Par6 is phosphorylated by aPKC to facilitate EMT

Expanding the Chemical Space of Transforming Growth Factor-β (TGFβ) Receptor Type II Degraders with 3,4-Disubstituted Indole Derivatives

The TGFβ type II receptor (TβRII) is a central player in all TGFβ signaling downstream events, has been linked to cancer progression, and thus, has emerged as an auspicious anti-TGFβ strategy. Especially its targeted degradation presents an excellent goal for effective TGFβ pathway inhibition. Here, cellular structure-activity relationship (SAR) data from the TβRII degrader chemotype 1 was successfully transformed into predictive ligand-based pharmacophore models that allowed scaffold hopping. Two distinct 3,4-disubstituted indoles were identified from virtual screening: tetrahydro-4-oxo-indole 2 and indole-3-acetate 3. Design, synthesis, and screening of focused amide libraries confirmed 2r and 3n as potent TGFβ inhibitors. They were validated to fully recapitulate the ability of 1 to selectively degrade TβRII, without affecting TβRI. Consequently, 2r and 3n efficiently blocked endothelial-to-mesenchymal transition and cell migration in different cancer cell lines while not perturbing the microtubule network. Hence, 2 and 3 present novel TβRII degrader chemotypes that will (1) aid target deconvolution efforts and (2) accelerate proof-of-concept studies for small-molecule-driven TβRII degradation in vivo.

Par6 Enhances Glioma Invasion by Activating MEK/ERK Pathway Through a LIN28/let-7d Positive Feedback Loop

The invasion of glioblastoma usually results in the recurrence and poor prognosis in patients with glioma. However, the underlying mechanisms involved in glioma invasion remains undefined. In this study, immunohistochemistry analyses of glioma specimens demonstrated that high expression of Par6 was positively correlated with malignancy and poor prognosis of patients with glioma. Par6-overexpressing glioma cells showed much more fibroblast-like morphology, suggesting that regulation of Par6 expression might be associated with tumor invasion in glioma cells. Further study indicated that Par6 overexpression subsequently increased CD44 and N-cadherin expression to enhance glioma invasion through activating MEK/ERK/STAT3 pathway, in vivo and in vitro. Moreover, we found that LIN28/let-7d axis was involved in this process via a positive feedback loop, suggesting that MEK/ERK/LIN28/let-7d/STAT3 cascade might be essential for Par6-mediated glioma invasion. Therefore, these data highlight the roles of Par6 in glioma invasion, and Par6 may serve as a potential therapeutic target for patients with glioma.

14-3-3 and Smad2/3 are crucial mediators of atypical-PKCs: Implications for neuroblastoma progression

Neuroblastoma (NB) is a cancer that develops in the neuroblasts. It is the most common cancer in children under the age of 1 year, accounting for approximately 6% of all cancers. The prognosis of NB is linked to both age and degree of cell differentiation. This results in a range of survival rates for patients, with outcomes ranging from recurrence and mortality to high survival rates and tumor regression. Our previous work indicated that PKC-ι promotes cell proliferation in NB cells through the PKC-ι/Cdk7/Cdk2 cascade. We report on two atypical protein kinase inhibitors as potential therapeutic candidates against BE(2)-C and BE(2)-M17 cells: a PKC-ι-specific 5-amino-1-2,3-dihydroxy-4-(methylcyclopentyl)-1H-imidazole-4-carboxamide and a PKC-ζ specific 8-hydroxy-1,3,6-naphthalenetrisulfonic acid. Both compounds induced apoptosis and retarded the epithelial-mesenchymal transition (EMT) of NB cells. Proteins 14-3-3 and Smad2/3 acted as central regulators of aPKC-driven progression in BE(2)-C and BE(2)-M17 cells in relation to the Akt1/NF-κB and TGF-β pathways. Data indicates that aPKCs upregulate Akt1/NF-κB and TGF-β pathways in NB cells through an association with 14-3-3 and Smad2/3 that can be diminished by aPKC inhibitors. In summary, both inhibitors appear to be promising potential neuroblastoma therapeutics and merit further research.

