The endoplasmic reticulum (ER) Unfolded Protein Response (UPR) restores equilibrium to the ER, but prolonged expression of the UPR effector CHOP (GADD153) is cytotoxic. We found that ER stress-induced CHOP expression was suppressed by prior engagement of toll-like receptor (TLR) 3 or 4 through a TRIF-dependent pathway. TLR engagement did not suppress phosphorylation of PERK or eIF-2α, which are upstream of CHOP, but phospho-eIF-2α failed to promote translation of the CHOP activator ATF4. In mice subjected to systemic ER stress, pre-treatment with low-dose lipopolysaccharide (LPS), a TLR4 ligand, suppressed CHOP expression and apoptosis in splenic macrophages, renal tubule cells, and hepatocytes, and prevented renal dysfunction and hepatosteatosis. This protective effect of LPS did not occur in Trif−/− mice nor in wild-type mice in which CHOP expression was genetically restored. Thus, TRIF-mediated signals from TLRs selectively attenuate translational activation of ATF4 and its downstream target gene CHOP. We speculate that this mechanism evolved to promote survival of TLR-expressing cells that experience prolonged levels of physiologic ER stress in the course of the host response to invading pathogens.

The transcriptionally active fragment of the yeast RNA polymerase II transcription elongation factor, TFIIS, comprises a three-helix bundle and a zinc ribbon motif joined by a linker region. We have probed the function of this fragment of TFIIS using structureguided mutagenesis. The helix bundle domain binds RNA polymerase II with the same affinity as does the full-length TFIIS, and this interaction is mediated by a basic patch on the outer face of the third helix. TFIIS mutants that were unable to bind RNA polymerase II were inactive for transcription activity, confirming the central role of polymerase binding in the TFIIS mechanism of action. The linker and zinc ribbon regions play roles in promoting cleavage of the nascent transcript and read-through past the block to elongation. Mutation of three aromatic residues in the zinc ribbon domain (Phe 269 , Phe 296 , and Phe 308 ) impaired both transcript cleavage and read-through. Mutations introduced in the linker region between residues 240 and 245 and between 250 and 255 also severely impaired both transcript cleavage and read-through activities. Our analysis suggests that the linker region of TFIIS probably adopts a critical structure in the context of the elongation complex.Elongating RNA polymerase II stalls upon encountering blocks to elongation in vitro (1). In some cases, these transiently stalled polymerases convert to very stable arrested complexes. Arrested complexes are unable to resume transcription even after hours to weeks of incubation (2). The inability of such complexes to resume transcription results from a structural change in the stalled polymerase, which causes the active site to disengage from the 3Ј-end of the transcript (3). The general elongation factor TFIIS 1 reactivates arrested transcription complexes within minutes (4). The reactivation process involves a TFIIS-stimulated endonucleolytic cleavage of the transcript by the RNA polymerase II (5, 6), which relocates the polymerase active site to the new 3Ј-end of the RNA chain and allows for chain extension. The reactivation of stalled elongation complexes involves multiple steps, with the first being the interaction of TFIIS with RNA polymerase II. The TFIIS-binding domain on RNA polymerase II was identified by Friesen and colleagues (7), who discovered mutants in the largest subunit of RNA polymerase II, RPB1, that displayed the same phenotype as a strain deleted for the TFIIS gene (sensitivity to the drug 6-azauracil) and that also could be suppressed by overexpression of TFIIS. These mutants localized to a part of RPB1 between regions G and H, which are conserved from bacteria to man and are in close proximity to the RNA polymerase active site (8, 9). The genetic evidence for a TFIIS interacting domain was confirmed biochemically, when two of the mutant RNA polymerases were purified and shown directly to have 500-fold lower affinity for TFIIS compared with the wild-type polymerase (10).Transcript cleavage is the next essential step in the reactivation process. It is now clear that R...

Patients with end-stage cardiomyopathy and congestive heart failure are increasingly undergoing implantation with left ventricular assist devices (LVADs). In addition, implantable cardioverter-defibrillator (ICD) therapy has been proven to be an important part of the treatment for cardiomyopathy/congestive heart failure. Previous reports have noted a potential and dramatic electromagnetic interference from LVADs on ICDs that cause impaired telemetry communication between the ICD and ICD programmer. Such interference has necessitated explantation and generator replacement in order to resume communication between the ICD and programmer. We report two patients with advanced congestive heart failure and ICD programming impairment caused by a HeartMate II LVAD (Thoratec Corporation, Pleasanton, CA, USA) that was overcome by placing aluminum shielding around the ICD programmer wand and steel shielding around the extension cable during ICD interrogation.