Rac1 activates HIF-1 in retinal pigment epithelium cells under hypoxia.
BACKGROUND
Upregulation of vascular endothelial growth factor (VEGF) in hypoxic retinal pigment epithelium (RPE) cells, mediated by hypoxia-inducible factor-1 (HIF-1) is responsible for choroidal neovascularization (CNV). HIF-1alpha is the inducible subunit of HIF-1, but the underlying mechanisms by which RPE cells sense a decrease in oxygen concentration and transduce this signal to HIF-1alpha are largely unknown. Rho family small GTPase Rac1, as a potential intermediate, possibly plays a pivotal role in activating HIF-1alpha in RPE cells under hypoxia.


OBJECTIVE
To further define Rac1 playing an essential role in the induction of HIF-1alpha expression in RPE cells under hypoxia.


METHODS
In this study, we examined the expression of HIF-1alpha and Rac1 in human RPE cells under hypoxia for 0, 1, 2, 4, 8, 12 and 24 h by RT-PCR and Western blot. To elucidate whether Rac1 is responsible for activating the expression of hypoxia-induced HIF-1alpha, human RPE cells were treated with Rac1 inhibitor NSC23766 under hypoxia for 0, 1, 2, 4, 8, 12 and 24 h, and expression of HIF-1alpha and Rac1 measured by RT-PCR and Western blot.


RESULTS
The mRNA expression of HIF-1alpha and Rac1 in RPE cells significantly increased in a time-dependent manner, reaching the maximum at 4 h, and thereafter slowly declined. HIF-1alpha protein induction in human RPE cells was found after 1 h of hypoxia, reaching the maximum at 8 h, and then slowly declined. In response to hypoxia, the levels of Rac1 protein significantly increased, reaching the maximum at 4 h, and then slowly declined. After treatment with NSC23766, both HIF-1alpha and Rac1 expression were significantly inhibited in hypoxic RPE cells.


CONCLUSIONS
Rac1 is crucial to activate HIF-1 in RPE cells under hypoxia, which may be a novel target other than VEGF and HIF-1 in developing CNV inhibitors.
Zhang
Peng
P
Department of Ophthalmology, Xijing Hospital, Fourth Military Medical University, Xi'an, Shaanxi Province, 710032, PR China.
Zhang
Xing
X
Hao
Xiaofeng
X
Wang
Yusheng
Y
Hui
Yannian
Y
Wang
Haiyan
H
Hu
Dan
D
Zhou
Jian
J
D000634:Aminoquinolines / Q000494:pharmacology; D015153:Blotting, Western; D002478:Cells, Cultured; D015536:Down-Regulation; D005786:Gene Expression Regulation / Q000502:physiology*; D006801:Humans; D000860:Hypoxia / Q000378:metabolism*; D051795:Hypoxia-Inducible Factor 1, alpha Subunit / Q000037:antagonists & inhibitors / Q000235:genetics* / Q000378:metabolism; D007124:Immunoenzyme Techniques; D011743:Pyrimidines / Q000494:pharmacology; D012333:RNA, Messenger / Q000378:metabolism; D055213:Retinal Pigment Epithelium / Q000187:drug effects / Q000378:metabolism*; D020133:Reverse Transcriptase Polymerase Chain Reaction; D013997:Time Factors; D020830:rac1 GTP-Binding Protein / Q000037:antagonists & inhibitors / Q000502:physiology*
D000634:Aminoquinolines; C497442:HIF1A protein, human; D051795:Hypoxia-Inducible Factor 1, alpha Subunit; C487513:NSC 23766; D011743:Pyrimidines; C107953:RAC1 protein, human; D012333:RNA, Messenger; D020830:rac1 GTP-Binding Protein