Cyclic AMP and the differentiation of adrenal cortical cells grown in tissue culture

Basic fibroblast growth factor expression is regulated by corticotropin in the human fetal adrenal: a model for adrenal growth regulation

Human fetal adrenal growth after midgestation is very rapid and appears to be dependent upon pituitary adrenocorticotropin (ACTH) in vivo. We hypothesized that the regulation of fetal adrenal growth by ACTH is mediated by ACTH-stimulated local growth factor production. As we have found basic fibroblast growth factor (bFGF) to be a potent mitogen for human fetal adrenal cells in culture, we conducted studies to determine whether bFGF is synthesized by the human fetal adrenal gland and whether bFGF gene expression in primary cultures of human fetal adrenal cells is regulated by ACTH. Bioassayable bFGF-like activity was detected in extracts of whole human fetal adrenal glands and primary cultures of human fetal adrenal cells. Northern blot analysis of total RNA from whole human fetal adrenal glands revealed a characteristic 7-kilobase bFGF mRNA, indicating that the fetal adrenal bFGF bioactivity was most likely due to local synthesis. Slot blot and ribonuclease protection analysis showed that bFGF mRNA was present in very low amounts in total RNA from primary cultures of unstimulated human fetal adrenal cells but was increased 2- to 3-fold in cells exposed to 10 nM ACTH-(1-24) or 1 mM 8-bromoadenosine 3',5'-cyclic monophosphate for 24 hr. bFGF mRNA was localized to adrenocortical cells and not fibroblasts by in situ hybridization. bFGF mRNA was barely detectable in unstimulated cells, whereas it was markedly increased in cells exposed to either ACTH or 8-bromoadenosine 3',5'-cyclic monophosphate. These data support our hypothesis that the regulation of human fetal adrenal growth by ACTH at midgestation may be mediated by the stimulation of local growth factor production, and we suggest that bFGF may play a major role in this process.

The effects of corticotrophin (ACTH1-24), cyclic AMP and TPA (12-O-tetradecanoyl phorbol-13-acetate) on DNA replication and proliferation of primary rabbit adrenocortical cells in a synthetic medium

ACTH1-24 stimulated the parenchymal cells in cultures of rat adrenal cortex in serum-free synthetic HiWoBa 2000 medium to replicate DNA, enter mitosis and divide. But ACTH's principal mediator, cyclic AMP, was not a complete mitogen: the adenylate cyclase-stimulating cholera toxin and dibutyryl cyclic AMP stimulated parenchymal cells to replicate DNA but not to enter mitosis. Thus, there must have been an additional mediator of the response to ACTH1-24 that enabled the parenchymal cells to enter mitosis. This additional mediator might have been protein kinase C because a protein kinase C activator and cyclic AMP elevator, TPA, stimulated the adrenocortical parenchymal cells to replicate DNA, enter mitosis and divide.

The ultrastructure of functional mouse adrenal cortical tumor cells in vitro

Cells derived from a transplantable mouse adrenal cortical tumor maintain their differentiated function in vitro and secrete steroids in response to ACTH and other stimulatory agents. The cell line has been widely employed for various biochemical investigations but there have been few attempts to correlate this work with morphologic data. This communication describes the electron microscopic appearance of the tumor transplant in vivo and primary cultures derived from it at various intervals after the cells are placed in culture. Tumor cells in vivo bear considerable resemblance to normal adult mouse adrenal cortical cells. Organelles generally considered to be directly involved in steroid biosynthesis (mitochondria, smooth endoplasmic reticulum and lipid droplets) are not drastically altered. Certain modifications of the vasculature and cell membrane, seemingly related to steroidogenesis, are present in both the tumor and normal adrenal cortex. Within 2 days after the tumor cells are introduced to culture, their cytoplasm assumes a more simplified appearance. Smooth endoplasmic reticulum is less conspicuous and free ribosomes and polysomes are very abundant. Mitchondrial inner membranes are reorganized from a saccular arrangement in the cells in vivo into distinct lamellar cristae. The tumor cells now resemble undifferentiated embryonic adrenal cells, or cultured adrenal cells from various mammalian sources which have dedifferentiated in the absence of ACTH. In their morphologically unspecialized state, the normal cells are incapable of functional responses to ACTH. In contrast, the cultured, dedifferentiated tumor cells respond within minutes to this hormone and can demonstrate 5-20 fold increases in their basal steroid output. These data suggest that substantial steroidogenic activity can occur although the characteristic appearance of adrenal mitochondria is absent.

