Loss of keratins 8 and 18 leads to alterations in α6β4-integrin-mediated signalling and decreased neoplastic progression in an oral-tumour-derived cell line

ARID2 suppression promotes tumor progression and upregulates cytokeratin 8, 18 and β-4 integrin expression in TP53-mutated tobacco-related oral cancer and has prognostic implications

Mutations in ARID2 and TP53 genes are found to be implicated in the tobacco related tumorigeneses. However, the effect of loss of ARID2 in the TP53 mutated background in tobacco related cancer including oral cancer has not been investigated yet. Hence, in this study we knockdown ARID2 using shRNA mediated knockdown strategy in TP53 mutated oral squamous cell carcinoma (OSCC) cell line and studied its tumorigenic role. Our study revealed that suppression of ARID2 in TP53 mutated oral cancer cells increases cell motility and invasion, induces drastic morphological changes and leads to a marked increase in the expression levels of cytokeratins, and integrins, CK8, CK18 and β4-Integrin, markers of cell migration/invasion in oral cancer. ARID2 suppression also showed early onset and increased tumorigenicity in-vivo. Interestingly, transcriptome profiling revealed differentially expressed genes associated with migration and invasion in oral cancer cells including AKR1C2, NCAM2, NOS1, ADAM23 and genes of S100A family in ARID2 knockdown TP53 mutated oral cancer cells. Pathway analysis of differentially regulated genes identified "cancer pathways" and "PI3K/AKT Pathway" to be significantly dysregulated upon suppression of ARID2 in TP53 mutated OSCC cells. Notably, decreased ARID2 expression and increased CK8, CK18 expression leads to poor prognosis in Head and Neck cancer (HNSC) patients as revealed by Pan-Cancer TCGA data analysis. To conclude, our study is the first to demonstrate tumor suppressor role of ARID2 in TP53 mutated background indicating their cooperative role in OSCC, and also highlights its prognostic implications suggesting ARID2 as an important therapeutic target in OSCC.

The role of fascin-1 in the pathogenesis, diagnosis and management of respiratory related cancers

Human cancer statistics report that respiratory related cancers such as lung, laryngeal, oral and nasopharyngeal cancers account for a large proportion of tumors, and tumor metastasis remains the major reason for patient death. The metastasis of tumor cells requires actin cytoskeleton remodeling, in which fascin-1 plays an important role. Fascin-1 can cross-link F-actin microfilaments into bundles and form finger-like cell protrusions. Some studies have shown that fascin-1 is overexpressed in human tumors and is associated with tumor growth, migration and invasion. The role of fascin-1 in respiratory related cancers is not very clear. The main purpose of this study was to provide an updated literature review on the role of fascin-1 in the pathogenesis, diagnosis and management of respiratory related cancers. These studies suggested that fascin-1 can serve as an emerging biomarker and potential therapeutic target, and has attracted widespread attention.

Utility of Keratins as Biomarkers for Human Oral Precancer and Cancer

Human oral cancer is the single largest group of malignancies in the Indian subcontinent and the sixth largest group of malignancies worldwide. Squamous cell carcinomas (SCC) are the most common epithelial malignancy of the oral cavity, constituting over 90% of oral cancers. About 90% of OSCCs arise from pre-existing, potentially malignant lesions. According to WHO, OSCC has a 5-year survival rate of 45–60%. Late diagnosis, recurrence, and regional or lymph nodal metastases could be the main causes of the high mortality rates. Biomarkers may help categorize and predict premalignant lesions as high risk of developing malignancy, local recurrence, and lymph nodal metastasis. However, at present, there is a dearth of such markers, and this is an area of ongoing research. Keratins (K) or cytokeratins are a group of intermediate filament proteins that show paired and differentiation dependent expression. Our laboratory and others have shown consistent alterations in the expression patterns of keratins in both oral precancerous lesions and tumors. The correlation of these changes with clinicopathological parameters has also been demonstrated. Furthermore, the functional significance of aberrant keratins 8/18 expression in the malignant transformation and progression of oral tumors has also been documented. This article reviews the literature that emphasizes the value of keratins as biomarkers for the prognostication of human oral precancers and cancers.

Generation of a tissue-specific transgenic model for K8 phosphomutants: A tool to investigate the role of K8 phosphorylation during skin carcinogenesis in vivo

Keratin 8/18, the predominant keratin pair of simple epithelia, is known to be aberrantly expressed in several squamous cell carcinomas (SCCs), where its expression is often correlated with increased invasion, neoplastic progression, and poor prognosis. The majority of keratin 8/18 structural and regulatory functions are governed by posttranslational modifications, particularly phosphorylation. Apart from filament reorganization, cellular processes including cell cycle, cell growth, cellular stress, and apoptosis are known to be orchestrated by K8 phosphorylation at specific residues in the head and tail domains. Even though deregulation of K8 phosphorylation at two significant sites (Serine⁷³ /Serine⁴³¹ ) has been implicated in neoplastic progression of SCCs by various in vitro studies, including ours, it is reported to be highly context-dependent. Therefore, to delineate the precise role of Kereatin 8 phosphorylation in cancer initiation and progression, we have developed the tissue-specific transgenic mouse model expressing Keratin 8 wild type and phosphodead mutants under Keratin 14 promoter. Subjecting these mice to 7,12-dimethylbenz(a)anthracene/12-O-tetradecanoylphorbol-13-acetate-mediated skin carcinogenesis revealed that Keratin 8 phosphorylation may lead to an early onset of tumors compared to Keratin 8 wild-type expressing mice. Conclusively, the transgenic mouse model developed in the present study ascertained a positive impact of Keratin 8 phosphorylation on the neoplastic transformation of skin-squamous cells.

The Role of Keratin-8 and Keratin-18 Polymorphisms and Protein Levels in the Occurrence and Progression of Vocal Leukoplakia

OBJECTIVE

This study aimed to evaluate the association between the single-nucleotide polymorphism (SNP) and tissue protein level of keratin-8/18 and the occurrence and progression of vocal leukoplakia.

METHODS

The case-control study enrolled 158 patients with vocal leukoplakia, 326 patients with laryngeal squamous cell carcinoma (LSCC), and 268 healthy controls, which were tested for genotype analysis with keratin-8 and keratin-18 gene polymorphisms using pyrosequencing. The tissue protein expression levels of keratin-8 and keratin-18 were evaluated using immunohistochemistry.

RESULTS

The keratin-8 SNP RS1907671 showed an obvious increased risk for vocal leukoplakia (OR 1.56, p = 0.002), while the other SNPs (RS2035875, RS2035878, RS4300473) were tested as protective factors for vocal leukoplakia and LSCC (OR <1, p < 0.05). In keratin-18 SNP test, both RS2070876 and RS2638526 polymorphisms demonstrated decreased risks for vocal leukoplakia and LSCC (OR <1, p < 0.05). The protein levels of keratin-8 and keratin-18 in vocal leukoplakia group were significantly higher than those of the LSCC group (p < 0.05).

CONCLUSIONS

Keratin-8 and keratin-18 polymorphisms and protein levels are associated with the occurrence and progression of vocal leukoplakia.

Biomarkers of tumor invasiveness in proteomics (Review)

Over the past two decades, quantitative proteomics has emerged as an important tool for deciphering the complex molecular events involved in cancers. The number of references involving studies on the cancer metastatic process has doubled since 2010, while the last 5 years have seen the development of novel technologies combining deep proteome coverage capabilities with quantitative consistency and accuracy. To highlight key findings within this huge amount of information, the present review identified a list of tumor invasive biomarkers based on both the literature and data collected on a biocollection of experimental cell lines, tumor models of increasing invasiveness and tumor samples from patients with colorectal or breast cancer. Crossing these different data sources led to 76 proteins of interest out of 1,245 mentioned in the literature. Information on these proteins can potentially be translated into clinical prospects, since they represent potential targets for the development and evaluation of innovative therapies, alone or in combination. Herein, a systematical review of the biology of each of these proteins, including their specific subcellular/extracellular or multiple localizations is presented. Finally, as an important advantage of quantitative proteomics is the ability to provide data on all these molecules simultaneously in cell pellets, body fluids or paraffin‑embedded sections of tumors/invaded tissues, the significance of some of their interconnections is discussed.

