Sg. Liu et al., TRANSFORMING GROWTH-FACTOR-BETA-1 REGULATES THE EXPRESSION OF PAX-2, A DEVELOPMENTAL CONTROL GENE, IN RENAL TUBULE CELLS, Experimental nephrology, 5(4), 1997, pp. 295-300
Background/Aims: The pattern-forming event of kidney tubulogenesis is
initiated by the inductive transition of mesenchymal cells to epitheli
al phenotype; a transition that is critically dependent on the regulat
ed expression of the developmental control gene, Pax-2. Because of a d
efined role in in vitro renal tubulogenesis, the effects of epidermal
growth factor (EGF), transforming growth factor (TGF)-beta 1 and retin
oic acid on Pax-2 gene expression in proximal tubule cells (PTC) were
evaluated. Methods: Rabbit PTC were isolated and grown in tissue cultu
re. Under confluent quiescent conditions, the effect of various factor
s on Pax-2 gene expression was assessed by Northern blot analysis. To
assess whether the effect of TGF-beta 1 to alter Pax-2 gene expression
was due to transcriptional or posttranscriptional events, nuclear run
-on assays were also undertaken. Results: Under control, confluent gro
wth conditions, PTC expressed high levels of Pax-2. A 24-hour exposure
to EGF (10 nM), a potent mitogen of PTC, increased this level of expr
ession. In contrast, Pax-2 gene expression was suppressed by treating
PTC with retinoic acid (10 mM), a well-described differentiating facto
r, and with TGF-beta 1 (10 ng/ml), a recognized antiproliferative agen
t for these cells, which suggests that Pax-2 has a role in renal cell
proliferation. The mechanism of the effect of TGF-beta 1 on Pax-2 mRNA
levels was further detailed. TGF-beta 1 did not affect Pax-2 transcri
ption rates, as assessed by nuclear run-on assays; however, in a dose-
dependent manner, it diminished the stability of Pax-2 mRNA. At a conc
entration of 10 ng/ml, TGF-beta 1 reduced Pax-2 mRNA stability from a
control half-life of 120 min to a half-life of less than 60 min. Concl
usion: This study demonstrates that various soluble inductive factors
affect Pax-2 gene expression in renal tubule cells. Also, TGF-beta 1 d
ownregulates Pax-2 gene expression through a posttranscriptional proce
ss, an acknowledged mechanism for modulating important growth regulato
ry gene products.