Phorbol ester or epidermal growth factor (EGF) stimulates the concurrent accumulation of mRNA for the EGF receptor and its ligand transforming growth factor-alpha in a breast cancer cell line.
We have previously reported that both 12-O-tetradecanoylphorbol-13-acetate (TPA) and epidermal growth factor (EGF) can stimulate the synthesis rate of EGF receptors. We now show that the MDA468 breast cancer cells express the mRNA for the EGF-like molecule, transforming growth factor-alpha (TGF-alpha), and demonstrate that TPA or EGF cause an accumulation of both EGF receptor and TGF-alpha mRNA. The levels of EGF receptor mRNA paralleled our earlier protein data, with peak accumulations of 2-3-fold with 10(-9) M EGF and 3-5-fold with 100 ng/ml TPA seen between 6 and 8 h. A 7-fold accumulation of TGF-alpha mRNA was seen following 4 h of treatment with TPA, and a 2-fold accumulation was seen after 8 h with EGF. These changes in EGF receptor and TGF-alpha mRNAs were observed in the absence of any change in the mRNA level of the alpha-subunit of hexosaminidase A (a lysosomal enzyme), demonstrating some degree of specificity. Detectable quantities of immunoreactive TGF-alpha accumulated in the cell culture medium of MDA468 cell treated with the blocking anti-EGF receptor monoclonal antibody B1D8 while no immunoreactive TGF-alpha was detected in the medium of cells with unblocked receptors. The concentration of B1D8 used was sufficient to block the binding of exogenously added 125I-EGF to undetectable levels but had only minor effects on cell growth and no effect on the expression of the TGF-alpha and EGF receptor mRNA.
Bjorge
J D
JD
Department of Clinical Biochemistry, University of Toronto, Ontario, Canada.
Paterson
A J
AJ
Kudlow
J E
JE
D000911:Antibodies, Monoclonal / Q000276:immunology; D000937:Antigen-Antibody Reactions; D001943:Breast Neoplasms / Q000235:genetics*; D004815:Epidermal Growth Factor / Q000494:pharmacology*; D066246:ErbB Receptors / Q000235:genetics* / Q000276:immunology / Q000378:metabolism; D005786:Gene Expression Regulation / Q000187:drug effects; D054818:Hexosaminidase A; D006801:Humans; D011233:Precipitin Tests; D011493:Protein Kinase C / Q000502:physiology; D012333:RNA, Messenger / Q000235:genetics; D012334:RNA, Neoplasm / Q000235:genetics; D013755:Tetradecanoylphorbol Acetate / Q000494:pharmacology*; D015291:Transforming Growth Factors / Q000235:genetics*; D014407:Tumor Cells, Cultured; D001619:beta-N-Acetylhexosaminidases / Q000235:genetics
D000911:Antibodies, Monoclonal; D012333:RNA, Messenger; D012334:RNA, Neoplasm; D004815:Epidermal Growth Factor; D015291:Transforming Growth Factors; D066246:ErbB Receptors; D011493:Protein Kinase C; D054818:Hexosaminidase A; D001619:beta-N-Acetylhexosaminidases; D013755:Tetradecanoylphorbol Acetate