LncRNA NEAT1 promotes nucleus pulposus cell matrix degradation through regulating Nrf2/ARE axis.

BACKGROUND: This study aimed to assess the role and mechanism of lncRNA NEAT1 in intervertebral disc degeneration (IVD). METHODS: LncRNA profile (GSE56081) between IVD and healthy control was downloaded from the Gene Expression Omnibus (GEO) database and analyzes differential lncRNA expression. Expression of lncRNA NEAT1 in IVD tissue and TNF-α/IL-1ß-stimulated nucleus pulposus cells were further measured by RT-PCR. The lncRNA NEAT1 overexpression plasmids (pcDNA-NEAT1) were constructed and transfected into nucleus pulposus cells. Catabolic biomarkers (MMP-3 and MMP-13), anabolic biomarkers (Col II and Aggrecan) and Nrf2 expression were further measured. To further investigate the function of Nrf2, nucleus pulposus cells were pretreated with or without 25 µM tert-Butylhydroquinone (TBHQ), a Nrf2 activator, for 18 h and subsequently cotreated with pcDNA-NEAT1. RESULTS: A total of 1432 lncRNAs were differentially expressed in GSE56081. Bioinformatic analysis found that these lncRNAs mainly enriched in Nrf2/ARE signaling pathway. LncRNA NEAT1 was highly expressed in IVD tissues than that of healthy control. Moreover, TNF-α/IL-1ß induced a time- and dose-dependent increase in the mRNA expression of lncRNA NEAT1 in the nucleus pulposus cells. Overexpression of lncRNA NEAT1 abates promotes nucleus pulposus cells proliferation but induces matrix degradation. Meanwhile, nucleus and cytoplasm Nrf2 expression was significantly down-regulated by lncRNA NEAT1 upregulation. Nrf2 activator (TBHQ) could partially reverse the inhibitory effects of overexpression of lncRNA NEAT1 on matrix degradation. CONCLUSION: Collectively, our data unveiled the lncRNA NEAT1 promotes matrix degradation by regulating Nrf2/ARE signaling pathway, suggesting a potential therapeutic for IVD in the future.

Plexin-B2 facilitates glioblastoma infiltration by modulating cell biomechanics.

Infiltrative growth is a major cause of high lethality of malignant brain tumors such as glioblastoma (GBM). We show here that GBM cells upregulate guidance receptor Plexin-B2 to gain invasiveness. Deletion of Plexin-B2 in GBM stem cells limited tumor spread and shifted invasion paths from axon fiber tracts to perivascular routes. On a cellular level, Plexin-B2 adjusts cell adhesiveness, migratory responses to different matrix stiffness, and actomyosin dynamics, thus empowering GBM cells to leave stiff tumor bulk and infiltrate softer brain parenchyma. Correspondingly, gene signatures affected by Plexin-B2 were associated with locomotor regulation, matrix interactions, and cellular biomechanics. On a molecular level, the intracellular Ras-GAP domain contributed to Plexin-B2 function, while the signaling relationship with downstream effectors Rap1/2 appeared variable between GBM stem cell lines, reflecting intertumoral heterogeneity. Our studies establish Plexin-B2 as a modulator of cell biomechanics that is usurped by GBM cells to gain invasiveness.

Cell-Extracellular Matrix Interactions Play Multiple Essential Roles in Aortic Arch Development.

RATIONALE: Defects in the morphogenesis of the fourth pharyngeal arch arteries (PAAs) give rise to lethal birth defects. Understanding genes and mechanisms regulating PAA formation will provide important insights into the etiology and treatments for congenital heart disease. OBJECTIVE: Cell-ECM (extracellular matrix) interactions play essential roles in the morphogenesis of PAAs and their derivatives, the aortic arch artery and its major branches; however, their specific functions are not well-understood. Previously, we demonstrated that integrin α5ß1 and Fn1 (fibronectin) expressed in the Isl1 lineages regulate PAA formation. The objective of the current studies was to investigate cellular mechanisms by which integrin α5ß1 and Fn1 regulate aortic arch artery morphogenesis. METHODS AND RESULTS: Using temporal lineage tracing, whole-mount confocal imaging, and quantitative analysis of the second heart field (SHF) and endothelial cell (EC) dynamics, we show that the majority of PAA EC progenitors arise by E7.5 in the SHF and contribute to pharyngeal arch endothelium between E7.5 and E9.5. Consequently, SHF-derived ECs in the pharyngeal arches form a plexus of small blood vessels, which remodels into the PAAs by 35 somites. The remodeling of the vascular plexus is orchestrated by signals dependent on the pharyngeal ECM microenvironment, extrinsic to the endothelium. Conditional ablation of integrin α5ß1 or Fn1 in the Isl1 lineages showed that signaling by the ECM regulates aortic arch artery morphogenesis at multiple steps: (1) accumulation of SHF-derived ECs in the pharyngeal arches, (2) remodeling of the EC plexus in the fourth arches into the PAAs, and (3) differentiation of neural crest-derived cells adjacent to the PAA endothelium into vascular smooth muscle cells. CONCLUSIONS: PAA formation is a multistep process entailing dynamic contribution of SHF-derived ECs to pharyngeal arches, the remodeling of endothelial plexus into the PAAs, and the remodeling of the PAAs into the aortic arch artery and its major branches. Cell-ECM interactions regulated by integrin α5ß1 and Fn1 play essential roles at each of these developmental stages.

