Mechanisms of Transcriptional Regulation by an ER Stress‐Responsive Enhancer

ATF6α is a transcription factor that functions as a master regulator of many ER stress‐responsive target genes. HSPA5 (also known as Grp78) is an ATF6α‐targeted ER‐stress responsive genes. It contains 3 tandemly repeated ER stress response elements (ERSE). The ERSE enhancer‐like sites are very close to the core promoter, making it an excellent model for studies of enhancer function using a natural promoter with its regulatory regions. Previous studies have shown that a collection of transcription factors contribute to transcriptional regulation via the HSPA5 ERSE region; however, little is known about how these transcription factors collaborate to drive activation. To gain insight into this question, we have established an in vitro system that recapitulates ATF6α‐dependent transcriptional activation with purified RNA polymerase II, Mediator, and transcription factors. An unexpected finding from this work is our discovery that Elongin, best known as an RNA polymerase II elongation factor, plays an important role in ATF6α and NF‐Y dependent activation of the HSPA5 promoter. Mechanistic studies suggest that Elongin functions with TFIID and Mediator at an early stage in assembly of active initiation complexes. These results provide a foundation for future efforts to dissect the interplay of ERSE‐binding transcription factors and coregulators in HSPA5 activation. Support or Funding Information This work was supported in part by a grant to the Stowers Institute for Medical Research from the Helen Nelson Medical Research Fund at the Greater Kansas City Community Foundation.