Mdm2 enhances ligase activity of parkin and facilitates mitophagy

Abstract

Loss-of-function mutations in the E3 ubiquitin ligase parkin have been implicated in the death of dopaminergic neurons in the substantia nigra, which is the root cause of dopamine deficit in the striatum in Parkinson's disease. Parkin ubiquitinates proteins on mitochondria that lost membrane potential, promoting the elimination of damaged mitochondria. Neuroprotective activity of parkin has been linked to its critical role in the mitochondria maintenance. Here we report a novel regulatory mechanism: another E3 ubiquitin ligase Mdm2 directly binds parkin and enhances its enzymatic activity in vitro and in intact cells. Mdm2 translocates to damaged mitochondria independently of parkin, enhances parkin-dependent ubiquitination of the outer mitochondria membrane protein mitofusin1. Mdm2 facilitates and its knockdown reduces parkin-dependent mitophagy. Thus, ubiquitously expressed Mdm2 might enhance cytoprotective parkin activity. The data suggest that parkin activation by Mdm2 could be targeted to increase its neuroprotective functions, which has implications for antiparkinsonian therapy.Parkin was first identified through its association with autosomal recessive juvenile parkinsonism, a familial form of Parkinson's disease (PD) with early onset 1 . Loss-of-function mutations in parkin gene, including exon deletions and rearrangements, as well as nonsense and missense mutations, are commonly associated not only with familial, but also with apparently sporadic early onset PD 2-5 . Functionally, parkin is an E3 ubiquitin ligase 6 . Initially, the studies of parkin function in PD concentrated on the search for parkin substrates and the role of parkin loss in the dysfunction of the ubiquitin-proteasome system (UBS), which appears to play a prominent role in the PD-related neurodegeneration 7 . Further studies implicated parkin in the regulation of the mitochondrial dynamics 8-10 . PINK1, another protein associated with a recessive form of early onset familial PD 11 , acts upstream of parkin, recruiting parkin to damaged mitochondria and stimulating its ligase activity 10,12-15 . Parkin then ubiquitinates proteins of the outer mitochondrial membrane causing their proteosomal degradation and elimination of the damaged mitochondria via mitophagy [16][17][18][19] . Mitochondrial dysfunction has been implicated in PD 20-23 , although the role of mitophagy in the quality control of neuronal mitochondria remains controversial [24][25][26] . Parkin exists in an autoinhibited basal state [27][28][29][30] . Its activity is regulated, in addition to the PINK1-dependent phosphorylation 15,31,32 , via a variety of mechanisms including formation of multiprotein signaling complexes [33][34][35] . Full spectrum of parkin interactions that regulate its activity is not yet understood. However, it is clear that this regulation is complex and often involves scaffolding proteins 36 , which may impact on parkin-dependent control of the mitochondrial dynamics and, consequently, its functions in the normal and diseased brain.We have recently de...

Mitochondrial Ca2+ oscillation induces mitophagy initiation through the PINK1-Parkin pathway

“…These mutations affect many mitochondrial functions and have secondary effects on oxidative phosphorylation and other processes [3,4]. Mitophagy has been found regulated by the activity of Parkin and PINK1 and usually becomes abnormal in PD [5,6]. Specifically, dysregulation of mitophagy by PINK1-Parkin is believed as one of the main factors contributing to cell death and pathogenesis in PD [7][8][9].…”

Endosomes facilitate mitochondrial clearance by enhancing Parkin recruitment to mitochondria

“…As recycling endocytic vesicles are shown to contribute to autophagosomes formation and mitophagy [15], further studies in this area further our understanding of the biogenesis of autophagosomes in Parkin-mediated mitophagy. An important role of CARP2 in mitophagy is further supported by reports of modulation of Parkin recruitment to mitochondria and its activity by two other molecules p53 and MDM2 [35,36], though many details of this process remain unknown. Importantly, both p53 and MDM2 are interacting partners of CARP2 [37].…”

FOXO3a-dependent PARKIN negatively regulates cardiac hypertrophy by restoring mitophagy

“…Upon phosphorylated by PINK1, PARKIN is recruited to the outer membrane of the damaged mitochondria where PARKIN extensively catalyzes ubiquitination of OMM substrates [22,25]. During above processes, another E3 ubiquitin ligase MDM2 accumulates to OMM and enhances enzymatic activity of PARKIN, whereas cytosolic p53 hinders PARKIN from translocation to damaged mitochondria and PICK1 suppresses E3 ligase activity of PARKIN [48][49][50]. Our results identified FOXO3a as a novel regulator of PARKIN, in which FOXO3a promotes Parkin transcription by binding to its promoter region, and activates PARKIN-dependent mitophagy.…”