Serotonin 2A (5-HT2A) receptor affects cell-matrix adhesion and the formation and maintenance of stress fibers in HEK293 cells.

5-HT2A, a G-protein coupled receptor, is widely expressed in the human body, including in the gastrointestinal tract, platelets and the nervous system. It mediates various functions, for e.g. learning, memory, mood regulation, platelet aggregation and vasoconstriction, but its involvement in cell-adhesion remains largely unknown. Here we report a novel role for 5-HT2A in cell-matrix adhesion.In HEK293 cells, which are loosely adherent, expression and stimulation of human or rat 5-HT2A receptor by agonists such as serotonin or 2,5-dimethoxy-4-iodoamphetamine (DOI) led to a significant increase in adhesion, while inhibition of 5-HT2A by antipsychotics, such as risperidone, olanzapine or chlorpromazine prevented it. 5-HT2A activation gave rise to stress fibers in these cells and was also required for their maintenance. Mechanistically, the 5-HT2A-mediated adhesion was mediated by downstream PKC and Rho signaling. Since 5-HT2A is associated with many disorders such as dementia, depression and schizophrenia, its role in cell-matrix adhesion could have implications for neural circuits.

Global phosphotyrosinylated protein profile of cell-matrix adhesion complexes of trabecular meshwork cells.

Dysregulation of the mechanical properties and cell adhesive interactions of trabecular meshwork (TM) are known to impair aqueous humor drainage and elevate intraocular pressure in glaucoma patients. The identity of regulatory mechanisms underlying TM mechanotransduction, however, remains elusive. Here we analyzed the phosphotyrosine proteome of human TM cell-extracellular matrix (ECM) adhesion complexes, which play a key role in sensing and transducing extracellular chemical and mechanical cues into intracellular activities, using a two-level affinity pull-down (phosphotyrosine antibody and titanium dioxide beads) method and mass spectrometry. This analysis identified ~1,000 tyrosine-phosphorylated proteins of TM cell-ECM adhesion complexes. Many consensus adhesome proteins were found to be tyrosine phosphorylated. Interestingly, several of the phosphotyrosinylated proteins found in TM cell-ECM adhesion complexes are known to be required for podocyte glomerular filtration, indicating the existence of molecular parallels that are likely relevant to the shared fluid barrier and filtration functions of the two mechanosensitive cell types.

MicroRNA-30b-5p functions as a metastasis suppressor in colorectal cancer by targeting Rap1b.

Colorectal liver metastasis (CRLM) is the leading cause of death in patients with colorectal cancer (CRC). MiR-30b-5p can function as an oncogene or tumor suppressor in cancers, but its role in CRLM is still unknown. Here, we found that miR-30b-5p overexpression suppressed the invasion, migration, adhesion, and motility of HCT116 and LoVo cells. The expression of EMT (Zeb1, Snail, and vimentin) and adhesion-related proteins (p-paxillin and p-Src) was decreased. We validated Rap1b, a Ras family small GTPase that regulates cell adhesion and mobility, as the direct and functional target of miR-30b-5p. Rap1b overexpression rescued the aggressive characteristics of CRC cells that were inhibited by miR-30b-5p. Rap1b knockdown suppressed invasion and migration and decreased CRC cell-matrix adhesion and spreading, which was consistent with the results of miR-30b-5p overexpression. Further in vivo experiments demonstrated that miR-30b-5p overexpression inhibited CRLM, but Rap1b rescue attenuated the inhibitory effect of miR-30b-5p. In addition, miR-30b-5p was downregulated in CRC specimens, and Rap1b showed a negative correlation with miR-30b-5p expression in primary CRC and LM tissues. These results indicate that miR-30b-5p functions as a metastasis suppressor by targeting Rap1b and may provide a new target for the treatment of CRLM.

