_Mβ₂/CR3, α_Xβ₂/CR4, and a brief mention of α_Vβ₅/α_Vβ₃integrins.

Targeted Drug Delivery via the Use of ECM-Mimetic Materials

The use of drug delivery vehicles to improve the efficacy of drugs and to target their action at effective concentrations over desired periods of time has been an active topic of research and clinical investigation for decades. Both synthetic and natural drug delivery materials have facilitated locally controlled as well as targeted drug delivery. Extracellular matrix (ECM) molecules have generated widespread interest as drug delivery materials owing to the various biological functions of ECM. Hydrogels created using ECM molecules can provide not only biochemical and structural support to cells, but also spatial and temporal control over the release of therapeutic agents, including small molecules, biomacromolecules, and cells. In addition, the modification of drug delivery carriers with ECM fragments used as cell-binding ligands has facilitated cell-targeted delivery and improved the therapeutic efficiency of drugs through interaction with highly expressed cellular receptors for ECM. The combination of ECM-derived hydrogels and ECM-derived ligand approaches shows synergistic effects, leading to a great promise for the delivery of intracellular drugs, which require specific endocytic pathways for maximal effectiveness. In this review, we provide an overview of cellular receptors that interact with ECM molecules and discuss examples of selected ECM components that have been applied for drug delivery in both local and systemic platforms. Finally, we highlight the potential impacts of utilizing the interaction between ECM components and cellular receptors for intracellular delivery, particularly in tissue regeneration applications.

Evaluation of the mRNA expression levels of integrins α3, α5, β1 and β6 as tumor biomarkers of oral squamous cell carcinoma

Integrin signaling may modulate several different functions involved in cell migration, invasion, proliferation and motility, and is a potential candidate biomarker for oral cancer. In the present study, a total of four integrin genes were evaluated as potential biomarkers of oral squamous cell carcinoma (OSCC). Gene expression was determined using the reverse transcription-quantitative polymerase chain reaction in 55 OSCC and 55 matched normal oral tissues. The performance of individual and combined biomarkers was analyzed by receiver operating characteristic (ROC) analysis based on the relative mRNA expression (OSCC vs. matched oral tissue from the tumor-free margin), which was calculated using the ΔΔCq value (ΔCq of OSCC-ΔCq of oral tissue from the tumor-free margin of the same patient). In the individual ROC analysis, the areas under the ROC curve (AUCs) of relative mRNA expression (ΔΔCq) of integrin subunit α3 (ITGA3), integrin subunit α5 (ITGA5), integrin subunit β1 (ITGB1) and integrin subunit β6 (ITGB6) in all tumor locations were 0.724, 0.698, 0.640 and 0.657, respectively. For locations 2 (tongue/mouth part) and 3 (edentulous ridge), their individual AUC values were 0.840, 0.765, 0.725 and 0.763, respectively. In the cumulative ROC analysis, ITGA3, ITGA5 and ITGB1 genes exhibited the highest combined AUC values (0.809 and 0.871 for all locations and locations 2 and 3 combined, respectively) compared with other biomarker combinations. In conclusion, the results of the present study identified that higher mRNA expressions of ITGA3, ITGA5, ITGB1 and ITGB6 genes are suitable for OSCC diagnosis biomarkers. Cumulative ROC analysis indicated an improved overall performance compared with the best individual integrin biomarker of OSCC.

High Expression of ITGA3 Promotes Proliferation and Cell Cycle Progression and Indicates Poor Prognosis in Intrahepatic Cholangiocarcinoma

Integrin subunit alpha 3 (ITGA3) interacts with a beta 1 subunit to form a member of the integrin family. Integrins are heterodimeric integral membrane proteins that serve as cell surface adhesion proteins. In this research, we investigated the biological function of this protein in human intrahepatic cholangiocarcinoma (ICC) for the first time. Here, using Western blotting and immunohistochemistry assays, we discovered that ITGA3 was overexpressed in ICC cell lines and ICC patients. Moreover, we found ITGA3 expression correlated with several clinicopathological features, including tumor size, lymph node metastasis, and the TNM stage. Patients with high ITGA3 expression underwent a worse prognosis after complete resection compared with patients with low ITGA3 expression in terms of overall survival. Furthermore, we demonstrated that ITGA3 could significantly promote ICC cell proliferation and cell cycle progression in vitro. However, as a classical cell surface adhesion molecule, we found ITGA3 correlated negatively with the migration and invasion of ICC cell lines, which differs from other malignant tumors. Generally, these findings suggest that ITGA3 may play a role as a potential oncogene in ICC and suppression of ITGA3 expression may establish a novel target for guiding the therapy of ICC patients.

Extracellular matrix endocytosis in controlling matrix turnover and beyond: emerging roles in cancer

The extracellular matrix (ECM) is a network of secreted proteins that, beyond providing support for tissues and organs, is involved in the regulation of a variety of cell functions, including cell proliferation, polarity, migration and oncogenic transformation. ECM homeostasis is maintained through a tightly controlled balance between synthesis, deposition and degradation. While the role of metalloproteases in ECM degradation is widely recognised, the contribution of ECM internalisation and intracellular degradation to ECM maintenance has been mostly overlooked. In this review, I will summarise what is known about the molecular mechanisms mediating ECM endocytosis and how this process impacts on diseases, such as fibrosis and cancer.

Tumor-targeting peptides from combinatorial libraries

Cancer is one of the major and leading causes of death worldwide. Two of the greatest challenges in fighting cancer are early detection and effective treatments with no or minimum side effects. Widespread use of targeted therapies and molecular imaging in clinics requires high affinity, tumor-specific agents as effective targeting vehicles to deliver therapeutics and imaging probes to the primary or metastatic tumor sites. Combinatorial libraries such as phage-display and one-bead one-compound (OBOC) peptide libraries are powerful approaches in discovering tumor-targeting peptides. This review gives an overview of different combinatorial library technologies that have been used for the discovery of tumor-targeting peptides. Examples of tumor-targeting peptides identified from each combinatorial library method will be discussed. Published tumor-targeting peptide ligands and their applications will also be summarized by the combinatorial library methods and their corresponding binding receptors.

