Andrew B. West

Inhibitors of leucine-rich repeat kinase-2 protect against models of Parkinson's disease

Leucine-rich repeat kinase-2 (LRRK2) mutations are a common cause of Parkinsons disease. Here we identify inhibitors of LRRK2 kinase that are protective in in vitro and in vivo models of LRRK2-induced neurodegeneration. These results establish that LRRK2-induced degeneration of neurons in vivo is kinase dependent and that LRRK2 kinase inhibition provides a potential new neuroprotective paradigm for the treatment of Parkinsons disease.

Transcriptional repression of p53 by parkin and impairment by mutations associated with autosomal recessive juvenile Parkinson's disease

Mutations of the ubiquitin ligase parkin account for most autosomal recessive forms of juvenile Parkinsons disease (AR-JP). Several studies have suggested that parkin possesses DNA-binding and transcriptional activity. We report here that parkin is a p53 transcriptional repressor. First, parkin prevented 6-hydroxydopamine-induced caspase-3 activation in a p53-dependent manner. Concomitantly, parkin reduced p53 expression and activity, an effect abrogated by familial parkin mutations known to either abolish or preserve its ligase activity. ChIP experiments indicate that overexpressed and endogenous parkin interact physically with the p53 promoter and that pathogenic mutations abolish DNA binding to and promoter transactivation of p53. Parkin lowered p53 mRNA levels and repressed p53 promoter transactivation through its Ring1 domain. Conversely, parkin depletion enhanced p53 expression and mRNA levels in fibroblasts and mouse brains, and increased cellular p53 activity and promoter transactivation in cells. Finally, familial parkin missense and deletion mutations enhanced p53 expression in human brains affected by AR-JP. This study reveals a ubiquitin ligase-independent function of parkin in the control of transcription and a functional link between parkin and p53 that is altered by AR-JP mutations.

Localization of Parkinson's disease-associated LRRK2 in normal and pathological human brain

Mutations in the LRRK2 gene cause autosomal dominant, late-onset parkinsonism, which presents with pleomorphic pathology including alpha-synucleopathy. To promote our understanding of the biological role of LRRK2 in the brain we examined the distribution of LRRK2 mRNA and protein in postmortem human brain tissue from normal and neuropathological subjects. In situ hybridization and immunohistochemical analysis demonstrate the expression and localization of LRRK2 to various neuronal populations in brain regions implicated in Parkinsons disease (PD) including the cerebral cortex, caudate-putamen and substantia nigra pars compacta. Immunofluorescent double labeling studies additionally reveal the prominent localization of LRRK2 to cholinergic-, calretinin- and GABA(B) receptor 1-positive, dopamine-innervated, neuronal subtypes in the caudate-putamen. The distribution of LRRK2 in brain tissue from sporadic PD and dementia with Lewy bodies (DLB) subjects was also examined. In PD brains, LRRK2 immunoreactivity localized to nigral neuronal processes is dramatically reduced which reflects the disease-associated loss of dopaminergic neurons in this region. However, surviving nigral neurons occasionally exhibit LRRK2 immunostaining of the halo structure of Lewy bodies. Moreover, LRRK2 immunoreactivity is not associated with Lewy neurites or with cortical Lewy bodies in sporadic PD and DLB brains. These observations indicate that LRRK2 is not a primary component of Lewy bodies and does not co-localize with mature fibrillar alpha-synuclein to a significant extent. The localization of LRRK2 to key neuronal populations throughout the nigrostriatal dopaminergic pathway is consistent with the involvement of LRRK2 in the molecular pathogenesis of familial and sporadic parkinsonism.

To die or grow : Parkinson's disease and cancer

Epidemiological evidence suggests a reduced incidence of many common types of non-smoking-related cancers in individuals with Parkinsons disease (PD). Genes that underlie familial forms of PD are often abnormally expressed in cancer, owing to their differential regulation or mutation. Functional studies implicate these genes in maintenance of the cell cycle, in some cases through interaction in the ubiquitin-proteasome system. Variation in genes associated with familial-linked PD could therefore modify susceptibility to both cancer and PD, implying some degree of overlap in the underlying biochemical dysfunction. When considering the normal function of these PD-linked genes in the periphery and their potential role in cancer, further emphasis might be placed on protein handling relating to cell-cycle control in the etiology of PD.

Parkin mediates the degradation-independent ubiquitination of Hsp70.

Mutations in the parkin gene cause autosomal recessive, juvenile‐onset parkinsonism. Parkin is an E3 ubiquitin ligase that mediates the ubiquitination of protein substrates. Disease‐associated mutations cause a loss‐of‐function of parkin which may compromise the poly‐ubiquitination and proteasomal degradation of specific protein substrates, potentially leading to their deleterious accumulation. Here, we identify the molecular chaperones, Hsp70 and Hsc70, as substrates for parkin. Parkin mediates the ubiquitination of Hsp70 both in vitro and in cultured cells. Parkin interacts with Hsp70 via its second RING finger domain and mutations in/near this domain compromise Hsp70 ubiquitination. Ubiquitination of Hsp70 fails to alter its steady‐state levels or turnover, nor does it promote its proteasomal degradation. Consistent with this observation, Hsp70 levels remain unaltered in brains from parkin‐deficient autosomal recessive, juvenile‐onset parkinsonism subjects, whereas alternatively, Hsp70 levels are elevated in the detergent‐insoluble fraction of sporadic Parkinson’s disease/dementia with Lewy bodies brains. Parkin mediates the multiple mono‐ubiquitination of Hsp70/Hsc70 consistent with a degradation‐independent role for this ubiquitin modification. Our observations support a novel functional relationship between parkin and Hsc/Hsp70 and support the notion that parkin is a multi‐purpose E3 ubiquitin ligase capable of modifying proteins either via attachment of alternatively linked poly‐ubiquitin chains or through multiple mono‐ubiquitination to achieve alternate biological outcomes.