Bacterial targeting of host paraspeckles uncovers a new SFPQ-based regulation

Nuclear functions are key in protecting cells against infections, yet intracellular pathogens like Legionella pneumophila can exploit these mechanisms to survive. We characterized a L. pneumophila protein, LpDot1, which shares sequence similarity with the eukaryotic catalytic domain of the histone methyltransferase DOT1. Structure determination, together with biochemical and biophysical analyses, revealed that LpDot1 methylates non-histone nuclear proteins, notably the splicing factor proline-glutamine rich protein (SFPQ). Importantly, LpDot1 targets the previously uncharacterized K518, located on an important structural motif of SFPQ, therefore impairing its dimerization in vitro. During infection, L. pneumophila modulates SFPQ abundance and activities in a LpDot1-dependent manner, thereby hijacking paraspeckle organization and the host cell splicing machinery, leading to alternative splice variants of infection related genes such as NF-kB2 and CD45. To our knowledge, this is the first report of a bacterial effector directly modifying paraspeckle dynamics, providing new insight into previously uncharacterized eukaryotic regulatory pathways.