Attenuation of EGF signaling in senescent cells by caveolin

Staphylococcus aureus phagocytosis is affected by senescence

Senescent cells accumulate in multicellular animals with aging, resulting in organ or tissue dysfunction. These alterations increase the incidence of a variety of illnesses, including infectious diseases, and, in certain instances, its severity. In search of a rationale for this phenomenon, we focused on the endophagocytic pathway in senescent cells. We first described the endocytic vesicle populations at different stages of maturation using confocal microscopy. There was an increase in the number of vacuoles per cell, which was partially explained by an increase in cell size. No changes in vesicle maturation or degradation capacities were determined by microscopy or Western blot assays. Also, we studied the internalization of various endophagocytic cargoes in senescent cells and observed only a decrease in the intracellular recovery of bacteria such as Staphylococcus aureus. Afterwards, we studied the intracellular traffic of S. aureus, and observed no differences in the infection between control and senescent cells. In addition we quantified the recovery of bacteria from control and senescent cells infected in the presence of several inhibitors of endophagosomal maturation, and no changes were observed. These results suggest that bacterial internalization is affected in senescent cells. Indeed, we confirmed this hypothesis by determining minor bacterial adherence and internalization by confocal microscopy. Furthermore, it is important to highlight that we found very similar results with cells from aged animals, specifically BMDMs. This alteration in senescent cells enlightens the diminished bacterial clearance and may be a factor that increases the propensity to suffer severe infectious conditions in the elderly.

Crosstalk between Lipid Rafts and Aging: New Frontiers for Delaying Aging

With the rapid aging in the global population, delay of aging has become a hot research topic. Lipid rafts (LRs) are microdomains in the plasma membrane that contain sphingolipids and cholesterol. Emerging evidence indicates an interesting interplay between LRs and aging. LRs and their components are altered with aging. Further, the aging process is strongly influenced by LRs. In recent years, LRs and their component signaling molecules have been recognized to affect aging by interfering with its hallmarks. Therefore, targeting LRs is a promising strategy to delay aging.

Renal carcinoma/kidney progenitor cell chimera organoid as a novel tumorigenesis gene discovery model

Three-dimensional (3D) organoids provide a new way to model various diseases, including cancer. We made use of recently developed kidney-organ-primordia tissue-engineering technologies to create novel renal organoids for cancer gene discovery. We then tested whether our novel assays can be used to examine kidney cancer development. First, we identified the transcriptomic profiles of quiescent embryonic mouse metanephric mesenchyme (MM) and of MM in which the nephrogenesis program had been induced ex vivo. The transcriptome profiles were then compared to the profiles of tumor biopsies from renal cell carcinoma (RCC) patients, and control samples from the same kidneys. Certain signature genes were identified that correlated in the developmentally induced MM and RCC, including components of the caveolar-mediated endocytosis signaling pathway. An efficient siRNA-mediated knockdown (KD) of Bnip3, Gsn, Lgals3, Pax8, Cav1, Egfr or Itgb2 gene expression was achieved in mouse RCC (Renca) cells. The live-cell imaging analysis revealed inhibition of cell migration and cell viability in the gene-KD Renca cells in comparison to Renca controls. Upon siRNA treatment, the transwell invasion capacity of Renca cells was also inhibited. Finally, we mixed E11.5 MM with yellow fluorescent protein (YFP)-expressing Renca cells to establish chimera organoids. Strikingly, we found that the Bnip3-, Cav1- and Gsn-KD Renca-YFP+ cells as a chimera with the MM in 3D organoid rescued, in part, the RCC-mediated inhibition of the nephrogenesis program during epithelial tubules formation. Altogether, our research indicates that comparing renal ontogenesis control genes to the genes involved in kidney cancer may provide new growth-associated gene screens and that 3D RCC-MM chimera organoids can serve as a novel model with which to investigate the behavioral roles of cancer cells within the context of emergent complex tissue structures.

Editor’s Choice: Chimeras between embryonic kidney cells and renal carcinoma cells serve as a novel model to assay the roles of co-regulated genes in kidney development and renal carcinogenesis.

Versatile Functions of Caveolin-1 in Aging-related Diseases

Caveolin-1 (Cav-1) is a trans-membrane protein that is a major component of the caveolae structure on the plasma membrane. Cav-1 is involved in the regulation of various cellular processes, including cell growth, differentiation, endocytosis, and in particular it has been implied in cellular senescence. Here we review current knowledge about Cav-1 in cellular signaling and discuss the role of Cav-1 in aging-related diseases.

