Attachment of ribosomes to endoplasmic membranes in mouse pancreas. Degranulation in vivo caused by the inducers of autophagocytosis neutral red, vinblastine, puromycin, and cadmium ions, and prevention by cycloheximide

Autophagic proteolysis: control and specificity

The rate of proteolysis is an important determinant of the intracellular protein content. Part of the degradation of intracellular proteins occurs in the lysosomes and is mediated by macroautophagy. In liver, macroautophagy is very active and almost completely accounts for starvation-induced proteolysis. Factors inhibiting this process include amino acids, cell swelling and insulin. In the mechanisms controlling macroautophagy, protein phosphorylation plays an important role. Activation of a signal transduction pathway, ultimately leading to phosphorylation of ribosomal protein S6, accompanies inhibition of macroautophagy. Components of this pathway may include a heterotrimeric Gi3-protein, phosphatidylinositol 3-kinase and p70S6 kinase. Recent evidence indicates that lysosomal protein degradation can be selective and occurs via ubiquitin-dependent and -independent pathways.

Dynamics of vinblastine-induced autophagocytosis in murine pancreatic acinar cells: influence of cycloheximide post-treatments

Accumulation of autophagic vacuoles (AVs) was monitored by electron microscopic morphometry in murine pancreatic acinar cells during the 5-hr period after a single injection of vinblastine (VBL). The expansion of the autophagic compartment (AC) occurred in two waves. AVs accumulated in the first 90 min and regressed in the next hour, but thereafter AC expanded again, and 5 hr following the VBL injection, as much as 5.3% of the cytoplasmic volume was found sequestered into the AC. The high rates of accumulation of AVs indicated that VBL stimulated AV formation (segregation) during both expansion phases. To have a deeper insight into the dynamics of the process segregational inhibitor cycloheximide (CHI) was given 1 and 3 hr after VBL and the subsequent regression of the AC and its subcompartments (i.e., early, advanced, and late AVs) were measured during the next 90 min. We found that regression of AVs was fast in the first expansion and slowed down in the second expansion phase during which only early AVs regressed. CHI proved to be a fast and effective inhibitor of autophagic segregation, whether it was given before, simultaneously, or after the VBL injection. The aforementioned results argue for a dual mode of action of VBL (i.e., a prompt stimulation of segregation and a delayed retardation of AV maturation). The two effects of the alkaloid prevail differently along the time course. A further analysis of the behavior of the AC subcompartments showed that CHI perhaps inhibits segregational step(s) occurring prior to the actual formation of the autolysosomes.

Time course of the quantitative changes in the autophagic-lysosomal and secretory granule compartments of murine liver cells under the influence of vinblastine

The dynamics of the transient expansion of the autophagic-lysosomal (ALC) and secretory granule (SGC) compartments in mouse liver cells were monitored by electron microscopic morphometry after a single injection of 10 mg/kg b.w. vinblastine sulfate (VBL). Initially (first phase) the cytoplasmic volume fractions of the total ALC and its subcompartments, as well as of the SGC increased by an order of magnitude and peaked at the second h. In the second phase, all the aforementioned compartments regressed gradually, approaching their normal size between 12 and 36 h after VBL injection. Analysis of the dynamic changes in fractional volumes of subcompartments of the ALC showed that early autophagic vacuoles (AV1) were the first to enlarge. Advanced AVs (AV2) reacted 30 min later and a further 30 min time lag was required before late autolysosomes, appearing as dense bodies (DB), started to expand. We regard these data as kinetic proof that the bodies of the later reacting subcompartments developed from the earlier reacting ones. The time lag between the expansion of AV1 and AV2 subcompartments may be explained by a period of retardation of conversion of nascent autophagosomes (AV1) to autolysosomes (AV2) which is known to occur normally by fusion of AV1 with enzyme-carrying lysosomes. However, transformation of AV1 to AV2 and later to DB resumed after the respective time lags. Moreover, our quantitative data lend support to the view that segregation of cytoplasmic portions into newly-formed autophagosomes was stimulated by VBL, at least in the first 2 h of treatment. The expansion of ALC accelerated during this period and led to an obvious overload of the lysosomal apparatus.(ABSTRACT TRUNCATED AT 250 WORDS)

