Abstract The transcriptional co-activator with PDZ-binding domain (TAZ) is a transcriptional co-activator and major component of an emerging signaling pathway called the Hippo pathway that plays critical roles in tumorigenesis, organ size control, stem cell renewal, drug resistance, etc. Recently, we have provided the first biological evidence that TAZ is over-expressed in non-small cell lung cancer (NSCLC) cells and over-expression of TAZ can transform HBE135 immortalized non-tumorigenic human lung epithelial cells (Zhou et al., 2011). However, the cellular genes mediating TAZ-induced transformation are unknown. In addition, there is no in vivo mouse model established to study the roles of TAZ in lung tumorigenesis in vivo. To address these issues, we have carried out the following experiments: First, a Dox-inducible lentiviral expression system was used to overexpress constitutively active TAZ (TAZ-S89A) in a mouse immortalized lung epithelial cell line (E10). Overexpression of TAZ-S89A in E10 cells caused increased cell proliferation, transformation, and tumor formation in vivo in nude mice. Next, tumorigenic stable cell lines (TAZS89A-TM) were established after isolating TAZS89A-induced tumors from mice. Second, to identify the downstream genes mediating TAZ-induced tumor formation, the technology of Next-generation sequencing (RNA-seq) was performed on the new tumorigenic cell line E10-TAZ-TM to identify downstream genes transcriptionally regulated by TAZ after induction of TAZ by Dox. By analyzing the data and confirming them using qRT-PCR, multiple significant oncogenes were found activated by TAZ overexpression. Third, these genes were knocked down by shRNAs in the tumorigenic E10-TAZS89A-TM cell line and tested whether they are important in TAZ-induced cell proliferation, transformation and tumor formation in mice. Finally, since previous studies indicate that TAZ is involved in mammary cell growth by interacting with transcription factor TEAD or through its WW domain, we also tested whether these genes are activated through TEAD-binding domain or WW-domain of TAZ. E10 stable cell lines overexpressing inducible TAZ mutant with amino acid mutations in TEAD-binding domain (TAZ-F52A/F53A) or WW domain (TAZ-W152A/P155A) were established, followed by qRT-PCR analysis. The TEAD-binding domain of TAZ was found necessary for activation of the identified genes and maintaining TAZ-induced oncogenic effects in lung cells. In conclusion, this project established the first in vivo xenograft mouse model system using TAZ-overexpressing lung epithelial cells, and identified the downstream target genes mediating TAZ-induced lung tumorigenesis. Citation Format: Adel B. Alharbi, Hongchao Shan, Yawei Hao, Xiaolong Yang. Molecular mechanism of TAZ-induced lung tumorigenesis. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr LB-90. doi:10.1158/1538-7445.AM2014-LB-90