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Updated: Feb 22, 2026
Spatial and Temporal Control of Murine Melanoma Initiation from Mutant Melanocyte Stem Cells
Published on: June 7, 2019
Loss of p16INK4A stimulates aberrant mitochondrial biogenesis through a CDK4/Rb-independent pathway
Ethika Tyagi1, Bin Liu1, Chelsea Li1
1The Huntsman Cancer Institute, University of Utah Health Sciences Center, Salt Lake, Utah, USA.
Abstract:
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.
Insights
The tumor suppressor p16INK4A (p16) regulates mitochondrial function and biogenesis independently of cell cycle control. Loss of p16 enhances mitochondrial superoxide production and cell migration.
Area of Science:
- Cell Biology
- Mitochondrial Biology
- Cancer Research
Background:
- The tumor suppressor p16INK4A (p16) is known to inhibit cell cycle progression via the CDK4/Rb pathway.
- Previous research indicated p16's role in regulating cellular oxidative stress, independent of cell cycle control.
Purpose of the Study:
- To investigate the direct impact of p16 loss on mitochondrial function and biogenesis.
- To determine if p16's effects on mitochondria are linked to the CDK4/Rb pathway.
Main Methods:
- Comparison of mitochondrial mass, respiratory protein expression, and transcription factor levels (PRC, TFAM) in p16-null and wild-type mouse fibroblasts.
- Assessment of mitochondrial respiration capacity and morphology using electron microscopy.
- Measurement of mitochondrial superoxide production and membrane potential.
- Evaluation of cell migration in response to ROS scavengers and p16 expression levels.
- Analysis of p16's effects in human melanocytes and melanoma cells, including experiments with CDK4 inhibition.
Main Results:
- p16-null fibroblasts exhibited increased mitochondrial mass, respiratory protein expression, and elevated PRC/TFAM levels.
- Reduced mitochondrial respiration capacity and abnormal mitochondrial morphology were observed in p16-deficient cells.
- p16-deficient cells showed increased mitochondrial superoxide production and enhanced migration, which was ROS-dependent and required mitochondrial membrane potential.
- Restoration of p16 expression normalized mitochondrial function and reduced cell migration.
- Overexpression of p16 in human cells decreased mitochondrial respiratory proteins, enhanced respiration, and reduced migration.
- CDK4 inhibition did not replicate the effects of p16 loss on mitochondria or migration.
Conclusions:
- p16 directly regulates mitochondrial biogenesis and function.
- These regulatory effects of p16 on mitochondria are independent of its canonical role in the CDK4/Rb pathway.
- p16 influences cellular processes like migration through its impact on mitochondrial oxidative stress and function.
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