Lysosomal movements during heterophagy and autophagy: with special reference to nematolysosome and wrapping lysosome

Recent studies on lysosomal movements during heterophagy and autophagy performed in our laboratory for the past several years were reviewed; methods for the investigation of lysosomes and the cytoskeleton in these studies mainly involved electron microscopic cytochemistry. Lysosomal movements during heterophagy were observed in cultured rat alveolar macrophages taking up horseradish peroxidase (HRP) and rat peroxidase-antiperoxidase (PAP) by fluid-phase pinocytosis and adsorptive pinocytosis, respectively. A characteristic lysosomal change which was induced by the pinocytosis was the appearance of long, threadlike lysosomes (nematolysosomes) in the cytoplasm. The effects of actin filament destabilizer and antimicrotubular drug on lysosomal changes revealed that the appearance of nematolysosomes was dependent on the presence of both actin filaments and microtubules. The close morphological relationship between lysosomes and cytoskeletal elements, such as actin filaments and microtubules in the alveolar macrophages, supports the participation of the cytoskeletal system in the regulatory mechanism of lysosomal movements. In the study of the lysosomal wrapping mechanism (LWM), which is one type of lysosomal movement that occurs during autophagy, it was found that the occurrence of LWM was dependent on energy--namely, the supply of ATP--and on the presence of actin filaments. However, deconstruction of microtubules induced or favored the occurrence of LWM. It is conceivable that the LWM is also related to the cytoskeletal system. We conclude that intracellular dynamics of lysosomes during heterophagy and autophagy are largely a consequence of complicated modulation by the cytoskeletal system.

Morphometric evaluation of the turnover of autophagic vacuoles after treatment with Triton X-100 and vinblastine in murine pancreatic acinar and seminal vesicle epithelial cells

Large numbers of autophagic vacuoles were found in murine pancreatic acinar and seminal vesicle epithelial cells following the administration of Triton X-100 or vinblastine for 4 h. The autophagic vacuoles disappeared rapidly from the cells after the administration of cycloheximide to animals pretreated with Triton X-100. The decay in seminal vesicle cells appeared to follow first-order kinetics with an estimated t1/2 of 8.7 min. The regression in pancreatic cells was equally rapid and less than half the initial volume of autophagic vacuoles was found at the 12th min after cycloheximide injection. This time, the decay curve appeared to be linear rather than exponential. Our data, together with the work of others, support the view that the average half-life of autophagic vacuoles is a fairly constant parameter kept within the range of 6-9 min in various types of mouse and rat cell when the late steps of autophagocytosis (i.e. the fusion of autophagosomes and lysosomes and the degradation within lysosomes) are not affected. The regression of autophagic vacuoles was slow in mice pretreated with vinblastine (t1/2 of about 27-30 min) suggesting that this drug slows down the turnover of autophagic vacuoles. Morphometric evaluation of the regression of the autophagic vacuole compartment after cycloheximide treatment can be used as a tool to distinguish between treatments which elevate the amount of autophagic vacuoles within the cells by increasing the rate of sequestration from those which expand the autophagic vacuole compartment by causing accumulation of autophagic vacuoles as a result of blockade of the late steps of the autophagic process.

Autophagocytosis in mouse seminal vesicle cells in vitro. Temperature dependence and effects of vinblastine and inhibitors of protein synthesis

Spontaneous autophagocytosis was observed in mouse seminal vesicle cells during incubation for 2 h in vitro. The number of autophagic vacuoles formed was greatest at 37 degrees C and decreased when the temperature was lowered. At 22 degrees C it reached the near-zero value characteristic of non-incubated control cells. Incubation of the cells at 37 degrees C in the presence of 0.1 mg/ml vinblastine sulfate resulted in a marked increase in the number of autophagic vacuoles, but the drug was ineffective at 22 degrees C. Puromycin (10(-3) M) exerted no influence on spontaneous autophagocytosis, but cycloheximide in concentrations from 10(-7) M to 10(-3) M inhibited both spontaneous and vinblastine-induced autophagocytosis. The formation of tubulin paracrystals in vinblastine treated cells was not prevented either by low (22 degrees C) temperature or in the presence of cycloheximide.