FADS1 promotes the progression of laryngeal squamous cell carcinoma through activating AKT/mTOR signaling

Metabolic abnormality is the major feature of laryngeal squamous cell carcinoma (LSCC), however, the underlying mechanism remain largely elusive. Fatty acid desaturase 1 (FADS1), as the key rate-limiting enzyme of polyunsaturated fatty acids (PUFAs), catalyzes dihomo-gamma-linolenic acid (DGLA) to arachidonic acid (AA). In this study, we reported that the expression of FADS1 was upregulated in LSCC, high FADS1 expression was closely associated with the advanced clinical features and poor prognosis of the recurrent LSCC patients after chemotherapy. Liquid chromatograph-mass spectrometry (LC-MS) analysis revealed that FADS1 overexpression induced greater conversion of DGLA to AA, suggesting an increased activity of FADS1. Similarly, the level of prostaglandin E2 (PGE₂), a downstream metabolite of AA, was also elevated in cancerous laryngeal tissues. Functional assays showed that FADS1 knockdown suppressed the proliferation, migration and invasion of LSCC cells, while FADS1 overexpression had the opposite effects. Bioinformatic analysis based on microarray data found that FADS1 could activate AKT/mTOR signaling. This hypothesis was further validated by both in vivo and in vitro assays. Hence, our data has supported the viewpoint that FADS1 is a potential promoter in LSCC progression, and has laid the foundation for further functional research on the PUFA dietary supplementation interventions targeting FADS1/AKT/mTOR pathway for LSCC prevention and treatment.

Expression of keratins 8, 18, and 19 in epithelia of atrophic oral lichen planus

Keratins form intermediate filaments of the cytoskeleton in keratinocytes and have roles in cell structure, signaling, intracellular transport, and cell death. Oral lichen planus (OLP) is an oral inflammatory disease with derangements in basal keratinocytes and disruption of the basal membrane. Here, we focused on epithelial expression of keratins 8, 18, and 19 because these proteins are known to modulate cell death. Biopsies were taken from buccal oral mucosa of persons with normal oral mucosa (n = 10) or atrophic OLP (n = 10). Cultured normal oral keratinocytes (n = 4) showed expression of mRNA and protein for keratins 8, 18, and 19. Immunohistochemistry showed consistent staining for keratins 8 and 18 in basal keratinocytes of normal oral mucosa. In OLP, staining for keratin (K)8 was mostly negative and staining for K18 was weak. Keratin 19 was expressed irregularly in most biopsies of normal oral mucosa and not at all in OLP. Several mononuclear leukocytes in the cellular infiltrate showed membrane staining for K8 and K18. Positive staining for K16 confirmed partial collapse of the basal cell layer in OLP. The basal cell niche in OLP therefore appeared to be partly populated with keratinocytes demonstrating a higher degree of differentiation (K8^-  K18^-  K19^-  K16⁺ ); consequently, such areas may be more susceptible to the action of cell death factors released from the cell infiltrate as a result of lacking the protective, normal keratin present in the basal epithelial cell layer of normal oral mucosa.

Epithelial-to-mesenchymal transition and invadopodia markers in breast cancer: Lumican a key regulator

A great hallmark of breast cancer is the absence or presence of estrogen receptors ERα and ERβ, with a dominant role in cell proliferation, differentiation and cancer progression. Both receptors are related with Epithelial-to-Mesenchymal Transition (EMT) since there is a relation between ERs and extracellular matrix (ECM) macromolecules expression, and therefore, cell-cell and cell-ECM interactions. The endocrine resistance of ERα endows epithelial cells with increased aggressiveness and induces cell proliferation, resulting into a mesenchymal phenotype and an EMT status. ERα signaling may affect the transcriptional factors which govern EMT. Knockdown or silencing of ERα and ERβ in MCF-7 and MDA-MB-231 breast cancer cells respectively, provoked pivotal changes in phenotype, cellular functions, mRNA and protein levels of EMT markers, and consequently the EMT status. Mesenchymal cells owe their migratory and invasive properties to invadopodia, while in epithelial cells, lamellipodia and filopodia are mostly observed. Invadopodia, are actin-rich protrusions of plasma membrane, promoting proteolytic degradation of ECM and tumor invasion. Cortactin and MMP-14 govern the formation and principal functions of invadopodia. In vitro experiments proved that lumican inhibits cortactin and MMP-14 expression, alters the formation of lamellipodia and transforms mesenchymal cells into epithelial-like. Conclusively, lumican may inhibit or even reverse the several metastatic features that EMT endows in breast cancer cells. Therefore, a lumican-based anti-cancer therapy which will pharmacologically target and inhibit EMT might be interesting to be developed.

Activin A-mediated epithelial de-differentiation contributes to injury repair in an in vitro gastrointestinal reflux model

Reflux esophagitis is a result of esophageal exposure to acid and bile during episodes of gastroesophageal reflux. Aside from chemical injury to the esophageal epithelium, it has been shown that acid and bile induce cytokine-mediated injury by stimulating the release of pro-inflammatory cytokines. During the repair and healing process following reflux injury, the squamous esophageal cells are replaced with a columnar epithelium causing Barrett's metaplasia, which predisposes patients to esophageal adenocarcinoma. We identified a novel player in gastroesophageal reflux injury, the TGFβ family member Activin A (ActA), which is a known regulator of inflammation and tissue repair. In this study, we show that in response to bile salt and acidified media (pH 4) exposure, emulating the milieu to which the distal esophagus is exposed during gastroesophageal reflux, long-term treated, tolerant esophageal keratinocytes exhibit increased ActA secretion and a pro-inflammatory cytokine signature. Furthermore, we noted increased motility and expression of the stem cell markers SOX9, LGR5 and DCLK1 supporting the notion that repair mechanisms were activated in the bile salt/acid-tolerant keratinocytes. Additionally, these experiments demonstrated that de-differentiation as characterized by the induction of YAP1, FOXO3 and KRT17 was altered by ActA/TGFβ signaling. Collectively, our results suggest a pivotal role for ActA in the inflammatory GERD environment by modulating esophageal tissue repair and de-differentiation.

Cytoplasmic Intermediate Filaments in Cell Biology

Intermediate filaments (IFs) are one of the three major elements of the cytoskeleton. Their stability, intrinsic mechanical properties, and cell type-specific expression patterns distinguish them from actin and microtubules. By providing mechanical support, IFs protect cells from external forces and participate in cell adhesion and tissue integrity. IFs form an extensive and elaborate network that connects the cell cortex to intracellular organelles. They act as a molecular scaffold that controls intracellular organization. However, IFs have been revealed as much more than just rigid structures. Their dynamics is regulated by multiple signaling cascades and appears to contribute to signaling events in response to cell stress and to dynamic cellular functions such as mitosis, apoptosis, and migration.

Quantitative phosphoproteomic analysis reveals system-wide signaling pathways regulated by site-specific phosphorylation of Keratin-8 in skin squamous cell carcinoma derived cell line

Keratin 8/18, a simple epithelia specific keratin pair, is often aberrantly expressed in squamous cell carcinomas (SCC) where its expression is correlated with increased invasion and poor prognosis. Majority of Keratin 8 (K8) functions are governed by its phosphorylation at Serine⁷³ (head-domain) and Serine⁴³¹ (tail-domain) residues. Although, deregulation of K8 phosphorylation is associated with progression of different carcinomas, its role in skin-SCC and the underlying mechanism is obscure. In this direction, we performed tandem mass tag-based quantitative phosphoproteomics by expressing K8 wild type, phosphodead, and phosphomimetic mutants in K8-deficient A431 cells. Further analysis of our phosphoproteomics data showed a significant proportion of total phosphoproteome associated with migratory, proliferative, and invasive potential of these cells to be differentially phosphorylated. Differential phosphorylation of CDK1^T14,Y15 , EIF4EBP1^T46,T50 , EIF4B^S422 , AKT1S1^T246,S247 , CTTN1^{T401,S405,Y421} , and CAP1^S307/309 in K8-S73A/D mutant and CTTN1^{T401,S405,Y421} , BUB1B^S1043 , and CARHSP1^S30,S32 in K8-S431A/D mutants as well as some anonymous phosphosites including MYC^S176 , ZYX^S344 , and PNN^S692 could be potential candidates associated with K8 phosphorylation mediated tumorigenicity. Biochemical validation followed by phenotypic analysis further confirmed our quantitative phosphoproteomics data. In conclusion, our study provides the first global picture of K8 site-specific phosphorylation function in neoplastic progression of A431 cells and suggests various potential starting points for further mechanistic studies.