The hallmarks of fibroblast ageing

Ageing is influenced by the intrinsic disposition delineating what is maximally possible and extrinsic factors determining how that frame is individually exploited. Intrinsic and extrinsic ageing processes act on the dermis, a post-mitotic skin compartment mainly consisting of extracellular matrix and fibroblasts. Dermal fibroblasts are long-lived cells constantly undergoing damage accumulation and (mal-)adaptation, thus constituting a powerful indicator system for human ageing. Here, we use the systematic of ubiquitous hallmarks of ageing (Lopez-Otin et al., 2013, Cell 153) to categorise the available knowledge regarding dermal fibroblast ageing. We discriminate processes inducible in culture from phenomena apparent in skin biopsies or primary cells from old donors, coming to the following conclusions: (i) Fibroblasts aged in culture exhibit most of the established, ubiquitous hallmarks of ageing. (ii) Not all of these hallmarks have been detected or investigated in fibroblasts aged in situ (in the skin). (iii) Dermal fibroblasts aged in vitro and in vivo exhibit additional features currently not considered ubiquitous hallmarks of ageing. (iv) The ageing process of dermal fibroblasts in their physiological tissue environment has only been partially elucidated, although these cells have been a preferred model of cell ageing in vitro for decades.

The role of caveolae in the pathophysiology of lung diseases

Caveolae are flask-shaped plasma membrane invaginations formed by constitutive caveolin proteins and regulatory cavin proteins. Caveolae harbor a range of signaling components such as receptors, ion channels and regulatory molecules. There is now increasing evidence that caveolins and cavins play an important role in a variety of diseases. However, the mechanisms by which these caveolar proteins affect lung health and disease are still under investigation, with emerging data suggesting complex roles in disease pathophysiology. This review summarizes the current state of understanding of how caveolar proteins contribute to lung structure and function and how their altered expression and/or function can influence lung diseases.

The mitogen-inducible gene-6 is involved in regulation of cellular senescence in normal diploid fibroblasts

BACKGROUND INFORMATION

The mitogen-inducible gene-6 (Mig-6) is a non-kinase scaffolding adaptor protein. It has been shown that Mig-6 may play important roles in regulating stress response, maintaining homeostasis and functioning as a tumour suppressor. In this study, we investigated the role of Mig-6 in cellular senescence.

RESULTS

Our results showed that Mig-6 is up-regulated during the senescence process. Functional analysis indicated that cells over-expressing Mig-6 have reduced DNA synthesis and showed the signs of senescence. Knockdown of Mig-6 delayed the initiation of Ras-induced cellular senescence. These results suggest that the increase of Mig-6 expression contributes to establishment of cellular senescence. Furthermore, our results showed that Mig-6 induction of senescence is related to its inhibition of EGF receptor (EGFR)/Erb B signalling. Subsequent analysis of the mechanism responsible for the up-regulation of its expression showed that FOXO3A transcriptionally up-regulates Mig-6 expression via directly binding to the FOXO response element in Mig-6 5'-flanking regulatory sequences.

CONCLUSIONS

Mig-6 induces premature senescence via functioning in regulation of cellular senescence in normal diploid fibroblasts.

17AAG Treatment Accelerates Doxorubicin Induced Cellular Senescence: Hsp90 Interferes with Enforced Senescence of Tumor Cells

Hsp90 chaperone has been identified as an attractive pharmacological target to combat cancer. However, some metastatic tumors either fail to respond to Hsp90 inhibition or show recovery necessitating irreversible therapeutic strategies. In response to this enforced senescence has been proposed as an alternate strategy. Here, we demonstrate that inhibiting Hsp90 with 17AAG sensitizes human neuroblastoma to DNA damage response mediated cellular senescence. Among individual and combination drug treatments, 17AAG pre-treatment followed by doxorubicin treatment exhibited senescence-like characteristics such as increased nucleus to cytoplasm ratio, cell cycle arrest, SA-β-gal staining and the perpetual increase in SAHF. Doxorubicin induced senescence signaling was mediated by p53-p21(CIP/WAF-1) and was accelerated in the absence of functional Hsp90. Sustained p16(INK4a) and H3K4me3 expressions correlating with unaffected telomerase activation annulled replicative senescence and appraised stress induced senescence. Despite increases in [(ROS)i] and [(Ca(2+))i], a concomitant increase in cellular antioxidant defense system suggested oxidation independent senescence activation. Sustained activation of survival (Akt) and proliferative (ERK1/2) kinases fosters robustness of cells. Invigorating senescent cells with growth factor or snooping with mTOR or PI3 kinase inhibitors compromised cell survival but not senescence. Intriguingly, senescence-associated secretory factors from the senescence cells manifested established senescence in neuroblastoma, which offers clinical advantage to our approach. Our study discusses tumor selective functions of Hsp90 and discusses irrefutable strategies of Hsp90 inhibition in anticancer treatments.

