Gamma secretase dependent release of the CD44 cytoplasmic tail upregulates IFI16 in cd44-/- tumor cells, MEFs and macrophages

Inhibiting CD44-ICD Attenuates LPS-Induced Initiation of Hepatic Inflammation in Septic Mice

Sepsis is a severe condition induced by microbial infection. It elicits a systemic inflammatory response, leading to multi-organ failure, and the liver, as a scavenger, plays a significant role in this process. Controlling hepatic inflammation and maintaining liver function is crucial in managing sepsis. CD44-ICD, as a CD44 signal transductor, is involved in multiple inflammatory responses. However, the role of CD44-ICD in lipopolysaccharide (LPS)-induced hepatic inflammation has not been investigated. Therefore, we aimed to examine whether CD44-ICD initiates hepatic inflammation in septic mice. We induced hepatic inflammation in mice by administering LPS. DAPT, a CD44-ICD inhibitor, was given to mice or Chang cells 30 min or 1 h before LPS administration (10 mg/kg, i.p., or 100 ng/mL, respectively). Inhibition of CD44-ICD decreased the level of aspartate aminotransferase (AST), alanine aminotransferase (ALT), hepatic necrosis, inflammatory cell infiltration, interleukin (IL)-1β, inducible NO synthase (iNOS), nitric oxide (NO) production, nuclear factor (NF)κB signaling pathway proteins, and CD44 expression in mice. CD44-ICD inhibition also decreased IL-1β and CD44 expression levels in Chang cells. CD44-ICD may be a primary regulatory function in CD44-associated LPS-induced initiation of hepatic inflammation in mice.

Endolysosomal impairment by binding of amyloid beta or MAPT/Tau to V-ATPase and rescue via the HYAL-CD44 axis in Alzheimer disease

Impaired activities and abnormally enlarged structures of endolysosomes are frequently observed in Alzheimer disease (AD) brains. However, little is known about whether and how endolysosomal dysregulation is triggered and associated with AD. Here, we show that vacuolar ATPase (V-ATPase) is a hub that mediates proteopathy of oligomeric amyloid beta (Aβ) and hyperphosphorylated MAPT/Tau (p-MAPT/Tau). Endolysosomal integrity was largely destroyed in Aβ-overloaded or p-MAPT/Tau-positive neurons in culture and AD brains, which was a necessary step for triggering neurotoxicity, and treatments with acidic nanoparticles or endocytosis inhibitors rescued the endolysosomal impairment and neurotoxicity. Interestingly, we found that the lumenal ATP6V0C and cytosolic ATP6V1B2 subunits of the V-ATPase complex bound to the internalized Aβ and cytosolic PHF-1-reactive MAPT/Tau, respectively. Their interactions disrupted V-ATPase activity and accompanying endolysosomal activity in vitro and induced neurodegeneration. Using a genome-wide functional screen, we isolated a suppressor, HYAL (hyaluronidase), which reversed the endolysosomal dysfunction and proteopathy and alleviated the memory impairment in 3xTg-AD mice. Further, we found that its metabolite hyaluronic acid (HA) and HA receptor CD44 attenuated neurotoxicity in affected neurons via V-ATPase. We propose that endolysosomal V-ATPase is a bona fide proteotoxic receptor that binds to pathogenic proteins and deteriorates endolysosomal function in AD, leading to neurodegeneration in proteopathy.Abbreviations: AAV, adeno-associated virus; Aβ, amyloid beta; AD, Alzheimer disease; APP, amyloid beta precursor protein; ATP6V0C, ATPase H+ transporting V0 subunit c; ATP6V1A, ATPase H+ transporting V1 subunit A; ATP6V1B2, ATPase H+ transporting V1 subunit B2; CD44.Fc, CD44-mouse immunoglobulin Fc fusion construct; Co-IP, co-immunoprecipitation; CTSD, cathepsin D; HA, hyaluronic acid; HMWHA, high-molecular-weight hyaluronic acid; HYAL, hyaluronidase; i.c.v, intracerebroventricular; LMWHA, low-molecular-weight hyaluronic acid; NPs, nanoparticles; p-MAPT/Tau, hyperphosphorylated microtubule associated protein tau; PI3K, phosphoinositide 3-kinase; V-ATPase, vacuolar-type H+-translocating ATPase; WT, wild-type.

