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.

• Klíčová slova
• NM1, PI(4,5)P2, cell nucleus, lamin A/C, nuclear lamina, nuclear myosin 1, nucleoplasm, phosphoinositides, phosphorylation,
• MeSH
• buněčné jádro * metabolismus   MeSH
• interfáze MeSH
• intermediární filamenta metabolismus   MeSH
• lamin typ A * metabolismus   MeSH
• lidé MeSH
• nádorové buněčné linie MeSH
• Check Tag
• lidé MeSH
• Publikační typ
• časopisecké články MeSH
• práce podpořená grantem MeSH
• Názvy látek
• lamin typ A * MeSH

Here, we provide evidence for the presence of Myosin phosphatase rho-interacting protein (MPRIP), an F-actin-binding protein, in the cell nucleus. The MPRIP protein binds to Phosphatidylinositol 4,5-bisphosphate (PIP2) and localizes to the nuclear speckles and nuclear lipid islets which are known to be involved in transcription. We identified MPRIP as a component of RNA Polymerase II/Nuclear Myosin 1 complex and showed that MPRIP forms phase-separated condensates which are able to bind nuclear F-actin fibers. Notably, the fibrous MPRIP preserves its liquid-like properties and reforms the spherical shaped condensates when F-actin is disassembled. Moreover, we show that the phase separation of MPRIP is driven by its long intrinsically disordered region at the C-terminus. We propose that the PIP2/MPRIP association might contribute to the regulation of RNAPII transcription via phase separation and nuclear actin polymerization.

• Klíčová slova
• MPRIP, PIP2, actin, nucleus, phase separation,
• MeSH
• adaptorové proteiny signální transdukční chemie   metabolismus   MeSH
• aktiny metabolismus   MeSH
• buněčné jádro účinky léků   metabolismus   MeSH
• fosfatidylinositol-4,5-difosfát metabolismus   MeSH
• glykoly farmakologie   MeSH
• lidé MeSH
• myosin typu I metabolismus   MeSH
• nádorové buněčné linie MeSH
• proteinové domény MeSH
• RNA-polymerasa II metabolismus   MeSH
• subcelulární frakce metabolismus   MeSH
• vazba proteinů účinky léků   MeSH
• zelené fluorescenční proteiny metabolismus   MeSH
• Check Tag
• lidé MeSH
• Publikační typ
• časopisecké články MeSH
• práce podpořená grantem MeSH
• Názvy látek
• adaptorové proteiny signální transdukční MeSH
• aktiny MeSH
• fosfatidylinositol-4,5-difosfát MeSH
• glykoly MeSH
• hexamethylene glycol MeSH Prohlížeč
• MPRIP protein, human MeSH Prohlížeč
• MYO1C protein, human MeSH Prohlížeč
• myosin typu I MeSH
• RNA-polymerasa II MeSH
• zelené fluorescenční proteiny MeSH

Specific nuclear sub-compartments that are regions of fundamental processes such as gene expression or DNA repair, contain phosphoinositides (PIPs). PIPs thus potentially represent signals for the localization of specific proteins into different nuclear functional domains. We performed limited proteolysis followed by label-free quantitative mass spectrometry and identified nuclear protein effectors of the most abundant PIP-phosphatidylinositol 4,5-bisphosphate (PIP2). We identified 515 proteins with PIP2-binding capacity of which 191 'exposed' proteins represent a direct PIP2 interactors and 324 'hidden' proteins, where PIP2 binding was increased upon trypsin treatment. Gene ontology analysis revealed that 'exposed' proteins are involved in the gene expression as regulators of Pol II, mRNA splicing, and cell cycle. They localize mainly to non-membrane bound organelles-nuclear speckles and nucleolus and are connected to the actin nucleoskeleton. 'Hidden' proteins are linked to the gene expression, RNA splicing and transport, cell cycle regulation, and response to heat or viral infection. These proteins localize to the nuclear envelope, nuclear pore complex, or chromatin. Bioinformatic analysis of peptides bound in both groups revealed that PIP2-binding motifs are in general hydrophilic. Our data provide an insight into the molecular mechanism of nuclear PIP2 protein interaction and advance the methodology applicable for further studies of PIPs or other protein ligands.