Enhanced tumor targeting of cRGD peptide-conjugated albumin nanoparticles in the BxPC-3 cell line

The emerging albumin nanoparticle brings new hope for the delivery of antitumor drugs. However, a lack of robust tumor targeting greatly limits its application. In this paper, cyclic arginine-glycine-aspartic-conjugated, gemcitabine-loaded human serum albumin nanoparticles (cRGD-Gem-HSA-NPs) were successfully prepared, characterized, and tested in vitro in the BxPC-3 cell line. Initially, 4-N-myristoyl-gemcitabine (Gem-C14) was formed by conjugating myristoyl to the 4-amino group of gemcitabine. Then, cRGD-HSA was synthesized using sulfosuccinimidyl-(4-N-maleimidomethyl)cyclohexane-1-carboxylate (Sulfo-SMCC) cross-linkers. Finally, cRGD-Gem-HSA-NPs were formulated based on the nanoparticle albumin-bound (nab) technology. The resulting NPs were characterized for particle size, zeta potential, morphology, encapsulation efficiency, and drug loading efficiency. In vitro cellular uptake and inhibition studies were conducted to compare Gem-HSA-NPs and cRGD-Gem-HSA-NPs in a human pancreatic cancer cell line (BxPC-3). The cRGD-Gem-HSA-NPs exhibited an average particle size of 160 ± 23 nm. The encapsulation rate and drug loading rate were approximately 83 ± 5.6% and 11 ± 4.2%, respectively. In vitro, the cRGD-anchored NPs exhibited a significantly greater affinity for the BxPC-3 cells compared to non-targeted NPs and free drug. The cRGD-Gem-HSA-NPs also showed the strongest inhibitory effect in the BxPC-3 cells among all the analyzed groups. The improved efficacy of cRGD-Gem-HSA-NPs in the BxPC-3 cell line warrants further in vivo investigations.

Discovery and characterization of a high-affinity and high-specificity peptide ligand LXY30 for in vivo targeting of α3 integrin-expressing human tumors

Background

α3β1 integrin is overexpressed in several types of human cancer and is associated with poor prognosis, metastasis, and resistance to cancer treatment. We previously identified a cyclic peptide ligand LXY1 that specifically binds to the α3β1 integrin on human glioblastoma U-87MG cells. Here, we optimized LXY1 through one-bead one-compound combinatorial library screening and site-specific modifications to improve its in vivo binding property.

Methods

Three bead libraries were synthesized and whole-cell binding assays were performed. The binding capacity of individual peptide ligands against different tumor cells was determined by flow cytometry and confirmed by optical imaging. A complex joining biotinylated ligand with streptavidin-Cy5.5 was used for in vivo target imaging in both subcutaneous and orthotopic U-87MG xenograft mouse models.

Results

LXY30, a cyclic peptide with the sequence cdG-Phe(3,5-diF)-G-Hyp-NcR, emerged as the most potent and selective ligand for the α3 subunit of α3β1 integrin with improved in vitro and in vivo tumor-targeting effects compared to LXY1 in U-87MG cells. LXY30 is considerably stable in plasma as demonstrated in an in vitro stability study in 90 % human plasma. LXY30 also binds to several other known α3β1 integrin-expressing glioblastoma, lung, and breast cancer cell lines with various affinities.

Conclusions

Our data support further investigating the role of LXY30 as a human tumor-targeting peptide ligand for systemic and intracranial delivery of imaging agents and cancer therapeutics.

Electronic supplementary material

The online version of this article (doi:10.1186/s13550-016-0165-z) contains supplementary material, which is available to authorized users.

Digging a little deeper: the stages of invadopodium formation and maturation

Invadopodia are actin-rich protrusions that degrade the extracellular matrix and are required for penetration through the basement membrane, stromal invasion and intravasation. Invadopodia are enriched in actin regulators, such as cortactin, cofilin, N-WASp, Arp2/3 and fascin. Much of the work to date has centered around identifying the proteins involved in regulating actin polymerization and matrix degradation. Recently, there have been significant advances in characterization of the very early stages of invadopodium precursor assembly and the role of adhesion proteins, such as β1 integrin, talin, FAK and Hic-5, in promoting invadopodium maturation. This review summarizes these findings in the context of our current model of invadopodial function and highlights some of the important unanswered questions in the field.

Rab5c promotes AMAP1-PRKD2 complex formation to enhance β1 integrin recycling in EGF-induced cancer invasion

EGF signaling activates Rab5c and promotes the intracellular association of AMAP1 and PRKD2 to enhance β1 integrin recycling and promote the invasiveness of breast cancer cells.

Epidermal growth factor receptor (EGFR) signaling is one of the crucial factors in breast cancer malignancy. Breast cancer cells often overexpress Arf6 and its effector, AMAP1/ASAP1/DDEF1; in these cells, EGFR signaling may activate the Arf6 pathway to induce invasion and metastasis. Active recycling of some integrins is crucial for invasion and metastasis. Here, we show that the Arf6–AMAP1 pathway links to the machinery that recycles β1 integrins, such as α3β1, to promote cell invasion upon EGFR stimulation. We found that AMAP1 had the ability to bind directly to PRKD2 and hence to make a complex with the cytoplasmic tail of the β1 subunit. Moreover, GTP-Rab5c also bound to AMAP1, and activation of Rab5c by EGFR signaling was necessary to promote the intracellular association of AMAP1 and PRKD2. Our results suggest a novel mechanism by which EGFR signaling promotes the invasiveness of some breast cancer cells via integrin recycling.

Invasive matrix degradation at focal adhesions occurs via protease recruitment by a FAK-p130Cas complex

Tumor cell migration and the concomitant degradation of extracellular matrix (ECM) are two essential steps in the metastatic process. It is well established that focal adhesions (FAs) play an important role in regulating migration; however, whether these structures contribute to matrix degradation is not clear. In this study, we report that multiple cancer cell lines display degradation of ECM at FA sites that requires the targeted action of MT1-MMP. Importantly, we have found that this MT1-MMP targeting is dependent on an association with a FAK-p130Cas complex situated at FAs and is regulated by Src-mediated phosphorylation of Tyr 573 at the cytoplasmic tail of MT1. Disrupting the FAK-p130Cas-MT1 complex significantly impairs FA-mediated degradation and tumor cell invasion yet does not appear to affect invadopodia formation or function. These findings demonstrate a novel function for FAs and also provide molecular insights into MT1-MMP targeting and function.

