The latency-associated nuclear antigen of Kaposi's sarcoma-associated herpesvirus modulates cellular gene expression and protects lymphoid cells from p16 INK4A-induced cell cycle arrest

Latently infected Kaposi's sarcoma-associated herpesvirus (KSHV)-associated tumor cells have both endothelial and lymphoid origins and express a limited set of latent viral genes. One such gene, ORF73, encodes the latency-associated nuclear antigen (LANA), a multifunctional protein that plays roles in viral DNA replication, episome maintenance, and transcriptional regulation. LANA interacts with cellular proteins involved in transcriptional regulation such as the tumor suppressors, retinoblastoma (Rb) and p53, and RING3 family members. Although several reports about specific LANA-regulated promoters exist, only limited data are available that address how LANA expression in KSHV-infected cells globally affects cellular gene expression, thereby potentially contributing to KSHV pathogenicity. To investigate this question, we generated an Epstein-Barr virus-negative Burkitts lymphoma line that expresses LANA from a tetracycline-inducible promoter (BJAB/Tet-On/LANA), and we performed microarray-based gene expression profiling. Expression profiling at different time points post-induction revealed that 186 genes were activated or repressed over 2-fold in the presence of LANA. Of these genes, 41 are regulated in the Rb/E2F pathway, whereas 7 are related to p53 signaling. To determine whether these gene expression changes translate into LANA-dependent changes in cell cycle regulation, we overexpressed p16 INK4a, a CDK4/6 inhibitor that efficiently induces cell cycle arrest in Rb-positive cells. Under these conditions, LANA expression protects lymphoid cells from p16 INK4a-induced cell cycle arrest and induces S-phase entry.