sAPP as a regulator of dendrite motility and melanin release in epidermal melanocytes and melanoma cells

Melanoma-secreted Amyloid Beta Suppresses Neuroinflammation and Promotes Brain Metastasis

Brain metastasis is a significant cause of morbidity and mortality in multiple cancer types and represents an unmet clinical need. The mechanisms that mediate metastatic cancer growth in the brain parenchyma are largely unknown. Melanoma, which has the highest rate of brain metastasis among common cancer types, is an ideal model to study how cancer cells adapt to the brain parenchyma. Our unbiased proteomics analysis of melanoma short-term cultures revealed that proteins implicated in neurodegenerative pathologies are differentially expressed in melanoma cells explanted from brain metastases compared to those derived from extracranial metastases. We showed that melanoma cells require amyloid beta (AB) for growth and survival in the brain parenchyma. Melanoma-secreted AB activates surrounding astrocytes to a pro-metastatic, anti-inflammatory phenotype and prevents phagocytosis of melanoma by microglia. Finally, we demonstrate that pharmacological inhibition of AB decreases brain metastatic burden.

CD2-associated protein (CD2AP) overexpression accelerates amyloid precursor protein (APP) transfer from early endosomes to the lysosomal degradation pathway

A hallmark of Alzheimer's disease (AD) pathology is the appearance of senile plaques, which are composed of β-amyloid (Aβ) peptides. Aβ is produced by sequential cleavages of amyloid precursor protein (APP) by β- and γ-secretases. These cleavages take place in endosomes during intracellular trafficking of APP through the endocytic and recycling pathways. Genome-wide association studies have identified several risk factors for late-onset AD, one of which is CD2-associated protein (CD2AP), an adaptor molecule that regulates membrane trafficking. Although CD2AP's involvement in APP trafficking has recently been reported, how APP trafficking is regulated remains unclear. We sought to address this question by investigating the effect of CD2AP overexpression or knockdown on the intracellular APP distribution and degradation of APP in cultured COS-7 and HEK293 cells. We found that overexpression of CD2AP increases the localization of APP to Rab7-positive late endosomes, and decreases its localization to Rab5-positive early endosomes. CD2AP overexpression accelerated the onset of APP degradation without affecting its degradation rate. Furthermore, nutrient starvation increased the localization of APP to Rab7-positive late endosomes, and CD2AP overexpression stimulated starvation-induced lysosomal APP degradation. Moreover, the effect of CD2AP on the degradation of APP was confirmed by CD2AP overexpression and knockdown in primary cortical neurons from mice. We conclude that CD2AP accelerates the transfer of APP from early to late endosomes. This transfer in localization stimulates APP degradation by reducing the amount of time before degradation initiation. Taken together, these results may explain why impaired CD2AP function is a risk factor for AD.

Substituted 2-hydroxy-N-(arylalkyl)benzamide sensitizes cancer cells to metabolic stress by disrupting actin cytoskeleton and inhibiting autophagic flux

N-((R)-1-(4-chlorophenylcarbamoyl)-2-phenylethyl)-5-chloro-2-hydroxybenzamide (Compound 6k), was recently isolated during the preparation of amino acids esters with salicylanilides. We show here that 6k disrupts the dynamics of actin cytoskeleton in human melanoma cells, affecting processes essential for the maintenance and expansion of tumours such as cell adhesion, motility, proliferation, vesicular transport, and autophagic flux. We demonstrated that inhibition of autophagy by 6k increased the sensitivity of melanoma cells to metabolic stress induced by rotenone or nutrient starvation and potentiated the anti-proliferative activity of small molecule multikinase inhibitor sorafenib. Since autophagy plays an important role in survival of cancer cells subjected to chemotherapy, the above mentioned properties are interesting from clinical point of view as 6k could promote metabolic stress within the tumour microenvironment and potentiate the effect of cytostatics in combination therapy.

Substituted dithiazole piperazine benzamides as novel amyloid beta peptide reducing agents

Alzheimer's disease is a persistent neurodegenerative disorder of elderly characterized clinically by irreversible loss of memory due to accumulation of amyloid beta peptides within the amyloid plaques. We report the parallel synthesis and screening results of diverse substituted di-thiazole piperazine benzamides. A new compound TPI-1917-49 was identified as a promising amyloid reducing agent by lowering the levels of Aβ at least in two cell types and in vivo.

