Aggregation of Disrupted in Schizophrenia 1 arises from a central region of the protein

Abstract

An emerging approach to studying major mental illness is through proteostasis, with the identification of several proteins that form insoluble aggregates in the brains of patients. One of these is Disrupted in Schizophrenia 1 (DISC1), a neurodevelopmentally-important scaffold protein, and the product of a classic schizophrenia risk gene. DISC1 was seen to aggregate in post mortem tissue from patients with schizophrenia, bipolar disorder and major depressive disorder, as well as in a variety of model systems, although the mechanism by which it does so is still unclear. Aggregation of two other proteins implicated in mental illness, TRIOBP-1 and NPAS3, was shown to be dependent on very specific structural regions of the protein. We therefore looked to the recently determined domain structure of DISC1, and investigated which structural elements were key for its aggregation. While none of the known DISC1 regions (named D, I, S and C respectively) formed aggregates individually when expressed in neuroblastoma cells, the combination of the D and I regions, plus the linker region between them, formed visible aggregates. Further refinement revealed that a region of approximately 30 amino acids between these two regions is critical to aggregation, with deletion of this region from full length DISC1 sufficient to abolish its aggregation propensity. This finding from mammalian cell culture contrasts with the recent determination that the extreme C-terminal of DISC1 can aggregate in vitro, although we did see some indication that combinations of C-terminal DISC1 regions can also aggregate in our system. It therefore appears likely that DISC1 aggregation, implicated in mental illness, can occur through at least two distinct mechanisms.