Hemidesmosomes modulate force generation via focal adhesions.

Hemidesmosomes are specialized cell-matrix adhesion structures that are associated with the keratin cytoskeleton. Although the adhesion function of hemidesmosomes has been extensively studied, their role in mechanosignaling and transduction remains largely unexplored. Here, we show that keratinocytes lacking hemidesmosomal integrin α6ß4 exhibit increased focal adhesion formation, cell spreading, and traction-force generation. Moreover, disruption of the interaction between α6ß4 and intermediate filaments or laminin-332 results in similar phenotypical changes. We further demonstrate that integrin α6ß4 regulates the activity of the mechanosensitive transcriptional regulator YAP through inhibition of Rho-ROCK-MLC- and FAK-PI3K-dependent signaling pathways. Additionally, increased tension caused by impaired hemidesmosome assembly leads to a redistribution of integrin αVß5 from clathrin lattices to focal adhesions. Our results reveal a novel role for hemidesmosomes as regulators of cellular mechanical forces and establish the existence of a mechanical coupling between adhesion complexes.

Adducins inhibit lung cancer cell migration through mechanisms involving regulation of cell-matrix adhesion and cadherin-11 expression.

Cell migration is a critical mechanism controlling tissue morphogenesis, epithelial wound healing and tumor metastasis. Migrating cells depend on orchestrated remodeling of the plasma membrane and the underlying actin cytoskeleton, which is regulated by the spectrin-adducin-based membrane skeleton. Expression of adducins is altered during tumorigenesis, however, their involvement in metastatic dissemination of tumor cells remains poorly characterized. This study investigated the roles of α-adducin (ADD1) and γ-adducin (ADD3) in regulating migration and invasion of non-small cell lung cancer (NSCLC) cells. ADD1 was mislocalized, whereas ADD3 was markedly downregulated in NSCLC cells with the invasive mesenchymal phenotype. CRISPR/Cas9-mediated knockout of ADD1 and ADD3 in epithelial-type NSCLC and normal bronchial epithelial cells promoted their Boyden chamber migration and Matrigel invasion. Furthermore, overexpression of ADD1, but not ADD3, in mesenchymal-type NSCLC cells decreased cell migration and invasion. ADD1-overexpressing NSCLC cells demonstrated increased adhesion to the extracellular matrix (ECM), accompanied by enhanced assembly of focal adhesions and hyperphosphorylation of Src and paxillin. The increased adhesiveness and decreased motility of ADD1-overexpressing cells were reversed by siRNA-mediated knockdown of Src. By contrast, the accelerated migration of ADD1 and ADD3-depleted NSCLC cells was ECM adhesion-independent and was driven by the upregulated expression of pro-motile cadherin-11. Overall, our findings reveal a novel function of adducins as negative regulators of NSCLC cell migration and invasion, which could be essential for limiting lung cancer progression and metastasis.

CASP4 gene silencing in epithelial cancer cells leads to impairment of cell migration, cell-matrix adhesion and tissue invasion.

Inflammatory caspases, including human caspase-4 (CASP4), play key roles in innate immune responses to promote fusion of phagosomes harboring pathogenic bacteria with lysosomes, halt intracellular replication of pathogens, maturation and secretion of pro-inflammatory cytokines. The role of inflammatory caspases in cancer cells remains poorly investigated. Here, we explored the consequences of modulating CASP4 expression levels on the migratory behavior of epithelial cancer cell lines. By a gene silencing approach and in vitro and in vivo studies we show that down-regulation of CASP4 leads to impaired cell migration and cell-matrix adhesion. This phenotype is accompanied by an increased actin cytoskeleton polymerization, changes in the overall organization of adherens junctions (AJs) and number and size of focal adhesions. Interestingly, the cell migration deficit could be reversed by epithelial growth factor treatment, and depletion of calcium ions unveiled a role of CASP4 in the novo assembly of AJs, suggesting that the role of CASP4 is not cell-autonomous. Finally, CASP4-silenced A431 cells exhibited a severe reduction in their ability to invade lung tissue, when injected into nude mice. Overall, our data support the emerging evidence that inflammatory caspases can regulate cell migration through actin remodeling and uncover a novel role of CASP4 in cancer cell behavior.

