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
• buněčná membrána metabolismus   MeSH
• buněčné jádro metabolismus   MeSH
• exocytóza fyziologie   MeSH
• fibroblasty cytologie   metabolismus   MeSH
• HeLa buňky MeSH
• kultivované buňky MeSH
• kůže cytologie   metabolismus   MeSH
• lidé MeSH
• mikrofilamenta metabolismus   MeSH
• myosin typu I metabolismus   MeSH
• myši knockoutované MeSH
• myši MeSH
• pohyb buněk MeSH
• tvar buňky MeSH
• zvířata MeSH
• Check Tag
• lidé MeSH
• myši MeSH
• zvířata MeSH
• Publikační typ
• časopisecké články MeSH
• práce podpořená grantem MeSH
• Názvy látek
• myosin typu I MeSH

BACKGROUND: Nuclear myosin I (NM1) is a nuclear isoform of the well-known "cytoplasmic" Myosin 1c protein (Myo1c). Located on the 11(th) chromosome in mice, NM1 results from an alternative start of transcription of the Myo1c gene adding an extra 16 amino acids at the N-terminus. Previous studies revealed its roles in RNA Polymerase I and RNA Polymerase II transcription, chromatin remodeling, and chromosomal movements. Its nuclear localization signal is localized in the middle of the molecule and therefore directs both Myosin 1c isoforms to the nucleus. METHODOLOGY/PRINCIPAL FINDINGS: In order to trace specific functions of the NM1 isoform, we generated mice lacking the NM1 start codon without affecting the cytoplasmic Myo1c protein. Mutant mice were analyzed in a comprehensive phenotypic screen in cooperation with the German Mouse Clinic. Strikingly, no obvious phenotype related to previously described functions has been observed. However, we found minor changes in bone mineral density and the number and size of red blood cells in knock-out mice, which are most probably not related to previously described functions of NM1 in the nucleus. In Myo1c/NM1 depleted U2OS cells, the level of Pol I transcription was restored by overexpression of shRNA-resistant mouse Myo1c. Moreover, we found Myo1c interacting with Pol II. The ratio between Myo1c and NM1 proteins were similar in the nucleus and deletion of NM1 did not cause any compensatory overexpression of Myo1c protein. CONCLUSION/SIGNIFICANCE: We observed that Myo1c can replace NM1 in its nuclear functions. Amount of both proteins is nearly equal and NM1 knock-out does not cause any compensatory overexpression of Myo1c. We therefore suggest that both isoforms can substitute each other in nuclear processes.

• MeSH
• buněčné jádro metabolismus   MeSH
• DNA primery genetika   MeSH
• fenotyp * MeSH
• genotyp MeSH
• imunoprecipitace MeSH
• myosin typu I genetika   metabolismus   MeSH
• myši knockoutované MeSH
• myši MeSH
• plazmidy genetika   MeSH
• polymerázová řetězová reakce s reverzní transkripcí MeSH
• protein - isoformy genetika   metabolismus   MeSH
• western blotting MeSH
• zvířata MeSH
• Check Tag
• myši MeSH
• zvířata MeSH
• Publikační typ
• časopisecké články MeSH
• práce podpořená grantem MeSH
• Názvy látek
• DNA primery MeSH
• Myo1c protein, mouse MeSH Prohlížeč
• myosin typu I MeSH
• protein - isoformy MeSH

BACKGROUND: Nuclear myosin I (NM1) was the first molecular motor identified in the cell nucleus. Together with nuclear actin, they participate in crucial nuclear events such as transcription, chromatin movements, and chromatin remodeling. NM1 is an isoform of myosin 1c (Myo1c) that was identified earlier and is known to act in the cytoplasm. NM1 differs from the "cytoplasmic" myosin 1c only by additional 16 amino acids at the N-terminus of the molecule. This amino acid stretch was therefore suggested to direct NM1 into the nucleus. METHODOLOGY/PRINCIPAL FINDINGS: We investigated the mechanism of nuclear import of NM1 in detail. Using over-expressed GFP chimeras encoding for truncated NM1 mutants, we identified a specific sequence that is necessary for its import to the nucleus. This novel nuclear localization sequence is placed within calmodulin-binding motif of NM1, thus it is present also in the Myo1c. We confirmed the presence of both isoforms in the nucleus by transfection of tagged NM1 and Myo1c constructs into cultured cells, and also by showing the presence of the endogenous Myo1c in purified nuclei of cells derived from knock-out mice lacking NM1. Using pull-down and co-immunoprecipitation assays we identified importin beta, importin 5 and importin 7 as nuclear transport receptors that bind NM1. Since the NLS sequence of NM1 lies within the region that also binds calmodulin we tested the influence of calmodulin on the localization of NM1. The presence of elevated levels of calmodulin interfered with nuclear localization of tagged NM1. CONCLUSIONS/SIGNIFICANCE: We have shown that the novel specific NLS brings to the cell nucleus not only the "nuclear" isoform of myosin I (NM1 protein) but also its "cytoplasmic" isoform (Myo1c protein). This opens a new field for exploring functions of this molecular motor in nuclear processes, and for exploring the signals between cytoplasm and the nucleus.

• MeSH
• adenosindifosfát metabolismus   MeSH
• aktiny metabolismus   MeSH
• aktivní transport - buněčné jádro MeSH
• buněčné jádro metabolismus   MeSH
• buněčné linie MeSH
• jaderné lokalizační signály MeSH
• kalmodulin metabolismus   MeSH
• karyoferiny metabolismus   MeSH
• lidé MeSH
• molekulární sekvence - údaje MeSH
• myosin typu I chemie   metabolismus   MeSH
• myosiny chemie   metabolismus   MeSH
• myši MeSH
• sekvence aminokyselin MeSH
• terciární struktura proteinů MeSH
• zvířata MeSH
• Check Tag
• lidé MeSH
• myši MeSH
• zvířata MeSH
• Publikační typ
• časopisecké články MeSH
• práce podpořená grantem MeSH
• Názvy látek
• adenosindifosfát MeSH
• aktiny MeSH
• jaderné lokalizační signály MeSH
• kalmodulin MeSH
• karyoferiny MeSH
• Myo1c protein, mouse MeSH Prohlížeč
• myosin typu I MeSH
• myosiny MeSH