RanBP9 overexpression accelerates loss of pre and postsynaptic proteins in the APΔE9 transgenic mouse brain

There is now compelling evidence that the neurodegenerative process in Alzheimer's disease (AD) begins in synapses. Loss of synaptic proteins and functional synapses in the amyloid precursor protein (APP) transgenic mouse models of AD is well established. However, what is the earliest age at which such loss of synapses occurs, and whether known markers of AD progression accelerate functional deficits is completely unknown. We previously showed that RanBP9 overexpression leads to robustly increased amyloid β peptide (Aβ) generation leading to enhanced amyloid plaque burden in a mouse model of AD. In this study we compared synaptic protein levels among four genotypes of mice, i.e., RanBP9 single transgenic (Ran), APΔE9 double transgenic (Dbl), APΔE9/RanBP9 triple transgenic (Tpl) and wild-type (WT) controls. We found significant reductions in the levels of synaptic proteins in both cortex and hippocampus of 5- and 6-months-old but not 3- or 4-months-old mice. Specifically, at 5-months of age, rab3A was reduced in the triple transgenic mice only in the cortex by 25% (p<0.05) and gap43 levels were reduced only in the hippocampus by 44% (p<0.01) compared to wild-type (WT) controls. Interestingly, RanBP9 overexpression in the Tpl mice reduced gap43 levels by a further 31% (p<0.05) compared to APΔE9 mice. RanBP9 also further decreased the levels of drebrin in the hippocampus by 32% (p<0.01) and chromogranin in the cortex by 24% (p<0.05) compared to APΔE9 mice. At 6-months of age, RanBP9 expression in the cortex led to further reduction of rab3A by 30% (p<0.05) and drebrin by 38% (p<0.01) compared to APΔE9 mice. RanBP9 also increased Aβ oligomers in the cortex at 6 months. Similarly, in the hippocampus, RanBP9 expression further reduced rab3A levels by 36% (p<0.01) and drebrin levels by 33% (p<0.01). Taken together these data suggest that RanBP9 overexpression accelerates loss of synaptic proteins in the mouse brain.

Role of RanBP9 on amyloidogenic processing of APP and synaptic protein levels in the mouse brain

We previously reported that RanBP9 binds low-density lipoprotein receptor-related protein (LRP), amyloid precursor protein (APP), and BACE1 and robustly increased Aβ generation in a variety of cell lines and primary neuronal cultures. To confirm the physiological/ pathological significance of this phenotype in vivo, we successfully generated transgenic mice overexpressing RanBP9 as well as RanBP9-null mice. Here we show that RanBP9 overexpression resulted in >2-fold increase in Aβ40 levels as early as 4 mo of age. A sustained increase in Aβ40 levels was seen at 12 mo of age in both CHAPS-soluble and formic acid (FA)-soluble brain fractions. In addition, Aβ42 levels were also significantly increased in FA-soluble fractions at 12 mo of age. More important, increased Aβ levels were translated to increased deposition of amyloid plaques. In addition, RanBP9 overexpression significantly decreased the levels of synaptophysin and PSD-95 proteins. Conversely, RanBP9-null mice showed increased levels of synaptophysin, PSD-95, and drebrin A protein levels. Given that loss of synapses is the best pathological correlate of cognitive deficits in Alzheimer's disease (AD), increased Aβ levels by RanBP9 observed in the present study provides compelling evidence that RanBP9 may indeed play a key role in the etiology of AD. If so, RanBP9 provides a great opportunity to develop novel therapy for AD.

Identification and biology of α-secretase

'Secretase' is a generic term coined more than 20 years ago to refer to a group of proteases responsible for the cleavage of a vast number of membrane proteins. These endoproteolytic events result in the extracellular or intracellular release of soluble metabolites associated with a broad range of intrinsic physiological functions. α-Secretase refers to the activity targeting the amyloid precursor protein (APP) and generating sAPPα, a soluble extracellular fragment potentially associated with neurotrophic and neuroprotective functions. Several proteases from the a disintegrin and metalloproteinase (ADAM) family, including ADAM10 and ADAM17, have been directly or indirectly associated with the constitutive and regulated α-secretase activities. Recent evidence in primary neuronal cultures indicates that ADAM10 may represent the genuine constitutive α-secretase. Mainly because α-secretase cleaves APP within the sequence of Aβ, the core component of the cerebral amyloid plaques in Alzheimer's disease, α-secretase activation is considered to be of therapeutic value. In this article, we will provide a historical perspective on the characterization of α-secretase and review the recent literature on the identification and biology of the current α-secretase candidates.

