Kaposi’s Sarcoma Associated Herpesvirus LANA Modulates the Stability of the E3 Ubiquitin Ligase RLIM

The Kaposi’s sarcoma associated herpesvirus (KSHV) encoded LANA protein functions in latently infected cells as an essential participant in KSHV genome replication and as a driver of dysregulated cell growth. In a previous study, we have identified LANA interacting proteins using a protein array screen. Here, we explore the effect of LANA on the stability and activity of RLIM (RING-finger LIM-domain-interacting protein, encoded by the RNF12 gene) a novel LANA interacting protein identified in that protein screen. RLIM is an E3 ubiquitin ligase that leads to the ubiquitination and degradation of several transcription regulators, such as LMO2, LMO4, LHX2, LHX3, LDB1 and the telomeric protein TRF1. Expression of LANA leads to down-regulation of RLIM protein levels. This LANA-mediated RLIM degradation is blocked in the presence of the proteasome inhibitor, MG132. Therefore, the interaction between LANA and RLIM could be detected in co-immunoprecipitation assay only in the presence of MG132 to prevent RLIM degradation. A RING finger mutant RLIM (HH 590, 593 EE) is resistant to LANA mediated degradation, suggesting that LANA promotes RLIM auto-ubiquitination. Interestingly, we find that LANA enhance the degradation of some RLIM substrates, such as LDB1 and LMO2, and prevent RLIM mediated degradation of others such as LHX3 and TRF1. We also show that transcription regulation by RLIM substrates is modulated by LANA. RLIM substrates are assembled into multi-protein transcription regulator complexes that regulate the expression of many cellular genes. Therefore, our study identified another way KSHV can modulate cellular gene expression.