Targeting integrin α6 stimulates curative-type bone metastasis lesions in a xenograft model

The Potential of Extracellular Matrix- and Integrin Adhesion Complex-Related Molecules for Prostate Cancer Biomarker Discovery

Prostate cancer is among the top five cancer types according to incidence and mortality. One of the main obstacles in prostate cancer management is the inability to foresee its course, which ranges from slow growth throughout years that requires minimum or no intervention to highly aggressive disease that spreads quickly and resists treatment. Therefore, it is not surprising that numerous studies have attempted to find biomarkers of prostate cancer occurrence, risk stratification, therapy response, and patient outcome. However, only a few prostate cancer biomarkers are used in clinics, which shows how difficult it is to find a novel biomarker. Cell adhesion to the extracellular matrix (ECM) through integrins is among the essential processes that govern its fate. Upon activation and ligation, integrins form multi-protein intracellular structures called integrin adhesion complexes (IACs). In this review article, the focus is put on the biomarker potential of the ECM- and IAC-related molecules stemming from both body fluids and prostate cancer tissue. The processes that they are involved in, such as tumor stiffening, bone turnover, and communication via exosomes, and their biomarker potential are also reviewed.

Regulation and Functions of α6-Integrin (CD49f) in Cancer Biology

Over the past decades, our knowledge of integrins has evolved from being understood as simple cell surface adhesion molecules to receptors that have a complex range of intracellular and extracellular functions, such as delivering chemical and mechanical signals to cells. Consequently, they actively control cellular proliferation, differentiation, and apoptosis. Dysregulation of integrin signaling is a major factor in the development and progression of many tumors. Many reviews have covered the broader integrin family in molecular and cellular studies and its roles in diseases. Nevertheless, further understanding of the mechanisms specific to an individual subunit of different heterodimers is more useful. Thus, we describe the current understanding of and exploratory investigations on the α6-integrin subunit (CD49f, VLA6; encoded by the gene itga6) in normal and cancer cells. The roles of ITGA6 in cell adhesion, stemness, metastasis, angiogenesis, and drug resistance, and as a diagnosis biomarker, are discussed. The role of ITGA6 differs based on several features, such as cell background, cancer type, and post-transcriptional alterations. In addition, exosomal ITGA6 also implies metastatic organotropism. The importance of ITGA6 in the progression of a number of cancers, including hematological malignancies, suggests its potential usage as a novel prognostic or diagnostic marker and useful therapeutic target for better clinical outcomes.

The role of integrin family in bone metabolism and tumor bone metastasis

Integrins have been the research focus of cell-extracellular matrix adhesion (ECM) and cytokine receptor signal transduction. They are involved in the regulation of bone metabolism of bone precursor cells, mesenchymal stem cells (MSCs), osteoblasts (OBs), osteoclasts (OCs), and osteocytes. Recent studies expanded and updated the role of integrin in bone metabolism, and a large number of novel cytokines were found to activate bone metabolism pathways through interaction with integrin receptors. Integrins act as transducers that mediate the regulation of bone-related cells by mechanical stress, fluid shear stress (FSS), microgravity, hypergravity, extracellular pressure, and a variety of physical factors. Integrins mediate bone metastasis of breast, prostate, and lung cancer by promoting cancer cell adhesion, migration, and survival. Integrin-mediated targeted therapy showed promising prospects in bone metabolic diseases. This review emphasizes the latest research results of integrins in bone metabolism and bone metastasis and provides a vision for treatment strategies.

Regulation of Kinase Signaling Pathways by α6β4-Integrins and Plectin in Prostate Cancer

Hemidesmosomes (HDs) are adhesive structures that ensure stable anchorage of cells to the basement membrane. They are formed by α6β4-integrin heterodimers and linked to intermediate filaments via plectin. It has been reported that one of the most common events during the pathogenesis of prostate cancer (PCa) is the loss of HD organization. While the expression levels of β4-integrins are strongly reduced, the expression levels of α6-integrins and plectin are maintained or even elevated, and seem to promote tumorigenic properties of PCa cells, such as proliferation, invasion, metastasis, apoptosis- and drug-resistance. In this review, we discuss the potential mechanisms of how HD components might contribute to various cellular signaling pathways to promote prostate carcinogenesis. Moreover, we summarize the current knowledge on the involvement of α6β4-integrins and plectin in PCa initiation and progression.

