No abstract

The actin-binding protein filamin links membrane receptors to the underlying cytoskeleton. The cytoplasmic domains of these membrane receptors have been shown to bind to various filamin immunoglobulin repeats. Notably, among 24 human filamin repeats, repeat 17 was reported to specifically bind to platelet receptor glycoprotein Ib␣ and repeat 21 to integrins. However, a complete sequence alignment of all 24 human filamin repeats reveals that repeats 17 and 21 actually belong to a distinct filamin repeat subgroup (containing repeats 4, 9, 12, 17, 19, 21, and 23) that shares a conserved ligand-binding site. Using isothermal calorimetry and NMR analyses, we show that all repeats in this subgroup can actually bind glycoprotein Ib␣, integrins, and a cytoskeleton regulator migfilin in similar manners. These data provide a new view on the ligand specificity of the filamin repeats. They also suggest a multiple ligand binding mechanism where similar repeats within a filamin monomer may promote receptor clustering or receptor cross-talking for regulation of the cytoskeleton organization and diverse filaminmediated cellular activities.

Protein aggregation is a common feature of several neurodegenerative diseases, including amyotrophic lateral sclerosis (ALS) and frontotemporal lobar degeneration. How protein aggregates are formed and contribute to neurodegeneration, however, is not clear. Mutation of Ubiquilin 2 (UBQLN2) has recently been linked to ALS and frontotemporal lobar degeneration. Therefore, we examined the effect of ALS-linked UBQLN2 mutation on endoplasmic reticulum-associated protein degradation (ERAD). Compared to its wild-type counterpart, mutated UBQLN2 caused greater accumulation of the ERAD substrate Hong Kong variant of a-1-antitrypsin, although ERAD was disturbed by both UBQLN2 overexpression and knockdown. Also, UBQLN2 interacted with ubiquitin regulatory X domain-containing protein 8 (UBXD8) in vitro and in vivo, and this interaction was impaired by pathogenic mutation of UBQLN2. As UBXD8 is an endoplasmic membrane protein involved in the translocation of ubiquitinated ERAD substrates, UBQLN2 likely cooperates with UBXD8 to transport defective proteins from the endoplasmic reticulum to the cytosol for degradation, and this cell-protective function is disturbed by pathogenic mutation of UBQLN2.

Because of clerical errors in preparing the figures, in Fig. 1A, the last portions of the mouse and human TILRR sequences are not aligned with the consensus sequence, and the human form is mislabeled as 716 amino acids (aa). In Fig. 2C (and on page 7227, right column, line 4), the most potent form of the human protein is mislabeled as 710 aa. Supplemental Fig. S1 correctly shows the alignment and the length of the human TILRR protein as 715 aa, with the most potent form, lacking the N-terminal 6 aa, as 709 aa. The amino acid sequence is correct as shown in all figures, and the clerical errors have no impact on any of the results, including the function of the protein, the probes used, or the numbering of the mutants.

DEN at the time of initial stent placement reduces the number of necrosectomy sessions required for successful clinical resolution of WON.