Caveolin-1 Inhibits the Growth of Human Laryngeal Squamous Cell Carcinoma and Down Regulates EGFR-MAPKs Signaling Pathway

Involvement of caveolin-1 in skin diseases

The skin is the outermost layer and largest organ in the human body. Since the skin interfaces with the environment, it has a variety of roles, including providing a protective barrier against external factors, regulating body temperature, and retaining water in the body. It is also involved in the immune system, interacting with immune cells residing in the dermis. Caveolin-1 (CAV-1) is essential for caveolae formation and has multiple functions including endocytosis, lipid homeostasis, and signal transduction. CAV-1 is known to interact with a variety of signaling molecules and receptors and may influence cell proliferation and migration. Several skin-related disorders, especially those of the inflammatory or hyperproliferative type such as skin cancers, psoriasis, fibrosis, and wound healing, are reported to be associated with aberrant CAV-1 expression. In this review, we have explored CAV-1 involvement in skin physiology and skin diseases.

Mechanisms underlying Nrf2 nuclear translocation by non-lethal levels of hydrogen peroxide: p38 MAPK-dependent neutral sphingomyelinase2 membrane trafficking and ceramide/PKCζ/CK2 signaling

Hydrogen peroxide is an aerobic metabolite playing a central role in redox signaling and oxidative stress. H₂O₂ could activate redox sensitive transcription factors, such as Nrf2, AP-1 and NF-κB by different manners. In some cells, treatment with non-lethal levels of H₂O₂ induces rapid activation of Nrf2, which upregulates expression of a set of genes involved in glutathione (GSH) synthesis and defenses against oxidative damage. It depends on two steps, the rapid translational activation of Nrf2 and facilitation of Nrf2 nuclear translocation. We review the molecular mechanisms by which H₂O₂ induces nuclear translocation of Nrf2 in cultured cells by highlighting the role of neutral sphingomyelinase 2 (nSMase2), a GSH sensor. H₂O₂ enters cells through aquaporin channels in the plasma membrane and is rapidly reduced to H₂O by GSH peroxidases to consume cellular GSH, resulting in nSMase2 activation to generate ceramide. H₂O₂ also activates p38 MAP kinase, which enhances transfer of nSMase2 from perinuclear regions to plasma membrane lipid rafts to accelerate ceramide generation. Low levels of ceramide activate PKCζ, which then activates casein kinase 2 (CK2). These protein kinases are able to phosphorylate Nrf2 to stabilize and activate it. Notably, Nrf2 also binds to caveolin-1 (Cav1), which protects Nrf2 from Keap1-mediated degradation and limits Nrf2 nuclear translocation. We propose that Cav1serves as a signaling hub for the control of H₂O₂-mediated phosphorylation of Nrf2 by kinases, which results in release of Nrf2 from Cav1 to facilitate nuclear translocation. In summary, H₂O₂ induces GSH depletion which is recovered by Nrf2 activation dependent on p38/nSMase2/ceramide signaling.

Cav1/EREG/YAP Axis in the Treatment Resistance of Cav1-Expressing Head and Neck Squamous Cell Carcinoma

Simple Summary

The EGFR-targeting antibody cetuximab (CTX) combined with radiotherapy has been proven effective for the treatment of locally advanced head and neck squamous cell carcinoma (LA-HNSCC). Due to resistance to CTX, some patients do not benefit from the treatment and recurrence is observed. As caveolin-1 (Cav1) has been reported to affect the EGFR pathway, we aimed to elucidate how it might affect the response to CTX-radiotherapy. We showed that Cav1 expression conferred surviving, growing and motile capacities that protect cells against the combination of CTX-radiotherapy. The protecting effects of Cav1 are mediated by the Cav1/EREG/YAP axis. We also showed in a retrospective study that a high expression of Cav1 was predictive of locoregional relapse of LA-HNSCC. Cav1 should be taken into consideration in the future as a prognosis marker to identify the subgroup of advanced HNSCC at higher risk of recurrence, but also to help clinicians to choose the more appropriate therapeutic strategies.

