Mechanism And Function Of The Interaction Between Parkin And Cell Structure Associated Proteins

Parkin is an E3 ubiquitin ligase encoded by the Parkin gene (also called PARK2, located at 6q25.2-q27) and is involved in the pathogenesis of both Parkinson's disease and the development of cancer. Reduced expression and inactivation of Parkin are frequently observed in human cancers. It is reported that Parkin expression can be epigenetically regulated; its expression can be reduced due to abnormal DNA methylation. These studies suggest that Parkin may play a role in tumour suppression. Although the precise mechanisms of how Parkin is involved in the development of Parkinson's disease and cancer remain elusive, alterations in its ubiquitin ligase activity are evident in a significant proportion of these patients.In addition to its function as an ubiquitin ligase, Parkin has recently been identified as a molecule capable of interacting with microtubules. However, the biological implication of the Parkin-microtubule axis has been poorly explored. In this study, we report for the first time that Parkin modulates sensitivity of the chemotherapeutic agent paclitaxel in breast cancer, via a microtubule-dependent mechanism. Our data reveal that Parkin binds to the outer surface of microtubules and increases paclitaxel-microtubule interaction, resulting in enhanced paclitaxel-induced microtubule assembly and stabilization. Our data further show that Parkin promotes the activity of paclitaxel to trigger multinucleation and apoptosis, rendering breast cancer cells more sensitive to this drug. Moreover, Parkin expression correlates with the pathological response of tumours to preoperative paclitaxel-containing chemotherapy. In addition, expression of Parkin also correlates with the sensitivity of paclitaxel in primary cultures of breast cancer cells. Our results identify Parkin as a novel mediator of paclitaxel sensitivity in breast cancer. In addition, our study suggests that patients harbouring tumours with high Parkin level would be more likely to benefit from paclitaxel-containing regimens.Parkin gene mutations have been implicated in autosomal-recessive early-onset parkinsonism and lead to specific degeneration of dopaminergic neurons in midbrain. A putative mechanism by which mutations of Parkin cause PD would be abnormal accumulation of its substrates due to altered E3 ligase activity for ubiquitin-proteasome dependent protein turnover. Over the past few decades, accumulating evidence has suggested that mitochondrial dysfunction and the resulting oxidative damage which occur prior to the neuronal loss are associated with PD. Mitochondria undergo frequent fission, fusion, and redistribution throughout the cytoplasm in response to the energy needs. Strong evidence has showed that Parkin plays a critical role in regulating mitochondrial fission and fusion and mitochondrial quality control. However, the precise mechanism of how parkin regulates mitochondrial dynamics remains a subject of debate, and so far, no substrate responsible for altered mitochondrial dynamics and functions was found to be accumulated due to the mutation of Parkin.In our study, we demonstrate that Parkin interacts with and subsequently ubiquitinates dynamin-related protein 1 (Drp1), a key molecule responsible for mitochondrial fission, for promoting its proteasome-dependent degradation. Knockdown of Parkin expression significantly increases the level of Drpl leading to mitochondrial fragmentation. In addition, neurotoxins known to induce PD reduce the level of Parkin and remarkably enhance the expression of Dip1 whereas knockdown of Drpl inhibits neurotoxin-induced cell death. Interestingly, inhibition of Drpl activity prevents MPP+-induced mitochondrial fragmentation and neuronal loss in cell and animal PD model systems. Immunohistochemical and biochemical analyses of PD patient brain samples further confirm the inverse correlation between Parkin and Drp1. These results identify Drp1 as a novel substrate of Parkin and uncover a novel mechanism linking abnormal Parkin expression to mitochondrial dysfunction in the pathogenesis of PD.