Post-translational modification of cellular proteins by ubiquitin and ubiquitin-like molecules: role in cellular senescence and aging

Ubiquitination ofendogenous proteins is one of the key regulatory steps that guides protein degradation through regulation of proteasome activity. During the last years evidence has accumulated that proteasome activity is decreased during the aging process in various model systems and that these changes might be causally related to aging and age-associated diseases. Since in most instances ubiquitination is the primary event in target selection, the system ofubiquitination and deubiquitination might be of similar importance. Furthermore, ubiquitination and proteasomal degradation are not completely congruent, since ubiquitination confers also functions different from targeting proteins for degradation. Depending on mono- and polyubiquitination and on how ubiquitin chains are linked together, post-translational modifications of cellular proteins by covalent attachment of ubiquitin and ubiquitin-like proteins are involved in transcriptional regulation, receptor internalization, DNA repair, stabilization of protein complexes and autophagy. Here, we summarize the current knowledge regarding the ubiquitinome and the underlying ubiquitin ligases and deubiquitinating enzymes in replicative senescence, tissue aging as well as in segmental progeroid syndromes and discuss potential causes and consequences for aging.

Senescence-related functional nuclear barrier by down-regulation of nucleo-cytoplasmic trafficking gene expression

One of the characteristic natures of senescent cells is the hypo- or irresponsiveness not only to growth factors but also to apoptotic stress. In the present study, we confirmed the inhibition of nuclear translocation of activated p-ERK1/2 and NF-kB p50 in response to growth stimuli or LPS in the senescent human diploid fibroblasts. In order to elucidate the underlying mechanism for the senescence-associated hypo-responsiveness, we carried out the comparison study for gene expression profiles through microarray analysis. In consequence, we observed the vast reduction in expression of nucleo-cytoplasmic trafficking genes in senescent cells, when compared with those in young cells. Expression levels of several nucleoporins, karyopherin alpha, karyopherin beta, Ran, and Ran-regulating factors were confirmed to be down-regulated in senescent HDFs by using RT-PCR and Western blot methods. Taken together, these data suggest the operation of certain senescence-associated functional nuclear barriers by down-regulation of the nucleo-cytoplasmic trafficking genes in the senescent cells.

Epidermal growth factor receptor and cancer: control of oncogenic signalling by endocytosis

The epidermal growth factor receptor (EGFR) and other members of the EGFR/ErbB receptor family of receptor tyrosine kinases (RTKs) are important regulators of proliferation, angiogenesis, migration, tumorigenesis and metastasis. Overexpression, mutations, deletions and production of autocrine ligands contribute to aberrant activation of the ErbB proteins. The signalling output from EGFR is complicated given that other ErbB proteins are often additionally expressed and activated in the same cell, resulting in formation of homo-and/or heterodimers. In particular, association of EGFR with ErbB2 prevents its down-regulation, underscoring the importance of the cellular background for EGFR effects. Signalling from ErbB proteins can either be terminated by dissociation of ligand resulting in dephosphorylation, or blunted by degradation of the receptors. Although proteasomal targeting of ErbB proteins has been described, lysosomal degradation upon ligand-induced endocytosis seems to play the major role in EGFR down-regulation. Preclinical and clinical data have demonstrated that EGFR is a central player in cancer, especially in carcinomas, some brain tumours and in non-small cell lung cancer. Such studies have further validated EGFR as an important molecular target in cancer treatment. This review focuses on mechanisms involved in ligand-induced EGFR activation and endocytic down-regulation. A better understanding of EGFR biology should allow development of more tumour-selective therapeutic approaches targeting EGFR-induced signalling.

