SMURF2 facilitates GAP17 Isoform 1 membrane displacement to promote mutant p53-KRAS oncogenic synergy.

Abstract

Cooperativity between mutant p53 and mutant KRAS, although recognized, is poorly understood. In pancreatic cancer, mutant p53 induces splicing factor hnRNPK causing isoform switch producing overexpression of GTPase activating protein 17 isoform 1 (GAP17-1). GAP17-1 is mis-localized in the cytosol, instead of the membrane, due to insertion of exon 17 encoding a PPLP motif, thus allowing mutant KRAS to remain in the GTP bound hyperactive state. However, the role of PPLP in influencing GAP17-1 mis-localization remains unclear. We show that Smad Ubiquitination Regulatory Factor 2 (SMURF2), a known stabilizer of mutant KRAS, interacts with GAP17-1 via the PPLP motif and displaces it from the membrane, facilitating mutant p53 mediated mutant KRAS hyperactivation. We used cell lines with known KRAS and TP53 mutations, characterized Smurf2 expression in multiple pancreatic cancer mouse models (iKras*; iKras*, p53*, and p48-Cre; Kras*) and performed single cell RNAseq and tissue microarray on preclinical and clinical samples. We found that SMURF2 silencing profoundly reduces survival of mutant TP53; KRAS driven cells. We show that a GAP17-1 AALA mutant does not bind to SMURF2, stays in the membrane, and keeps mutant KRAS in the GDP bound state to inhibit downstream signaling. In mouse models, mutant KRAS and SMURF2 upregulation are correlated in pancreatic intraepithelial neoplasia (PanIN) and ductal adenocarcinoma (PDA) lesions. Furthermore, PDA patients who received neoadjuvant therapy and express moderate to high SMURF2 show decreased overall survival (p=0.04). Implications: In TP53 and KRAS double mutated pancreatic cancer, SMURF2 driven GAP17-1 membrane expulsion facilitates mutant p53-KRAS oncogenic synergy.