Caveolin-1, TGF-β receptor internalization, and the pathogenesis of systemic sclerosis

PURPOSE OF REVIEW: To review the scientific literature supporting the participation of caveolin-1 in the pathogenesis of tissue fibrosis and the notion that modulation of the caveolin-1 pathway may represent a novel treatment for systemic sclerosis and other fibrotic diseases. RECENT FINDINGS: Caveolin-1 plays an important role in the regulation of transforming growth factor-beta (TGF-beta) signaling owing to its participation in TGF-beta receptor internalization. TGF-beta receptor internalized through caveolin-1 lipid rafts undergoes rapid degradation, effectively decreasing TGF-beta signaling. Studies have shown that caveolin-1 knockdown in vitro markedly increased collagen gene expression in normal human lung fibroblasts. Caveolin-1 was reduced in affected systemic sclerosis lungs and skin and in idiopathic pulmonary fibrosis lung tissues and fibroblasts. Increasing caveolin-1 expression markedly improved bleomycin-induced pulmonary fibrosis. Restoration of caveolin bioavailability employing penetratin, a cell-permeable peptide carrier for a bioactive caveolin-1 fragment, abrogated TGF-beta activation of cultured human dermal fibroblasts. Systemic administration of penetratin-caveolin-1 peptide to mice with bleomycin-induced lung fibrosis reduced fibrosis. SUMMARY: Caveolin-1 plays an important role in the regulation of TGF-beta signaling and participates in the pathogenesis of systemic sclerosis and idiopathic pulmonary fibrosis. Restoration of caveolin function employing active caveolin-1 fragments coupled to cell-permeable carrier peptides may represent a novel approach for their treatment

Decreased expression of caveolin 1 in patients with systemic sclerosis: crucial role in the pathogenesis of tissue fibrosis.

OBJECTIVE: Recent studies have implicated caveolin 1 in the regulation of transforming growth factor beta (TGFbeta) downstream signaling. Given the crucial role of TGFbeta in the pathogenesis of systemic sclerosis (SSc), we sought to determine whether caveolin 1 is also involved in the pathogenesis of tissue fibrosis in SSc. We analyzed the expression of CAV1 in affected SSc tissues, studied the effects of lack of expression of CAV1 in vitro and in vivo, and analyzed the effects of restoration of caveolin 1 function on the fibrotic phenotype of SSc fibroblasts in vitro. METHODS: CAV1 expression in tissues was analyzed by immunofluorescence and confocal microscopy. The extent of tissue fibrosis in Cav1-knockout mice was assessed by histologic/histochemical analyses and quantified by hydroxyproline assays. Cav1-null and SSc fibroblast phenotypes and protein production were analyzed by real-time polymerase chain reaction, immunofluorescence, Western blot, and multiplexed enzyme-linked immunosorbent assay techniques. The effects of restoration of caveolin 1 function in SSc fibroblasts in vitro were also examined using a cell-permeable recombinant CAV1 peptide. RESULTS: CAV1 was markedly decreased in the affected lungs and skin of SSc patients. Cav1-knockout mice developed pulmonary and skin fibrosis. Down-regulation of caveolin 1 was maintained in cultured SSc fibroblasts, and restoration of caveolin 1 function in vitro normalized their phenotype and abrogated TGFbeta stimulation through inhibition of Smad3 activation. CONCLUSION: Caveolin 1 appears to participate in the pathogenesis of tissue fibrosis in SSc. Restoration of caveolin 1 function by treatment with a cell-permeable peptide corresponding to the CAV1 scaffolding domain may be a novel therapeutic approach in SSc

Phenotypic Behavior of Caveolin-3 Mutations That Cause Autosomal Dominant Limb Girdle Muscular Dystrophy (LGMD-1C) RETENTION OF LGMD-1C CAVEOLIN-3 MUTANTS WITHIN THE GOLGI COMPLEX

