Transcriptional regulation of VEGF-A by the unfolded protein response pathway.
BACKGROUND
Angiogenesis is crucial to many physiological and pathological processes including development and cancer cell survival. Vascular endothelial growth factor-A (VEGFA) is the predominant mediator of angiogenesis in the VEGF family. During development, adverse environmental conditions like nutrient deprivation, hypoxia and increased protein secretion occur. IRE1alpha, PERK, and ATF6alpha, master regulators of the unfolded protein response (UPR), are activated under these conditions and are proposed to have a role in mediating angiogenesis.


RESULTS
Here we show that IRE1alpha, PERK, and ATF6alpha powerfully regulate VEGFA mRNA expression under various stress conditions. In Ire1alpha(-/-) and Perk(-/-) mouse embryonic fibroblasts and ATF6alpha-knockdown HepG2 cells, induction of VEGFA mRNA by endoplasmic reticulum stress is attenuated as compared to control cells. Embryonic lethality of Ire1alpha-/- mice is due to the lack of VEGFA induction in labyrinthine trophoblast cells of the developing placenta. Rescue of IRE1alpha and PERK in Ire1alpha(-/-) and Perk(-/-) cells respectively, prevents VEGFA mRNA attenuation. We further report that the induction of VEGFA by IRE1alpha, PERK and ATF6 involves activation of transcription factors, spliced-XBP-1, ATF4 and cleaved ATF6 respectively.


CONCLUSIONS
Our results reveal that the IRE1alpha-XBP-1, PERK-ATF4, and ATF6alpha pathways constitute novel upstream regulatory pathways of angiogenesis by modulating VEGF transcription. Activation of these pathways helps the rapidly growing cells to obtain sufficient nutrients and growth factors for their survival under the prevailing hostile environmental conditions. These results establish an important role of the UPR in angiogenesis.
Ghosh
Rajarshi
R
Program in Gene Function and Expression, University of Massachusetts Medical School, Worcester, Massachusetts, United States of America.
Lipson
Kathryn L
KL
Sargent
Karen E
KE
Mercurio
Arthur M
AM
Hunt
Joan S
JS
Ron
David
D
Urano
Fumihiko
F
D051702:Activating Transcription Factor 6 / Q000378:metabolism; D017398:Alternative Splicing; D000818:Animals; D004268:DNA-Binding Proteins / Q000378:metabolism; D004722:Endoribonucleases / Q000378:metabolism; D005786:Gene Expression Regulation; D006801:Humans; D051379:Mice; D008822:Mice, Transgenic; D017346:Protein Serine-Threonine Kinases / Q000378:metabolism; D000071701:Regulatory Factor X Transcription Factors; D014157:Transcription Factors / Q000378:metabolism; D056811:Unfolded Protein Response; D042461:Vascular Endothelial Growth Factor A / Q000378:metabolism*; D000071717:X-Box Binding Protein 1; D019892:eIF-2 Kinase / Q000378:metabolism
D051702:Activating Transcription Factor 6; D004268:DNA-Binding Proteins; D004722:Endoribonucleases; D017346:Protein Serine-Threonine Kinases; D000071701:Regulatory Factor X Transcription Factors; D014157:Transcription Factors; D042461:Vascular Endothelial Growth Factor A; D000071717:X-Box Binding Protein 1; D019892:eIF-2 Kinase; C497111:ATF6 protein, human; C497112:Atf6 protein, mouse; C000605543:XBP1 protein, human; C000605544:Xbp1 protein, mouse; C528229:ERN1 protein, human; C510185:Ern1 protein, mouse