Identification of morphological and biochemical changes in keratin-8/18 knock-down cells using Raman spectroscopy

Accurate understanding of cellular processes and responses to stimuli is of paramount importance in biomedical research and diagnosis. Raman spectroscopy (RS), a label-free and nondestructive spectroscopic method has the potential to serve as a novel 'theranostics' tool. Both fiber-optic and micro-Raman studies have demonstrated efficacy in diagnostics and therapeutic response monitoring. In the present study, we have evaluated the potential of micro-Raman spectroscopic maps in identifying changes induced by loss of K8/18 proteins in a tongue cancer cell line. Furthermore, we also evaluated the efficacy of less expensive and commercially available fiber probes to identify K8/18 wild and knock-down cell pellets, in view of the utility of cell pellet-based studies. The findings suggest that major differences in the cellular morphology and biochemical composition can be objectively identified and can be utilized for classification using both micro-Raman and fiber-probe-based RS. These findings highlight the potential of fiber-optic probe-based RS in noninvasive cellular phenotyping for diagnosis and therapeutic response monitoring, especially in low-resource settings.

Hemidesmosomal linker proteins regulate cell motility, invasion and tumorigenicity in oral squamous cell carcinoma derived cells

BPAG1e and Plectin are hemidesmosomal linker proteins which anchor intermediate filament proteins to the cell surface through β4 integrin. Recent reports indicate that these proteins play a role in various cellular processes apart from their known anchoring function. However, the available literature is inconsistent. Further, the previous study from our laboratory suggested that Keratin8/18 pair promotes cell motility and tumor progression by deregulating β4 integrin signaling in oral squamous cell carcinoma (OSCC) derived cells. Based on these findings, we hypothesized that linker proteins may have a role in neoplastic progression of OSCC. Downregulation of hemidesmosomal linker proteins in OSCC derived cells resulted in reduced cell migration accompanied by alterations in actin organization. Further, decreased MMP9 activity led to reduced cell invasion in linker proteins knockdown cells. Moreover, loss of these proteins resulted in reduced tumorigenic potential. SWATH analysis demonstrated upregulation of N-Myc downstream regulated gene 1 (NDRG1) in linker proteins downregulated cells as compared to vector control cells. Further, the defects in phenotype upon linker proteins ablation were rescued upon loss of NDRG1 in linker proteins knockdown background. These data together indicate that hemidesmosomal linker proteins regulate cell motility, invasion and tumorigenicity possibly through NDRG1 in OSCC derived cells.

Intermediate Filaments and the Regulation of Cell Motility during Regeneration and Wound Healing

SUMMARYIntermediate filaments (IFs) comprise a diverse group of flexible cytoskeletal structures, the assembly, dynamics, and functions of which are regulated by posttranslational modifications. Characteristically, the expression of IF proteins is specific for tissues, differentiation stages, cell types, and functional contexts. Recent research has rapidly expanded the knowledge of IF protein functions. From being regarded as primarily structural proteins, it is now well established that IFs act as powerful modulators of cell motility and migration, playing crucial roles in wound healing and tissue regeneration, as well as inflammatory and immune responses. Although many of these IF-associated functions are essential for tissue repair, the involvement of IF proteins has been established in many additional facets of tissue healing and regeneration. Here, we review the recent progress in understanding the multiple functions of cytoplasmic IFs that relate to cell motility in the context of wound healing, taking examples from studies on keratin, vimentin, and nestin. Wound healing and regeneration include orchestration of a broad range of cellular processes, including regulation of cell attachment and migration, proliferation, differentiation, immune responses, angiogenesis, and remodeling of the extracellular matrix. In this respect, IF proteins now emerge as multifactorial and tissue-specific integrators of tissue regeneration, thereby acting as essential guardian biopolymers at the interface between health and disease, the failing of which contributes to a diverse range of pathologies.

High KRT8 expression promotes tumor progression and metastasis of gastric cancer

Keratin8 (KRT8) is the major component of the intermediate filament cytoskeleton and predominantly expressed in simple epithelial tissues. Aberrant expression of KRT8 is associated with multiple tumor progression and metastasis. However, the role of KRT8 in gastric cancer (GC) remains unclear. In this study, KRT8 expression was investigated and it was found to be upregulated along with human GC progression and metastasis at both mRNA and protein levels in human gastric cancer tissues. In addition, KRT8 overexpression enhanced the proliferation and migration of human gastric cancer cells, whereas the knock‐down of KRT8 by siRNA only inhibited migration of human gastric cancer cells. Integrinβ1‐FAK‐induced epithelial‐mesenchymal‐transition (EMT) only existed in the high KRT8 cells. Furthermore, KRT8 overexpression led to increase in p‐smad2/3 levels and TGFβ dependent signaling events. KRT8 expression in GC was related to tumor clinical stage and worse survival. Kaplan–Meier analysis proved that KRT8 was associated with overall survival of patients with GC that patients with high KRT8 expression tend to have unfavorable outcome. Moreover, Cox's proportional hazards analysis showed that high KRT8 expression was a prognostic marker of poor outcome. These results provided that KRT8 expression may therefore be a biomarker or potential therapeutic target to identify patients with worse survival.

Vimentin regulates differentiation switch via modulation of keratin 14 levels and their expression together correlates with poor prognosis in oral cancer patients

Vimentin is an intermediate filament protein, predominantly expressed in cells of mesenchymal origin, although its aberrant expression is seen in many carcinomas during epithelial mesenchymal transition. In cancer, vimentin expression is associated with the transition from a more differentiated epithelial phenotype to a dedifferentiated state. In view of the perceived role of keratins (Ks) as regulators of differentiation in epithelia, it was important to understand whether vimentin modulates differentiation through the reprogramming of keratins, in transformed cells. To address this, vimentin was stably downregulated in oral cancer derived cells. Further, global keratin profiling was performed after high salt keratin extraction. K5/K14 pair was found to be significantly downregulated, both at protein and mRNA levels upon vimentin downregulation. The previous study from our laboratory has shown a role of the K5/K14 pair in proliferation and differentiation of squamous epithelial cells. Vimentin depleted cells showed an increase in the differentiation state, marked by an increase in the levels of differentiation specific markers K1, involucrin, filaggrin and loricrin while its proliferation status remained unchanged. Rescue experiments with the K5/K14 pair overexpressed in vimentin knockdown background resulted in decreased differentiation state. ΔNp63 emerged as one of the indirect targets of vimentin, through which it modulates the expression levels of K5/K14. Further, immunohistochemistry showed a significant correlation between high vimentin-K14 expression and recurrence/poor survival in oral cancer patients. Thus, in conclusion, vimentin regulates the differentiation switch via modulation of K5/K14 expression. Moreover, vimentin-K14 together may prove to be the novel markers for the prognostication of human oral cancer.

Keratin 13 Is Enriched in Prostate Tubule-Initiating Cells and May Identify Primary Prostate Tumors that Metastasize to the Bone

Background

Benign human prostate tubule-initiating cells (TIC) and aggressive prostate cancer display common traits, including tolerance of low androgen levels, resistance to apoptosis, and microenvironment interactions that drive epithelial budding and outgrowth. TIC can be distinguished from epithelial and stromal cells that comprise prostate tissue via cell sorting based upon Epcam, CD44, and CD49f antigenic profiles. Fetal prostate epithelial cells (FC) possess a similar antigenic profile to adult TIC and are capable of inducing tubule formation. To identify the TIC niche in human prostate tissue, differential keratin (KRT) expression was evaluated.

