SMYD3: A PLAYER IN STEMNESS AND CHROMOSOME INSTABILITY IN TRIPLE NEGATIVE BREAST CANCER

The lysine methylase SMYD3 was shown to be overexpressed in various types of cancer and linked to the epithelial-mesenchymal transition (EMT) (1). Moreover, it is known that cancer stem cells (CSCs) are tumor initiating cells with importance in metastasis formation and a very strong link with EMT (2). With this state of the art, our goal was to investigate a possible link between CSCs and SMYD3 in triple negative breast cancer (TNBC), possibly through EMT. SMYD3 KO reduced the expression of stemness and EMT markers in MDA-MB-231 cells, reducing the ability of cells to form primary and secondary tumor spheroids. BT549 cells seem to be affected by SMYD3 depletion only in terms of proliferation and growth. RNA sequencing results deriving from MDA-MB-231 tumor spheroids revealed a possible SMYD3 involvement in chromosome instability (CIN), in the interferon response and in the cGAS-STING pathway. Cancer cells can be characterized usually by a high state of CIN, leading to the release of genomic DNA in the cytoplasm, associated with the activation of the cGAS-STING pathway, which acts as a pro-survival pathway (3). We investigated the link between SMYD3 and CIN, confirming that SMYD3 KO diminishes the activation of the cGAS-STING pathway, particularly the pro-survival one, upregulating the pro-apoptotic pathway that drives cell death instead, in both cell lines. Moreover, genomic DNA presence in the cytoplasm was evalu-ated and it revealed a high state of CIN, which diminishes following SMYD3 KO in both cell lines. Particularly in BT549, centrosomes were analysed, revealing a possible link between SMYD3 depletion and interference with their duplication process. Moreover, SMYD3 was found to be localized in the centrosomes. Finally, a SMYD3 interactor, Nucleophosmin (NPM1), was confirmed in BT549 cells, leading to a possible mechanism behind the involvement of SMYD3 in CIN.