Dysregulation of ADAM10 shedding activity in naked mole-rat fibroblasts is due to deficient phosphatidylserine externalization

The naked mole-rat (NMR, Heterocephalus glaber) is of significant interest to biogerontological research, rarely developing age-associated diseases, such as cancer. The transmembrane glycoprotein CD44 is upregulated in certain cancers and CD44 cleavage by a disintegrin and metalloproteinase 10 (ADAM10) regulates cellular migration. Here we provide evidence that mature ADAM10 is expressed in NMR primary skin fibroblasts (NPSF), and that ionomycin increases cell surface ADAM10 localization. However, we observed an absence of ADAM10 mediated CD44 cleavage, as well as shedding of exogenous and overexpressed betacellulin in NPSF, whereas in mouse primary skin fibroblasts ionomycin induced ADAM10-dependent cleavage of both CD44 and betacellulin. Overexpressing a hyperactive form of the Ca²⁺ -dependent phospholipid scramblase ANO6 in NPSF increased phosphatidylserine (PS) externalization, which rescued the ADAM10 sheddase activity and promoted cell migration in NPSF in an ADAM10-dependent manner. These findings suggest that dysregulation of ADAM10 shedding activity is due to a deficient PS externalization in NMR.

CD44 Contributes to the Regulation of MDR1 Protein and Doxorubicin Chemoresistance in Osteosarcoma

Osteosarcoma is the most common type of pediatric bone tumor. Despite great advances in chemotherapy during the past decades, the survival rates of osteosarcoma patients remain unsatisfactory. Drug resistance is one of the main reasons, leading to treatment failure and poor prognosis. Previous reports correlated expression of cluster of differentiation 44 (CD44) with drug resistance and poor survival of osteosarcoma patients, however the underlying mechanisms are poorly defined. Here, we investigated the role of CD44 in the regulation of drug chemoresistance, using osteosarcoma cells isolated from mice carrying a mutation of the tumor suppressor neurofibromatosis type 2 (Nf2) gene. CD44 expression was knocked-down in the cells using CRISPR/Cas9 approach. Subsequently, CD44 isoforms and mutants were re-introduced to investigate CD44-dependent processes. Sensitivity to doxorubicin was analyzed in the osteosarcoma cells with modified CD44 expression by immunoblot, colony formation- and WST-1 assay. To dissect the molecular alterations induced by deletion of Cd44, RNA sequencing was performed on Cd44-positive and Cd44-negative primary osteosarcoma tissues isolated from Nf2-mutant mice. Subsequently, expression of candidate genes was evaluated by quantitative reverse transcription PCR (qRT-PCR). Our results indicate that CD44 increases the resistance of osteosarcoma cells to doxorubicin by up-regulating the levels of multidrug resistance (MDR) 1 protein expression, and suggest the role of proteolytically released CD44 intracellular domain, and hyaluronan interactions in this process. Moreover, high throughput sequencing analysis identified differential regulation of several apoptosis-related genes in Cd44-positive and -negative primary osteosarcomas, including p53 apoptosis effector related to PMP-22 (Perp). Deletion of Cd44 in osteosarcoma cells led to doxorubicin-dependent p53 activation and a profound increase in Perp mRNA expression. Overall, our results suggest that CD44 might be an important regulator of drug resistance and suggest that targeting CD44 can sensitize osteosarcoma to standard chemotherapy.

Proteolytic Processing of CD44 and Its Implications in Cancer

CD44 is a transmembrane glycoprotein expressed in several healthy and tumor tissues. Modifications in its structure contribute differently to the activity of this molecule. One modification that has provoked interest is the consecutive cleavage of the CD44 extracellular ectodomain by enzymes that belong mainly to the family of metalloproteases. This process releases biologically active substrates, via alternative splice forms of CD44, that generate CD44v3 or v6 isoforms which participate in the transcriptional regulation of genes and proteins associated to signaling pathways involved in the development of cancer. These include the protooncogene tyrosine-protein kinase Src (c-Src)/signal transducer and activator of transcription 3 (STAT3), the epithelial growth factor receptor, the estrogen receptor, Wnt/βcatenin, or Hippo signaling pathways all of which are associated to cell proliferation, differentiation, or cancer progression. Whereas CD44 still remains as a very useful prognostic cell marker in different pathologies, the main topic is that the generation of CD44 intracellular fragments assists the regulation of transcriptional proteins involved in the cell cycle, cell metabolism, and most importantly, the regulation of some stem cell-associated markers.

