Methylation of KSHV vCyclin by PRMT5 contributes to cell cycle progression and cell proliferation

Kaposi’s sarcoma-associated herpesvirus (KSHV), a double-stranded DNA virus, encodes a wide variety of cellular homologs that contribute to its oncogenic properties. These include homologs of key cellular proteins such as cyclin D, G protein-coupled receptors, interleukin-6, and macrophage inflammatory proteins 1 and 2. One of the critical viral proteins, KSHV vCyclin, which is encoded by open reading frame 72 (ORF72), functions as a homolog of cellular cyclin D2. KSHV vCyclin plays a pivotal role in regulating viral replication and cellular proliferation by constitutively activating cyclin-dependent kinase 6 (CDK6). However, the precise mechanisms by which KSHV vCyclin is regulated remain poorly understood.

In this study, we identified a host protein, protein arginine methyltransferase 5 (PRMT5), which interacts with KSHV vCyclin. Further investigations revealed that PRMT5 expression is upregulated by latency-associated nuclear antigen (LANA) through transcriptional activation. This finding highlights the complex regulatory relationship between KSHV and host proteins during latency. Notably, we demonstrated that the knockdown or pharmacological inhibition of PRMT5 using the small molecule inhibitor EPZ015666 significantly impaired cell cycle progression and inhibited the proliferation of tumor cells latently infected with KSHV.

At the mechanistic level, we discovered that PRMT5 methylates vCyclin symmetrically at arginine 128, and this methylation stabilizes vCyclin in a manner that is dependent on PRMT5’s methyltransferase activity. Additionally, we observed that the methylation of vCyclin by PRMT5 plays a crucial role in the activation of the retinoblastoma protein (pRB) pathway, a key regulator of cell cycle progression. This phosphorylation of pRB is critical for the continued proliferation of KSHV-infected cells.

Our findings collectively reveal a novel and important regulatory role for PRMT5 in controlling the stability and function of KSHV vCyclin. By facilitating the activation of the pRB pathway, PRMT5 promotes cell cycle progression and cellular proliferation in KSHV-infected tumor cells. These insights open up new avenues for the development of therapeutic strategies targeting PRMT5, which could offer potential treatments for KSHV-associated malignancies, providing an opportunity to inhibit viral-induced cell proliferation at the molecular level.