Antitumor agent PX-12 inhibits HIF-1α protein levels through an Nrf2/PMF-1-mediated increase in spermidine/spermine acetyl transferase.
OBJECTIVE
Thioredoxin-1 (Trx-1) redox signaling regulates multiple aspects of cell growth and survival, and elevated tumor levels of Trx-1 have been associated with decreased patient survival. PX-12, an inhibitor of Trx-1 currently in clinical development, has been found to decrease tumor levels of the HIF-1α transcription factor. SSAT1 has been reported to bind to HIF-1α and RACK1, resulting in oxygen-independent HIF-1 ubiquitination and degradation. SSAT2, a related protein, stabilizes the interaction of the VHL protein and elongin C with HIF-1 leading to oxygen-dependent HIF-1α ubiquitination and degradation. We investigated the effects of PX-12 and Trx-1 on SSAT1, SSAT2, and inhibition of HIF-1α.


METHODS
A panel of cell lines was treated with PX-12 to investigate its effects on SSAT1 and SSAT2 expression, and on HIF-1α protein levels. We also evaluated the regulation of SSAT1 through the Nrf2 and PMF-1, two trans-acting transcription factors.


RESULTS
We found that PX-12 increased nuclear Nrf2 activity and antioxidant response element binding. PX-12 also increased the expression of SSAT1 but not SSAT2 in a PMF-1-dependent manner that was independent of Trx-1. Inhibition of Nrf2 or PMF-1 prevented the increase in SSAT1 caused by PX-12.


CONCLUSIONS
The results show that PX-12, acting independently of Trx-1, increases nuclear Nrf2, which interacts with PMF-1 to increase the expression of SSAT1. The degradation of HIF-1α that results from binding with SSAT1 may explain the decrease in HIF-1α caused by PX-12 and could contribute to the antitumor activity of PX-12.
Department of Experimental Therapeutics, The University of Texas M. D. Anderson Cancer Center, Houston, TX 77030, USA. yhkim@mdanderson.org
Yon Hui
YH
Kim
Amy
A
Coon
Amanda F
AF
Baker
Garth
G
Powis
D000123:Acetyltransferases / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism*; D000970:Antineoplastic Agents / Q000494:pharmacology*; D000975:Antioxidants / Q000378:metabolism; D015687:Cell Hypoxia / Q000187:drug effects; D002461:Cell Line, Transformed; D045744:Cell Line, Tumor; D004268:DNA-Binding Proteins / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism; D004220:Disulfides / Q000494:pharmacology*; D015972:Gene Expression Regulation, Neoplastic / Q000187:drug effects; D020868:Gene Silencing; D006801:Humans; D051795:Hypoxia-Inducible Factor 1, alpha Subunit / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism*; D007093:Imidazoles / Q000494:pharmacology*; D007527:Isoenzymes / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism; D051267:NF-E2-Related Factor 2 / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism*; D009363:Neoplasm Proteins / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism; D009369:Neoplasms / Q000188:drug therapy / Q000378:metabolism*; D012333:RNA, Messenger / Q000378:metabolism; D034741:RNA, Small Interfering; D020218:Response Elements / Q000187:drug effects; D015398:Signal Transduction / Q000187:drug effects; D013879:Thioredoxins / Q000037:antagonists & inhibitors / Q000235:genetics; D014157:Transcription Factors / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism*; D000099228:Diamine N-Acetyltransferase
D000123:Acetyltransferases; D000970:Antineoplastic Agents; D000975:Antioxidants; D004268:DNA-Binding Proteins; D004220:Disulfides; D051795:Hypoxia-Inducible Factor 1, alpha Subunit; D007093:Imidazoles; D007527:Isoenzymes; D051267:NF-E2-Related Factor 2; D009363:Neoplasm Proteins; D012333:RNA, Messenger; D034741:RNA, Small Interfering; D013879:Thioredoxins; D014157:Transcription Factors; D000099228:Diamine N-Acetyltransferase; C497442:HIF1A protein, human; C495635:NFE2L2 protein, human; C120655:PMF1 protein, human; C412893:1-methylpropyl-2-imidazolyl disulfide