Transmission and scanning electron microscopic observations of mouse adrenocortical adenoma cells (Y-1) in non-stimulated and stimulated states

ACTH sensitive murine adrenocortical adenoma cells (Y-1) were examined by transmission and scanning electron microscopes under non-stimulated and stimulated conditions. They showed the ultrastructural characteristics which were fairly different from those of the original adrenocortical cells of LAF1 mice. The smooth-surfaced endoplasmic reticulum (sER) were poorly developed, and the mitochondrial cristae showed lamellar rather than tubular or tubulo-vesicular type. Administration of ACTH induced rounding-up of the Y-1 cells with slight increase in sER, BUt no mitochondria with vesicular inner structure appeared. The effects of dbcAMP on the morphology of the Y-1 cells were similar to those of ACTH except that the rounding-up occurred more rapidly and uniformly.

Membrane changes during cartilage maturation. Increase in 5'-nucleotidase and decrease in adenosine inhibition of adenylate cyclase

To examine the potential participation of the plasma membrane in differentiation, we studied the enzymatic activities of 5'-nucleotidase and adenylate cyclase as a function of chondrocyte maturation. 16-day-old chick embryo tibiae epiphyses were dissected into proliferative, growing and hypertrophying zones. Partially purified membrane fractions prepared by differential centrifugation from the respective tissue segments were assayed for enzymatic activity. Cell suspensions from the same segments were examined cytochemically for the presence of 5'-nucleotidase. The findings show that the 5'-nucleotidase activity of the chick embryo epiphyseal cartilage has the following characteristics: (a) it has a Km of about 25 muM for 5'AMP, and is inhibited by a mixture of 2' and 3'AMP (apparent Ki about 10(-4) M) and by AOPCP; (b) it is predominantly localized at the cell surface but is also detected in the cytoplasm and in association with nuclear heterochromatin; and (c) it increases 10-fold (on a DNA basis) during the maturation of the epiphyseal cartilage cells. The adenylate cyclase activity has these characteristics: (a) it does not change during chondrocyte maturation (on a DNA basis); (b) its susceptibility to adenosine inhibition decreases at least 10-fold. The implication of these findings relative to a possible role of adenosine in cellular communication is discussed.

The role of calcium in the inhibition of cAMP accumulation in epiphyseal cartilage cells exposed to physiological pressure

A hydrostatic pressure of 60g/cm sq (0.85 psi) inhibits the accumulation of cAMP in cells isolated from the proliferative zone of chick-tibia epiphyseal cartilage. The following findings indicate that this effect is mediated by a translocation of calcium: (i) the pressure enhances the cellular uptake of radiocalcium; (ii) the pressure effect on cAMP can be simulated by the calcium-ionophore A23187; (iii) the effects of pressure and A23187 are non-additive; (iv) the pressure effect is not produced in the presence of ethylenebis-(oxyethylenenitrilo)-pressure effect is not produced in the presence of ethylenebis-(oxyethylenenitrilo)-tetraacetic-acid (EGTA); (v) the particulate adenyl cyclase activity of the proliferative zone is susceptible to non-competitive calcium inhibition. Throughout this study cells from the hypertrophic zone of the same epiphyses were used as controls. In these cells the calcium uptake was enhanced by pressure, but the cAMP level was not affected by pressure, A23187 or EGTA. This change in responsiveness, which accompanies the maturation of the cartilage cells, was shown to be due to a decrease in the calcium-inhibition of adenylate cyclase.