Abstract

The EGFR-targeting antibody cetuximab (CTX) combined with radiotherapy is the only targeted therapy that has been proven effective for the treatment of locally advanced head and neck squamous cell carcinoma (LA-HNSCC). Recurrence arises in 50% of patients with HNSCC in the years following treatment. In clinicopathological practice, it is difficult to assign patients to classes of risk because no reliable biomarkers are available to predict the outcome of HPV-unrelated HNSCC. In the present study, we investigated the role of Caveolin-1 (Cav1) in the sensitivity of HNSCC cell lines to CTX-radiotherapy that might predict HNSCC relapse. Ctrl- and Cav-1-overexpressing HNSCC cell lines were exposed to solvent, CTX, or irradiation, or exposed to CTX before irradiation. Growth, clonogenicity, cell cycle progression, apoptosis, metabolism and signaling pathways were analyzed. Cav1 expression was analyzed in 173 tumor samples and correlated to locoregional recurrence and overall survival. We showed that Cav1-overexpressing cells demonstrate better survival capacities and remain proliferative and motile when exposed to CTX-radiotherapy. Resistance is mediated by the Cav1/EREG/YAP axis. Patients whose tumors overexpressed Cav1 experienced regional recurrence a few years after adjuvant radiotherapy ± chemotherapy. Together, our observations suggest that a high expression of Cav1 might be predictive of locoregional relapse of LA-HNSCC.

The different functions and clinical significances of caveolin-1 in human adenocarcinoma and squamous cell carcinoma

Caveolin-1 (Cav-1), a major structural protein of caveolae, is an integral membrane protein which plays an important role in the progression of carcinoma. However, whether Cav-1 acts as a tumor promoter or a tumor suppressor still remains controversial. For example, the tumor-promoting function of Cav-1 has been found in renal cancer, prostate cancer, tongue squamous cell carcinoma (SCC), lung SCC and bladder SCC. In contrast, Cav-1 also plays an inhibitory role in esophagus adenocarcinoma, lung adenocarcinoma and cutaneous SCC. The role of Cav-1 is still controversial in thyroid cancer, hepatocellular carcinoma, gastric adenocarcinoma, colon adenocarcinoma, breast cancer, pancreas cancer, oral SCC, laryngeal SCC, head and neck SCC, esophageal SCC and cervical SCC. Besides, it has been reported that the loss of stromal Cav-1 might predict poor prognosis in breast cancer, gastric cancer, pancreas cancer, prostate cancer, oral SCC and esophageal SCC. However, the accumulation of stromal Cav-1 has been found to be promoted by the progression of tongue SCC. Taken together, Cav-1 seems playing a different role in different cancer subtypes even of the same organ, as well as acting differently in the same cancer subtype of different organs. Thus, we hereby explore the functions of Cav-1 in human adenocarcinoma and SCC from the perspective of clinical significances and pathogenesis. We envision that novel targets may come with the further investigation of Cav-1 in carcinogenesis.

The prognostic role of E-cadherin and β-catenin overexpression in laryngeal squamous cell carcinoma

OBJECTIVES/HYPOTHESIS

Epithelial-to-mesenchymal transition (EMT) consists of a rapid and reversible change in the cellular phenotype toward the mesenchymal cell phenotype that facilitates cell migration and invasion of the tumor into surrounding tissues followed by metastasis. In the present study, we sought to determine the clinical significance of E-cadherin, N-cadherin, β-catenin, α-catenin, γ-catenin, caveolin-1, and vimentin in a cohort of patients with stage I to IVA laryngeal squamous cell carcinoma (LSCC) treated with surgery with or without adjuvant therapy using immunohistochemical analyses.

STUDY DESIGN

Individual retrospective cohort study.

METHODS

E-cadherin, N-cadherin, β-catenin, α-catenin, γ-catenin, caveolin-1, and vimentin immunohistochemical expression were evaluated in a cohort of 82 patients with stages I to IVA LSCC. The Fisher exact test was used for categorical variables, and the Mann-Whitney test where appropriate for continuous variables. Survival comparisons was performed using the log-rank test. A multivariate analysis using the Cox proportional hazards model was performed and considered all EMT markers.

RESULTS

In multivariate analysis, T stage was an independent risk factor for adverse disease-specific survival (DSS) and overall survival (OS) (P = .025 and .019, respectively). Cytoplasmic β-catenin overexpression was independently associated with a longer DSS (P = .0007), and E-cadherin overexpression was found to be an independent risk factor for poor OS (P = .030).