Integrin alpha 6 is upregulated and drives hepatocellular carcinoma progression through integrin α6β4 complex

Integrin α6 (ITGA6) forms integrin receptors with either integrin β1 (ITGB1) or integrin β4 (ITGB4). How it functions to regulate hepatocellular carcinoma (HCC) progression is not well-elucidated. We found that ITGA6 RNA and protein expression levels are significantly elevated in human HCC tissues in comparison with paired adjacent nontumor tissues by RNA sequencing, RT-qPCR, Western blotting and immunofluorescence staining. Stable knockdown of ITGA6 with different ITGA6 shRNA expression lentivectors significantly inhibited proliferation, migration and anchorage-independent growth of HCC cell lines in vitro, and xenograft tumor growth in vivo. The inhibition of anchorage-dependent and -independent growth of HCC cell lines was also confirmed with anti-ITGA6 antibody. ITGA6 knockdown was shown to induce cell-cycle arrest at G0/G1 phase. Immunoprecipitation assay revealed apparent interaction of ITGA6 with ITGB4, but not ITGB1. Expression studies showed that ITGA6 positively regulates the expression of ITGB4 with no or negative regulation of ITGB1 expression. Finally, while high levels of ITGA6 and ITGB4 together were associated with significantly worse survival of HCC patients in TCGA data set, the association was not significant for high levels of ITGA6 and ITGB1. In conclusion, ITGA6 is upregulated in HCC tumors and has a malignant promoting role in HCC cells through integrin α6β4 complex. Thus, integrin α6β4 may be a therapeutic target for treating patients with HCC.

TNF-α regulates the composition of the basal lamina and cell-matrix adhesions in gingival epithelial cells

Laminin 5, type 4 collagen, and α6β4 integrin contribute to the formation of hemidesmosomes in the epithelia of periodontal tissues, which is critical for the development and maintenance of the dentogingival junction. As it is not known whether TNF-α alters the composition of the epithelial pericellular matrix, human gingival epithelial cells were cultured in the presence or absence of TNF-α. Treatment with TNF-α accelerated epithelial cell migration and closure of in vitro wounds. These data indicate unexpectedly, that TNF-α promotes the formation of the pericellular matrix around epithelial cells and enhances adhesion of epithelial cells to the underlying matrix, properties which are important for cell migration and the integrity of the dentogingival junction.

Integrin expression in correlation to clinicopathological features and prognosis of prostate cancer: A systematic review and meta-analysis

BACKGROUND

The prompt identification of patients with poor prognosis is essential in order to improve the treatment outcomes in prostate cancer (CaP); as a novel approach, several molecular markers, including integrins, have been discussed as prognostic biomarkers. Our aim was to comprehensively examine aberrant expression of integrins in correlation with clinicopathological features and prognosis in CaP by synthesizing all available evidence, in a systematic review and meta-analysis.

METHODS

A systematic review and meta-analysis was performed in accordance with the Preferred Reporting Items for Systematic Review and Meta-analysis (PRISMA) guidelines. Scientific literature databases (Pubmed, Embase, and Scopus) were systematically searched until May 10, 2020. Random-effects (DerSimonian-Laird) models were used to estimate pooled odds ratios (ORs) for cross-sectional correlations with clinicopathological characteristics and relative risks for longitudinal associations with prognosis.

RESULTS

Fourteen studies were included with a total number of 3,194 CaP cases examined (13 cross-sectional and four longitudinal cohort study arms). Correlation of low expression of α₆ (pooled OR = 0.10, 95% confidence interval [CI]: 0.04-0.28, P < 0.001) and β₁ (pooled OR = 0.45; 95% CI: 0.21-1.00, P = 0.049) integrin with high Gleason score was noted. A borderline trend between reduced expression of α₆ integrin and an advanced clinical stage of CaP (pooled OR = 0.48; 95% CI: 0.22-1.03, P = 0.06) was observed. No associations with biochemical recurrence and survival were documented.

CONCLUSIONS

Evidence on the association of low expression of integrins α₆ and β₁ and more advanced CaP exist, whereas significant results on survival were not documented; further studies are warranted.

Cohesive cancer invasion of the biophysical barrier of smooth muscle

Smooth muscle is found around organs in the digestive, respiratory, and reproductive tracts. Cancers arising in the bladder, prostate, stomach, colon, and other sites progress from low-risk disease to high-risk, lethal metastatic disease characterized by tumor invasion into, within, and through the biophysical barrier of smooth muscle. We consider here the unique biophysical properties of smooth muscle and how cohesive clusters of tumor use mechanosensing cell-cell and cell-ECM (extracellular matrix) adhesion receptors to move through a structured muscle and withstand the biophysical forces to reach distant sites. Understanding integrated mechanosensing features within tumor cluster and smooth muscle and potential triggers within adjacent adipose tissue, such as the unique damage-associated molecular pattern protein (DAMP), eNAMPT (extracellular nicotinamide phosphoribosyltransferase), or visfatin, offers an opportunity to prevent the first steps of invasion and metastasis through the structured muscle.

Overexpression of SNTG2, TRAF3IP2, and ITGA6 transcripts is associated with osteoporotic vertebral fracture in elderly women from community

Background

Vertebral fractures (VFs) are the most common clinical manifestation of osteoporosis associated with high morbimortality. A personal/familiar history of fractures increases the risk of fractures. The purpose of this study is to identify possible molecular markers associated with osteoporotic VFs in elderly women from community.

Methods

Transcriptomic analysis using Affymetrix HTA2 microarray was performed using whole blood samples of 240 subjects from a population‐based survey (Sao Paulo Ageing & Health [SPAH] study). Only elderly women with osteoporosis diagnosis by densitometry were analyzed, and divided in two groups: VF: women with osteoporosis and VFs versus no vertebral fracture (NVF): women with osteoporosis and NVFs. They were matched for age, chronic disease, medication use, and bone mineral density (BMD). The logistic regression model adjusted for age was applied for transcriptome data analysis. SYBR green‐based quantitative polymerase chain reaction (qPCR) was used to validate the most significant expression changes obtained in the microarray experiment.