Viral-mediated gene therapy for the muscular dystrophies: successes, limitations and recent advances

Much progress has been made over the past decade elucidating the molecular basis for a variety of muscular dystrophies (MDs). Accordingly, there are examples of mouse models of MD whose disease progression has been halted in large part with the use of viral vector technology. Even so, we must acknowledge significant limitations of present vector systems that must be overcome prior to successful treatment of humans with such approaches. This review will present a variety of viral-mediated therapeutic strategies aimed at counteracting the muscle-wasting symptoms associated with muscular dystrophy. We include viral vector systems used for muscle gene transfer, with a particular emphasis on adeno-associated virus. Findings of several encouraging studies focusing on repair of the mutant dystrophin gene are also included. Lastly, we present a discussion of muscle compensatory therapeutics being considered that include pathways involved in the up-regulation of utrophin, promotion of cellular adhesion, enhancement of muscle mass, and antagonism of the inflammatory response. Considering the complexity of the muscular dystrophies, it appears likely that a multilayered approach tailored to a patient sub-group may be warranted in order to effectively contest the progression of this devastating disease.

Caveolin regulates microtubule polymerization in the vascular smooth muscle cells

Microtubule and caveolin have common properties in intracellular trafficking and the regulation of cellular growth. Overexpression of caveolin in vascular smooth muscle cells increased the polymer form of microtubule without changing in the total amount of tubulin, and downregulation of caveolin decreased the polymer form of microtubule. Fractionation of cellular proteins followed by immunodetection as well as immunostaining of caveolin and microtubule revealed that caveolin and a portion of microtubule were co-localized in caveolar fractions. A caveolin scaffolding domain peptide, which mimics caveolin function, did not alter the polymerization of microtubule in vitro, but dramatically inhibited the depolymerization of microtubule induced by stathmin, a microtubule destabilizing protein, which was also found in caveolar fractions. Accordingly, it is most likely that caveolin increased the polymer form of microtubule through the inhibition of a microtubule destabilizer, stathmin, suggesting a novel role of caveolin in regulating cellular network and trafficking.

Caveolin-3 inhibits growth signal in cardiac myoblasts in a Ca2+-dependent manner

Caveolin, a major protein component of caveolae, directly interacts with multiple signaling molecules, such as Ras and growth factor receptors, and inhibits their function. However, the role of the second messenger system in mediating this inhibition by caveolin remains poorly understood. We examined the role of Ca2+-dependent signal in caveolin- mediated growth inhibition using a rat cardiac myoblast cell line (H9C2), in which the expression of caveolin- 3, the muscle specific subtype, can be induced using the LacSwitch system. Upon induction with IPTG and serum-starvation, the expression of caveolin-3 was increased by 3.3-fold relative to that of mock-induced cells. The recombinant caveolin-3 was localized to the same subcellular fraction as endogenous caveolin-3 after sucrose gradient purification. Angiotensin II enhanced ERK phosphorylation, but this enhancement was significantly decreased in caveolin-3-induced cells in comparison to that in mock-induced cells. Similarly, when cells were stimulated with fetal calf serum, DNA synthesis, as determined by [3H]-thymidine incorporation, was significantly decreased in caveolin- 3-induced cells. When cells were treated with Ca2+ chelator (BAPTA and EGTA), however, this attenuation was blunted. Calphostin (PKC inhibitor), but not cyclosporine A treatment (calcineurin inhibitor), blunted this attenuation in caveolin-3 induced cells. Our findings suggest that caveolin exhibits growth inhibition in a Ca2+-dependent manner, most likely through PKC, in cardiac myoblasts.

Overexpression of caveolin-1 and -2 in cell lines and in human samples of inflammatory breast cancer

PURPOSE

Inflammatory breast cancer (IBC) is the most aggressive form of locally advanced breast cancer (LABC). The IBC phenotype is characterized by an infiltrative growth pattern, increased (lymph)angiogenesis and the propensity to invade dermal lymphatics. In pancreatic cancer, interactions between caveolin-1 and RhoC GTPase, a key molecule in causing the IBC phenotype, regulate tumour cell motility and invasion. In this study we sought to investigate the role of caveolin-1 and -2 in IBC cell lines and in human IBC samples.