Crystal structure of the E2 domain of amyloid precursor protein-like protein 1 in complex with sucrose octasulfate

Missense mutations in the amyloid precursor protein (APP) gene can cause familial Alzheimer disease. It is thought that APP and APP-like proteins (APLPs) may play a role in adhesion and signal transduction because their ectodomains interact with components of the extracellular matrix. Heparin binding induces dimerization of APP and APLPs. To help explain how these proteins interact with heparin, we have determined the crystal structure of the E2 domain of APLP1 in complex with sucrose octasulfate (SOS). A total of three SOS molecules are bound to the E2 dimer. Two SOSs are bound inside a narrow intersubdomain groove, and the third SOS is bound near the two-fold axis of the protein. Mutational analyses show that most residues interacting with SOS also contribute to heparin binding, although in varying degrees; a deep pocket, defined by His-376, Lys-422, and Arg-429, and an interfacial site between Lys-314 and its symmetry mate are most important in the binding of the negatively charged polysaccharide. Comparison with a lower resolution APP structure shows that all key heparin binding residues are conserved and identically positioned, suggesting that APLP1 and APP may bind heparin similarly. In transfected HEK-293 cells, mutating residues responsible for heparin binding causes little change in the proteolysis of APP by the secretases. However, mutating a pair of conserved basic residues (equivalent to Arg-414 and Arg-415 of APLP1) immediately adjacent to the heparin binding site affects both the maturation and the processing of APP.

The E2 domains of APP and APLP1 share a conserved mode of dimerization

Amyloid precursor protein (APP) is genetically linked to Alzheimer's disease. APP is a type I membrane protein, and its oligomeric structure is potentially important because this property may play a role in its function or affect the processing of the precursor by the secretases to generate amyloid β-peptide. Several independent studies have shown that APP can form dimers in the cell, but how it dimerizes remains controversial. At least three regions of the precursor, including a centrally located and conserved domain called E2, have been proposed to contribute to dimerization. Here we report two new crystal structures of E2, one from APP and the other from APLP1, a mammalian APP homologue. Comparison with an earlier APP structure, which was determined in a different space group, shows that the E2 domains share a conserved and antiparallel mode of dimerization. Biophysical measurements in solution show that heparin binding induces E2 dimerization. The 2.1 Å resolution electron density map also reveals phosphate ions that are bound to the protein surface. Mutational analysis shows that protein residues interacting with the phosphate ions are also involved in heparin binding. The locations of two of these residues, Arg-369 and His-433, at the dimeric interface suggest a mechanism for heparin-induced protein dimerization.

Identification of the amyloid β-protein precursor and cystatin C as novel epidermal growth factor receptor regulated secretory proteins in nasopharyngeal carcinoma by proteomics

The epidermal growth factor receptor (EGFR) is usually overexpressed in nasopharyngeal carcinoma (NPC) and is associated with pathogenesis of NPC. However, while EGFR-modulated intracellular proteins have been extensively studied, little is known concerning their extracellular counterparts. To identify EGFR-regulated secreted proteins in NPC, we compared the secretome profiles of TGF-α-stimulated and unstimulated NPC cell line CNE-2. CNE-2 cells were cultured in the absence or presence of TGF-α for 24 h, and secreted proteins were obtained from conditioned serum-free media and enriched by ultrafiltration centrifugation. Using 2-DE and subsequent mass spectrometry, we identified 16 differential secreted proteins, among which the amyloid β-protein precursor (APP) was up-regulated and cystatin C was down-regulated after TGF-α stimulation. We further showed that the secretory changes of APP and cystatin C in CNE-2 after TGF-α stimulation could be abrogated by pretreatment of EGFR tyrosine kinase inhibitor PD153035 and PI3 kinase inhibitor Wortmannin, validating that APP and cystatin C are EGFR-regulated secreted proteins in NPC cells. Immunohistochemistry showed that the expression level of EGFR was positively correlated with the expression level of APP and negatively correlated with the expression level of cystatin C in NPC tissues, indicating that EGFR also regulates expression of APP and cystatin C in clinical NPC tissues. Furthermore, functional analysis showed that the growth and migration of CNE-2 cells decreased after neutralization of secretory APP in the medium using the anti-APP antibody. Our data provide substantial evidence that APP and cystatin C are target secreted proteins of EGFR in NPC, and upregulation of secretory APP by EGFR may be involved in the pathogenesis of NPC.

