Enhanced SREBP2-driven cholesterol biosynthesis by PKCλ/ι deficiency in intestinal epithelial cells promotes aggressive serrated tumorigenesis

Article https://doi.org/10.1038/s41467-023-43690-5 Enhanced SREBP2-driven cholesterol biosynthesis by PKCλ/ι deficiency in intestinal epithelial cells promotes aggressive serrated tumorigenesis Received: 25 August 2023 1234567890():,; 1234567890():,; Accepted: 16 November 2023 Check for updates Yu Muta 1,2,3, Juan F. Linares1, Anxo Martinez-Ordoñ ez1, Angeles Duran1, Tania Cid-Diaz1, Hiroto Kinoshita 1, Xiao Zhang1, Qixiu Han1, Yuki Nakanishi 2, Naoko Nakanishi4, Thekla Cordes 5,6, Gurpreet K. Arora7, Marc Ruiz-Martinez 1, Miguel Reina-Campos 8, Hiroaki Kasashima 9, Masakazu Yashiro9, Kiyoshi Maeda9, Ana Albaladejo-Gonzalez10,11, Daniel Torres-Moreno10,12, José García-Solano10,11, Pablo Conesa-Zamora 10,12, Giorgio Inghirami 1, Christian M. Metallo 5, Timothy F. Osborne 13, Maria T. Diaz-Meco 1 & Jorge Moscat 1 The metabolic and signaling pathways regulating aggressive mesenchymal colorectal cancer (CRC) initiation and progression through the serrated route are largely unknown. Although relatively well characterized as BRAF mutant cancers, their poor response to current targeted therapy, difficult preneoplastic detection, and challenging endoscopic resection make the identification of their metabolic requirements a priority. Here, we demonstrate that the phosphorylation of SCAP by the atypical PKC (aPKC), PKCλ/ι promotes its degradation and inhibits the processing and activation of SREBP2, the master regulator of cholesterol biosynthesis. We show that the upregulation of SREBP2 and cholesterol by reduced aPKC levels is essential for controlling metaplasia and generating the most aggressive cell subpopulation in serrated tumors in mice and humans. Since these alterations are also detected prior to neoplastic transformation, together with the sensitivity of these tumors to cholesterol metabolism inhibitors, our data indicate that targeting cholesterol biosynthesis is a potential mechanism for serrated chemoprevention. Colorectal cancer (CRC) is the third most common malignancy worldwide1. Despite advances in prevention, early detection, and systemic treatment strategies, the prognosis remains poor in the advanced stage1. CRC is a complex and heterogeneous disease that can be stratified into different subsets based on anatomical, histopathological, genomic, and transcriptomic features, but it is in need of a better understanding at the mechanistic signaling and metabolic level2. CRC originates through two alternative histologically A full list of affiliations appears at the end of the paper. Nature Communications | (2023)14:8075 identifiable premalignant states: conventional adenomas (CA) and the serrated route3–6. CAs were initially considered the only mechanism leading to CRC, which features APC inactivation and the association with mutations in other key genes, including p53, KRAS, and members of the TGFβ pathway7. However, it is evident now that the serrated pathway is an alternative route to CRC, mostly originating from sessile serrated lesions (SSL)4–6. The clinical implications of this type of CRC tumor are enormous because their flat shape poses serious challenges e-mail: ; 1 Article for their detection and complete endoscopic resection and are considered the main cause of post-colonoscopy/interval cancers6. Furthermore, their unclear morphology and diagnostic challenges in pathology lead to a lack of reliable longitudinal observational data on the natural history of SSLs. Therefore, while much is known about the CA-originating CRCs, our understanding of the molecular mechanisms regulating the initiation and eventual progression from serrated lesions is quite limited. In this regard, although several mouse models recapitulate at least partially different aspects of the CA-CRC sequence, only recently serrated CRC has been modeled in mice by the expression of key drivers like KRAS, BRAF, or NOTCH8–10. These models have provided invaluable information on the mechanisms of serrated carcinogenesis post-appearance of genetic mutations. However, the cellular and molecular understanding of the chain of events triggered by the spontaneous initiation mechanisms before oncogenic alterations emerged was lacking. In addition, despite reports on the association between alterations in lipid metabolism and serrated lesions11–13, the extent to which the metabolic changes contribute to serrated tumorigenesis remains to be elucidated. We have recently developed a mouse model of SSL that rapidly progresses to cancer without the initial ectopic expression of any oncogene or the inactivation of tumor suppressors. This model was based on our observation that the loss of both atypical protein kinase Cs (aPKCs; PKCλ/ι and PKCζ) in the mouse intestinal epithelium led to the spontaneous development of SSL14. These tumors showed, like in humans, a preference for the proximal location in the colon and a significantly large proportion progressed to intramucosal and even invasive adenocarcinoma, which contained areas of poorly differentiated or signet-ring cell carcinomas with severe desmoplastic change indicating the highly aggressive nature of those tumors, which were also immune-excluded14. The desmoplastic response in these aPKC-deficient serrated tumors was characterized by a profound remodeling of the fibroblast compartment with an accumulation of collagen and hyaluronan, recapitulating the most salient features of human mesenchymal (m)CRC14,15. Therefore, this is a unique model system to study the initiation and progression of serrated CRC in an oncogenic-agnostic manner without the confounding predetermined expression of a particular oncogene or other type of stimuli. The human relevance of the role of the aPKCs as repressors of serrated tumorigenesis was further demonstrated by interrogating publicly available bulk and single-cell gene expression datasets, as well as by multiplex immunofluorescence analyzes of large collections of intestinal tumor specimens in our laboratory. Those analyzes established aPKC deficiency as a driver of serrated mCRC4,14,16. These studies also revealed a previously unrecognized bottom-up mechanism of transformation whereby the intestinal crypt differentiation hierarchy, although preserved during serrated initiation and progression, is largely “metaplastically” subverted, resulting in the accumulation of a cancer cell population with metaplastic and fetal features (termed tumor fetal metaplastic cell; TFMC)15. Importantly, the gene signature of the TFMCs, and key markers expressed by that mouse cell population, allowed us to define transcriptional and immunofluorescence biomarkers that predicted the poorest survival in CRC15. These intrinsic features of the aPKCdeficient tumors together with the extensive stromal reaction model the most aggressive CRCs termed CMS4, or more recently iCMS3F15,17–19. However, what remained to be determined is the signaling and metabolic pathways activated by aPKC deficiency that trigger the initial steps in the transformati (...truncated)