Down-regulation of the Mitochondrial Translation System during Terminal Differentiation of HL-60 cells by 12-O-Tetradecanoyl-1-phorbol-13-acetate

Abstract

Mitochondrial (mt) biogenesis depends on both the nuclear and mt genomes, and a coordination of these two genetic systems is necessary for proper cell functioning. Little is known about the regulatory mechanisms of mt translation or about the expression of mt translation factors. Here, we studied the expression of mt translation factors during 12-O-tetradecanoyl-1-phorbol-13-acetate (TPA)-induced terminal differentiation of HL-60 cells. For all mt translation factors investigated, mRNA expression was markedly downregulated in a coordinate and specific manner, whereas mRNA levels for the cytoplasmic translation factors showed only a slight reduction. An actinomycin D chase study and nuclear run-on assay revealed that the TPAinduced decrease in mt elongation factor Tu (EF-Tumt) mRNA mainly results from decreased mRNA stability. Polysome analysis showed that there was no significant translational control of mt translation factor (EF-Tumt, ribosomal proteins L7/L12mt and S12mt) mRNA expression during differentiation. Thus, the decreased protein level of one of these mt translation factors (EF-Tumt) simply reflects its decreased mRNA level. It was also demonstrated by pulse labeling of mt translation products that the down-regulation of mt translational activity is actually associated with down-regulated mt translation factor expression during cellular differentiation. Our results illustrate that the regulatory mechanisms of mt translational activity upon terminal differentiation (in response to the growth arrest) is different to that of the cytoplasmic system, where the control of mRNA translational efficiency of major translation factors is the central mechanism for their down-regulation.Mitochondrial (mt) biogenesis depends on both the nuclear and mitochondrial genomes (1, 2). Mitochondrial DNA (mtDNA) 1 is present in 10 3 -10 4 copies per cell and encodes 13proteins, which are critical subunits of the respiratory chain complexes I, III, IV, and V, as well as 2 ribosomal RNAs and 22 transfer RNAs, which are necessary for mitochondrial protein synthesis (3). Nuclear genes encode the majority of the respiratory chain subunits and all protein components necessary for maintenance and expression of mtDNA. Mitochondria play pivotal roles in eukaryotic cells in producing cellular energy and essential metabolites as well as in controlling apoptosis by integrating numerous death signals (4). Recently, evidence has emerged that mitochondria are also implicated in the regulation of cell growth and differentiation. Inhibition of mitochondrial activity either by deleting mtDNA (rho°cells) or by blocking translation in the organelle has been shown to arrest or decrease proliferation in various cell lines (5-9). Mitochondrial protein synthesis inhibition is associated with the impairment of differentiation in different cell types, including mouse erythroleukemia (10) and mastocytoma cells (11), neurons (12), and human (13), avian (14), or murine myoblasts (15). The coordination of mitochondrial and nuclear genetic systems in t...

Megakaryocytic Differentiation of K562 Cells Induced by PMA Reduced the Activity of Respiratory Chain Complex IV

“…In addition, the mitochondria contain about 1000 kind of proteins, more than 98% of them are encoded by nuclear DNA, and they are synthesized in the cytoplasmic ribosomes, then transported to the mitochondria and sorted and located in various parts, this process is important to maintain the steady-state mitochondrial functions. It has been reported that in the 12-O-Tetradecanoyl-1-phorbol-13-acetate (TPA) -induced differentiation of HL-60 cells, the mitochondrial transport system was down-regulated [47]. Our research found that PMA treatment down-regulate the expression levels of Tim9 and Tim10 proteins.…”

Induction of ANGPTL4 expression in human airway smooth muscle cells by PMA through activation of PKC and MAPK pathways

“…PMA has been reported to regulate gene expression by transcriptional as well as post-transcriptional mechanisms. For example, the induction of VEGF by PMA in human keratinocytes depends on an AP-1 binding site in its promoter flanking region of the VEGF gene [49] while it regulates the expression of mitochondrial elongation factor Tu in HL60 cells at the level of RNA stability [50]. Our results show that PMA does not induce ANGPTL4 expression by increasing the stability of its respective mRNA.…”

Comprehensive detection of human terminal oligo-pyrimidine (TOP) genes and analysis of their characteristics

“…The translational controls were evaluated by sedimentation experiments. For this, mRNAs were extracted for every fraction of either sub-polysomes or polysomes (Figure 3A) before and after the TPA treatment in human HL-60RG cells (23) and the relative abundance of them was detected by semi-quantitative real-time PCR. Before the sedimentation experiment, the RNA levels (transcription level) of all 239 genes with and without TPA treatment (TPA+/TPA-) were measured by real-time PCR.…”

“…We used exactly the same methods and samples as those previously reported (23). Namely, HL-60 rapid growth cell (RG) derived from HL-60 cell lines was cultured.…”