Cell budding from pre-invasive tumors: Intrinsic precursor of invasive breast lesions?

Our previous studies showed that in patients with ductal carcinoma in situ (DCIS) of the breast, the tumor cells that overlie focal myoepithelial cell layer disruptions (FMCLDs) are generally arranged as finger-like projections that bud into the stroma. These budding cells have significantly more genetic instability and invasion-related gene expression, and less estrogen receptor (ER) expression, than their epithelial cell counterparts. This study aimed to assess these cells for potential molecular markers that are uniquely associated with cell adhesion and motility. Seventeen ER-positive DCIS cases were screened by immunostaining for ER, and 7 cases which harbored FMCLD lesions were used to examine the expression of the potential markers. Two cases with both DCIS and invasive lesions were selected for comparing the differences in molecular expression between these lesion types. The results showed that expression levels of talin, E-cadherin and focal adhesion kinase (FAK) in tumor cells overlying FMCLDs were higher than those within the corresponding duct. Integrin β1 staining was detected only in a small number of the tumor cells overlying the FMCLDs. Vinculin staining was weak (18%) or not detected (82%), and no expression was found in the tumor cells within the corresponding duct or in the pure isolated DCIS. By contrast, the expression levels of talin, vinculin and integrin β1 in the invasive tumors were distinctly higher than those in DCIS, and the expression of FAK and E-cadherin was lower. Using electron microscopy, we found that the tight junctions between tumor cells overlying the FMCLDs were reduced compared to the adjacent tumor cells in the lumen. These results indicate that the tumor cells overlying FMCLDs are likely to represent the specific precursors of invasive breast lesions. Our findings may also facilitate the identification of specific targets for further molecular profiling, which will more completely characterize this important cell population.

Cellular responses to patterned poly(acrylic acid) brushes

We use patterned poly(acrylic acid) (PAA) polymer brushes to explore the effects of surface chemistry and topography on cell-surface interactions. Most past studies of surface topography effects on cell adhesion have focused on patterned feature sizes that are larger than the dimensions of a cell, and PAA brushes have been characterized as cell repellent. Here we report cell adhesion studies for RBL mast cells incubated on PAA brush surfaces patterned with a variety of different feature sizes. We find that when patterned at subcellular dimensions on silicon surfaces, PAA brushes that are 30 or 15 nm thick facilitate cell adhesion. This appears to be mediated by fibronectin, which is secreted by the cells, adsorbing to the brushes and then engaging cell-surface integrins. The result is detectable accumulation of plasma membrane within the brushes, and this involves cytoskeletal remodeling at the cell-surface interface. By decreasing brush thickness, we find that PAA can be 'tuned' to promote cell adhesion with down-modulated membrane accumulation. We exemplify the utility of patterned PAA brush arrays for spatially controlling the activation of cells by modifying brushes with ligands that specifically engage IgE bound to high-affinity receptors on mast cells.

Type I gamma phosphatidylinositol phosphate kinase modulates invasion and proliferation and its expression correlates with poor prognosis in breast cancer

Introduction

The loss of E-cadherin based cell-cell contacts and tumor cell migration to the vasculature and lymphatic system are hallmarks of metastasis of epithelial cancers. Type I gamma phosphatidylinositol phosphate kinase (PIPKIγ), an enzyme that generates phosphatidylinositol 4,5-bisphosphate (PI4,5P₂) a lipid messenger and precursor to many additional second messengers, was found to regulate E-cadherin cell-cell contacts and growth factor-stimulated directional cell migration, indicating that PIPKIγ regulates key steps in metastasis. Here, we assess the expression of PIPKIγ in breast cancers and have shown that expression correlated with disease progression and outcome.

Methods

Using a tissue microarray, we analyzed 438 breast carcinomas for the levels of PIPKIγ and investigated the correlation of PIPKIγ expression with patient survival via Kaplan-Meier survival analysis. Moreover, via knockdown of the expression of PIPKIγ in cultured breast cancer cells with siRNA, the roles of PIPKIγ in breast cancer migration, invasion, and proliferation were examined.

Results

Tissue microarray data shows that ~18% of the cohort immunostained showed high expression of PIPKIγ. The Kaplan-Meier survival analysis revealed a significant inverse correlation between strong PIPKIγ expression and overall patient survival. Expression of PIPKIγ correlated positively with epidermal growth factor receptor (EGFR) expression, which regulates breast cancer progression and metastasis. In cultured breast cancer cells, PIPKIγ is required for growth factor stimulated migration, invasion, and proliferation of cells.

Conclusions

The results reveal a significant correlation between PIPKIγ expression and the progression of breast cancer. This is consistent with PIPKIγ 's role in breast cancer cell migration, invasion, and proliferation.

The EGFR-GEP100-Arf6-AMAP1 signaling pathway specific to breast cancer invasion and metastasis

Tumors are tissue-specific diseases, and their mechanisms of invasion and metastasis are highly diverse. In breast cancer, biomarkers that specifically correlate with the invasive phenotypes have not been clearly identified. A small GTPase Arf6 primarily regulates recycling of plasma membrane components. We have shown that Arf6 and its effector AMAP1 (DDEF1, DEF1, ASAP1 and centaurin β4) are abnormally overexpressed in some breast cancers and used for their invasion and metastasis. Overexpression of these proteins is independent of the transcriptional upregulation of their genes, and occurs only in highly malignant breast cancer cells. We recently identified GEP100 (BRAG2) to be responsible for the Arf6 activation to induce invasion and metastasis, by directly binding to ligand-activated epidermal growth factor receptor (EGFR). A series of our studies revealed that for activation of the invasion pathway of EGFR, it is prerequisite that Arf6 and AMAP1 both are highly overexpressed, and that EGFR is activated by ligands. Pathological analyses indicate that a significant large population of human ductal cancers may utilize the EGFR-GEP100-Arf6-AMAP1 pathway for their malignancy. Microenvironments have been highly implicated in the malignancy of mammary tumors. Our results reveal an aspect of the precise molecular mechanisms of some breast cancers, in which full invasiveness is not acquired just by intracellular alterations of cancer cells, but extracellular factors from microenvironments may also be necessary. Possible translation of our knowledge to cancer therapeutics will also be discussed.

