title: Prolactin receptors in explant cultures of carcinogen-induced rat mammary tumors.
abstract: The turnover, down-regulation and role of intracellular organelles in the down-regulation of prolactin (PRL) receptors have been investigated in N-nitrosomethylurea (NMU)-induced rat mammary tumors cultured in short-term explants. Tumor explants are capable of maintaining PRL receptors for 24-48 hr. This maintenance reflects a dynamic phenomenon involving receptor synthesis, since addition of cycloheximide (1 microgram/ml) in the culture medium results within 12 hr in a marked decline of PRL receptor levels. A down-regulation of total PRL receptors (measured after exposure of membranes to 3M MgCl2) is observed in cultures containing concentrations of 20 micrograms/ml or greater of ovine PRL (oPRL). Lysosomotropic agents, such as chloroquine (100 microM) are ineffective in either increasing basal PRL receptor levels or in preventing the PRL-induced down-regulation in NMU-induced mammary tumor explants. Cytochalasin B (20 microM), without effect on basal PRL binding, prevents the down-regulation of PRL receptors, whereas colchicine (10 microM) results in a decline of PRL receptor levels both in the absence and in the presence of oPRL. The present data suggest a different pattern of PRL receptor regulation in vitro for tumors compared to normal rabbit mammary explants.
mesh_terms: D015127:9,10-Dimethyl-1,2-benzanthracene; D000818:Animals; D002738:Chloroquine / Q000494:pharmacology; D003078:Colchicine / Q000494:pharmacology; D003513:Cycloheximide / Q000494:pharmacology; D003571:Cytochalasin B / Q000494:pharmacology; D005260:Female; D008325:Mammary Neoplasms, Experimental / Q000139:chemically induced / Q000378:metabolism*; D008770:Methylnitrosourea; D009924:Organ Culture Techniques; D009940:Organoids / Q000378:metabolism; D051381:Rats; D011919:Rats, Inbred Strains; D011956:Receptors, Cell Surface / Q000187:drug effects / Q000378:metabolism*; D011981:Receptors, Prolactin
chemical_list: D011956:Receptors, Cell Surface; D011981:Receptors, Prolactin; D003571:Cytochalasin B; D015127:9,10-Dimethyl-1,2-benzanthracene; D008770:Methylnitrosourea; D002738:Chloroquine; D003513:Cycloheximide; D003078:Colchicine