No abstract

Vascular endothelial growth factor (VEGF) plays a pivotal role in angiogenesis. Previous studies focused on transcriptional regulation modulated by proximal upstream cis-regulatory elements (CREs) of the human vegfa promoter. However, we hypothesized that distal upstream CREs may also be involved in controlling vegfa transcription. In this study, we found that the catalytic domain of Seryl-tRNA synthetase (SerRS) interacted with transcription factor Yin Yang 1 (YY1) to form a SerRS/YY1 complex that negatively controls vegfa promoter activity through binding distal CREs at −4654 to −4623 of vegfa. Particularly, we demonstrated that the −4654 to −4623 segment, which predominantly controls vegfa promoter activity, is involved in competitive binding between SerRS/YY1 complex and NFKB1. We further showed that VEGFA protein and blood vessel development were reduced by overexpression of either SerRS or YY1, but enhanced by the knockdown of either SerRS or yy1. In contrast, these same parameters were enhanced by overexpression of NFKB1, but reduced by knockdown of nfkb1. Therefore, we suggested that SerRS does not bind DNA directly but form a SerRS/YY1 complex, which functions as a negative effector to regulate vegfa transcription through binding at the distal CREs; while NFKB1 serves as a positive effector through competing with SerRS/YY1 binding at the overlapping CREs.

No abstract

Upstream open reading frames (uORFs) are known to negatively affect translation of the downstream ORF. The regulatory proteins involved in relieving this inhibition are however poorly characterized. In response to cellular stress, eIF2a phosphorylation leads to an inhibition of global protein synthesis, while translation of specific factors such as CHOP is induced. We analyzed a 105-nt inhibitory uORF in the transcript of human CHOP (huORF chop ) and found that overexpression of the zebrafish or human ENDOU poly(U)-endoribonuclease (Endouc or ENDOU-1, respectively) increases CHOP mRNA translation also in the absence of stress. We also found that Endouc/ ENDOU-1 binds and cleaves the huORF chop transcript at position 80G-81U, which induces CHOP translation independently of phosphorylated eIF2a. However, both ENDOU and phospho-eIF2a are nonetheless required for maximal translation of CHOP mRNA. Increased levels of ENDOU shift a huORF chop reporter as well as endogenous CHOP transcripts from the monosome to polysome fraction, indicating an increase in translation. Furthermore, we found that the uncapped truncated huORF chop -69-105-nt transcript contains an internal ribosome entry site (IRES), facilitating translation of the cleaved transcript. Therefore, we propose a model where ENDOU-mediated transcript cleavage positively regulates CHOP translation resulting in increased CHOP protein levels upon stress. Specifically, CHOP transcript cleavage changes the configuration of huORF chop thereby releasing its inhibition and allowing the stalled ribosomes to resume translation of the downstream ORF.

Background: Dkk3a regulates the promoter activity of myf5 through an unknown receptor. Results: Itg␣6b is a high affinity Dkk3a receptor through its ␤-propeller domains. Conclusion: Dkk3a regulates the promoter activity of myf5 through interaction with receptor Itg␣6b. Significance: This study discovered a novel mechanism for Dkk3a to regulate the promoter activity of myf5 during myogenesis.