Breast cancer cell movement: imaging invadopodia by TIRF and IRM microscopy

Invadopodia are hair-like membrane protrusions projecting from the ventral side of the plasma membrane of tumor cells invading into an extracellular matrix (ECM). Formation of invadopodia and phagocytosis of partially degraded ECM is correlated with invasiveness of cancer cells. Many proteins associated with actin-rich punctae associated with invadopodia have been identified. However, the dynamic temporal and spatial relationship of invadopodia-related proteins and the mechanisms required for invadopodia formation remain largely unknown. Total Internal Reflection Fluorescence (TIRF) microscopy provides a powerful tool to directly visualize the dynamic membrane transportation of invadopodia-related, GFP-tagged proteins and to simultaneously monitor invadopodia formation by observation of localized degradation and phagocytosis of fluorescently labeled gelatin. Cell-substratum contacts can be visualized using a related technique, Interference Reflection Microscopy (IRM). In this chapter, we provide detailed methodologies to monitor the dynamic localizations of c-Src-eGFP using two-color TIRF microscopy along with IRM to simultaneously visualize translocation of c-Src-eGFP and invadopodia formation by degradation of AlexaFluor 568-labeled gelatin.

In vitro invasion assays: phagocytosis of the extracellular matrix

Degradation of the extracellular matrix is an essential component of phagocytosis by tumor cells and can be correlated with their invasive capacity. This unit presents flow cytometry based assays for rapid quantitative assessment of both proteolysis and internalization or internalization alone. These assays provide high-throughput, low-cost methods to compare cell lines and test the efficacy of treatments designed to stimulate or inhibit invasion.

Adhesions ring: a structural comparison between podosomes and the immune synapse

Podosomes and the immune synapse are integrin-mediated adhesive structures that share a common ring-like morphology. Both podosomes and immune synapses have a central core surrounded by a peripheral ring containing talin, vinculin and paxillin. Recent progress suggests significant parallels between the regulatory mechanisms that contribute to the formation of these adhesive structures. In this review, we compare the structures, functions and regulation of podosomes and the immune synapse.

Near-infrared optical imaging in glioblastoma xenograft with ligand-targeting alpha 3 integrin

PURPOSE

Patients with glioblastoma usually have a very poor prognosis. Even with a combination of radiotherapy plus temozolomide, the median survival of these patients is only 14.6 months. New treatment approaches to this cancer are needed. Our purpose is to develop new cell surface-binding ligands for glioblastoma cells and use them as targeted imaging and therapeutic agents for this deadly disease.

METHODS

One-bead one-compound combinatorial cyclic peptide libraries were screened with live human glioblastoma U-87MG cells. The binding affinity and targeting specificity of peptides identified were tested with in vitro experiments on cells and in vivo and ex vivo experiments on U-87MG xenograft mouse model.

RESULTS

A cyclic peptide, LXY1, was identified and shown to be binding to the alpha 3 integrin of U-87MG cells with moderately high affinity (K (d) = 0.5 +/- 0.1 microM) and high specificity. Biotinylated LXY1, when complexed with streptavidin-Cy5.5 (SA-Cy5.5) conjugate, targeted both subcutaneous and orthotopic U-87MG xenograft implants in nude mice. The in vivo targeting specificity was further verified by strong inhibition of tumor uptake of LXY1-biotin-SA-Cy5.5 complex when intravenously injecting the animals with anti-alpha 3 integrin antibody or excess unlabeled LXY1 prior to administrating the imaging probe. The smaller univalent LXY1-Cy5.5 conjugate (2,279 Da) was found to have a faster accumulation in the U-87MG tumor and shorter retention time compared with the larger tetravalent LXY1-biotin-SA-Cy5.5 complex (approximately 64 kDa).

CONCLUSIONS

Collectively, the data reveals that LXY1 has the potential to be developed into an effective imaging and therapeutic targeting agent for human glioblastoma.

CIN85, a Cbl-interacting protein, is a component of AMAP1-mediated breast cancer invasion machinery

Expression of AMAP1 correlates well with the invasive phenotypes and malignancy of human primary breast carcinomas. AMAP1 recruits its binding proteins, such as cortactin and paxillin, to sites of Arf6 activation to form invadopodia. A mouse ortholog of AMAP1, ASAP1, is known to bind to CIN85, a binding partner of an E3 ligase, Cbl. Here, we found that CIN85 colocalizes with AMAP1 at invadopodia, and binding of AMAP1 with CIN85 is important for the invasive activities of breast cancer cells, including MDA-MB-231. siRNA-mediated silencing of CIN85, as well as Cbl, also inhibited the invasion. We moreover found that AMAP1 is monoubiquitinated, rather than polyubiquitinated, by virtue of Cbl and provide evidence that the ability of AMAP1 to be monoubiquitinated is important for its involvement in invasion. Our results indicate that CIN85, as well as Cbl, which is a well-known suppressor of growth factor receptor signaling, can be positively involved in tumor invasion, and suggest that a complex epigenetic process is involved in AMAP1 function in breast cancer cell invasion.