EXPERIMENTAL DESIGN

Differential methylation techniques identified the methylation status of the caveolin-1 and -2 promoters in human mammary epithelial cells (HMECs) and the SUM149 cell line. In cell line experiments, caveolin-1 and -2 mRNA and protein expression were compared in HMECs, MCF10A, the SUM102 non-IBC cell lines and 2 IBC cell lines (SUM149 and SUM190). Furthermore, caveolin-1 and -2 mRNA and protein expression were compared in human IBC and non-IBC samples using cDNA microarray, real-time qRT-PCR and immunohistochemistry. Results were correlated with RhoC protein expression data.

RESULTS

In the SUM149 cell line, the caveolin-1 and -2 promoter sites were hypomethylated. A significantly increased expression of caveolin-1 and -2, both at the mRNA and protein level was found in IBC cell lines and in human samples of IBC: caveolin-1 and -2 mRNA were respectively 1.7 (p = 0.02) and 2.2 (p = 0.03) fold more expressed in IBC compared to non IBC and at the protein level, 41.4% of IBC specimens expressed either caveolin-1 or -2, compared to 15.6% of non-IBC specimens (p = 0.03). Furthermore a correlation was found between RhoC protein expression and caveolin-1 (p = 0.1) or caveolin-2 (p = 0.09) or either caveolin-1 or -2 protein expression (p = 0.04).

CONCLUSIONS

Although considered a tumour suppressor in breast cancer, we demonstrated overexpression of caveolin-1 and -2 in IBC cell lines and in human samples of IBC, most likely due to hypomethylation of their respective promoters. These results confirm the distinct molecular signature of IBC. Our data further suggest interaction between RhoC GTPase and the caveolins in IBC.

Variation in gene expression patterns in effusions and primary tumors from serous ovarian cancer patients

Background

While numerous studies have characterized primary ovarian tumors, little information is available regarding expression patterns of metastatic sites of this cancer. To define sets of genes that distinguish primary and metastatic ovarian tumors, we used cDNA microarrays to characterize global gene expression patterns in 38 effusions (28 peritoneal, 10 pleural) and 8 corresponding primary ovarian tumors, and searched for associations between expression patterns and clinical parameters.

Results

We observed multidimensional variation in expression patterns among the cancers. Coordinate variation in expression of genes from two chromosomal regions, 8q and 19q, was seen in subsets of the cancers indicating possible amplifications in these regions. A set of 112 unique genes of known function was differentially expressed between primary tumors and effusions using supervised analysis. Relatively few differences were seen between effusions isolated from the pleural and peritoneal cavities or between effusions from patients diagnosed with stage III and stage IV cancers. A set of 84 unique genes was identified that distinguished high from lower grade ovarian cancers. The results were corroborated using immunocytochemistry, mRNA in situ hybridization, and immunoblotting.

Conclusion

The extensive variation in expression patterns observed underscores the molecular heterogeneity of ovarian cancer, but suggests a similar molecular profile for ovarian carcinoma cells in serosal cavities.

Neuroprotective gene expression profiles in ischemic cortical cultures preconditioned with IGF-1 or bFGF

The mechanisms underlying growth factor preconditioning of neurons are only partially elucidated, and no studies have been conducted in this area using a gene profiling approach. We used cDNA microarrays to compare the transcriptional profiles of cells preconditioned either with insulin-like growth factor I (IGF-1) or basic fibroblast growth factor (bFGF), to identify differentially regulated genes that may function in growth factor signaling, response to oxygen-glucose deprivation (OGD), and most importantly, cell survival. Primary rat cortical cultures were treated with bFGF or IGF-1 for 2, 24, or 24 h followed by OGD for 90 min, and compared with cells that were subject to OGD without growth factor pretreatment. Although the majority of surveyed genes were unchanged in all experimental treatments, 175 genes (10% of the cDNAs on the chip) were found to be differentially regulated in at least one of the treatment conditions. Hierarchical clustering of these 175 genes was used to identify four expression clusters: IGF-1 regulated, bFGF regulated, OGD regulated, and putative neuroprotective genes. Further analysis using realtime RT-PCR confirmed that we had identified genes that are regulated by single growth factors, as well as several more that are co-regulated by both IGF-1 and bFGF. These genes can influence neuronal survival by affecting diverse pathways such as growth factor signal transduction (CD44, DTR, DUSP6, EPS8, IGFBP3), DNA repair and transcription (FOXJ1), metabolic homeostasis (RASA1, SHMT2), cytoskeletal stability (MSN, MAPT) and cholesterol biosynthesis (FDFT1, FDPS).