CONCLUSIONS

E-cadherin and β-catenin pathways could represent future therapeutic targets in the treatment of LSCC. However, validation of our results in prospective cohorts of patients with LSCCs is required before their clinical implementation.

LEVEL OF EVIDENCE

NA.

Caveolin-1 aggravates cigarette smoke extract-induced MUC5AC secretion in human airway epithelial cells

Airway mucus hypersecretion is a major pathological characteristic of chronic obstructive pulmonary disease (COPD), and cigarette smoke is highly implicated in mucus secretion and the development of COPD. Cigarette smoke reportedly induces mucin overproduction through the epidermal growth factor receptor (EGFR) in the airway epithelium; however, the underlying mechanisms responsible for the activation of EGFR remain unknown. Caveolin-1, a component protein in the cytomembrane, reportedly regulates airway inflammation and lung injury. In this study, we aimed to determine whether caveolin-1 modulates mucin hyperproduction induced by cigarette smoke. Our results revealed that cigarette smoke extract (CSE) significantly increased MUC5AC production, as well as the levels of phosphorylated EGFR (p-EGFR) and phosphorylated Akt (p-Akt) in human bronchial epithelial cells (16HBE cells), as shown by ELISA, RT-PCR and western blot analysis. These effects were prevented by treatment with EGFR inhibitor (AG1478) and phosphatidylinostol-3-kinase (PI3K) inhibitor (LY294002). We also found that the overexpression of caveolin-1 enhanced the expression of MUC5AC, p-EGFR and p-Akt induced by CSE. Conversely, the downregulation of caveolin-1 by siRNA against caveolin-1 inhibited the expression of MUC5AC, p-EGFR and p-Akt. Taken together, our data suggest that caveolin-1 enhances CSE-induced MUC5AC hypersecretion through the EGFR/PI3K/Akt signaling pathway.

Caveolin-1 promotes gastric cancer progression by up-regulating epithelial to mesenchymal transition by crosstalk of signalling mechanisms under hypoxic condition

Gastric cancer is the second most fatal common form of cancer. The crosstalk among signalling pathways that results in the acceleration of epithelial to mesenchymal transition (EMT) plays a pivotal role in the molecular mechanism of gastric carcinogenesis. To understand the role of caveolin-1 (Cav-1), the expression pattern was studied in human gastric adenocarcinoma tissues and also in AGS and KATO III cell lines. Here, we show that during hypoxic condition, the increase in the levels of hypoxia-inducible factor-1α (HIF-1α) results in a significant decrease in the expression of caveolin-1 which is regulated by heat shock protein 90 (HSP90). The reduced levels of Cav-1 correlated with the increased epidermal growth factor receptor (EGFR) activation resulting in the significant activation of its downstream target STAT3. Accumulation of pSTAT3 in the nucleus results in the decreased expression of E-cadherin and increased expression of mesenchymal markers (Slug, α-SMA, N-cadherin and vimentin). Crosstalk of EGFR and transforming growth factor β (TGF-β) signalling with Wnt signalling enhances cell proliferation, cell survival and upregulates EMT. There was no significant alteration in the expression of epithelial and mesenchymal molecules in both the cell lines studied. Thus, we provide evidence that Cav-1 was modulated by HSP90 and functions as a crucial regulator of EMT in gastric cancer.

Hepatitis B virus X protein suppresses caveolin-1 expression in hepatocellular carcinoma by regulating DNA methylation

Background

To understand the molecular mechanisms of caveolin-1 downregulation by hepatitis B virus X protein (HBx).

Methods

The DNA methylation status of the caveolin-1 promoter was examined by nested methylation-specific PCR of 33 hepatitis B virus (HBV)-infected hepatocellular carcinoma (HCC) samples. The SMMC-7721 hepatoma cell line was transfected with a recombinant HBx adenoviral vector, and the effects of HBx protein on caveolin-1 expression and promoter methylation were examined and confirmed by sequencing. A reporter gene containing the caveolin-1 promoter region was constructed, and the effects of HBx on the transcriptional activity of the promoter were also studied.