Transforming growth factor-β in tumour development

Transforming growth factor-β (TGFβ) is a ubiquitous cytokine essential for embryonic development and postnatal tissue homeostasis. TGFβ signalling regulates several biological processes including cell growth, proliferation, apoptosis, immune function, and tissue repair following injury. Aberrant TGFβ signalling has been implicated in tumour progression and metastasis. Tumour cells, in conjunction with their microenvironment, may augment tumourigenesis using TGFβ to induce epithelial-mesenchymal transition, angiogenesis, lymphangiogenesis, immune suppression, and autophagy. Therapies that target TGFβ synthesis, TGFβ-TGFβ receptor complexes or TGFβ receptor kinase activity have proven successful in tissue culture and in animal models, yet, due to limited understanding of TGFβ biology, the outcomes of clinical trials are poor. Here, we review TGFβ signalling pathways, the biology of TGFβ during tumourigenesis, and how protein quality control pathways contribute to the tumour-promoting outcomes of TGFβ signalling.

Autophagy regulates transforming growth factor β signaling and receptor trafficking

Transforming growth factor beta (TGFβ) stimulates tumorigenesis by inducing epithelial to mesenchymal transition (EMT) and cell migration. TGFβ signaling is regulated by the endocytosis of cell surface receptors and their subcellular trafficking into the endo-lysosomal system. Here we investigated how autophagy, a cellular quality control network that delivers material to lysosomes, regulates TGFβ signaling pathways that induce EMT and cell migration. We impaired autophagy in non-small cell lung cancer cells using chloroquine, spautin-1, ULK-101, or small interfering RNA (siRNA) targeting autophagy-related gene (ATG)5 and ATG7 and observed that inhibiting autophagy results in a decrease in TGFβ1-dependent EMT transcription factor and cell marker expression, as well as attenuated stress fiber formation and cell migration. This correlated with decreased internalization of cell surface TGFβ receptors and their trafficking to early/late endosomal and lysosomal compartments. The effects of autophagy inhibition on TGFβ signaling were investigated by Smad2/Smad3 phosphorylation and cellular localization using western blotting, subcellular fractionation, and immunofluorescence microscopy. We observed that inhibiting autophagy decreased the amount and timeframe of Smad2/Smad3 signaling. Taken together, our results suggest that inhibiting autophagy attenuates pro-tumorigenic TGFβ signaling by regulating receptor trafficking, resulting in impaired Smad2/Smad3 phosphorylation and nuclear accumulation.

Apical-basal polarity and the control of epithelial form and function

Epithelial cells are the most common cell type in all animals, forming the sheets and tubes that compose most organs and tissues. Apical-basal polarity is essential for epithelial cell form and function, as it determines the localization of the adhesion molecules that hold the cells together laterally and the occluding junctions that act as barriers to paracellular diffusion. Polarity must also target the secretion of specific cargoes to the apical, lateral or basal membranes and organize the cytoskeleton and internal architecture of the cell. Apical-basal polarity in many cells is established by conserved polarity factors that define the apical (Crumbs, Stardust/PALS1, aPKC, PAR-6 and CDC42), junctional (PAR-3) and lateral (Scribble, DLG, LGL, Yurt and RhoGAP19D) domains, although recent evidence indicates that not all epithelia polarize by the same mechanism. Research has begun to reveal the dynamic interactions between polarity factors and how they contribute to polarity establishment and maintenance. Elucidating these mechanisms is essential to better understand the roles of apical-basal polarity in morphogenesis and how defects in polarity contribute to diseases such as cancer.

