An RNA-Dependent Innate Immune Response Pathway to Base-Damaging Chemotherapeutics

PROJECT SUMMARY The objective of this proposal is to define the mechanism and functional role of innate immune signaling events during base damaging cancer chemotherapy. These agents induce base damage on RNA as well as DNA. We have recently discovered that cells elicit an RNA-dependent innate immune response upon encountering alkylating agents, which represent one of the most commonly used systemic chemotherapies for cancer treatment. Our preliminary data demonstrates that alkylating agents induce a DAMP (damage associated molecular pattern) response, akin to the signaling observed during viral infection, which is known to impact downstream cellular events such as apoptosis. In contrast to other types of DNA damaging agents, this pathway depends on the RNA-associated DAMP receptor RIG-I and requires spliceosomal activity. Furthermore, we have found that ASCC1, which encodes a protein with a metal-independent RNA phosphoesterase domain, associates with intronic RNAs upon damage and is required for the induction of the DAMP response during alkylation. These and other data strongly suggest a model where spliceosome-associated processing of damaged RNA activates DAMP signaling, and may have functional consequences for tumor cell fate upon base damage. In this proposal, we will determine the mechanism by which ASCC1 functions with its associated partner proteins to gain access to damaged nascent RNAs and process them as part of this response, and determine the function consequence of this signaling pathway (Aim 1). In turn, we will characterize the RNA structures that activate RIG-I during alkylation stress and reconstitute RIG-I signaling with purified components (Aim 2). Together, these studies will shed light on a hitherto undescribed mechanism by which a nuclear RNA quality control pathway is connected to innate immune signaling.