Phosphorylated Lamin A/C in the Nuclear Interior Binds Active Enhancers Associated with Abnormal Transcription in Progeria

The segregation of heterochromatin domains (LADs) at the nuclear periphery by the nuclear lamina, composed by polymerized nuclear Lamin A/C, provides a longstanding paradigm for the control of gene expression and for the mechanisms underlying Lamin-A/C-associated disorders, including progeria and cardiomyopathy. Here, we provide evidence supporting a novel paradigm that Lamin A/C functions as a transcription factor in the nuclear interior. We discovered that Ser22-phosphorylated Lamin A/C (pS22-Lamin A/C), required for lamin depolymerization during mitosis, populated the nuclear interior throughout the cell cycle. pS22-Lamin A/C ChIP-deq demonstrated localization at a large subset of putative active enhancers, not LADs. pS22-Lamin A/C-binding sites were co-occupied by the transcriptional activator c-Jun. In progeria patient-derived fibroblasts, a subset of pS22-Lamin A/C-binding sites were lost whereas new pS22-Lamin A/C-binding sites emerged. New pS22-Lamin A/C binding was accompanied by increased histone acetylation and increased c-Jun binding, whereas loss of pS22-Lamin A/C-binding was accompanied by loss of histone acetylation and c-Jun binding. New pS22-Lamin A/C enhancer binding in progeria was associated with upregulated expression of genes implicated in progeria pathophysiology, including cardiovascular disease. In contrast, alteration of LADs in progeria-patient cells could not explain the observed gene expression changes. These results suggest that Lamin A/C regulates gene expression by enhancer binding in the nuclear interior, independent of its function at the nuclear lamina, providing a new paradigm for the pathogenesis of lamin-associated disorders. pS22-Lamin A/C was also present in the nuclear interior of adult mouse cardiomyocytes. Cardiomyocyte-specific deletion of Lmna encoding Lamin A/C in adult mice caused extensive transcriptional changes in the heart and dilated cardiomyopathy, without apparent reduction of nuclear peripheral Lamin A/C. Disruption of the gene regulatory rather than LAD tethering function of Lamin A/C may underlie the pathogenesis of disorders caused by LMNA mutations, including cardiomyopathy.

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LAP2alpha maintains a mobile and low assembly state of A-type lamins in the nuclear interior

10.1101/2020.09.25.313296 ◽

2020 ◽

Author(s):

Nana Naetar ◽

Konstantina Georgiou ◽

Christian Knapp ◽

Irena Bronshtein ◽

Elisabeth Zier ◽

...

Keyword(s):

Nuclear Periphery ◽

Higher Order ◽

Lamin A ◽

Independent Manner ◽

Nuclear Interior ◽

Order Structures

AbstractLamins form stable filaments at the nuclear periphery in metazoans. Unlike B-type lamins, lamins A and C localize also in the nuclear interior, where they interact with lamin-associated polypeptide 2 alpha (LAP2α). We show that lamin A in the nuclear interior is formed from newly expressed pre-lamin A during processing and from soluble mitotic mature lamins in a LAP2α-independent manner. Binding of LAP2α to lamins A/C in the nuclear interior during interphase inhibits formation of higher order structures of lamin A/C in vitro and in vivo, keeping lamin A/C in a mobile low assembly state independent of lamin A/C S22 phosphorylation. Loss of LAP2α causes formation of larger, less mobile and biochemically stable lamin A/C structures in the nuclear interior, which reduce the mobility of chromatin. We propose that LAP2α is essential to maintain a mobile lamin A/C pool in the nuclear interior, which is required for proper nuclear functions.

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Phosphorylated Lamin A/C in the nuclear interior binds active enhancers associated with abnormal transcription in progeria

10.1101/682260 ◽

2019 ◽

Cited By ~ 1

Author(s):

Kohta Ikegami ◽

Stefano Secchia ◽

Omar Almakki ◽

Jason D. Lieb ◽

Ivan P. Moskowitz

Keyword(s):