Results

Gene expression data generated from Affymetrix Gene Chip human U133 Plus 2.0 array of sorted adult and fetal epithelial cells revealed KRT13 to be significantly enriched in FC and TIC compared to basal cells (BC) and luminal cells (LC) (p<0.001). Enriched KRT13 expression was confirmed by RT-PCR and cytospin immunostaining. Immunohistochemical analysis of KRT13 expression revealed rare KRT13⁺ epithelia throughout prostatic ducts/acini in adult tissue specimens and differentiated tubules in 24-week recombinant grafts, In contrast, abundant KRT13 expression was observed in developing ducts/acini in fetal prostate and cord-like structures composing 8-week recombinant grafts. Immunostaining of a prostate tissue microarray revealed KRT13⁺ tumor foci in approximately 9% of cases, and this subset displayed significantly shorter time to recurrence (p = 0.031), metastases (p = 0.032), and decreased overall survival (p = 0.004). Diagnostic prostate needle biopsies (PNBX) from untreated patients with concurrent bone metastases (clinical stage M1) displayed KRT13⁺ tumor foci, as did bone metastatic foci.

Conclusions

The expression profile of KRT13 in benign fetal and adult prostate tissue and in recombinant grafts, as well as the frequency of KRT13 expression in primary and metastatic prostate cancer indicates that it may be a marker of a stem/progenitor-like cell state that is co-opted in aggressive tumor cells. KRT13 is enriched in benign stem-like cells that display androgen-resistance, apoptosis-resistance, and branching morphogenesis properties. Collectively our data demonstrate that KRT13 expression is associated with poor prognosis at multiple stages of disease progression and may represent an important biomarker of adverse outcome in patients with prostate cancer.

Quantitative Proteomic Profiling the Molecular Signatures of Annexin A5 in Lung Squamous Carcinoma Cells

Lung cancer remains the leading cancer killer around the world. It's crucial to identify newer mechanism-based targets to effectively manage lung cancer. Annexin A5 (ANXA5) is a protein kinase C inhibitory protein and calcium dependent phospholipid-binding protein, which may act as an endogenous regulator of various pathophysiological processes. However, its molecular mechanism in lung cancer remains poorly understood. This study was designed to determine the mechanism of ANXA5 in lung cancer with a hope to obtain useful information to provide a new therapeutic target. We used a stable isotope dimethyl labeling based quantitative proteomic method to identify differentially expressed proteins in NSCLC cell lines after ANXA5 transfection. Out of 314 proteins, we identified 26 and 44 proteins that were down- and up-regulated upon ANXA5 modulation, respectively. The IPA analysis revealed that glycolysis and gluconeogenesis were the predominant pathways modulated by ANXA5. Multiple central nodes, namely HSPA5, FN1, PDIA6, ENO1, ALDOA, JUP and KRT6A appeared to occupy regulatory nodes in the protein-protein networks upon ANXA5 modulation. Taken together, ANXA5 appears to have pleotropic effects, as it modulates multiple key signaling pathways, supporting the potential usefulness of ANXA5 as a potential target in lung cancer. This study might provide a new insight into the mechanism of ANXA5 in lung cancer.

14-3-3σ Gene Loss Leads to Activation of the Epithelial to Mesenchymal Transition Due to the Stabilization of c-Jun Protein

Loss of 14-3-3σ has been observed in multiple tumor types; however, the mechanisms by which 14-3-3σ loss leads to tumor progression are not understood. The experiments in this report demonstrate that loss of 14-3-3σ leads to a decrease in the expression of epithelial markers and an increase in the expression of mesenchymal markers, which is indicative of an induction of the epithelial to mesenchymal transition (EMT). The EMT was accompanied by an increase in migration and invasion in the 14-3-3σ(-/-) cells. 14-3-3σ(-/-) cells show increased stabilization of c-Jun, resulting in an increase in the expression of the EMT transcription factor slug. 14-3-3σ induces the ubiquitination and degradation of c-Jun in an FBW7-dependent manner. c-Jun ubiquitination is dependent on the presence of an intact nuclear export pathway as c-Jun is stabilized and localized to the nucleus in the presence of a nuclear export inhibitor. Furthermore, the absence of 14-3-3σ leads to the nuclear accumulation and stabilization of c-Jun, suggesting that 14-3-3σ regulates the subcellular localization of c-Jun. Our results have identified a novel mechanism by which 14-3-3σ maintains the epithelial phenotype by inhibiting EMT and suggest that this property of 14-3-3σ might contribute to its function as a tumor suppressor gene.

Cytokeratin and protein expression patterns in squamous cell carcinoma of the oral cavity provide evidence for two distinct pathogenetic pathways

Squamous cell carcinoma (SCC) of the oral cavity is a morphological heterogeneous disease. Various cytokeratin (CK) expression patterns with different prognostic values have been described, but little is known concerning the underlying biological cell mechanisms. Therefore, the present study investigated 193 cases of oral SCCs using immunohistochemistry for α/β/γ-catenin, glucose transporter 1, caspase-3, X-linked inhibitor of apoptosis protein, hypoxia inducible factor-1α, carbonic anhydrase 9, heat shock protein (hsp) 70, mast/stem cell growth factor receptor, p21, p27, p16, p53, B-cell lymphoma 6, epidermal growth factor receptor, cyclin D1 and CK1, 5/6, 8/18, 10, 14 and 19. Expression patterns were analyzed with biomathematical permutation analysis. The present results revealed a significant association between the expression of low-molecular weight CK8/18 and 19 and a high-tumor grade, β and γ-catenin expression, deregulated cell cycle proteins and a predominant localization of the tumor on the floor of the mouth. By contrast, expression of high-molecular weight CK1, 5/6, 10 and 14 was significantly associated with the expression of p21 and hsp70. In conclusion, the current study presents evidence for the existence of two parallel pathogenetic pathways in oral SCCs, characterized by the expression of low- and high-molecular weight CKs. Additional studies are required to demonstrate the extent that these results may be used to improve therapeutic regimens.

Binding of MMP-9-degraded fibronectin to β6 integrin promotes invasion via the FAK-Src-related Erk1/2 and PI3K/Akt/Smad-1/5/8 pathways in breast cancer

Fibronectin (FN) has been recognized as the key element in promoting cell adhesion, migration and oncogenic transformation. αvβ6 integrin binds with FN in an RGD-dependent manner and is associated with invasion and poor prognosis in many types of cancers. The extracellular matrix (ECM) is commonly degraded and becomes disorganized in cancers. Previous studies have shown that FN can be degraded into fragments by MMP-9 in vitro; MMP-9 expression is upregulated in breast cancer, therefore, the role of degraded FN in breast cancer progression needs to be investigated. In the present study, expression of β6 integrin in breast cancer tissues was analyzed. The data were quite consistent with the hypothesis that β6 integrin expression is an indicator of poor prognosis. Cell surface expression of β6 integrin was correlated with the invasive behavior of the breast cancer cell lines. MMP-9-degraded FN was used to explore its effects on cell invasion and expression of β6 integrin. The results indicated that MMP-9-degraded FN can adjust constituents of the αvβ6 heterodimers at the early phase and significantly elevate amounts of β6 integrin subunits at a later period. To better elucidate the mechanism by which β6 integrin regulates FN-induced cell migration and invasion, we determined the expression and activity of the downstream kinases of β6 integrin, and elucidated that focal adhesion kinase (FAK)-Src interaction promoted the invasion and migration of breast cancer cells after treatment of MMP-9-degraded FN through the Erk1/2 and PI3K/Akt/Smad‑1/5/8 pathways.

CSN5 silencing reverses sorafenib resistance of human hepatocellular carcinoma HepG2 cells

Hepatocellular carcinoma (HCC) is one of the most common tumor types, and is the third leading cause of cancer mortalities worldwide. A large number of patients with HCC are diagnosed at a late stage when the curative treatment of surgical resection and liver transplantation are no longer applicable. Sorafenib has been proved to improve overall survival in advanced HCC; however, drug resistance is common. The present study reported that the CSN5 is correlated with sorafenib resistance of the HCC cell line HepG2/S. Following silencing of CSN5, resistance to sorafenib was reversed, and multi-drug‑resistance proteins, including as adenosine triphosphate binding cassette (ABC)B1, ABCC2 and ABCG2 as well as CDK6, cyclin D1 and B‑cell lymphoma 2 were downregulated. In addition, it was demonstrated that the integrin beta-1, transforming growth factor‑β1 and nuclear factor‑κB pathways were modified by CSN5.

