Studies of novel REST / NRSF-Interlacing LIM domain Protein (RILP) in Huntington's Disease

The goal of this proposal is to study the involvement of a novel protein "RILP" in cotrolling REST/NRSF nuclear localization and elucidate its involvement in Alzheimer’s disease (AD). RILP, REST-Interacting LIM domain Protein, is required for REST/NRSF nuclear targeting and function. We have focused on this novel protein cloned from a human brain library, which interacts with REST/NRSF, the transcriptional repressor of many neuronal genes. Biochemical analysis of RILP shows that RILP is localized to the nuclear membrane and functions in the nuclear localization of REST. In the course of this study, we have found that RILP interacts with Dynactin p150Glued (p150) and Huntingtin. The p150 is a subunit of Dynein, a microtubule motor protein which is involved in trafficking transcription factors between the cytoplasm and nucleus. The neuronal microtubuleassociated protein, such as tau plays an important role in the organization of axonal microtubules. Tau is also the major component of the neurofibrillary pathology that defines AD and other related neurodegenerative disorders. Mutations in the tau gene cause a familial form of dementia, indicating that dysfunction of tau protein is sufficient to cause neurodegeneration. Impaired axonal transport may promote the pathogenesis in neurodegenerative disorders, such as AD. It was recently reported that age-related attenuation of dynactin level in nerve-ending fractions and the interaction between dynactin and dynein attenuation caused the impairment of dynactin function. Wild-type Huntingtin has been reported to interact with REST, in which Huntingtin and neuron-specific Huntingtin Associated Protein-1 (HAP1) keeps REST in the cytosol in neuronal cells, thereby preventing REST target gene expression. In Huntington’s disease polyQ-Htt, either directly or indirectly, looses the ability to prevent REST transport to the nucleus permitting inappropriate repression of a neuronal genes. Recently we have reported that the interaction between Htt, RILP, p150 and HAP1 keeps REST in the cytosol, thereby preventing REST target gene expression. We have shown that RILP and p150 are involved in targeting cytoplasmically synthesized REST to the nucleus. We hypothesize that mutant tau which interacts p150 normally prevents this complex from transporting REST to the nucleus of neurons, permitting REST target genes to be expressed. In AD, mutant tau may cause a loss of this regulation permitting REST to inappropriately be transported to the nucleus resulting in the repression of a host of neuronal genes. We propose to test the hypothesis that tau contributes to AD through its effect on REST trafficking.