BIOCHEMICAL AND MOLECULAR CHARACTERIZATION OF SMYD3-DEPENDENT SIGNALING PATHWAYS IN PROSTATE TUMORIGENESIS

Abstract

Metastatic prostate cancer (PCa) is associated with poor clinical outcomes due to limited treatment modalities. Aberrant activation of Ras/Raf/MAPK signaling is frequently linked to advanced PCa and implicated in epithelial-mesenchymal transition (EMT). The identification and characterization of modulators of this pathway is therefore critical in defining new therapeutic vulnerabilities for metastatic prostate cancer. The lysine methyltransferase SMYD3, a member of the SMYD family of lysine methyltransferases (KMTs) is known to target MAP3K2 for methylation in some cancer types, causing enhanced activation of MAPK signaling. In PCa, SMYD3 is frequently overexpressed and associated with disease severity, however its molecular function in promoting tumorigenesis has not been defined. Here, we demonstrate that SMYD3 is a critical regulator of migration, invasion, adhesion, and anchorage-independent growth in PCa cells via its methyltransferase activity on the substrate MAP3K2. In PCa cells, SMYD3 is present in the cytoplasm where it methylates Lys 260 of MAP3K2 and all its domains except for the C-terminal domain are required for its enzymatic activity. SMYD3 and its catalytic activity are also essential for tumor growth and metastatic spread in mouse xenograft models. SMYD3-dependent lysine methylation of MAP3K2 promotes EMT-associated behaviors in PCa cells by altering the abundance of key proteins, primarily the intermediate filament vimentin. Furthermore, activation of the SMYD3-MAP3K2 signaling axis supports a positive feedback loop continually promoting high levels of SMYD3. Together, our data provide new insight into signaling pathways involved in metastatic prostate cancer and enhances our understanding of mechanistic functions for SMYD3 to potentially reveal new therapeutic opportunities for prostate cancer.