TRPV4 mediates the Ca2+ influx required for the interaction between flightless-1 and non-muscle myosin, and collagen remodeling.

Fibroblasts remodel extracellular matrix collagen, in part, through phagocytosis. This process requires formation of cell extensions, which in turn involves interaction of the actin-binding protein flightless-1 (FliI) with non-muscle myosin IIA (NMMIIA; heavy chain encoded by MYH9) at cell-matrix adhesion sites. As Ca2+ plays a central role in controlling actomyosin-dependent functions, we examined how Ca2+ controls the generation of cell extensions and collagen remodeling. Ratio fluorimetry demonstrated localized Ca2+ influx at the extensions of fibroblasts. Western blotting and quantitative (q)PCR showed high expression levels of the Ca2+-permeable transient receptor potential vanilloid-4 (TRPV4) channel, which co-immunoprecipitated with ß1 integrin and localized to adhesions. Treatment with α2ß1-integrin-blocking antibody or the TRPV4-specific antagonist AB159908, as well as reduction of TRPV4 expression through means of siRNA, blocked Ca2+ influx. These treatments also inhibited the interaction of FliI with NMMIIA, reduced the number and length of cell extensions, and blocked collagen remodeling. Pulldown assays showed that Ca2+ depletion inhibited the interaction of purified FliI with NMMIIA filaments. Fluorescence resonance energy transfer experiments showed that FliI-NMMIIA interactions require Ca2+ influx. We conclude that Ca2+ influx through the TRPV4 channel regulates FliI-NMMIIA interaction, which in turn enables generation of the cell extensions essential for collagen remodeling.

3D culture increases pluripotent gene expression in mesenchymal stem cells through relaxation of cytoskeleton tension.

Three-dimensional (3D) culture has been shown to improve pluripotent gene expression in mesenchymal stem cells (MSCs), but the underlining mechanisms were poorly understood. Here, we found that the relaxation of cytoskeleton tension of MSCs in 3D culture was critically associated with the expressional up-regulation of Nanog. Cultured in spheroids, MSCs showed decreased integrin-based cell-matrix adhesion but increased cadherin-based cell-cell interaction. Different from that in 2D culture, where MSCs exhibited branched and multiple-directed F-actin stress bundles at the cell edge and strengthened stress fibres transversing the cell body, MSCs cultured in spheroids showed compact cell body, relaxed cytoskeleton tension with very thin cortical actin filament outlining the cell, and increased expression of Nanog along with reduced levels of Suv39h1 (H3K9 methyltransferase) and H3K9me3. Notably, pharmaceutical inhibition of actin polymerization with cytochalasin D or silencing Suv39h1 expression with siRNA in 2D-cultured MSCs elevated the expression of Nanog via H3K9 demethylation. Thus, our data suggest that 3D culture increases the expression of Nanog through the relaxation of actin cytoskeleton, which mediates reduced Suv39h1 and H3K9me3 levels.

High-throughput proteomics reveal alarmins as amplifiers of tissue pathology and inflammation after spinal cord injury.

Spinal cord injury is characterized by acute cellular and axonal damage followed by aggressive inflammation and pathological tissue remodelling. The biological mediators underlying these processes are still largely unknown. Here we apply an innovative proteomics approach targeting the enriched extracellular proteome after spinal cord injury for the first time. Proteomics revealed multiple matrix proteins not previously associated with injured spinal tissue, including small proteoglycans involved in cell-matrix adhesion and collagen fibrillogenesis. Network analysis of transcriptomics and proteomics datasets uncovered persistent overexpression of extracellular alarmins that can trigger inflammation via pattern recognition receptors. In mechanistic experiments, inhibition of toll-like receptor-4 (TLR4) and the receptor for advanced glycation end-products (RAGE) revealed the involvement of alarmins in inflammatory gene expression, which was found to be dominated by IL1 and NFκΒ signalling. Extracellular high-mobility group box-1 (HMGB1) was identified as the likely endogenous regulator of IL1 expression after injury. These data reveal a novel tissue remodelling signature and identify endogenous alarmins as amplifiers of the inflammatory response that promotes tissue pathology and impedes neuronal repair after spinal cord injury.

Tetraspanin CD82: a suppressor of solid tumors and a modulator of membrane heterogeneity.