A novel non‑selective atypical PKC agonist could protect neuronal cell line from Aβ‑oligomer induced toxicity by suppressing Aβ generation

Atypical protein kinase C (aPKCs) serve key functions in embryonic development by regulating apical-basal polarity. Previous studies have shed light on their roles during adulthood, especially in the development of Alzheimer's disease (AD). Although the crystal structure of PKCι has been resolved, an agonist of aPKCs remains to be discovered. In the present study, by using the Discovery Studio program and LibDock methodology, a small molecule library (K66-X4436 KINA Set) of compounds were screened for potential binding to PKCι. Subsequently, the computational docking results were validated using affinity selection-mass spectrometry, before in vitro kinase activity was used to determine the function of the hit compounds. A cell-based model assay that can mimic the pathology of AD was then established and used to assess the function of these hit compounds. As a result, the aPKC agonist Z640 was identified, which could bind to PKCι in silico, in vitro and in this cell-based model. Z640 was further confirmed as a non-selective aPKC agonist that can activate the kinase activity of both PKCι and PKCζ. In the cell-based assay, Z640 was found to protect neuronal cell lines from amyloid-β (Aβ) oligomer-induced cell death by reducing reactive oxygen species production and restore mitochondrial function. In addition, Z640 could reduce Aβ40 generation in a dose-dependent manner and shift amyloid precursor protein processing towards the non-amyloid pathway. To conclude, the present study is the first, to the best of the authors' knowledge to identify an aPKC agonist by combining computer-assisted drug discovery and cell-based assays. The present study also revealed that aPKC agonists have therapeutic potential for the treatment of AD.

Canonical and Non-canonical TGFβ Signaling Activate Autophagy in an ULK1-Dependent Manner

The mechanism(s) in which transforming growth factor beta 1 (TGFβ) modulates autophagy in cancer remain unclear. Here, we characterized the TGFβ signaling pathways that induce autophagy in non-small cell lung cancer cells, using cells lines stably expressing GFP-LC3-RFP-LC3ΔG constructs that measure autophagic flux. We demonstrated that TGFβ1 increases Unc 51-like kinase 1 (ULK1) protein levels, 5' adenosine monophosphate-activated protein kinase (AMPK)-dependent ULK1 phosphorylation at serine (S) 555 and ULK1 complex formation but decreases mechanistic target of rapamycin (mTOR) activity on ULK1. Further analysis revealed that the canonical Smad4 pathway and the non-canonical TGFβ activated kinase 1/tumor necrosis factor receptor-associated factor 6/P38 mitogen activated protein kinase (TAK1-TRAF6-P38 MAPK) pathway are important for TGFβ1-induced autophagy. The TAK1-TRAF6-P38 MAPK pathway was essential for downregulating mTOR S2448 phosphorylation, ULK1 S555 phosphorylation and autophagosome formation. Furthermore, although siRNA-mediated Smad4 silencing did not alter mTOR-dependent ULK1 S757 phosphorylation, it did reduce AMPK-dependent ULK1 S555 phosphorylation and autophagosome formation. Additionally, Smad4 silencing and inhibiting the TAK1-TRAF6-P38 MAPK pathway decreased autophagosome-lysosome co-localization in the presence of TGFβ. Our results suggest that the Smad4 and TAK1-TRAF6-P38 MAPK signaling pathways are essential for TGFβ-induced autophagy and provide specific targets for the inhibition of TGFβ in tumor cells that utilize autophagy in their epithelial-mesenchymal transition program.

p62/Sequestosome 1 regulates transforming growth factor beta signaling and epithelial to mesenchymal transition in A549 cells

Transforming growth factor beta (TGFβ) receptor trafficking regulates many TGFβ-dependent cellular outcomes including epithelial to mesenchymal transition (EMT). EMT in A549 non-small cell lung cancer (NSCLC) cells has recently been linked to the regulation of cellular autophagy. Here, we investigated the role of the autophagy cargo receptor, p62/sequestosome 1 (SQSTM1), in regulating TGFβ receptor trafficking, TGFβ1-dependent Smad2 phosphorylation and EMT in A549 NSCLC cells. Using immunofluorescence microscopy, p62/SQSTM1 was observed to co-localize with TGFβ receptors in the late endosome. Small interfering RNA (SiRNA)-mediated silencing of p62/SQSTM1 resulted in an attenuated time-course of Smad2 phosphorylation but did not alter Smad2 nuclear translocation. However, p62/SQSTM1 silencing promoted TGFβ1-dependent EMT marker expression, actin stress fiber formation and A549 cell migration. We further observed that Smad4-independent TGFβ1 signaling decreased p62/SQSTM1 protein levels via a proteasome-dependent mechanism. Although p62/SQSTM1 silencing did not impede TGFβ-dependent autophagy, our results suggest that p62/SQSTM1 may aid in maintaining A549 cells in an epithelial state and TGFβ1 decreases p62/SQSTM1 prior to inducing EMT and autophagy.

