Dual induction of PKR with E2F-1 and IFN-α to enhance gene therapy against hepatocellular carcinoma

Roh, Vincent; Laemmle, Alexander; Holzen, Urs von; Stroka, Deborah; Dufour, Jean–François; Hunt, Kelly K.; Candinas, Daniel; Vorburger, Stephan A.

doi:10.1038/cgt.2008.34

Cited by 10 publications

(11 citation statements)

References 32 publications

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“…The importance of E2F-1 activation and overexpression as a marker of poor patient prognosis in HCC has already been reported [11] and remains to be confirmed in large clinicopathological studies. Furthermore, overexpression of E2F-1 has been shown to exert tumor-suppressor activity in selectively targeted subcutaneous xenograft tumors, introducing adenoviral vectors expressing E2F-1 as a new therapeutic approach through gene therapy of HCC [33].…”

Section: Discussionmentioning

confidence: 99%

E2F-1 is overexpressed and pro-apoptotic in human hepatocellular carcinoma

et al. 2012

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E2F-1 is a transcription factor involved in DNA synthesis and repair, cell proliferation, and apoptosis. Hyposphorylated pRb represses E2F-1 action in early G1 phase, while in late G1, pRb hyperphosphorylation leads to E2F-1 release and activation. In vitro studies have shown that E2F-1 may act either as oncogene or as tumor suppressor gene. We evaluated immunohistochemical expression of E2F-1 protein in chronic viral liver disease and hepatocellular carcinoma (HCC) and correlated this with clinicopathological parameters, cell proliferation, apoptosis, and the expression of E2F-1-regulators, pRb, and phospho-pRb (Ser795). In liver biopsies from 30 patients with chronic viral hepatitis, including 22 with cirrhosis without HCC, and 57 with cirrhosis with HCC, E2F-1 expression was assessed by immunohistochemistry. In chronic hepatitis and cirrhosis, hepatocytes and cholangiocytes demonstrated mild cytoplasmic and/or nuclear membrane E2F-1 immunostaining. In contrast, all HCC (100 %) showed strong nuclear E2F-1 immunostaining, with or without membrane accentuation, while a minority demonstrated additional moderate cytoplasmic immunostaining. Abnormally low pRb and phospho-pRb expression was seen in 70 % and 67.9 % of HCC, respectively. In HCC, nuclear E2F-1 expression was inversely correlated with phospho-pRb expression (p = 0.001) and positively related to tumor apoptotic index (p = 0.025). No significant correlation was found between E2F-1 expression and patient demographics, HCC etiology, tumor grade, pRb, p53 expression, or cell proliferation. In conclusion, we show that the increased expression of E2F-1 protein in human HCC is correlated with enhanced tumor cell apoptosis supporting a pro-apoptotic role of E2F-1 in human HCC.

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Section: Discussionmentioning

confidence: 99%

E2F-1 is overexpressed and pro-apoptotic in human hepatocellular carcinoma

et al. 2012

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“…Examples of direct interaction include the cellular protein p58 IPK , which binds to PKR and prevents its dimerization, tRNA-dihydrouridine synthetase-2, TRBP and ADAR1, which bind through their dsRNA Binding Domains (dsRBDs) and exert a strong inhibitory activity [12,19,22,32,34-40]. Besides dsRNA and heparin, PACT, the cytokine MDA-7/interleukin 24 and the transcription factor E2F-1 induce PKR activation [32,41-45]. PKR activation upon virus infection is also observed in some specialized cells.…”

