The p.R482W substitution in A-type lamins deregulates SREBP1 activity in Dunnigan-type familial partial lipodystrophy

Abstract

Nuclear lamins are involved in many cellular functions due to their ability to bind numerous partners including chromatin and transcription factors, and affect their properties. Dunnigan type familial partial lipodystrophy (FPLD2; OMIM#151660) is caused in most cases by the A-type lamin R482W mutation. We report here that the R482W mutation affects the regulatory activity of sterol response element binding protein 1 (SREBP1), a transcription factor that regulates hundreds of genes involved in lipid metabolism and adipocyte differentiation. Using in situ proximity ligation assays (PLA), reporter assays and biochemical and transcriptomic approaches, we show that interactions of SREBP1 with lamin A and lamin C occur at the nuclear periphery and in the nucleoplasm. These interactions involve the Ig-fold of A-type lamins and are favored upon SREBP1 binding to its DNA target sequences. We show that SREBP1, LMNA and sterol response DNA elements form ternary complexes in vitro. In addition, overexpression of A-type lamins reduces transcriptional activity of SREBP1. In contrast, both overexpression of LMNA R482W in primary human preadipocytes and endogenous expression of A-type lamins R482W in FPLD2 patient fibroblasts, reduce A-type lamins-SREBP1 in situ interactions and upregulate a large number of SREBP1 target genes. As this LMNA mutant was previously shown to inhibit adipogenic differentiation, we propose that deregulation of SREBP1 by mutated A-type lamins constitutes one underlying mechanism of the physiopathology of FPLD2. Our data suggest that SREBP1 targeting molecules could be considered in a therapeutic context.

Various lamin A/C mutations alter expression profile of mesenchymal stem cells in mutation specific manner

“…Similar discrepancy between the final differentiation effect and the expression of differentiation promoting markers was earlier reported in the model of C2C12 cells and in R482W-transfected 3 T3-L1 cells [37,[43][44][45]. Thus, resulting cellular phenotype due to LMNA mutations could be associated with ineffective activation and dysregulation of some major tissue-specific transcriptional programs, leading to variability of observed gene expression f-Change describes mean fold change of differential expression compared to the wild type, SEM -standard error of the mean.…”

Muscular Dystrophy Mutations Impair the Nuclear Envelope Emerin Self-assembly Properties

“…Primary antibodies were rabbit antilamin A/C (1:500; 40 ), rabbit anti-FLAG (Sigma, 1:150), and mouse anti-GFP (Roche, 1:150). Fluorescent labeled secondary antibodies (donkey antimouse Cy2 1:60 and donkey antirabbit Cy3 1:200) were from Jackson ImmunoResearch.…”

The Roles of SUMO in Metabolic Regulation

“…Lamin A mutations linked to familial partial lipodystrophy alter lamin A sumoylation (Simon et al 2013). The FPLD-causing mutations decrease lamin A binding to SREBP1 and upregulate a large number of SREBP1 target genes (Lloyd et al 2002; Vadrot et al 2015). Thus, a model has been proposed where lamin A K486 modification by SUMO blocks binding of interacting proteins, including SREBP1 (Simon et al 2013).…”