Results

Methylation of the caveolin-1 promoter was detected in 84.8% (28/33) of HBV-infected HCC samples. Expression of caveolin-1 was significantly downregulated (P = 0.022), and multiple CpG sites in the promoter region of caveolin-1 were methylated in SMMC-7721 cells after HBx transfection. Transfected HBx significantly suppressed caveolin-1 promoter activity (P = 0.001).

Conclusions

HBx protein induces methylation of the caveolin-1 promoter region and suppresses its expression.

Integrin alpha1beta1 regulates epidermal growth factor receptor activation by controlling peroxisome proliferator-activated receptor gamma-dependent caveolin-1 expression

Integrin alpha1beta1 negatively regulates the generation of profibrotic reactive oxygen species (ROS) by inhibiting epidermal growth factor receptor (EGFR) activation; however, the mechanism by which it does this is unknown. In this study, we show that caveolin-1 (Cav-1), a scaffolding protein that binds integrins and controls growth factor receptor signaling, participates in integrin alpha1beta1-mediated EGFR activation. Integrin alpha1-null mesangial cells (MCs) have reduced Cav-1 levels, and reexpression of the integrin alpha1 subunit increases Cav-1 levels, decreases EGFR activation, and reduces ROS production. Downregulation of Cav-1 in wild-type MCs increases EGFR phosphorylation and ROS synthesis, while overexpression of Cav-1 in the integrin alpha1-null MCs decreases EGFR-mediated ROS production. We further show that integrin alpha1-null MCs have increased levels of activated extracellular signal-regulated kinase (ERK), which leads to reduced activation of peroxisome proliferator-activated receptor gamma (PPARgamma), a transcription factor that positively regulates Cav-1 expression. Moreover, activation of PPARgamma or inhibition of ERK increases Cav-1 levels in the integrin alpha1-null MCs. Finally, we show that glomeruli of integrin alpha1-null mice have reduced levels of Cav-1 and activated PPARgamma but increased levels of phosphorylated EGFR both at baseline and following injury. Thus, integrin alpha1beta1 negatively regulates EGFR activation by positively controlling Cav-1 levels, and the ERK/PPARgamma axis plays a key role in regulating integrin alpha1beta1-dependent Cav-1 expression and consequent EGFR-mediated ROS production.

Caveolin-1 acts as a tumor suppressor by down-regulating epidermal growth factor receptor-mitogen-activated protein kinase signaling pathway in pancreatic carcinoma cell lines

OBJECTIVE

To investigate the effect of caveolin-1 (cav1) in pancreatic carcinoma panc1 cell growth in vitro and in vivo.

METHODS

Caveolin-1 gene was transferred into panc1 cells, and stably overexpressed cav1 clones were established. Proliferation and anchorage-independent growth capacity in vitro were detected by 3-[4,5-dimethylthiazol-2-yl]-2,5-diphenyltetrazolium bromide and colony formation assays in soft agar. Flow cytometry was used to analyze cell cycle and apoptosis. The invasion ability was measured by Transwell invasion assay. Activities of signal molecules in epidermal growth factor receptor-mitogen-activated protein kinase (EGFR-MAPK) signal pathway were determined by Western blots. Tumor growth in vivo was evaluated by tumorigenesis assay in nude mice.

RESULTS

Stably overexpressing cav1 cells exhibited slower growth and reduced the capacity of anchorage-independent growth. Overexpression of cav1 reduced cell invasion capacity and promoted cell apoptosis. The activities of EGFR-MAPK signal pathway were also inhibited significantly by overexpression of cav1, in addition, overexpression of cav1 in panc1 cells reduced tumor formation in vivo.

CONCLUSIONS

The cav1 may act as a candidate tumor suppressor gene in human panceatic carcinoma, and this effect may be related with the inhibition of EGFR-MAPK signal cascade.

