GRP78 is a stress-inducible chaperone protein with antiapoptotic properties that is overexpressed in transformed cells and cells under glucose starvation, acidosis, and hypoxic conditions that persist in poorly vascularized tumors. Previously we demonstrated that the Grp78 promoter is able to eradicate tumors using murine cells in immunocompetent models by driving expression of the HSV-tk suicide gene. Here, through the use of positron emission tomography (PET) imaging, we provide direct evidence of spontaneous in vivo activation of the HSV-tk suicide gene driven by the Grp78 promoter in growing tumors and its activation by photodynamic therapy (PDT) in a controlled manner. In this report, we evaluated whether this promoter can be applied to human cancer therapy. We observed that the Grp78 promoter, in the context of a retroviral vector, was highly activated by stress and PDT in three different types of human breast carcinomas independent of estrogen receptor and p53. Complete regression of sizable human tumors was observed after prodrug ganciclovir treatment of the xenografts in immunodeficient mice. In addition, the Grp78 promoter-driven suicide gene is strongly expressed in a variety of human tumors, including human osteosarcoma. In contrast, the activity of the murine leukemia virus (MuLV) long-terminal repeat (LTR) promoter varied greatly in different human breast carcinoma cell lines, and in some cases, stress resulted in partial suppression of the LTR promoter activity. In transgenic mouse models, the Grp78 promoter-driven transgene is largely quiescent in major adult organs but highly active in cancer cells and cancer-associated macrophages, which can diffuse to tumor necrotic sites devoid of vascular supply and facilitate cell-based therapy. Thus, transcriptional control through the use of the Grp78 promoter offers multiple novel approaches for human cancer gene therapy.
"GFP has been utilized extensively as the reporter gene to evaluate the spatial and temporal control of gene expression driven by HSP70 promoters 36-39. With PET imaging, spontaneous in vivo activation of the HSV1-tk suicide gene driven by the Grp78 promoter, a member of HSP70 family, in growing tumors and its activation by photodynamic therapy (PDT) in a controlled manner has been observed 40. Noguchi et al. 41 have established a dual-color transgenic mouse that carries transgenes encoding green-emitting luciferase (ELuc, λmax = 538 nm) expressed under the control of the Bmal1 promoter and red-emitting luciferase (SLR2, λmax=630 nm) expressed under the control of the Per2 promoter. "
[Show abstract][Hide abstract] ABSTRACT: Molecular imaging is a newly emerged multiple disciplinary field that aims to visualize, characterize and quantitatively measure biological processes at cellular and molecular levels in humans and other living systems. A reporter gene is a piece of DNA encoding reporter protein, which presents as a readily measurable phenotype that can be distinguished easily from the background of endogenous protein. After being transferred into cells of organ systems (transgenes), the reporter gene can be utilized to visualize transcriptional and posttranscriptional regulation of gene expression, protein-protein interactions, or trafficking of proteins or cells in living subjects. Herein, we review previous classification of reporter genes and regroup the reporter gene based imaging as basic, inducible and activatable, based on the regulation of reporter gene transcription and post-translational modification of reporter proteins. We then focus on activatable reporters, in which the signal can be activated at the posttranslational level for visualizing protein-protein interactions, protein phosphorylation or tertiary structure changes. The applications of several types of activatable reporters will also be summarized. We conclude that activatable reporter imaging can benefit both basic biomedical research and drug development.
"Its expression also varies with developmental stages and tissue specificity. A low basal level is identified in most adult tissues whereas it is highly induced in cancer  . GRP78 expression is induced under such conditions as hypoxia and nutrient deprivation, partially explaining its high level in tumour cells . "
[Show abstract][Hide abstract] ABSTRACT: Glucose-regulated protein of 78 kD (GRP78) is a chaperone protein mainly located in the endoplasmic reticulum (ER). This protein is normally present at low levels in adult cells but its expression is triggered by ER stress including glucose deprivation and hypoxia. In tumor cells, it is overexpressed with fraction of protein found at the cell surface. This paper presents the physiology of GRP78 in the context of ovarian cancer and its potential use as drug delivery systems targeting ovarian cancer cell.
Journal of Oncology 03/2012; 2012(5):468615. DOI:10.1155/2012/468615
"The first direct evidence for the involvement of GRP78 in cancer progression came from the demonstration that GRP78 knockdown in fibrosarcoma cells using antisense prevented tumor formation in nude mice . It was further shown that a suicide transgene driven by the GRP78 promoter in breast cancer cells completely blocked tumor growth in mice . More recently, it was demonstrated that GRP78 heterozygous mice develop normally but are resistant to transgene-induced mammary tumor growth . "
[Show abstract][Hide abstract] ABSTRACT: Cripto is a small, GPI-anchored signaling protein that regulates cellular survival, proliferation, differentiation and migration during normal developmental processes and tumorigenesis. Cripto functions as an obligatory co-receptor for the TGF-β ligands Nodal, GDF1 and GDF3 but attenuates signaling of others such as activin-A, activin-B and TGF-β1. Soluble, secreted forms of Cripto also activate Src, ras/raf/MAPK and PI3K/Akt pathways via a mechanism that remains largely obscure. This review describes the biological roles and signaling mechanisms of Cripto, highlighting our identification of the 78 kDa glucose regulated protein (GRP78) as a cell surface receptor/co-factor required for Cripto signaling via both TGF-β and Src/MAPK/PI3K pathways. We discuss emerging evidence indicating that Cripto/GRP78 signaling regulates normal somatic stem cells and their tumorigenic counterparts.
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