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.

Contribution of the Transcription Factors Sp1/Sp3 and AP-1 to Clusterin Gene Expression during Corneal Wound Healing of Tissue-Engineered Human Corneas

“…Transfection analyses revealed that one positive and two negative (a strong and a moderate one) regulatory regions are present along the CLU gene promoter and 5 -flanking region (Figure 2C). Among reports identifying TF binding sites along the CLU gene promoter [37,38], only a few characterized the regulatory sequences needed to ensure proper transcription of the CLU gene [39][40][41][42][43][44][45][46]. However, none of them have been done in the context of human wound healing of the cornea.…”

“…Few reports identified multiple binding sites for a variety of transcription factors (TFs) along the CLU gene promoter, including activator Protein 1 (AP-1), Specificity Protein 1 (Sp1), Nuclear Factor 1 (NFI), Signal Transducers and Activators of Transcription (STAT), MYCN Proto-oncogene and Heat Shock Factor (HSF), to name a few [37,38]. Although a handful of them reported the characterization of the regulatory sequences that are critical to ensure proper transcription of the CLU gene [39][40][41][42][43][44][45][46], none have ever investigated their contribution to human wound healing.…”

Clusterin interacts with SCLIP (SCG10-like protein) and promotes neurite outgrowth of PC12 cells

“…It is noteworthy that most putative clusterin-binding proteins contain more than one coiled-coil motifs, implying that interactions between clusterin and its binding partners might be mediated by the coiled-coil motifs. Of these, SCLIP is further characterized because it is up-regulated in NGF-induced differentiation of PC12 cells, in much the same way as clusterin [15,17].…”

“…In PC12 cells, NGF increases the SCLIP mRNA level and induces neurite outgrowth, known as a marker of neuronal differentiation [15]. In addition, NGF treatment enhances clusterin expression [17]. In this study, we determined the interacting domains of clusterin and SCLIP and examined the subcellular distribution of clusterin in PC12 cells.…”

Clusterin/apolipoprotein J, its isoforms and Alzheimer's disease

“…The specific functions of CLU in the brain, however, are not as well-understood. Studies have shown that CLU expression is upregulated in degenerative conditions, such as AD (Calero et al, 2005 ; Nuutinen et al, 2009 ), due to cellular and oxidative stress or dysregulation of specific signaling pathways (Wong et al, 1994 ; Gutacker et al, 1999 ; Schepeler et al, 2007 ; Trougakos and Gonos, 2009 ). However, the literature provides conflicting results as to whether CLU expression improves or exacerbates cellular stress (Schreiber et al, 1993 ; Han et al, 2001 ; Imhof et al, 2006 ; Kim et al, 2012 ; Trindade et al, 2016 ; Troakes et al, 2017 ).…”