PROJECT SUMMARY Esophageal Squamous Cell Carcinoma (ESCC), the predominant subtype of esophageal cancer worldwide is one of the most known lethal cancers. The prognosis of metastatic ESCC is dismal with a 5-year relative survival rate of only 5%. Mutations in TP53 (mouse homolog Trp53), which are detected in approximately 70% of ESCC patients, contribute to tumor metastasis and poor prognosis. To understand the mechanisms of Trp53R172H- mediated metastasis, which is one of the “hotspot” mutations in ESCC, we utilized mouse models and performed RNA-Seq on metastatic ESCC cells generated from this model, from which I identified Colony stimulating factor- 1 (Csf-1) to be significantly upregulated. While it is canonically involved in polarization of tumor-associated macrophages through binding to its receptor CSF-1R, my data demonstrate the existence of autocrine signaling that is potentially co-regulated by epigenetic reader Bromodomain-Containing Domain 4 (BRD4). The overarching hypothesis of this study is that CSF-1/CSF-1R autocrine signaling is one of the major mechanisms by which missense TP53 mutations can promote invasion and lung metastasis in ESCC. I will test this hypothesis through the following interrelated Specific Aims: (1) Elucidate the role of Trp53R172H-mediated CSF-1/CSF-1R signaling pathway in promoting invasion and lung metastasis in ESCC, (2) Investigate BRD4 as a candidate co- regulator of Trp53R172H that contributes to CSF-1 upregulation and assess the anti-tumorigenic efficacy of inhibiting BRD4, and (3) Delineate the tumorigenic, as well as epigenetic/transcriptomic states mediated by missense p53 mutations recurrent in ESCC patients and impact upon CSF-1/CSF-1R signaling. To accomplish Aim 1, I will assess the role of CSF-1/CSF-1R signaling in proliferation, migration, primary tumor and 3D organoid formation, invasion and lung metastasis, as well as its downstream effectors through utilizing in vitro and complementary in vivo approaches. I will accomplish Aim 2 by studying the direct interaction of p53-R172H and BRD4, and also their shared DNA binding motifs through CUT&RUN-Seq. Additionally, I will genetically delete and pharmacologically inhibit BRD4 to evaluate their effects on tumorigenesis and lung metastasis. To accomplish Aim 3, I will introduce p53 mutations through base editing and evaluate their distinct roles in pro- oncogenic activities. I will also investigate how these mutations affect the transcriptional expression of factors in CSF-1/CSF-1R signaling pathway during metastasis, and also conduct single-cell ATAC-Seq on mouse primary and metastatic tumors to evaluate their chromatin accessibility. This study will elucidate the tumor cell intrinsic mechanisms underlying ESCC metastasis, which will ultimately open new avenues in developing therapeutic strategies for metastatic ESCC patients that can be extended to other SCCs. I will develop skills in analytical thinking, technical approaches, scientific communicat...