Mitochondrial-Localized Keratin 17 Promotes Chemoresistance in Basal-like Pancreatic Cancer.

The basal-like molecular subtype of pancreatic ductal adenocarcinoma (PDAC) is highly lethal and therapy resistant. A better understanding of the underlying molecular mechanisms driving this aggressive tumor subtype is necessary for the development of effective therapies. Notably, upregulation of keratin 17 (K17) in cancer is associated with poor patient outcome and the basal-like PDAC subtype. In this study, we identified a critical dependency of basal-like PDACs on de novo pyrimidine biosynthesis, driven by intramitochondrial K17. Mechanistically, K17 translocated into the mitochondrial intermembrane space via a mitochondrial localization signal recognized by the translocase of outer mitochondrial membrane 20. In the mitochondria, K17 bound to and stabilized dihydroorotate dehydrogenase, the rate-limiting enzyme of de novo pyrimidine biosynthesis, by preventing its ubiquitination-mediated degradation. Blocking the entry of K17 into the mitochondria sensitized cancer cells to gemcitabine, a pyrimidine analogue and standard chemotherapeutic agent. In animal studies, pharmacologic inhibition of dihydroorotate dehydrogenase combined with gemcitabine treatment decreased tumor growth and doubled survival in mice bearing K17+ but not K17- PDAC. These findings define a mitochondrial role for K17 in driving pyrimidine biosynthesis and uncover a metabolic vulnerability in K17+ basal-like PDACs that can be therapeutically targeted. SIGNIFICANCE: Targeting the mitochondrial role of keratin 17 in pyrimidine biosynthesis represents a promising strategy to sensitize basal-like pancreatic cancer to gemcitabine and improve outcomes in this lethal subtype.