Protein renewal in mitochondria as revealed by electron microscope radioautography

Opposite effects of microtubule-stabilizing and microtubule-destabilizing drugs on biogenesis of mitochondria in mammalian cells

Distribution of mitochondria as well as other intracellular organelles in mammalian cells is regulated by interphase microtubules. Here, we demonstrate a role of microtubules in the mitochondrial biogenesis using various microtubule-active drugs and human osteosarcoma cell line 143B cells and rat liver-derived RL-34 cells. Depolymerization of microtubules by nocodazole or colchicine, as well as 2-methoxyestradiol, a natural estrogen metabolite, arrested asynchronously cultured cells in G(2)/M phase of cell cycle and at the same time inhibited the mitochondrial mass increase and mtDNA replication. These drugs also inhibited the mitochondrial mass increase in the cells that were synchronized in cell cycle, which should occur during G(1) to G(2) phase progression in normal conditions. However, stabilization of microtubules by taxol did not affect the proliferation of mitochondria during the cell cycle, yet a prolonged incubation of cells with taxol induced an abnormal accumulation of mitochondria in cells arrested in G(2)/M phase of cell cycle. Taxol-induced accumulation of mitochondria was not only demonstrated by mitochondria-specific fluorescent dyes but also evidenced by the examination of cells transfected with yellow fluorescent protein fused with mitochondrial targeting sequence from subunit VIII of human cytochrome c oxidase (pEYFP) and by enhanced mtDNA replication. Two subpopulations of mitochondria were detected in taxol-treated cells: mitochondria with high Delta(psi)(m), detectable either by Mito Tracker Red CMXRos or by Green FM, and those with low Delta(psi)(m), detectable only by Green FM. However, taxol-induced increases in the mitochondrial mass and in the level of acetylated (alpha)-tubulin were abrogated by a co-treatment with taxol and nocodazole or taxol and colchicine. These data strongly suggest that interphase microtubules may be essential for the regulation of mitochondrial biogenesis in mammalian cells.

Autoradiographic study of labeled amino acid incorporation into clear cells of mouse epididymis

Protein synthesis in clear cells of mouse epididymis was investigated by quantitative autoradiography after intravenous injection of tritium-labeled leucine, arginine, and lysine. Labeling occurred in the cytoplasm after 2 min and persisted for 240 min after injection. The silver grains were located not only on the organelles involved in protein synthesis (rough endoplasmic reticulum, Golgi apparatus) but also on those implicated in reabsorption (multivesicular bodies). Quantitative analysis showed a peak in radioactivity in the rough endoplasmic reticulum, at 10-15 min, followed by a peak in the multivesicular bodies at 15 min. Labeling of the Golgi apparatus reached its maximum at 30 min. Radioactivity in the apical plasma membrane remained low and relatively stable. These results indicate that clear cells synthesize proteins, a large part of which is transferred to the multivesicular bodies that participate in the cellular absorptive function.

Rapid axoplasmic transport of free leucine

Axoplasmic transport of free 3H-leucine has been studied in vivo in the pike olfactory nerve following application of labeled leucine to the olfactory mucosa. A considerable amount of free 3H-leucine is transported at constant velocity along the axon in the form of a distinct peak. The maximum transport velocity for free 3H-leucine is the same as for rapidly transported 3H-protein (130 and 135 mm/day, respectively, at 19 degrees C). Microtubule inhibitors block or significantly reduce the amount of free 3H-leucine transported, but do not influence the transport velocity. Disruption of the oxygen supply abolishes free 3H-leucine transport, so that this phenomenon cannot be explained by diffusion. The amount of free leucine in the rapidly moving peak decreases with time and distance along the axon and is not detectable after 5 h or more. The transported 3H-leucine is not derived from the circulation or from proteolysis of rapidly transported proteins. This study may help to resolve the controversy over the axoplasmic transport of free amino acids since it shows that free 3H-leucine is transported rapidly but does not travel by rapid axoplasmic transport to the end of axons longer than about 30 mm.

Glycogenosis type I (glucose 6-phosphatase deficiency): I. Ultrastructural morphometric analysis of juvenile liver cells

The essential biochemical characteristic of von Gierke's disease is an inborn glucose-6-phosphatase deficiency and glycogen storage in the liver and kidney. This expresses itself morphometrically as an increased volume of glycogen per unit volume of the hepatocellular cytoplasm. Since glucose-6-phosphatase activity in patients studied is practically at the zero level, and the endoplasmic reticulum loses a large part of its membrane values, we conclude that the remaining endoplasmic reticulum represents glucose-6-phosphatase free membranes. A typical structural feature of the endoplasmic reticulum in von Gieke's disease is the appearance of "double contoured vesicles" (= pockets). These vesicles comprise approximately 3,5% of the total membrane system. The mitochondria play an important role in glycolysis and glycogen synthesis. It is thus to be expected that these organelles change in terms of their morphometric parameters in the course of glycogenosis type I. An important point in this direction is numerical mitochondrion reduction in combination with an unchanged mitochondrial volume.

