Prostaglandin E-2 (EP1) receptor agonist-induced DNA synthesis and proliferation in primary cultures of adult rat hepatocytes: The involvement of TGF-alpha
M. Kimura et al., Prostaglandin E-2 (EP1) receptor agonist-induced DNA synthesis and proliferation in primary cultures of adult rat hepatocytes: The involvement of TGF-alpha, ENDOCRINOL, 142(10), 2001, pp. 4428-4440
We investigated the effects of prostaglandin (EP) receptor subtype agonists
on DNA synthesis and proliferation in primary cultures of adult rat hepato
cytes to elucidate their mechanisms of action. Maintained in short-term cul
tures (ie. 3.5 h) in a serum-free, defined medium, hepatocyte parenchymal c
ells underwent DNA synthesis and proliferation in the presence of sulprosto
ne (10(-6) m), PGE(2) (10(-6) m), and 17-phenyl-trinor-PGE(2) (10(-9) ig) i
n a time- and dose-dependent man ner. PGE(2) was less potent than 17-phenyl
-trinor-PGE2 in stimulating hepatocyte mitogenesis. Sulprogtone (10(-6) M)
and 11-deoxy-PGE(1) (10(-6) M) showed weak and insignificant stimulation, r
espectively, for hepatocyte mitogenesis. These effects of PGE(2), 17-phenyl
-trinor-PGE(2), and sulprostone were abolished by treatment with a specific
EP1 receptor antagonist, SC-51322, or the PLC inhibitor U-73122. The effec
ts of these EP1 receptor agonists were potentiated by ionomycin and blocked
by verapamil. Hepatocyte mitogenesis was almost completely blocked by spec
ific inhibitors of growth-related signal transducers, such as genistein, wo
rtmannin, PD98059, and rapamycin. A monoclonal antibody against TGF-alpha d
ose-dependently inhibited PGE(2)- and 17-phenyl-trinor-PGE(2)-induced hepat
ocyte mitogenesis. Treatment with the EP1 receptor agonists significantly i
ncreased the secretion of TGF-alpha, reaching a maximum within 5 min. The i
ncrease in TGF-alpha secretion was blocked by SC-51322, U-73122, somatostat
in, and verapamil and potentiated by ionomycin. These results indicate that
the proliferative mechanisms of action of EP1 receptor agonists are mediat
ed through an increase in the autocrine secretion of TGF-alpha, which is de
pendent on the EP1 receptor/G-protein involved in PLC regulation/PLC/Ca2+ s
ystem. The locally secreted TGF-alpha, in turn, acts as a complete mitogen
that stimulates the tyrosine kinase/MAPK pathway in these cells.