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Articles by Jeffery T. Sample
Total Records ( 2 ) for Jeffery T. Sample
  Mikio Yoshioka , Michelle M. Crum and Jeffery T. Sample
  Epstein-Barr virus (EBV) latent infection, and its associated oncogenic potential, is dependent on genome maintenance functions of EBV nuclear antigen 1 (EBNA-1), one of six EBNAs expressed from a common promoter (Wp and then Cp) upon infection of naive B cells. Subsequent host-mediated silencing, however, necessitates the expression of EBNA-1 from the EBNA-1-specific promoter Qp to ensure against genome loss during cell division, including EBV-associated malignancy. Here we addressed the mechanism by which EBNA-1 represses Qp through binding downstream of the transcription start site and the role of this autoregulatory function in EBV latency. Our results revealed that EBNA-1 does not inhibit transcription from Qp, as previously predicted, but acts post- or cotranscriptionally to block the processing of primary transcripts. This does not, however, require the RGG motifs responsible for strong but nonspecific RNA binding by EBNA-1. Within isogenic B-cell lines using either Cp/Wp or Qp, EBNA-1 occupancy of Qp is equivalent, suggesting that autoregulation occurs, albeit to different degrees, during full and restricted EBV latency programs. Finally, in cell lines using Cp or Wp for EBNA expression, unprocessed transcripts from Qp are detectable in the absence of corresponding mRNAs, providing further evidence that this novel mechanism of EBNA-1 action functions during latency. This posttranscriptional mechanism of regulation would provide an efficient means to monitor and regulate EBNA-1 expression from Qp, ensuring levels adequate for genome maintenance but, perhaps more importantly, below an immunogenic threshold above which latently infected cells may be at risk for elimination by EBNA-1-specific cytotoxic T cells.
  Sean P. Garrison , John R. Jeffers , Chunying Yang , Jonas A. Nilsson , Mark A. Hall , Jerold E. Rehg , Wen Yue , Jian Yu , Lin Zhang , Mihaela Onciu , Jeffery T. Sample , John L. Cleveland and Gerard P. Zambetti
  The p53 tumor suppressor pathway limits oncogenesis by inducing cell cycle arrest or apoptosis. A key p53 target gene is PUMA, which encodes a BH3-only proapoptotic protein. Here we demonstrate that Puma deletion in the Eµ-Myc mouse model of Burkitt lymphoma accelerates lymphomagenesis and that ~75% of Eµ-Myc lymphomas naturally select against Puma protein expression. Furthermore, approximately 40% of primary human Burkitt lymphomas fail to express detectable levels of PUMA and in some tumors this is associated with DNA methylation. Burkitt lymphoma cell lines phenocopy the primary tumors with respect to DNA methylation and diminished PUMA expression, which can be reactivated following inhibition of DNA methyltransferases. These findings establish that PUMA is silenced in human malignancies, and they suggest PUMA as a target for the development of novel chemotherapeutics.
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