Anti-oestrogen stimulation of ERBB2 ectodomain shedding from BT-474 human breast cancer cells with ERBB2 gene amplification.
Oestrogen has previously been shown to downregulate the expression of ERBB2 oncogene in human breast cancer cells, which contain a normal non-amplified ERBB2 gene. However, amplified ERBB2 seems to escape from hormonal regulation. We studied shedding of the extracellular domain (ectodomain, ECD) of the ERBB2 encoded protein in BT-474 human breast cancer cells treated with oestrogen or anti-oestrogen. Oestrogen-responsiveness of these cells has been previously demonstrated by stimulation of cell growth and expression of pS2, a marker gene known to be regulated by oestrogen receptor at transcriptional level. The concentration of the soluble ECD in the culture medium was increased by the anti-oestrogen toremifene as a function of time. In contrast, the level of ERBB2 mRNA and protein in cell lysates was not stimulated, but was transiently suppressed by toremifene. In the presence of oestrogen, the level of ECD remained low. The increased shedding of ECD in the presence of toremifene, without parallel change in ERBB2 transcripts (4.8 and 2.3 kb) and in cellular ERBB2 protein level, suggests that toremifene specifically contributes to the shedding of the ERBB2 ectodomain. These results show that shedding of ECD is an additional level of regulation of ERBB2 by the anti-oestrogen toremifene. This may contribute to resistance to growth inhibition by anti-oestrogens of breast cancers which overexpress ERBB2.
Wärri
A M
AM
Orion Corporation, Orion-Farmos Cancer Research Laboratory, Turku.
Isola
J J
JJ
Härkönen
P L
PL
D015152:Blotting, Northern; D001943:Breast Neoplasms / Q000235:genetics / Q000378:metabolism*; D002455:Cell Division / Q000187:drug effects; D017077:Culture Media, Conditioned; D004965:Estrogen Antagonists / Q000494:pharmacology*; D005110:Extracellular Space / Q000378:metabolism; D005260:Female; D015870:Gene Expression / Q000187:drug effects*; D006801:Humans; D015151:Immunoblotting; D012333:RNA, Messenger / Q000235:genetics; D012334:RNA, Neoplasm / Q000235:genetics; D018719:Erb-b2 Receptor Tyrosine Kinases / Q000187:drug effects* / Q000235:genetics / Q000378:metabolism; D017312:Toremifene / Q000494:pharmacology*; D014407:Tumor Cells, Cultured
D017077:Culture Media, Conditioned; D004965:Estrogen Antagonists; D012333:RNA, Messenger; D012334:RNA, Neoplasm; D018719:Erb-b2 Receptor Tyrosine Kinases; D017312:Toremifene