Coordination of Growth and Endoplasmic Reticulum Stress Signaling by Regulator of Calcineurin 1 (RCAN1), a Novel ATF6-inducible Gene

Abstract

Exposing cells to conditions that modulate growth can impair endoplasmic reticulum (ER) protein folding, leading to ER stress and activation of the transcription factor, ATF6. ATF6 binds to ER stress response elements in target genes, inducing expression of proteins that enhance the ER protein folding capacity, which helps overcome the stress and foster survival. To examine the mechanism of ATF6-mediated survival in vivo, we developed a transgenic mouse model that expresses a novel conditionally activated form of ATF6. We previously showed that activating ATF6 protected the hearts of ATF6 transgenic mice from ER stresses. In the present study, transcript profiling identified modulatory calcineurin interacting protein-1 (MCIP1), also known as regulator of calcineurin 1 (RCAN1), as a novel ATF6-inducible gene that encodes a known regulator of calcineurin/nuclear factor of activated T cells (NFAT)-mediated growth and development in many tissues. The ability of ATF6 to induce RCAN1 in vivo was replicated in cultured cardiac myocytes, where adenoviral (AdV)-mediated overexpression of activated ATF6 induced the RCAN1 promoter, up-regulated RCAN1 mRNA, inhibited calcineurin phosphatase activity, and exerted a striking growth modulating effect that was inhibited by RCAN1-targeted small interfering RNA. These results demonstrate that RCAN1 is a novel ATF6 target gene that may coordinate growth and ER stress signaling pathways. By modulating growth, RCAN1 may reduce the need for ER protein folding, thus helping to overcome the stress and enhance survival. Moreover, these results suggest that RCAN1 may also be a novel integrator of growth and ER stress signaling in many other tissues that depend on calcineurin/NFAT signaling for optimal growth and development.About 35% of all proteins, including secreted, cell surface and most organelle-targeted proteins are synthesized in the ER (1).Conditions that perturb ER calcium, protein glycosylation or redox status, impair nascent protein folding, triggering the ER stress response (ERSR), 4 also known as the unfolded protein response (2, 3). The ERSR has central roles in all metazoan cells, and has been shown to be important in the differentiation and function of secretory cells, including B lymphocytes, ␤-cells of the pancreas and the liver. Moreover, ER stress has been associated with neurodegenerative diseases (4), as well as pathologies that are precipitated upon impaired oxygen and nutrient delivery (i.e. ischemia) resulting from cardiovascular disease. Ischemia has been shown to activate the ERSR in brain, kidney, liver, and heart, as well as in tumor tissue in vivo (5-9).Initially, ER stress leads to remodeling of the ER protein biosynthetic machinery in attempts to overcome the stress. This initial phase of remodeling includes the transcriptional induction of genes that encode ER-targeted chaperones and folding enzymes that help proteins fold in the ER lumen. In addition, ER stress up-regulates genes encoding components of an ERassociated degradation system, which is respon...

Ischemia Activates the ATF6 Branch of the Endoplasmic Reticulum Stress Response

“…The resulting N-terminal fragment of ATF6 translocates to the nucleus, where it binds to several types of regulatory sequences in target genes, such as ER stress elements (ERSEs), and activates ER stress response gene transcription (7, 10, 14, 26 -37). A microarray study in the mouse heart showed that upon activation, ATF6 induced nearly 400 genes (38), supporting the hypothesis that ATF6 is a central regulator of numerous ER stress response genes, many of which may serve protective roles. The current study was undertaken to examine roles for ATF6 in ischemia-mediated ER stress gene induction of a prototypical ER stress response gene, GRP78, in a cultured cardiac myocyte model system of simulated ischemia/reperfusion.…”

“…Each well was incubated for 5 h with 10 pmol of each Stealth siRNA using TransMessenger TM transfection reagent (Qiagen, Valencia, CA), as described previously (38). The cells were then washed off the plates and replated at a density of 0.7 ϫ 10 6 cells/well on fibronectincoated 6-well plates.…”

“…glucose and oxygen deprivation (no glucose, 0.1% O 2 )), as described previously (20,38,41). Upon sI, rat grp78 mRNA progressively increased with time, attaining a maximum after 20 h of sI (Fig.…”

Sublethal endoplasmic reticulum stress caused by the mutation of immunoglobulin heavy chain-binding protein induces the synthesis of a mitochondrial protein, pyrroline-5-carboxylate reductase 1

“…A previous study reported that the expression of PYCR1 mRNA was enhanced in transgenic mice with an activated form of ATF6 (Belmont et al 2008). In fact, we found an ATF6 inhibitor, AEBSF, reduced the expression of PYCR1 under ER stress condition.…”

Novel CDNF/MANF family of neurotrophic factors

“…Upregulation of Manf by ER stress conditions has been shown by microarray analyses (Lee et al, 2003;Mizobuchi et al, 2007;Belmont et al, 2008), suggesting that Manf has a role in the quality control of proteins during ER stress (Lee et al, 2003). Manf was also upregulated in cell lines by different UPR inducers (Apostolou et al, 2008).…”