Tetraspanin CD82 suppresses the progression and metastasis of a wide range of solid malignant tumors. However, its roles in tumorigenesis and hematopoietic malignancy remain unclear. Ubiquitously expressed CD82 restrains cell migration and cell invasion by modulating both cell-matrix and cell-cell adhesiveness and confining outside-in pro-motility signaling. This restraint at least contributes to, if not determines, the metastasis-suppressive activity and, also likely, the physiological functions of CD82. As a modulator of cell membrane heterogeneity, CD82 alters microdomains, trafficking, and topography of the membrane by changing the membrane molecular landscape. The functional activities of membrane molecules and the cytoskeletal interaction of the cell membrane are subsequently altered, followed by changes in cellular functions. Given its pathological and physiological importance, CD82 is a promising candidate for clinically predicting and blocking tumor progression and metastasis and also an emerging model protein for mechanistically understanding cell membrane organization and heterogeneity.

The integrin expression profile modulates orientation and dynamics of force transmission at cell-matrix adhesions.

Integrin adhesion receptors connect the extracellular matrix (ECM) to the cytoskeleton and serve as bidirectional mechanotransducers. During development, angiogenesis, wound healing and cancer progression, the relative abundance of fibronectin receptors, including integrins α5ß1 and αvß3, changes, thus altering the integrin composition of cell-matrix adhesions. Here, we show that enhanced αvß3 expression can fully compensate for loss of α5ß1 and other ß1 integrins to support outside-in and inside-out force transmission. α5ß1 and αvß3 each mediate actin cytoskeletal remodeling in response to stiffening or cyclic stretching of the ECM. Likewise, α5ß1 and αvß3 support cellular traction forces of comparable magnitudes and similarly increase these forces in response to ECM stiffening. However, cells using αvß3 respond to lower stiffness ranges, reorganize their actin cytoskeleton more substantially in response to stretch, and show more randomly oriented traction forces. Centripetal traction force orientation requires long stress fibers that are formed through the action of Rho kinase (ROCK) and myosin II, and that are supported by α5ß1. Thus, altering the relative abundance of fibronectin-binding integrins in cell-matrix adhesions affects the spatiotemporal organization of force transmission.

Electrospun nanofiber scaffolds for investigating cell-matrix adhesion.

It has become increasingly clear that the cellular microenvironment, in particular the extracellular matrix, plays an important role in regulating cell function. However, the extracellular matrix is extraordinarily complex in both its makeup and its physical properties. Therefore, there is a need to develop model systems to independently evaluate the effect of specific extracellular matrix features upon cells. Here we describe a model system to evaluate one aspect of the extracellular matrix, its fibrous topology. We describe how to generate bio-mimetic nanofibers by electrospinning, how to grow cells on these fibers, and also some methods for fixing and visualizing cells grown on these fibers. These methods can be used to investigate a wide range of biological questions, including, but not limited to, cell-extracellular matrix adhesion and cell motility on extracellular matrix.

Five linkage regions each harbor multiple type 2 diabetes genes in the African American subset of the GENNID Study.

We previously localized type 2 diabetes (T2D)-susceptibility genes to five chromosomal regions through a genome-wide linkage scan of T2D and age of diagnosis (AOD) in the African American subset of the GENNID sample. To follow up these findings, we repeated the linkage and association analysis using genotypes on an additional 9203 fine-mapping single nucleotide polymorphisms (SNPs) selected to tag genes under the linkage peaks. In each of the five regions, we confirmed linkage and inferred the presence of ≥2 susceptibility genes. The evidence of multiple susceptibility genes consisted of: (1) multiple linkage peaks in four of the five regions; and (2) association of T2D and AOD with SNPs within ≥2 genes in every region. The associated genes included 3 previously reported to associate with T2D or related traits (GRB10, NEDD4L, LIPG) and 24 novel candidate genes, including genes in lipid metabolism (ACOXL) and cell-cell and cell-matrix adhesion (MAGI2, CLDN4, CTNNA2).

Matrix adhesion polarizes heart progenitor induction in the invertebrate chordate Ciona intestinalis.