Results

Microarray analysis identified 142 differentially expressed genes (DEGs, p < .01), 57 upregulated and 85 downregulated, compared VF versus NVF groups. The DEG with the greatest expression difference was the Gamma2‐Syntrophin (SNTG2) (β = 31.88, p = .005). Validation by qPCR confirmed increased expression in VF group of Syntrophin (SNTG2, fold change = 2.79, p = .009), TRAF3 Interacting Protein2 (TRAF3IP2, fold change = 2.79, p = .020), and Integrin Subunit Alpha 6 (ITGA6, fold change = 2.86, p = .038).

Conclusion

Our data identified and validated the association of SNTG2 (608715), TRAF3IP2 (607043), and ITGA6 (147556) with osteoporotic VF in elderly women, independently of BMD. These results suggest that these transcripts have potential clinical significance and may help to explain the molecular mechanisms and biological functions of vertebral fracture.

MicroRNA-377-3p alleviates IL-1β-caused chondrocyte apoptosis and cartilage degradation in osteoarthritis in part by downregulating ITGA6

Increasing evidence indicates that altered expression of microRNAs (miRNAs) is associated with osteoarthritis (OA) progression. In our study, we demonstrated that miR-377-3p is underexpressed in OA-affected cartilage and IL-1β-treated chondrocytes. Overexpression of miR-377-3p enhanced chondrocyte proliferation and restrained apoptosis and signs of cartilage matrix degradation and of an inflammatory response. Furthermore, ITGA6 was identified as a target gene of miR-377-3p. The latter was found to directly bind to the 3' untranslated region (3'UTR) of ITGA6 mRNA and downregulate ITGA6. In addition, ITGA6 expression was high in OA-affected tissues and negatively correlated with miR-77-3p expression. Overexpression of ITGA6 reversed the effects of miR-377-3p on IL-1β-caused chondrocyte apoptosis, cartilage matrix degradation, and the inflammatory response. Moreover, bioinformatic analysis and a luciferase assay indicated that miR-377-3p expression is regulated by long noncoding RNA NEAT1, which binds to miR-377-3p and inactivates it. We showed that NEAT1 was highly expressed in OA-affected cartilage, negatively correlated with miR-377-3p levels, and positively correlated with ITGA6 levels. These findings provide information for the development of future treatments of OA, suggesting that miR-377-3p may be a therapeutic target in OA.

A Method to Reuse Archived H&E Stained Histology Slides for a Multiplex Protein Biomarker Analysis

Archived Hematoxylin and Eosin (H&E) stained pathology slides are routinely stored to index formalin-fixed paraffin-embedded (FFPE) sample tissue blocks. FFPE blocks are clinically annotated human tumor specimens that can be valuable in studies decades after the tissue is collected. If stored properly, they have the potential to yield a valuable number of serial sectioned slides for diagnostic or research purposes. However, some retrospective studies are limited in scope because the tissue samples have been depleted or not enough material is available in stored blocks for serial sections. The goal of these studies was to determine if archived H&E-stained slides can be directly reutilized by optimizing methods to de-stain and then re-stain the H&E stained slides to allow the detection of several biomarkers of interest using a conjugated antibody with chromogen multiplex immunohistochemistry procedure. This simple but innovative procedure, combined with image analysis techniques, demonstrates the ability to perform precise detection of relevant markers correlated to disease progression in initially identified tumor regions in tissue. This may add clinical value in retaining H&E slides for further use.

Gene Editing of α6 Integrin Inhibits Muscle Invasive Networks and Increases Cell-Cell Biophysical Properties in Prostate Cancer

Human prostate cancer confined to the gland is indolent (low-risk), but tumors outside the capsule are aggressive (high-risk). Extracapsular extension requires invasion within and through a smooth muscle-structured environment. Because integrins respond to biomechanical cues, we used a gene editing approach to determine if a specific region of laminin-binding α6β1 integrin was required for smooth muscle invasion both in vitro and in vivo. Human tissue specimens showed prostate cancer invasion through smooth muscle and tumor coexpression of α6 integrin and E-cadherin in a cell-cell location and α6 integrin in a cell-extracellular matrix (ECM) distribution. Prostate cancer cells expressing α6 integrin (DU145 α6WT) produced a 3D invasive network on laminin-containing Matrigel and invaded into smooth muscle both in vitro and in vivo. In contrast, cells without α6 integrin (DU145 α6KO) and cells expressing an integrin mutant (DU145 α6AA) did not produce invasive networks, could not invade muscle both in vitro and in vivo, and surprisingly formed 3D cohesive clusters. Using electric cell-substrate impedance testing, cohesive clusters had up to a 30-fold increase in normalized resistance at 400 Hz (cell-cell impedance) as compared with the DU145 α6WT cells. In contrast, measurements at 40,000 Hz (cell-ECM coverage) showed that DU145 α6AA cells were two-fold decreased in normalized resistance and were defective in restoring resistance after a 1 μmol/L S1P challenge as compared with the DU145 α6WT cells. The results suggest that gene editing of a specific α6 integrin extracellular region, not required for normal tissue function, can generate a new biophysical cancer phenotype unable to invade the muscle, presenting a new therapeutic strategy for metastasis prevention in prostate cancer. SIGNIFICANCE: This study shows an innovative strategy to block prostate cancer metastasis and invasion in the muscle through gene editing of a specific α6 integrin extracellular region.

