Dependence of site-2 protease cleavage of ATF6 on prior site-1 protease digestion is determined by the size of the luminal domain of ATF6
ABSTRACT ATF6 is an endoplasmic reticulum (ER) membrane-anchored transcription factor activated by regulated intramembrane proteolysis in the ER stress response. The release of the cytosolic transcription factor domain of ATF6 requires the sequential processing by the Golgi site-1 and site-2 proteases (S1P and S2P). It has been unclear why S2P proteolysis relies on previous site-1 cleavage. One possibility is that S2P localizes to a different cellular compartment than S1P; however, here we show that S2P localizes to the same compartment as S1P, the cis/medial-Golgi. In addition, we have re-localized S1P and S2P to the ER with brefeldin A and find that the sequential cleavage of ATF6 is reconstituted in the ER. The mapping of the region of ATF6 required for sequential S1P and S2P cleavage showed that short luminal domains resulted in S1P-independent S2P cleavage. The addition of artificial domains onto these short ATF6 luminal domains restored the S1P dependence of S2P cleavage, suggesting that it is the size rather than specific sequences in the luminal domain that determines the S1P dependence of S2P cleavage. These results suggest that the bulky ATF6 luminal domain blocks S2P cleavage and that the role of S1P is to reduce the size of the luminal domain to prepare ATF6 to be an optimal S2P substrate.
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ABSTRACT: The study of gene expression in gonadotropes has largely focused on the variety of mechanisms regulating transcription of the gonadotropin genes and ancillary factors that contribute to the overall phenotype and function of these cells in reproduction. However, there are aspects of the response to GNRH signaling that are not readily explained by changes at the level of transcription. As our understanding of regulation at the level of mRNA translation has increased, it has become evident that GNRH receptor signaling engages multiple aspects of translational regulation. This includes activation of cap-dependent translation initiation, translational pausing caused by the unfolded protein response and RNA binding protein interaction. Gonadotropin mRNAs and the mRNAs of other factors that control the transcriptional and signaling responses to GNRH have been identified as targets of regulation at the level of translation. In this review we examine the impact of translational control of the expression of gonadotropin genes and other genes relevant to GNRH-mediated control of gonadotrope function.Molecular and Cellular Endocrinology 09/2013; DOI:10.1016/j.mce.2013.09.007 · 4.24 Impact Factor
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ABSTRACT: Over the past years, knowledge and evidence about the existence of crosstalks between cellular organelles and their potential effects on survival or cell death have been constantly growing. More recently, evidence accumulated showing an intimate relationship between endoplasmic reticulum and mitochondria. These close contacts not only establish extensive physical links allowing exchange of lipids and calcium but they can also coordinate pathways involved in cell life and death. It is now obvious that ER dysfunction/stress and Unfolded Protein Response (UPR) as well as mitochondria play major roles in apoptosis. However, while the effects of major ER stress on cell death have been largely studied and reviewed, it becomes more and more evident that cells might regularly deal with sublethal ER stress, a condition that does not necessarily lead to cell death but might affect the function/activity of other organelles such as mitochondria. In this review, we will particularly focus on these new, interesting and intriguing metabolic and morphological events that occur during the early adaptative phase of the ER stress, before the onset of cell death, and that remain largely unknown. Relevance and implication of these mitochondrial changes in response to ER stress conditions for human diseases such as type II diabetes and Alzheimer's disease will also be considered. J. Cell. Physiol. © 2013 Wiley Periodicals, Inc.Journal of Cellular Physiology 09/2013; 228(9). DOI:10.1002/jcp.24360 · 3.87 Impact Factor
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ABSTRACT: The endoplasmic reticulum (ER) is a dynamic intracellular organelle with multiple functions essential for cellular homeostasis, development, and stress responsiveness. In response to cellular stress, a well-established signaling cascade, the unfolded protein response (UPR), is activated. This intricate mechanism is an important means of re-establishing cellular homeostasis and alleviating the inciting stress. Now, emerging evidence has demonstrated that the UPR influences cellular metabolism through diverse mechanisms, including calcium and lipid transfer, raising the prospect of involvement of these processes in the pathogenesis of disease, including neurodegeneration, cancer, diabetes mellitus and cardiovascular disease. Here, we review the distinct functions of the ER and UPR from a metabolic point of view, highlighting their association with prevalent pathologies.International review of cell and molecular biology 01/2013; 301:215-90. DOI:10.1016/B978-0-12-407704-1.00005-1 · 4.52 Impact Factor