Lamins, the nuclear intermediate filaments, are important regulators of nuclear structural integrity as well as nuclear functional processes such as DNA transcription, replication and repair, and epigenetic regulations. A portion of phosphorylated lamin A/C localizes to the nuclear interior in interphase, forming a lamin A/C pool with specific properties and distinct functions. Nucleoplasmic lamin A/C molecular functions are mainly dependent on its binding partners; therefore, revealing new interactions could give us new clues on the lamin A/C mechanism of action. In the present study, we show that lamin A/C interacts with nuclear phosphoinositides (PIPs), and with nuclear myosin I (NM1). Both NM1 and nuclear PIPs have been previously reported as important regulators of gene expression and DNA damage/repair. Furthermore, phosphorylated lamin A/C forms a complex with NM1 in a phosphatidylinositol-4,5-bisphosphate (PI(4,5)P2)-dependent manner in the nuclear interior. Taken together, our study reveals a previously unidentified interaction between phosphorylated lamin A/C, NM1, and PI(4,5)P2 and suggests new possible ways of nucleoplasmic lamin A/C regulation, function, and importance for the formation of functional nuclear microdomains.

• Keywords
• NM1, PI(4,5)P2, cell nucleus, lamin A/C, nuclear lamina, nuclear myosin 1, nucleoplasm, phosphoinositides, phosphorylation,
• MeSH
• Cell Nucleus * metabolism   MeSH
• Interphase MeSH
• Intermediate Filaments metabolism   MeSH
• Lamin Type A * metabolism   MeSH
• Humans MeSH
• Cell Line, Tumor MeSH
• Check Tag
• Humans MeSH
• Publication type
• Journal Article MeSH
• Research Support, Non-U.S. Gov't MeSH
• Names of Substances
• Lamin Type A * MeSH

Nuclear myosin 1 (NM1) has been implicated in key nuclear functions. Together with actin, it has been shown to initiate and regulate transcription, it is part of the chromatin remodeling complex B-WICH, and is responsible for rearrangements of chromosomal territories in response to external stimuli. Here we show that deletion of NM1 in mouse embryonic fibroblasts leads to chromatin and transcription dysregulation affecting the expression of DNA damage and cell cycle genes. NM1 KO cells exhibit increased DNA damage and changes in cell cycle progression, proliferation, and apoptosis, compatible with a phenotype resulting from impaired p53 signaling. We show that upon DNA damage, NM1 forms a complex with p53 and activates the expression of checkpoint regulator p21 (Cdkn1A) by PCAF and Set1 recruitment to its promoter for histone H3 acetylation and methylation. We propose a role for NM1 in the transcriptional response to DNA damage response and maintenance of genome stability.

• MeSH
• Apoptosis MeSH
• Cell Nucleus drug effects   genetics   metabolism   pathology   MeSH
• Cell Line MeSH
• Cell Cycle MeSH
• Epigenesis, Genetic MeSH
• Etoposide toxicity   MeSH
• Transcription, Genetic * MeSH
• Histone-Lysine N-Methyltransferase genetics   metabolism   MeSH
• Cyclin-Dependent Kinase Inhibitor p21 genetics   metabolism   MeSH
• Myosin Type I genetics   metabolism   MeSH
• Mice MeSH
• Tumor Suppressor Protein p53 genetics   metabolism   MeSH
• DNA Damage * MeSH
• Cell Proliferation MeSH
• Chromatin Assembly and Disassembly * MeSH
• p300-CBP Transcription Factors genetics   metabolism   MeSH
• Animals MeSH
• Check Tag
• Mice MeSH
• Animals MeSH
• Publication type
• Journal Article MeSH
• Research Support, Non-U.S. Gov't MeSH
• Names of Substances
• Cdkn1a protein, mouse MeSH Browser
• Etoposide MeSH
• Histone-Lysine N-Methyltransferase MeSH
• Cyclin-Dependent Kinase Inhibitor p21 MeSH
• Myo1c protein, mouse MeSH Browser
• Myosin Type I MeSH
• Tumor Suppressor Protein p53 MeSH
• Nsccn1 protein, mouse MeSH Browser
• p300-CBP-associated factor MeSH Browser
• p300-CBP Transcription Factors MeSH
• Trp53 protein, mouse MeSH Browser

Plasma membrane tension is an important feature that determines the cell shape and influences processes such as cell motility, spreading, endocytosis and exocytosis. Unconventional class 1 myosins are potent regulators of plasma membrane tension because they physically link the plasma membrane with adjacent cytoskeleton. We identified nuclear myosin 1 (NM1) - a putative nuclear isoform of myosin 1c (Myo1c) - as a new player in the field. Although having specific nuclear functions, NM1 localizes predominantly to the plasma membrane. Deletion of NM1 causes more than a 50% increase in the elasticity of the plasma membrane around the actin cytoskeleton as measured by atomic force microscopy. This higher elasticity of NM1 knock-out cells leads to 25% higher resistance to short-term hypotonic environment and rapid cell swelling. In contrast, overexpression of NM1 in wild type cells leads to an additional 30% reduction of their survival. We have shown that NM1 has a direct functional role in the cytoplasm as a dynamic linker between the cell membrane and the underlying cytoskeleton, regulating the degree of effective plasma membrane tension.

• MeSH
• Cell Membrane metabolism   MeSH
• Cell Nucleus metabolism   MeSH
• Exocytosis physiology   MeSH
• Fibroblasts cytology   metabolism   MeSH
• HeLa Cells MeSH
• Cells, Cultured MeSH
• Skin cytology   metabolism   MeSH
• Humans MeSH
• Actin Cytoskeleton metabolism   MeSH
• Myosin Type I metabolism   MeSH
• Mice, Knockout MeSH
• Mice MeSH
• Cell Movement MeSH
• Cell Shape MeSH
• Animals MeSH
• Check Tag
• Humans MeSH
• Mice MeSH
• Animals MeSH
• Publication type
• Journal Article MeSH
• Research Support, Non-U.S. Gov't MeSH
• Names of Substances
• Myosin Type I MeSH