B cell expression of E3 ubiquitin ligase Cul4b promotes chronic gammaherpesvirus infection in vivo

Abstract

ABSTRACT The gammaherpesviruses, including human Epstein-Barr virus, human Kaposi’s sarcoma-associated herpesvirus, and murine gammaherpesvirus 68 (MHV68, γHV68, MuHV-4), are ubiquitous pathogens that directly contribute to the genesis of a wide variety of malignancies, including B cell lymphomas. In vivo , these viruses infect naïve B cells and then usurp B cell signaling pathways to drive infected cells, independent of antigen stimulation, through germinal center (GC) reactions and thereby establish lifelong latency in the memory B cell compartment. However, the specific molecular determinants by which these viruses establish chronic latent infection in B cells in vivo remain largely unknown. The E3 ubiquitin ligase Cullin 4b (Cul4b) is well recognized as a central player in regulating cell proliferation, DNA damage repair, and gene transcription by catalyzing the ubiquitination and degradation of numerous cellular proteins. Here, we determined whether B cell-intrinsic expression of Cul4b is required for chronic gammaherpesvirus infection in vivo . Through MHV68 infection of mice with B cell-specific Cul4b deficiency, we found that loss of Cul4b expression in B cells severely impeded the establishment of latency at peripheral sites. In particular, a lack of Cul4b expression in B cells significantly attenuated the expansion of virus-infected GC B cells, suggesting that gammaherpesviruses may manipulate a previously unknown function of Cul4b in GC B cell biology. Cumulatively, these findings demonstrate that Cul4b promotes chronic gammaherpesvirus infection in vivo . IMPORTANCE The human gammaherpesviruses Epstein-Barr virus and Kaposi’s sarcoma-associated herpesvirus are etiologic agents of numerous B cell lymphomas. A hallmark of gammaherpesvirus infection is their ability to establish lifelong latency in B cells. However, the specific mechanisms that mediate chronic infection in B cells in vivo remain elusive. Cellular E3 ubiquitin ligases regulate numerous biological processes by catalyzing ubiquitylation and modifying protein location, function, or half-life. Many viruses hijack host ubiquitin ligases to evade antiviral host defense and promote viral fitness. Here, we used the murine gammaherpesvirus 68 in vivo system to demonstrate that the E3 ligase Cul4b is essential for this virus to establish latency in germinal center B cells. These findings highlight an essential role for this E3 ligase in promoting chronic gammaherpesvirus infection in vivo and suggest that targeted inhibition of E3 ligases may provide a novel and effective intervention strategy against gammaherpesvirus-associated diseases.