Neurodegenerative diseases of the retina and potential for protection and recovery

Recent advances in our understanding of the mechanisms in the cascade of events resulting in retinal cell death in ocular pathologies like glaucoma, diabetic retinopathy and age-related macular degeneration led to the common descriptive term of neurodegenerative diseases of the retina. The final common pathophysiologic pathway of these diseases includes a particular form of metabolic stress, resulting in an insufficient supply of nutrients to the respective target structures (optic nerve head, retina). During metabolic stress, glutamate is released initiating the death of neurones containing ionotropic glutamate (N-methyl-D-aspartat, NMDA) receptors present on ganglion cells and a specific type of amacrine cells. Experimental studies demonstrate that several drugs reduce or prevent the death of retinal neurones deficient of nutrients. These agents generally block NMDA receptors to prevent the action of glutamate or halt the subsequent pathophysiologic cycle resulting in cell death. The major causes for cell death following activation of NMDA receptors are the influx of calcium and sodium into cells, the generation of free radicals linked to the formation of advanced glycation endproducts (AGEs) and/or advanced lipoxidation endproducts (ALEs) as well as defects in the mitochondrial respiratory chain. Substances preventing these cytotoxic events are considered to be potentially neuroprotective.

The hunt for natural skin whitening agents

Skin whitening products are commercially available for cosmetic purposes in order to obtain a lighter skin appearance. They are also utilized for clinical treatment of pigmentary disorders such as melasma or postinflammatory hyperpigmentation. Whitening agents act at various levels of melanin production in the skin. Many of them are known as competitive inhibitors of tyrosinase, the key enzyme in melanogenesis. Others inhibit the maturation of this enzyme or the transport of pigment granules (melanosomes) from melanocytes to surrounding keratinocytes. In this review we present an overview of (natural) whitening products that may decrease skin pigmentation by their interference with the pigmentary processes.

Induction of terminal differentiation in melanoma cells on downregulation of beta-amyloid precursor protein

The incidence of melanoma, the most aggressive type of skin cancer, is increasing dramatically, and an effective treatment for patients with advanced disease is as yet unavailable. Greater insight into the molecular features of primary and metastatic melanoma is required, particularly the identification of key regulatory genes that shield the tumor cells from terminal differentiation and apoptosis. The beta-amyloid precursor protein (APP) is a cell surface receptor and the transmembrane precursor of the Abeta-peptide, which has an important role in Alzheimer's disease. The study presented here provides evidence that APP is expressed at high levels in advanced-stage melanomas, and that the cells cleave APP and secrete sAPP. We show that blocking the expression of APP by RNA interference impairs the proliferation of metastatic melanoma cells and leads to their terminal and irreversible differentiation. In addition, suppressing APP expression in a metastatic melanoma cell line renders the cells susceptible to several chemotherapeutic agents. Targeting APP may thus constitute a new approach to the treatment of this disease.

Structure and functions of the human amyloid precursor protein: the whole is more than the sum of its parts

The amyloid precursor protein (APP) is a transmembrane protein that plays major roles in the regulation of several important cellular functions, especially in the nervous system, where it is involved in synaptogenesis and synaptic plasticity. The secreted extracellular domain of APP, sAPPalpha, acts as a growth factor for many types of cells and promotes neuritogenesis in post-mitotic neurons. Alternative proteolytic processing of APP releases potentially neurotoxic species, including the amyloid-beta (Abeta) peptide that is centrally implicated in the pathogenesis of Alzheimer's disease (AD). Reinforcing this biochemical link to neuronal dysfunction and neurodegeneration, APP is also genetically linked to AD. In this review, we discuss the biological functions of APP in the context of tissue morphogenesis and restructuring, where APP appears to play significant roles both as a contact receptor and as a diffusible factor. Structural investigation of APP, which is necessary for a deeper understanding of its roles at a molecular level, has also been advancing rapidly. We summarize recent progress in the determination of the structure of isolated APP fragments and of the conformations of full-length sAPPalpha, in both monomeric and dimeric states. The potential role of APP dimerization for the regulation of its biological functions is also discussed.