Caveolin-1 Interacts with 5-HT2A Serotonin Receptors and Profoundly Modulates the Signaling of Selected Gαq-coupled Protein Receptors

5-Hydroxytryptamine 2A (5-HT(2A)) serotonin receptors are important for a variety of functions including vascular smooth muscle contraction, platelet aggregation, and the modulation of perception, cognition, and emotion. In a search for 5-HT(2A) receptor-interacting proteins, we discovered that caveolin-1 (Cav-1), a scaffolding protein enriched in caveolae, complexes with 5-HT(2A) receptors in a number of cell types including C6 glioma cells, transfected HEK-293 cells, and rat brain synaptic membrane preparations. To address the functional significance of this interaction, we performed RNA interference-mediated knockdown of Cav-1 in C6 glioma cells, a cell type that endogenously expresses both 5-HT(2A) receptors and Cav-1. We discovered that the in vitro knockdown of Cav-1 in C6 glioma cells nearly abolished 5-HT(2A) receptor-mediated signal transduction as measured by calcium flux assays. RNA interference-mediated knockdown of Cav-1 also greatly attenuated endogenous Galpha(q)-coupled P2Y purinergic receptor-mediated signaling without altering the signaling of PAR-1 thrombin receptors. Cav-1 appeared to modulate 5-HT(2A) signaling by facilitating the interaction of 5-HT(2A) receptors with Galpha(q). These studies provide compelling evidence for a prominent role of Cav-1 in regulating the functional activity of not only 5-HT(2A) serotonin receptors but also selected Galpha(q)-coupled receptors.

Morphological adjustment of senescent cells by modulating caveolin-1 status

Morphological change is one of the cardinal features of the senescent phenotype; for example, senescent human diploid cells have a flat large shape. However, the mechanisms underlying such senescence-related morphological alterations have not been well studied. To investigate this situation, we characterized the senescence-dependent changes of cellular structural determinants in terms of their levels and activities. These determinants included integrins, focal adhesion complexes, and small Rho GTPases, and special emphasis was placed on their relationships with caveolin-1 status. We observed that the expression integrin beta(1) and focal adhesion kinase (FAK) were increased and that the phosphorylations of FAK and paxillin, hallmarks of focal adhesion formation, were also increased in senescent human diploid fibroblast cells. Moreover, the Rho GTPases Rac1 and Cdc42 were found to be highly activated in senescent cells. In addition, focal adhesion complexes and Rho GTPases were up-regulated in the caveolin-rich membrane domain in the senescent cells. Activated Rac1 and Cdc42 directly interacted with caveolin-1 in senescent cells. Interestingly, caveolin-1 knock-out senescent cells, achieved by using small interfering RNA and antisense oligonucleotide, showed disrupted focal adhesion formation and actin stress fibers via the inactivation of FAK, which resulted in morphological adjustment to the young cell-like small spindle shape. Based on the results obtained, we propose that caveolin-1 plays an important role in senescence-associated morphological changes by regulating focal adhesion kinase activity and actin stress fiber formation in the senescent cells.

Age-related changes of cardiac gene expression following myocardial ischemia/reperfusion

Young and old (4 and 25 months of age, respectively) Fisher 344/Brown Norway hybrid female rats were subjected to four 3 min episodes of ischemia separated by 5 min of reperfusion. Corresponding open-chest sham-operated groups received 32 min of no intervention. All rats were allowed to recover, and 24h later hearts were removed and frozen in liquid nitrogen. Global gene profiling in the ischemic and the non-ischemic areas and in the sham-operated hearts as well was carried out by using Affymetrix Gene Chips. Young ischemic hearts demonstrated down-regulation of gene expression associated with early-remodeling including down-regulation of tissue inhibitor of metalloproteinase 1, decorin, collagen, tropoelastin, and fibulin, as well as decreases in hypertrophy-related transcripts. In contrast, old hearts showed a unique injury-related response, which included up-regulation of mRNAs for proteins associated with hypertrophy or apoptosis (including H36-alpha7 integrin, alpha-actin, tubulin, filamin, connective tissue growth factor, calcineurin, serine protease, and apoptosis inducing factor). These injury-related changes in gene expression could in part explain increased gravity of outcomes of ischemia and myocardial infarction in elderly hearts.

