Krüppel-like factor 4 (KLF4) induces mitochondrial fusion and increases spare respiratory capacity of human glioblastoma cells

Abstract

Krüppel-like factor 4 (KLF4) is a zinc finger transcription factor critical for the regulation of many cellular functions in both normal and neoplastic cells. Here, using human glioblastoma cells, we investigated KLF4's effects on cancer cell metabolism. We found that forced KLF4 expression promotes mitochondrial fusion and induces dramatic changes in mitochondrial morphology. To determine the impact of these changes on the cellular functions following, we analyzed how KLF4 alters glioblastoma cell metabolism, including glucose uptake, glycolysis, pentose phosphate pathway, and oxidative phosphorylation. We did not identify significant differences in baseline cellular metabolism between control and KLF4-expressing cells. However, when mitochondrial function was impaired, KLF4 significantly increased spare respiratory capacity and levels of reactive oxygen species in the cells. To identify the biological effects of these changes, we analyzed proliferation and survival of control and KLF4-expressing cells under stress conditions, including serum and nutrition deprivation. We found that following serum starvation, KLF4 altered cell cycle progression by arresting the cells at the G/M phase and that KLF4 protected cells from nutrition deprivation-induced death. Finally, we demonstrated that methylation-dependent KLF4-binding activity mediates mitochondrial fusion. Specifically, the downstream targets of KLF4-mCpG binding, guanine nucleotide exchange factors, serve as the effector of KLF4-induced mitochondrial fusion, cell cycle arrest, and cell protection. Our experimental system provides a robust model for studying the interactions between mitochondrial morphology and function, mitochondrial dynamics and metabolism, and mitochondrial fusion and cell death during tumor initiation and progression.

Kruppel-Like Factor 4 (KLF4) and its Regulation on Mitochondrial Homeostasis

“…In the work from Wan, et al, genome-wide RNA sequencing revealed KLF4’s role in both the up- and down-regulation of mitochondrial genes, suggesting its direct involvement in mitochondrial homeostasis [29]. In the recent work from Wang, et al [30], we observed extensive flux in mitochondrial architecture, consistent with increased mitochondrial fusion in KLF4-expressing GBM tumor cells. Mitochondrial dynamic changes did not substantially influence mitochondrial function under basal conditions when cells were cultured in full serum.…”

“…Mechanistically, KLF4 did not directly regulate the three major modulators of mitochondrial fusion: Mfn1, Mfn1, and Opa-1. However, for the first time, KLF4 has been found to interact with members of the Guanine Exchange Factor (GEF) family to modulate mitochondrial dynamics [30], including Neuronal Guanine Nucleotide Exchange Factor (NGEF) and Rho/Rac Guanine Nucleotide Exchange Factor 2 (ARHGEF2).…”

Clinically Actionable Insights into Initial and Matched Recurrent Glioblastomas to Inform Novel Treatment Approaches

“…In this GBM cohort, amongst the BRCA2 variants were confirmed somatic mutations in haemangioblastoma (BRCA2 : COSM3753648, COSM5019704) [43], which is a rare, benign tumour that typically occurs in the cerebellum [3]. Many IDH WT tumours had alterations impacting WNT [59][60][61][62][63] signalling pathway genes (58%) including CREBBP(4), KLF4 (2) [64,65], TERT(2) [17], and APC(3) [66][67][68][69][70]; however, targeting this pathway is currently challenging. Initial IDH WT tumours also showed predicted pathogenic variation in NOTCH (11%) [71] and SHH (13%) pathways [72] including PTCH1 (PATCHED-1) and SMO (Smoothened) [73][74][75].…”

Mitochondrion-Directed Nanoparticles Loaded with a Natural Compound and a microRNA for Promoting Cancer Cell Death via the Modulation of Tumor Metabolism and Mitochondrial Dynamics

“…Intriguingly, another study has shown that Krüppel-like factor 4, a zinc finger transcription factor, considerably increases ROS levels and triggers mitochondrial fusion, thus inducing the G2/M cell cycle arrest and protecting cells from nutrient deprivation-induced death in human glioblastoma cells [54]. Consistent with our current finding, previous evidence has suggested that excessive mitochondrial fission may happen during cell metabolism, proliferation, apoptosis, and migration through the activation of the intrinsic (mitochondrial) apoptotic pathway [3].…”