S100B proteins that lack one or both cysteine residues can induce inflammatory responses in astrocytes and microglia

The astrocytic protein S100B stimulates neurite outgrowth and neuronal surv ival during CNS development. S100B can also stimulate glial activation, lea ding to induction of pro-inflammatory molecules like interleukin-1 beta (IL -1 beta) and inducible nitric oxide synthase (NOS). Although it is known th at S100B's neurotrophic activity requires a disulfide-linked dimeric form o f the protein, the structural features of S100B that are important for glia l activation have not been defined. As an initial step towards understandin g the structural features of S100B required for its action on glia and to d etermine if these features are different from those required for its action on neurons, we tested two mutants of S100B for their ability to activate g lia. The C68VC84S mutant lacks S100B's two cysteine residues (cys68, cys84) and lacks neurotrophic activity (Winningham-Major et al., 1989, J. Cell Bi ol. 109 3063-3071), and the truncation mutant S100B83stop lacks the C-termi nal nine residues (including cys84) that have been shown to be important fo r some S100B:target protein interactions. We report here that both C68VC84S and S100B83stop stimulate glial activation, as determined by induction of NOS and lL-I beta in rat primary astrocyte and microglial cultures. C68VC84 S showed activation profiles similar to those of wild-type S100B, demonstra ting that a disulfide-linked dimer is not required for glial activation. S1 00B83stop also stimulated both NOS and IL-1 beta, although S100B83stop was significantly less effective than wild-type S100B in inducing NOS. These re sults indicate that the C-terminal region of S100B is not required for glia l activation; however, its presence may influence the degree of activation by the protein. Altogether, these studies demonstrate that the structural f eatures required for S100B's neurotrophic activity are distinct from those affecting its glial activation activity. (C) 2001 Elsevier Science Ltd. All rights reserved.