Impairment of Fas-ligand-caveolin-1 interaction inhibits Fas-ligand translocation to rafts and Fas-ligand-induced cell death

Molecular Mechanisms of Glaucoma Pathogenesis with Implications to Caveolin Adaptor Protein and Caveolin-Shp2 Axis

Glaucoma is a common retinal disorder characterized by progressive optic nerve damage, resulting in visual impairment and potential blindness. Elevated intraocular pressure (IOP) is a major risk factor, but some patients still experience disease progression despite IOP-lowering treatments. Genome-wide association studies have linked variations in the Caveolin1/2 (CAV-1/2) gene loci to glaucoma risk. Cav-1, a key protein in caveolae membrane invaginations, is involved in signaling pathways and its absence impairs retinal function. Recent research suggests that Cav-1 is implicated in modulating the BDNF/TrkB signaling pathway in retinal ganglion cells, which plays a critical role in retinal ganglion cell (RGC) health and protection against apoptosis. Understanding the interplay between these proteins could shed light on glaucoma pathogenesis and provide potential therapeutic targets.

Clusters of apoptotic signaling molecule-enriched rafts, CASMERs: membrane platforms for protein assembly in Fas/CD95 signaling and targets in cancer therapy

Mammalian cells show the ability to commit suicide through the activation of death receptors at the cell surface. Death receptors, among which Fas/CD95 is one of their most representative members, lack enzymatic activity, and depend on protein-protein interactions to signal apoptosis. Fas/CD95 death receptor-mediated apoptosis requires the formation of the so-called death-inducing signaling complex (DISC), bringing together Fas/CD95, Fas-associated death domain-containing protein and procaspase-8. In the last two decades, cholesterol-rich lipid raft platforms have emerged as scaffolds where Fas/CD95 can be recruited and clustered. The co-clustering of Fas/CD95 and rafts facilitates DISC formation, bringing procaspase-8 molecules to be bunched together in a limited membrane region, and leading to their autoproteolytic activation by oligomerization. Lipid raft platforms serve as a specific region for the clustering of Fas/CD95 and DISC, as well as for the recruitment of additional downstream signaling molecules, thus forming the so-called cluster of apoptotic signaling molecule-enriched rafts, or CASMER. These raft/CASMER structures float in the membrane like icebergs, in which the larger portion lies inside the cell and communicates with other subcellular structures to facilitate apoptotic signal transmission. This allows an efficient spatiotemporal compartmentalization of apoptosis signaling machinery during the triggering of cell death. This concept of proapoptotic raft platforms as a basic chemical-biological structure in the regulation of cell death has wide-ranging implications in human biology and disease, as well as in cancer therapy. Here, we discuss how these raft-centered proapoptotic hubs operate as a major linchpin for apoptosis signaling and as a promising target in cancer therapy.

Recruitment of TNF ligands to lipid rafts is mediated by their physical association with caveolin-1

Activities of the tumour necrosis factor (TNF) family members are associated with their targeting to lipid rafts, specialised regions of the plasma membrane. Herein, we investigated the physical association of TNF and its family members cluster of differentiation 40 ligand (CD40L) and tumour necrosis factor-related apoptosis-inducing ligand with caveolin-1, a lipid raft resident protein. We discovered that the intracellular domains of TNF and CD40L interact with caveolin-1, and the membrane proximal region of TNF is required for the binding of caveolin-1 domains. Full-length TNF can form a complex with caveolin-1 in membrane rafts of HeLa cells, and caveolin-1 knockdown leads to impaired TNF transport to rafts. These findings provide the first evidence of a direct interaction between TNF, CD40L and caveolin-1 and suggest that caveolin-1 may be responsible for recruiting TNF to lipid rafts.

Advances in Understanding TKS4 and TKS5: Molecular Scaffolds Regulating Cellular Processes from Podosome and Invadopodium Formation to Differentiation and Tissue Homeostasis

Scaffold proteins are typically thought of as multi-domain "bridging molecules." They serve as crucial regulators of key signaling events by simultaneously binding multiple participants involved in specific signaling pathways. In the case of epidermal growth factor (EGF)-epidermal growth factor receptor (EGFR) binding, the activated EGFR contacts cytosolic SRC tyrosine-kinase, which then becomes activated. This process leads to the phosphorylation of SRC-substrates, including the tyrosine kinase substrates (TKS) scaffold proteins. The TKS proteins serve as a platform for the recruitment of key players in EGFR signal transduction, promoting cell spreading and migration. The TKS4 and the TKS5 scaffold proteins are tyrosine kinase substrates with four or five SH3 domains, respectively. Their structural features allow them to recruit and bind a variety of signaling proteins and to anchor them to the cytoplasmic surface of the cell membrane. Until recently, TKS4 and TKS5 had been recognized for their involvement in cellular motility, reactive oxygen species-dependent processes, and embryonic development, among others. However, a number of novel functions have been discovered for these molecules in recent years. In this review, we attempt to cover the diverse nature of the TKS molecules by discussing their structure, regulation by SRC kinase, relevant signaling pathways, and interaction partners, as well as their involvement in cellular processes, including migration, invasion, differentiation, and adipose tissue and bone homeostasis. We also describe related pathologies and the established mouse models.