The SRC homology 2 domain of Rin1 mediates its binding to the epidermal growth factor receptor and regulates receptor endocytosis

Activated epidermal growth factor receptors (EGFRs) recruit intracellular proteins that mediate receptor signaling and endocytic trafficking. Rin1, a multifunctional protein, has been shown to regulate EGFR internalization (1). Here we show that EGF stimulation induces a specific, rapid, and transient membrane recruitment of Rin1 and that recruitment is dependent on the Src homology 2 (SH2) domain of Rin1. Immunoprecipitation of EGFR is accompanied by co-immunoprecipitation of Rin1 in a time- and ligand-dependent manner. Association of Rin1 and specifically the SH2 domain of Rin1 with the EGFR was dependent on tyrosine phosphorylation of the intracellular domain of the EGFR. The recruitment of Rin1, observed by light microscopy, indicated that although initially cytosolic, Rin1 was recruited to both plasma membrane and endosomes following EGF addition. Moreover, the expression of the SH2 domain of Rin1 substantially impaired the internalization of EGF without affecting internalization of transferrin. Finally, we found that Rin1 co-immunoprecipitated with a number of tyrosine kinase receptors but not with cargo endocytic receptors. These results indicate that Rin1 provides a link via its SH2 domain between activated tyrosine kinase receptors and the endocytic pathway through the recruitment and activation of Rab5a.

Common mechanisms for declines in oxidative stress tolerance and proliferation with aging

Aging is often characterized by reduced stress tolerance and decreased proliferative capacity, but little is known about the effects of aging on signaling pathways important in regulating these responses. Recent studies from our laboratory have implicated impairments in epidermal growth factor receptor (EGFR) signaling and extracellular signal-regulated kinase (ERK) activation to both effects in rat hepatocytes. Here we investigated the responsiveness of hepatocytes derived from young (4-5 months) and aged (24-29 months) mice to proliferative signals (low concentrations of H2O2 and epidermal growth factor [EGF] stimulation), and oxidant injury (high H2O2 concentrations). Old hepatocytes displayed lower levels of DNA synthesis in response to low H(2)O(2) concentrations (5-10 microM) and EGF stimulation, and reduced survival following treatment with high H2O2 concentrations (20-50 microM). Both effects were associated with reduced activation of ERK and diminished phosphorylation of EGFR tyrosine residue 1173. p38 was also activated by H2O2, but to a greater extent in old cells. Pharmacologic inhibition of ERK increased the sensitivity of young cells to H2O2-induced cell death, while inhibition of p38 decreased the sensitivity of old cells. Our findings suggest that impairments in common signaling events underlie age-related declines in proliferative capacity and oxidative stress tolerance in mouse hepatocytes, and that an imbalance in ERK and p38 activities contributes to the greater sensitivity of aged cells to H2O2.

Bidirectional signaling between the estrogen receptor and the epidermal growth factor receptor

Interactions between the estrogen receptor (ER) and the epidermal growth factor receptor (EGFR) contribute to the biological effects of these binding protein families. EGFR stimulates DNA synthesis and gene transcription in the uterus, related in part to estrogen-independent activation of the nuclear ER. This results from signal transduction enacted by the plasma membrane tyrosine kinase growth factor receptor, leading to 1) phosphorylation and activation of the nuclear ER, and 2) phosphorylation of coregulator proteins. More recently, it has been shown that a pool of ERalpha resides in or associates with the plasma membrane as a cytoplasmic protein. These ERs utilize the membrane EGFR to rapidly signal through various kinase cascades that influence both transcriptional and nontranscriptional actions of estrogen in breast cancer cells. This is congruent with a general theme of receptor signaling, where membrane G protein-coupled receptors activate tyrosine kinase growth factor receptors (EGFR, IGF-I receptor) that subsequently signal to MAPKs and other pathways. Overall, the bidirectional cross-talk between EGFR and cellular pools of ER contributes to reproductive organ physiology and pathophysiology.

