Cholesterol metabolism in mesenchymal colorectal cancer

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PROJECT SUMMARY The overarching goal of this proposal is to identify novel addictions in mesenchymal colorectal cancer (CRC) that will create new vulnerabilities to be targeted therapeutically. This type of aggressive CRC shows a microsatellite stable phenotype, characterized by a strong reactive desmoplastic stroma and immunosuppressed microenvironment. Mesenchymal CRC is enriched in a transcriptomic CMS4 signature, affects about 30-40% of all CRCs with the poorest prognosis, and lacks effective therapies. Our recently published and preliminary data demonstrated that the loss of the two atypical protein kinase Cs (aPKCs; PKC/ and PKC, encoded by PRKCI and PRKCZ genes) drives the mesenchymal phenotype in mouse intestinal tumors. Furthermore, interrogation of human specimens and transcriptional datasets of CRC patients established the aPKCs as new suppressors of mesenchymal CRC. Our data also show that PKC/ is the one whose inactivation unleashes transformation through the mesenchymal route, and new preliminary results, which constitute the foundation of this proposal, demonstrated that aPKC inactivation in several models results in the upregulation of a cholesterol biosynthetic signature and promotes cholesterol synthesis in vivo as evidenced by metabolic tracing experiments in mice. Analysis of human CRC data and samples demonstrate a positive correlation between the activation of the cholesterol biosynthetic pathway and mesenchymal CRC, associated with a negative correlation with aPKC levels. Also, PKC/ directly phosphorylates SCAP, an obligate regulator of SREBP2 processing, which is the master regulator of cholesterol biosynthesis. Therefore, the central hypothesis of this application is that PKC/ by phosphorylating SCAP restrains the cholesterol biosynthetic pathway to repress tumorigenesis in mesenchymal CRC. Building on our strong preliminary data, we will (Aim 1) determine the role of increased cholesterol metabolism in mesenchymal CRC initiation and progression. To that end, we will determine the impact of feeding a high-cholesterol diet (Aim 1.1) or blocking cholesterol metabolism in vivo (Aim 1.2) in tumor initiation and progression of mesenchymal CRC tumors driven by PKC/ deficiency; and determine the human relevance of PKC/-regulated cholesterol metabolism in mesenchymal CRC (Aim 1.3). We will also (Aim 2) determine the molecular mechanisms whereby PKC/ regulates cholesterol biosynthesis in mesenchymal CRC tumorigenesis. Therefore, we will (Aim 2.1) determine the impact of PKC/-mediated SCAP phosphorylation on regulating the SCAP/SREBP2 complex at a mechanistic level; and (Aim 2.2) determine the functional contribution of PKC/-mediated SCAP phosphorylation to CRC in vivo. The results from this proposal will allow the identification of new targets as therapeutic points for intervention in mesenchymal CRC.