Absence of keratins 8 and 18 in rodent epithelial cell lines associates with keratin gene mutation and DNA methylation: Cell line selective effects on cell invasion

Epithelial-mesenchymal transition (EMT) in carcinoma is associated with dramatic up-regulation of vimentin and down-regulation of the simple-type keratins 8 and 18 (K8/K18), but the mechanisms of these changes are poorly understood. We demonstrate that two commonly-studied murine (CT26) and rat (IEC-6) intestinal cell lines have negligible K8/K18 but high vimentin protein expression. Proteasome inhibition led to a limited increase in K18 but not K8 stabilization, thereby indicating that K8/K18 absence is not due, in large part, to increased protein turnover. CT26 and IEC-6 cells had <10% of normal K8/K18 mRNA and exhibited decreased mRNA stability, with K8 mRNA levels being higher in IEC-6 versus CT26 and K18 being higher in CT26 versus IEC-6 cells. Keratin gene sequencing showed that KRT8 in CT26 cells had a 21-nucleotide deletion while K18 in IEC-6 cells had a 9-amino acid in-frame insertion. Furthermore, the KRT8 promoter in CT26 and the KRT18 promoter in IEC-6 are hypermethylated. Inhibition of DNA methylation using 5-azacytidine increased K8 or K18 in some but all the tested rodent epithelial cell lines. Restoring K8 and K18 by lentiviral transduction reduced CT26 but not IEC-6 cell matrigel invasion. K8/K18 re-introduction also decreased E-cadherin expression in IEC-6 but not CT26 cells, suggesting that the effect of keratin expression on epithelial to mesenchymal transition is cell-line dependent. Therefore, some commonly utilized rodent epithelial cell lines, unexpectedly, manifest barely detectable keratin expression but have high levels of vimentin. In the CT26 and IEC-6 intestinal cell lines, keratin expression correlates with keratin gene insertion or deletion and with promoter methylation, which likely suppress keratin transcription and mRNA or protein stability.

Intermediate filaments in cell migration and invasion: the unusual suspects

Cell migration is a multistep process which relies on the coordination of cytoskeletal structures in space and time. While the roles of actin and microtubules have been investigated in great details, the lack of inhibitors and visualizing tools and the large number of proteins forming intermediate filaments (IFs) have delayed the characterization of IF functions during migration. However, a large body of evidence has progressively pointed to changes in IF composition as an important parameter in the regulation of cell migratory properties both during development and tumor invasion. More recent in-depth analyses show that IFs are dynamically reorganized to participate, together with microfilaments and microtubules, to the key steps leading to cell migration.

Combination of cyclopamine and tamoxifen promotes survival and migration of mcf-7 breast cancer cells--interaction of hedgehog-gli and estrogen receptor signaling pathways

Hedgehog-Gli (Hh-Gli) signaling pathway is one of the new molecular targets found upregulated in breast tumors. Estrogen receptor alpha (ERα) signaling has a key role in the development of hormone-dependent breast cancer. We aimed to investigate the effects of inhibiting both pathways simultaneously on breast cancer cell survival and the potential interactions between these two signaling pathways. ER-positive MCF-7 cells show decreased viability after treatment with cyclopamine, a Hh-Gli pathway inhibitor, as well as after tamoxifen (an ERα inhibitor) treatment. Simultaneous treatment with cyclopamine and tamoxifen on the other hand, causes short-term survival of cells, and increased migration. We found upregulated Hh-Gli signaling under these conditions and protein profiling revealed increased expression of proteins involved in cell proliferation and migration. Therefore, even though Hh-Gli signaling seems to be a good potential target for breast cancer therapy, caution must be advised, especially when combining therapies. In addition, we also show a potential direct interaction between the Shh protein and ERα in MCF-7 cells. Our data suggest that the Shh protein is able to activate ERα independently of the canonical Hh-Gli signaling pathway. Therefore, this may present an additional boost for ER-positive cells that express Shh, even in the absence of estrogen.

Transcriptional repression of histone deacetylase 3 by the histone demethylase KDM2A is coupled to tumorigenicity of lung cancer cells

Dysregulated expression of histone methyltransferases and demethylases is an emerging epigenetic mechanism underlying cancer development and metastasis. We recently showed that the histone H3 lysine 36 (H3K36) demethylase KDM2A (also called FBXL11 and JHDM1A) is necessary for tumorigenic and metastatic capabilities of KDM2A-overexpressing non-small cell lung cancer (NSCLC) cells. Here, we report that KDM2A transcriptionally represses the histone deacetylase 3 (HDAC3) gene by removing methyl groups from dimethylated H3K36 at the HDAC3 promoter in KDM2A-overexpressing NSCLC cells. KDM2A depletion reduced expression levels of cell cycle-associated genes (e.g. CDK6) and cell invasion-related genes (e.g. NANOS1); these levels were rescued by ectopic expression of KDM2A but not its catalytic mutant. These genes were occupied and down-regulated by HDAC3. HDAC3 knockdown significantly recovered the proliferation and invasiveness of KDM2A-depleted NSCLC cells as well as the levels of CDK6 and NANOS1 expression in these cells. Similar to their previously reported functions in other cell types, CDK6 and NANOS1 were required for the proliferation and invasion, respectively, of KDM2A-overexpressing NSCLC cells. In a mouse xenograft model, HDAC3 depletion substantially restored the tumorigenic ability of KDM2A knockdown cells. These findings reveal a novel cancer-epigenetic pathway in which the antagonistic effect of KDM2A on HDAC3 expression releases cell cycle-associated genes and cell invasion-related genes from HDAC3 repression and indicate the importance of this pathway for tumorigenicity and invasiveness of KDM2A-overexpressing NSCLC cells.

Physical biology in cancer. 5. The rocky road of metastasis: the role of cytoskeletal mechanics in cell migratory response to 3D matrix topography

The tumor microenvironment is a milieu of heterogeneous architectural features that affect tumor growth and metastatic invasion. Pore size, density, stiffness, and fiber architecture change dramatically from location to location throughout the tumor matrix. While many studies have addressed the effects of two-dimensional extracellular matrix structure and composition on cell migration, less is known about how cancer cells navigate complex, heterogeneous three-dimensional (3D) microenvironments. Mechanical structures such as actin and keratin, part of the cytoskeletal framework, and lamins, part of the nucleoskeletal framework, play a key role in migration and are altered during cancer progression. Recent evidence suggests that these changes in cytoskeletal and nucleoskeletal structures may enable cancer cells to efficiently respond to features such as pore size and stiffness to invade and migrate. Here we discuss the role of cell mechanics and the cytoskeleton in the ability of cells to navigate and respond to 3D matrix features and heterogeneities.

The role of focal adhesion kinase in the regulation of cellular mechanical properties

The regulation of mechanical properties is necessary for cell invasion into connective tissue or intra- and extravasation through the endothelium of blood or lymph vessels. Cell invasion is important for the regulation of many healthy processes such as immune response reactions and wound healing. In addition, cell invasion plays a role in disease-related processes such as tumor metastasis and autoimmune responses. Until now the role of focal adhesion kinase (FAK) in regulating mechanical properties of cells and its impact on cell invasion efficiency is still not well known. Thus, this review focuses on mechanical properties regulated by FAK in comparison to the mechano-regulating protein vinculin. Moreover, it points out the connection between cancer cell invasion and metastasis and FAK by showing that FAK regulates cellular mechanical properties required for cellular motility. Furthermore, it sheds light on the indirect interaction of FAK with vinculin by binding to paxillin, which then impairs the binding of paxillin to vinculin. In addition, this review emphasizes whether FAK fulfills regulatory functions similar to vinculin. In particular, it discusses the differences and the similarities between FAK and vinculin in regulating the biomechanical properties of cells. Finally, this paper highlights that both focal adhesion proteins, vinculin and FAK, synergize their functions to regulate the mechanical properties of cells such as stiffness and contractile forces. Subsequently, these mechanical properties determine cellular invasiveness into tissues and provide a source sink for future drug developments to inhibit excessive cell invasion and hence, metastases formation.

