Cell anchorage determines whether mammary tumor virus glycoproteins are processed for plasma membranes or secretion.

Abstract

The subcellular localization of mouse mammary tumor virus (MMTV) glycoproteins was analyzed in infected and. cloned rat hepatocarcinoma cells cultured with the MMTV transcriptional inducer dexamethasone. When reacted with protein A~coated erythrocytes in the presence of antisera specific for viral glycoproteins or with fluorescent antisera, only some of the cells acquired surface label. This diversity was dependent on cell anchorage to the substratum. In general, the more rounded, less adherent cells contained the MMTV glycoproteins on their surfaces, whereas the flatter, more adherent cells did not. After a change in adherence, a delay preceded complete remodeling of the plasma membranes. Fluorescent antibody studies of fixed cells and analyses of viral glycoprotein synthesis and shedding using L-[35S]methionine indicated that the different expression of MMTV glycoproteins in round versus flat cells is caused by a switch in posttranslational processing. In round cells, the MMTVencoded precursor glycoprotein is proteolytically cleaved and then transported to plasma membranes as a complex of two subunits, the smaller being the membrane anchor. In flat adherent cells, the smaller subunit is rapidly degraded in an intracellular organelle and the larger is then secreted into the medium. As indicated by labeling of cells with 1251, the concentrations of several host-encoded plasma membrane components are also influenced by cell anchorage. We propose that this switch in cell surfaces and in secetions dependent upon cell-substratum attachments may be a common control mechanism important for embryogenesis, wound healing, and cancer.

Attachment of human bone cells to tissue culture polystyrene and to unmodified polystyrene: the effect of surface chemistry upon initial cell attachment

“…We have chosen to study the attachment of bone cells upon first contact with the surfaces, as this initial attachment during the first 90 min after cell seeding is readily quantitated and amenable to mechanistic analysis. This attachment step is also imperative for cellular spreading and subsequent secretion and assembly of an extracellular matrix [33] and the differences observed between these surfaces would also be relevant to, and reflected in, the subsequent assembly of extracellular matrices on these substrata by the bone-derived cells [10,11,32]. It should be noted, however, that the initial cell attachment reaction would be of limited value as an end point for a screening assay of potential material surfaces.…”

The cellular level of prostatic acid phosphatase and the growth of human prostate carcinoma cells

“…7~ 1 O4 cells/cmz in a 6-well plate containing a coverglass on the bottom. After growth at 37 "C with 7 % CO, in RPMl 1640 containing 10 % FBS for 3 days, cells were fed with the same fresh medium-FBS and grown for an additional 24 h. Cells were fixed with 3.7 % formaldehyde in 20 mM HEPES-0.9 c/c NaCl for 10 inin at 24 "C, permeabilized by 0.2 % Triton X-I00 in 20 mM HEPES-0.9 % NaCl for 5 min at 24 "C then rinsed with RPMl 1640 containing 5 % FBS [13].…”

Growth inhibition of androgen‐insensitive human prostate carcinoma cells by a 19‐norsteroid derivative agent, mifepristone

“…Cells were plated in 6-well culture plates containing a coverglass on the bottom in RPMI-1640 medium containing 7% FBS as described previously [31]. After being fixed with 3.7% formaldehyde in 20 mM Hepes, pH 7.2, containing 0.9% NaC1, cells were permeabilized by 0.2% Triton X-100 in Hepes-saline buffer and then rinsed with medium containing 5% FBS.…”