CD44 is an adhesion molecule that serves as a cell surface receptor for several extracellular matrix components, including hyaluronan (HA). The proteolytic cleavage of CD44 from the cell surface plays a critical role in the migration of tumor cells. Although this cleavage can be induced by certain stimuli such as phorbol ester and anti-CD44 antibodies in vitro, the physiological inducer of CD44 cleavage in vivo is unknown. Here, we demonstrate that HA oligosaccharides of a specific size range induce CD44 cleavage from tumor cells. Fragmented HA containing 6-mers to 14-mers enhanced CD44 cleavage dose-dependently by interacting with CD44, whereas a large polymer HA failed to enhance CD44 cleavage, although it bound to CD44. Examination using uniformly sized HA oligosaccharides revealed that HAs smaller than 36 kDa significantly enhanced CD44 cleavage. In particular, the 6.9-kDa HA (36-mers) not only enhanced CD44 cleavage but also promoted tumor cell motility, which was completely inhibited by an anti-CD44 monoclonal antibody. These results raise the possibility that small HA oligosaccharides, which are known to occur in various tumor tissues, promote tumor invasion by enhancing the tumor cell motility that may be driven by CD44 cleavage.

CD44 is a cell surface adhesion molecule for hyaluronan and is implicated in tumor invasion and metastasis. Proteolytic cleavage of CD44 plays a critical role in the migration of tumor cells and is regulated by factors present in the tumor microenvironment, such as hyaluronan oligosaccharides and epidermal growth factor. However, molecular mechanisms underlying the proteolytic cleavage on membranes remain poorly understood. In this study, we demonstrated that cholesterol depletion with methyl-␤-cyclodextrin, which disintegrates membrane lipid rafts, enhances CD44 shedding mediated by a disintegrin and metalloproteinase 10 (ADAM10) and that cholesterol depletion disorders CD44 localization to the lipid raft. We also evaluated the effect of long term cholesterol reduction using a statin agent and demonstrated that statin enhances CD44 shedding and suppresses tumor cell migration on a hyaluronan-coated substrate. Our results indicate that membrane lipid organization regulates CD44 shedding and propose a possible molecular mechanism by which cholesterol reduction might be effective for preventing and treating the progression of malignant tumors.CD44 is a cell surface receptor for several extracellular matrix components, including hyaluronan (1), and is implicated in a wide variety of biological processes, including cell migration (2) and tumor metastasis (3). The migratory properties of invasive tumor cells are affected both by the interaction between their adhesion molecules and the surrounding extracellular matrices and by growth factor signaling (4). The proteolytic ectodomain cleavage and release (shedding) of membrane proteins is a critical regulatory step in both physiological and pathological processes (5, 6).Recently, physiological inducers of CD44 shedding have been identified; hyaluronan small fragments, frequently detected in association with pathological conditions including cancer (7), induce CD44 shedding from tumor cells (8). Intracellular signaling via Rac GTPase, elicited by CD44 engagement, leads to ADAM 2 (a disintegrin and metalloproteinase)-mediated CD44 shedding and tumor cell migration (9). A prominent abnormality of tumor cells such as gliomas is the overexpression of the EGF receptor (10), and EGF induces the shedding of CD44 (11). Although the molecular mechanisms underlying CD44 shedding induced by spatio-temporally ordered intracellular signaling in the tumor microenvironment have been partly clarified (9, 11), the mechanism that triggers CD44 shedding on the membrane is not yet understood.Lipid rafts, which are microdomains of the plasma membrane that are rich in cholesterol and sphingolipids (12), are thought to exhibit a liquid-ordered phase floating in the liquid-disordered matrix of the plasma membrane. Recent studies have confirmed the importance of lipid rafts and their associated proteins, including CD44, in cancer progression (13). A number of reports have shown that CD44 is present in lipid rafts (14 -18). Recently, several reports have demonstrated that lipid rafts play a cruci...

Abstract:The accumulation of cholesterol is a general feature of cancer tissue, and recent evidence suggests that cholesterol plays critical roles in the progression of cancers, including breast, prostate, and colorectal cancers. The dysregulation of metabolic pathways, including those involved in cholesterol biosynthesis, is implicated in tumor development and cancer progression. Lipid rafts are highly dynamic cholesterol-enriched domains of the cell membrane, involved in various cellular functions, including the regulation of transmembrane signaling at the cell surface. It was recently demonstrated that lipid rafts also play critical roles in cancer cell adhesion and migration. This review focuses on our current understanding of how cholesterol regulation, lipid rafts, and dysregulated cholesterol biosynthesis contribute to cancer development and progression, and the therapeutic potential of cholesterol lowering for cancer prevention and treatment.

