Adhesion and counteradhesion: morphogenetic functions of the cell surface

Adhesion molecules: opportunities for modulation and a paradigm for novel therapeutic approaches in cancer

In the past decade, there have been major advances in the elucidation of processes underlying tumour invasion and metastasis, in which adhesion molecules play a critical role. These advances have revolutionised our ability to devise novel approaches for cancer treatment. This review gives an insight into the adhesion pathways, and highlights the current status of adhesion molecules as potential therapeutic targets.

High pressure matrix-assisted laser desorption/ionization Fourier transform mass spectrometry for minimization of ganglioside fragmentation

Transiently elevating pressure in a matrix-assisted laser desorption/ionization Fourier transform mass spectrometry (MALDI-FTMS) source into the 1-10 mbar range during ionization decreases the metastable fragmentation of gangliosides. This allows detection of the molecular ion species without loss of the highly labile sialic acid residues. In these experiments, gangliosides with up to five sialic acids were ionized by MALDI and detected with the FTMS. In each case, when the high pressure collisional cooling was used, the singly charged molecular ion was the base peak in the spectra, both in the positive and negative ion modes, and minimal metastable fragmentation was observed. This result is promising, as the previously developed TLC separation methods can be coupled to MALDI-FTMS.

In vitro transformation of human congenital naevus to malignant melanoma

The incidence of melanoma is estimated to be growing at the second fastest rate among all cancers in the United States. The progression of the melanocyte to a malignant melanoma involves various sequential steps: development of benign naevocellular naevus, preneoplastic dysplastic naevus, primary melanoma, and metastatic melanoma. Despite these clearly defined stages, very little is known about the molecular events leading to melanoma progression. We established a human congenital naevus cell line (UISO-CMN-1). UISO-CMN-1 cells were confirmed to have melanocytic origin by S100 immunoreactivity and the presence of melanin granules and melanosomes. UISO-CMN-1 cells, even though they showed structural and numerical abnormalities in karyotype, were non-tumorigenic when transplanted into athymic mice. However, following frequent exposure to ultraviolet C radiation, UISO-CMN-1 cells acquired tumorigenic potential. Transformation of UISO-CMN-1 cells into tumorigenic cells was accompanied by induction of ganglioside-2 expression without any significant changes in cellular ganglioside-3. These transformed and non-transformed UISO-CMN-1 cell lines can serve as excellent research tools for studying the molecular changes associated with melanoma development and progression, and for identifying agents that might prevent development of malignant melanoma.

Mutations with sensory ray defect unmask cuticular glycoprotein antigens in Caenorhabditis elegans male tail

Caenorhabditis elegans male tail has nine pairs of bilaterally symmetric ray processes extended into a cuticular fan. The formation of these structures involves both cell lineage differentiation and cellular morphogenesis. Nine mutations were examined, all of which presented an amorphous ray phenotype. Glycoconjugates carrying an N-acetylglucosamine (GlcNAc) epitope were detected at a high level in their male bursa. It was shown that these antigens are not responsible for the morphological defects. It was further demonstrated that these ram and mab gene products represent critical components for male tail cuticle organization. Mutations of them abolish the integrity of the male bursal cuticle and unmask the underlying GlcNAc epitope.

Anosmin-1 underlying the X chromosome-linked Kallmann syndrome is an adhesion molecule that can modulate neurite growth in a cell-type specific manner

Anosmin-1 is an extracellular matrix glycoprotein which underlies the X chromosome-linked form of Kallmann syndrome. This disease is characterized by hypogonadism due to GnRH deficiency, and a defective sense of smell related to the underdevelopment of the olfactory bulbs. This study reports that anosmin-1 is an adhesion molecule for a variety of neuronal and non-neuronal cell types in vitro. We show that cell adhesion to anosmin-1 is dependent on the presence of heparan sulfate and chondroitin sulfate glycosaminoglycans at the cell surface. A major cell adhesion site of anosmin-1 was identified in a 32 amino acid (32R1) sequence located within the first fibronectin-like type III repeat of the protein. The role of anosmin-1 as a substrate for neurite growth was tested on either coated culture dishes or monolayers of anosmin-1-producing CHO cells. In both experimental systems, anosmin-1 was shown to be a permissive substrate for the neurite growth of different types of neurons. Mouse P5 cerebellar neurons cultured on anosmin-1 coated wells developed long neurites; the 32R1 peptide was found to underly part of this neurite growth activity. When the cerebellar neurons were cultured on anosmin-1-producing CHO cells, neurite growth was reduced as compared to wild-type CHO cells; in contrast, no difference was observed for E18 hippocampal and P1 dorsal root ganglion neurons in the same experimental system. These results indicate that anosmin-1 can modulate neurite growth in a cell-type specific manner. Finally, anosmin-1 induced neurite fasciculation of P5 cerebellar neuron aggregates cultured on anosmin-1-producing CHO cells. The pathogenesis of the olfactory defect in the X-linked Kallmann syndrome is discussed in the light of the present results and the recent data reporting the immunohistochemical localisation of anosmin-1 during early embryonic development.

