Lung cancer-enriched p53 mutants occupy canonical p53 target genes without activating transcription, revealing a distinct loss-of-function behavior [RNA-Seq]

Lung cancer is the most common cause of cancer-related death in the U.S. and globally. Cigarette smoking remains the leading risk factor for lung cancer, in part by inducing loss-of-function mutations in tumor suppressor genes, including TP53. While most cancers share a set of common “hotspot” mutations in p53, lung cancer exhibits an additional, distinct cluster of hotspot mutations. This cluster is typified by the missense mutations TP53:p.V157F and TP53:p.R158L. While canonical hotspot mutations cause broad misfolding of p53 or eliminate specific DNA contact residues, mechanistic studies of the lung cancer mutants reported here demonstrate that they retain the ability to bind the same genomic sites as wild-type p53. Despite actively binding to traditional p53 target genes, the lung cancer mutants are defective in activating transcription. To our knowledge, this represents the first demonstration of functional inactivation of the p53 tumor suppressor at a point after DNA binding, but prior to target gene activation. Relevant to the sequential inactivation of each p53 allele during cancer progression, the lung cancer mutants block the activity of a wild-type p53 allele when co-expressed in a dominant negative manner. Identification of this loss-of-function mechanism has key implications for therapeutic strategies aimed at restoring p53 function in lung cancer. Overall design: RNA-seq was performed on H1299 cells containing a tetracycline-inducible plasmid for WT, V157F, or R158L p53. Cells were treated with tetracycline alone or with tetracycline followed by camptothecin for an additional 24 hours prior to RNA extraction (3 replicates per condition).