The Quest for the Mechanism of Melanin Transfer

Skin pigmentation is accomplished by production of melanin in specialized membrane-bound organelles termed melanosomes and by transfer of these organelles from melanocytes to surrounding keratinocytes. The mechanism by which these cells transfer melanin is yet unknown. A central role has been established for the protease-activated receptor-2 of the keratinocyte which effectuates melanin transfer via phagocytosis. What exactly is being phagocytosed - naked melanin, melanosomes or melanocytic cell parts - remains to be defined. Analogy of melanocytes to neuronal cells and cells of the haemopoietic lineage suggests exocytosis of melanosomes and subsequent phagocytosis of naked melanin. Otherwise, microscopy studies demonstrate cytophagocytosis of melanocytic dendrites. Other plausible mechanisms are transfer via melanosome-containing vesicles shed by the melanocyte or transfer via fusion of keratinocyte and melanocyte plasma membranes with formation of tunnelling nanotubes. Molecules involved in transfer are being identified. Transfer is influenced by the interactions of lectins and glycoproteins and, probably, by the action of E-cadherin, SNAREs, Rab and Rho GTPases. Further clues as to what mechanism and molecular machinery will arise with the identification of the function of specific genes which are mutated in diseases that affect transfer.

Increasing our understanding of pigmentary disorders

This article focuses on developments in pigmentary disorders that extend dermatologists' understanding of the field. Areas that are reviewed include the basic biochemistry, pharmacology, and physiology of the melanocortin system; melanosome development; genetic diseases associated with pigmentary disorders; pigmentary disorders secondary to systemic disease; drug-induced hyperpigmentation; environmental exposure to chemicals; and primary disorders of hyperpigmentation such as melasma and lentigines. Basic, clinical, and epidemiological research, along with a number of clinical case reports, were included in the review. This article also reports on the new health-related quality-of-life instrument (MELASQOL) that has been developed for women with melasma.

Keratinocytes from APP/APLP2-deficient mice are impaired in proliferation, adhesion and migration in vitro

Growing evidence shows that the soluble N-terminal form (sAPPalpha) of the amyloid precursor protein (APP) represents an epidermal growth factor fostering keratinocyte proliferation, migration and adhesion. APP is a member of a protein family including the two mammalian amyloid precursor-like proteins APLP1 and APLP2. In the mammalian epidermis, only APP and APLP2 are expressed. APP and APLP2-deficient mice die shortly after birth but do not display a specific epidermal phenotype. In this report, we investigated the epidermis of APP and/or APLP2 knockout mice. Basal keratinocytes showed reduced proliferation in vivo by about 40%. Likewise, isolated keratinocytes exhibited reduced proliferation rates in vitro, which could be completely rescued by either exogenously added recombinant sAPPalpha, or by co-culture with dermal fibroblasts derived from APP knockout mice. Moreover, APP-knockout keratinocytes revealed reduced migration velocity resulting from severely compromised cell substrate adhesion. Keratinocytes from double knockout mice died within the first week of culture, indicating essential functions of APP-family members for survival in vitro. Our data indicate that sAPPalpha has to be considered as an essential epidermal growth factor which, however, in vivo can be functionally compensated to a certain extent by other growth factors, e.g., factors released from dermal fibroblasts.

