Role For PTEN-induced Putative Kinase 1 Research Articles

PTEN-induced kinase PINK1 supports colorectal cancer growth by regulating the labile iron pool

Mitophagy is a cargo-specific autophagic process that recycles damaged mitochondria to promote mitochondrial turnover. PTEN-induced putative kinase 1 (PINK1) mediates the canonical mitophagic pathway. However, the role of PINK1 in diseases where mitophagy has been purported to play a role, such as colorectal cancer, is unclear. Our results here demonstrate that higher PINK1 expression is positively correlated with decreased colon cancer survival, and mitophagy is required for colon cancer growth. We show that doxycycline-inducible knockdown (KD) of PINK1 in a panel of colon cancer cell lines inhibited proliferation, whereas disruption of other mitophagy receptors did not impact cell growth. We observed that PINK KD led to a decrease in mitochondrial respiration, membrane hyperpolarization, accumulation of mitochondrial DNA, and depletion of antioxidant glutathione. In addition, mitochondria are important hubs for the utilization of iron and synthesizing iron-dependent cofactors such as heme and iron sulfur clusters. We observed an increase in the iron storage protein ferritin and a decreased labile iron pool in the PINK1 KD cells, but total cellular iron or markers of iron starvation/overload were not affected. Finally, cellular iron storage and the labile iron pool are maintainedviaautophagic degradation of ferritin (ferritinophagy). We found overexpressing nuclear receptor coactivator 4, a key adaptor for ferritinophagy, rescued cell growth and the labile iron pool in PINK1 KD cells. These results indicate that PINK1 integrates mitophagy and ferritinophagy to regulate intracellular iron availability and is essential for maintaining intracellular iron homeostasis to support survival and growth in colorectal cancer cells.

Depletion of PINK1 affects mitochondrial metabolism, calcium homeostasis and energy maintenance

Loss-of-function mutations in the gene encoding the mitochondrial PTEN-induced putative kinase 1 (PINK1) are a major cause of early-onset familial Parkinson's disease (PD). Recent studies have highlighted an important function for PINK1 in clearing depolarized mitochondria by mitophagy. However, the role of PINK1 in mitochondrial and cellular functioning in physiological conditions is still incompletely understood. Here, we investigate mitochondrial and cellular calcium (Ca(2+)) homeostasis in PINK1-knockdown and PINK1-knockout mouse cells, both in basal metabolic conditions and after physiological stimulation, using unbiased automated live single-cell imaging in combination with organelle-specific fluorescent probes. Our data reveal that depletion of PINK1 induces moderate fragmentation of the mitochondrial network, mitochondrial membrane depolarization and increased production of reactive oxygen species. This results in reduced uptake of Ca(2+) by mitochondria after physiological stimulation. As a consequence, cells with knockdown or knockout of PINK1 display impaired mitochondrial ATP synthesis, which is exacerbated under conditions of increased ATP demand, thereby affecting cytosolic Ca(2+) extrusion. The impairment in energy maintenance was confirmed in the brain of PINK1-knockout mice by in vivo bioluminescence imaging. Our findings demonstrate a key role for PINK1 in the regulation of mitochondrial homeostasis and energy metabolism under physiological conditions.

Targeting Mitochondrial Dysfunction: Role for PINK1 and Parkin in Mitochondrial Quality Control

Mitochondria, which convert energy for the cell, accumulate damage with age, and the resulting mitochondrial dysfunction has been linked to the development of degenerative diseases and aging. To curb the accumulation of damaged mitochondria, the cell has elaborated a number of mitochondrial quality control processes. We describe recent work suggesting that Parkin and PTEN-induced putative kinase 1 (PINK1), two gene products linked to familial forms of parkinsonism, may constitute one of the cell's mitochondrial quality control pathways-identifying impaired mitochondria and selectively trimming them from the mitochondrial network by mitophagy. In particular, we discuss the regulation of PINK1 protein expression and Parkin localization by the bioenergetic status of individual mitochondria; the mechanism by which PINK1 recruits Parkin to the outer mitochondrial membrane; and Parkin's promotion of mitophagy through its ubiquitination of outer mitochondrial membrane proteins. This recent work suggests that Parkin and PINK1 may be among the first mammalian proteins identified with a direct role in regulating mitophagy, and implicate a failure of mitophagy in the pathogenesis of Parkinson's disease.