Section: Introductionmentioning

confidence: 99%

The PKR activator, PACT, becomes a PKR inhibitor during HIV-1 replication

et al. 2013

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BackgroundHIV-1 translation is modulated by the activation of the interferon (IFN)-inducible Protein Kinase RNA-activated (PKR). PKR phosphorylates its downstream targets, including the alpha subunit of the eukaryotic translation Initiation Factor 2 (eIF2α), which decreases viral replication. The PKR Activator (PACT) is known to activate PKR after a cellular stress. In lymphocytic cell lines, HIV-1 activates PKR only transiently and not when cells replicate the virus at high levels. The regulation of this activation is due to a combination of viral and cellular factors that have been only partially identified.ResultsPKR is transiently induced and activated in peripheral blood mononuclear cells after HIV-1 infection. The addition of IFN reduces viral replication, and induces both the production and phosphorylation of PKR. In lymphocytic Jurkat cells infected by HIV-1, a multiprotein complex around PKR contains the double-stranded RNA binding proteins (dsRBPs), adenosine deaminase acting on RNA (ADAR)1 and PACT. In HEK 293T cells transfected with an HIV-1 molecular clone, PACT unexpectedly inhibited PKR and eIF2α phosphorylation and increased HIV-1 protein expression and virion production in the presence of either endogenous PKR alone or overexpressed PKR. The comparison between different dsRBPs showed that ADAR1, TAR RNA Binding Protein (TRBP) and PACT inhibit PKR and eIF2α phosphorylation in HIV-infected cells, whereas Staufen1 did not. Individual or a combination of short hairpin RNAs against PACT or ADAR1 decreased HIV-1 protein expression. In the astrocytic cell line U251MG, which weakly expresses TRBP, PACT mediated an increased HIV-1 protein expression and a decreased PKR phosphorylation. In these cells, a truncated PACT, which constitutively activates PKR in non-infected cells showed no activity on either PKR or HIV-1 protein expression. Finally, PACT and ADAR1 interact with each other in the absence of RNAs.ConclusionIn contrast to its previously described activity, PACT contributes to PKR dephosphorylation during HIV-1 replication. This activity is in addition to its heterodimer formation with TRBP and could be due to its binding to ADAR1. HIV-1 has evolved to replicate in cells with high levels of TRBP, to induce the expression of ADAR1 and to change the function of PACT for PKR inhibition and increased replication.

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“…In which ΔCT is the difference between the CT of a given target cDNA and an endogenous reference cDNA. Thus, this value yields the amount of the target normalized to an endogenous reference [41]. …”

Section: Methodsmentioning

confidence: 99%

Implication of protein kinase R Gene quantification in hepatitis C Virus Genotype 4 induced Hepatocarcinogenesis

2012

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BackgroundProtein kinase RNA (PKR-regulated) is a double-stranded RNA activated protein kinase whose expression is induced by interferon. The role of PKR in cell growth regulation is controversial, with some studies supporting a tumour suppressor function and others suggesting a growth-promoting role. However, it is possible that the function of PKR varies with the type of cancer in question.MethodsWe report here a detailed study to evaluate the function of PKR in hepatitis C virus genotype 4 (HCV-4) infected patients. PKR gene was quantitated in HCV related malignant and non-malignant liver tissue by RT-PCR technique and the association of HCV core and PKR was assessed.ResultsIf PKR functions as a tumour suppressor in this system, its expression would be higher in chronic hepatitis tissues. On the contrary our study demonstrated the specific association of HCV-4 with PKR expressed in hepatocellular carcinoma (HCC) tissues, leading to an increased gene expression of the kinase in comparison to chronic hepatitis tissues. This calls into question its role as a tumour suppressor and suggests a positive regulatory role of PKR in growth control of liver cancer cells. One limitation of most of other studies is that they measure the levels rather than the quantitation of PKR gene.ConclusionThe findings suggest that PKR exerts a positive role in cell growth control of HCV-4 related HCC, obtaining a cut-off value for PKR expression in liver tissue provides the first evidence for existence of a viral activator of PKR.Virtual SlidesThe virtual slide(s) for this article can be found here: http://www.diagnosticpathology.diagnomx.eu/vs/1267826959682402.

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Dual induction of PKR with E2F-1 and IFN-α to enhance gene therapy against hepatocellular carcinoma

Cited by 10 publications

References 32 publications

E2F-1 is overexpressed and pro-apoptotic in human hepatocellular carcinoma

E2F-1 is overexpressed and pro-apoptotic in human hepatocellular carcinoma

The PKR activator, PACT, becomes a PKR inhibitor during HIV-1 replication

Implication of protein kinase R Gene quantification in hepatitis C Virus Genotype 4 induced Hepatocarcinogenesis

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