Co-Regulation Mechanism of Host p53 and Fos in Transcriptional Activation of ILTV Immediate-Early Gene ICP4

Infectious laryngotracheitis virus (ILTV) exhibits a cascade expression pattern of encoded genes, and <i>ICP4</i> is the only immediate-early gene of ILTV, which plays a crucial role in initiating the subsequent viral genes. Therefore, studying the transcriptional regulation mechanism of <i>ICP4</i> holds promise for effectively blocking ILTV infection and spread. Host transcriptional factors p53 and Fos are proven to regulate a variety of viral infections, and our previous studies have demonstrated their synergistic effects in regulating ILTV infection. In this study, we constructed eukaryotic expression vectors for p53 and Fos as well as their specific siRNAs and transfected them into a chicken hepatoma cell line. The results showed that knocking down p53 or Fos significantly inhibited <i>ICP4</i> transcription, while overexpressing p53 or Fos had an opposite effect. A further CoIP and ChIP-qPCR assay suggested p53 and Fos physically interacted with each other, and jointly bound to the upstream transcriptional regulatory region of <i>ICP4</i>. To elucidate the specific mechanisms of p53 and Fos in regulating <i>ICP4</i> transcription, we designed p53 and Fos protein mutants by mutating their DNA binding domains, which significantly reduced their binding ability to DNA without affecting their interaction. The results showed that Fos directly bound to the promoter region of <i>ICP4</i> as a binding target of p53, and the p53-Fos protein complex acted as a transcriptional co-regulator of I<i>CP4</i>. Studying the transcriptional process and regulatory pattern of <i>ICP4</i> is of great significance for understanding the molecular mechanism of ILTV infection, and thus for finding effective methods to control and prevent it.