Abstract
Many sources of stress cause accumulation of unfolded or misfolded proteins in endoplasmic reticulum (ER), which elicits the unfolded protein response (UPR) to either promote cell survival or programmed cell death depending on different developmental context or stress severity. The Arabidopsis membrane-associated transcription factor, bZIP28, is the functional equivalent of mammalian ATF6, which relocates from the ER to the Golgi where it is proteolytically processed and released from the membrane to the nucleus to mediate the UPR. Although the canonical site-1 protease (S1P) cleavage site on the ER lumen-facing domain is well conserved between bZIP28 and ATF6, the importance of S1P cleavage on bZIP28 has not been experimentally demonstrated. Here we provide genetic evidence that the RRIL(573) site, but not the RVLM(373) site, on the lumen-facing domain of bZIP28 is critical for the biological function of bZIP28 under ER stress condition. Further biochemistry and cell biology studies demonstrated that the RRIL(573) site, but not the RVLM(373) site, is required for proteolytic processing and nuclear relocation of bZIP28 in response to ER stress. Our results reveal that S1P cleavage site plays a pivotal role in activation and function of bZIP28 during UPR in plants.
Highlights
State Key Laboratory of Genetic Engineering, Institute of Plant Biology, School of Life Sciences, Fudan University, Shanghai 200433, China
In response to endoplasmic reticulum (ER) stress, ATF6 relocates from the ER to the Golgi where it is processed by two Golgi-resident site-1 protease (S1P) and site-2 protease (S2P) [21]
Ortholog of ATF6 is not presented in the Arabidopsis genome, the ER membrane-associated bZIP transcription factor bZIP28 is found to be the functional equivalent of mammalian ATF6, which is activated in a similar way to ATF6 [22 24]
Summary
The Arabidopsis membrane-associated transcription factor, bZIP28, is the functional equivalent of mammalian ATF6, which relocates from the ER to the Golgi where it is proteolytically processed and released from the membrane to the nucleus to mediate the UPR. The canonical site-1 protease (S1P) cleavage site on the ER lumen-facing domain is well conserved between bZIP28 and ATF6, the importance of S1P cleavage on bZIP28 has not been experimentally demonstrated. Further biochemistry and cell biology studies demonstrated that the RRIL573 site, but not the RVLM373 site, is required for proteolytic processing and nuclear relocation of bZIP28 in response to ER stress. Ortholog of ATF6 is not presented in the Arabidopsis genome, the ER membrane-associated bZIP transcription factor bZIP28 is found to be the functional equivalent of mammalian ATF6, which is activated in a similar way to ATF6 [22 24]. The importance of the S1P cleavage site in the lumen-facing domain of bZIP28 has not been experimentally demonstrated
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