Introduction: TP53 mutants are involved in the pathogenesis of most solid tumors and are known to gain oncogenic functions distinct from their original wild-type form. The existence of such gain-of-function (GOF) activities is supported by ample evidence, however only in a cell-autonomous fashion. Since tumor-associated-macrophages (TAM) are also a hallmark of solid tumors typically correlated with poor prognosis, we investigated the link between mutations in the TP53 gene (mutp53) occurring in epithelial tumor cells and the formation of a surrounding TAM population in-situ.
Methods: By designing a co-culture system we incubated human primary monocytes together with colorectal cancer (CRC) cells differing in their p53 status. Relevant macrophages markers were evaluated on RNA level and protein level. In addition, co-cultured macrophages were subjected to various functional assays (phagocytosis, migration, and invasion). In attempt to confirm clinical relevance, samples from a cohort of human CRC patients were analyzed using genomic and immunohistochemical methods. To identify the interaction between the tumor cells and the macrophages, we isolated exosomes from the CRC cells and subjected them to a Nanostring analysis to learn about their microRNAs composition.
Results: In this study, we discovered that mutp53 exerts a non-cell-autonomous effect over neighboring macrophages by using specific microRNAs (miRs) which are shuttled through an exosomal transfer resulting with a phenotype change of the affected macrophages. Mutp53-specific exosomes containing cargoes such as miR-1246 were shown to be used by macrophages at the receiving end, thus promoting the formation of TAM subset also observed in surgical specimens resected from cancer patients.
Conclusions: Altogether, these findings are consistent with a microenvironmental role for specific “hot-spot” p53 mutants tightening the interaction between the tumor cell and the immune compartment. Additionally, this study is the first to show a non-cell-autonomous role played by mutant p53 - the most common form of mutation found in human cancers. Deciphering the intricate regulation shared by the tumor cell and its surrounding macrophages may give rise to novel prognostic and diagnostic tools as well as to therapeutic approaches targeting TAM, specific tumor-promoting miRs and mutp53-specific subsets of exosomes.
Citation Format: Tomer Cooks, Ioannis S. Pateras, Keval M. Patel, Tim Forshew, Vassilis G. Gorgoulis, Curtis C. Harris. Exosomes from mutant TP53 cancer cells polarize tumor associated macrophages. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 906.