Cell-matrix adhesion strongly influences developmental signaling. Resulting impacts on cell migration and tissue morphogenesis are well characterized. However, the in vivo impact of adhesion on fate induction remains ambiguous. Here, we employ the invertebrate chordate Ciona intestinalis to delineate an essential in vivo role for matrix adhesion in heart progenitor induction. In Ciona pre-cardiac founder cells, invasion of the underlying epidermis promotes localized induction of the heart progenitor lineage. We found that these epidermal invasions are associated with matrix adhesion along the pre-cardiac cell/epidermal boundary. Through targeted manipulations of RAP GTPase activity, we were able to manipulate pre-cardiac cell-matrix adhesion. Targeted disruption of pre-cardiac cell-matrix adhesion blocked heart progenitor induction. Conversely, increased matrix adhesion generated expanded induction. We were also able to selectively restore cell-matrix adhesion and heart progenitor induction through targeted expression of Ci-Integrin ß2. These results indicate that matrix adhesion functions as a necessary and sufficient extrinsic cue for regional heart progenitor induction. Furthermore, time-lapse imaging suggests that cytokinesis acts as an intrinsic temporal regulator of heart progenitor adhesion and induction. Our findings highlight a potentially conserved role for matrix adhesion in early steps of vertebrate heart progenitor specification.

EMT as the ultimate survival mechanism of cancer cells.

Epithelial cancers make up the vast majority of cancer types and, during the transition from benign adenoma to malignant carcinoma and metastasis, epithelial tumor cells acquire a de-differentiated, migratory and invasive behavior. This process of epithelial-mesenchymal transition (EMT) goes along with dramatic changes in cellular morphology, the loss and remodeling of cell-cell and cell-matrix adhesions, and the gain of migratory and invasive capabilities. EMT itself is a multistage process, involving a high degree of cellular plasticity and a large number of distinct genetic and epigenetic alterations, as fully differentiated epithelial cells convert into poorly differentiated, migratory and invasive mesenchymal cells. In the past years, a plethora of genes have been identified that are critical for EMT and metastasis formation. Notably, the EMT process not only induces increased cancer cell motility and invasiveness but also allows cancer cells to avoid apoptosis, anoikis, oncogene addiction, cellular, senescence and general immune defense. Notably, EMT seems to play a critical role in the generation and maintenance of cancer stem cells, highly consistent with the notion that metastatic cells carry the ability to initiate new tumors.

Inhibition of androgen-responsive LNCaP prostate cancer cell tumor xenograft growth by dietary phenethyl isothiocyanate correlates with decreased angiogenesis and inhibition of cell attachment.

Phenethyl isothiocyanate (PEITC) is a candidate anticancer compound found in certain cruciferous vegetables. In our tumor cell xenograft model, dietary administration of PEITC (100-150 mg/kg body weight/d) inhibited androgen-responsive LNCaP human prostate cancer cell tumor growth. We found that dietary treatment with PEITC significantly inhibited tumor platelet/endothelial cell adhesion molecule (PECAM-1/CD31) expression, a marker of angiogenesis. By contrast, we did not find the inhibitory effects of PEITC on tumor growth to be associated with alteration of specific markers for apoptosis, cell proliferation or androgen receptor-mediated pathways. Consistent with in vivo results, PEITC exerted little effects on cell proliferation, cell cycle and androgen-dependent pathways. Interestingly, PEITC significantly attenuated LNCaP cell plating efficiency that correlated with inhibition of integrin family proteins integrin ß1, α2 and α6 mRNA expression. Thus, PEITC may be a dietary factor that inhibits androgen-responsive prostate tumor growth indirectly by selectively targeting factors involved in the tumor microenvironment.

Cell surface adhesion molecules and adhesion-initiated signaling: understanding of anoikis resistance mechanisms and therapeutic opportunities.

Cells express various cell surface adhesion molecules (receptors) that not only mechanically serve as contacting sites between the cell and extracellular matrix (ECM) or adjacent cells, but also initiate intracellular signaling pathways modulating important cellular events including survival and proliferation. Normal cells undergo apoptosis when lacking ECM attachment. This type of cell death has been termed anoikis. Anoikis can be viewed as a normal process which ensures tissue homeostasis and failure to execute the anoikis program or resistance to anoikis could result in adherent cells surviving under suspension condition and proliferating at ectopic sites where the matrix proteins are different from those the cells originally contact. Resistance to anoikis is emerging as a hallmark of metastatic cancers which enables cancer cells to disseminate to distant organs through systemic circulation. In this review, we will discuss the molecular basis of adhesion-initiated signaling, the impact of loss of cell-ECM adhesion on normal cell survival, the role of cancer cell aggregate formation via intercellular adhesion under non-adherent condition, and mechanisms of anoikis resistance developed in metastatic cancer cells. Understanding of these aspects will provide opportunities to find new potential molecular targets, and therapeutic strategies based on these findings will likely prove to be more specific and effective.