Tour-de-Force

Tour-de-Force: Interplay between Mitochondria and Cell Cycle Progression Fall 2007IntroductionA lot of research has been dedicated to the general function of mitochondria within the cell as well asfocus on mitochondrial related diseases such as the mitochondrial DNA depletion syndrome, which ischaracterized by reduced activity of mitochondrial DNA – encoded respiratory chain complexes (I, III, IVand V) and mitochondrial depletion (Taanman et al., 1997). However, not a lot is known about the actualdynamics of mitochondria during the cell cycle and which signals and stimuli control these processes. Dueto requirements of energy and division of mitochondria during cell division, mitochondria need to preparefor the cell cycle by increasing energy output capacity as well as ensuring enough material to be dividedinto the daughter cells. This is achieved through mitochondrial biogenesis.This research is designed to answer the following question: What are the patterns of mitochondrialbiogenesis observed during the cell cycle and what are the regulatory mechanisms that coordinate thisbiogenesis with progression through the cell cycle?For the purposes of this research we define and measure mitochondrial biogenesis as the increase inmitochondrial mass as well as the replication of mitochondrial DNA. We specifically want to look at theguidance of the mitochondrial biogenesis in response to cell cycle induction signals via the linking proteinsPGC-1 and PRC, the transcriptional regulatory proteins of the Peroxisome Proliferator Activated GammaCoactivator (PPAR) family. Additionally, we wish to establish how these processes are related tomechanisms involved in the regulation of the cell cycle itself (such as the cyclins), coordinatingmitochondrial biogenesis with progression through the cell cycle. Research indicates that PRC might beinvolved in inducing the cell cycle via the metabolic burst (Vercauteren et al., 2006). However, toinvestigate whether the PPAR family is involved in mitochondrial biogenesis during and over subsequentcell cycles irrespective of the metabolic burst, the research will be carried out on a cell line in which thecell cycle is induced and in a cell line that is continuously proliferating to account for possible differences.Our motivation for focusing on the roles of the PPAR family of proteins comes from the simple reason thatknowledge of these proteins in relation to the cell cycle and mitochondrial cycle is rather limited. Researchhas sparked interest in these proteins as recent studies in mice KO indicate that the role of thesecoactivator proteins is crucial for the normal expression of mitochondrial genes (Lin et al., 2005). Otherstudies have associated the involvement of the PPAR family proteins with the SIRT1 proteins, whichregulate metabolism and cell survival through influencing gene silencing as well as regulating cellmetabolism. Increased SIRT1 action induces hepatic gluconeogensis and inhibits glycolysis through PGC-1α during fasting state (Kuningas et al., 2007). Possible further research into this area may reveal furtherfunctions and implications of the PPAR family proteins and this insight may provide a pharmaceuticalbasis for treatment of mitochondrial disease and dysfunction.Our linking factor of the PGC1 family proteins with cell cycle and mitochondrial biogenesis comesfrom its interaction with Nuclear Respiratory Factor 1 (NRF). NRF-1 has been characterized as animportant regulator of transcription of mitochondrial genes encoded in the cell nucleus, as well asregulating the expression of mitochondrial transcription factors that regulate mitochondrial DNA geneexpression and replication (Andersson et al., 1999; Gleyzer et al., 2005; Martinez-Diez et al., 2006). Forexample, the Beta-F1-ATPase subunit of complex IV in the respiratory chain and cytochrome c expression,both of which are essential for normal mitochondrial function, have been shown to be mediated by NRF-1activity (Martinez-Diez et al., 2006; Chau, Evans and Scarpulla, 1992). Additionally, the mTFA and mTFBtranscription factors responsible for regulating mitochondrial DNA transcription and replication have beenshown to be regulated through NRF-1 activity (Gleyzer et al., 2005). These studies have also revealedthat PRC and PGC-1 expression in cells increase NRF-1 transcriptional activity and in doing so, promotemitochondrial biogenesis. We hypothesize that PRC and PGC1 are involved in the cell cycle as importantregulators of mitochondrial biogenesis, in cells transitioning from quiescent to proliferating, directly via themetabolic burst.SCI 332 Advanced Molecular Cell Biology Research Proposal 58