MEN1-mediated CD44 alternative splicing depression is required for ferroptosis during lung cancer suppression

Ferroptosis is a characteristic form of cell death triggered by excessive iron-dependent reactive oxygen species (ROS) and plays an important role in suppressing tumor development. Although MEN1-regulated cell-cycle arrest, apoptosis, and cell senescence have been considered foremost barriers to lung tumorigenesis, its other functions, such as RNA splicing regulation, are also important for its tumor suppression activity. Here, MEN1 was found to facilitate lipid ROS generation and sensitizes lung cancer cells to ferroptosis by depressing alternative CD44 pre-mRNA splicing. CD44 variant isoforms are highly expressed and correlated with poor prognosis in human lung cancers. Loss of Men1 profoundly accelerates the progression of Kras-mutant driven lung adenocarcinoma (LUAD), which is associated with the accumulation of CD44 variant isoforms found in a KrasG12D;Men1-specific deficient mouse model. Mechanistically, MEN1 maintains a relatively slow RNA polymerase II (Pol II) elongation by controlling the release of Pol II-associated factor 1 (PAF1) from the CD44 gene body, which in turn prevents the inclusion of CD44 variable exon (CD44v). Furthermore, CD44v6-interfering peptides effectively abrogate the growth and metastasis of established Kras-mutant LUAD and MEN1-deficient tumors by activating ferroptosis. The efficacy of CD44v6 peptides was stronger than that of erastin, a ferroptosis inducer, in MEN1-deficient tumors. Collectively, our study unveils a novel way of tumor suppression based on MEN1 regulation of CD44 alternative splicing, ROS production and ferroptosis.