The proliferative response of hepatic peroxidomes of neonatal rats to treatment with SU-13 437 (nafenopin)

The repeated administration of the hypolipidemic agent Su-13 437 (nafenopin) to neonatal rats roughly doubled the number of peroxisomes in the liver tissue and caused a sixfold volumetric expansion of the peroxisomal compartment. During the proliferative response, the size-distribution of the peroxisomes was reversibly altered, enlarged particles appearing in numbers varying according to the dose given. By means of a new method for quantitative autoradiography, it was shown that (a) the concentration of silver grains over peroxisomes was comparable to that found over the endoplasmic reticulum; (b) the peak incorporation of [3H]arginine into the peroxisomes was dealyed in comparison with that into the endoplasmic reticulum; (c) the label, once incorporated into the expanding peroxisomal compartment, displayed the same shift to large particles as did the whole population. These results are compatible with the biosynthetic pathway for peroxisomal catalase proposed earlier (cf. reference 12), and with the notion that the drug-induced size-shift might have resulted from progressive growth of a particular class of peroxisomes formed in the presence of the agent. Evidence is presented to show that during the recovery period the larger peroxisomes are removed preferentially.

Investigations on the turnover of adrenocortical mitochondria. VI. An autoradiographic study of the effect of ACTH on the radioactivity decay in the mitochondrial compartment from the zona fasciculata of 3H-thymidine injected rats

The radioactivity decay of the mitochondrial compartment from the zona fasciculata of the adrenal cortex of 3H-thymidine-injected rats was followed by high resolution autoradiography. The number of days in which the radioactivity of the mitochondrial compartment was reduced to a half was calculated from the semilogarithmic plots of radioactivity versus time. Since DNA is a very stable molecule, it was assumed that this parameter can be an estimate of the half-life of adrenocortical mitochondria. The half-life of mitochondria from the zona fasciculata of the normal rat averaged 11.17 days, and ACTH was found to increase significantly this figure to about 15 days. It is hypothesized that the ACTH-elicited stimulation of the growth of rat adrenal zona fasciculata mitochondria involves not only hypertrophy and proliferation of the organelles (Nussdorfer et al., '74b), but also the slowing down of the degeneration rate of mitochondria.

Studies on in vitro carcinogenesis. I. Autoradiographic and biochemical study on the incorporation of labelled methylcholantrene into mouse embryonic cells

The incorporation of radioactive labelled Methylcholanthrene into CBA/T6T6 mouse embryonic fibroblast cultures was studied by using light and electronmicroscopic autoradiographic and also liquid scintillation counting techniques. During 24 hrs treatment time at the applied Methylcholanthrene concentrations (0.01-2.5 mug/ml) the proportion of cells labelled with 3H-Methylcholanthrene and the number of grains above the cells showed a relationship with the duration of treatment and also with the doses. Up to 24 hrs all cells were labelled after treatment with 2.5 mug/ml whereas at 0.01 and at 0.1 mug/ml concentrations Methylcholanthrene could have been detected only 2 and 10% of the cell population resp. The presented results suggested that labelling index reached saturation level earlier than the average number of grains. Electronmicroscopic autoradiography revealed a rather even distribution of grains and there were no signs for preferential binding site of Methylcholanthrene. Biochemical separation showed that 59 and 44% of the radioactivity was bound to macromolecules at 1 and 24 hrs after commencing treatment resp.

Autoradiographic studies on the protein synthesis and the distribution of the newly synthesized proteins in oligodendroglial cells

The protein-synthesizing activity of oligodendroglial cells in the rat hippocampus as well as the migration of the newly synthesized proteins within these cells were examined by means of light and microscopic autoradiography when injecting 3H-leucine into the lateral ventricle. The autoradiographs of oligodendroglial cells were compared with the autoradiographs on hippocampal pyramidal cells of the same area. According to the quantitative evaluation of the autoradiographs the protein-synthesizing activity of the oligodendrocytes equals or may even exceed that of the pyramidal cells. In oligodendroglial cells most of the newly synthesized proteins migrate very rapidly from the rough-surfaced endoplasmic reticulum into the cisternae of the Golgi apparatus and disappear continuously. The proteins disappear from the Golgi apparatus simultaneously with the decrease in the radioactive concentration of the perikaryon.