Galectin-3 is a member of the galectin family and belongs to a group of soluble beta-galactoside-binding animal lectins. The molecule is expressed by neural and nonneural cells intra- (cytoplasm and nucleus) as well as extra-cellularly (plasma membrane and extracellular space). By using an in vitro cell-substratum adhesion assay, we have addressed the question whether galectin-3 present in the extracellular milieu may support the adhesion and/or neurite outgrowth of neural cells in a manner analogous to cell adhesion molecules. Galectin-3 was immobilized as a substratum and various cell types, N2A (neuroblastoma), PC12 (pheochromocytoma), and TSC (transformed Schwann cells) cell lines, neural cells from early postnatal mouse cerebellum, and dorsal root ganglion neurons from newborn mice were allowed to adhere to the lectin. Here we show that all cell types studied specifically adhered to galectin-3 by the following criteria: 1) the number of adherent cells was dependent on the galectin-3 concentration used for coating; 2) adhesion of cells to galectin-3, but not to collagen type I or laminin was inhibited by polyclonal antibodies to galectin-3; 3) upon addition of asialofetuin (a polyvalent carrier of terminal beta-galactosides) to the cell suspension prior to the adhesion assay, cell adhesion to galectin-3 was inhibited in a dose-dependent manner; and 4) cell adhesion to galectin-3 was abolished by treatment of cells with endo-beta-galactosidase. In addition, the adhesion of dorsal root ganglion neurons to galectin-3 could be inhibited by lactose. Notably, substratum-bound galectin-3 promoted the outgrowth of neurites from dorsal root ganglia explants and this neurite outgrowth promoting activity could be inhibited by polyclonal antibodies to galectin-3.

No abstract

Galectin-3, an animal lectin specific for fl-galactosides, is composed of three different domains. The N-terminal half of the molecule (N domain) consists of a short N-terminal segment followed by glycine-, proline-, and tyrosirie-rich tandem repeats. The C-terminal domain

Galectin-3 (gal-3) is a member of the galectin family of lectins whose expression strongly depends on the cellular state. Here we show that in PC12 cells the expression of gal-3 protein is regulated via Ras-and mitogen-activated protein kinase (MAPK)-dependent and -independent signalling pathways and correlates with nerve growth factor (NGF)-mediated neuronal differentiation. Gal-3 expression, activation of the MAPK ERK1/2 and neurite outgrowth are induced by NGF and basic fibroblast growth factor (bFGF), but not by ciliary neurotrophic factor (CNTF), epidermal growth factor, insulin or interleukin-6 (IL-6). In addition, in NGF-treated PC12 cells, gal-3 expression, ERK1/2 activation and neurite outgrowth could be specifically inhibited at the level of TrkA, Ras and MAPK-kinase, whereas expression of an oncogenic form of Ras leads to gal-3 expression and neurite outgrowth in the absence of growth factors. In NGF-primed PC12 cells, subsequent treatment with CNTF or IL-6 induces ERK1/2 activation and neurite outgrowth, but not gal-3 expression. Treatment of PC12 cells with staurosporine induces gal-3 expression and neurite outgrowth without ERK1/2 activation. NGF-and staurosporineinduced gal-3-expression is also regulated at the transcriptional level. Our data suggest the presence of complex induction mechanisms of gal-3 expression in neuronally differentiating PC12 cells involving NGF-, but not CNTF-and IL-6-driven (in NGF-primed cells) Ras/MAPK-related signalling pathways. Staurosporine, in contrast, induces gal-3 expression by a Ras/MAPK-independent mechanism. Keywords: ERK, galectin-3, interleukin-6, nerve growth factor, PC12 cells, Ras. Galectin-3 (gal-3) belongs to the galectin family of soluble lectins as defined by (i) amino acid sequence homology and (ii) their affinitiy to b-galactosidic carbohydrate structures (reviewed by Cooper 2002). Dependent on the cell type, gal-3 can be expressed intracellularly (cytoplasm and nucleus) and/or extracellularly (plasma membrane or extracellular space). The expression of gal-3 has been associated with a number of different normal biological and pathological processes, such as apoptotic cell death, differentiation, growth and transformation (reviewed by Rabinovich 1999). Thus, gal-3 expression generally correlates with alterations in the state of cell activation. In this context, a basic question concerns the mechanisms of regulation of gal-3 expression in different cell types (reviewed by Chiariotti et al. 1999). First investigated in mouse and human fibroblasts, the expression of gal-3, which is low or absent in quiescent growth-arrested cells, has been found to be induced after serum addition (reviewed by Kadrofske et al. 1998). In activated Schwann and microglial Received March 13, 2002; revised manuscript received July 2, 2003; accepted August 6, 2003. Address correspondence and reprint requests to Rainer Probstmeier, Neuro-and Tumor Cell Biology Group, Department of Nuclear Medicine, University of Bonn, Sigmund Freud Str. 25, 53105 Bonn, Germany. E-mai...

No abstract