Binding Sites ◽

Human Fibroblasts ◽

Nuclear Periphery ◽

Transcriptional Activator ◽

Premature Aging ◽

Lamin A ◽

List Type ◽

Enhancer Activity ◽

Nuclear Interior ◽

Specific Subset

ABSTRACTLMNA encodes nuclear lamin A/C that tethers lamina-associated heterochromatin domains (LADs) to the nuclear periphery. Point mutations in LMNA cause degenerative disorders including the premature aging disorder Hutchinson-Gilford progeria, but the mechanisms are unknown. We report that Ser22-phosphorylated Lamin A/C (pS22-Lamin A/C) was localized to the interior of the nucleus in human fibroblasts throughout the cell cycle. pS22-Lamin A/C interacted with a specific subset of putative active enhancers, not LADs, primarily at locations co-bound by the transcriptional activator c-Jun. In progeria-patient fibroblasts, a subset of pS22-Lamin A/C-binding sites were lost whereas new pS22-Lamin A/C-binding sites emerged in normally quiescent loci. These new pS22-Lamin A/C-binding sites displayed increased histone acetylation and c-Jun binding, implying increased enhancer activity. The genes near these new binding sites, implicated in clinical components of progeria including carotid artery diseases, hypertension, and cardiomegaly, were upregulated in progeria. These results suggest that Lamin A/C regulates gene expression by direct enhancer binding in the nuclear interior. Disruption of the gene regulatory rather than LAD function of Lamin A/C presents a novel mechanism for disorders caused by LMNA mutations including progeria.HIGHLIGHTSpS22-Lamin A/C is present in the nuclear interior throughout interphase.pS22-Lamin A/C associates with active enhancers, not lamina-associated domains.pS22-Lamin A/C-genomic binding sites are co-bound by the transcriptional activator c-Jun.New pS22-Lamin A/C binding in progeria accompanies upregulation of disease-related genes.

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LAP2alpha maintains a mobile and low assembly state of A-type lamins in the nuclear interior

eLife ◽

10.7554/elife.63476 ◽

2021 ◽

Vol 10 ◽

Author(s):

Nana Naetar ◽

Konstantina Georgiou ◽

Christian Knapp ◽

Irena Bronshtein ◽

Elisabeth Zier ◽

...

Keyword(s):

Nuclear Periphery ◽

Higher Order ◽

Lamin A ◽

Independent Manner ◽

Mobile State ◽

Nuclear Interior ◽

Mouse Cells ◽

Antibody Labeling ◽

Order Structures

Lamins form stable filaments at the nuclear periphery in metazoans. Unlike B-type lamins, lamins A and C localize also in the nuclear interior, where they interact with lamin-associated polypeptide 2 alpha (LAP2α). Using antibody labeling, we previously observed a depletion of nucleoplasmic A-type lamins in mouse cells lacking LAP2α. Here, we show that loss of LAP2α actually causes formation of larger, biochemically stable lamin A/C structures in the nuclear interior that are inaccessible to lamin A/C antibodies. While nucleoplasmic lamin A forms from newly expressed pre-lamin A during processing and from soluble mitotic lamins in a LAP2α-independent manner, binding of LAP2α to lamin A/C during interphase inhibits formation of higher order structures, keeping nucleoplasmic lamin A/C in a mobile state independent of lamin A/C S22 phosphorylation. We propose that LAP2α is essential to maintain a mobile lamin A/C pool in the nuclear interior, which is required for proper nuclear functions.

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Use of human autoantibodies and immunoelectron microscopy to study structure and function of the nucleolus and nuclear bodies

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100122939 ◽

1992 ◽

Vol 50 (1) ◽

pp. 506-507

Author(s):

Robert L. Ochs

Keyword(s):

Electron Microscopy ◽

Structure And Function ◽

Nuclear Bodies ◽

Nuclear Interior ◽

Coiled Bodies ◽

Interchromatin Granules ◽

And Function ◽

Conventional Electron Microscopy ◽

Perichromatin Granules ◽

Perichromatin Fibrils

By conventional electron microscopy, the formed elements of the nuclear interior include the nucleolus, chromatin, interchromatin granules, perichromatin granules, perichromatin fibrils, and various types of nuclear bodies (Figs. 1a-c). Of these structures, all have been reasonably well characterized structurally and functionally except for nuclear bodies. The most common types of nuclear bodies are simple nuclear bodies and coiled bodies (Figs. 1a,c). Since nuclear bodies are small in size (0.2-1.0 μm in diameter) and infrequent in number, they are often overlooked or simply not observed in any random thin section. The rat liver hepatocyte in Fig. 1b is a case in point. Historically, nuclear bodies are more prominent in hyperactive cells, they often occur in proximity to nucleoli (Fig. 1c), and sometimes they are observed to “bud off” from the nucleolar surface.

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