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[Protein phosphatases and nucleolin in osteoblastic cells: cleavage of nucleolin in apoptotic cells]

Tatsuji Haneji1

  • 1Department of Histology and Oral Histology, School of Dentistry, University of Tokushima, 3-18-15, Kuramoto, Tokushima 770-8504, Japan.

Kaibogaku Zasshi. Journal of Anatomy
|October 9, 2003
PubMed

Insights

Okadaic acid induces apoptosis by inhibiting protein phosphatases. This study reveals that PP1 delta binds to nucleolin in the nucleolus, and nucleolin is cleaved during apoptosis.

Area of Science:

  • Cell Biology
  • Molecular Biology
  • Biochemistry

Context:

  • Protein phosphorylation and dephosphorylation are critical regulators of cellular processes, including proliferation, differentiation, and apoptosis.
  • Okadaic acid, a potent inhibitor of protein phosphatase type 1 (PP1) and type 2A, is known to induce apoptosis in human osteoblastic cells (Saos-2 and MG63).
  • Nucleolin is a major nucleolar phosphoprotein involved in various cellular functions.

Purpose:

  • To investigate the interaction between nucleolin and protein phosphatase 1 delta (PP1 delta) during okadaic acid-induced apoptosis.
  • To elucidate the molecular mechanisms underlying nucleolin's fate in apoptotic cells.

Summary:

  • Nucleolin exhibits a staining pattern similar to PP1 delta in Saos-2 and MG63 cells.
  • Immunocytochemical and immunoprecipitation studies confirmed that nucleolin directly binds to PP1 delta within the nucleolus.
  • During apoptosis induced by okadaic acid, nucleolin and AgNORs disappeared from the nucleus. A 110 kDa nucleolin band decreased, while an 80 kDa band appeared, indicating nucleolin cleavage.

Impact:

  • This research demonstrates a direct interaction between PP1 delta and nucleolin in the nucleolus.
  • The findings reveal that nucleolin undergoes cleavage as a molecular event during apoptosis.
  • Establishes a novel link between protein phosphatase activity, nucleolin dynamics, and the apoptotic process.

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