Overexpression of the Csk homologous kinase (Chk tyrosine kinase) induces multinucleation: A possible role for chromosome-associated Chk in chromosome dynamics

Naoto Yamaguchi, Yuji Nakayama, Takeo Urakami, Saeko Suzuki, Tatsunosuke Nakamura, Toshio Suda, Naoto Oku

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The Csk family of non-receptor-type tyrosine kinases consists of Csk and the Csk homologous kinase Chk. Each enzyme suppresses the catalytic activity of Src family kinases by phosphorylating their C-terminal negative regulatory tyrosine residues. Ectopic and transient expression of Chk in COS-1 cells showed nuclear localization of Chk and growth inhibition. To further explore the role of Chk in cell growth, we overexpressed Chk in human immature myeloid KMT-2 cells. Chk overexpression brought about growth retardation and aberrant chromosome movement leading to multinucleation, and these events were accompanied by insufficient formation of mitotic spindles. In vitro kinase assays showed that Chk overexpression suppressed the tyrosine kinase activity of Lyn, a member of the Src family, immunoprecipitated from Triton X-100 lysates. Subcellular fractionation studies revealed that fractions of Chk and Lyn, resistant to Triton X-100 solubilization, are associated with mitotic chromosome scaffolds and spindles. Chk overexpression induced a decrease in autophosphorylation of Lyn and concomitant changes in levels of tyrosine phosphorylation of proteins associated with both fractions. These results indicate that Chk, Lyn and the tyrosine-phosphorylated proteins localize to mitotic chromosomes and spindles, suggesting that Chk-dependent tyrosine phosphorylation, presumably through Lyn, may be involved in chromosome dynamics.

Original languageEnglish
Pages (from-to)1631-1641
Number of pages11
JournalJournal of Cell Science
Issue number9
Publication statusPublished - 2001 May 30



  • Chk
  • Csk
  • Nuclear localization
  • Src tyrosine kinase

ASJC Scopus subject areas

  • Cell Biology

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