The Lamin B receptor is essential for cholesterol synthesis and perturbed by disease-causing mutations

Abstract

Lamin B receptor (LBR) is a polytopic membrane protein residing in the inner nuclear membrane in association with the nuclear lamina. We demonstrate that human LBR is essential for cholesterol synthesis. LBR mutant derivatives implicated in Greenberg skeletal dysplasia or Pelger-Huët anomaly fail to rescue the cholesterol auxotrophy of a LBR-deficient human cell line, consistent with a loss-of-function mechanism for these congenital disorders. These disease-causing variants fall into two classes: point mutations in the sterol reductase domain perturb enzymatic activity by reducing the affinity for the essential cofactor NADPH, while LBR truncations render the mutant protein metabolically unstable, leading to its rapid degradation at the inner nuclear membrane. Thus, metabolically unstable LBR variants may serve as long-sought-after model substrates enabling previously impossible investigations of poorly understood protein turnover mechanisms at the inner nuclear membrane of higher eukaryotes.DOI: http://dx.doi.org/10.7554/eLife.16011.001

Selective clearance of the inner nuclear membrane protein emerin by vesicular transport during ER stress

“…This 209 indicates that mature, INM-localized proteins can be degraded in a proteasome-210 there (Albert et al, 2017). This is also consistent with a recent report that an unstable 213 INM protein mutant accumulates within the nucleus of mammalian cells when the 214 proteasome is inhibited (Tsai et al, 2016). 215…”

Dissecting Torsin/cofactor function at the nuclear envelope: a genetic study

“…As guide RNA sequences, we used Tor2a, 5′-CGCGCGTCGCAGCCGCCATC-3′, and Tor3a, 5′-GCGCCACGGACCGCGAAGCA-3′. Genotyping PCR was performed as described previously (Tsai et al ., 2016) with the following primers: Tor2a forward, 5′-GAGACCAG­CCCGAGCAGCC-3′; Tor2a reverse, 5′-GTTGACTGCCCCACAACGAG-3′; glyceraldehyde-3-phosphate dehydrogenase (GAPDH) forward, 5′-CGACCGGAGTCAACGGA­TTTGGTCG-3′; and GAPDH reverse, 5′-GGCAACAATATCCAC­TTTACCAGA-3′.…”

“…Indirect immunofluorescence and confocal microscopy were performed as previously described (Rose et al ., 2014; Tsai et al ., 2016). The following antibodies were used, all at 1:500 dilution: anti–K48 Ub (AB_11213655; Millipore); anti–lamin A (AB_306909, Abcam); anti-p97 (AB_298039, Abcam); anti-PDI (AB_303304, Abcam); anti–proteasome 20S α4 subunit (AB_10541440; Enzo Life Sciences); anti-Hrd1 (a gift from Malaiyalam Mariappan); and anti-calnexin (AB_1310022; Abcam).…”

Dynamic functional assembly of the Torsin AAA+ ATPase and its modulation by LAP1

“…Indirect immunofluorescence and confocal microscopy were performed as previously described (Rose et al , 2014; Tsai et al , 2016). Briefly, cells were fixed with 4% paraformaldehyde and permeabilized with 0.1% Triton X-100.…”