Amphoterin is a protein enhancing process extension and migration in embryonic neurons and in tumor cells through binding to receptor for advanced glycation end products (RAGE), a multiligand transmembrane receptor. S100 proteins, especially S100B, are abundantly expressed in the nervous system and are suggested to function as cytokines with both neurotrophic and neurotoxic effects. However, the cell surface receptor for the cytokine function of S100B has not been identified. Here we show that two S100 family proteins, S100B and S100A1, activate RAGE in concert with amphoterin inducing neurite outgrowth and activation of transcription factor NF-B. Furthermore, activation of RAGE by amphoterin and S100B promotes cell survival through increased expression of the anti-apoptotic protein Bcl-2. However, whereas nanomolar concentrations of S100B induce trophic effects in RAGE-expressing cells, micromolar concentrations of S100B induce apoptosis in an oxidant-dependent manner. Both trophic and toxic effects are specific for cells expressing full-length RAGE since cells expressing a cytoplasmic domain deletion mutant of RAGE are unresponsive to these stimuli. These findings suggest that activation of RAGE by multiple ligands is able to promote trophic effects whereas hyperactivation of RAGE signaling pathways promotes apoptosis. We suggest that RAGE is a signal-transducing receptor for both trophic and toxic effects of S100B.Receptor for advanced glycation end products (RAGE) 1 is a member of the immunoglobulin superfamily of cell surface proteins interacting with a range of ligands, including advanced glycation end products (AGE) (1), amyloid-␤ peptide (2), amphoterin (3), and members of the S100 family (4). Whereas AGE and amyloid-␤ peptide are known to induce cellular perturbation through their interaction with RAGE, amphoterin and S100 proteins are considered to be physiological ligands of RAGE in migratory and inflammatory cellular responses. However, mechanistically it is not understood how RAGE-mediated cellular responses can change from trophic to toxic.Amphoterin is a heparin-binding, neurite outgrowth-promoting protein that is highly expressed in embryonic and transformed cells (5-7). RAGE has been shown to mediate neurite outgrowth of cortical neurons and neuroblastoma cells on amphoterin-coated substrates (3, 8). Furthermore, amphoterin and RAGE co-localize at the leading edge of advancing neurites in the developing central nervous system (3). Our previous results suggesting that amphoterin might be a more general regulator of cell migration (reviewed in Ref. 9) are supported by the recent findings showing that blockade of amphoterin-RAGE interaction decreases invasion and growth of both implanted and spontaneously developing tumors (10). S100B is a member of a multigenic family of Ca 2ϩ -regulated proteins of the EF-hand type that has been implicated in the regulation of protein phosphorylation, the dynamics of cytoskeleton constituents, the cell cycle, and some enzymes (11,12). S100B is abundant in the n...

S100B is a Ca2؉ -modulated protein of the EF-hand type with both intracellular and extracellular roles. S100B, which is most abundant in the brain, has been shown to exert trophic and toxic effects on neurons depending on the concentration attained in the extracellular space. S100B is also found in normal serum, and its serum concentration increases in several nervous and nonnervous pathological conditions, suggesting that S100B-expressing cells outside the brain might release the protein and S100B might exert effects on nonnervous cells. We show here that at picomolar to nanomolar levels, S100B inhibits myogenic differentiation of rat L6 myoblasts via inactivation of p38 kinase with resulting decrease in the expression of the myogenic differentiation markers, myogenin, muscle creatine kinase, and myosin heavy chain, and reduction of myotube formation. Although myoblasts express the multiligand receptor RAGE, which has been shown to transduce S100B effects on neurons, S100B produces identical effects on myoblasts overexpressing either full-length RAGE or RAGE lacking the transducing domain. This suggests that S100B affects myoblasts by interacting with another receptor and that RAGE is not the only receptor for S100B. Our data suggest that S100B might participate in the regulation of muscle development and regeneration by inhibiting crucial steps of the myogenic program in a RAGE-independent manner. S100B, a member of a multigenic family of Ca 2ϩ -regulated proteins of the EF-hand type, is highly abundant in astrocytes and is expressed in relatively large amounts in a variety of nonneural cell types (for reviews, see references 12, 13, and 36). Besides being implicated in the Ca 2ϩ -dependent regulation of several intracellular activities (12, 13, 36), S100B is released by astrocytes into the extracellular space (45) and is also found in serum (13). S100B has been shown to interact with neurons, astrocytes, and microglia and to exert various effects on these cells depending on its concentration. S100B has also been shown to enhance neuronal survival and stimulate neurite outgrowth and astrocyte proliferation at nanomolar concentrations (2,3,6,7,16,20,21,23,39,47) and to cause neuronal and astrocyte apoptosis and stimulate interleukin-6 secretion by neurons and nitric oxide release by astrocytes and microglia at micromolar concentrations (1, 18-20, 25, 27, 31). Therefore, S100B has been hypothesized to play roles in brain development and neuronal protection (2,3,6,7,16,20,21,23,39,47) and in the pathophysiology of neurodegenerative disorders (15,20,30,40,41), depending on the concentration attained in the extracellular space. Trophic effects of S100B on neurons have been shown to depend on activation of the transcription factor NF-B (3). The receptor for advanced glycation end products (RAGE), a multiligand receptor of the immunoglobulin superfamily (for reviews, see references 37 and 38), has been shown to bind S100B (17) and to mediate the effects of both low and high levels of S100B on a neuronal cell line (20...

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Previous in vitro studies have shown that the Ca2+-regulated S100B protein modulates the assembly-disassembly of microtubules (MTs) and type III intermediate filaments (IFs). In the present report, by double immunofluorescence cytochemistry S 100B was localized to both GFAP/vimentin IFs and MTs as well as to centrosomes in U251 glial cells. In cells treated with the MT-depolymerizing agent, colchicine, S100B remained associated with the rearranged GFAP IFs throughout the cell and, at the cell periphery, vimentin IFs. In cells treated with the MT stabilizing agent, taxol, S100B followed partly the rearrangement of MTs and partly the rearrangement of IFs. Under the latter condition, bundles of MTs with their associated S100B appeared surrounded and/or flanked by rearranged IFs with their associated S100B. Colocalization of S100B with closely arranged IFs and MTs was best evident in cells manipulated with taxol and in triton-cytoskeletons. In these cases, MTs and their associated S100B appeared surrounded and/or flanked by and/or intermingled with IFs and their associated S100B. Also, a preferential association of S100B with GFAP vs. vimentin IFs could be observed near the nucleus where colocalization of S100B with MTs was also maximal. Condensation of IFs and alteration of the MT network caused by treatment of cells with the phosphatase inhibitor, okadaic acid, resulted in a concomitant condensation/alteration of the S100B immunoreactivity. The present results lend support to the possibility that S100B may be an important factor implicated in the regulation of the dynamics of MTs and IFs.

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