CD44 is a major cell surface adhesion molecule for hyaluronan, a component of the extracellular matrix, and is implicated in tumor metastasis and invasion. We reported previously that hyaluronan oligosaccharides induce CD44 cleavage from tumor cells. Here we show that engagement of CD44 promotes CD44 cleavage and tumor cell migration, both of which were suppressed by a metalloproteinase inhibitor KB-R7785 and tissue inhibitor of metalloproteinases-1 (TIMP-1) but not by TIMP-2. We also present evidence that blockade of metalloproteinase-disintegrin ADAM10 (a disintegrin and metalloproteinase 10) by RNA interference suppresses CD44 cleavage induced by its ligation. Engagement of CD44 concurrently induced activation of the small GTPase Rac1 and led to drastic changes in cell morphology and actin cytoskeleton with redistribution of CD44 to newly generated membrane ruffling areas. A fluorescence resonance energy transfer approach to visualize GTP-bound Rac1 in living cells revealed the localization of the active Rac1 in the leading edge of the membrane ruffling areas upon ligation of CD44. Taken together, our results indicate that the cleavage of CD44 catalyzed by ADAM10 is augmented by the intracellular signaling elicited by engagement of CD44, through Rac-mediated cytoskeletal rearrangement, and suggest that CD44 cleavage contributes to the migration and invasion of tumor cells.CD44 is a cell surface receptor for several extracellular matrix components including hyaluronan (HA) 1 (1) and is implicated in a wide variety of biological processes including lymphocyte homing (2), cell migration (3), and metastasis (4). It has been demonstrated that CD44 expressed in tumor cells is proteolytically cleaved at the extracellular domain by metalloproteinases and that CD44 cleavage plays a critical role in CD44-mediated tumor cell migration (5, 6). CD44 cleavage on the tumor cell surface is enhanced by phorbol 12-myristate 13-acetate (PMA) or ionomycin treatment, indicating that the cleavage is under the regulation of the activation of protein kinase C (PKC) or the extracellular calcium influx (7). CD44 cleavage is also induced by introducing dominant active mutant of Ha-Ras small GTPase (8). In addition to these CD44 cleavage inducers acting on intracellular signaling molecules, we have shown recently (9) that HA fragments also enhance CD44 cleavage from tumor cells. HA fragments probably bind and cross-link CD44 and then induce certain intracellular signals to cause CD44 cleavage. However, almost no information is available regarding the intracellular signals transmitted upon stimulation of CD44 to the induction of CD44 cleavage. The relationship between CD44 cleavage and the enhanced cell migration also remains largely unknown.Tumor cells migrate by regulating adhesion to and detachment from extracellular matrix, dynamically changing their cytoskeleton (10). Rho family small GTPases are the key regulators of actin organization in cytoskeleton, and the changes of their activation state influence cell morphology (11). The ma...

