The effects of ACTH on acid phosphatase activity in endosomes, GERL and lysosomes of cultured adrenal tumor cells

Microtubules, organelle transport, and steroidogenesis in cultured adrenocortical tumor cells. 2. Reversibility of taxol's inhibition of basal and ACTH-induced steroidogenesis is unaccompanied by reversibility of taxol-induced changes in cell ultrastructure

Taxol inhibits the basal and ACTH-stimulated steroidogenesis of cultured mouse adrenocortical tumor cells, presumably by preventing the arrival of cholesterol in mitochondria. In these cells, taxol polymerizes and rearranges microtubules, disperses SER masses, disrupts the Golgi, and impedes the formation of cholesterol-containing lysosomes. However, taxol's alterations in ultrastructure appear likely to permit both a microtubule-based organelle transport proposed to bring mitochondria of unstimulated cells close to alternate sources of cholesterol--the SER and lipid droplets--and postulated ACTH-caused increases in these encounters. Conceivably, taxol may prevent the transfer of cholesterol from the SER and lipid droplets to mitochondria, once the meetings are achieved. To investigate this possibility, we determined the reversibility of taxol's ultrastructural effects and inhibition of steroidogenesis. Primary cultured adrenal tumor cells were incubated for 4 hr with and without ACTH (10 mU/ml). with taxol (50 micrograms/ml), and with ACTH and taxol 50 simultaneously. Some cultures from each set were washed with fresh medium and re-incubated for 1.5 hr. with and without ACTH. Media taken from cultures at the ends of pre- and post-washout incubations were analyzed for the presence of secreted steroids. Sample cultures were fixed for electron microscopy at the ends of both incubations. Data derived from pre-washout incubations confirmed previous reports of taxol's ultrastructural changes and inhibition of steroidogenesis. When cells recovered from taxol in the absence of ACTH, the inhibition of steroidogenesis was completely reversed. In the presence of ACTH, ex-taxol-treated cells demonstrated a "rounding up' and an increased steroid production that are characteristic responses to the hormone. However, in all cases, there was a persistence of taxol's alterations in organelle numbers and arrangements. Our findings establish that the ultrastructural effects of taxol which we recorded cannot prevent mitochondria of unstimulated and ACTH-stimulated adrenal tumor cells from gaining cholesterol. They strengthened the possibility that in pre-washout incubations, taxol allowed organelle motility to bring mitochondria adjacent to cholesterol-containing SER tubules and lipid droplets, but inhibited steroidogenesis by preventing the cholesterol transfer. Taxol might limit the availability of a protein required for the transfer, an effect not visible in our electron micrographs.

Microtubules, organelle transport, and steroidogenesis in cultured adrenocortical tumor cells. 1. An ultrastructural analysis of cells in which basal and ACTH-induced steroidogenesis was inhibited by taxol

