Adhesive interactions of trophoblast cells with endometrium are essential for embryo implantation in the uterus. Choriocarcinoma cells, the malignant counterpart of trophoblast, show pronounced invasiveness and are of interest for model studies. We describe here an in vitro model system for the study of adhesion of human JAR choriocarcinoma multicellular spheroids to different human endometrial epithelial cell lines (RL95-2, HEC-1A, KLE, AN3-CA) grown as monolayers. Cell characterization showed JAR spheroids to s++ecrete the placental hormones human chorionic gonadotropin and progesterone into the culture medium; distinct patterns of keratin, vimentin, and uvomorulin expression were seen in the endometrial cell lines. Spheroid attachment to endometrial monolayers was quantified using a centrifugal force-based adhesion assay, and morphology was examined by light and electron microscopy. Results showed the JAR spheroids to attach to three of the endometrial monolayers (RL95-2, HEC-1A, KLE) progressively over a 24-h period (by which time > or = 80% of the spheroids attached). Significant differences in spheroid attachment were most pronounced at 5 h (RL95-2 > HEC-1A > KLE and poly-D-lysine control, i.e. 90:45:17:17% attached). JAR spheroids did not attach to the endometrial cell line AN3-CA. Morphology revealed choriocarcinoma cells to begin to intrude between the uterine RL95-2 epithelial cells at 5 h. At 24 h, this intrusive type of penetration continued to be seen only with the RL95-2 monolayer. The assay system thus identifies differences in attachment properties between choriocarcinoma cells and various endometrial cell lines and forms the basis for further studies on the molecular interactions involved.

Abstract. Glucocorticoid hormones can regulate the posttranslational maturation of mouse mammary tumor virus (MTV) precursor polyproteins in M1.54, a stably infected rat hepatoma cell line. We have used complement-mediated cytolysis to recover variants of M1.54 that fail to express MTV cell surface glycoproteins in a hormone-regulated manner (Firestone, G. L., and K. R. Yamamoto, 1983, Mol. Cell. Biol., 3:149-160). One such clonal isolate, CR4, is similar to wild-type with respect to synthesis of MTV mRNAs, production of the MTV glycoprotein precursor (gPr74 °nv) and a glycosylated maturation product (gp51), and hormone-induced processing of two MTV phosphoproteins. In contrast, three viral cell surface glycoproteins (gp78, gp70, and gp32) and one extracellular species (gp70s), which derive from gPr74 env in glucocorticoid-treated wild-type cells, fail to appear in CR4. CR4 showed no apparent alterations in proliferation rate, cell shape, or expression of total functional mRNA and bulk glycoproteins. We conclude that the genetic lesion in CR4 defines a highly selective hormone-regulated glycoprotein maturation pathway that alters the fate of a restricted subset of precursor species.

Abstract. Glucocorticoid hormones regulate the posttranslational 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 monensintreated cells revealed that gp70 can be localized to the cell surface only in the presence of 1 ~ 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.

We have utilized the rat hepatoma (HTC) cell sorting variant CR4 to examine the glucocorticoidregulated pathways that localize mouse mammary tumor virus glycoproteins to the cell surface. The defective sorting of cell surface mouse mammary tumor virus glycoproteins in CR4 cells was complemented after fusion with either normal rat hepatocytes or uninfected HTC cells. Indirect immunofluorescence of transient heterokaryons revealed that the regulated localization of mouse mammary tumor virus glycoproteins was dependent upon glucocorticoid treatment and required de novo RNA and protein synthesis. Thus, a glucocorticoid-regulated trafficking activity, unrelated to mouse mammary tumor virus sequences, which is induced in both adult rat liver and cultured hepatoma cells, can act in trans to mediate an intracellular sorting pathway for membrane glycoproteins.