Nerve growth factor and epidermal growth factor stimulate clusterin gene expression in PC12 cells

Abstract

Clusterin (apolipoprotein J) is an extracellular glycoprotein that might exert functions in development, cell death and lipid transport. Clusterin gene expression is elevated at sites of tissue remodelling, such as differentiation and apoptosis; however, the signals responsible for this regulation have not been identified. We use here the clusterin gene as a model system to examine expression in PC12 cells under the control of differentiation and proliferation signals produced by nerve growth factor (NGF) and by epidermal growth factor (EGF) respectively. NGF induced clusterin mRNA, which preceded neurite outgrowth typical of neuronal differentiation. EGF also activated the clusterin mRNA, demonstrating that both proliferation and differentiation signals regulate the gene. To localize NGF- and EGF-responsive elements we isolated the clusterin promoter and tested it in PC12 cell transfections. A 2.5 kb promoter fragment and two 1.5 and 0.3 kb deletion mutants were inducible by NGF and EGF. The contribution to this response of a conserved activator protein 1 (AP-1) motif located in the 0.3 kb fragment was analysed by mutagenesis. The mutant promoter was not inducible by NGF or EGF, which identifies the AP-1 motif as an element responding to both factors. Binding studies with PC12 nuclear extracts showed that AP-1 binds to this sequence in the clusterin promoter. These findings suggest that NGF and EGF, which give differential gene regulation in PC12 cells, resulting in neuronal differentiation and proliferation respectively, use the common Ras/extracellular signal-regulated kinase/AP-1 signalling pathway to activate clusterin expression.

Clusterin expression during regeneration of pancreatic islet cells in streptozotocin-induced diabetic rats

“…Together, these data suggest that clusterin must be involved in differentiation-and proliferation-signalling pathways. Further, it was found that NGF and EGF use the common Ras-extracellular signal-regulated kinase-AP1 (activator protein 1, a transcription factor of clusterin) signalling pathway to activate clusterin gene expression [10]. We also found simultaneous activation of MAPKs and an increase of clusterin expression during islet-cell regeneration.…”

“…However, the mechanism for islet cell regeneration has not been shown. Clusterin is known to be up-regulated at sites of tissue remodelling through differentiation and proliferation after apoptosis [10,14,16,41]. We have reported the expression of clusterin in the developing pancreas and in the pancreatic tissue of the streptozotocin treated rats and suggested that this protein must play important roles [7,20].…”

“…Interaction between clusterin and TGF-beta receptor implies that clusterin could act as a member of the TGF-b receptor-associated protein regulating cell proliferation and differentiation of a wide variety of cell types [18,19]. Some growth factors including TGF use the common Ras-extracellular signal-regulated kinase-AP1 signalling pathway to activate clusterin expression for cell proliferation or differentiation [10].…”

Challenge and promise: roles for clusterin in pathogenesis, progression and therapy of cancer

“…CLU mRNA was induced and activated in PC12 prostate cancer cells by nerve growth factor and epidermal growth factor. 34 Transforming growth factor beta (TGF-b) induces CLU gene expression in a variety of cell types. Transforming growth factor beta-1 (TGF-b1) was shown to enhance sCLU protein and mRNA expression in thyroid epithelial cells, and it was proposed that upregulation of CLU expression may be a marker of TGF-b1-mediated thyrocyte dedifferentiation.…”

“…Transforming growth factor beta-1 (TGF-b1) was shown to enhance sCLU protein and mRNA expression in thyroid epithelial cells, and it was proposed that upregulation of CLU expression may be a marker of TGF-b1-mediated thyrocyte dedifferentiation. 34 In rodent cells, CLU gene expression was proposed to occur via a consensus AP-1-binding site located in the promoter region of this gene. 15 Furthermore, TGF-b1-induced CLU expression in CCL64 mink lung cancer cells was repressed by overexpression of the c-Fos proto-oncogene, and it was speculated that TGF-b1 could exert effects on c-Fos protein synthesis and/or stability, resulting in the repression of c-Fos, and thus increased CLU gene expression.…”