ATAC-seq analysis of differential peaks in parental and MPND knockout cells

The Mpr1/Pad1 N-terminal domain-containing protein (MPND) belongs to the JAMM family of deubiquitinases and is ubiquitously expressed across human tissues. However, its role in non-small cell lung cancer (NSCLC) remains unexplored. In this study, we demonstrate that MPND expression is frequently reduced in NSCLC, and that low levels of MPND correlate with poor clinical outcomes. Depletion of MPND in vitro enhances cell migration, invasion, and cancer stem cell (CSC)-like characteristics in NSCLC cells. Mechanistically, MPND interacts with histones, removing ubiquitin from H2A K119 monoubiquitination (H2A K119ub) and H2B K120 monoubiquitination (H2B K120ub). Loss of MPND elevates these ubiquitination marks, leading to alterations in chromatin architecture. Furthermore, MPND influences gene transcription, and its depletion activates the TGF-beta/SMAD3 signaling pathway. Specifically, knockout of MPND increases H2B K120 ubiquitination and chromatin accessibility at the SMAD3 locus, facilitating its transcriptional activation. Using mouse tumor models and clinical samples from NSCLC patients, we show that loss of MPND triggers activation of the TGF-beta/SMAD3 axis, thereby promoting tumor growth and metastasis. Collectively, these findings deepen our understanding of the epigenetic mechanisms underlying NSCLC progression and suggest that anti-TGF-beta therapies may be particularly beneficial for treating MPND-deficient tumors.