ISSN:
0730-2312
Keywords:
TGF-α
;
mitogenic signal
;
tyrosine kinase activity
;
SP1
;
transcription
;
Life and Medical Sciences
;
Cell & Developmental Biology
Source:
Wiley InterScience Backfile Collection 1832-2000
Topics:
Biology
,
Chemistry and Pharmacology
,
Medicine
Notes:
In an attempt to elucidate the mechanism by which c-myc and transforming growth factor-α (TGF-α) cooperate in hepatocyte tumor development, we have analyzed signaling by the epidermal growth factor (EGF) receptor and the consequent regulation of receptor number in transgenic mice bearing the c-myc transgene under the control of the albumin enhancer/promoter. 125I-EGF binding and Scatchard analysis indicated a single class of high affinity receptors with the total number of binding sites of 1.2 × 104 ± 600 and 2.5 × 105 ± 1000 sites/cell in the normal and c-myc hepatocytes in primary culture, respectively. After 72 h of EGF exposure in culture, the number of detectable EGF receptors on the cell surface of the c-myc hepatocytes was not reduced, whereas the number of EGF receptors on normal hepatocytes was reduced to 32% that of untreated hepatocytes. Nuclear run-on experiments done with nuclei isolated from intact livers demonstrated that transcription of the EGF receptor was 4.9-fold higher in c-myc mice. Increased levels of the transcriptional factor SP1 in the c-myc hepatocytes in vivo and in primary culture, suggest a mechanism for the increased transcription of the EGF receptor. c-myc also increases the expression of TGF-α; a consequent increase in tyrosine phosphorylation is also detected in vivo. Thus, the increased number of EGF receptors in c-myc expressing hepatocytes, even after prolonged exposure to EGF, or TGF-α in vivo, may allow greater triggering of the EGF receptor signaling cascade. J. Cell. Biochem. 64:651-660. © 1997 Wiley-Liss, Inc. This article is a U.S. Government work and, as such, is in the public domain in the United States of America.
Additional Material:
3 Ill.
Type of Medium:
Electronic Resource
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