N-myc regulates parkin expression.

Mutations in the parkin gene are common in early-onset and familial Parkinson's disease (PD), and the parkin protein interacts in the ubiquitin-proteasome system as an E3 ligase. However, the regulatory pathways that govern parkin expression are unknown. In this study, we showed that a phylogenetically conserved N-myc binding site in the bi-directional parkin promoter interacted with myc-family transcription factors in reporter assays, and N-myc bound to the parkin promoter in chromatin immunoprecipitation assays and repressed transcription activity. Parkin expression was inversely correlated with N-myc levels in the developing mouse and human brain, in human neuroblastoma cell lines with various levels of n-myc amplification, and in an inducible N-myc cell line. Although parkin and N-myc expression were dramatically altered upon retinoic acid-induced differentiation of a human neuroblastoma cell line, modulation of parkin expression did not significantly affect either rates of cellular proliferation or levels of cyclin E. Analysis of additional genes associated with familial PD revealed a shared basis of transcription regulation mediated by N-myc and the cell cycle. Our results, in combination with functional knowledge of the proteins encoded by these genes, suggest a common pathway linking together PD, the ubiquitin-proteasome system, and cell cycle control.

Parkin is not regulated by the unfolded protein response in human neuroblastoma cells.

Mutations in the parkin gene cause the majority of cases of familial-linked Parkinson's disease, and mounting evidence suggests that parkin may play a role in idiopathic disease. Previous reports suggest that parkin may respond to and relieve, via E3-ligase activity, cellular stress at the endoplasmic reticulum caused by the accumulation of unfolded proteins. However, parkin's relationship to the mammalian unfolded protein response is unclear. Here, we comprehensively evaluate endogenous parkin in SH-SY5Y neuroblastomas at the promoter, RNA, and protein levels in response to unfolded protein stress induced by tunicamycin. While we find strong up-regulation of genes linked to the unfolded protein stress pathway, we detect no significant changes in parkin. These data suggest a lack of association between parkin and the unfolded protein response in SH-SY5Y cells.