Integrin α6 targeted positron emission tomography imaging of hepatocellular carcinoma in mouse models

Integrin α6 emerges to be a diagnostic biomarker for hepatocellular carcinoma (HCC). Here, we translated our previously identified integrin α6 targeted peptide RWY into a positron emission tomography (PET) tracer ¹⁸F-RWY for the detection of HCC lesions in following four HCC mouse models including subcutaneous, orthotopic, genetically engineered and chemical induced HCC mice. ¹⁸F-RWY produced high PET signals in liver tumor tissues that were reduced by blocking studies using nonradiolabeled RWY peptide. We compared the integrin α6 targeted PET tracer ¹⁸F-RWY with the integrin αvβ3-targeted PET tracer ¹⁸F-3PRGD₂ and the clinical PET tracer ¹⁸F-FDG in chemical induced HCC mice. Among 12 HCC identified by enhanced magnetic resonance imaging (MRI) with hepatocellular specific gadoxetate disodium Gd-EOB-DTPA, the sensitivities of ¹⁸F-RWY, ¹⁸F-3PRGD₂ and ¹⁸F-FDG were approximately 92%, 73% and 50% while the tumor-to-liver ratios were 4.36 ± 1.41, 1.97 ± 0.43 and 1.63 ± 0.23 respectively. Additionally, PET imaging with the integrin α6 targeted ¹⁸F-RWY enabled to visualize small HCC lesions with diameters approximately 0.2 cm that was hard to be distinguished from surround hepatic vascular by enhanced MRI with Gd-EOB-DTPA. These findings potentiate the use of integrin α6 targeted PET tracer ¹⁸F-RWY for the detection of HCC.

The Tumor Microenvironments of Lethal Prostate Cancer

Localized prostate cancer (confined to the gland) generally is considered curable, with nearly a 100% 5-year-survival rate. When the tumor escapes the prostate capsule, leading to metastasis, there is a poorer prognosis and higher mortality rate, with 5-year survival dropping to less than 30%. A major research question has been to understand the transition from indolent (low risk) disease to aggressive (high risk) disease. In this chapter, we provide details of the changing tumor microenvironments during prostate cancer invasion and their role in the progression and metastasis of lethal prostate cancer. Four microenvironments covered here include the muscle stroma, perineural invasion, hypoxia, and the role of microvesicles in altering the extracellular matrix environment. The adaptability of prostate cancer to these varied microenvironments and the cues for phenotypic changes are currently understudied areas. Model systems for understanding smooth muscle invasion both in vitro and in vivo are highlighted. Invasive human needle biopsy tissue and mouse xenograft tumors both contain smooth muscle invasion. In combination, the models can be used in an iterative process to validate molecular events for smooth muscle invasion in human tissue. Understanding the complex and interacting microenvironments in the prostate holds the key to early detection of high-risk disease and preventing tumor invasion through escape from the prostate capsule.

Alpha-6 integrin promotes radioresistance of glioblastoma by modulating DNA damage response and the transcription factor Zeb1

Radiotherapy is the cornerstone of glioblastoma (GBM) standard treatment. However, radioresistance of cancer cells leads to an inevitable recurrence. In the present study, we showed that blocking α6-integrin in cells derived from GBM biopsy specimens cultured as neurospheres, sensitized cells to radiation. In cells downregulated for α6-integrin expression, we observed a decrease in cell survival after irradiation and an increase in radio-induced cell death. We also demonstrated that inhibition of α6-integrin expression affects DNA damage checkpoint and repair. Indeed, we observed a persistence of γ-H2AX staining after IR and the abrogation of the DNA damage-induced G2/M checkpoint, likely through the downregulation of the checkpoint kinase CHK1 and its downstream target Cdc25c. We also showed that α6-integrin contributes to GBM radioresistance by controlling the expression of the transcriptional network ZEB1/OLIG2/SOX2. Finally, the clinical data from TCGA and Rembrandt databases demonstrate that GBM patients with high levels of the five genes signature, including α6-integrin and its targets, CHK1, ZEB1, OLIG2 and SOX2, have a significantly shorter overall survival. Our study suggest that α6-integrin is an attractive therapeutic target to overcome radioresistance of GBM cancer cells.