Regulation of CD44 in the regenerating mouse facial motor nucleus

CD44 is a cell adhesion molecule which plays an important role in cell movement and adhesion, e.g. in lymphocyte homing and tumour metastasis. Here we studied the expression of CD44 mRNA and protein immunoreactivity in the facial nucleus after nerve injury and during the ensuing regeneration. Transection of the facial nerve led to a strong up-regulation of CD44, peaking 4 days after injury on the motoneurons of the axotomized facial nucleus. Use of the polymerase chain reaction confirmed the de novo expression of CD44 and detected only the standard haematopoietic CD44 isoform. Western blotting also detected the 76 kDa protein subtype, in line with the predicted size of the haematopoietic CD44 variant. At the ultrastructural level, CD44 immunoreactivity was restricted to the surface of the neuronal perikarya, their dendrites and axons. It was not seen in the adjacent activated astrocytes, microglia or vascular endothelia. This study shows strong up-regulation of the cell adhesion molecule CD44 on the regenerating motoneurons in the axotomized facial nucleus. These data suggest that CD44 may play a role in neurite outgrowth, in synaptic stripping or in the adhesion of activated glial cells to the perikaryal surface of the axotomized motoneurons.

Cyclic changes in the organization of cell adhesions and the associated cytoskeleton, induced by stimulation of tyrosine phosphorylation in bovine aortic endothelial cells

In this study we have investigated the relationships between the stimulation of tyrosine-specific protein phosphorylation and the state of assembly of cell-cell and cell-matrix adherens-type junctions. Bovine aortic endothelial (BAE) cells were treated with either the phosphotyrosine phosphatase inhibitor pervanadate or with epidermal growth factor (EGF), and the effect of the treatment on the organization of cell contacts and the actin cytoskeleton was evaluated by digital immunomicroscopy. We show here that pervanadate induced a dramatic (about 40-fold) increase in the level of phosphotyrosine labeling of cell-cell junctions, which reached maximal values following 20 minutes of incubation. Concomitantly, the junctional levels of vinculin, actin and plakoglobin increased, followed by a slower recruitment of cadherins to these sites. Upon longer incubation cell-cell junctions deteriorated and stress fibers and focal adhesions were formed. EGF stimulation of serum-starved BAE cells induced a rapid ‘wave’ of junctional tyrosine phosphorylation, followed by cyclic changes in the local levels of phosphotyrosine labeling. Periodic changes were also found in the intensity of labeling of junctional actin, vinculin and cadherins. These results suggest that tyrosine phosphorylation and the assembly of cell-cell adherens junctions are interdependent processes, and raise the possibility that the cross-talk between the two is responsible both for the regulation of junction formation and for adhesion-mediated signaling.

Polysialylation of NCAM by a single enzyme

The addition of poly-alpha2,8-N-acetylneuraminic acid (polysialic acid; PSA) to the neural cell adhesion molecule NCAM plays a crucial role in neural development [1-3], neural regeneration [4], and plastic processes in the vertebrate brain associated with neurite outgrowth [5], axonal pathfinding [6], and learning and memory [7,-9]. PSA levels are decreased in people affected by schizophrenia [10], and PSA has been identified as a specific marker for some neuroendocrine and lymphoblastoid tumours [11-13]; expression of PSA on the surface of these tumour cells modulates their metastatic potential [11-13]. Studies aimed at understanding PSA biosynthesis and the dynamics of its production have largely been promoted by the cloning of polysialyltransferases (PST-1 in hamster; PST in human and mouse) [14-16]. However, the number of enzymes involved in the biosynthesis of PSA has not been identified. Using incompletely glycosylated NCAM variants and soluble recombinant glycosyltransferases, we reconstituted the site at which PST-1 acts to polysialylate NCAM in vitro. The data presented here clearly demonstrate that polysialylation of NCAM is catalyzed by a single enzyme, PST-1, and that terminal sialylation of the N-glycan core is sufficient to generate the PSA acceptor site. Our results also show that PST-1 can act on core structures with the terminal sialic acid connected to galactose via an alpha2,3 or alpha2,6 linkage.

Adhesion molecules as determinants of disease: from molecular biology to surgical research

Cellular adhesion is mediated by distinct cell surface receptors (adhesion molecules) and plays a pivotal role in the biological processes of morphogenesis, cell migration and cell-cell communication. During the past decade many adhesion molecules have been identified and structurally analysed. This has allowed an understanding of their role in the pathophysiology of disease, including inflammation and sepsis, ischaemia and reperfusion, transplant rejection, atherosclerosis and thrombosis, angiogenesis and wound healing, as well as carcinogenesis and tumour metastasis. Understanding of the molecular mechanisms of cellular communication is not only vital for advances in surgical pathophysiology, it also has the potential to widen the spectrum of diagnosis and therapy of disease. Analysis of expression of individual surface molecules may help in the diagnosis of transplant rejection and allow a prognostic determination of tumour progression and metastasis formation. Moreover, manipulation of adhesion molecule function by monoclonal antibodies, antisense oligonucleotides or single gene products may open the door for novel therapeutic regimens to prevent transplant rejection and ischaemia-, sepsis- and shock-induced tissue injury.