Studies on the sequestration of hCdc73 into stress granules regulating p53 mRNA stability during cellular stress response

Abstract

Mammalian cells initiate the formation of stress granules (SGs) in response to diverse stress conditions. Among the numerous proteins recruited to SGs are RNA- binding proteins and transcription regulators. This study describes the translocation of hCdc73, a component of the PAF1 transcription complex, to cytosolic SGs during arsenic stress. The hCdc73 protein contains an intrinsically disordered region (IDR) spanning amino acids 256-416, which is essential for its translocation to cytosolic SGs. In vitro experiments demonstrated that the purified hCdc73 IDR can form molecular condensates, and the light-activated assembly of hCdc73 IDR-Cry2 was confirmed. Additionally, for the translocation of hCdc73 to SGs, physical interactions with SG carrier proteins, such as FMR1, are necessary. A previous report revealed that hCdc73, in conjunction with eEF1Bγ, forms a complex responsible for binding and regulating the stability of p53 mRNA in the cytosol. Under conditions of sodium arsenite treatment, the selective sequestration of cytosolic hCdc73, but not eEF1Bγ or p53 mRNA was observed. Consequently, a transient increase in p53 mRNA levels was noted, likely reflecting the pool of p53 mRNA subject to regulation by cytosolic hCdc73. In summary, this study suggests that controlling the availability of mRNAs for stress-responsive genes involves sequestering their negative regulators within SGs.