KDM2A promotes lung tumorigenesis by epigenetically enhancing ERK1/2 signaling

Epigenetic dysregulation has emerged as a major contributor to tumorigenesis. Histone methylation is a well-established mechanism of epigenetic regulation that is dynamically modulated by histone methyltransferases and demethylases. The pathogenic role of histone methylation modifiers in non-small cell lung cancer (NSCLC), which is the leading cause of cancer deaths worldwide, remains largely unknown. Here, we found that the histone H3 lysine 36 (H3K36) demethylase KDM2A (also called FBXL11 and JHDM1A) is frequently overexpressed in NSCLC tumors and cell lines. KDM2A and its catalytic activity were required for in vitro proliferation and invasion of KDM2A-overexpressing NSCLC cells. KDM2A overexpression in NSCLC cells with low KDM2A levels increased cell proliferation and invasiveness. KDM2A knockdown abrogated tumor growth and invasive abilities of NSCLC cells in mouse xenograft models. We identified dual-specificity phosphatase 3 (DUSP3) as a key KDM2A target gene and found that DUSP3 dephosphorylates ERK1/2 in NSCLC cells. KDM2A activated ERK1/2 through epigenetic repression of DUSP3 expression via demethylation of dimethylated H3K36 at the DUSP3 locus. High KDM2A levels correlated with poor prognosis in NSCLC patients. These findings uncover an unexpected role for a histone methylation modifier in activating ERK1/2 in lung tumorigenesis and metastasis, suggesting that KDM2A may be a promising therapeutic target in NSCLC.

Proteomic profile of keratins in cancer of the gingivo buccal complex: consolidating insights for clinical applications

Keratins play a major role in several cellular functions. Each tissue type expresses a specific set of keratins. The immense potential of keratins as diagnostic and prognostic markers for different cancers is emerging. Oral cancer is the fifteenth most common cancer worldwide. However, comprehensive information on the profile of keratins in the oral cavity is not available. Several independent reports have identified keratins using antibody based techniques which have pitfalls due to the cross reactivity of the antibodies to this set of very homologous proteins. A few recent proteomic studies have reported the identification of keratins in head and neck cancer. Majority of the studies have used tissues from the head and neck region without specifying subsites. This study reports the analysis of enriched preparations of keratins from cancer of the gingivo buccal complex (GBC) using MS, 2DE, WB, silver staining of 2DE gels and IHC. Our study reveals the absence of K4 and K13 and presence of K14, K16, and K17, in cancers of the GBC and combination of these expression patterns in the cut margins. This report also shows that K13 is glycosylated. This well characterized profile of keratins may have potential to be used in clinics.

BIOLOGICAL SIGNIFICANCE

In recent years the immense potential of keratins as diagnostic and prognostic markers for different cancers is emerging. However, comprehensive information on the profile of keratins in the oral cavity is not available. Several independent reports have identified keratins using only antibody based techniques which have pitfalls due to the cross reactivity of the antibodies to this set of very homologous proteins. This study reports the analysis of enriched preparations of keratins from a subsite of the oral cavity, the gingivo buccal complex (GBC) using mass spectrometry, 2DE, western blotting, silver staining of 2DE gels and IHC. The proteomic analysis shows the absence of K4 and K13 and presence of K14, K16, and K17 in cancers of the GBC and combination of these expression patterns in the cut margins. This well characterized profile of keratins from the gingivo buccal complex provides defined markers which may have potential to be used in the clinics.

Lumican expression, localization and antitumor activity in prostate cancer

The stromal reaction surrounding tumors leads to the formation of a tumor-specific microenvironment, which may play either a restrictive role or a supportive role in the growth and progression of the tumors. Lumican, a small leucine-rich proteoglycan (SLRP) of the extracellular matrix (ECM), regulates collagen fibrillogenesis. Recently, lumican has also been shown to regulate cell behavior during embryonic development, tissue repair and tumor progression. The role of lumican in cancer varies according to the type of tumor. In this study we analyze the role of lumican in the pathogenesis of prostate cancer both in vivo and in vitro. Overall lumican up-regulation was observed in the primary tumors analyzed through both real-time PCR and immunostaining. The increase in lumican expression was observed in the reactive stroma surrounding prostate primary tumors with fibrotic deposition surrounding the acinar glands. In vitro analysis demonstrated that lumican inhibited both the migration and invasion of metastatic prostate cancer cells isolated from lymph node, bone and brain. Moreover, prostate cancer cells seeded on lumican presented a decrease in the formation of cellular projections, lamellipodia detected by a decreased rearrangement in ZO-1, keratin 8/18, integrin β1 and MT1-MMP, and invadopodia detected by disruption of α-smooth muscle actin, cortactin and N-WASP. Moreover, a significant increase in prostate cancer cell invasion was observed through the peritoneum of lumican knockout mice, further demonstrating the restrictive role lumican present in the ECM has on prostate cancer invasion. In conclusion, lumican present in the reactive stroma surrounding prostate primary tumors plays a restrictive role on cancer progression, and we therefore postulate that lumican could be a valuable marker in prostate cancer staging.

Understanding the role of keratins 8 and 18 in neoplastic potential of breast cancer derived cell lines

Background

Breast cancer is a complex disease which cannot be defined merely by clinical parameters like lymph node involvement and histological grade, or by routinely used biomarkers like estrogen receptor (ER), progesterone receptor (PGR) and epidermal growth factor receptor 2 (HER2) in diagnosis and prognosis. Breast cancer originates from the epithelial cells. Keratins (K) are cytoplasmic intermediate filament proteins of epithelial cells and changes in the expression pattern of keratins have been seen during malignant transformation in the breast. Expression of the K8/18 pair is seen in the luminal cells of the breast epithelium, and its role in prognostication of breast cancer is not well understood.

Methodology/Principal Findings

In this study, we have modulated K8 expression to understand the role of the K8/18 pair in three different breast epithelium derived cell lines: non-transformed MCF10A, transformed but poorly invasive MDA MB 468 and highly invasive MDA MB 435. The up-regulation of K8 in the invasive MDA MB 435 cell line resulted in a significant decrease in proliferation, motility, in-vitro invasion, tumor volume and lung metastasis. The down-regulation of K8 in MDA MB 468 resulted in a significant increase in transformation potential, motility and invasion in-vitro, while MCF10A did not show any changes in cell transformation assays.

Conclusions/Significance

These results indicate the role of K8/18 in modulating invasion in breast cancer -its presence correlating with less invasive phenotype and absence correlating with highly invasive, dedifferentiated phenotype. These data may have important implications for prognostication of breast cancer.

Understanding the role of keratins 8 and 18 in neoplastic potential of breast cancer derived cell lines

BACKGROUND

Breast cancer is a complex disease which cannot be defined merely by clinical parameters like lymph node involvement and histological grade, or by routinely used biomarkers like estrogen receptor (ER), progesterone receptor (PGR) and epidermal growth factor receptor 2 (HER2) in diagnosis and prognosis. Breast cancer originates from the epithelial cells. Keratins (K) are cytoplasmic intermediate filament proteins of epithelial cells and changes in the expression pattern of keratins have been seen during malignant transformation in the breast. Expression of the K8/18 pair is seen in the luminal cells of the breast epithelium, and its role in prognostication of breast cancer is not well understood.

METHODOLOGY/PRINCIPAL FINDINGS

In this study, we have modulated K8 expression to understand the role of the K8/18 pair in three different breast epithelium derived cell lines: non-transformed MCF10A, transformed but poorly invasive MDA MB 468 and highly invasive MDA MB 435. The up-regulation of K8 in the invasive MDA MB 435 cell line resulted in a significant decrease in proliferation, motility, in-vitro invasion, tumor volume and lung metastasis. The down-regulation of K8 in MDA MB 468 resulted in a significant increase in transformation potential, motility and invasion in-vitro, while MCF10A did not show any changes in cell transformation assays.