Assays and properties of the ArfGAPs, AMAP1 and AMAP2, in Arf6 function

The GTPase-activating protein (GAP) domain for Arfs primarily consists of a zinc-finger structure, which is not present in known GAPs for the other Ras-superfamily GTPases. More than 20 genes have been found to encode proteins bearing the ArfGAP domain in the human genome: a number that is much larger than that of the Arf isoforms. Several Arf isoforms, such as Arf1 and Arf6, indeed have been shown to each employ multiple different ArfGAPs for their regulation and function. We have found that two ArfGAPs, namely AMAP1 and AMAP2, exhibit a novel biochemical property of directly and selectively binding to GTP-Arf6 without immediate GAPing activity, while they were previously shown to exhibit efficient catalytic GAPing activities to Arf isoforms except Arf6 in vitro. Such property of AMAPs appears to be important for AMAPs-mediated recruitment of auxiliary molecules, including paxillin, cortactin, amphiphysin, and intersectin, to sites of Arf6 activation. AMAPs thus appear to act as "effectors" rather than simple GAPs in some aspects of Arf6 function. This article presents methods and protocols developed for the functional characterization of AMAPs in Arf6 function. These methods may be applied to other types of ArfGAPs to further clarify the cellular functions of ArfGAPs as well as Arfs.

Angiostatin's molecular mechanism: aspects of specificity and regulation elucidated

Tumor growth requires the development of new vessels that sprout from pre-existing normal vessels in a process known as "angiogenesis" [Folkman (1971) N Engl J Med 285:1182-1186]. These new vessels arise from local capillaries, arteries, and veins in response to the release of soluble growth factors from the tumor mass, enabling these tumors to grow beyond the diffusion-limited size of approximately 2 mm diameter. Angiostatin, a naturally occurring inhibitor of angiogenesis, was discovered based on its ability to block tumor growth in vivo by inhibiting the formation of new tumor blood vessels [O'Reilly et al. (1994a) Cold Spring Harb Symp Quant Biol 59:471-482]. Angiostatin is a proteolytically derived internal fragment of plasminogen and may contain various members of the five plasminogen "kringle" domains, depending on the exact sites of proteolysis. Different forms of angiostatin have measurably different activities, suggesting that much remains to be elucidated about angiostatin biology. A number of groups have sought to identify the native cell surface binding site(s) for angiostatin, resulting in at least five different binding sites proposed for angiostatin on the surface of endothelial cells (EC). This review will consider the data supporting all of the various reported angiostatin binding sites and will focus particular attention on the angiostatin binding protein identified by our group: F(1)F(O) ATP synthase. There have been several developments in the quest to elucidate the mechanism of action of angiostatin and the regulation of its receptor. The purpose of this review is to describe the highlights of research on the mechanism of action of angiostatin, its' interaction with ATP synthase on the EC surface, modulators of its activity, and issues that should be explored in future research related to angiostatin and other anti-angiogenic agents.

Invadopodia: a guided tour

The controlled degradation of extracellular matrix is crucial in physiological and pathological cell invasion alike. In cultured cells, degradation occurs at specific sites where invasive cells make contact with the extracellular matrix via specialized plasma membrane protrusions termed invadopodia. Considerable progress has been made in recent years towards understanding the basic molecular components and the ultrastructural features of invadopodia. This current knowledge will be reviewed here together with some of the most important open questions in invadopodia biology. Considering the substantial interest and momentum in the field, the need for an operational framework to correctly define and identify invadopodia will also be discussed.

Near-Infrared Optical Imaging of Ovarian Cancer Xenografts with Novel α3-Integrin Binding Peptide “OA02”

Through screening of random one-bead one-compound (OBOC) libraries, we previously identified cyclic peptides with the cDGXGXXc motif that bind to α3 integrin subunit on ovarian adenocarcinoma cell lines ES-2, SKOV-3, and CaOV-3. We subsequently synthesized two secondary libraries based on this motif and identified new peptides that bound with a higher affinity to these cell lines. One of the peptides identified from the 20% “down-substituted” focused library was the cdG-HCit-GPQc (“OA02”) peptide. The goal of this study was to determine whether this peptide labeled with near-infrared probes could be detected after intravenous injection in ovarian tumor-bearing mice and if it would selectively localize in the tumor. Three different forms of this peptide were synthesized, “OA02”-biotin (noncovalently linked to streptavidin-Cy5.5); “OA02”-Cy5.5 and “OA02”-AlexaFluo 680. Using a KODAK IS2000MM image station, these peptide probes were used at the near-infrared (NIR) spectra to image nude mice bearing ES-2 (α3 integrin positive) and Raji (α3 integrin negative) xenografts. The peptide probe displayed highly specific tumor uptake within 15 min, which lasted for 70 min for “OA02”-Cy5.5 and “OA02”-AlexaFluo 680 and for 24 hours for “OA02”-biotin-streptavidin-Cy5.5. Some kidney and bladder signal were noted. Prior injection with anti-α3 monoclonal antibody blocked the binding of this peptide to the ES-2 tumors.

Nitroxide tempo, a small molecule, induces apoptosis in prostate carcinoma cells and suppresses tumor growth in athymic mice

BACKGROUND

In previous studies, nitroxide tempo (2, 2, 6, 6-tetramethyl-piperidine-1-oxyl), a small molecule, induced cell death in cancer cells. The current study examined the antineoplastic properties of tempo in the human hormone-dependent/hormone-independent prostate carcinoma models (LNCaP, DU-145, and PC-3).

METHODS

The apoptotic effects of tempo were examined by the flow cytometric analysis of cells labeled with fluorescein isothiocyanate-conjugated annexin-V, and by electron microscopy. Enzymatic assays were performed to measure the activities of 2 cysteine proteases, i.e., caspase-9 and caspase-3, in tempo-treated cells. The effects of tempo on cell proliferation and on cell cycle distribution profiles were measured by the flow cytometric assay using immunofluorescent staining of incorporated 5'-bromo-2'-deoxyuridine (BrdU) coupled with 7-amino-actinomycin D (7-AAD) staining of total DNA. The number of proliferating cells was also determined independently by enzyme-linked immunosorbent assay using chemiluminescent detection of incorporated BrdU. Subcutaneous growth of human prostate carcinoma in athymic mice was monitored after intratumoral administration of tempo into tumor-bearing mice. In addition, cell viability assays were performed to compare the cytotoxic effect of a combination of doxorubicin or mitoxantrone and tempo with single agents.

