p53 target Siva regulates apoptosis in ischemic kidneys

Abstract

The role of p53 in inducing apoptosis following acute kidney injury is well-established; however, the molecular mechanisms remain largely unknown. We report here that the p53 proapoptotic target Siva and its receptor CD27, a member of the tumor necrosis factor receptor family, are upregulated following renal ischemia-reperfusion injury (IRI). Inhibition of Siva using antisense oligonucleotides conferred functional and morphological protection, and it prevented apoptosis postrenal IRI in mice. Renal IRI in CD27-deficient mice displayed functional protection and partial inhibition of apoptosis, suggesting an incomplete role for CD27 in Siva-mediated apoptosis. To further elucidate mechanisms by which Siva elicits apoptosis, in vitro studies were performed. In Siva-transfected LLC-PK(1)cells, Siva is persistently expressed in the nucleus at 3 h onwards and its translocation to mitochondria and the plasma membrane occurred at 6 h. Moreover, Siva overexpression induced mitochondrial permeability, cytochrome c release, caspase-8 and -9 activation, translocation of apoptosis-inducing factor (AIF) to the nucleus, and apoptosis. Inhibition of Siva in ischemic kidneys prevented mitochondrial release of cytochrome c and AIF. These data indicate that Siva function is pivotal in regulating apoptosis in the pathology of renal IRI. Targeting Siva may offer a potential therapeutic strategy for renal IRI.

Targeted Deletion of p53 in the Proximal Tubule Prevents Ischemic Renal Injury

“…In a previous report, Dong and colleagues 28 showed that Bid deficiency attenuated tubular disruption, tubular cell apoptosis, and caspase-3 activation during 48 hours of reperfusion. We previously reported that the expression of the proapoptotic p53 target Siva and its cognate receptor CD27 is highly upregulated and coexpressed in the ischemic rat and mouse renal tissues, 29 indicating that Siva plays a critical role in apoptosis after IRI. It is likely that synergic functions of these proapoptotic molecules may lead to the execution of apoptosis after IRI.…”

Thromboxane A2 modulates cisplatin-induced apoptosis through a Siva1-dependent mechanism

“…Another possibility would be that in cells destined to enter apoptosis, the anti-apoptotic Siva1/Mdm2 interaction is completely lost and that the impression of its conservation results from the fact that western blots study an unsynchronized cell population. Whatever the case, we do suggest that the Siva1 function at the nucleus might indeed be anti-apoptotic through the reported p53-Mdm2 scaffold and that its pro-apoptotic properties might appear once it has translocated to the cytoplasm where it can access not only TRAF2 and XIAP, but also the mitochondria 5 where Bcl-2 and Bcl-xL are located. We believe this is the first model unifying the pro-and anti-apoptotic roles of Siva1 and showcasing a live modulation of Siva1 localization and function by agonist stimulation of a receptor.…”

“…Cytosolic staining was usually diffuse, but punctate accumulations could often be seen (Figure 6b), as reported by others. 5 In some cells, apoptosis -as evidenced by blebbing seen in the differential interference contrast channel and Hoechst condensation -followed Siva1 translocation by 2 to 12 h (Figure 6a). Co-transfection of GFP-TPb along with Cherry-HA-Siva1 appeared to accelerate and amplify all of the aforementioned processes (Figure 6b), with Siva1 translocation to the cytoplasm usually complete after 4-6 h and cell blebbing/contraction initiated after 6-8 h of receptor stimulation.…”

“…4,5 Various studies demonstrated that Siva1 expression is upregulated in contexts where apoptosis is induced, such as ischemic insults 6 and treatments with chemotherapeutic agents like cisplatin. 7 Siva1 was shown to be a direct transcriptional target of p53 and E2F1 8 and suggested mechanisms of apoptosis induction include Siva1 interaction with and inhibition of Bcl-xL 9 and binding to TRAF2 (Nakahata 1 ) or XIAP 10 to inhibit NFkB activity and promote sustained JNK activation.…”

“…Siva1 was reported to be predominantly located in the nucleus, 4 although subpopulations have been described in the cytosol, plasma membrane and mitochondria. 5,7 Because Mdm2 is mostly nuclear 22 while XIAP and TRAF2 are both cytosolic proteins, 23,24 we hypothesized that TP stimulation might induce a translocation of Siva1 from its nuclear location to the cytoplasm, thereby decreasing its interaction with Mdm2 and enhancing its association with XIAP and TRAF2. We thus performed live confocal microscopy imaging of HeLa cells expressing low levels of a Cherry-HA-Siva1 construct ( Figure 6 and Supplementary Material 3).…”