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. 2016 Apr 27:3:16012.
doi: 10.1038/mto.2016.12. eCollection 2016.

Tumor control by human cytomegalovirus in a murine model of hepatocellular carcinoma

Amit Kumar  1 , Laurie Coquard  1 , Sébastien Pasquereau  1 , Laetitia Russo  2 , Séverine Valmary-Degano  2 , Christophe Borg  3 , Pierre Pothier  4 , Georges Herbein  1
Affiliations

Tumor control by human cytomegalovirus in a murine model of hepatocellular carcinoma

Amit Kumar et al. Mol Ther Oncolytics. .

Abstract

Although viruses can cause cancer, other studies reported the regression of human tumors upon viral infections. We investigated the cytoreductive potential of human cytomegalovirus (HCMV) in a murine model of human hepatocellular carcinoma (HCC) in severe-immunodeficient mice. Infection of HepG2 cells with HCMV resulted in the absence of tumor or in a limited tumor growth following injection of cells subcutaneously. By contrast all mice injected with uninfected HepG2 cells and with HepG2 cells infected with UV-treated HCMV did develop tumors without any significant restriction. Analysis of tumors indicated that in mice injected with HCMV-infected-HepG2 cells, but not in controls, a restricted cellular proliferation was observed parallel to a limited activation of the STAT3-cyclin D1 axis, decreased formation of colonies in soft agar, and activation of the intrinsic apoptotic pathway. We conclude that HCMV can provide antitumoral effects in a murine model of HCC which requires replicative virus at some stages that results in limitation of tumor cell proliferation and enhanced apoptosis mediated through the intrinsic caspase pathway.