Sorting and function of the human folate receptor is independent of the caveolin expression in Fisher rat thyroid epithelial cells

Caveolae are small, flask-shaped, non-clathrin coated invaginations of the plasma membrane of many mammalian cells. Caveolae have a coat that includes caveolin. They have been implicated in numerous cellular processes, including potocytosis. Since the human folate receptor (hFR) and other glycosyl-phosphatidylinositol GPI)-tailed proteins have been co-localized to caveolae, we studied the caveolin role in the hFR function by transfecting hFR and/or caveolin cDNA into Fisher rat thyroid epithelial (FRT) cells that normally do not express detectable levels of either protein. We isolated and characterized stable clones as follows: they express (1) high levels of caveolin alone, (2) hFR and caveolin, or (3) hFR alone. We discovered that hFR is correctly processed, sorted, and anchored by a GPI tail to the plasma membrane in FRT cells. No difference in the total folic acid binding or cell surface folic acid binding activity were found between the FRT cells that were transfected with hFR, or cells that were transfected with hFR and caveolin. The hFR that was expressed on the cell surface of clones that were transfected with hFR was also sensitive to phosphatidylinositol-specific phospholipase C (PI-PLC) release, and incorporated radiolabeled ethanolamine that supports the attachment of a GPI-tail on hFR. We conclude that the processing, sorting, and function of hFR is independent on the caveolin expression in FRT cells.

Functional recovery of senescent cells through restoration of receptor-mediated endocytosis

The functional deterioration of an organism with age causes the major problem of maintaining the quality of life at old age. Degenerative changes in the organism may to some extent reflect alterations that can be observed in cells during in vitro replicative senescence. At the cellular level, the receptor-mediated endocytosis in the membrane might be emphasized as a responsible mechanism for functional decay, since the endocytosis is in charge of many important biological phenomena: nutrient uptake, growth factor sensitivity, immune response, protection from environment and pathogen uptake, etc. We found that two major endocytotic pathways, i.e. clathrin-mediated and caveolae-dependent endocytosis, are down regulated in senescent cells. For the down regulation of the clathrin dependent receptor-mediated endocytosis, the reduction of amphiphysin-1 was found responsible, which was confirmed by Western blot analysis, dominant negative mutant transfection and restoration of gene activity by microinjection. With respect to the hypo-responsiveness of senescent cells to growth factors, the upregulation of caveolins has been suggested to be a causal factor. The overexpression of caveolins caused senescent-like changes in epidermal growth factor (EGF) response of the young cells, while down regulation of caveolins by use of antisense-oligonucleotides restored the EGF response in old cells, suggesting that caveolin system would be one of the major mechanisms responsible for decreased responses to growth factors in the senescent cells. Based on these results, it can be suggested that the functional deterioration of the senescent cells may be explained in terms of the down regulation of receptor mediated endocytosis, at least in part, and that the restoration of endocytosis apparatus either with amphiphysin supplementation or with reduction of caveolins might lead to functional recovery of the senescent cells.

Down-regulation of receptor-mediated endocytosis is responsible for senescence-associated hyporesponsiveness

Human diploid fibroblasts (HDF) do not divide indefinitely and eventually lead to an arrest of cell division by a process termed cellular or replicative senescence. Irreversible growth arrest of senescent cells is strongly related to the attenuated response to growth factors. Recently, we reported that up-regulation of caveolin in the senescent cells is responsible for the attenuated response to growth factors. Senescent cells did not phosphorylate Erk-1/2 after EGF stimulation, whereas young cells did. In those senescent cells, we found an increased level of caveolin proteins and strong interactions between caveolin-1 and EGFR. When we overexpressed caveolin-1 in young HDF, the activation of Erk-1/2 on EGF stimulation was significantly suppressed. These results suggest that the hyporesponsiveness of senescent fibroblasts to EGF stimulation might be due to the overexpression of caveolin. In addition, the clathrin-dependent endocytosis system plays the more active and dominant role over the caveolae system. Therefore, we monitored the efficiency of clathrin-dependent receptor-mediated endocytosis in the senescent cells in order to elucidate the exact mode of the attenuated response to growth factors in the senescent cells. Using a transferrin-uptake assay and Western blot analysis of endocytosis-related proteins, we found a significant decrease of amphiphysin-1 in human diploid fibroblasts of multipassages. By adjusting the level of amphiphysin, we could modulate the efficiency of receptor-mediated endocytosis either in young or old cells toward growth factors: that is, a dominant negative mutant of amphiphysin-1 blocked the endocytosis in the young cells, while microinjection of the gene resumed its activity in the old cells. Taken together, we conclude that the loss of endocytotic activity of senescent cells is directly related to the down-regulation of amphiphysin-1 and/or up-regulation of caveolins. This opens a new field of functional recovery of the senescent cells simply through adjusting the receptor-mediated endocytosis capacity.