Sequential Serum-dependent Activation of CREB and NRF-1 Leads to Enhanced Mitochondrial Respiration through the Induction of Cytochrome c

Abstract

Progression through the cell cycle requires ATP for protein synthesis, cytoskeletal rearrangement, chromatin remodeling, and protein degradation. The mechanisms by which mammalian cells increase respiratory capacity and ATP production in preparation for cell division are largely unexplored. Here, we demonstrate that serum induction of cytochrome c mRNA and processed protein in quiescent BALB/3T3 fibroblasts is associated with a marked increase in mitochondrial respiration. Cytochrome c was induced in the absence of any increase in citrate synthase activity or in subunit IV of the cytochrome c oxidase complex mRNA or protein, indicating that the enhanced respiratory rate did not require a general increase in mitochondrial biogenesis or respiratory chain expression. Transfections with a series of cytochrome c promoter mutants showed that both nuclear respiratory factor 1 (NRF-1) and cAMPresponse element-binding protein (CREB) binding sites contributed equally to induced expression by serum. Moreover, CREB and NRF-1 were phosphorylated sequentially in response to serum, and the NRF-1 phosphorylation was accompanied by an increase in its ability to trans-activate target gene expression. The results demonstrate that the differential transcriptional expression of cytochrome c, through sequential transcription factor phosphorylations, leads to enhanced mitochondrial respiratory capacity upon serum-induced entry to the cell cycle.Entry into the cell cycle requires energy in the form of ATP for the execution of a number of regulatory and metabolic events. Protein synthesis consumes large amounts of cellular energy and is required for entry into S phase (1). In quiescent 3T3 fibroblasts, cellular protein content increases within 4 -5 h of serum stimulation and precedes DNA replication by several hours (2). Nontoxic inhibition of mitochondrial respiratory function inhibits progression to G1 in parallel with a reduction in cellular ATP (3). Protein synthesis (1) and degradation (4) as well as the depolymerization of the microtubular network during interphase (5) all depend upon the intracellular ATP concentration. ATP has also been implicated in the regulation of cyclin-dependent kinases, which in turn control cell proliferation (6).

TALE Homeodomain Proteins Regulate Gonadotropin-releasing Hormone Gene Expression Independently and via Interactions with Oct-1

“…Thus, tissuespecific expression in this rare cell type may be promoted by a unique combination of these broadly expressed proteins. The contribution of Pbx proteins to tissue-specific expression in a combinatorial manner has been described by several studies (52,53). For example, the pancreatic cell-specific activity of the homeodomain factor Pdx1 changes due to interactions with TALE proteins.…”

The dynein light chain 8 binding motif of rabies virus phosphoprotein promotes efficient viral transcription

“…Interaction with the tricho-rhinophalangeal syndrome 1 protein inhibits the suppressor activity of tricho-rhino-phalangeal syndrome 1 and increases the transcriptional activity of GATA-consensus sequences. LC8 was also shown to interact with nuclear respiratory factor 1, which has been shown to be involved in the regulation of cytochrome c expression and mitochondrial DNA transcription (20).…”

“…Likewise, the interaction of LC8 with P53 binding protein 1 regulates the nuclear distribution of p53-binding protein 1 and p53 (19). In fact, LC8 binds to several transcription factors, including nuclear respiratory factor 1 (20) and Drosophila swallow (21).…”

Regulation and Quantification of Cellular Mitochondrial Morphology and Content

“…NRF-1 binds to the recognition site in the target gene promoter region, as a homodimer, and activates transcription of the gene [72,73]. NRF-1 DNA binding and trans-activation function is enhanced by serine phosphorylation of its N-terminal domain [74,75]. NRF-1 recognition sites are found in in the proximal promoter of ubiquitously expressed genes [76], many of which are involved in mitochondrial biogenesis and metabolism [77].…”