S100B Increases Proliferation in PC12 Neuronal Cells and Reduces Their Responsiveness to Nerve Growth Factor via Akt Activation

Abstract

S100B is a Ca 2؉ -modulated protein of the EF-hand type expressed in high abundance in a restricted set of cell types including certain neuronal populations. S100B has been suggested to participate in cell cycle progression, and S100B levels are high in tumor cells, compared with normal parental cells. We expressed S100B in the neuronal cell line PC12, which normally does not express the protein, by the Tet-Off technique, and found the following: (i) proliferation was higher in S100B ؉ PC12 cells than in S100B ؊ PC12 cells; (ii) nerve growth factor (NGF), which decreased the proliferation of S100B ؊ PC12 cells, was less effective in the case of S100B ؉ PC12 cells; (iii) expression of S100B made PC12 cells resistant to the differentiating effect of NGF; and (iv) interruption of S100B expression did not result in an immediate restoration of PC12 cell sensitivity to the differentiating effect of NGF. Expression of S100B in PC12 cells resulted in activation of Akt; increased levels of p21 WAF1 , an inhibitor of cyclin-dependent kinase (cdk) 2 and a positive regulator of cdk4; increased p21 WAF1 -cyclin D1 complex formation; and increased phosphorylation of the retinoblastoma suppressor protein, Rb. These S100B-induced effects, as well as the reduced ability of S100B ؉ PC12 cells to respond to NGF, were dependent on Akt activation because they were remarkably reduced or abrogated in the presence of LY294002, an inhibitor of the Akt upstream kinase phosphatidylinositol 3-kinase. Thus, S100B might promote cell proliferation and interfere with NGF-induced PC12 cell differentiation by stimulating a p21 WAF1 /cyclin D1/ cdk4/Rb/E2F pathway in an Akt-mediated manner. S100B, a member of a multigenic family of Ca 2ϩ -modulated proteins of the EF-hand type with both intracellular and extracellular regulatory activities, is expressed in varying abundance in astrocytes, Schwann cells, adipocytes, melanocytes, chondrocytes, skin Langerhans cells, lymphocyte subpopulations, skeletal muscle cells, and many neuronal populations (1, 2). Several intracellular target proteins have been identified for S100B (1, 2), many of which share a consensus sequence (3), and S100B has been shown to regulate protein phosphorylation, the dynamics of cytoskeleton components, Ca 2ϩ homeostasis, some enzyme activities, and transcription factors (1, 2). Moreover, S100B has been shown to be secreted by astrocytes, thereby affecting neuronal, astrocyte, and microglia functions within the brain (1, 2). S100B likely can be released by S100B-expressing cells outside the nervous system because it is found in normal serum (1), thereby affecting functions of non-nervous cells (4).Among the intracellular regulatory roles attributed to S100B is its participation in cell cycle progression. It has long been known that S100B levels are high in tumor cells, compared with normal parental cells (1, 2), and inhibition of S100B synthesis in an astrocyte cell line results in a decreased proliferation (5). However, the molecular mechanism underlying the potential role of ...

S100B-p53 disengagement by pentamidine promotes apoptosis and inhibits cellular migration via aquaporin-4 and metalloproteinase-2 inhibition in C6 glioma cells

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Fibronectin induces cell proliferation and inhibits apoptosis in human bronchial epithelial cells: pro-oncogenic effects mediated by PI3-kinase and NF-κB

“…We found that fibronectin stimulated the phosphorylation of the PI3-K downstream signal Akt, and that the inhibitor of the PI3-K blocked the effects of fibronectin on p21, cyclin D1, PTEN, and c-Myc protein expression indicating an important role for this kinase in controlling gene expression and cell growth regulated by fibronectin. The PI3-K signal pathway has been demonstrated to be involved in the regulation of these genes in different cells (Asano and Yao, 2004;Arcuri et al, 2005;Halder et al, 2005). In pancreatic cancer cells, the PI3-k/Akt signaling pathway is activated because of aberrant PTEN expression, and it targets the transcription factor c-Myc (Asano and Yao, 2004).…”

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