13-cis retinoic acid exerts its specific activity on human sebocytes through selective intracellular isomerization to all-trans retinoic acid and binding to retinoid acid receptors
M. Tsukada et al., 13-cis retinoic acid exerts its specific activity on human sebocytes through selective intracellular isomerization to all-trans retinoic acid and binding to retinoid acid receptors, J INVES DER, 115(2), 2000, pp. 321-327
Despite its potent biologic effect on human sebocytes, 13-cis retinoic acid
exhibits low binding affinity for cellular retinoic acid binding proteins
and nuclear retinoid receptors. Hence, 13-cis retinoic acid may represent a
pro-drug possibly acting through all-trans isomerization. In this study, m
arked isomerization of 13-cis retinoic acid has been confirmed in cultured
SZ95 sebocytes showing 2- to 15-fold higher levels of all-trans retinoic ac
id at 12-72 h, as measured by high performance liquid chromatography. In co
ntrast, only low amounts of all-trans retinoic acid were converted intracel
lularly to its 13-cis isoform. 9-cis retinoic acid was not detected after e
ither 13-cis retinoic acid or all-trans retinoic acid treatment. The rapid
isomerization of 13-cis retinoic acid to high levels of all-trans retinoic
acid was a sebocyte-specific event, as no significant isomerization of 13-c
is retinoic acid to all-trans retinoic acid occurred in HaCaT keratinocytes
. De novo mRNA expression of cytochrome P450 1A1, a major xenobiotic metabo
lizing enzyme, in SZ95 sebocytes was induced by all-trans retinoic acid, bu
t not by 13-cis retinoic acid. In addition, mRNA levels of cellular retinoi
c acid-binding protein II, which is supposed to regulate the concentration
of intracellular all-trans retinoic acid, rapidly increased under all-trans
retinoic acid treatment (30 min-6 h), whereas the 13-cis retinoic acid eff
ect was markedly weaker and delayed. Both 13-cis retinoic acid and all-tran
s retinoic acid suppressed mRNA expression of cytochrome P450 1A2. In paral
lel experiments, 13-cis retinoic acid significantly reduced SZ95 sebocyte p
roliferation at 10(-7) M, show- ing 30-40% inhibition after 9 d. All-trans
retinoic acid and 9-cis retinoic acid exhibited similar anti-proliferative
effects. AGN 193109, a pan-antagonist of the retinoic acid receptors, antag
onized the anti-proliferative activity of all retinoic acid isomers tested
in a concentration-dependent manner with complete abolishment at ratios of
1:10 13-cis retinoic acid and 1:1 all-trans retinoic acid. Coincubation of
SZ95 sebocytes with 13-cis retinoic acid and AGN 193109 did not alter the i
ntracellular concentration of 13-cis retinoic acid and its isomerization pr
ofile. In contrast, the retinoid X receptor antagonist CD 3507 did not affe
ct the inhibition of SZ95 sebocyte proliferation induced by retinoic acids.
Our findings indicate: (i) a selective 13-cis retinoic acid isomerization
to all-trans retinoic acid in the intracellular compartment of SZ95 sebocyt
es; (ii) a reduced all-trans retinoic acid inactivation process after 13-ci
s retinoic acid treatment as compared with treatment with all-trans retinoi
c acid; and (iii) a retinoic acid receptor-mediated inhibition of SZ95 sebo
cyte proliferation. These data explain the sebocyte-specific activity of 13
-cis retinoic acid and support a pro-drug/drug relation between 13-cis reti
noic acid and all-trans retinoic acid.