In adrenocortical cells, the first step in the enzymatic processing of cholesterol to steroid end products occurs in the mitochondria. ACTH increases mitochondrial cholesterol and steroidogenesis. In cultured mouse adrenocortical tumor cells, microtubule-based organelle motility may increase the proximity of mitochondria to the SER, lipid droplets and endoscome-derived lysosomes, thereby facilitating the transfer of cholesterol from these organelles to the mitochondrial outer membrane. ACTH may increase opportunities for the transfer by promoting organelle motility and by increasing the number of lysosomes. Taxol, a microtubule polymerizer, inhibits basal and ACTH-induced steroidogenesis in these cells, presumably at the step where mitochondria obtain cholesterol. We examined the ultrastructure of taxol-treated, unstimulated and ACTH-stimulated cells, seeking alterations which conceivably could interefer with the proposed organelle transport and encounters, and thus correlate with taxol's inhibition of steroidogenesis. Primary cultured cells were incubated in serum-containing medium for 4 hr with and without ACTH (10 mU/ml), with 10 micrograms/ml and 50 micrograms/ml of taxol, and with ACTH and taxol 10 or taxol 50 simultaneously. Culture media were analyzed for the presence of secreted steroids at the end of 1, 2, and 4 hr of incubation. At the end of the fourth hour, unstimulated cells and cells treated with ACTH, taxol 50, and both agents simultaneously, were fixed and processed for EM. Taxol inhibited basal and ACTH-induced steroidogenesis in a dose-dependent fashion. In both unstimulated and ACTH-stimulated cells, taxol 50 formed numerous microtubule bundles, but did not markedly change the distribution of mitochondria and lipid droplets. SER tubules, and clusters of Golgi fragments, endosomes, and lysosomes appeared to be translocated towards the cell periphery along some of the microtubules. Taxol permitted an ACTH-induced cell rounding and microfilament rearrangement considered to facilitate organelle motility. Our data indicate that taxol disrupts the formation of lysosomes by these adrenal cells, but it seemed unlikely that taxol's ultrastructural effects could prevent organelle transport proposed to cause meetings between mitochondria and the SER or lipid droplets, or prevent ACTH-caused increases in these encounters. Taxol may instead prevent the transfer of lipid droplet or SER-contained cholesterol to adjacent mitochondria, by a means not detectable in our electron micrographs.

Autophagic mechanisms in diethylnitrosamine-induced tracheal papillomas of Syrian golden hamster

Treatment with diethylnitrosamine induced tracheal papillomas in the Syrian golden hamster. Enlarged lysosomes (EL) occurred in a particular type of cells situated at the periphery of tumor lobules. The differentiated phenotype of these cells in secretory in nature. As to the significance of EL occurrence, two possibilities are considered: 1) EL formation is a part of disposal mechanisms after the autophagocytosis of undischarged secretory products by secondary lysosomes and 2) ELs are indicative of sublethal injury to cells of the outermost layer of tracheal papillomas.

Cinemicrographic observations of cultured adrenocortical tumor cells. Dynamic responses to ACTH and cytochalasin B

ACTH increases the basal steroidogenic activity of cultured adrenocortical tumor cells, whereas moderate-high doses of cytochalasin B (CB) inhibit both basal and ACTH-induced steroidogenesis. Previous ultrastructural studies have revealed that ACTH rearranges microfilaments in these adrenal cells, whereas CB causes microfilaments to aggregate into felt-like masses. It has been postulated that the ACTH effects may facilitate organelle motility and increase organelle interactions that are required for steroid biosynthesis, and that the CB-created "foci" may impede or prevent the organelle meetings. To shed light on these possibilities, we have employed 16 mm cinemicrography of unstimulated adrenal tumor cells and cells incubated for 1-2 h with ACTH (10 mU/ml), or low (10 micrograms/ml), or high (50 micrograms/ml) doses of CB. ACTH caused initial increases in membrane ruffling and a "flurry" of particle (organelle) activity above that seen in unstimulated cells. The stimulated cells then retracted from each other and began their characteristic "rounding up" in response to the hormone. Particles appeared to move towards the nucleus, and in fully-rounded cells were extremely congested. Steroid production rose several fold above basal levels. CB10 produced slight-marked cell convexities, nearly stopped particle motility and inhibited steroid production moderately. CB50 produced an asymmetrical, spidery cell form, stopped membrane ruffling and particle motility and abolished steroidogenesis. After a washout of CB50, particle motility resumed nearly immediately. Our CB data indicate that associations between particles, presumably between mitochondria and various sources of cholesterol, are prerequisite for basal steroidogenesis in the adrenal tumor cells. In ACTH-stimulated cells, increases in steroid output correspond with increased opportunities for particle associations. These opportunities appear to arise directly or indirectly from ACTH effects on microfilaments. The responses of microfilaments to the hormone may be particularly intense in tumorous forms. By these means, the cells may express their differentiated function, although their cytoplasm has a distinctly unspecialized appearance.