Interplay between LINE-1 retrotransposons, condensins, and IFN - Project summary- Longworth, Michelle S. The expression and retrotransposition of Long Interspersed Element-1s (L1s), a type of endogenous retroelement (RTE), induces Type I IFN (IFNα and IFNβ) in epithelial cells through activation of Pattern Recognition Receptors (PRRs) including retinoic acid-inducible gene I (RIG-I)-like receptors (RLRs). Interferon stimulated genes drive mechanisms which repress L1, as part of a feedback loop, and which can also lead to cell death. Therefore, RTE/L1 de- repression and subsequent IFN induction (termed viral mimcry) is currently being studied as a potential mechanism to kill cancer cells, and a better understanding of the underlying mechanisms will benefit cancer therapeutic development. Our lab discovered that condensin I and condensin II complexes inhibit endogenous and transfected L1 expression and retrotransposition in primary and transformed epithelial cells. Condensins are essential, multi- subunit complexes that are known for their canonical functions in organizing the genome. Our preliminary data show that condensin I and condensin II proteins are necessary for L1-mediated induction of Type I IFNs in both cancer-derived and primary epithelial cells, and may cooperate with one another in the cytoplasm to induce IFN. Importantly, condensin insufficient cells fail to induce transcription of Type I IFN, even though endogenous L1 expression is increased, placing condensin proteins downstream of L1 in this pathway and suggesting a novel role for condensins in RTE-mediated innate immune signaling. The overall objectives of this proposal are to determine how L1 expression influences condensins to promote Type I IFN transcription and uncover novel roles for condensins in L1-mediated innate immune signaling responses. Our central hypothesis is that condensin I and condensin II complexes cooperate to promote RLR pathway-driven Type I IFN induction in response to increased levels of L1 RNA. We will test this hypothesis through the following aims: AIM 1. Determine whether increased L1 RNA levels impact condensin protein localization, association, and activity, and AIM 2. Identify the mechanisms by which condensin proteins facilitate Type I IFN induction in response to L1 expression. The expected outcomes of the proposed work include the identification of new roles for condensins in innate immune signaling, identification of potential roles for cytoplasmic condensin proteins, and a better understanding of how L1 expression facilitates Type I IFN induction in both tumor-derived and primary cells. These findings will lay the foundation for future development of novel therapeutics that modulate RTE-mediated IFN induction to kill cancer cells.