CONCLUSIONS/SIGNIFICANCE

These results indicate the role of K8/18 in modulating invasion in breast cancer -its presence correlating with less invasive phenotype and absence correlating with highly invasive, dedifferentiated phenotype. These data may have important implications for prognostication of breast cancer.

Cav1 suppresses tumor growth and metastasis in a murine model of cutaneous SCC through modulation of MAPK/AP-1 activation

Caveolin-1 (Cav1) is a scaffolding protein that serves to regulate the activity of several signaling molecules. Its loss has been implicated in the pathogenesis of several types of cancer, but its role in the development and progression of cutaneous squamous cell carcinoma (cSCC) remains largely unexplored. Herein, we use the keratinocyte cell line PAM212, a murine model of cSCC, to determine the function of Cav1 in skin tumor biology. We first show that Cav1 overexpression decreases cell and tumor growth, whereas Cav1 knockdown increases these attributes in PAM212 cells. In addition, Cav1 knockdown increases the invasive ability and incidence of spontaneous lymph node metastasis. Finally, we demonstrate that Cav1 knockdown increases extracellular signaling-related kinase 1/2 mitogen-activated protein kinase/activator protein-1 pathway activation. We attribute the growth and invasive advantage conferred by Cav1 knockdown to increased expression of activator protein-1 transcriptional targets, including cyclin D1 and keratin 18, which show inverse expression in PAM212 based on the expression level of Cav1. In summary, we demonstrate that loss of Cav1 affects several characteristics associated with aggressive human skin tumors and that this protein may be an important modulator of tumor growth and invasion in cSCC.

Alterations in keratins and associated proteins during 4- Nitroquinoline-1-oxide induced rat oral carcinogenesis

Background:

Oral squamous cell carcinoma (OSCC) is the sixth largest group of malignancies globally and the single largest group of malignancies in the Indian subcontinent. Despite the advances in treatment and therapeutic modalities the five year survival rate of OSCC has not changed in the last few decades, and remains less than 40%. Several studies have focused on defining molecular markers that can either detect cancer at an early stage or can predict patient's outcome. However, such markers are still undefined. Keratins (K) are epithelia predominant intermediate filament proteins which are expressed in a differentiation dependent and site specific manner. Keratins are being used as biomarkers in different epithelial disorders including cancer. They are associated with desmoplakin and α6β4 integrin which are components of desmosomes and hemidesmosomes respectively.

Materials and Methods:

4-Nitroquinoline 1-Oxide (4NQO) was used as a carcinogen for the development of various stages of oral carcinogenesis in rat lingual mucosa. Two-Dimentional gel electrophoresis was performed for the separation of Keratins followed by western blotting for their specific identification. Western blotting and RT PCR was carried out for desmoplakin and α6β4 integrin respectively to understand their levels. Immunohistochemical analysis was carried out to further study the localization of desmoplakin and α6 integrin.

Results:

In this study we have analysed the alterations in Keratins and associated proteins during sequential stages of 4NQO induced rat oral carcinogenesis. Our results showed that the alterations primarily begin after the dysplastic changes in the lingual epithelium like the elevation of Keratins 5/6a, ectopic expression of Keratin 8, increase in suprabasal expression of α6 integrin and increase in desmoplakin levels. Most of these alterations persisted till the development of SCC except desmoplakin, the levels of which were downregulated in papillomatous lesions and SCC. Many of these alterations have also been documented in human oral carcinogensis.

Conclusion:

Thus, 4NQO model of rat lingual carcinogenesis reproduces majority of the changes that are seen in human oral carcinogenesis and it can be exploited for the development of biomarkers.

Keratin 8/18 regulation of glucose metabolism in normal versus cancerous hepatic cells through differential modulation of hexokinase status and insulin signaling

As differentiated cells, hepatocytes primarily metabolize glucose for ATP production through oxidative phosphorylation of glycolytic pyruvate, whereas proliferative hepatocellular carcinoma (HCC) cells undergo a metabolic shift to aerobic glycolysis despite oxygen availability. Keratins, the intermediate filament (IF) proteins of epithelial cells, are expressed as pairs in a lineage/differentiation manner. Hepatocyte and HCC (hepatoma) cell IFs are made solely of keratins 8/18 (K8/K18), thus providing models of choice to address K8/K18 IF functions in normal and cancerous epithelial cells. Here, we demonstrate distinctive increases in glucose uptake, glucose-6-phosphate formation, lactate release, and glycogen formation in K8/K18 IF-lacking hepatocytes and/or hepatoma cells versus their respective IF-containing counterparts. We also show that the K8/K18-dependent glucose uptake/G6P formation is linked to alterations in hexokinase I/II/IV content and localization at mitochondria, with little effect on GLUT1 status. In addition, we find that the insulin-stimulated glycogen formation in normal hepatocytes involves the main PI-3 kinase-dependent signaling pathway and that the K8/K18 IF loss makes them more efficient glycogen producers. In comparison, the higher insulin-dependent glycogen formation in K8/K18 IF-lacking hepatoma cells is associated with a signaling occurring through a mTOR-dependent pathway, along with an augmentation in cell proliferative activity. Together, the results uncover a key K8/K18 regulation of glucose metabolism in normal and cancerous hepatic cells through differential modulations of mitochondrial HK status and insulin-mediated signaling.

Keratin 8/18 regulation of cell stiffness-extracellular matrix interplay through modulation of Rho-mediated actin cytoskeleton dynamics

Cell mechanical activity generated from the interplay between the extracellular matrix (ECM) and the actin cytoskeleton is essential for the regulation of cell adhesion, spreading and migration during normal and cancer development. Keratins are the intermediate filament (IF) proteins of epithelial cells, expressed as pairs in a lineage/differentiation manner. Hepatic epithelial cell IFs are made solely of keratins 8/18 (K8/K18), hallmarks of all simple epithelia. Notably, our recent work on these epithelial cells has revealed a key regulatory function for K8/K18 IFs in adhesion/migration, through modulation of integrin interactions with ECM, actin adaptors and signaling molecules at focal adhesions. Here, using K8-knockdown rat H4 hepatoma cells and their K8/K18-containing counterparts seeded on fibronectin-coated substrata of different rigidities, we show that the K8/K18 IF-lacking cells lose their ability to spread and exhibit an altered actin fiber organization, upon seeding on a low-rigidity substratum. We also demonstrate a concomitant reduction in local cell stiffness at focal adhesions generated by fibronectin-coated microbeads attached to the dorsal cell surface. In addition, we find that this K8/K18 IF modulation of cell stiffness and actin fiber organization occurs through RhoA-ROCK signaling. Together, the results uncover a K8/K18 IF contribution to the cell stiffness-ECM rigidity interplay through a modulation of Rho-dependent actin organization and dynamics in simple epithelial cells.

Plakophilin3 loss leads to an increase in PRL3 levels promoting K8 dephosphorylation, which is required for transformation and metastasis

The desmosome anchors keratin filaments in epithelial cells leading to the formation of a tissue wide IF network. Loss of the desmosomal plaque protein plakophilin3 (PKP3) in HCT116 cells, leads to an increase in neoplastic progression and metastasis, which was accompanied by an increase in K8 levels. The increase in levels was due to an increase in the protein levels of the Phosphatase of Regenerating Liver 3 (PRL3), which results in a decrease in phosphorylation on K8. The increase in PRL3 and K8 protein levels could be reversed by introduction of an shRNA resistant PKP3 cDNA. Inhibition of K8 expression in the PKP3 knockdown clone S10, led to a decrease in cell migration and lamellipodia formation. Further, the K8 PKP3 double knockdown clones showed a decrease in colony formation in soft agar and decreased tumorigenesis and metastasis in nude mice. These results suggest that a stabilisation of K8 filaments leading to an increase in migration and transformation may be one mechanism by which PKP3 loss leads to tumor progression and metastasis.