Caveolin-1 Ablation Imparts Partial Protection Against Inner Retinal Injury in Experimental Glaucoma and Reduces Apoptotic Activation

Retinal ganglion cell degeneration is a characteristic feature of glaucoma, and accordingly, protection of these cells constitutes a major therapeutic objective in the disease. Here, we demonstrate the key influence of caveolin (Cav) in regulating the inner retinal homeostasis in two models of experimentally elevated intraocular pressure (IOP). Two groups of Cav-1^-/- and wild-type mice were used in the study. Animals were subjected to experimentally induced chronic and acutely elevated IOP and any changes in their retinal function were assessed by positive scotopic threshold response recordings. TUNEL and cleaved caspase-3 assays were performed to evaluate apoptotic changes in the retina while Brn3a immunostaining was used as a marker to assess and quantify ganglion cell layer (GCL) changes. H&E staining was carried out on retinal sections to evaluate histological differences in retinal laminar structure. Cav-1 ablation partially protected the inner retinal function in both chronic and acute models of elevated IOP. The protective effects of Cav-1 loss were also evident histologically by reduced loss of GCL density in both models. The phenotypic protection in Cav-1^-/- glaucoma mice paralleled with increased TrkB phosphorylation and reduced endoplasmic reticulum stress markers and apoptotic activation in the inner retinas. This study corroborated previous findings of enhanced Shp2 phosphorylation in a chronic glaucoma model and established a novel role of Cav-1 in mediating activation of this phosphatase in the inner retina in vivo. Collectively, these findings highlight the critical involvement of Cav-1 regulatory mechanisms in ganglion cells in response to increased IOP, implicating Cav-1 as a potential therapeutic target in glaucoma.

Dephosphorylation of Fas-ligand and caveolin-1 is a prerequisite step in Fas-ligand - caveolin-1 complex formation and cell death stimulation

Fas-ligand/CD178 belongs to the TNF family proteins and is the well-characterized inducer of cell death. We showed previously that the interaction of Fas-ligand and caveolin-1 is necessary for Fas-ligand translocation to rafts, and the subsequent induction of Fas-ligand-dependent cell death. Both molecules can undergo phosphorylation, however the role of the phosphorylation state of Fas-ligand and caveolin-1 in their physical association, and consequently in of Fas - mediated cell death induction is currently unknown. In this study, we show that in control cells Fas-ligand interaction with caveolin-1 is not observed, and both molecules are phosphorylated. The intracellular part of Fas-ligand was shown to form a complex with p59Fyn-kinase. Upon cell death activation, the expression and activity of p59Fyn-kinase decreases substantially, leading to the disruption of Fas-ligand - p59Fyn-kinase association, dephosphorylation of Fas-ligand and caveolin-1, and formation of a complex between them (Fas-ligand - caveolin-1). The analysis of the effects of kinase and phosphatase inhibitors revealed that phosphorylation of Fas-ligand and caveolin-1 at tyrosine residues suppressed Fas-mediated cell death. Thus, dephosphorylation of Fas-ligand and caveolin-1 is critical for triggering Fas-ligand-mediated apoptotic pathway and cell death execution.

A review of the role of cav-1 in neuropathology and neural recovery after ischemic stroke

Ischemic stroke starts a series of pathophysiological processes that cause brain injury. Caveolin-1 (cav-1) is an integrated protein and locates at the caveolar membrane. It has been demonstrated that cav-1 can protect blood–brain barrier (BBB) integrity by inhibiting matrix metalloproteases (MMPs) which degrade tight junction proteins. This article reviews recent developments in understanding the mechanisms underlying BBB dysfunction, neuroinflammation, and oxidative stress after ischemic stroke, and focuses on how cav-1 modulates a series of activities after ischemic stroke. In general, cav-1 reduces BBB permeability mainly by downregulating MMP9, reduces neuroinflammation through influencing cytokines and inflammatory cells, promotes nerve regeneration and angiogenesis via cav-1/VEGF pathway, reduces apoptosis, and reduces the damage mediated by oxidative stress. In addition, we also summarize some experimental results that are contrary to the above and explore possible reasons for these differences.