Hyaluronan (HA) is an extracellular matrix glycosaminoglycan that interacts with cell-surface receptors, including CD44. Although HA usually exists as a high molecular mass polymer, HA of a much lower molecular mass that shows a variety of biological activities can be detected under certain pathological conditions, particularly in tumors. We previously reported that low molecular weight HAs (LMW-HAs) of a certain size range induce the proteolytic cleavage of CD44 from the surface of tumor cells and promote tumor cell migration in a CD44-dependent manner. Here, we show that MIA PaCa-2, a human pancreatic carcinoma cell line, secreted hyaluronidases abundantly and generated readily detectable levels of LMW-HAs ranging from ϳ10-to 40-mers. This occurred in the absence of any exogenous stimulation. The tumor-derived HA oligosaccharides were able to enhance CD44 cleavage and tumor cell motility. Inhibition of the CD44-HA interaction resulted in the complete abrogation of these cellular events. These results are consistent with the concept that tumor cells generate HA oligosaccharides that bind to tumor cell CD44 through the expression of their own constitutive hyaluronidases. This enhances their own CD44 cleavage and cell motility, which would subsequently promote tumor progression. Such an autocrine/paracrine-like process may represent a novel activation mechanism that would facilitate and promote the malignant potential of tumor cells.Hyaluronan (HA), 2 one of the major components of the extracellular matrix, is a high molecular weight linear glycosaminoglycan consisting of repeating disaccharide units of D-glucuronic acid and N-acetyl-Dglucosamine, whose molecular size can reach 10 7 kDa (1, 2). Despite its simple composition, HA possesses a number of functions. It influences the hydration and physical properties of tissues (1, 3), interacts with other extracellular matrix macromolecules such as aggrecan (4) and versican (5), and interacts with cell-surface receptors, notably CD44 (6). Through these functions, HA forms a pericellular coat around cells (2, 7) and participates in physiological events such as cell adhesion, migration, and proliferation (8). It is also involved in pathological conditions, including cancer (7). An increased synthesis of HA has been reported in various malignant tumors such as breast and ovarian carcinomas, and predicts a poor prognosis (9, 10). HA enhances tumor cell adhesion and migration (11) and influences several signaling pathways, including some that promote tumor cell growth and survival, such as ErbB2, Ras, mitogen-activated protein kinase, and phosphatidylinositol 3-kinase/ Akt (12-14).Hyaluronidases play critical roles in HA metabolism (15). Six human hyaluronidase-like sequences are present in the human genome. These are HYAL1, HYAL2, HYAL3, HYAL4, SPAM1, and PHYAL1, which, respectively, encode Hyal-1, Hyal-2, Hyal-3, Hyal-4, PH-20, and a pseudogene that is transcribed but not translated (16). Of these hyaluronidases, only Hyal-1 and Hyal-2 have been characterized well. Hyal...

Lipid rafts are cholesterol-enriched microdomains of the cell membrane and possess a highly dynamic nature. They have been involved in various cellular functions including the regulation of cell adhesion and membrane signaling through proteins within lipid rafts. The dynamic features of the cancer cell surface may modulate the malignant phenotype of cancer, including adhesion disorders and aggressive phenotypes of migration and invasion. Recently, it was demonstrated that lipid rafts play critical roles in cancer cell adhesion and migration. This article summarizes the important roles of lipid rafts in cancer cell adhesion and migration, with a focus on the current state of knowledge. This article will improve the understanding of cancer progression and lead to the development of novel targets for cancer therapy.

Hyaluronan is a major component of the extracellular matrix and plays pivotal roles in inflammation and cancer. Hyaluronan oligomers are frequently found in these pathological conditions, in which they exert their effects via association with the transmembrane receptor CD44. Lipid rafts are cholesterol- and glycosphingolipid-enriched membrane microdomains that may regulate membrane receptors while serving as platforms for transmembrane signaling at the cell surface. This article focuses on the recent discovery that lipid rafts regulate the interaction between CD44 and hyaluronan, which depends largely on hyaluronan’s size. Lipid rafts regulate CD44’s ability to bind hyaluronan in T cells, control the rolling adhesion of lymphocytes on vascular endothelial cells, and regulate hyaluronan- and CD44-mediated cancer cell migration. The implications of these findings for preventing inflammatory disorders and cancer are also discussed.

Alzheimer’s disease is a neurodegenerative sickness, where the speed of personal disease progression differs prominently due to genetic and environmental factors such as life style. Alzheimer’s disease is described by the construction of neuronal plaques and neurofibrillary tangles composed of phosphorylated tau protein. Mitochondrial dysfunction may be a noticeable feature of Alzheimer’s disease and increased production of reactive oxygen species has long been described. Superoxide dismutases (SODs) protect from excess reactive oxygen species to form less reactive hydrogen peroxide. It is suggested that SODs can play a protective role in neurodegeneration. In addition, PI3K/AKT pathway has been shown to play a critical role on the neuroprotection and inhibiting apoptosis via the enhancing expression of the SODs. This pathway appears to be crucial in Alzheimer’s disease because it is related to the tau protein hyper-phosphorylation. Dietary supplementation of several ordinary compounds may provide a novel therapeutic approach to brain disorders by modulating the function of the PI3K/AKT pathway. Understanding these systems may offer a better efficacy of new therapeutic approaches. In this review, we summarize recent progresses on the involvement of the SODs and PI3K/AKT pathway in neuroprotective signaling against Alzheimer’s disease.