Upregulation of lncRNA ADAMTS9-AS2 Promotes Salivary Adenoid Cystic Carcinoma Metastasis via PI3K/Akt and MEK/Erk Signaling

Neurotropic infiltrative growth and distant metastasis are the main causes of death in salivary adenoid cystic carcinoma (SACC) patients. Long noncoding RNAs (lncRNAs) are involved in many human neoplasms, however, their potential roles in SACC are unclear. In our study, we found that ADAM metallopeptidase with thrombospondin type 1 motif, 9 (ADAMTS9) antisense RNA 2 (ADAMTS9-AS2) was significantly upregulated in SACC patients with metastasis and SACC-lung metastasis (LM) cells. Moreover, ADAMTS9-AS2 expression was closely associated with the prognosis and distant metastasis in SACC patients. Next, we found that c-myc could specifically bind to the promoter of ADAMTS9-AS2 and activated its transcription. Knockdown of ADAMTS9-AS2 significantly inhibited migration and invasion of SACC cells in vitro and distant lung metastasis in vivo. Furthermore, ADAMTS9-AS2, which mainly expressed in the cytoplasm, shared microRNA (miRNA) response elements with Integrin α6 (ITGA6). Overexpression of ADAMTS9-AS2 competitively bound to miR-143-3p that inhibited ITGA6 from miRNA-mediated degradation, and thus it activated the activity of PI3K/Akt and MEK/Erk signaling and facilitated SACC metastasis. In summary, ADAMTS9-AS2 promotes migration and invasion in SACC by competing with miR-143-3p. This sheds a new insight into the regulation mechanism of ADAMTS9-AS2, and it provides a possible application for the SACC treatment.

Patient-derived ovarian cancer xenografts re-growing after a cisplatinum treatment are less responsive to a second drug re-challenge: a new experimental setting to study response to therapy

Even if ovarian cancer patients are very responsive to a cisplatinum-based therapy, most will relapse with a resistant disease. New experimental animal models are needed to explore the mechanisms of resistance, to better tailor treatment and improve patient prognosis. To address these aims, seven patient-derived high-grade serous/endometrioid ovarian cancer xenografts were characterized for the antitumor response after one and two cycles of cisplatinum and classified as Very Responsive, Responsive, and Low Responsive to drug treatment. Xenografts re-growing after the first drug cycle were much less responsive to the second one. The expression of epithelial-mesenchymal transition (EMT) and cancer stem cells (CSCs) genes was investigated in cisplatinum-treated and not-treated tumors. We found that different EMT (TCF3, CAMK2N1, EGFR, and IGFBP4) and CSCs (SMO, DLL1, STAT3, and ITGA6) genes were expressed at higher levels in Low Responsive than in Responsive and Very Responsive xenografts. The expression of STAT3 was found to be associated with lower survival (HR = 13.7; p = 0.013) in the TCGA patient data set. MMP9, CD44, DLL4, FOXP1, MERTK, and PTPRC genes were found more expressed in tumors re-growing after cisplatinum treatment than in untreated tumors. We here describe a new in vivo ovarian carcinoma experimental setting that will be instrumental for specific trials of combination therapy to counteract cisplatinum resistance in order to improve the prognosis of ovarian patients.

Integrins as Therapeutic Targets: Successes and Cancers

Integrins are transmembrane receptors that are central to the biology of many human pathologies. Classically mediating cell-extracellular matrix and cell-cell interaction, and with an emerging role as local activators of TGFβ, they influence cancer, fibrosis, thrombosis and inflammation. Their ligand binding and some regulatory sites are extracellular and sensitive to pharmacological intervention, as proven by the clinical success of seven drugs targeting them. The six drugs on the market in 2016 generated revenues of some US$3.5 billion, mainly from inhibitors of α4-series integrins. In this review we examine the current developments in integrin therapeutics, especially in cancer, and comment on the health economic implications of these developments.

Fyn/heterogeneous nuclear ribonucleoprotein E1 signaling regulates pancreatic cancer metastasis by affecting the alternative splicing of integrin β1

Pancreatic cancer is characterized by a dense desmoplastic reaction in which extracellular matrix proteins accumulate and surround tumor cells. Integrins and their related signaling molecules are associated with progression of pancreatic cancer. In the present study, the association between the metastasis of pancreatic cancer and the expression of hnRNP E1 and integrin β1 was evaluated. In vitro and in vivo experiments were designed to study the mechanism underlying the regulation of integrin β1 splicing by the Fyn/hnRNP E1 spliceosome. Expression of hnRNP E1 and integrin β1A were associated with metastasis of pancreatic cancer. Inhibition of Fyn activity upregulated the expression of P21-activated kinase 1 and promoted the phosphorylation and nuclear localization of hnRNP E1, leading to the construction of a spliceosome complex that affected the alterative splicing of integrin β1. In the hnRNP E1 spliceosome complex, hnRNP A1 and serine/arginine-rich splicing factor 1 were responsible for binding to the pre-mRNA of integrin β1. Suppression of Fyn activity and/or overexpression of hnRNP E1 decreased the metastasis of pancreatic cancer cells. In pancreatic cancer, the present study demonstrated a novel mechanism by which Fyn/hnRNP E1 signaling regulates pancreatic cancer metastasis by affecting the alternative splicing of integrin β1. hnRNP E1 and integrin β1A are associated with the metastasis of pancreatic cancer and may be novel molecular targets for pancreatic cancer treatment.