RESULTS

Tempo treatment of prostate carcinoma cells caused a significant increase in the number of apoptotic cells compared with control groups (tempo, 2.5 mM, 24 hours: DU-145, approximately 3.4-fold; PC-3, approximately 6-7-fold; tempo 1 mM, 24 hours: LNCaP, approximately 12-fold). Tempo-induced loss of cell viability was blocked partially or completely after pretreatment of cells with actinomycin-D or cycloheximide, suggesting a de novo macromolecule synthesis-dependent mechanism of cell death. Electron microscopy revealed aggregation and marginalization of chromatin in the nuclei of a large number of tempo-treated LNCaP cells. Tempo treatment of LNCaP cells resulted in enhanced activities of caspase-9 (tempo, 5 mM, 15 hours: approximately 2-fold) and caspase-3 (tempo, 2.5 mM, 24 hours: approximately 12-fold). Tempo treatment also led to an enhanced number of cells in G2/M phase of the cell cycle (tempo, 5.0 mM, 24 hours: DU-145, approximately 1.6-fold; PC-3, approximately 1.5-fold; LNCaP, approximately 5.3-fold), and decreased BrdU incorporation indicative of a decline in the number of proliferating cells (tempo, 2.5 mM, 24 or 48 hours; DU-145, approximately 2-3-fold; PC-3, approximately 1.2-fold; LNCaP, approximately 5-10-fold). Administration of tempo into LNCaP tumor-bearing mice resulted in a significant inhibition of tumor growth (percent initial tumor volume [Day 30, n = 4]: vehicle, 845.35 +/- 272.83; tempo, 9.72 +/- 9.72; tempo vs. vehicle, P < 0.02). In hormone-refractory prostate carcinoma cells, a combination of relatively low doses of tempo and doxorubicin or mitoxantrone caused enhanced cytotoxicity as compared with single agents.

CONCLUSIONS

These data demonstrated that nitroxide tempo induced apoptosis and activated a caspase-mediated signaling pathway in prostate carcinoma cells. Tempo treatment also caused cell cycle arrest in G2/M phase and decreased the number of proliferating cells (S phase). Tempo treatment of tumor-bearing mice led to inhibition of tumor growth, suggesting that tempo is a novel member of the small-molecule family of antineoplastic agents.

Expression of AMAP1, an ArfGAP, provides novel targets to inhibit breast cancer invasive activities

Identification of the molecular machinery employed in cancer invasion, but not in normal adult cells, will greatly contribute to cancer therapeutics. Here we found that an ArfGAP, AMAP1/PAG2, is expressed at high levels in highly invasive breast cancer cells, but at very low levels in noninvasive breast cancer cells and normal mammary epithelial cells. siRNA-mediated silencing of AMAP1 effectively blocked the invasive activities. AMAP1 expression in human breast primary tumors also indicated its potential correlation with malignancy. Paxillin and cortactin have been shown to colocalize at invadopodia and play a pivotal role in breast cancer invasion. We found that AMAP1 is also localized at invadopodia, and acts to bridge paxillin and cortactin. This AMAP1-mediated trimeric protein complex was detected only in invasive cancer cells, and blocking this complex formation effectively inhibited their invasive activities in vitro and metastasis in mice. Our results indicate that AMAP1 is a component involved in invasive activities of different breast cancers, and provide new information regarding the possible therapeutic targets for prevention of breast cancer invasion and metastasis.

Foot and mouth: podosomes, invadopodia and circular dorsal ruffles

The plasma membrane of many motile cells undergoes highly regulated protrusions and invaginations that support the formation of podosomes, invadopodia and circular dorsal ruffles. Although they are similar in appearance and in their formation--which is mediated by a highly conserved actin-membrane apparatus--these transient surface membrane distortions are distinct. Their function is to help the cell as it migrates, attaches and invades.

Phagocytosis of Candida albicans by metastatic and non metastatic human breast cancer cell lines in vitro

Experiments were carried out to investigate the kinetic characteristics of phagocytosis of candida by metastatic (MCF-7 and ZR-75-1) and nonmetastatic (HCC70) breast cancer cell (BCC) lines. Cancer cells were mixed with candida at a ratio of 1:10 and attachment/phagocytosis were examined using cytospin preparations stained with either Giemsa or tannic acid and May-Grünwald Giemsa and by using flow cytometry. A high attachment of candida to cancer cells (29-39%) was detected as early as 10 min. Following attachment, cancer cells phagocytized yeast. The phagocytic activity of MCF-7 and ZR-75 cells was significantly higher (58-61%) than that of HCC70 cells (26%). A similar trend was observed with respect to the phagocytic index. Phagocytosis of candida by tumor cells was inhibited significantly by both cytochalasin B (50%) and by lowering temperature to 4 degrees C (66%). Phagocytosis was not associated with oxidative burst in any cell lines used. In conclusion, metastatic breast cancer cells possess phagocytic activity which may explain their invasive property.

Requirement for Arf6 in breast cancer invasive activities

In most human breast cancer cell lines, there is a direct correlation between their in vivo invasive phenotypes and in vitro invasion activities. Here, we found that ADP-ribosylation factor 6 (Arf6) is localized at the invadopodia of the cultured breast cancer cells MDA-MB-231, and its suppression by a small-interfering RNA duplex effectively blocks the invasive activities of the cells, such as invadopodia formation, localized matrix degradation and Matrigel transmigration but not the cell-adhesion activity. We also found that the GTP hydrolysis-defective mutant Arf6(Q67L) and the GTP-binding defective mutant Arf6(T27N) both blocked these invasive activities but not cell adhesion, suggesting the necessity of continued activation and cycling of the Arf6 GTPase cycle in invasion. Among the different human breast cancer cell lines that we examined, cell lines with high invasive activities expressed higher amounts of Arf6 protein than those in weakly invasive and noninvasive cell lines, although no notable correlation was found between Arf6 mRNA expression levels and invasive activities. Moreover, Matrigel-transmigration activity of all of these invasive cells was blocked effectively by an Arf6 small-interfering RNA duplex. Hence, Arf6 appears to be an integral component of breast cancer invasive activities, and we propose that Arf6 and the intracellular machinery regulating Arf6 during invasion should be considered as therapeutic targets for the prevention of breast cancer invasion.