Atypical PKCs activate Vimentin to facilitate prostate cancer cell motility and invasion

Atypical protein kinase C (aPKC) are involved in progression of many human cancers. Vimentin is expressed during epithelial to mesenchymal transition (EMT). Molecular dynamics of Vimentin intermediate filaments (VIFs) play a key role in metastasis. This article is an effort to provide thorough understanding of the relationship between Vimentin and aPKCs . We demonstrate that diminution of aPKCs lead to attenuate prostate cellular metastasis through the downregulation of Vimentin expression. siRNA knocked-down SNAIL1 and PRRX1 reduce aPKC activity along with Vimentin. Results suggest that aPKCs target multiple activation sites (Ser33/39/56) on Vimentin and therefore is essential for VIF dynamics regulation during the metastasis of prostate cancer cells. Understanding the aPKC related molecular mechanisms may provide a novel therapeutic path for prostate carcinoma.

Adipose-Derived Molecules-Untouched Horizons in Alzheimer's Disease Biology

The global incidence of Alzheimer's disease (AD) is on the rise with the increase in obesity and metabolic disease epidemic. Obesity is co-morbid with the increase in mass of adipose tissue, which secretes numerous molecules that are biologically important. Obesity and its associated conditions are perhaps involved in the causative pathway of AD. Immunologically important cytokines such as IL-1β, IL-10, and IL-18, which are released by adipose tissue, are also found to be associated with AD. Besides, the expression of IL-6, IFNγ, and TNF alpha are also associated with AD. Ang-I and Ang-II are found to mediate the progression of AD. Complement factors B, C4b, and H are differentially expressed in AD. Overall, several adipocyte-derived cytokines are found to be dysregulated in AD, and their role in AD remains to be studied. The induction of autophagy is a very promising strategy in the treatment of AD. A variety of adipose-derived molecules have been shown to modulate autophagy. However, very little literature is available on the role of adipose-derived molecules in inducing autophagy in microglial cells of AD. Understanding the role of adipose-derived molecules in the development of AD, especially in the induction of autophagy, would open up new avenues in devising strategies for the treatment of AD.

MiRNAs and LncRNAs: Dual Roles in TGF-β Signaling-Regulated Metastasis in Lung Cancer

Lung cancer is one of the most malignant cancers around the world, with high morbidity and mortality. Metastasis is the leading cause of lung cancer deaths and treatment failure. MicroRNAs (miRNAs) and long non-coding RNAs (lncRNAs), two groups of small non-coding RNAs (nc-RNAs), are confirmed to be lung cancer oncogenes or suppressors. Transforming growth factor-β (TGF-β) critically regulates lung cancer metastasis. In this review, we summarize the dual roles of miRNAs and lncRNAs in TGF-β signaling-regulated lung cancer epithelial-mesenchymal transition (EMT), invasion, migration, stemness, and metastasis. In addition, lncRNAs, competing endogenous RNAs (ceRNAs), and circular RNAs (circRNAs) can act as miRNA sponges to suppress miRNAs, thereby mediating TGF-β signaling-regulated lung cancer invasion, migration, and metastasis. Through this review, we hope to cast light on the regulatory mechanisms of miRNAs and lncRNAs in TGF-β signaling-regulated lung cancer metastasis and provide new insights for lung cancer treatment.

