PubMed · 6877153
The source did not provide an abstract. Follow the original record for more information.
Explore connections, maps & timelines
1983-08-20. External breast prostheses.. https://doi.org/10.5694/j.1326-5377.1983.tb122376.x
Cite the original work for its findings. Save a collection to share your selection of sources.
KEEP EXPLORING
Cell surface association of extracellular matrix (ECM)-degrading enzymes has been suggested to facilitate proteolysis of ECM in areas of cell-matrix contacts and to be crucial for the process of tumor cell invasion. Matrix metalloproteinase-9 (MMP-9) is a member of the MMP family of endopeptidases that has been shown to play a critical role in hydrolysis of ECM components and has been localized on the surface of tumor cells. However, the nature of the cell surface association of MMP-9 is unknown. Here, we report the cell surface association of MMP-9 in human breast epithelial MCF10A cells treated with 12-O-tetradecanoylphorbol-13-acetate (TPA). Surface biotinylation and immunoprecipitation with anti-MMP-9 antibodies revealed the presence of two MMP-9 forms (M(r) 92,000 and 85,000) on the surface of TPA-treated MCF10A cells, whereas in the media, only the M(r) 92,000 form was detected, mostly in complex with TIMP-1, a specific MMP-9 inhibitor. The MMP-9 forms were also found in purified plasma membranes of TPA-treated cells. In contrast, the plasma membranes contained little or no TIMP-1. The surface-bound MMP-9 forms were recognized by an antibody to the NH2-terminal prodomain, indicating that both represent latent enzymes. Pulse-chase analysis and endoglycosidase H digestion of surface-biotinylated MMP-9 forms demonstrated that the M(r) 85,000 species was endoglycosidase H sensitive, suggesting targeting of the precursor form of MMP-9 to the cell surface. These studies demonstrate a specific cell surface association of MMP-9 in response to TPA that may help to localize TIMP-1-free enzyme on the surface of breast epithelial cells.
To determine whether normal breast cells have different levels of activating protein 1 (AP-1) expression and activation relative to breast cancer cells, we have compared the level of c-Jun and c-Fos expression and AP-1 activity in human mammary epithelial cells (HMECs) at different stages of transformation (normal proliferating HMECs, immortal HMECs, oncogene-transformed HMECs, and breast cancer cell lines). These studies demonstrated that normal and immortal HMECs have a high basal level of expression of cJun and cFos and higher AP-1 DNA-binding and transcriptional activating activities than do oncogene-transformed HMECs or human breast cancer cells, with a gradual decrease in AP-1 transactivating activity as cells progress through the carcinogenesis pathway (normal > immortal > oncogene-transformed > cancer cell lines). The AP-1 activity in normal or immortal cells was not modulated by growth factor supplementation or oncogene overexpression, as it is in breast cancer cells. However, the addition of suramin, a nonspecific growth factor antagonist, did inhibit AP-1 in these HMECs, suggesting that this high level of AP-1 present in normal HMECs may be due to autocrine stimulation of growth factor pathways. The differences in AP-1 activity in normal and malignant breast cells may indicate that normal cells are more dependent on AP-1-mediated signals for their growth than are breast cancer cells.
Normal human breast epithelial (HBE) cells which reached confluence ceased growth and tightly adhered to each other, forming a monolayer. In quiescent cells thus arrested by density, E-cadherin colocalized and coimmunoprecipitated with alpha- and beta-catenins in the boundary region between adjacent cells. By contrast, immunocytostaining and Western blot analyses revealed that E-cadherin colocalized and coprecipitated with beta-catenin but not with alpha-catenin in exponentially growing cells at low density. As a comparable amount of alpha-catenin was detected in the total cell lysate of cells at different densities, it is suggested that alpha-catenin is present but dissociates from the E-cadherin-beta-catenin complex in growing cells. beta-Catenin was tyrosine phosphorylated in growing cells at low density but not in quiescent cells at confluence. Tyrosine phosphorylation of beta-catenin was concomitantly induced with association of beta-catenin with EGF receptor (EGFR) when quiescent cells at confluence were dissociated into single cells by tryptic digestion, being accompanied by dissociation of alpha-catenin from E-cadherin. Both tyrosine phosphorylation and association of beta-catenin with EGFR were inhibited by tyrphostin, a specific inhibitor of the EGFR tyrosine kinase, whereas dissociation of alpha-catenin from E-cadherin was not. The results suggest that tyrosine phosphorylation of beta-catenin is achieved by EGFR upon tryptic digestion of cells and concurrent with but independent of dissociation of alpha-catenin from E-cadherin. beta-Catenin thus phosphorylated at tyrosine is suggested to play the role in preventing alpha-catenin once dissociated from reassociating with E-cadherin until cells reach confluence.