Seprase, a membrane-bound protease, alleviates the serum growth requirement of human breast cancer cells

Seprase is a cell surface serine protease that is expressed to high levels by infiltrating ductal carcinomas of the breast but its function in malignancy is unknown. MDA-MB-435 (WT435) and MDA-MB-436 (WT436) human breast cancer cells express high levels of seprase as do the carcinoma cells in tumors of human breast cancer patients. To investigate its role in the pathobiology of breast cancer, seprase was specifically reduced in WT436 and WT435 cells by expression of antisense seprase cDNA. Decreased expression of seprase was confirmed in the antisense transfectants by zymography, immunoblotting, and fluorescence-activated cell sorting of cells labeled with antibody to seprase. Control-transfectants continued to express high levels of seprase. Seprase-deficient cells growing on type I collagen gels reveal a markedly different morphology than the parental or control-transfected cells that express high levels of seprase. The seprase-deficient cells grow in islands and aggregates of tightly attached cells while cells with high seprase expression grow as groups of separate individual cells. Interestingly, the aggregated growth of the seprase-deficient cells was not correlated with increased expression of E-cadherin. Seprase-deficient breast cancer cells also exhibit altered growth properties. Seprase-deficient cells and those with high seprase levels proliferate in serum-containing media. However, in serum-free medium seprase-deficient cells proliferate much more slowly than their seprase-expressing counterparts. These findings indicate that seprase promotes the aberrant growth of breast cancer cells by reducing their dependence on exogenous growth factors. Seprase may contribute to the pathogenesis of breast cancer by promoting growth of the primary tumor and by facilitating the growth of breast cancer cells in metastases at other sites of the body.

Clinical, cellular, and molecular aspects of cancer invasion

Invasion causes cancer malignancy. We review recent data about cellular and molecular mechanisms of invasion, focusing on cross-talk between the invaders and the host. Cancer disturbs these cellular activities that maintain multicellular organisms, namely, growth, differentiation, apoptosis, and tissue integrity. Multiple alterations in the genome of cancer cells underlie tumor development. These genetic alterations occur in varying orders; many of them concomitantly influence invasion as well as the other cancer-related cellular activities. Examples discussed are genes encoding elements of the cadherin/catenin complex, the nonreceptor tyrosine kinase Src, the receptor tyrosine kinases c-Met and FGFR, the small GTPase Ras, and the dual phosphatase PTEN. In microorganisms, invasion genes belong to the class of virulence genes. There are numerous clinical and experimental observations showing that invasion results from the cross-talk between cancer cells and host cells, comprising myofibroblasts, endothelial cells, and leukocytes, all of which are themselves invasive. In bone metastases, host osteoclasts serve as targets for therapy. The molecular analysis of invasion-associated cellular activities, namely, homotypic and heterotypic cell-cell adhesion, cell-matrix interactions and ectopic survival, migration, and proteolysis, reveal branching signal transduction pathways with extensive networks between individual pathways. Cellular responses to invasion-stimulatory molecules such as scatter factor, chemokines, leptin, trefoil factors, and bile acids or inhibitory factors such as platelet activating factor and thrombin depend on activation of trimeric G proteins, phosphoinositide 3-kinase, and the Rac and Rho family of small GTPases. The role of proteolysis in invasion is not limited to breakdown of extracellular matrix but also causes cleavage of proinvasive fragments from cell surface glycoproteins.

Dynamin participates in focal extracellular matrix degradation by invasive cells

The degradation of extracellular matrix (ECM) by matrix metalloproteases is crucial in physiological and pathological cell invasion alike. Degradation occurs at specific sites where invasive cells make contact with the ECM via specialized plasma membrane protrusions termed invadopodia. Herein, we show that the dynamin 2 (Dyn2), a GTPase implicated in the control of actin-driven cytoskeletal remodeling events and membrane transport, is necessary for focalized matrix degradation at invadopodia. Dynamin was inhibited by using two approaches: 1) expression of dominant negative GTPase-impaired or proline-rich domain-deleted Dyn2 mutants; and 2) inhibition of the dynamin regulator calcineurin by cyclosporin A. In both cases, the number and extension of ECM degradation foci were drastically reduced. To understand the site and mechanism of dynamin action, the cellular structures devoted to ECM degradation were analyzed by correlative confocal light-electron microscopy. Invadopodia were found to be organized into a previously undescribed ECM-degradation structure consisting of a large invagination of the ventral plasma membrane surface in close spatial relationship with the Golgi complex. Dyn2 seemed to be concentrated at invadopodia.

Following matrix metalloproteinases activity near the cell boundary by infrared micro-spectroscopy

Matrix Metalloproteinases (MMPs) are cell-secreted soluble and membrane-tethered enzymes that degrade extracellular matrix (ECM) proteins. These proteases play a key role in diverse physiological and pathological processes, including embryonic development, wound repair, inflammatory diseases and cancer. Yet, there is insufficient knowledge on the mode by which cell-produced MMPs conduct their action on the ECM. Specifically, the localization and the mode of the degradation within the pericellular space are of great interest. To provide new insights to these questions we utilized Fourier transform infrared (FTIR) micro-spectroscopy to follow proteolytic processes, induced by invasive cancer cells, on insoluble collagen-based matrices. Here we show that FTIR micro-spectroscopy have a great potential for monitoring degradation events near cells. Using this tool we demonstrate that the net proteolysis is unevenly distributed around the cell boundary. The degradation patterns show different levels of proteolytic activity by MMPs within the pericellular space. In addition, our spectral analysis suggests that the enzymatic proteolysis of the collagen-based matrices induces unwinding of the triple helical structures of the macromolecules within the collagen network.

Cathepsin expression in oral squamous cell carcinoma: relationship with clinicopathologic factors

OBJECTIVE

Proteases are involved in the invasion and metastasis of carcinoma cells. In vivo, oral carcinoma cells easily invade the bone tissue and metastasize to the submandibular and neck lymph nodes. Cathepsin expression has been shown in some neoplastic tissues and serves as a prognostic indicator. The purpose of this study was to investigate the relationship between clinicopathohistologic grades and cathepsin expressions in oral squamous cell carcinoma and to investigate which cathepsin provides prognostic information for patients with oral carcinoma.

