Modulation of mutantKrasG12D-driven lung tumorigenesisin vivoby gain or loss of PCDH7 function
Authors: Zhou Xiaorong , Evers Bret M. , Padanad Mahesh S. , Richardson James A. , Stein Emily , Zhu Jingfei , Hammer Robert E. , O’Donnell Kathryn A. 
Published: June 2018

ABSTRACTPROTOCADHERIN 7 (PCDH7), a transmembrane receptor and member of the Cadherin superfamily, is frequently overexpressed in lung adenocarcinoma and is associated with poor clinical outcome. While PCDH7 was recently shown to promote transformation and facilitate brain metastasis in lung and breast cancers, decreased PCDH7 expression has also been documented in colorectal, gastric, and invasive bladder cancers. These data suggest context-dependent functions for PCDH7 in distinct tumor types. Given that PCDH7 is a potentially targetable molecule on the surface of cancer cells, further investigation of its role in tumorigenesisin vivois needed to evaluate the therapeutic potential of its inhibition. Here we report the analysis of novel PCDH7 gain- and loss-of-function mouse models and provide compelling evidence that this cell-surface protein acts as a potent lung cancer driver. Employing a Cre-inducible transgenic allele, we demonstrated that enforced PCDH7 expression significantly acceleratesKrasG12D-driven lung tumorigenesis and potentiates MAPK pathway activation. Furthermore, we performedin vivosomatic genome editing with CRISPR/Cas9 inKrasLSL-G12D;Tp53fl/fl(KP) mice to assess the consequences of PCDH7 loss of function. Inactivation of PCDH7 in KP mice significantly reduced lung tumor development, prolonged survival, and diminished phospho-activation of ERK1/2. Together, these findings establish a critical oncogenic function for PCDH7in vivoand highlight the therapeutic potential of PCDH7 inhibition for lung cancer. Moreover, given recent reports of elevated or reduced PCDH7 in distinct tumor types, the new inducible transgenic model described here provides a robust experimental system for broadly elucidating the effects of PCDH7 overexpressionin vivo.AUTHOR SUMMARYLung cancer is the leading cause of cancer-associated deaths worldwide. PROTOCADHERIN 7 (PCDH7), cell surface protein and member of the Cadherin superfamily, is frequently overexpressed in lung adenocarcinomas and is associated with poor clinical outcome. Nevertheless, it has yet to be shownin vivowhether PCDH7 plays a role in the initiation and progression of lung cancer, and whether it represents an actionable therapeutic target. Here we demonstrate, using a novel transgenic mouse model, that PCDH7 overexpression acceleratesKrasG12D-driven lung tumorigenesis. Furthermore, we validate PCDH7 as a therapeutic target by knocking it out usingin vivosomatic genome editing in theKrasLSL-G12D;Tp53fl/fl(KP) model. Our results provide new insight into the mechanisms that drive lung cancer pathogenesis and, because targeting oncogenic cell-surface proteins with antibodies has proven to be a highly effective anti-cancer therapeutic strategy, establish a new target for cancer treatment. Moreover, given recent reports of elevated or reduced PCDH7 in distinct tumor types, the transgenic PCDH7 model described here provides a robust experimental system for elucidating the effects of PCDH7 overexpression in differentin vivosettings. This model will also provide an ideal system for future testing of therapeutics directed at PCDH7.