Transforming growth factor-beta 1 regulates the expression of Pax-2, a developmental control gene, in renal tubule cells.
OBJECTIVE
The pattern-forming event of kidney tubulogenesis is initiated by the inductive transition of mesenchymal cells to epithelial phenotype; a transition that is critically dependent on the regulated expression of the developmental control gene, Pax-2. Because of a defined role in in vitro renal tubulogenesis, the effects of epidermal growth factor (EGF), transforming growth factor (TGF)-beta 1 and retinoic acid on Pax-2 gene expression in proximal tubule cells (PTC) were evaluated.


METHODS
Rabbit PTC were isolated and grown in tissue culture. Under confluent quiescent conditions, the effect of various factors 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 growth 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 expression. In contrast, Pax-2 gene expression was suppressed by treating PTC with retinoic acid (10 mM), a well-described differentiating factor, and with TGF-beta 1 (10 ng/ml), a recognized antiproliferative agent 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 transcription rates, as assessed by nuclear run-on assays; however, in a dose-dependent manner, it diminished the stability of Pax-2 mRNA. At a concentration 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.


CONCLUSIONS
This study demonstrates that various soluble inductive factors affect Pax-2 gene expression in renal tubule cells. Also, TGF-beta 1 downregulates Pax-2 gene expression through a posttranscriptional process, an acknowledged mechanism for modulating important growth regulatory gene products.
Liu
S
S
Veterans Administration Medical Center, Ann Arbor, Mich., USA.
Cieslinski
D A
DA
Funke
A J
AJ
Humes
H D
HD
D000818:Animals; D002454:Cell Differentiation; D002455:Cell Division; D002467:Cell Nucleus / Q000378:metabolism; D002478:Cells, Cultured; D015342:DNA Probes; D004268:DNA-Binding Proteins / Q000096:biosynthesis*; D005786:Gene Expression Regulation / Q000187:drug effects*; D007687:Kidney Tubules, Proximal / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*; D051762:PAX2 Transcription Factor; D012323:RNA Processing, Post-Transcriptional; D012333:RNA, Messenger / Q000378:metabolism; D011817:Rabbits; D014157:Transcription Factors / Q000096:biosynthesis*; D014158:Transcription, Genetic; D016212:Transforming Growth Factor beta / Q000494:pharmacology*; D014212:Tretinoin / Q000494:pharmacology
D015342:DNA Probes; D004268:DNA-Binding Proteins; D051762:PAX2 Transcription Factor; D012333:RNA, Messenger; D014157:Transcription Factors; D016212:Transforming Growth Factor beta; D014212:Tretinoin