Genetic evidence that the steroid-regulated trafficking of cell surface glycoproteins in rat hepatoma cells is mediated by glucocorticoid-inducible cellular components

Retinoic acid decreases attachment of JAR choriocarcinoma spheroids to a human endometrial cell monolayer in vitro

The ability of retinoic acid (RA) to modulate attachment of JAR choriocarcinoma multicellular spheroids to monolayers of a human uterine epithelial cell line (RL95-2) was examined using a centrifugal force-based adhesion assay. Exposure of choriocarcinoma spheroids to RA (10(-7) to 10(-5) M) over a 3-day culture period resulted in a dose-dependent decrease of attachment. Significant decreases in attachment were detected after 30 min (75 per cent versus 25 per cent) and 1 h (92 per cent versus 26 per cent) of confrontation-culture between choriocarcinoma and uterine cells for control versus 10(-5) M RA; by 5 h 100 per cent spheroid attachment was detected in all treatment groups. RA had no effect on cell proliferation in JAR spheroids, but 10(-5) M RA treatment induced a fivefold increase in secretion of human chorionic gonadotrophin (hCG), a known marker of conversion of cytotrophoblast to syncytiotrophoblast-like cells. These findings demonstrate that RA modulates cellular attachment and differentiation in choriocarcinoma spheroids in vitro.

Glucocorticoid responsiveness of mouse mammary tumor virus (MMTV) promoters in a down-transcription hepatoma tissue culture (HTC) variant

Complement-mediated cytolysis of the mouse mammary tumor virus (MMTV)-infected rat hepatoma (HTC) cell line, M1.54, resulted in recovery of a mutant derivative, designated CR5, in which the magnitude of both basal and dexamethasone-induced proviral MMTV RNA expression was selectively reduced. Variant CR5 cells were transfected with a plasmid containing the glucocorticoid-regulated MMTV promoter linked to the neomycin resistance gene (pLNL). Half-maximal resistance to G418 killing was glucocorticoid inducible in both pLNL-transfected CR5 and M1.54 cells and was dependent on glucocorticoid receptor occupancy. The down-transcription of MMTV provirus sequences cannot be conferred to transfected genes driven by the same viral promoter suggesting that CR5 cells are defective in cis acting factors. Consistent with this notion, indirect immunofluorescence of transient heterokaryons revealed that uninfected wild-type HTC cells failed to complement the defect in CR5 while CR5 cells did not suppress the wild-type phenotype of M1.54 cells.

Glucocorticoid receptor-dependent inhibition of cellular proliferation in dexamethasone-resistant and hypersensitive rat hepatoma cell variants

Exposure of the Fu5 rat hepatoma cell line to glucocorticoids, such as dexamethasone and hydrocortisone, suppressed the growth rate and final density of cells grown in the presence of serum. This hormonal effect was proportional to receptor occupancy and affinity and, in addition, the glucocorticoid antagonist RU38486 prevented this response. Two classes of dexamethasone-resistant variants that failed to be growth inhibited were recovered from ethyl methylsulfonate-mutagenized populations by continuous culture in the presence of 1 microM dexamethasone. The first class, represented by the EDR3 subclone, was completely glucocorticoid unresponsive and failed to express receptor transcripts. The second class, represented by the EDR1, EDR5, and EDR7 subclones, possessed significant levels of glucocorticoid receptor but were only partially glucocorticoid responsive when stimulated with saturating levels of hormone. Introduction of functional glucocorticoid receptor genes into both classes of dexamethasone-resistant variants by a recombinant retrovirus expression vector restored glucocorticoid responsiveness and suppression of cell growth. A hypersensitive variant (BDS1), recovered by bromodeoxyuridine selection, was fully glucocorticoid responsive, and its inhibition of proliferation was more acutely regulated by dexamethasone. Taken together, our results established that the inhibition of proliferation in Fu5 rat hepatoma cells represents a new glucocorticoid response that requires the expression of a functional glucocorticoid receptor.

Glucocorticoid-regulated localization of cell surface glycoproteins in rat hepatoma cells is mediated within the Golgi complex

Glucocorticoid hormones regulate the post-translational maturation and sorting of cell surface and extracellular mouse mammary tumor virus (MMTV) glycoproteins in M1.54 cells, a stably infected rat hepatoma cell line. Exposure to monensin significantly reduced the proteolytic maturation and externalization of viral glycoproteins resulting in a stable cellular accumulation of a single 70,000-Mr glycosylated polyprotein (designated gp70). Cell surface- and intracellular-specific immunoprecipitations of monensin-treated cells revealed that gp70 can be localized to the cell surface only in the presence of 1 microM dexamethasone, while in uninduced cells gp70 is irreversibly sequestered in an intracellular compartment. Analysis of oligosaccharide processing kinetics demonstrated that gp70 acquired resistance to endoglycosidase H with a half-time of 65 min in the presence or absence of hormone. In contrast, gp70 was inefficiently galactosylated after a 60-min lag in uninduced cells while rapidly acquiring this carbohydrate modification in the presence of dexamethasone. Furthermore, in the absence or presence of monensin, MMTV glycoproteins failed to be galactosylated in hormone-induced CR4 cells, a complement-selected sorting variant defective in the glucocorticoid-regulated compartmentalization of viral glycoproteins to the cell surface. Since dexamethasone had no apparent global effects on organelle morphology or production of total cell surface-galactosylated species, we conclude that glucocorticoids induce the localization of cell surface MMTV glycoproteins by regulating a highly selective step within the Golgi apparatus after the acquisition of endoglycosidase H-resistant oligosaccharide side chains but before or at the site of galactose attachment.

Glucocorticoid receptor-dependent inhibition of cellular proliferation in dexamethasone-resistant and hypersensitive rat hepatoma cell variants

Exposure of the Fu5 rat hepatoma cell line to glucocorticoids, such as dexamethasone and hydrocortisone, suppressed the growth rate and final density of cells grown in the presence of serum. This hormonal effect was proportional to receptor occupancy and affinity and, in addition, the glucocorticoid antagonist RU38486 prevented this response. Two classes of dexamethasone-resistant variants that failed to be growth inhibited were recovered from ethyl methylsulfonate-mutagenized populations by continuous culture in the presence of 1 microM dexamethasone. The first class, represented by the EDR3 subclone, was completely glucocorticoid unresponsive and failed to express receptor transcripts. The second class, represented by the EDR1, EDR5, and EDR7 subclones, possessed significant levels of glucocorticoid receptor but were only partially glucocorticoid responsive when stimulated with saturating levels of hormone. Introduction of functional glucocorticoid receptor genes into both classes of dexamethasone-resistant variants by a recombinant retrovirus expression vector restored glucocorticoid responsiveness and suppression of cell growth. A hypersensitive variant (BDS1), recovered by bromodeoxyuridine selection, was fully glucocorticoid responsive, and its inhibition of proliferation was more acutely regulated by dexamethasone. Taken together, our results established that the inhibition of proliferation in Fu5 rat hepatoma cells represents a new glucocorticoid response that requires the expression of a functional glucocorticoid receptor.