Caveolin-3, a muscle-specific caveolin-related protein, is the principal structural protein of caveolae membrane domains in striated muscle cell types (cardiac and skeletal). Autosomal dominant limb girdle muscular dystrophy (LGMD-1C) in humans is due to mutations within the caveolin-3 gene: (i) a 9-base pair microdeletion that removes three amino acids within the caveolin scaffolding domain (DeltaTFT) or (ii) a missense mutation within the membrane spanning domain (P --> L). The molecular mechanisms by which these two mutations cause muscular dystrophy remain unknown. Here, we investigate the phenotypic behavior of these caveolin-3 mutations using heterologous expression. Wild type caveolin-3 or caveolin-3 mutants were transiently expressed in NIH 3T3 cells. LGMD-1C mutants of caveolin-3 (DeltaTFT or P --> L) were primarily retained at the level of a perinuclear compartment that we identified as the Golgi complex in double-labeling experiments, while wild type caveolin-3 was efficiently targeted to the plasma membrane. In accordance with these observations, caveolin-3 mutants formed oligomers of a much larger size than wild type caveolin-3 and were excluded from caveolae-enriched membrane fractions as seen by sucrose density gradient centrifugation. In addition, these caveolin-3 mutants were expressed at significantly lower levels and had a dramatically shortened half-life of approximately 45-60 min. However, caveolin-3 mutants were palmitoylated to the same extent as wild type caveolin-3, indicating that targeting to the plasma membrane is not required for palmitoylation of caveolin-3. In conclusion, we show that LGMD-1C mutations lead to formation of unstable high molecular mass aggregates of caveolin-3 that are retained within the Golgi complex and are not targeted to the plasma membrane. Consistent with its autosomal dominant form of genetic transmission, we demonstrate that LGMD-1C mutants of caveolin-3 behave in a dominant-negative fashion, causing the retention of wild type caveolin-3 at the level of the Golgi. These data provide a molecular explanation for why caveolin-3 levels are down-regulated in patients with this form of limb girdle muscular dystrophy (LGMD-1C)

Upregulation of caveolin-1 and caveolae organelles in Taxol-resistant A549 cells

AbstractCaveolin is a principal component of caveolae membranes. It has been demonstrated that the interaction of the caveolin scaffolding domain with signaling molecules can functionally inhibit the activity of these molecules. Taxol is an antitumor agent that suppresses microtubule dynamics and binds to microtubules thereby stabilizing them against depolymerization. The drug also has been implicated in the induction of apoptosis through activation of components in signal transduction cascades. Here we have investigated the role of caveolin in the development of drug resistance by examining the expression of caveolins in low- and high-level drug-resistant cell lines. Caveolin-1, but not caveolin-2, was upregulated in highly multidrug resistant SKVLB1 cells that express high levels of P-glycoprotein, and in low-level Taxol-resistant A549 cell lines that express low amounts of P-glycoprotein. Two drug-resistant A549 cell lines (one 9-fold resistant to Taxol and the other 1.5-fold resistant to epothilone B), both of which express no P-glycoprotein, demonstrate a significant increase in the expression of caveolin-1. These results indicate that in low-level epothilone B- or Taxol-resistant A549 cells, increased caveolin-1 expression occurs independently of P-glycoprotein expression. Electron microscopic studies clearly demonstrate the upregulation of caveolae organelles in Taxol-resistant A549 cells. Upregulation of caveolin-1 expression in drug-sensitive A549 cells was observed acutely beginning 48 h after incubation with 10 nM Taxol. Thus, caveolin-1 may play a role in the development of Taxol resistance in A549 cells

