A novel mechanism for mitogenic signaling via pro-transforming growth factor alpha within hepatocyte nuclei.
Transforming growth factor (TGF) alpha, an important mediator of growth stimulation, is known to act via epidermal growth factor receptor (EGF-R) binding in the cell membrane. Here we show by immunohistology, 2-dimensional immunoblotting, and mass spectrometry of nuclear fractions that the pro-protein of wild-type TGF-alpha occurs in hepatocyte nuclei of human, rat, and mouse liver. Several findings show a close association between nuclear pro-TGF-alpha and DNA synthesis. (1) The number of pro-TGF-alpha+ nuclei was low in resting liver and increased dramatically after partial hepatectomy and after application of hepatotoxic chemicals or the primary mitogen cyproterone acetate (CPA); in any case, S phase occurred almost exclusively in pro-TGF-alpha+ nuclei. The same was found in human cirrhotic liver. (2) In primary culture, 7% of hepatocytes synthesized pro-TGF-alpha, which then translocated to the nucleus; 70% of these nuclei subsequently entered DNA replication, whereas only 2% of pro-TGF-alpha- hepatocytes were in S phase. (3) The frequency of hepatocytes coexpressing pro-TGF-alpha and DNA synthesis was increased by the hepatomitogens CPA or prostaglandin E(2) and was decreased by the growth inhibitor TGF-beta1. (4) Treatment with mature TGF-alpha increased DNA synthesis exclusively in pro-TGF-alpha- hepatocytes, which was abrogated by the EGF-R tyrosine kinase inhibitor tyrphostin A25. In conclusion, TGF-alpha gene products may exert mitogenic effects in hepatocytes via 2 different signaling mechanisms: (1) the "classic" pathway of mature TGF-alpha via EGF-R in the membrane and (2) a novel pathway involving the presence of pro-TGF-alpha in the nucleus.
Grasl-Kraupp
Bettina
B
Institut für Krebsforschung, University of Vienna, Vienna, Austria. bettina.grasl-kraupp@univie.ac.at
Schausberger
Elisabeth
E
Hufnagl
Karin
K
Gerner
Christopher
C
Löw-Baselli
Alexandra
A
Rossmanith
Walter
W
Parzefall
Wolfram
W
Schulte-Hermann
Rolf
R
D000818:Animals; D002455:Cell Division / Q000502:physiology; D002467:Cell Nucleus / Q000737:chemistry / Q000378:metabolism; D002478:Cells, Cultured; D003593:Cytoplasm / Q000378:metabolism; D004261:DNA Replication; D005260:Female; D022781:Hepatocytes / Q000166:cytology* / Q000502:physiology*; D006801:Humans; D007150:Immunohistochemistry; D008099:Liver / Q000166:cytology / Q000502:physiology; D008297:Male; D051379:Mice; D008810:Mice, Inbred C57BL; D051381:Rats; D017208:Rats, Wistar; D015398:Signal Transduction / Q000502:physiology*; D019032:Spectrometry, Mass, Matrix-Assisted Laser Desorption-Ionization; D016211:Transforming Growth Factor alpha / Q000032:analysis / Q000502:physiology*
D016211:Transforming Growth Factor alpha