Characterization of Laminin Binding Integrin Internalization in Prostate Cancer Cells

Laminin binding integrins α6 (CD49f) and α3 (CD49c) are persistently but differentially expressed in prostate cancer (PCa). Integrin internalization is an important determinant of their cell surface expression and function. Using flow cytometry, and first order kinetic modeling, we quantitated the intrinsic internalization rates of integrin subunits in a single cycle of internalization. In PCa cell line DU145, α6 integrin internalized with a rate constant (kactual ) of 3.25 min-1 , threefold faster than α3 integrin (1.0 min-1 ), 1.5-fold faster than the vitronectin binding αv integrin (CD51) (2.2 min-1 ), and significantly slower than the unrelated transferrin receptor (CD71) (15 min-1 ). Silencing of α3 integrin protein expression in DU145, PC3, and PC3B1 cells resulted in up to a 1.71-fold increase in kactual for α6 integrin. The internalized α6 integrin was targeted to early endosomes but not to lamp1 vesicles. Depletion of α3 integrin expression resulted in redistribution of α6β4 integrin to an observed cell-cell staining pattern that is consistent with a suprabasal distribution observed in epidermis and early PIN lesions in PCa. Depletion of α3 integrin increased cell migration by 1.8-fold, which was dependent on α6β1 integrin. Silencing of α6 integrin expression however, had no significant effect on the kactual of α3 integrin or its distribution in early endosomes. These results indicate that α3 and α6 integrins have significantly different internalization kinetics and that coordination exists between them for internalization. J. Cell. Biochem. 118: 1038-1049, 2017. © 2016 Wiley Periodicals, Inc.

The Cohesive Metastasis Phenotype in Human Prostate Cancer

A critical barrier for the successful prevention and treatment of recurrent prostate cancer is detection and eradication of metastatic and therapy-resistant disease. Despite the fall in diagnoses and mortality, the reported incidence of metastatic disease has increased 72% since 2004. Prostate cancer arises in cohesive groups as intraepithelial neoplasia, migrates through muscle and leaves the gland via perineural invasion for hematogenous dissemination. Current technological advances have shown cohesive-clusters of tumor (also known as microemboli) within the circulation. Circulating tumor cell (CTC) profiles are indicative of disseminated prostate cancer, and disseminated tumor cells (DTC) are found in cohesive-clusters, a phenotypic characteristic of both radiation- and drug-resistant tumors. Recent reports in cell biology and informatics, coupled with mass spectrometry, indicate that the integrin adhesome network provides an explanation for the biophysical ability of cohesive-clusters of tumor cells to invade thorough muscle and nerve microenvironments while maintaining adhesion-dependent therapeutic resistance. Targeting cohesive-clusters takes advantage of the known ability of extracellular matrix (ECM) adhesion to promote tumor cell survival and represents an approach that has the potential to avoid the progression to drug- and radiotherapy-resistance. In the following review we will examine the evidence for development and dissemination of cohesive-clusters in metastatic prostate cancer.

Schwann Cells Increase Prostate and Pancreatic Tumor Cell Invasion Using Laminin Binding A6 Integrin

Human pancreatic and prostate cancers metastasize along nerve axons during perineural invasion. The extracellular matrix laminin class of proteins is an abundant component of both myelinated and non-myelinated nerves. Analysis of human pancreatic and prostate tissue revealed both perineural and endoneural invasion with Schwann cells surrounded or disrupted by tumor, respectively. Tumor and nerve cell co-culture conditions were used to determine if myelinating or non-myelinating Schwann cell (S16 and S16Y, respectively) phenotype was equally likely to promote integrin-dependent cancer cell invasion and migration on laminin. Conditioned medium from S16 cells increased tumor cell (DU145, PC3, and CFPAC1) invasion into laminin approximately 1.3-2.0 fold compared to fetal bovine serum (FBS) treated cells. Integrin function (e.g., ITGA6p formation) increased up to 1.5 fold in prostate (DU145, PC3, RWPE-1) and pancreatic (CFPAC1) cells, and invasion was dependent on ITGA6p formation and ITGB1 as determined by function-blocking antibodies. In contrast, conditioned medium isolated from S16Y cells (non-myelinating phenotype) decreased constitutive levels of ITGA6p in the tumor cells by 50% compared to untreated cells and decreased ITGA6p formation 3.0 fold compared to S16 treated cells. Flow cytometry and western blot analysis revealed loss of ITGA6p formation as reversible and independent of overall loss of ITGA6 expression. These results suggest that the myelinating phenotype of Schwann cells within the tumor microenvironment increased integrin-dependent tumor invasion on laminin.

Laminins and cancer stem cells: Partners in crime?

