Low dose IR-induced IGF-1-sCLU expression: a p53-repressed expression cascade that interferes with TGFβ1 signaling to confer a pro-survival bystander effect

Abstract

Inadvertent mammalian tissue exposures to low doses of ionizing radiation (IR) after radiation accidents, remediation of radioactive-contaminated areas, space travel, or a dirty bomb represents an interesting trauma to an organism. Possible low dose IR-induced bystander effects could impact our evaluation of human health effects, since cells within tissue are not equally damaged after doses of IR ≤10 cGy. To understand tissue responses after low IR doses, we generated a reporter system using the human clusterin promoter fused to firefly luciferase (hCLUp-Luc). Secretory clusterin (sCLU), an extra-cellular molecular chaperone, induced by low doses of cytotoxic agents, clears cell debris. Low dose IR (≥2 cGy) exposure induced hCLUp-Luc activity with peak levels at 96 h, consistent with endogenous sCLU levels. As doses increased (≥1 Gy), sCLU induction amplitudes increased and time to peak response decreased. sCLU expression was stimulated by IGF-1, but suppressed by p53. Responses in transgenic hCLUp-Luc reporter mice after low IR doses showed that specific tissues (i.e., colon, spleen, mammary, thymus, bone marrow) of female mice induced hCLUp-Luc activity more than male mice after whole body (≥10 cGy) irradiation. Tissue-specific, non-linear dose- and time-responses of hCLUp-Luc and endogenous sCLU levels were noted. Colon maintained homeostatic balance after 10 cGy. Bone marrow responded with delayed, but prolonged and elevated expression. Intraperitoneal administration of α-TGFβ1 (1D11), but not control (13C4) antibodies, immediately following IR exposure abrogated CLU induction responses. Induction in vivo also correlated with Smad signaling via activated TGFβ1 after IR. Mechanistically, media with elevated sCLU levels suppressed signaling, blocked apoptosis and increased survival of TGFβ1-exposed tumor or normal cells. Thus, sCLU is a pro-survival bystander factor that abrogates TGFβ1 signaling and promotes wound healing.

Cysteine protease cathepsin B mediates radiation-induced bystander effects

“…1b), reaching maximal death inhibitory activity at 100 J/m 2 . These results are consistent with published reports that reduced apoptosis or increased survival of unexposed cells is one of the endpoints of RIBE 3,7–9 .…”

The Molecular Chaperone Apolipoprotein J/Clusterin as a Sensor of Oxidative Stress: Implications in Therapeutic Approaches - A Mini-Review

“…Although these studies added to previous findings suggesting a tumor-suppressing effect of CLU, CLU expression levels were positively correlated with disease progression in the majority of reported studies [16]. More recently, it was found that AKT exerted its cytoprotective role in prostate tumor cells via the induction of CLU [70], as well as that low-dose ionizing radiation-induced IGF-1 mediates CLU expression that interferes with TGFβ1 signaling to confer a prosurvival bystander effect [71]. Moreover, in prostate cancer cells, CLU mediated TGF-β-induced epithelial-mesenchymal transition and metastasis via Twist1 [72], while transcriptome profiling in a TGF-β-induced epithelial-mesenchymal transition model revealed extracellular CLU as a target for therapeutic antibodies [73].…”

AAVPG: A vigilant vector where transgene expression is induced by p53

“…In addition to ionizing radiation (Hildesheim et al, 2002;Klokov et al, 2012;Rashi-Elkeles et al, 2011), p53 activity can also be induced by oncogenic stress (Feng et al, 2006;Yan et al, 2005), oxidative stress (Achanta and Huang, 2004;Sinthupibulyakit et al, 2010), signaling cytokines (Doman et al, 1999;Kim et al, 2005), changes in temperature Michalovitz et al, 1990;Zhang et al, 1994), hypoxia (Long et al, 1997;Sano et al, 2007;Sutton et al, 2008), chemotherapeutic agents (Chuang et al, 2012;el-Deiry et al, 1994;Lowe et al, 1993;Wang et al, 2005) and biomechanical stress (Leri et al, 1998(Leri et al, , 2000Liao et al, 2004). Molecular tools that reveal the activities of p53 would help deepen our understanding of many cellular processes.…”