The Influence of E1A C-Terminus on Adenovirus Replicative Cycle.

Leandro Crisostomo,Oladunni Olanubi,Andrea Soriano,Peter Pelka,Megan Mendez,Jasmine Frost

doi:10.3390/v9120387

Abstract

Adenovirus Early 1A proteins (E1A) are crucial for initiation of the viral life cycle after infection. The E1A gene is encoded at the left end of the viral genome and consists of two exons, the first encoding 185 amino acids in the 289 residues adenovirus 5 E1A, while the second exon encodes 104 residues. The second exon-encoded region of E1A is conserved across all E1A isoforms except for the 55 residues protein, which has a unique C-terminus due to a frame shift following splicing into the second exon. This region of E1A contributes to a variety of processes including the regulation of viral and cellular gene expression, immortalization and transformation. Here we evaluated the contributions that different regions of the second exon of E1A make to the viral life cycle using deletion mutants. The region of E1A encoded by the second exon was found to be important for overall virus growth, induction of viral and cellular gene expression, viral genome replication and deregulation of the cell cycle. Efficient viral replication was found to require exon 2 and the nuclear localization signal, as loss of either resulted in severe growth deficiency. Induction of cellular DNA synthesis was also deficient with any deletion of E1A within the C-terminus even if these deletions were outside of conserved region 4. Overall, our study provides the first comprehensive insight into the contributions of the C-terminus of E1A to the replicative fitness of human adenovirus 5 in arrested lung fibroblasts.

Highlights

Human adenovirus (HAdV) usually infects terminally differentiated epithelial cells [1]
Early 1A proteins (E1A) is encoded by the E1A gene; the pre-mRNA is spliced into five different splice variants that are expressed differentially during the course of viral infection [2]
No growth was observed at 24 h after infection, which was consistent with previous reports showing that in arrested cells virus does not begin to egress until after 24 h after initial infection [2,22]. dl311, which expresses E1A lacking most of the region encoded by exon 2, grew minimally throughout the assay duration. dl311 reached a titer of approximately 2E5 pfu/mL at 96 h, which is about 10,000× lower to the titer observed for dl309, expressing wt E1A and lower to what was previously observed for dl311 in transformed cells [16]

Summary

Introduction

Human adenovirus (HAdV) usually infects terminally differentiated epithelial cells [1]. Since this environment is unsuitable for replication, the immediate early E1A proteins reprogram the infected cell to facilitate viral replication, which involves induction of the cell cycle and entry of the infected cells into the S-phase to allow viral DNA to be copied [1]. E1A is encoded by the E1A gene; the pre-mRNA is spliced into five different splice variants that are expressed differentially during the course of viral infection [2]. The E1A gene is composed of two exons that splice alternatively to give the five different protein isoforms. The functions that E1A performs are largely executed via a large variety of protein-protein interactions between E1A and cellular

Methods

Results

Conclusion