STUDY DESIGN

Immunohistochemical studies were performed on 78 carcinoma samples with monoclonal antibodies against cathepsins B, H, and L, and a polyclonal antibody against cathepsin D. Serial sections were stained by hematoxylin-eosin staining and classified by Anneroth's classification. Cathepsin B, H, L and D activities of blood serum were determined. Positive results indicative of the presence of cathepsin were investigated to determine any correlation between a particular cathepsin and histologic malignancy grades, tumor cell growth, serum cathepsin activities, and clinical factors.

RESULTS

Cathepsins B, H, L, and D were positive in every case. Although the labeling indices for cathepsins B (CB-LI), H (CH-LI), and D (CD-LI) for the cancer cases showed significant differences from those of controls, cathepsin L (CL-LI) of cancer cases showed no difference from that of controls (P <.05). A close correlation was found between CD-LI and T categories of TNM classification (P <.05), and between CD-LI and PCNA-LI (P <.05). Furthermore, a close correlation was found between CD-LI and N categories in TNM classification (P <.05). Pathologically, a close correlation was found between CB-LI or CD-LI and the pattern and/or stage of invasion (P <.05).

CONCLUSION

Cathepsin D and B expression were closely correlated with carcinoma invasion and progression. These proteases may be useful in determining the prognoses of patients with oral carcinoma.

Phosphorylation of a conserved integrin alpha 3 QPSXXE motif regulates signaling, motility, and cytoskeletal engagement

Integrin alpha 3A cytoplasmic tail phosphorylation was mapped to amino acid S1042, as determined by mass spectrometry, and confirmed by mutagenesis. This residue occurs within a "QPSXXE" motif conserved in multiple alpha chains (alpha 3A, alpha 6A, alpha 7A), from multiple species. Phosphorylation of alpha 3A and alpha 6A did not appear to be directly mediated by protein kinase C (PKC) alpha, beta, gamma, delta, epsilon, zeta, or mu, or by any of several other known serine kinases, although PKC has an indirect role in promoting phosphorylation. A S1042A mutation did not affect alpha 3-Chinese hamster ovary (CHO) cell adhesion to laminin-5, but did alter 1) alpha 3-dependent tyrosine phosphorylation of focal adhesion kinase and paxillin (in the presence or absence of phorbol 12-myristate 13 acetate stimulation), and p130(CAS) (in the absence of phorbol 12-myristate 13 acetate stimulation), 2) the shape of cells spread on laminin-5, and 3) alpha 3-dependent random CHO cell migration on laminin-5. In addition, S1042A mutation altered the PKC-dependent, ligand-dependent subcellular distribution of alpha 3 and F-actin in CHO cells. Together, the results demonstrate clearly that alpha 3A phosphorylation is functionally relevant. In addition, the results strongly suggest that alpha 3 phosphorylation may regulate alpha 3 integrin interaction with the cytoskeleton.

Lysosomal augmentation during aminoglycoside uptake in cochlear hair cells

Aminoglycoside antibiotics, such as kanamycin, have ototoxic side effects, which often result in degeneration of cochlear and vestibular hair cells in the inner ear. Cytotoxic effects of aminoglycosides, however, do not appear immediately after cellular uptake of aminoglycosides. In order to understand the mechanisms responsible for the delayed emergence of aminoglycoside ototoxicity, changes in lysosomal activities in cochlear hair cells were evaluated during a repeated administration of kanamycin by two methods. Electron microscopic localization of acid phosphatase (AcPase) revealed that AcPase started to accumulate in vesicles 27 h after the start of kanamycin administration. In addition, the number and size of AcPase-filled vesicles increased with repeated kanamycin doses. Confocal microscopic localization of the LysoTracker probe, a vital lysosomal marker, showed an increase in the size of lysosomes in hair cells that were treated with kanamycin. The temporal changes in the augmentation of lysosomes paralleled those in intracellular kanamycin levels. These results suggest that the intralysosomal compartments can accumulate extensive amounts of aminoglycosides, which might lead to lysosomal swelling and subsequent rupture.

The integrins alpha3beta1 and alpha6beta1 physically and functionally associate with CD36 in human melanoma cells. Requirement for the extracellular domain OF CD36

Lateral association between different transmembrane glycoproteins can serve to modulate integrin function. Here we characterize a physical association between the integrins alpha(3)beta(1) and alpha(6)beta(1) and CD36 on the surface of melanoma cells and show that ectopic expression of CD36 by CD36-negative MV3 melanoma cells increases their haptotactic migration on extracellular matrix components. The association was demonstrated by co-immunoprecipitation, reimmunoprecipitation, and immunoblotting of surface-labeled cells lysed in Brij 96 detergent. Confocal microscopy illustrated the co-association of alpha(3) and CD36 in cell membrane projections and ruffles. A requirement for the extracellular domain of CD36 in this association was shown by co-immunoprecipitation experiments using surface-labeled MV3 melanoma or COS-7 cells that had been transiently transfected with chimeric constructs between CD36 and intercellular adhesion molecule 1 (ICAM-1) or with a truncation mutant of CD36. CD36 is known to engage in signal transduction and to localize to membrane microdomains or rafts in several cell types. Toward a mechanistic explanation for the functional effects of CD36 expression, we demonstrate that in fractionated Triton X-100 lysates of the MV3 cells stably transfected with CD36, CD36 was greatly enriched with the detergent-insoluble fractions that represent plasma membrane rafts. Significantly, when these fractionated lysates were reprobed for endogenous beta(1) integrin, it was found that a 4-fold increase in the proportion of the mature protein was contained within the detergent-insoluble fractions when extracted from the CD36-transfected cells compared with MV3 cells transfected with vector only. These results suggest that in melanoma cells CD36 expression may induce the sequestration of certain integrins into membrane microdomains and promote cell migration.