Azoxymethane enhances ligand-induced activation of EGF receptor tyrosine kinase in the colonic mucosa of rats.
Recent observations suggest that transforming growth factor alpha (TGF-alpha), which binds to the epidermal growth factor (EGF) receptor (EGFR), may induce neoplastic growth of the colonic mucosa through an autocrine mechanism. To assess the functional role of TGF-alpha in colonic carcinogenesis the present investigation examines the changes in TGF-alpha-and EGF-induced activation of intrinsic tyrosine kinase (Tyr-k) activity of EGFR in the colonic mucosa of rats after administration of the colonic carcinogen azoxymethane (AOM; 20 mg/kg body wt). Five days after a single injection of AOM to 4- to 5-month old rats proliferative activity (as assessed by 5-bromo-2'-deoxyuridine immunoreactivity) in the colonic mucosa was increased by approximately 700% over the corresponding saline-injected controls. This was accompanied by: (i) a marked rise in autophosphorylation of a number of mucosal proteins, including one with a M(r) of 170 kDa, a molecular mass that corresponds to EGFR; (ii) a 110-130% increase in basal EGFR Tyr-k activity. Despite this rise in basal EGFR Tyr-k activity, exposure of isolated colonocytes or detergent-solubilized colonic mucosa from AOM-treated animals to either 1 x 10(-8) M TGF-alpha or EGF caused a further 90-160% increase in EGFR Tyr-k activity over the corresponding basal levels. In contrast, bombesin produced no apparent change in EGFR Tyr-k activity. We conclude that increased ligand-induced activation of EGFR Tyr-k may be an important event for development of the hyperproliferative state associated with induction of colorectal neoplasia.
Malecka-Panas
E
E
VA Medical Center, Allen Park, MI 48101, USA.
Fligiel
S E
SE
Relan
N K
NK
Dutta
S
S
Majumdar
A P
AP
D000818:Animals; D001397:Azoxymethane / Q000633:toxicity*; D001839:Bombesin / Q000494:pharmacology; D002273:Carcinogens / Q000633:toxicity*; D002455:Cell Division / Q000187:drug effects; D003106:Colon / Q000166:cytology / Q000187:drug effects* / Q000201:enzymology; D004789:Enzyme Activation / Q000187:drug effects; D066246:ErbB Receptors / Q000187:drug effects*; D007413:Intestinal Mucosa / Q000166:cytology / Q000187:drug effects* / Q000201:enzymology; D008565:Membrane Proteins / Q000187:drug effects / Q000378:metabolism; D010766:Phosphorylation; D011505:Protein-Tyrosine Kinases / Q000096:biosynthesis / Q000187:drug effects*; D051381:Rats; D011916:Rats, Inbred F344; D016211:Transforming Growth Factor alpha / Q000494:pharmacology*
D002273:Carcinogens; D008565:Membrane Proteins; D016211:Transforming Growth Factor alpha; D066246:ErbB Receptors; D011505:Protein-Tyrosine Kinases; D001397:Azoxymethane; D001839:Bombesin