Amyotrophic Lateral Sclerosis and the DNA Damage Response

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Amyotrophic Lateral Sclerosis (ALS) is caused by premature/accelerated degeneration of motor neurones. Whereas some cases of ALS are sporadic and of unknown molecular cause, others are due to hereditary dominant mutations in one of approximately eight genes. It has emerged recently that several of the proteins encoded by these genes are involved in regulating the production of messenger RNA (mRNA); a process known as transcription by which genes are copied into mRNA during gene expression. Two of these proteins are Fused-in-Sarcoma/Translocated-in-Sarcoma (FUS/TLS) and TAR DNA-binding protein 43 (TDP-43). The association of FUS/TLS and TDP-43 with ALS suggests that, in some cases of this disease, neuronal cell death may involve loss-of-function defects in RNA processing. However, the putative roles fulfilled by RNA processing that prevent ALS are unclear. We now present a novel hypothesis and supporting preliminary evidence for how RNA processing might prevent ALS. We show that FUS/TLS and TDP-43 are redistributed in response to DNA damage, with FUS rapidly accumulating at sites of DNA damage and TDP-43 rapidly expelled. We show that this redistribution of FUS/TLS and TDP-43 is an active process that is regulated by proteins with established roles in DNA damage signaling, supporting the idea that RNA processing is a bona fide component of the cellular DNA damage response. Based on these observations, we propose that RNA processing by FUS/TLS and TDP-43 is required to ensure that transcription is properly managed and controlled in the presence of DNA lesions, and that mutation of these and likely other proteins involved in RNA processing results in dysfunctional gene expression and neuronal cell death. In this application, we plan to address this hypothesis directly, using a combination of molecular and cellular approaches. To do this we have divided the proposed work into three specific objectives. We will, 1. Identify the mechanism/s by which FUS/TLS and TDP-43 are redistributed in response to DNA damage. 2. Address the role of FUS/TLS and TDP-43 in DNA damage signaling and/or repair at sites of DNA damage, and how these proteins regulate transcription in the presence of DNA lesions that block this process. 3. Examine the importance of FUS/TLS and TDP-43 for cellular resistance to DNA damage, including motor neurons, and identify additional components of RNA processing during the DNA damage response.