Date Published: September 13, 2018
Publisher: Public Library of Science
Author(s): Fengchao Lang, Zhiguo Sun, Yonggang Pei, Rajnish Kumar Singh, Hem Chandra Jha, Erle S. Robertson, Richard Longnecker.
Shugoshin-1 (Sgo1) protects the integrity of the centromeres, and H2A phosphorylation is critical for this process. The mitotic checkpoint kinase Bub1, phosphorylates H2A and ensures fidelity of chromosome segregation and chromosome number. Oncogenic KSHV induces genetic alterations through chromosomal instability (CIN), and its essential antigen LANA regulates Bub1. We show that LANA inhibits Bub1 phosphorylation of H2A and Cdc20, important for chromosome segregation and mitotic signaling. Inhibition of H2A phosphorylation at residue T120 by LANA resulted in dislocation of Sgo1, and cohesin from the centromeres. Arrest of Cdc20 phosphorylation also rescued degradation of Securin and Cyclin B1 at mitotic exit, and interaction of H2A, and Cdc20 with Bub1 was inhibited by LANA. The N-terminal nuclear localization sequence domain of LANA was essential for LANA and Bub1 interaction, reversed LANA inhibited phosphorylation of H2A and Cdc20, and attenuated LANA-induced aneuploidy and cell proliferation. This molecular mechanism whereby KSHV-induced CIN, demonstrated that the NNLS of LANA is a promising target for development of anti-viral therapies targeting KSHV associated cancers.
Kaposi’s sarcoma-associated Herpesvirus, also referred as human herpes virus 8 (KSHV/HHV8), a tumor virus, has been documented to be a major contributor to human malignancies and lymphoproliferative disorders, including Kaposi’s sarcoma, Primary effusion lymphoma, and Multicentric Castleman’s disease. KSHV establishes a latent infection in the host after primary infection and continuously expresses genes to facilitate its persistence and evasion from the host immune surveillance . The oncogenic genes, include v-FLIP (ORF71), v-Cyclin (ORF72), LANA (ORF73) and some microRNAs, which manipulate cell cycle regulation, cell growth, proliferation and apoptosis . Disruption of cell cycle regulation by KSHV leads to genome instability and contributes to the oncogenic process .
The molecular mechanisms which drive virus-associated oncogenic activities are still not completely explored. Here we present a novel mechanism which shows that the oncogenic gene LANA can drive chromosomal instability, a hallmark of KSHV infected cells and KSHV-associated cancer. LANA can inhibit the mitotic checkpoint protein Bub1 kinase activity on H2A and Cdc20, which results in premature chromosomal segregation and mitotic exit. The interaction between LANA and Bub1, H2A or Cdc20, interferes with Bub1-mediated H2A or Cdc20 phosphorylation. The NNLS domain also plays an essential role in the interactions between LANA and Bub1, H2A or Cdc20 as competitive binding of NNLS will rescue LANA’s inhibition of Bub1 kinase activity through its ability to disrupt binding to LANA (Fig 6J and 6K).