The emergence of ErbB2 expression in cultured rat hepatocytes correlates with enhanced and diversified EGF-mediated signaling.
The proliferative effects of EGF in liver have been extensively investigated in cultured hepatocytes. We studied the effects of EGF, insulin, and other growth regulators on the expression, interaction, and signaling of ErbB receptors in primary cultures of adult rat hepatocytes. Using immunological methods and ErbB tyrosine kinase inhibitors, we analyzed the expression and signaling patterns of the ErbB kinases over 120 h of culture. Basal and EGF-stimulated protein tyrosine phosphorylation increased as cells adapted in vitro. EGF receptor (EGFr) expression declined in the first 24 h, whereas ErbB3 expression rose. Although ErbB2 was not present in freshly isolated hepatocytes, EGF and insulin independently induced ErbB2 while suppressing ErbB3 expression. Low concentrations of EGF and insulin synergistically stimulated ErbB2 expression and DNA synthesis. The greatest increase in ErbB2, which is normally expressed by fetal and neonatal hepatocytes, occurred shortly before the onset of DNA synthesis (> 40 h). EGF promoted EGFr and ErbB2 coassociation, stimulating tyrosine phosphorylation of both proteins. In contrast, heregulin beta1 (HRG-beta1) did not promote ErbB2 and ErbB3 coassociation. A selective tyrphostin inhibitor of ErbB2 suppressed EGF-stimulated DNA synthesis, but maximum suppression required the blockade of the EGFr kinase as well. Maximal EGF stimulation of DNA synthesis in vitro depends on the induction of ErbB2 and involves an EGFr-ErbB2 heterodimer. The ability of insulin to induce ErbB2 suggests both a mechanism for the synergy between insulin and EGF and a possible metabolic control of ErbB2 in vivo.
Scheving
Lawrence A
LA
Division of Endocrinology, Department of Pediatrics, Vanderbilt University Medical Center, Nashville, TN 37232-0710, USA. lawrence.a.scheving@vanderbilt.edu
Zhang
Linda
L
Stevenson
Mary C
MC
Kwak
Eun Soo
ES
Russell
William E
WE
D000818:Animals; D002478:Cells, Cultured; D004338:Drug Combinations; D004815:Epidermal Growth Factor / Q000008:administration & dosage*; D066246:ErbB Receptors / Q000378:metabolism*; D005786:Gene Expression Regulation / Q000187:drug effects / Q000502:physiology; D022781:Hepatocytes / Q000187:drug effects / Q000378:metabolism*; D007328:Insulin / Q000008:administration & dosage*; D008297:Male; D010766:Phosphorylation / Q000187:drug effects; D051381:Rats; D017207:Rats, Sprague-Dawley; D018719:Erb-b2 Receptor Tyrosine Kinases / Q000378:metabolism*; D015398:Signal Transduction / Q000187:drug effects / Q000502:physiology*; D013223:Statistics as Topic
D004338:Drug Combinations; D004815:Epidermal Growth Factor; D066246:ErbB Receptors; D007328:Insulin; D018719:Erb-b2 Receptor Tyrosine Kinases