Aberrant cyclin C nuclear release induces mitochondrial fragmentation and dysfunction in MED13L syndrome fibroblasts

Kai Ti Chang, Jan Jezek, Alicia N. Campbell, David C. Stieg, Zachary A. Kiss, Kevin Kemper, Ping Jiang, Hyung Ok Lee, Warren D. Kruger, Peter M. van Hasselt, Randy Strich

Research output: Contribution to journalArticlepeer-review

2 Scopus citations


MED13L syndrome is a haploinsufficiency developmental disorder characterized by intellectual disability, heart malformation, and hypotonia. MED13L controls transcription by tethering the cyclin C-Cdk8 kinase module (CKM) to the Mediator complex. In addition, cyclin C has CKM-independent roles in the cytoplasm directing stress-induced mitochondrial fragmentation and regulated cell death. Unstressed MED13LS1497F/fs patient fibroblasts exhibited aberrant cytoplasmic cyclin C localization, mitochondrial fragmentation, and a 6-fold reduction in respiration. In addition, the fibroblasts exhibited reduced mtDNA copy number, reduction in mitochondrial membrane integrity, and hypersensitivity to oxidative stress. Finally, transcriptional analysis of MED13L mutant fibroblasts revealed reduced mRNA levels for several genes necessary for normal mitochondrial function. Pharmacological or genetic approaches preventing cyclin C-mitochondrial localization corrected the fragmented mitochondrial phenotype and partially restored organelle function. In conclusion, this study found that mitochondrial dysfunction is an underlying defect in cells harboring the MED13LS1497F/fs allele and identified cyclin C mis-localization as the likely cause. These results provide a new avenue for understanding this disorder.

Original languageEnglish
Article number103823
Issue number2
StatePublished - Feb 18 2022


  • Biochemistry
  • Biological sciences
  • Cell biology


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