As one of the predominant protein families within the extracellular matrix both structurally and functionally, laminins have been shown to be heavily involved in tumor progression and drug resistance. Laminins participate in key cellular events for tumor angiogenesis, cell invasion and metastasis development, including the regulation of epithelial-mesenchymal transition and basement membrane remodeling, which are tightly associated with the phenotypic characteristics of stem-like cells, particularly in the context of cancer. In addition, a great deal of studies and reports has highlighted the critical roles of laminins in modulating stem cell phenotype and differentiation, as part of the stem cell niche. Stemming from these discoveries a growing body of literature suggests that laminins may act as regulators of cancer stem cells, a tumor cell subpopulation that plays an instrumental role in long-term cancer maintenance, metastasis development and therapeutic resistance. The accumulating evidence in this emerging research area suggests that laminins represent potential therapeutic targets for anti-cancer treatments against cancer stem cells, and that they may be used as predictive and prognostic markers to inform clinical management and improve patient survival.

AhR ligand Aminoflavone inhibits α6-integrin expression and breast cancer sphere-initiating capacity

Traditional chemotherapies debulk tumors but fail to produce long-term clinical remissions due to their inability to eradicate tumor-initiating cells (TICs). This necessitates therapy with activity against the TIC niche. Αlpha6-integrin (α6-integrin) promotes TIC growth. In contrast, aryl hydrocarbon receptor (AhR) signaling activation impedes the formation of mammospheres (clusters of cells enriched for TICs). We investigated the ability of AhR agonist Aminoflavone (AF) and AF pro-drug (AFP464) to disrupt mammospheres derived from breast cancer cells and a M05 mammary mouse model of breast cancer respectively. We further examined the capacity of AF and AFP464 to exhibit anticancer activity and modulate the expression of 'stemness' genes including α6-integrin using immunofluorescence, flow cytometry and qRT-PCR analysis. AF disrupted mammospheres and prevented secondary mammosphere formation. In contrast, AF did not disrupt mammospheres derived from AhR ligand-unresponsive MCF-7 cells. AFP464 treatment suppressed M05 tumor growth and disrupted corresponding mammospheres. AF and AFP464 reduced the expression and percentage of cells that stained for 'stemness' markers including α6-integrin in vitro and in vivo respectively. These data suggest AFP464 thwarts bulk breast tumor and TIC growth via AhR agonist-mediated α6-integrin inhibition.

ITGA6 is directly regulated by hypoxia-inducible factors and enriches for cancer stem cell activity and invasion in metastatic breast cancer models

Background

Hypoxia-inducible factors (HIFs) are well-established mediators of tumor growth, the epithelial to mesenchymal transition (EMT) and metastasis. In several types of solid tumors, including breast cancers, the HIFs play a critical role in maintaining cancer stem cell (CSC) activity. Thus, we hypothesized that HIFs may also regulate transcription of markers of breast CSC activity. One approach to enrich for breast cells with stem-like phenotypes is FACS sorting, in which sub-populations of live cells are gated based on the expression of cell surface antigens, including various integrin subunits. Integrin alpha 6 (ITGA6; CD49f) is routinely used in combination with other integrin subunits to enrich for breast stem cells by FACS. Integrins not only mediate interactions with the extracellular matrix (ECM), but also drive intracellular signaling events that communicate from the tumor microenvironment to inside of the tumor cell to alter phenotypes including migration and invasion.

Methods

We used two models of metastatic breast cancer (MBC), polyoma middle T (MMTV-PyMT) and MDA-MB-231 cells, to compare the expression of ITGA6 in wild type and knockout (KO) or knockdown cells. Chromatin immunoprecipitation (ChIP) and luciferase reporter assays verified that ITGA6 is a direct HIF transcriptional target. We also used FACS sorting to enrich for CD49f ⁺ cells to compare tumorsphere formation, tumor initiating cell activity, invasion and HIF activity relative to CD49f^{neg or low} cells. Knockdown of ITGA6 significantly reduced invasion, whereas re-expression of ITGA6 in the context of HIF knockdown partially rescued invasion. A search of public databases also revealed that ITGA6 expression is an independent prognostic factor of survival in breast cancer patients.

Results

We report that ITGA6 is a HIF-dependent target gene and that high ITGA6 expression enhances invasion and tumor-initiating cell activities in models of MBC. Moreover, cells that express high levels of ITGA6 are enriched for HIF-1α expression and the expression of HIF-dependent target genes.

Conclusions

Our data suggest that HIF-dependent regulation of ITGA6 is one mechanism by which sorting for CD49f ⁺ cells enhances CSC and metastatic phenotypes in breast cancers. Our results are particularly relevant to basal-like breast cancers which express higher levels of the HIFα subunits, core HIF-dependent target genes and ITGA6 relative to other molecular subtypes.

Electronic supplementary material

The online version of this article (doi:10.1186/s12943-016-0510-x) contains supplementary material, which is available to authorized users.

Laminin-binding integrin gene copy number alterations in distinct epithelial-type cancers

BACKGROUND

The laminin-binding integrin (LBI) family are cell adhesion molecules that are essential for invasion and metastasis of human epithelial cancers and cell adhesion mediated drug resistance. We investigated whether copy number alteration (CNA) or mutations of a five-gene signature (ITGB4, ITGA3, LAMB3, PLEC, and SYNE3), representing essential genes for LBI adhesion, would correlate with patient outcomes within human epithelial-type tumor data sets currently available in an open access format.