Keratins: markers and modulators of liver disease

PURPOSE OF REVIEW

Keratins are a subgroup of intermediate filaments expressed in the epithelia. Keratins emerged as important tissue-protecting genes and keratin variants cause/predispose to development of more than 50 human disorders. Our review focuses on the importance of keratins in context of liver disease.

RECENT FINDINGS

K8/K18 variants are found in approximately 4% of white population and predispose to development and adverse outcome of multiple liver diseases. K8/K18 are major constituents of Mallory-Denk bodies, that is inclusions found in alcoholic and nonalcoholic steatohepatitis (NASH) and dysregulated keratin expression, K8 hyperphosphorylation, misfolding and crosslinking via transglutaminase 2 facilitate aggregate formation. Necrosis-generated and apoptosis-generated keratin serum fragments are emerging as important noninvasive markers of multiple liver diseases, particularly NASH. Keratins are established markers of tumor origin and in hepatocellular carcinoma, K19 expression is associated with poor prognosis.

SUMMARY

Keratins are established tumor markers and are widely used as noninvasive markers of liver injury. In addition, the data that have become available in recent years have greatly advanced our understanding of keratins as modifiers of liver disease development.

Fascin overexpression promotes neoplastic progression in oral squamous cell carcinoma

Background

Fascin is a globular actin cross-linking protein, which plays a major role in forming parallel actin bundles in cell protrusions and is found to be associated with tumor cell invasion and metastasis in various type of cancers including oral squamous cell carcinoma (OSCC). Previously, we have demonstrated that fascin regulates actin polymerization and thereby promotes cell motility in K8-depleted OSCC cells. In the present study we have investigated the role of fascin in tumor progression of OSCC.

Methods

To understand the role of fascin in OSCC development and/or progression, fascin was overexpressed along with vector control in OSCC derived cells AW13516. The phenotype was studied using wound healing, Boyden chamber, cell adhesion, Hanging drop, soft agar and tumorigenicity assays. Further, fascin expression was examined in human OSCC samples (N = 131) using immunohistochemistry and level of its expression was correlated with clinico-pathological parameters of the patients.

Results

Fascin overexpression in OSCC derived cells led to significant increase in cell migration, cell invasion and MMP-2 activity. In addition these cells demonstrated increased levels of phosphorylated AKT, ERK1/2 and JNK1/2. Our in vitro results were consistent with correlative studies of fascin expression with the clinico-pathological parameters of the OSCC patients. Fascin expression in OSCC showed statistically significant correlation with increased tumor stage (P = 0.041), increased lymph node metastasis (P = 0.001), less differentiation (P = 0.005), increased recurrence (P = 0.038) and shorter survival (P = 0.004) of the patients.

Conclusion

In conclusion, our results indicate that fascin promotes tumor progression and activates AKT and MAPK pathways in OSCC-derived cells. Further, our correlative studies of fascin expression in OSCC with clinico-pathological parameters of the patients indicate that fascin may prove to be useful in prognostication and treatment of OSCC.

Lectin site ligation of CR3 induces conformational changes and signaling

Neutrophils provide an innate immune response to tissues infected with fungal pathogens such as Candida albicans. This response is tightly regulated in part through the interaction of integrins with extracellular matrix ligands that are distributed within infected tissues. The β(2) integrin, CR3 (CD11b/CD18), is unique among integrins in containing a lectin-like domain that binds the fungal pathogen-associated molecular pattern β-glucan and serves as the dominant receptor for recognition of fungal pathogens by human granulocytes. β-Glucan, when isolated in soluble form, has been shown to be a safe and effective immune potentiator when administered therapeutically. Currently a pharmaceutical grade preparation of β-glucan is in several clinical trials with an anti-cancer indication. CR3 binding of extracellular matrix, carbohydrate, or both ligands simultaneously differentially regulates neutrophil function through a mechanism not clearly understood. Using FRET reporters, we interrogated the effects of soluble β-glucan on intracellular and extracellular CR3 structure. Although the canonical CR3 ligand fibrinogen induced full activation, β-glucan alone or in conjunction with fibrinogen stabilized an intermediate conformation with moderate headpiece extension and full cytoplasmic tail separation. A set of phosphopeptides differentially regulated by β-glucan in a CR3-dependent manner were identified using functional proteomics and found to be enriched for signaling molecules and proteins involved in transcriptional regulation, mRNA processing, and alternative splicing. These data confirm that CR3 is a signaling pattern recognition receptor for β-glucan and represent the first direct evidence of soluble β-glucan binding and affecting a signaling-competent intermediate CR3 conformation on living cells.

Loss of keratin 8 phosphorylation leads to increased tumor progression and correlates with clinico-pathological parameters of OSCC patients

BACKGROUND

Keratins are cytoplasmic intermediate filament proteins expressed in tissue specific and differentiation dependent manner. Keratins 8 and 18 (K8 and K18) are predominantly expressed in simple epithelial tissues and perform both mechanical and regulatory functions. Aberrant expression of K8 and K18 is associated with neoplastic progression, invasion and poor prognosis in human oral squamous cell carcinomas (OSCCs). K8 and K18 undergo several post-translational modifications including phosphorylation, which are known to regulate their functions in various cellular processes. Although, K8 and K18 phosphorylation is known to regulate cell cycle, cell growth and apoptosis, its significance in cell migration and/or neoplastic progression is largely unknown. In the present study we have investigated the role of K8 phosphorylation in cell migration and/or neoplastic progression in OSCC.

METHODOLOGY AND PRINCIPAL FINDINGS

To understand the role of K8 phosphorylation in neoplastic progression of OSCC, shRNA-resistant K8 phospho-mutants of Ser73 and Ser431 were overexpressed in K8-knockdown human AW13516 cells (derived from SCC of tongue; generated previously). Wound healing assays and tumor growth in NOD-SCID mice were performed to analyze the cell motility and tumorigenicity respectively in overexpressed clones. The overexpressed K8 phospho-mutants clones showed significant increase in cell migration and tumorigenicity as compared with K8 wild type clones. Furthermore, loss of K8 Ser73 and Ser431 phosphorylation was also observed in human OSCC tissues analyzed by immunohistochemistry, where their dephosphorylation significantly correlated with size, lymph node metastasis and stage of the tumor.

CONCLUSION AND SIGNIFICANCE

Our results provide first evidence of a potential role of K8 phosphorylation in cell migration and/or tumorigenicity in OSCC. Moreover, correlation studies of K8 dephosphorylation with clinico-pathological parameters of OSCC patients also suggest its possible use in prognostication of human OSCC.

Novel function of keratins 5 and 14 in proliferation and differentiation of stratified epithelial cells

Keratin expression in stratified epithelia is tightly regulated during squamous cell differentiation. Keratins 5 and 14 are expressed in mitotically active basal layer cells, but their function is not well defined. Reported here is the possible role of K14 in regulation of cell proliferation/differentiation in stratified epithelial cells.

Keratins are cytoplasmic intermediate filament proteins preferentially expressed by epithelial tissues in a site-specific and differentiation-dependent manner. The complex network of keratin filaments in stratified epithelia is tightly regulated during squamous cell differentiation. Keratin 14 (K14) is expressed in mitotically active basal layer cells, along with its partner keratin 5 (K5), and their expression is down-regulated as cells differentiate. Apart from the cytoprotective functions of K14, very little is known about K14 regulatory functions, since the K14 knockout mice show postnatal lethality. In this study, K14 expression was inhibited using RNA interference in cell lines derived from stratified epithelia to study the K14 functions in epithelial homeostasis. The K14 knockdown clones demonstrated substantial decreases in the levels of the K14 partner K5. These cells showed reduction in cell proliferation and delay in cell cycle progression, along with decreased phosphorylated Akt levels. K14 knockdown cells also exhibited enhanced levels of activated Notch1, involucrin, and K1. In addition, K14 knockdown AW13516 cells showed significant reduction in tumorigenicity. Our results suggest that K5 and K14 may have a role in maintenance of cell proliferation potential in the basal layer of stratified epithelia, modulating phosphatidylinositol 3-kinase/Akt–mediated cell proliferation and/or Notch1-dependent cell differentiation.