Viral and cellular telomerase RNAs possess host-specific anti-apoptotic functions.

Human telomerase RNA (hTR) is overexpressed in many cancers and protects T cells from apoptosis in a telomerase-independent manner. The most prevalent cancer in the animal kingdom is caused by the highly oncogenic herpesvirus Marek's disease virus (MDV). MDV encodes a viral telomerase RNA (vTR) that plays a crucial role in MDV-induced tumorigenesis and shares all four conserved functional domains with hTR. In this study, we assessed whether hTR drives tumor formation in this natural model of herpesvirus-induced tumorigenesis. Therefore, we replaced vTR with hTR in the genome of a highly oncogenic MDV. Furthermore, we investigated the anti-apoptotic activity of vTR, hTR, and their counterpart in the chicken [chicken telomerase RNA (cTR)]. hTR was efficiently expressed and did not alter replication of the recombinant virus. Despite its conserved structure, hTR did not complement the loss of vTR in virus-induced tumorigenesis. Strikingly, hTR did not inhibit apoptosis in chicken cells, but efficiently inhibited apoptosis in human cells. Inverse host restriction has been observed for vTR and cTR in human cells. Our data revealed that vTR, cTR, and hTR possess conserved but host-specific anti-apoptotic functions that likely contribute to MDV-induced tumorigenesis. IMPORTANCE hTR is overexpressed in many cancers and used as a cancer biomarker. However, the contribution of hTR to tumorigenesis remains elusive. In this study, we assessed the tumor-promoting properties of hTR using a natural virus/host model of herpesvirus-induced tumorigenesis. This avian herpesvirus encodes a telomerase RNA subunit (vTR) that plays a crucial role in viral tumorigenesis and shares all conserved functional domains with hTR. Our data revealed that vTR and cellular TRs of humans and chickens possess host-specific anti-apoptotic functions. This provides important translational insights into therapeutic strategies, as inhibition of apoptosis is crucial for tumorigenesis.

In vitro infection of primary chicken lymphocytes with Marek's disease virus.

Marek's disease virus (MDV) is a highly oncogenic alphaherpesvirus that infects immune cells and causes a deadly lymphoproliferative disease in chickens. Cytokines and monoclonal antibodies promote the survival of chicken lymphocytes in vitro. Here, we describe protocols for the isolation, maintenance, and efficient MDV infection of primary chicken lymphocytes and lymphocyte cell lines. This facilitates the investigation of key aspects of the MDV life cycle in the primary target cells of viral replication, latency, genome integration, and reactivation. For complete details on the use and execution of this protocol, please refer to Schermuly et al.,1 Bertzbach et al. (2019),2 and You et al.3 For a comprehensive background on MDV, please see Osterrieder et al.4 and Bertzbach et al. (2020).5.