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Viral interleukin-6 encoded by an oncogenic virus promotes angiogenesis and cellular transformation by enhancing STAT3-mediated epigenetic silencing of caveolin 1


Kaposi’s sarcoma (KS) caused by oncogenic Kaposi’s sarcoma-associated herpesvirus (KSHV) is a highly angiogenic and invasive vascular tumor and the most common AIDS-associated cancer. KSHV-encoded viral interleukin-6 (vIL-6) is implicated in the development of KSHV-induced malignancies; however, the mechanisms underlying vIL-6-induced angiogenesis and tumorigenesis remain undefined. Here, we show that vIL-6 promotes angiogenesis, cell proliferation, and invasion by downregulating caveolin 1 (CAV1) that plays a pivotal and versatile role in multiple cancer-associated processes. Mechanistically, vIL-6 signaling led to the phosphorylation and acetylation of STAT3 that targeted DNA methyltransferase 1 (DNMT1) in a sequential manner. Specifically, the vIL-6-induced phosphorylated form of STAT3 transcriptionally activated DNMT1 expression. Furthermore, vIL-6-induced acetylated form of STAT3 interacted with DNMT1 to form a transcription factor complex that bound to and methylated the CAV1 promoter, leading to CAV1 expression silencing. In fact, downregulation of CAV1 expression resulted in the activation of AKT signaling, promoting cell invasion, and growth transformation induced by KSHV. Finally, genetic deletion of vIL-6 from the KSHV genome abolished KSHV-induced cellular transformation and impaired angiogenesis. Our results reveal that vIL-6 epigenetically silences CAV1 expression to promote angiogenesis and tumorigenesis by regulating the formation of STAT3-DNMT1 complex. These novel findings define a mechanism by which KSHV inhibits the CAV1 pathway and establish the scientific basis for targeting this pathway to treat KSHV-associated cancers.

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Fig. 1: CAV1 is downregulated in vIL-6-transduced cells, KSHV-infected cells, and KS lesions.
Fig. 2: Downregulation of CAV1 contributes to vIL-6-induced cell proliferation, invasion, and angiogenesis.
Fig. 3: The methylation of CAV1 promoter is enhanced in vIL-6-transduced cells and KSHV-infected cells.
Fig. 4: vIL-6 inhibits CAV1 to promote cell proliferation, invasion, and angiogenesis by upregulating DNMT1 to enhance the hypermethylation of CAV1 promoter.
Fig. 5: vIL-6 downregulates CAV1 by increasing acetylated STAT3 which interacts with DNMT1 and promotes the binding of DNMT1 to CAV1 promoter.
Fig. 6: vIL-6 promotes cell migration and invasion by activating AKT pathway.
Fig. 7: vIL-6-regulated CAV1/AKT pathway mediates KSHV-induced cellular transformation.


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We thank Drs Robert Yarchoan and Victoria Wang at the Center for Cancer Research, National Cancer Institute for providing the purified monoclonal rabbit anti-vIL-6 antibody and information related to the detection of vIL-6 in KSHV-infected HUVECs by western blotting. We also thank Drs Yuan Chang and Patrick Moore from University of Pittsburgh for providing reagent. We are also grateful to members from Dr Lu laboratory for helpful discussion.


This work was supported by grants from National Natural Science Foundation of China (81730062, 81761128003, 31800148, and 81503368), Natural Science Foundation of Jiangsu Province (BK20180681), Nanjing Medical University (KY101RC1710), a grant from NIH (R01CA213275), and grants (CA200422, AI073099, AI116585, AI129496, AI140718, AI140705, DE023926, DE027888, DE028521 and Fletcher Jones Foundation).

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Conceived and designed the experiments: CL. Performed the experiments: WL, QW, XQ, YG, YC and XZ. Providing reagents: HL and GT. Analyzed the data: WL, ZL, QY, XZ, JUJ, SJG and CL. Wrote the paper: WL, XZ, JUJ, SJG and CL.

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Correspondence to Xiaofei Zhu or Chun Lu.

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The clinical section of the research was reviewed and ethically approved by the Institutional Ethics Committee of the First Affiliated Hospital of Nanjing Medical University.

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Li, W., Wang, Q., Qi, X. et al. Viral interleukin-6 encoded by an oncogenic virus promotes angiogenesis and cellular transformation by enhancing STAT3-mediated epigenetic silencing of caveolin 1. Oncogene 39, 4603–4618 (2020).

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