Neurofibromatosis type 1 protein and amyloid precursor protein interact in normal human melanocytes and colocalize with melanosomes

The neurofibromatosis type 1 (NF1) gene product, neurofibromin, is known to interact with Ras, thereby negatively regulating its growth-promoting function. Although this is a well-established interaction, the discovery of other neurofibromin interacting partners could reveal new functional properties of this large protein. Using yeast two-hybrid analysis against a brain cDNA library, we identified a novel interaction between the amyloid precursor protein and the GTPase activating protein-related domain of neurofibromin. This interaction was further analyzed in human melanocytes and confirmed by immunoprecipitation and colocalization studies. In addition, we observed a colocalization of amyloid precursor protein and neurofibromin with melanosomes. Amyloid precursor protein has been proposed to function as a vesicle cargo receptor for the motor protein kinesin-1 in neurons. This colocalization of amyloid precursor protein and neurofibromin with melanosomes was lost in melanocytes obtained from normal skin of a NF1 patient. We suggest that a complex between amyloid precursor protein, neurofibromin, and melanosomes might be important in melanosome transport, which could shed a new light on the etiopathogenesis of pigment-cell-related manifestations in NF1.

Café-au-lait Patches and Senile Plaques: How APPt the Connection?

Neurofibromatosis type 1 (NF1) is a genetic disease caused by mutations in the NF1 gene, which encodes the protein neurofibromin. Patients exhibit characteristic hyperpigmented patches called café-au-lait patches. Melanocytes of NF1 patients differ from normal human melanocytes, but no differences account completely for lesional hyperpigmentation. An association between beta-amyloid precursor protein (APP) and neurofibromin, and their localization to the melanosome, may help explain the development of café-au-lait patches.

Solution Conformation and Heparin-induced Dimerization of the Full-length Extracellular Domain of the Human Amyloid Precursor Protein

Proteolytic cleavage of the amyloid precursor protein (APP) by beta and gamma-secretases gives rise to the beta-amyloid peptide, considered to be a causal factor in Alzheimer's disease. Conversely, the soluble extracellular domain of APP (sAPPalpha), released upon its cleavage by alpha-secretase, plays a number of important physiological functions. Several APP fragments have been structurally characterized at atomic resolution, but the structures of intact APP and of full-length sAPPalpha have not been determined. Here, ab initio reconstruction of molecular models from high-resolution solution X-ray scattering (SAXS) data for the two main isoforms of sAPPalpha (sAPPalpha(695) and sAPPalpha(770)) provided models of sufficiently high resolution to identify distinct structural domains of APP. The fragments for which structures are known at atomic resolution were fitted within the solution models of full-length sAPPalpha, allowing localization of important functional sites (i.e. glycosylation, protease inhibitory and heparin-binding sites). Furthermore, combined results from SAXS, analytical ultracentrifugation (AUC) and size-exclusion chromatography (SEC) analysis indicate that both sAPPalpha isoforms are monomeric in solution. On the other hand, SEC, bis-ANS fluorescence, AUC and SAXS measurements showed that sAPPalpha forms a 2:1 complex with heparin. A conformational model for the sAPPalpha:heparin complex was also derived from the SAXS data. Possible implications of such complex formation for the physiological dimerization of APP and biological signaling are discussed in terms of the structural models proposed.

The amyloid precursor protein and postnatal neurogenesis/neuroregeneration

The amyloid precursor protein (APP) is the source of amyloid-beta (Abeta) peptide, produced via its sequential cleavage beta- and gamma-secretases. Various biophysical forms of Abeta (and the mutations of APP which results in their elevated levels) have been implicated in the etiology and early onset of Alzheimer's disease. APP's evolutionary conservation and the existence of APP-like isoforms (APLP1 and APLP2) which lack the Abeta sequence, however, suggest that these might have important physiological functions that are unrelated to Abeta production. Soluble N-terminal fragments of APP have been known to be neuroprotective, and the interaction of its cytoplasmic C-terminus with a myriad of proteins associates it with diverse processes such as axonal transport and transcriptional regulation. The notion for an essential postnatal function of APP has been demonstrated genetically, as mice deficient in both APP and APLP2 or all three APP isoforms exhibit early postnatal lethality and neuroanatomical abnormalities. Recent findings have also brought to light two possible functions of the APP family in the brain-regulation of neural progenitor cell proliferation and axonal outgrowth after injury. Interestingly, these two apparently related neurogenic/neuroregenerative functions of APP involve two separate domains of the molecule.

