Formation of 11 beta-hydroxysteroids requires the integrity of the microfilament network in adrenocortical cells

Role of the cytoskeleton in the secretory response of the frog adrenal gland to calcitonin gene-related peptide

We have previously shown that calcitonin gene-related peptide (CGRP) stimulates the secretion of corticosterone and aldosterone from the frog adrenal gland in vitro. The aim of the present study was to investigate the role of cytoskeletal elements in the stimulatory effect of CGRP on corticosteroid production. Perifusion of adrenal explants with the microfilament-disrupting agent cytochalasin B (5 x 10(-5) M) induced a reversible inhibition of the spontaneous secretion of corticosterone and aldosterone, and markedly reduced the stimulatory effect of frog CGRP (3 x 10(-7) M) on corticosteroid release. In contrast, administration of the antimicrotubular agent vinblastine (10(-5) M) and the intermediate filament inhibitor beta-beta' iminodipropionitrile (10(-3) M) had no significant effect on either spontaneous or CGRP-evoked steroid secretion. Taken together, these data provide the first evidence for the involvement of microfilaments in CGRP-induced corticosteroid secretion. In contrast, microtubules and intermediate filaments are not implicated in the mechanism of action of CGRP.

Involvement of the cytoskeleton in the mechanism of action of endothelin on frog adrenocortical cells

In a previous report, we have shown that endothelin-1 (ET-1) is a potent stimulator of corticosterone and aldosterone secretion by frog adrenocortical cells. In the present study, we examine the possible involvement of cytoskeletal elements in the mechanism of action of ET-1 on corticosteroid secretion from frog adrenal gland. The microfilament disrupting agent cytochalasin B (5 x 10(-5) M) induced a reversible inhibition of the spontaneous secretion of corticosteroid and blocked the response of adrenocortical cells to ET-1 (5 x 10(-9) M). In contrast, the antimicrotubular agent vinblastine (10(-5) M) and the intermediate filament inhibitor beta-beta' iminodipropionitrile (10(-3) M) had virtually no effect on both spontaneous and endothelin-induced steroidogenesis. Taken together, these results indicate that, in the frog adrenal gland, the integrity of the microfilament network is required for the corticotropic activity of ET-1 whereas microtubules and intermediate filaments are apparently not involved in the mechanism of action of ET-1.

Effects of selective disruption of cytoskeletal elements on steroid secretion by human adrenocortical slices

The role of the cytoskeleton in corticosteroid secretion in normal human adrenal gland was investigated in vitro, using the perifusion technique and confocal laser scanning microscopy. Vinblastine, which selectively disrupted microtubules in adrenocortical cells, did not modify the basal release of cortisol but induced a 58% inhibition of the response to adrenocorticotropic hormone (ACTH). In contrast, vinblastine did not alter dibutyryl adenosine 3',5'-cyclic monophosphate (DBcAMP)-induced steroid secretion. Cytochalasin B treatment caused disappearance of microfilaments and blocked the stimulatory action of ACTH and DBcAMP on cortisol secretion. beta,beta'-Iminodipropionitrile disorganized the cytokeratin intermediate filaments but did not alter spontaneous and ACTH-evoked cortisol release. These results, which provide the first evidence for an action of cytoskeleton inhibitors on cortisol release from normal human adrenocortical cells, show that microtubules are involved in the mechanism of action of ACTH at a step preceding adenosine 3',5'-cyclic monophosphate formation, whereas microfilaments are involved in a late and common step of adrenal steroidogenesis.

Actin cytoskeletal network in aging and cancer

The cytoskeleton is being recognized as an important modulator of metabolic functions of the cell. The actin cytoskeletal network, in particular, is involved in events regulating cell proliferation and differentiation. The state of actin in a variety of cell types is regulated by signals arising from the cell surface through a wide spectrum of interactions. In this review, we explore the role of actin cytoskeletal network in a series of events which are known to influence cell proliferation and differentiation. These include interaction of actin network with extracellular matrix proteins, cell surface membranes, second messengers, cytoplasmic enzymes and the nucleus. Because of the involvement of the actin network in such diverse interactions, we propose that alterations in the actin cytoskeletal function may be an important aspect of generalized decrease in cellular functions associated with aging. Preliminary data indicate that alterations in the cytoskeletal network do occur in cells obtained from older individuals. Alterations in actin state are also reported during malignant transformation of cells in culture, and in naturally occurring tumors. Taken together, the existing data seem to suggest that changes in the actin cytoskeletal network may be a part of the aging process as well as malignant transformation. Therefore, the study of the actin cytoskeletal network and its regulation has the potential to yield important information regarding cellular senescence and neoplastic transformation.