• Klíčová slova
• limited proteolysis, mass spectrometry, nucleus, phosphatidylinositol 4,5-bisphosphate, phosphoinositides,
• MeSH
• buněčné jádro metabolismus   MeSH
• fosfatidylinositol-4,5-difosfát metabolismus   MeSH
• genová ontologie MeSH
• HeLa buňky MeSH
• hmotnostní spektrometrie * MeSH
• hydrofobní a hydrofilní interakce MeSH
• lidé MeSH
• peptidy metabolismus   MeSH
• proteolýza * MeSH
• proteom chemie   metabolismus   MeSH
• regulace genové exprese MeSH
• sekvence aminokyselin MeSH
• trypsin metabolismus   MeSH
• Check Tag
• lidé MeSH
• Publikační typ
• časopisecké články MeSH
• práce podpořená grantem MeSH
• Názvy látek
• fosfatidylinositol-4,5-difosfát MeSH
• peptidy MeSH
• proteom MeSH
• trypsin MeSH

Phosphoinositides are glycerol-based phospholipids, and they play essential roles in cellular signalling, membrane and cytoskeletal dynamics, cell movement, and the modulation of ion channels and transporters. Phosphoinositides are also associated with fundamental nuclear processes through their nuclear protein-binding partners, even though membranes do not exist inside of the nucleus. Phosphatidylinositol 4-phosphate (PI(4)P) is one of the most abundant cellular phosphoinositides; however, its functions in the nucleus are still poorly understood. In this study, we describe PI(4)P localisation in the cell nucleus by super-resolution light and electron microscopy, and employ immunoprecipitation with a specific anti-PI(4)P antibody and subsequent mass spectrometry analysis to determine PI(4)P's interaction partners. We show that PI(4)P is present at the nuclear envelope, in nuclear lamina, in nuclear speckles and in nucleoli and also forms multiple small foci in the nucleoplasm. Nuclear PI(4)P undergoes re-localisation to the cytoplasm during cell division; it does not localise to chromosomes, nucleolar organising regions or mitotic interchromatin granules. When PI(4)P and PI(4,5)P2 are compared, they have different nuclear localisations during interphase and mitosis, pointing to their functional differences in the cell nucleus. Mass spectrometry identified hundreds of proteins, including 12 potentially novel PI(4)P interactors, most of them functioning in vital nuclear processes such as pre-mRNA splicing, transcription or nuclear transport, thus extending the current knowledge of PI(4)P's interaction partners. Based on these data, we propose that PI(4)P also plays a role in essential nuclear processes as a part of protein-lipid complexes. Altogether, these observations provide a novel insight into the role of PI(4)P in nuclear functions and provide a direction for further investigation.

• Klíčová slova
• PI(4)P, nucleus, phosphoinositides,
• MeSH
• buněčné jadérko metabolismus   ultrastruktura   MeSH
• buněčné jádro metabolismus   ultrastruktura   MeSH
• buněčný cyklus MeSH
• fosfatidylinositolfosfáty metabolismus   MeSH
• jaderné proteiny metabolismus   MeSH
• jaderný obal metabolismus   ultrastruktura   MeSH
• lidé MeSH
• nádorové buněčné linie MeSH
• proteom metabolismus   MeSH
• shluková analýza MeSH
• vazba proteinů MeSH
• Check Tag
• lidé MeSH
• Publikační typ
• časopisecké články MeSH
• práce podpořená grantem MeSH
• Názvy látek
• fosfatidylinositolfosfáty MeSH
• jaderné proteiny MeSH
• phosphatidylinositol 4-phosphate MeSH Prohlížeč
• proteom MeSH

The many functions of phosphoinositides in cytosolic signaling were extensively studied; however, their activities in the cell nucleus are much less clear. In this review, we summarize data about their nuclear localization and metabolism, and review the available literature on their involvements in chromatin remodeling, gene transcription, and RNA processing. We discuss the molecular mechanisms via which nuclear phosphoinositides, in particular phosphatidylinositol (4,5)-bisphosphate (PI(4,5)P2), modulate nuclear processes. We focus on PI(4,5)P2's role in the modulation of RNA polymerase I activity, and functions of the nuclear lipid islets-recently described nucleoplasmic PI(4,5)P2-rich compartment involved in RNA polymerase II transcription. In conclusion, the high impact of the phosphoinositide-protein complexes on nuclear organization and genome functions is only now emerging and deserves further thorough studies.