Caveolin-1 plays important role in EGF-induced migration and proliferation of mouse embryonic stem cells: involvement of PI3K/Akt and ERK

The involvement of caveolin-1 in the regulation of embryonic stem (ES) cell growth by epidermal growth factor (EGF) is by no means clear cut. Thus we examined the relationship between EGF and caveolin-1 in mouse ES cell migration and proliferation. The results revealed that EGF increased Src, caveolin-1, focal adhesion kinase (FAK), Akt, and extracellular signal-regulated kinase-1/2 (ERK) phosphorylation levels. Especially, phosphorylation of caveolin-1 is attenuated by AG1478, herbimycin A (tyrosine kinase inhibitors), and pyrazolopyrimidine 2 (PP2, Src inhibitor) and EGF-induced ERK activation was blocked by PP2, methyl-β-cyclodextrin (MβCD), caveolin-1 small interfering RNA (siRNA), LY-294002 [phosphoinositol-3 kinase inhibitor (PI3K)], and Akt inhibitor. In addition, EGF promoted the cell migration, which was attenuated by PP2, caveolin-1 siRNA, FAK siRNA, LY-294002, Akt inhibitor, and PD-98059. EGF also increased matrix metalloproteinase (MMP-2) expression levels and EGF-induced MMP2 expression was inhibited by caveolin-1 siRNA, FAK siRNA, LY-294002, Akt inhibitor, and PD-98059. Furthermore, EGF-induced increase of cell cycle proteins expression level and [3H]thymidine incorporation was blocked by MMP inhibitor. EGF also significantly increases [3H]thymidine incorporation and cell number, which were significantly blocked by AG 1478, PP2, MβCD, caveolin-1 siRNA, FAK siRNA, LY-294002, and PD-98059 (ERK inhibitor). EGF-induced increase of protooncogenes (c- fos, c- myc, and c- Jun) and cell cycle regulatory proteins (cyclin D1, CDK4, cyclin E, and CDK2) expression levels were also attenuated by caveolin-1 siRNA and FAK siRNA. In conclusion, these results demonstrated that EGF-induced DNA synthesis and cell migration are mediated by caveolin-1, which is activated by Src, FAK, PI3K/Akt, ERK, and MMP-2 signals in mouse ES cells.

Caveolin-1 regulating the invasion and expression of matrix metalloproteinase (MMPs) in pancreatic carcinoma cells

The gelatinases B (MMP9) and A (MMP2) are two members of the matrix metalloproteinase (MMPs) family that are expressed in human cancer, and play a critical role in tumor cell invasion and metastasis. Caveolin-1 (Cav1) has recently been identified as a tumor metastasis modifier gene. However, the effect and mechanism of Cav1 in pancreatic carcinoma cell invasion remain unknown. In this study, we investigated the expression of Cav1, MMP2, and MMP9 in several different pancreatic carcinoma cell lines. We transfected pcDNA3.0-Cav1 plasmid and Cav1 siRNA into SW1990 and Bxpc3 cells, respectively. Using cell invasion assay, we found that overexpression of Cav1 inhibited cell invasion, whereas the knockdown of Cav1 in Bxpc3 cells promoted cell invasion. Moreover, to explore the mechanisms underlying these observations, we further investigated the expression of MMP2, MMP9, phospho-Akt, and phospho-Erk by Western blot, and the activities of MMP2 and MMP9 by gelatin zymography. The results indicated that Cav1 gene could inhibit pancreatic carcinoma cell invasion, at least in part, probably through Erk-MMP signal pathway, suggesting that the endogenous expression or re-expression of Cav1 might help therapeutically reduce their invasive potential in pancreatic carcinoma cells.

The regulation of the endosomal compartment by p53 the tumor suppressor gene

The endosomal compartment of the cell is involved in a number of functions including: (a) internalizing membrane proteins to multivesicular bodies and lysosomes; (b) producing vesicles that are secreted from the cell (exosomes); and (c) generating autophagic vesicles that, especially in times of nutrient deprivation, supply cytoplasmic components to the lysosome for degradation and recycling of nutrients. The p53 protein responds to various stress signals by initiating a transcriptional program that restores cellular homeostasis and prevents the accumulation of errors in a cell. As part of this process, p53 regulates the transcription of a set of genes encoding proteins that populate the endosomal compartment and impact upon each of these endosomal functions. Here, we demonstrate that p53 regulates transcription of the genes TSAP6 and CHMP4C, which enhance exosome production, and CAV1 and CHMP4C, which produce a more rapid endosomal clearance of the epidermal growth factor receptor from the plasma membrane. Each of these p53-regulated endosomal functions results in the slowing of cell growth and division, the utilization of catabolic resources and cell-to-cell communication by exosomes after a stress signal is detected by the p53 protein. These processes avoid errors during stress and restore homeostasis once the stress is resolved.