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Citation

  • Authors: Rogerson C. et al.
  • Year: 2021
  • Journal: Cell Death Differ 28 1849-1864
  • Applications: in vitro / shRNA plasmid / jetOPTIMUS
  • Cell type: Rat epidermal keratinocytes

Method

REKs were cultured in DMEM supplemented with 10% FBS, 1% penicillin/streptomycin at 37 °C and 5% CO2. Normal human epidermal keratinocytes (NHEK) were cultured in Epilife medium and keratinocytes were differentiated by treatment with 1.2 mM calcium chloride for 4 days. One day after seeding, cells were transfected with jetOptimus according to manufacturers’ guidelines. After transfection with Akt1 or Myh9 shRNA plasmids, knockdown REKs were selected for by addition of G418 (400 µg/ml) or puromycin (1.25 µg/ml), respectively, to the medium for 10 days.

Abstract

Keratinocyte cornification and epidermal barrier formation are tightly controlled processes, which require complete degradation of intracellular organelles, including removal of keratinocyte nuclei. Keratinocyte nuclear destruction requires Akt1-dependent phosphorylation and degradation of the nuclear lamina protein, Lamin A/C, essential for nuclear integrity. However, the molecular mechanisms that result in complete nuclear removal and their regulation are not well defined. Post-confluent cultures of rat epidermal keratinocytes (REKs) undergo spontaneous and complete differentiation, allowing visualisation and perturbation of the differentiation process in vitro. We demonstrate that there is dispersal of phosphorylated Lamin A/C to structures throughout the cytoplasm in differentiating keratinocytes. We show that the dispersal of phosphorylated Lamin A/C is Akt1-dependent and these structures are specific for the removal of Lamin A/C from the nuclear lamina; nuclear contents and Lamin B were not present in these structures. Immunoprecipitation identified a group of functionally related Akt1 target proteins involved in Lamin A/C dispersal, including actin, which forms cytoskeletal microfilaments, Arp3, required for actin filament nucleation, and Myh9, a component of myosin IIa, a molecular motor that can translocate along actin filaments. Disruption of actin filament polymerisation, nucleation or myosin IIa activity prevented formation and dispersal of cytoplasmic Lamin A/C structures. Live imaging of keratinocytes expressing fluorescently tagged nuclear proteins showed a nuclear volume reduction step taking less than 40 min precedes final nuclear destruction. Preventing Akt1-dependent Lamin A/C phosphorylation and disrupting cytoskeletal Akt1-associated proteins prevented nuclear volume reduction. We propose keratinocyte nuclear destruction and differentiation requires myosin II activity and the actin cytoskeleton for two intermediate processes: Lamin A/C dispersal and rapid nuclear volume reduction.

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