The Regulation of NFE2L2 (NRF2) Signalling and Epithelial-to-Mesenchymal Transition in Age-Related Macular Degeneration Pathology

Age-related macular degeneration (AMD) is a mounting cause of loss of sight in the elderly in the developed countries, a trend enhanced by the continual ageing of the population. AMD is a multifactorial and only partly understood, malady. Unfortunately, there is no effective treatment for most AMD patients. It is known that oxidative stress (OS) damages the retinal pigment epithelium (RPE) and contributes to the progression of AMD. We review here the potential importance of two OS-related cellular systems in relation to AMD. First, the nuclear factor erythroid 2-related factor 2 (NFE2L2; NRF2)-mediated OS response signalling pathway is important in the prevention of oxidative damage and a failure of this system could be critical in the development of AMD. Second, epithelial-to-mesenchymal transition (EMT) represents a change in the cellular phenotype, which ultimately leads to the fibrosis encountered in RPE, a characteristic of AMD. Many of the pathways triggering EMT are promoted by OS. The possible interconnections between these two signalling routes are discussed here. From a broader perspective, the control of NFE2L2 and EMT as ways of preventing OS-derived cellular damage could be potentially valuable in the therapy of AMD.

PAR3-PAR6-atypical PKC polarity complex proteins in neuronal polarization

Polarity is a fundamental feature of cells. Protein complexes, including the PAR3-PAR6-aPKC complex, have conserved roles in establishing polarity across a number of eukaryotic cell types. In neurons, polarity is evident as distinct axonal versus dendritic domains. The PAR3, PAR6, and aPKC proteins also play important roles in neuronal polarization. During this process, either aPKC kinase activity, the assembly of the PAR3-PAR6-aPKC complex or the localization of these proteins is regulated downstream of a number of signaling pathways. In turn, the PAR3, PAR6, and aPKC proteins control various effector molecules to establish neuronal polarity. Herein, we discuss the many signaling mechanisms and effector functions that have been linked to PAR3, PAR6, and aPKC during the establishment of neuronal polarity.

Axon Regeneration: Antagonistic Signaling Pairs in Neuronal Polarization

Genome-wide screens, proteomics, and candidate-based approaches have identified numerous genes associated with neuronal regeneration following central nervous system (CNS) injury. Despite significant progress, functional recovery remains a challenge, even in model systems. Neuronal function depends on segregation of axonal versus dendritic domains. A key to functional recovery may lie in recapitulating the developmental signals that instruct axon specification and growth in adult neurons post-injury. Theoretically, binary activator-inhibitor elements operating as a Turing-like system within neurons can specify axonal versus dendritic domains and promote axon growth. We review here various molecules implicated in axon specification that function as signaling pairs driving neuronal polarization and axon growth.

Oncogenic PKC-ι activates Vimentin during epithelial-mesenchymal transition in melanoma; a study based on PKC-ι and PKC-ζ specific inhibitors

Melanoma is one of the fastest growing cancers in the United States and is accompanied with a poor prognosis owing to tumors being resistant to most therapies. Atypical protein kinase Cs (aPKC) are involved in malignancy in many cancers. We previously reported that aPKCs play a key role in melanoma's cell motility by regulating cell signaling pathways which induce epithelial-mesenchymal Transition (EMT). We tested three novel inhibitors; [4-(5-amino-4-carbamoylimidazol-1-yl)-2,3-dihydroxycyclopentyl] methyl dihydrogen phosphate (ICA-1T) along with its nucleoside analog 5-amino-1-((1R,2S,3S,4R)-2,3-dihydroxy-4-methylcyclopentyl)-1H-imidazole-4-carboxamide (ICA-1S) which are specific to protein kinase C-iota (PKC-ι) and 8-hydroxy-1,3,6-naphthalenetrisulfonic acid (ζ-Stat) which is specific to PKC-zeta (PKC-ζ) on cell proliferation, apoptosis, migration and invasion of two malignant melanoma cell lines compared to normal melanocytes. Molecular modeling was used to identify potential binding sites for the inhibitors and to predict selectivity. Kinase assay showed >50% inhibition for specified targets beyond 5 μM for all inhibitors. Both ICA-1 and ζ-Stat significantly reduced cell proliferation and induced apoptosis, while ICA-1 also significantly reduced migration and melanoma cell invasion. PKC-ι stimulated EMT via TGFβ/Par6/RhoA pathway and activated Vimentin by phosphorylation at S39. Both ICA-1 and ζ-Stat downregulate TNF-α induced NF-κB translocation to the nucleus there by inducing apoptosis. Results suggest that PKC-ι is involved in melanoma malignancy than PKC-ζ. Inhibitors proved to be effective under in-vitro conditions and need to be tested in-vivo for the validity as effective therapeutics. Overall, results show that aPKCs are essential for melanoma progression and metastasis and that they could be used as effective therapeutic targets for malignant melanoma.

