Adenovirus E1B 55-Kilodalton Protein Targets SMARCAL1 for Degradation during Infection and Modulates Cellular DNA Replication.

Here, we show that the cellular DNA replication protein and ATR substrate SMARCAL1 is recruited to viral replication centers early during adenovirus infection and is then targeted in an E1B-55K/E4orf6- and cullin RING ligase-dependent manner for proteasomal degradation. In this regard, we have determined that SMARCAL1 is phosphorylated at S123, S129, and S173 early during infection in an ATR- and CDK-dependent manner, and that pharmacological inhibition of ATR and CDK activities attenuates SMARCAL1 degradation. SMARCAL1 recruitment to viral replication centers was shown to be largely dependent upon SMARCAL1 association with the RPA complex, while Ad-induced SMARCAL1 phosphorylation also contributed to SMARCAL1 recruitment to viral replication centers, albeit to a limited extent. SMARCAL1 was found associated with E1B-55K in adenovirus E1-transformed cells. Consistent with its ability to target SMARCAL1, we determined that E1B-55K modulates cellular DNA replication. As such, E1B-55K expression initially enhances cellular DNA replication fork speed but ultimately leads to increased replication fork stalling and the attenuation of cellular DNA replication. Therefore, we propose that adenovirus targets SMARCAL1 for degradation during infection to inhibit cellular DNA replication and promote viral replication. Viruses have evolved to inhibit cellular DNA damage response pathways that possess antiviral activities and utilize DNA damage response pathways that possess proviral activities. Adenovirus has evolved, primarily, to inhibit DNA damage response pathways by engaging with the ubiquitin-proteasome system and promoting the degradation of key cellular proteins. Adenovirus differentially regulates ATR DNA damage response signaling pathways during infection. The cellular adenovirus E1B-55K binding protein E1B-AP5 participates in ATR signaling pathways activated during infection, while adenovirus 12 E4orf6 negates Chk1 activation by promoting the proteasome-dependent degradation of the ATR activator TOPBP1. The studies detailed here indicate that adenovirus utilizes ATR kinase and CDKs during infection to promote the degradation of SMARCAL1 to attenuate normal cellular DNA replication. These studies further our understanding of the relationship between adenovirus and DNA damage and cell cycle signaling pathways during infection and establish new roles for E1B-55K in the modulation of cellular DNA replication.