Ribozyme-mediated down-regulation of ErbB-4 in estrogen receptor-positive breast cancer cells inhibits proliferation both in vitro and in vivo.
ErbB-4 is a recently discovered member of the class I receptor tyrosine kinase family (ErbB). Little is known about its expression and its importance in human malignancy. To delineate the biological function of ErbB-4 receptors in breast cancer, we used a hammerhead ribozyme strategy to achieve down-regulation of ErbB-4 receptors in various breast cancer cell lines. We observed that down-regulation of ErbB-4 in estrogen receptor-positive (ER+) human breast cancer cell lines (MCF-7 and T47D), which express relatively high levels of ErbB-4, significantly inhibited colony formation. No effects were observed in estrogen receptor-negative (ER-) MDA-MB-453 cells, which express low levels of endogenous ErbB4 and high levels of ErbB-2 and ErbB-3. This occurred despite the fact that fluorescence-activated cell sorter analysis of these latter cells revealed that the expression of the ErbB-4 receptor was completely abrogated by ribozyme treatment. Furthermore, down-regulation of ErbB-4 in T47D and MCF-7 cells significantly inhibited tumor formation in athymic nude mice (P < 0.03 and P < 0.001, respectively). In addition, NRG-stimulated phosphorylation of ErbB-4- and NRG-induced colony formation was significantly reduced in ribozyme-transfected T47D cells. These data provide the first evidence that elevation of ErbB-4 expression plays a role in the proliferation of some ER+ human breast cancer cell lines (T47D and MCF-7) that express high levels of ErbB-4. We have also investigated the expression of ErbB-4 in human primary breast carcinoma specimens, using immunohistochemical staining with an anti-ErbB-4 monoclonal antibody. ErbB-4 expression was found in 60% of the 50 primary breast tumors examined, and high intense immunoreactivity of ErbB-4 was detected in 18% of these primary breast tumors. ErbB-4 receptor expression appeared to correlate with ER+ primary breast tumors. A similar correlation was also observed in the human breast cancer cell lines. These results provide a better understanding of the biological significance of ErbB-4 receptor in breast cancer. Our data suggest that elevation of the ErbB-4 receptor plays a role in ER+ breast cancer cell proliferation. Moreover, ribozyme technology provides a useful tool to delineate the role of a particular gene product.
Tang
C K
CK
Lombardi Cancer Center, Department of Biochemistry, Georgetown University Medical Center, Washington, DC 20007-2197, USA. Tangc@gunet.georgetown.edu
Concepcion
X Z
XZ
Milan
M
M
Gong
X
X
Montgomery
E
E
Lippman
M E
ME
D000818:Animals; D001943:Breast Neoplasms / Q000737:chemistry / Q000473:pathology / Q000628:therapy*; D002455:Cell Division; D015536:Down-Regulation; D066246:ErbB Receptors / Q000032:analysis / Q000502:physiology*; D005260:Female; D006801:Humans; D008325:Mammary Neoplasms, Experimental / Q000628:therapy; D051379:Mice; D008819:Mice, Nude; D020890:Neuregulin-1 / Q000502:physiology; D010766:Phosphorylation; D016337:RNA, Catalytic / Q000502:physiology*; D066247:Receptor, ErbB-4; D011960:Receptors, Estrogen / Q000032:analysis*; D014162:Transfection; D014407:Tumor Cells, Cultured
D020890:Neuregulin-1; D016337:RNA, Catalytic; D011960:Receptors, Estrogen; C587689:ERBB4 protein, human; D066246:ErbB Receptors; C587690:Erbb4 protein, mouse; D066247:Receptor, ErbB-4