Two novel atypical PKC inhibitors; ACPD and DNDA effectively mitigate cell proliferation and epithelial to mesenchymal transition of metastatic melanoma while inducing apoptosis

Atypical protein kinase Cs (aPKC) are involved in cell cycle progression, tumorigenesis, cell survival and migration in many cancers. We believe that aPKCs play an important role in cell motility of melanoma by regulating cell signaling pathways and inducing epithelial to mesenchymal transition (EMT). We have investigated the effects of two novel aPKC inhibitors; 2-acetyl-1,3-cyclopentanedione (ACPD) and 3,4-diaminonaphthalene-2,7-disulfonic acid (DNDA) on cell proliferation, apoptosis, migration and invasion of two malignant melanoma cell lines compared to normal melanocytes. Molecular docking data suggested that both inhibitors specifically bind to protein kinase C-zeta (PKC-ζ) and PKC-iota (PKC-ι) and kinase activity assays were carried out to confirm these observations. Both inhibitors decreased the levels of total and phosphorylated PKC-ζ and PKC-ι. Increased levels of E-cadherin, RhoA, PTEN and decreased levels of phosphorylated vimentin, total vimentin, CD44, β-catenin and phosphorylated AKT in inhibitor treated cells. This suggests that inhibition of both PKC-ζ and PKC-ι using ACPD and DNDA downregulates EMT and induces apoptosis in melanoma cells. We also carried out PKC-ι and PKC-ζ directed siRNA treatments to prove the above observations. Immunoprecipitation data suggested an association between PKC-ι and vimentin and PKC-ι siRNA treatments confirmed that PKC-ι activates vimentin by phosphorylation. These results further suggested that PKC-ι is involved in signaling pathways which upregulate EMT and which can be effectively suppressed using ACPD and DNDA. Our results summarize that melanoma cells proliferate via aPKC/AKT/NF-κB mediated pathway while inducing the EMT via PKC-ι/Par6/RhoA pathway. Overall, results show that aPKCs are essential for melanoma progression and metastasis, suggesting that ACPD and DNDA can be effectively used as potential therapeutic drugs for melanoma by inhibiting aPKCs.

Suppression of CIP4/Par6 attenuates TGF-β1-induced epithelial-mesenchymal transition in NRK-52E cells

