Abstract LB209: YBX1 is a negative regulator of post-transcriptional program associated to EMT, invasion and metastasis in cSCC

Abstract Y-box binding protein 1 (YB-1), which is encoded by YBX1 gene, is a multifunctional cold-shock protein that binds both DNA and RNA to orchestrate transcription as well as RNA processing and translation. Recently, we demonstrated that YBX1 is a post-transcriptional effector required for the maintenance of epidermal homeostasis. Although it was well known that YBX1 plays prominent pro-oncogenic roles in malignant transformation and cell invasion in a wide variety of cancers, the role of YBX1 in cutaneous squamous cell carcinoma (cSCC) is poorly understood. Here, we report that YBX1 protein level is higher in cSCC tumor compared with non-neoplastic skin, but it goes down in metastatic states. According to this finding, YBX1-KD cSCC primary cell lines show an increase of cell migration and invasion in vitro assay and in a context that mimics the natural three-dimensional environment of tumor with organotypic skin equivalent cultures. Furthermore, we found that YBX1-KD promotes an epithelial-to-mesenchymal transition and leads to the detection of more metastases in vivo after tail vein injection of YBX1-KD cSCC cells when compared with the injection of control cells. YBX1 is predominantly found in the cytoplasm of SCC cells. Therefore, we focused on the role of YBX1 as a post-transcriptional regulatorand performed an eCLIP-seq (crosslinking immunoprecipitation sequencing) to identify its direct RNA targets. We found that YBX1 binds novel pro-invasive RNA regulons associated to cell-cell and cell-matrix adhesions. Through the interpolation of the analysis of RNA-seq and SILAC, we found that YBX1 KD up-modulates at post-transcriptional level several targets, involved into invasion and metastasis. Our study reveals that, in human cutaneous squamous cell carcinoma, loss of function of YBX1 promotes migration, invasiveness and metastasis, through the induction of an epithelial-to-mesenchymal transition regulated at post-transcriptional level. Citation Format: Stefano Sol, Fabiana Boncimino, Kristina Todorova, Anna Mandinova. YBX1 is a negative regulator of post-transcriptional program associated to EMT, invasion and metastasis in cSCC [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 2 (Late-Breaking, Clinical Trial, and Invited Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(7_Suppl):Abstract nr LB209.