Acute and persistent ultrastructural changes in rat liver after a single dose of 2-acetylaminofluorene: effect of co-administration of cycloheximide

Electron microscope studies have been made of rat hepatic cell morphology, 24 hr, 48 hr and 24 weeks after a single intragastric dose of 2-acetylaminofluorene (2-AFF), alone or together with a single s.c. dose of cycloheximide (CHM). CHM prevents the acute perinuclear glycogen pooling, peripheral displacement of cytoplasmic organelles and nuclear shrinkage induced by 2-AAF. However, the induction by 2-AAF of changes in the granular endoplasmic reticulum, mitochondria and bile canaliculi is enhanced by co-administration of CHM. These changes persist for at least 24 weeks and are similar to those induced during 2-AAF hepatocarcinogenesis and observed in hepatocellular tumours. In view of the similar results obtained in previous studies with the azocarcinogen, 3'-methyl-4-dimethylaminoazobenzene, the possibility is discussed that these persistent changes might be associated with the initiation phase of neoplastic induction.

Ultrastructural and functional changes in pancreatic acinar cells during autolysis

Effects of anoxemic cell injury on rat pancreatic acinar cells were studied in a preparation where tissue samples were incubated at temperature between 18-20 degrees C in a moist atmosphere for 0, 0.5, 1, 3, 6, 12, and 24 h in vitro. Electron microscopy revealed that disintegration of acinar cells began by swelling of various cell compartments and gradual breakdown of cell membranes. Zymogen granules remained morphologically intact for at least 3 h. There were no signs of increased autophagic activity during the period of observation. Myelin figures and other membranous remnants of disintegrated cells, together with individual cells and cell organelles whose morphology was relatively well preserved were seen even after w4 h incubation. The secretory response of acinar cells to pancreozymin stimulation, as measured by amylase release into the incubation medium in vitro, decreased progressively closer to zero during 12 h autolysis. No active trypsin could be detected in the tissue samples during the 24 h observation time. It was concluded that during hypoxic autolysis at room temperature between 18-20 degrees C in vitro: 1. Acinar cell disintegration results from breakdown of cellular membranes, 2. autophagocytosis is not involved, 3. most of zymogen granules remain morphologically intact even at the time when cell membranes show evidence of damage, 4. there is no trypsin activation taking place in the tissue, and 5. the acinar cells are capable of responding to secretory stimulation for 3 to 6 h after removal of the tissue from the experimental animal.

A morphometric study of the inhibition of autophagic degradation during restorative growth of liver cells in rats re-fed after starvation

In the parenchymal cells of the liver of adult male rats re-fed on the evening of the fifth day after a period of absolute starvation, a nearly complete absence of autophagic vacuoles (AV) has been found by the morphometric determination of the fractional cytoplasmic volume of AV. The mean value for that parameter increased only gradually during periods of re-feeding. The value was found to be in the range of the control values only on, or after, the fifth day of re-feeding. As in previous experiments, in the control animals the number of AV was again found to be dependent on a circadian rhythm with maxima during the light, and minima during the dark, periods. This rhythm reappeared in the period of re-feeding without a shift in phase. In the controls as well as in the re-fed animals the "segregated fraction" was highest for microbodies, intermediate for mitochondria and glycogen, but rather low for the remaining components of the cytoplasm. It is suggested that the long term inhibition of cellular autophagy, found in the present study, plays an important role in the restorative cellular growth of the liver during the recovery from the atrophy induced by starvation.