Antibiotics that target mitochondria extend lifespan in C. elegans

Aging is a continuous degenerative process caused by a progressive decline of cell and tissue functions in an organism. It is induced by the accumulation of damage that affects normal cellular processes, ultimately leading to cell death. It has been speculated for many years that mitochondria play a key role in the aging process. In the aim of characterizing the implications of mitochondria in aging, here we used ( ) as an organismal model treated a panel of mitochondrial inhibitors and assessed for survival. In our study, we assessed survival by evaluating worm lifespan, and we assessed aging markers by evaluating the pharyngeal muscle contraction, the accumulation of lipofuscin pigment and ATP levels. Our results show that treatment of worms with either doxycycline, azithromycin (inhibitors of the small and the large mitochondrial ribosomes, respectively), or a combination of both, significantly extended median lifespan of , enhanced their pharyngeal pumping rate, reduced their lipofuscin content and their energy consumption (ATP levels), as compared to control untreated worms, suggesting an aging-abrogating effect for these drugs. Similarly, DPI, an inhibitor of mitochondrial complex I and II, was capable of prolonging the median lifespan of treated worms. On the other hand, subjecting worms to vitamin C, a pro-oxidant, failed to extend lifespan and upregulated its energy consumption, revealing an increase in ATP level. Therefore, our longevity study reveals that mitochondrial inhibitors (i.e., mitochondria-targeting antibiotics) could abrogate aging and extend lifespan in

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

A mitochondrial based oncology platform for targeting cancer stem cells (CSCs) : MITO-ONC-RX

Here, we wish to propose a new systematic approach to cancer therapy, based on the targeting of mitochondrial metabolism, especially in cancer stem cells (CSCs). In the future, we envision that anti-mitochondrial therapy would ultimately be practiced as an add-on to more conventional therapy, largely for the prevention of tumor recurrence and cancer metastasis. This mitochondrial based oncology platform would require a panel of FDA-approved therapeutics (e.g. Doxycycline) that can safely be used to inhibit mitochondrial OXPHOS and/or biogenesis in CSCs. In addition, new therapeutics that target mitochondria could also be developed, to optimize their ability to eradicate CSCs. Finally, in this context, mitochondrial-based biomarkers (i.e. “Mito-signatures”) could be utilized as companion diagnostics, to identify high-risk cancer patients at diagnosis, facilitating the early detection of tumor recurrence and the prevention of treatment failure. In summary, we suggest that new clinical trials are warranted to test and possibly implement this emerging treatment strategy, in a variety of human cancer types. This general approach, using FDA-approved antibiotics to target mitochondria, was effective in killing CSCs originating from many different cancer types, including DCIS, breast (ER(+) and ER(-)), prostate, ovarian, lung and pancreatic cancers, as well as melanoma and glioblastoma, among others. Thus, we propose the term MITO-ONC-RX, to describe this anti-mitochondrial platform for targeting CSCs. The use of re-purposed FDA-approved drugs will undoubtedly help to accelerate the clinical evaluation of this approach, as these drugs can move directly into Phase II clinical trials, saving considerable amounts of time (10–15 y) and billions in financial resources

High ATP production fuels cancer drug resistance and metastasis : implications for mitochondrial ATP depletion therapy

Recently, we presented evidence that high mitochondrial ATP production is a new therapeutic target for cancer treatment. Using ATP as a biomarker, we isolated the “metabolically fittest” cancer cells from the total cell population. Importantly, ATP-high cancer cells were phenotypically the most aggressive, with enhanced stem-like properties, showing multi-drug resistance and an increased capacity for cell migration, invasion and spontaneous metastasis. In support of these observations, ATP-high cells demonstrated the up-regulation of both mitochondrial proteins and other protein biomarkers, specifically associated with stemness and metastasis. Therefore, we propose that the “energetically fittest” cancer cells would be better able to resist the selection pressure provided by i) a hostile micro-environment and/or ii) conventional chemotherapy, allowing them to be naturally-selected for survival, based on their high ATP content, ultimately driving tumor recurrence and distant metastasis. In accordance with this energetic hypothesis, ATP-high MDA-MB-231 breast cancer cells showed a dramatic increase in their ability to metastasize in a pre-clinical model in vivo. Conversely, metastasis was largely prevented by treatment with an FDA-approved drug (Bedaquiline), which binds to and inhibits the mitochondrial ATP-synthase, leading to ATP depletion. Clinically, these new therapeutic approaches could have important implications for preventing treatment failure and avoiding cancer cell dormancy, by employing ATP-depletion therapy, to target even the fittest cancer cells