Insolubility of Disrupted-in-Schizophrenia 1 Disrupts Oligomer-Dependent Interactions with Nuclear Distribution Element 1 and Is Associated with Sporadic Mental Disease

Abstract

Disrupted-in-schizophrenia 1 (DISC1) and other genes have been identified recently as potential molecular players in chronic psychiatric diseases such as affective disorders and schizophrenia. A molecular mechanism of how these genes may be linked to the majority of sporadic cases of these diseases remains unclear. The chronic nature and irreversibility of clinical symptoms in a subgroup of these diseases prompted us to investigate whether proteins corresponding to candidate genes displayed subtle features of protein aggregation. Here, we show that in postmortem brain samples of a distinct group of patients with phenotypes of affective disorders or schizophrenia, but not healthy controls, significant fractions of DISC1 could be identified as cold Sarkosyl-insoluble protein aggregates. A loss-offunction phenotype could be demonstrated for insoluble DISC1 through abolished binding to a key DISC1 ligand, nuclear distribution element 1 (NDEL1): in human neuroblastoma cells, DISC1 formed expression-dependent, detergent-resistant aggregates that failed to interact with endogenous NDEL1. Recombinant (r) NDEL1 expressed in Escherichia coli selectively bound an octamer of an rDISC1 fragment but not dimers or high molecular weight multimers, suggesting an oligomerization optimum for molecular interactions of DISC1 with NDEL1. For DISC1-related sporadic psychiatric disease, we propose a mechanism whereby impaired cellular control over self-association of DISC1 leads to excessive multimerization and subsequent formation of detergent-resistant aggregates, culminating in loss of ligand binding, here exemplified by NDEL1. We conclude that the absence of oligomer-dependent ligand interactions of DISC1 can be associated with sporadic mental disease of mixed phenotypes.

Understanding the Role of DISC1 in Psychiatric Disease and during Normal Development

“…Higher multimerization propensity of DISC1 degradation products in DISC1 transiently overexpressing NLF cells has been described (Leliveld et al, 2008). At this point, it is unclear, however, whether DISC1 is proteolytically processed, in whether such fragments are physiologically functional.…”

“…The middle part of DISC1 (residues 400-500) had been identified as a DISC1 self-association domain (Kamiya et al, 2005). The C-terminal part of DISC1 that is possibly deleted in the Scottish family harbors both a homomeric multimerization (residues 668-747) and a dimerization domain (residues 765-854), the concerted interaction between both being essential for ordered oligomerization to a functional C-terminal DISC1 domain in vitro (Leliveld et al, 2008(Leliveld et al, , 2009). We found that distinct octamers but not dimers or high-molecular-weight multimers of the DISC1 C terminus bind to important interacting molecule nuclear-distribution element-like 1 (NDEL1), indicating that the DISC1-NDEL1 interaction depends on assembly of DISC1 to a defined quartenary structure (Fig.…”

“…When transiently overexpressed in human neuroblastoma cells, DISC1 segregates into aggresomes and reveals insolubility in the presence of ionic detergents whereas under same conditions, for example, NDEL1 remains soluble (Leliveld et al, 2008). Insoluble DISC1 was unable to interact with NDEL1, and in a subset of patients with psychiatric disease of mixed phenotypes insoluble DISC1 was identified to be associated with a subset of patients (Leliveld et al, 2008). Thus, aberrant multimerization into insoluble forms could be a dysfunctional correlate of DISC1 in a subset of cases with sporadic disease.…”

Insoluble DISC1–Boymaw fusion proteins generated by DISC1 translocation

“…The DISC1-Boymaw chimeric proteins (DB7) displayed "punctate" staining, while proteins generated from BD13 appeared abundant and diffuse in the cytoplasm of hippocampal neuronal cells (Figure 2c). Insoluble DISC1 proteins have been reported in the post-mortem brains of patients with schizophrenia, bipolar mania, and major depression (13). The insolubility of DISC1 proteins therefore could be the common pathological defects to disrupt the normal functions of neuronal cells.…”

“…Western blot analysis of the protein expression in HEK293 cells. The cells were harvested two days after transfection, and the proteins (supernatant fraction) were extracted in the same lysis buffer in the presence of 2% Sarkosyl (13). The pellet was collected and solubilized in SDS loading buffer.…”