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Figures

Figure 1
Figure 1
Effect of HCMV on tumor growth of HepG2 cells in xenografted mice. (a) HepG2 cells were either left uninfected or infected with UV-inactivated HCMV (UV-HCMV) or wild-type HCMV (AD169). After 24 hours of infection, nude balb/c mice were injected subcutaneously with HepG2 cells (uninfected: HepG2-UI, infected with UV-inactivated HCMV: HepG2-UV-HCMV, and wild-type HCMV: HepG2-WT-HCMV). Tumor growth was assessed as shown in figure and tumor volume was determined as described in Materials and Methods. (b) Percentage of mice developing tumor in each group (HepG2-UI; n = 5, HepG2-UV-HCMV; n = 5, HepG2-WT-HCMV; n = 5) is shown. (c) Representative picture of tumor retrieved from mice injected with HepG2 cells infected with wild-type HCMV. (d) Size of tumor was recorded as described in Materials and Methods. Graph represents the relative size of tumor in each group with respect to control group (HepG2-UI).
Figure 2
Figure 2
Morphological assessment of tumors retrieved from different mice groups using immunohistochemistry (IHC). Upon killing the mice, tumors and organs (liver and lung) were retrieved and half of the tissues were fixed in formalin and half were stored in ice-cold PBS for molecular analysis. Sections were made and initial assessment of the tissue was made by IHC using hematoxylin/eosin (H/E) staining as mentioned in Materials and Methods. Figure is a representative picture of tumor sections stained with H/E retrieved from each mice group (original magnification ×25, ×200).
Figure 3
Figure 3
Absence of HCMV signatures (DNA, transcripts, and proteins) in tissues retrieved from different mice groups (HepG2-UI, HepG2-UV-HCMV, and HepG2-WT-HCMV). (a) Screening for the presence of HCMV DNA in organs (liver and lung) and tumors retrieved from different mice groups using polymerase chain reaction. DNA was isolated from tumors and organs isolated from different mice groups. Equal amount of DNA was amplified using MIEP and β-globin primers. Amplicons were electrophoresed on 2 % agarose gel and stained with Sybr green I nucleic acid stain. Positive control is viral DNA isolated from the supernatants of MRC5 post 3 days of infection. (b) Representative pictures of tumor biopsies from different mice group stained from HCMV IE1-Ag using IHC. No specific CMV IE staining was detected. (c) Absence of HCMV IE1 and US28 transcripts in tumors retrieved from mice infected with WT-HCMV. RNA was isolated from tumors obtained from mice. Equal amount of RNA was reverse transcribed into cDNA using oligo dT primer and presence of IE1, US28, and β-globin was determined using real-time PCR. Positive control is RNA isolated from MRC5 infected with AD169 post 3 days of infection. * denotes that no Ct value was observed, small bars have been added for presentation purpose only. MIEP, major immediate early promoter.
Figure 4
Figure 4
Tumor retrieved from mice injected with HepG2 infected with wild-type HCMV exhibits low proliferation and limited activation of STAT3-cyclin D1 axis. Ki67 antigen is considered as one of the hallmarks of cell proliferation. IHC was performed to determine the Ki67 Ag labeling index in tumor tissues retrieved from the different mice group. (a) Representative picture of tumor biopsies retrieved from mice showing Ki67 Ag labeling (brown precipitate shown by red arrow) (original magnification ×200). (b) Percentage of cells positive for Ki67 Ag were determined in silico by counting positive cells using automated software and plotted as a graph (P = 0.002; UI versus WT-HCMV, P = 0.01; UV-HCMV versus WT-HCMV). (c) Expression of Ki67 Ag, phosphoStat-3, total Stat-3, cyclin D1, and β-actin was determined by western blotting. Tumor tissues were weighed and crushed in liquid nitrogen. Protein was extracted using RIPA buffer and quantitated using Bradford protein estimation method and expression of proteins was determined using western blotting as described in Materials and Methods. Histogram represents Ki67 Ag, phosphoSTAT3, and cyclin D1 expression as measured using image J software. WT-HCMV, wild-type HCMV
Figure 5
Figure 5
Tumor cells retrieved from mice infected with WT-HCMV showed low tumorogenic potential. One fourth of the tumor tissues isolated from different mice groups were stored in 1× ice-cold PBS for determination of tumorogenic potential using soft agar assay. Individual populations of the cells were obtained from tumor tissues as described in the Materials and Methods. Cells were seeded in soft agar assay and post 8 days of seeding colony formation was determined using MTT assay. P = 0.02 (HepG2-UI versus HepG2-WT-HCMV); P = 0.038 (HepG2-UV-HCMV versus HepG2-WT-HCMV). HCMV, human cytomegalovirus; HepG2-UI, uninfected HepG2 cells; HepG2-UV-HCMV, UV-inactivated HCMV; HepG2-WT-HCMV, wild-type HCMV-infected HepG2 cells group; WT-HCMV, wild-type HCMV.
Figure 6
Figure 6
HCMV induces caspase-mediated apoptosis in hepatocellular carcinoma cells in a p53-independent manner. (a) To have a quick glimpse in the extent of apoptosis in tissue isolated from different groups (HepG2-UI, HepG2-UV-HCMV, and HepG2-WT-HCMV), genomic DNA was isolated from tumor tissues. DNA was visualized on 2% agarose gel stained with Sybr green I nucleic acid stains. M1 is a 100-bp DNA ladder (Fermentas, generuler 100-bp DNA ladder cat # SM0243) and M2 is a 1-kb DNA ladder (Fermentas, generuler 1-kb DNA ladder cat # SM0313). P: positive control is the genomic DNA isolated from HepG2 cells treated with Akt1/2 inhibitor for 30 hours in serum-deprived condition. (b,c) Further to understand the mechanism of delayed appearance of tumor in mice injected with WT-HCMV infected cells, expression of caspase-3 and caspase-9 proteins and transcripts in tumor biopsies was determined using immunohistochemistry (b), western blotting (c) and real-time quantitative PCR (d). For cytochrome c detection in the cytosol, cytosolic-enriched tumor fraction was prepared as described. As a loading control, levels of β-actin protein were determined. Mice injected with WT-HCMV-infected HepG2 cells exhibited higher levels of caspase-3 and caspase-9 in tumor biopsies as shown by IHC (b) and western blotting (b). (d) Relative expression of caspase-3 and caspase-9 transcripts was determined by reverse-transcriptase real- time PCR (RT-PCR) using 2−ΔΔCT method. (e) No significant difference was found in the expression of p53, p21, and MDM2 in tumor tissues isolated from different groups (HepG2-UI, n = 3; HepG2-UV-HCMV, n = 3; and HepG2-WT-HCMV, n = 2). Protein was isolated from tumors retrieved from different mice groups and expression of p53, p21 and MDM2, and β-actin was determined by western blotting. HCMV, human cytomegalovirus; HepG2-UI, uninfected HepG2 cells; HepG2-UV-HCMV, UV-inactivated HCMV; HepG2-WT-HCMV, wild-type HCMV-infected HepG2 cells group; WT-HCMV, wild-type HCMV.
Figure 7
Figure 7
Caspase activation in lung tissue of xenografted mice injected with HepG2 cells infected with WT-HCMV. Levels of active caspase-3 and active caspase-9 were determined in the organs (liver and lung) retrieved from different mice groups using western blotting. Intensity of bands was quantitated using image J software and plotted as a graph. HCMV, human cytomegalovirus; WT-HCMV, wild-type HCMV.
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