Transactivation of latent Marek's disease herpesvirus genes in QT35, a quail fibroblast cell line, by herpesvirus of turkeys

The QT35 cell line was established from a methylcholanthrene-induced tumor in Japanese quail (Coturnix coturnix japonica) (C. Moscovici, M, G, Moscovi ci, H, Jimenez, M. M. Lai, M, J. Hayman, and P. K. Vogt, Cell 11:95-103, 19 77), Two independently maintained sublines of QT35 were found to be positiv e for Marek's disease virus (MDV)-like genes by Southern blotting and PCR a ssays. Sequence analysis of fragments of the ICP4, ICP22, ICP27, VP16, meg, pp14, pp38, open reading frame (ORF) L1, and glycoprotein B (gB) genes sho wed a strong homology with the corresponding fragments of MDV genes. Subseq uently, a serotype 1 MDV-like herpesvirus, tentatively name QMDV, was rescu ed from QT35 cells in chicken kidney cell (CKC) cultures established from 6 - to 9-day-old chicks inoculated at 8 days of embryonation with QT35 cells. Transmission electron microscopy failed to show herpesvirus particles in Q T35 cells, but typical intranuclear herpesvirus particles were detected in CKCs, Reverse transcription-PCR analysis showed that the following QMDV tra nscripts were present in QT35 cells: sense and antisense meg, ORF L1, ICP4, and latency-associated transcripts, which are antisense to ICP4. A transcr ipt of approximately 4.5 kb was detected by Northern blotting using total R NA from QT35 cells. Inoculation of QT35 cells with herpesvirus of turkeys ( HVT)-infected chicken embryo fibroblasts (CEF) but not with uninfected CEF resulted in the activation of ICP22, ICP27, VP16, pp38, and gB. in addition , the level of ICP4 mRNA was increased compared to that in QT35 cells. The activation by HVT resulted in the production of pp38 protein. It was not po ssible to detect if the other activated genes were translated due to the la ck of serotype 1-specific monoclonal antibodies.