The Role of Mammalian Cyclin C in Stress Response and Thyroid Disease Progression

Author(s)

Kun Wang

Date Approved

2014

Document Type

Dissertation

Degree Name

PhD in Cell and Molecular Biology

Department

Molecular Biology

College

Graduate School of Biomedical Sciences

First Advisor

Randy Strich, PhD

Committee Member 1

Salvatore Caradonna, PhD

Committee Member 2

John Pastorino, PhD

Committee Member 3

Hristo Houbaviy, PhD

Committee Member 4

Maureen Murphy, PhD

Subject(s)

Apoptosis; Thyroid Diseases; Cyclin C; Transcription Factors, Neoplasms

Disciplines

Cancer Biology | Cell Biology | Endocrine System Diseases | Laboratory and Basic Science Research | Medicine and Health Sciences | Molecular Biology | Neoplasms

Abstract

The cellular response to stress involves changes in gene expression programs as well as the remodeling of subcellular organelles including the mitochondria. Important for this study, the mitochondria undergo extensive fragmentation when the cell is exposed to a variety of stressors. The cyclin C-Cdk8 kinase is a highly conserved transcription factor that associates with the RNA polymerase II holoenzyme. Using cyclin C knockout (CCNC^-/-) mouse embryonic fibroblast (MEF) cells, I revealed that cyclin C is required for the extensive mitochondrial fragmentation following treatment with pro-oxidants or the anti-cancer drug cisplatin. However, Cdk8 is not required for this process suggesting that cyclin C controls mitochondrial fission independent of its role as a transcription factor. In support of this model, biochemical and co-localization studies revealed that cyclin C undergoes stress-induced nuclear to cytoplasmic translocation where it associates with the mitochondria. In addition, cyclin C both interacts with Drp1, the dynamin like GTPase that mediates mitochondrial fission, and is required for its enhanced association with the mitochondria following cellular stress. Finally, the addition of purified cyclin C to permeabilized CCNC^-/- MEF cells rapidly induced extensive mitochondrial fragmentation. These results indicate that cyclin C is both necessary and sufficient to mediate mitochondrial hyper-fission. Interestingly, cyclin C, but not Cdk8, is required for loss of mitochondrial integrity and apoptotic cell death in MEF cells again indicating a new non-transcriptional function for this conserved protein. This study identifies cyclin C as a stress activated trigger of mitochondrial hyper-fission and programmed cell death.

The requirement of cyclin C for programmed cell death suggested a role for this protein as a tumor suppressor. In support of this possibility, FISH analysis showed that human cyclin C is located on chromosome 6q21, a locus that is frequently deleted in many kinds of cancers including thyroid disease. To test this hypothesis, we generated murine thyroid specific knockout of cyclin C and/or the tumor suppressor PTEN. The double mutant resulted in mouse death around 20 weeks. Conversely, deleting only PTEN or CCNC did not exhibit tumors until around 1 O months revealing a synergy between these two mutations. Pathology revealed that the double mutants died with enlarged thyroids and massive swollen lymph nodes. H&E staining showed that these mice had enlarged follicles filled with colloid. Ki-67 and Brdu proliferation assays indicated that their follicular cells also had increased proliferation. These data suggest that cyclin C functions as a tumor suppressor during thyroid disease progression.

Recommended Citation

Wang, Kun, "The Role of Mammalian Cyclin C in Stress Response and Thyroid Disease Progression" (2014). Graduate School of Biomedical Sciences Theses and Dissertations. 62.
https://rdw.rowan.edu/gsbs_etd/62