THE LYSOSOMAL-ASSOCIATED MEMBRANE-PROTEIN LAMP-1 IS A NOVEL DIFFERENTIATION MARKER FOR HC11 MOUSE MAMMARY EPITHELIAL-CELLS

HC11 cells are a model for mammary epithelial cell differentiation. Fo llowing treatment with the lactogenic hormones glucocorticoids, insuli n and prolactin, the HC11 cells synthesize milk proteins. Stereologica l analysis at the ultrastructural level suggested that lysosomal bioge nesis was activated following lactogenic hormone treatment of HC11 cel ls. Differentiation was also accompanied by an increase in the cellula r content of tri-and tetra-antennary oligosaccharides, which were reac tive with isolectin L4 from Phaseolus vulgaris (L-PHA). The lysosomal- associated membrane glycoproteins LAMP-1 and LAMP-2 are the major carr iers of this glycosylation pattern. An analysis of LAMP-1 and LAMP-2 e xpression levels showed that there was a dramatic increase in LAMP-1 f ollowing lactogenic hormone treatment of HC11 cells. The control of LA MP-1 expression is mainly post-transcriptional since the level of LAMP -1 RNA is not affected by lactogenic hormones. Stereological analysis also showed an increase in intermediate filament control of differenti ated cells. Analysis of the cytokeratins expressed in differentiated c ells suggests that HC11 cells have characteristics of a mammary-specif ic stem cell. Increase in lysosomal vesicles and their contents might play a role in intra- and extra-cellular remodeling, which is characte ristic of cell differentiation.