• Klíčová slova
• cell nucleus, gene expression, genome, phosphoinositides,
• MeSH
• buněčné jádro genetika   metabolismus   MeSH
• Eukaryota genetika   metabolismus   MeSH
• fosfatidylinositol-4,5-difosfát metabolismus   MeSH
• genetická transkripce MeSH
• genom * MeSH
• posttranskripční úpravy RNA MeSH
• restrukturace chromatinu MeSH
• RNA-polymerasa I metabolismus   MeSH
• RNA-polymerasa II metabolismus   MeSH
• vazba proteinů fyziologie   MeSH
• Publikační typ
• časopisecké články MeSH
• práce podpořená grantem MeSH
• přehledy MeSH
• Názvy látek
• fosfatidylinositol-4,5-difosfát MeSH
• RNA-polymerasa I MeSH
• RNA-polymerasa II MeSH

One of the most studied phosphoinositides is phosphatidylinositol 4,5-bisphosphate (PIP2), which localizes to the plasma membrane, nuclear speckles, small foci in the nucleoplasm, and to the nucleolus in mammalian cells. Here, we show that PIP2 also localizes to the nucleus in prophase I, during the gametogenesis of C. elegans hermaphrodite. The depletion of PIP2 by type I PIP kinase (PPK-1) kinase RNA interference results in an altered chromosome structure and leads to various defects during meiotic progression. We observed a decreased brood size and aneuploidy in progeny, defects in synapsis, and crossover formation. The altered chromosome structure is reflected in the increased transcription activity of a tightly regulated process in prophase I. To elucidate the involvement of PIP2 in the processes during the C. elegans development, we identified the PIP2-binding partners, leucine-rich repeat (LRR-1) protein and proteasome subunit beta 4 (PBS-4), pointing to its involvement in the ubiquitin⁻proteasome pathway.

• Klíčová slova
• C. elegans, PPK-1, nucleus, phosphatidylinositol 4,5-bisphosphate,
• MeSH
• buněčné jádro metabolismus   MeSH
• Caenorhabditis elegans genetika   růst a vývoj   metabolismus   MeSH
• chromozomy chemie   MeSH
• fosfatidylinositol-4,5-difosfát metabolismus   MeSH
• fosfotransferasy s alkoholovou skupinou jako akceptorem genetika   MeSH
• gametogeneze * MeSH
• hermafroditické organismy genetika   růst a vývoj   metabolismus   MeSH
• profáze meiózy I MeSH
• proteasomový endopeptidasový komplex metabolismus   MeSH
• proteiny Caenorhabditis elegans genetika   MeSH
• proteiny s repeticemi bohatými na leucin MeSH
• proteiny metabolismus   MeSH
• RNA interference MeSH
• vývojová regulace genové exprese MeSH
• zvířata MeSH
• Check Tag
• zvířata MeSH
• Publikační typ
• časopisecké články MeSH
• Názvy látek
• fosfatidylinositol-4,5-difosfát MeSH
• fosfotransferasy s alkoholovou skupinou jako akceptorem MeSH
• Ppk-1 protein, C elegans MeSH Prohlížeč
• proteasomový endopeptidasový komplex MeSH
• proteiny Caenorhabditis elegans MeSH
• proteiny s repeticemi bohatými na leucin MeSH
• proteiny MeSH

Even though the majority of knowledge about phospholipids comes from their cytoplasmic functions, in the last decade, it has been shown that nuclear phospholipids and their building blocks, inositol phosphates, have many important roles in the cell nucleus. There are clear connections of phospholipids with the regulation of gene expression and chromatin biology, however, this review focuses on less known functions of nuclear phospholipids in connection with the epigenome regulation. In particular, we highlight the roles of nuclear phospholipids and inositol phosphates that involve histone modifications, such as acetylation or methylation, tightly connected with the cell physiology. This demonstrates the importance of nuclear phospholipids in the regulation of cellular processes, and should encourage further research of nuclear phospholipids and inositol phosphates.

• Klíčová slova
• Acetylation, Inositol phosphate, Methylation, Phosphoinositide, Phospholipids,
• MeSH
• chromatin chemie   metabolismus   MeSH
• epigeneze genetická * genetika   MeSH
• fosfolipidy chemie   metabolismus   MeSH
• inositolfosfáty chemie   metabolismus   MeSH
• lidé MeSH
• molekulární struktura MeSH
• regulace genové exprese MeSH
• zvířata MeSH
• Check Tag
• lidé MeSH
• zvířata MeSH
• Publikační typ
• časopisecké články MeSH
• přehledy MeSH
• Názvy látek
• chromatin MeSH
• fosfolipidy MeSH
• inositolfosfáty MeSH