NIX compensates lost role of parkin in cd-induced mitophagy in HeLa cells through phosphorylation.

Our previous study demonstrated that cadmium (Cd) is an effective inducer of mitophagy, which is mainly mediated by PINK1/Parkin pathway. However, the role of other mitophagy pathways in Cd-induced mitophagy remains elusive. The present study employed HeLa cells, lacking fully functional Parkin, as a cell model to study Parkin-independent mitophagy pathway induced by Cd. Our results showed that BCL2/adenovirus E1B 19 kDa protein-interacting protein 3-like (Bnip3L/NIX), an outer mitochondrial membrane mitophagy receptor, could provide an alternate pathway for Cd-induced mitophagy in HeLa cells. Specifically, 10 µM Cd for 12 h induced mitophagy in GM00637 and HeLa cells which was assessed by mitochondrial fusion to lysosomes and decreased expression of mitochondrial markers such as COX-IV and HSP60. Notably, in GM00637 cells, Cd-induced mitophagy was predominantly mediated by PINK1/Parkin pathway as evinced by translocation of Parkin to mitochondria. Interestingly, in HeLa cells, significant increase in NIX expression was occurred and mitophagy was induced under Cd exposure, suggesting NIX compensates lost role of Parkin in Cd-induced mitophagy in HeLa cells. These results were verified by knocking down NIX using siRNA in HeLa cells, which lead to abolished mitophagy process. Moreover, NIX phosphorylation at serine-81 significantly increased in cells treated with Cd implying that phosphorylation of NIX plays an important role in NIX-mediated mitophagy. These findings reveal a novel mechanism of Cd toxicity and suggest a compensatory role of NIX in Cd-induced mitophagy.

[Protective effect of over-expression OGCP on HEK293 cells treated by rotenone and mutant Parkin protein].

OBJECTIVE: To study the effect of alpha-ketoglutarate carrier protein (2-oxoglutarate carrier protein, OGCP) and the Parkin protein on HEK293 cell function. METHODS: The cell apoptosis rate, mitochondrial membrane potential and intracellular reactive oxygen species of HEK293 cells treated with rotenone, OGCP and / or Parkin protein were detected by using flow cytometry methods (FCM). RESULTS: (1) Over-expression wild-type Parkin protein and/or OGCP can increase mitochondrial membrane potential of HEK293 cells induced by rotenone, reduce intracellular reactive oxygen species and cell apoptosis rate of HEK293 cells induced by rotenone, while over-expression mutant Parkin (R42P and T240R) protein can decrease the mitochondrial membrane potential of HEK293 cells, especially the HEK293 cells induced by rotenone, but increase intracellular reactive oxygen species and promote apoptosis. (2) In addition, we also found that OGCP can inhibit the increasing of mitochondrial membrane potential and reactive oxygen species and decreasing of cell apoptosis caused by mutant Parkin protein (R42P and T240R). CONCLUSION: (1) Parkin protein and OGCP may be associated with the maintenance of normal function of mitochondria. (2) Over-expression of mutant parkin (R42P and T240R) protein may inhibit mitochondrial function and promote apoptosis. (3) Over-expression OGCP has protective effect on cell toxicity caused by rotenone and mutant parkin protein.

A Drosophila model of mutant human parkin-induced toxicity demonstrates selective loss of dopaminergic neurons and dependence on cellular dopamine.

Mutations in human parkin have been identified in familial Parkinson's disease and in some sporadic cases. Here, we report that expression of mutant but not wild-type human parkin in Drosophila causes age-dependent, selective degeneration of dopaminergic (DA) neurons accompanied by a progressive motor impairment. Overexpression or knockdown of the Drosophila vesicular monoamine transporter, which regulates cytosolic DA homeostasis, partially rescues or exacerbates, respectively, the degenerative phenotypes caused by mutant human parkin. These results support a model in which the vulnerability of DA neurons to parkin-induced neurotoxicity results from the interaction of mutant parkin with cytoplasmic dopamine.