PROJECT ABSTRACT Lung cancer is the leading cause of cancer death worldwide. Although lung cancer rates have been steadily decreasing since the early 1990’s, it is still the deadliest cancer in the country, killing twice as many people in 2017 as the next four types of cancer combined. Lung adenocarcinoma is the most frequently diagnosed subtype of lung cancer, and approximately 25% of all LUAD cases are driven by Kras mutations. In patients, KRAS driven lung adenocarcinomas are significantly heterogeneous in cell identity and differentiation state; these characteristics correlate directly with patient prognosis and response to available therapies. Currently, the field lacks a comprehensive understanding of what governs LUAD cell identity and how these regulatory networks impact malignant potential. Identifying the master transcriptional regulators and the impact of their inactivation will provide novel insight into the mechanisms of cancer progression and lay the groundwork for the development of therapeutic strategies specific to tumor differentiation state. NKX2-1 is a master regulator of pulmonary identity in both healthy lung and neoplastic tissue. FOXA1 and FOXA2 (FOXA1/2) bind adjacent to NKX2-1 throughout the genome in both human and murine LUAD. NKX2-1 acts to retain a pulmonary differentiation state in LUAD in part by controlling FOXA1/2 binding at lineage-specific gene regulatory elements. FOXA1/2 directly interact with the DNA binding domain of NKX2-1; this interaction enhances NKX2-1 activity at promoters that also contain FOXA binding sites. It is also known that NKX2-1 coordinates with many other transcription factors and cofactors to facilitate the activation of lung- specific target genes. The objective of this grant is to identify cancer-relevant functions of FOXA1 and FOXA2 in lung adenocarcinomas that exhibit pulmonary differentiation by retaining NKX2-1 expression. We hypothesize that NKX2-1, FOXA1 and FOXA2 coordinately regulate growth, survival, and differentiation in LUAD. To test this hypothesis, we will examine how FOXA1 and FOXA2 govern LUAD cell identity and malignancy in established tumors, determine the impact of Foxa1/2 deletion on NKX2-1 transcriptional activity, and define the mechanisms by which tumors can escape the antiproliferative impact of Foxa1/2 deletion.