Transforming growth factor-β (TGF-β) induces epithelial-mesenchymal transition (EMT) primarily via a Smad-dependent mechanism. However, there are few studies available on TGF-β-induced EMT through the activation of non-canonical pathways. In this study, the Cdc42-interacting protein-4 (CIP4)/partitioning-defective protein 6 (Par6) pathway was investigated in TGF-β1-stimulated NRK-52E cells. Rat NRK-52E cells were obtained and stimulated with TGF-β1. The expression levels of E-cadherin, α-smooth muscle actin (α-SMA) and CIP4 were then examined by western blot analyses. Rat NRK-52E cells were transfected with Par6 or CIP4 small interfering RNA (siRNA), and scrambled siRNA as controls. The cells were incubated with 20 ng/ml of TGF-β1 for 72 h in order to observe the effects of Par6 and CIP4 silencing. Confocal fluorescence microscopy was also applied to reveal the expression and distribution of E-cadherin, α-SMA, Par6 and CIP4. The results demonstrated that E-cadherin expression was decreased, and α-SMA expression was increased in the TGF-β1-stimulated cells. Simultaneously, the increased expression of CIP4 and p-Par6 was confirmed by western blot analyses. The results of confocal fluorescence microscopy revealed that rat CIP4 exhibited cluster formations located adjacent to the cell periphery; however, as for the protein expression and distribution of Par6, there was no obvious difference between the control cells and cells exposed to TGF-β1. siRNA molecules capable of CIP4 and Par6 knockdown were used to demonstrate reversed TGF-β1-induced EMT. Moreover, CIP4 loss of function reversed the increase in p-Par6 protein expression in the TGF-β1-stimulated NRK-52E cells. A similar result was observed with the decreased CIP4 protein expression due to Par6 loss of function. Our data thus suggest that the CIP4/Par6 complex plays an important role in the occurrence of EMT in TGF-β1-stimulated NRK-52E cells. The underlying mechanisms are mediated, at least in part, through the upregulation of CIP4, which occurrs due to stimulation with TGF-β1; subsequently, CIP4 increases the phosphorylation of Par6, which accelerates the process of EMT.

Cell polarity signaling in the plasticity of cancer cell invasiveness

Apico-basal polarity is typical of cells present in differentiated epithelium while front-rear polarity develops in motile cells. In cancer development, the transition from epithelial to migratory polarity may be seen as the hallmark of cancer progression to an invasive and metastatic disease. Despite the morphological and functional dissimilarity, both epithelial and migratory polarity are controlled by a common set of polarity complexes Par, Scribble and Crumbs, phosphoinositides, and small Rho GTPases Rac, Rho and Cdc42. In epithelial tissues, their mutual interplay ensures apico-basal and planar cell polarity. Accordingly, altered functions of these polarity determinants lead to disrupted cell-cell adhesions, cytoskeleton rearrangements and overall loss of epithelial homeostasis. Polarity proteins are further engaged in diverse interactions that promote the establishment of front-rear polarity, and they help cancer cells to adopt different invasion modes. Invading cancer cells can employ either the collective, mesenchymal or amoeboid invasion modes or actively switch between them and gain intermediate phenotypes. Elucidation of the role of polarity proteins during these invasion modes and the associated transitions is a necessary step towards understanding the complex problem of metastasis. In this review we summarize the current knowledge of the role of cell polarity signaling in the plasticity of cancer cell invasiveness.

Apico-basal polarity complex and cancer

Apico-basal polarity is a cardinal molecular feature of adult eukaryotic epithelial cells and appears to be involved in several key cellular processes including polarized cell migration and maintenance of tissue architecture. Epithelial cell polarity is maintained by three well-conserved polarity complexes, namely, PAR, Crumbs and SCRIB. The location and interaction between the components of these complexes defines distinct structural domains of epithelial cells. Establishment and maintenance of apico-basal polarity is regulated through various conserved cell signalling pathways including TGF beta, Integrin and WNT signalling. Loss of cell polarity is a hallmark for carcinoma, and its underlying molecular mechanism is beginning to emerge from studies on model organisms and cancer cell lines. Moreover, deregulated expression of apico-basal polarity complex components has been reported in human tumours. In this review, we provide an overview of the apico-basal polarity complexes and their regulation, their role in cell migration, and finally their involvement in carcinogenesis.

Rewiring cell polarity signaling in cancer

Disrupted cell polarity is a feature of epithelial cancers. The Crumbs, Par and Scribble polarity complexes function to specify and maintain apical and basolateral membrane domains, which are essential to organize intracellular signaling pathways that maintain epithelial homeostasis. Disruption of apical-basal polarity proteins facilitates rewiring of oncogene and tumor suppressor signaling pathways to deregulate proliferation, apoptosis, invasion and metastasis. Moreover, apical-basal polarity integrates intracellular signaling with the microenvironment by regulating metabolic signaling, extracellular matrix remodeling and tissue level organization. In this review, we discuss recent advances in our understanding of how polarity proteins regulate diverse signaling pathways throughout cancer progression from initiation to metastasis.