Biological roles of APP in the epidermis

The amyloid precursor protein (APP) was initially detected in cells of the central nervous system where it is considered to be involved in the pathogenesis of Alzheimer's disease. However, APP is also found in peripheral organs with exceptionally strong expression in the mammalian epidermis where it fulfils a variety of distinct biological roles. Full length APP appears to facilitate keratinocyte adhesion due to its ability to interact with the extracellular matrix. The C-terminus of APP also serves as adapter protein for binding the motor protein kinesin thereby mediating the centripetal transport of melanosomes in epidermal melanocytes. By the action of alpha-secretase sAPPalpha, the soluble N-terminal portion of APP, is released. sAPPalpha has been shown to be a potent epidermal growth factor thus stimulating proliferation and migration of keratinocytes as well as the exocytic release of melanin by melanocytes. The release of sAPPalpha can be almost completely blocked by inhibiting alpha-secretase with hydroxamic acid-based zinc metalloproteinase inhibitors. In hyperproliferative keratinocytes from psoriatic skin this inhibition results in normalized growth.

Membrane ruffles in cell migration: indicators of inefficient lamellipodia adhesion and compartments of actin filament reorganization

During epithelial cell migration, membrane ruffles can be visualized by phase contrast microscopy as dark waves arising at the leading edge of lamellipodia that move centripetally toward the main cell body. Despite the common use of the term membrane ruffles, their structure, molecular composition, and the mechanisms leading to their formation remained largely unknown. We show here that membrane ruffles differ from the underlying cell lamella by more densely packed bundles of actin filaments that are enriched in the actin cross-linkers filamin and ezrin, pointing to a specific bundling process based on these cross-linkers. The accumulation of phosphorylated, that is, inactivated, cofilin in membrane ruffles suggests that they are compartments of inhibited actin filament turnover. High Rac1 and low RhoA activities were found under conditions of suboptimal integrin-ligand interaction correlating with low lamellipodia persistence, inefficient migration, and high ruffling rates. Based on these findings, we define membrane ruffles as distinct compartments of specific composition that form as a consequence of inefficient lamellipodia adhesion.

Melanoma-restricted genes

Human metastatic cutaneous melanoma has gained a well deserved reputation for its immune responsiveness. The reason(s) remain(s) unknown. We attempted previously to characterize several variables that may affect the relationship between tumor and host immune cells but, taken one at the time, none yielded a convincing explanation. With explorative purposes, high-throughput technology was applied here to portray transcriptional characteristics unique to metastatic cutaneous melanoma that may or may not be relevant to its immunogenic potential. Several functional signatures could be identified descriptive of immune or other biological functions. In addition, the transcriptional profile of metastatic melanoma was compared with that of primary renal cell cancers (RCC) identifying several genes co-coordinately expressed by the two tumor types. Since RCC is another immune responsive tumor, commonalities between RCC and melanoma may help untangle the enigma of their potential immune responsiveness. This purely descriptive study provides, therefore, a map for the investigation of metastatic melanoma in future clinical trials and at the same time may invite consideration of novel therapeutic targets.

Increased expression of amyloid precursor protein in oral squamous cell carcinoma

In our previous study, we identified amyloid precursor protein (APP) in an oral squamous cell carcinoma (OSCC)-enriching subtractive hybridization library. Our present study attempts to define the significance of APP expression in the genesis of OSCC. RT-PCR analysis showed increase in APP mRNA expression for more than 2-fold in 76% of OSCC (n = 55) relative to corresponding non-cancerous matched tissues (NCMT). The majority of esophageal SCCs also had increase in APP mRNA expression. OSCC patients exhibiting increase in APP mRNA expression had significantly lower survival rate compared to patients exhibiting the opposite status. Western blotting analysis identified APP751 and APP770 as the major APP isoforms in oral keratinocytes. A high correlation between mRNA and protein expressions of APP was noted in OSCC/NCMT pairs. Immunohistochemistry further showed a remarkable increase of APP in OSCC tissue relative to NCMT. Treatment with an antisense oligonucleotide against APP reduced cellular and secreted APP as well as growth in an OSCC cell line. Our study provides novel clues that APP expression is involved in the proliferation and carcinogenesis of OSCC. Correlated with such pathogenesis was the survival of its victims. The degree of APP expression could serve as an invaluable marker for oral carcinogenesis.