Mitochondria produce the bulk of cellular energy and thus are essential to normal physiological function. Defects in mitochondrial maintenance and activity have been widely implicated in human disease including myopathies, neurodegenerative disease, diabetes and ageing. Mutations in both nuclear and mitochondrial genes have been linked to mitochondrial pathologies. Although mitochondrial DNA encodes essential respiratory subunits, nuclear genes specify the vast majority of products required for mitochondrial functions, including the maintenance and expression of the mitochondrial genetic system. This is a proposal to continue studies on the molecular mechanisms governing nucleo-mitochondrial interactions in mammalian cells. The specific aims will focus on transcriptional activators and coactivators that integrate the expression of the respiratory apparatus with cell growth. Our previous studies led to the discovery, purification and molecular cloning of nuclear respiratory factors (NRFs). These transcription factors act on the majority of nuclear genes whose products are required for expression of the mitochondrial respiratory apparatus and include those encoding respiratory subunits, heme biosynthetic enzymes, protein import and assembly factors, and key components of the mitochondrial transcription and replication machinery. In recent years, NRFs have been identified as important targets for the PGC-1 family of transcriptional coactivators. These coactivators are induced by physiological signals and have the ability to integrate the actions of NRFs and other transcription factors in orchestrating programs of gene expression essential to cellular energetics. We have identified and characterized a novel PGC-1 family member, which we have designated as PGC-1-related coactivator (PRC). PRC is induced during proliferative growth and may play an important role in integrating the cell growth program with the expression of the respiratory chain. PRC regulatory functions occur in part through its interactions with NRFs and other transcription factors and coactivators. The specific aims of this proposal are directed at understanding PRC molecular interactions and biological functions as follows: 1) Define the PRC- dependent molecular mechanisms that link respiratory chain expression to organelle biogenesis. The focus will be on defining PRC-dependent regulatory pathways and on the characterization of novel PRC target genes. 2) Define the role of PRC as a cell growth regulator. The focus will be on identifying the PRC-dependent lesion in the cell growth cycle and on the contribution of specific PRC target genes required for cell proliferation. 3) Define the role of host cell factor (HCF) and HCF C1 regulator 1 (HPIP) in PRC-regulated functions. The emphasis will be on the mechanisms regulating the nucleo-cytoplasmic distribution of transcription factors that complex with HCF in the control of respiratory chain expression and cell growth. PUBLIC HEALTH RELEVANCE: Mitochondria are structures within the cell that produce the bulk of energy required for normal cell and tissue function. Mitochondrial deficiencies have been linked to aging and to many common human diseases including muscle weakness, Alzheimer's disease, diabetes and cancer. This research seeks to define how cells maintain mitochondrial energy production and may lead to therapies designed to improve the health of an aging population and to the treatment of human degenerative diseases.