METHODS

We investigated the relative alteration frequency of an LBI signature panel (integrin β4 (ITGB4), integrin α3 (ITGA3), laminin β3 chain (LAMB3), plectin (PLEC), and nesprin 3 (SYNE3)), independent of the epithelial cancer type, within publically available and published data using cBioPortal and Oncomine software. We rank ordered the results using a 20% alteration frequency cut-off and limited the analysis to studies containing at least 100 samples. Kaplan-Meier survival curves were analyzed to determine if alterations in the LBI signature correlated with patient survival. The Oncomine data mining tool was used to compare the heat map expression of the LBI signature without SYNE3 (as this was not included in the Oncomine database) to drug resistance patterns.

RESULTS

Twelve different cancer types, representing 5,647 samples, contained at least a 20% alteration frequency of the five-gene LBI signature. The frequency of alteration ranged from 38.3% to 19.8%. Within the LBI signature, PLEC was the most commonly altered followed by LAMB3, ITGB4, ITGA3, and SYNE3 across all twelve cancer types. Within cancer types, there was little overlap of the individual amplified genes from each sample, suggesting different specific amplicons may alter the LBI adhesion structures. Of the twelve cancer types, overall survival was altered by CNA presence in bladder urothelial carcinoma (p=0.0143*) and cervical squamous cell carcinoma and endocervical adenocarcinoma (p=0.0432*). Querying the in vitro drug resistance profiles with the LBI signature demonstrated a positive correlation with cells resistant to inhibitors of HDAC (Vorinostat, Panobinostat) and topoisomerase II (Irinotecan). No correlation was found with the following agents: Bleomycin, Doxorubicin, Methotrexate, Gemcitabine, Docetaxel, Bortezomib, and Shikonen.

CONCLUSIONS

Our work has identified epithelial-types of human cancer that have significant CNA in our selected five-gene signature, which was based on the essential and genetically-defined functions of the protein product networks (in this case, the LBI axis). CNA of the gene signature not only predicted overall survival in bladder, cervical, and endocervical adenocarcinoma but also response to chemotherapy. This work suggests that future studies designed to optimize the gene signature are warranted.

GENERAL SIGNIFICANCE

The copy number alteration of structural components of the LBI axis in epithelial-type tumors may be promising biomarkers and rational targets for personalized therapy in preventing or arresting metastatic spread.

The host microenvironment influences prostate cancer invasion, systemic spread, bone colonization, and osteoblastic metastasis

Prostate cancer (PCa) is the second leading cause of cancer death in men worldwide. Most PCa deaths are due to osteoblastic bone metastases. What triggers PCa metastasis to the bone and what causes osteoblastic lesions remain unanswered. A major contributor to PCa metastasis is the host microenvironment. Here, we address how the primary tumor microenvironment influences PCa metastasis via integrins, extracellular proteases, and transient epithelia-mesenchymal transition (EMT) to promote PCa progression, invasion, and metastasis. We discuss how the bone-microenvironment influences metastasis; where chemotactic cytokines favor bone homing, adhesion molecules promote colonization, and bone-derived signals induce osteoblastic lesions. Animal models that fully recapitulate human PCa progression from primary tumor to bone metastasis are needed to understand the PCa pathophysiology that leads to bone metastasis. Better delineation of the specific processes involved in PCa bone metastasize is needed to prevent or treat metastatic PCa. Therapeutic regimens that focus on the tumor microenvironment could add to the PCa pharmacopeia.

Intracellular modifiers of integrin alpha 6p production in aggressive prostate and breast cancer cell lines

Cancer metastasis is a multi-step process in which tumor cells gain the ability to invade beyond the primary tumor and colonize distant sites. The mechanisms regulating the metastatic process confer changes to cell adhesion receptors including the integrin family of receptors. Our group previously discovered that the α6 integrin (ITGA6/CD49f) is post translationally modified by urokinase plasminogen activator (uPA) and its receptor, urokinase plasminogen activator receptor (uPAR), to form the variant ITGA6p. This variant of ITGA6 is a cleaved form of the receptor that lacks the ligand-binding domain. Although it is established that the uPA/uPAR axis drives ITGA6 cleavage, the mechanisms regulating cleavage have not been defined. Intracellular integrin dependent "inside-out" signaling is a major regulator of integrin function and the uPA/uPAR axis. We hypothesized that intracellular signaling molecules play a role in formation of ITGA6p to promote cell migration during cancer metastasis. In order to test our hypothesis, DU145 and PC3B1 prostate cancer and MDA-MB-231 breast cancer cell lines were treated with small interfering RNA targeting actin and the intracellular signaling regulators focal adhesion kinase (FAK), integrin linked kinase (ILK), and paxillin. The results demonstrated that inhibition of actin, FAK, and ILK expression resulted in significantly increased uPAR expression and ITGA6p production. Inhibition of actin increased ITGA6p, although inhibition of paxillin did not affect ITGA6p formation. Taken together, these results suggest that FAK and ILK dependent "inside-out" signaling, and actin dynamics regulate extracellular production of ITGA6p and the aggressive phenotype.