High molecular weight form of hyaluronic acid reduces neuroinflammatory response in injured sciatic nerve via the intracellular domain of CD44

Inflammatory response after peripheral nerve injury is required for clearance of tissue debris and effective regeneration. Studies have revealed that hyaluronic acid (HA) may exert different properties depending on their molecular size. High molecular weight HA (>>1,000 kDa; HMW-HA) displays immunosuppressive properties, whereas low molecular weight HA (<800 kDa; LMW-HA) induces proinflammatory responses. The role of HMW-HA interaction with CD44, a major HA receptor, in neuroinflammatory responses has not been fully elucidated. The purpose of this experimental study was to investigate the effects of topical applications of HMW-HA on the sciatic nerve injury in an adult rat model. At the crush site on the sciatic nerve, the recordings of compound muscle action potential (CMAP) and the levels of several proteins related to inflammatory response were assessed at time intervals of 2, 4, and 6 weeks postsurgery. Here, we show that the recovery effect of HMW-HA treatment had significantly shortened latency and increased amplitude of CMAP compared with crushed alone, crushed plus γ-secretase inhibitor with or without HA treatment at 6 weeks after surgery. Our data reveal that HMW-HA could downregulate the expression of IL1-β, TLR4, and MMP-9, whereas these proteins expression were increased when the CD44-ICD activity was inhibited using γ-secretase inhibitor. Our findings demonstrated a novel role of CD44-ICD in HA-mediated recovery of peripheral nerve injury. Clinical relevance: an alternative for the regeneration of peripheral nerve injury.

L-selectin: A Major Regulator of Leukocyte Adhesion, Migration and Signaling

L-selectin (CD62L) is a type-I transmembrane glycoprotein and cell adhesion molecule that is expressed on most circulating leukocytes. Since its identification in 1983, L-selectin has been extensively characterized as a tethering/rolling receptor. There is now mounting evidence in the literature to suggest that L-selectin plays a role in regulating monocyte protrusion during transendothelial migration (TEM). The N-terminal calcium-dependent (C-type) lectin domain of L-selectin interacts with numerous glycans, including sialyl Lewis X (sLe^x) for tethering/rolling and proteoglycans for TEM. Although the signals downstream of L-selectin-dependent adhesion are poorly understood, they will invariably involve the short 17 amino acid cytoplasmic tail. In this review we will detail the expression of L-selectin in different immune cell subsets, and its influence on cell behavior. We will list some of the diverse glycans known to support L-selectin-dependent adhesion, within luminal and abluminal regions of the vessel wall. We will describe how each domain within L-selectin contributes to adhesion, migration and signal transduction. A significant focus on the L-selectin cytoplasmic tail and its proposed contribution to signaling via the ezrin-radixin-moesin (ERM) family of proteins will be outlined. Finally, we will discuss how ectodomain shedding of L-selectin during monocyte TEM is essential for the establishment of front-back cell polarity, bestowing emigrated cells the capacity to chemotax toward sites of damage.

Presenilins and γ-Secretase in Membrane Proteostasis

The presenilin (PS) proteins exert a crucial role in the pathogenesis of Alzheimer disease (AD) by mediating the intramembranous cleavage of amyloid precursor protein (APP) and the generation of amyloid β-protein (Aβ). The two homologous proteins PS1 and PS2 represent the catalytic subunits of distinct γ-secretase complexes that mediate a variety of cellular processes, including membrane protein metabolism, signal transduction, and cell differentiation. While the intramembrane cleavage of select proteins by γ-secretase is critical in the regulation of intracellular signaling pathways, the plethora of identified protein substrates could also indicate an important role of these enzyme complexes in membrane protein homeostasis. In line with this notion, PS proteins and/or γ-secretase has also been implicated in autophagy, a fundamental process for the maintenance of cellular functions and homeostasis. Dysfunction in the clearance of proteins in the lysosome and during autophagy has been shown to contribute to neurodegeneration. This review summarizes the recent knowledge about the role of PS proteins and γ-secretase in membrane protein metabolism and trafficking, and the functional relation to lysosomal activity and autophagy.