FTO promotes multiple myeloma progression by posttranscriptional activation of HSF1 in an m6A-YTHDF2-dependent manner.

N6-methyladenosine (m6A), as the most pervasive internal modification of eukaryotic mRNA, plays a crucial role in various cancers, but its role in multiple myeloma (MM) pathogenesis has not yet been investigated. In this study, we revealed significantly decreased m6A methylation in plasma cells (PCs) from MM patients and showed that the abnormal m6A level resulted mainly from upregulation of the demethylase fat mass and obesity-associated protein (FTO). Gain- and loss-of-function studies demonstrated that FTO plays a tumor-promoting and pro-metastatic role in MM. Combined m6A and RNA sequencing (RNA-seq) and subsequent validation and functional studies identified heat shock factor 1 (HSF1) as a functional target of FTO-mediated m6A modification. FTO significantly promotes MM cell proliferation, migration, and invasion by targeting HSF1/HSPs in a YTHDF2-dependent manner. FTO inhibition, especially when combined with bortezomib (BTZ) treatment, synergistically inhibited myeloma bone tumor formation and extramedullary spread in NOD-Prkdcem26Cd52il2rgem26Cd22/Nju (NCG) mice. We demonstrated the functional importance of m6A demethylase FTO in MM progression, especially in promoting extramedullary myeloma (EMM) formation, and proposed the FTO-HSF1/HSP axis as a potential novel therapeutic target in MM.