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2017 ; 8
(34
): 55848-55862
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Loss of p16(INK4A) stimulates aberrant mitochondrial biogenesis through a
CDK4/Rb-independent pathway
#MMPMID28915557
Tyagi E
; Liu B
; Li C
; Liu T
; Rutter J
; Grossman D
Oncotarget
2017[Aug]; 8
(34
): 55848-55862
PMID28915557
show ga
The tumor suppressor p16INK4A (p16) inhibits cell cycle progression through the
CDK4/Rb pathway. We have previously shown that p16 regulates cellular oxidative
stress, independent of its role in cell cycle control. We investigated whether
loss of p16 had a direct impact on the mitochondria. We found that p16-null
primary mouse fibroblasts (PMFs) displayed increased mitochondrial mass and
expression of mitochondrial respiratory subunit proteins compared to wild-type
(WT) PMFs. These findings in p16-null PMFs were associated with increased
expression of the mitochondrial biogenesis transcription factors PRC and TFAM. On
the other hand, p16-deficient PMFs demonstrated reduced mitochondrial respiration
capacity consistent with electron microscopy findings showing that mitochondria
in p16-deficient PMFs have abnormal morphology. Consistent with increased
mitochondrial mass and reduced respiratory capacity, p16-deficient PMFs generated
increased mitochondrial superoxide. One biological consequence of elevated ROS in
p16-deficient PMFs was enhanced migration, which was reduced by the ROS scavenger
N-acetylcysteine. Finally, p16-deficient PMFs displayed increased mitochondrial
membrane potential, which was also required for their enhanced migration. The
mitochondrial and migration phenotype was restored in p16-deficient PMFs by
forced expression of p16. Similarly, over-expression of p16 in human melanocytes
and A375 melanoma cells led to decreased expression of some mitochondrial
respiratory proteins, enhanced respiration, and decreased migration. Inhibition
of Rb phosphorylation in melanocytes and melanoma cells, either by addition of
chemical CDK4 inhibitors or RNAi-mediated knockdown of CDK4, did not mimic the
effects of p16 loss. These results suggest that p16 regulates mitochondrial
biogenesis and function, which is independent of the canonical CDK4/Rb pathway.