Characterization of distinct molecular interactions responsible for IRF3 and IRF7 phosphorylation and subsequent dimerization.

IRF3 and IRF7 are critical transcription factors in the innate immune response. Their activation is controlled by phosphorylation events, leading to the formation of homodimers that are transcriptionally active. Phosphorylation occurs when IRF3 is recruited to adaptor proteins via a positively charged surface within the regulatory domain of IRF3. This positively charged surface also plays a crucial role in forming the active homodimer by interacting with the phosphorylated sites stabilizing the homodimer. Here, we describe a distinct molecular interaction that is responsible for adaptor docking and hence phosphorylation as well as a separate interaction responsible for the formation of active homodimer. We then demonstrate that IRF7 can be activated by both MAVS and STING in a manner highly similar to that of IRF3 but with one key difference. Regulation of IRF7 appears more tightly controlled; while a single phosphorylation event is sufficient to activate IRF3, at least two phosphorylation events are required for IRF7 activation.

Genotoxic stress in constitutive trisomies induces autophagy and the innate immune response via the cGAS-STING pathway.

Gain of even a single chromosome leads to changes in human cell physiology and uniform perturbations of specific cellular processes, including downregulation of DNA replication pathway, upregulation of autophagy and lysosomal degradation, and constitutive activation of the type I interferon response. Little is known about the molecular mechanisms underlying these changes. We show that the constitutive nuclear localization of TFEB, a transcription factor that activates the expression of autophagy and lysosomal genes, is characteristic of human trisomic cells. Constitutive nuclear localization of TFEB in trisomic cells is independent of mTORC1 signaling, but depends on the cGAS-STING activation. Trisomic cells accumulate cytoplasmic dsDNA, which activates the cGAS-STING signaling cascade, thereby triggering nuclear accumulation of the transcription factor IRF3 and, consequently, upregulation of interferon-stimulated genes. cGAS depletion interferes with TFEB-dependent upregulation of autophagy in model trisomic cells. Importantly, activation of both the innate immune response and autophagy occurs also in primary trisomic embryonic fibroblasts, independent of the identity of the additional chromosome. Our research identifies the cGAS-STING pathway as an upstream regulator responsible for activation of autophagy and inflammatory response in human cells with extra chromosomes, such as in Down syndrome or other aneuploidy-associated pathologies.