Cells deficient for Kruppel-like factor 4 exhibit mitochondrial dysfunction and impaired mitophagy

Kruppel-like factor 4 (Human Protein: KLF4; Human Gene: Klf4; Murine Protein: KLF4; Murine Gene: Klf4) is a zinc finger-containing transcription factor with diverse regulatory functions. Mouse embryonic fibroblasts (MEFs) lacking Klf4 exhibit genomic instability, increased reactive oxygen species (ROS), and decreased autophagy. Elevated ROS is linked to impairments in mitochondrial damage recovery responses and is often tied to disruption in mitochondrial-targeted autophagy known as mitophagy. In this study, we sought to identify a mechanistic connection between KLF4 and mitophagy. Using flow cytometry, we found that Klf4-null MEFs have diminished ability to recover mitochondrial health and regulate ROS levels after mitochondrial damage. Confocal microscopy indicated decreased localization of autophagy protein LC3 to mitochondria following mitochondrial damage in Klf4-null cells, suggesting decreased mitophagy. Western blotting and RT-PCR revealed decreased mRNA and protein expression of the mitophagy-associated protein Bnip3 and antioxidant protein GST alpha 4 in Klf4-null cells, providing a rationale for their impaired mitophagy and ROS accumulation. Inducing Bnip3 expression in these cells recovered mitophagy but did not decrease ROS accumulation. Our findings suggest that in Klf4-null cells, decreased Bnip3 expression impairs mitophagy and is associated with increased mitochondrial ROS production after mitochondrial damage, providing a rationale for their genomic instability and supports a tumor suppressive role for KLF4 in certain tumors as previously observed.