Opposing action of casein kinase 1 and calcineurin in nucleo-cytoplasmic shuttling of mammalian translation initiation factor eIF6

Arunima Biswas, Shaeri Mukherjee, Supratik Das, Dennis Shields, Chi Wing Chow, Umadas Maitra

Research output: Contribution to journalArticle

27 Scopus citations


Eukaryotic initiation factor 6 (eIF6), a highly conserved protein from yeast to mammals, is essential for 60 S ribosome biogenesis and assembly. Both yeast and mammalian eIF6 are phosphorylated at Ser-174 and Ser-175 by the nuclear isoform of casein kinase 1 (CK1). The molecular basis of eIF6 phosphorylation, however, remains elusive. In the present work, we show that subcellular distribution of eIF6 in the nuclei and the cytoplasm of mammalian cells is mediated by dephosphorylation and phosphorylation, respectively. This nucleo-cytoplasmic shuttling is dependent on the phosphorylation status at Ser-174 and Ser-175 of eIF6. We demonstrate that Ca2+-activated calcineurin phosphatase binds to and promotes nuclear localization of eIF6. Increase in intracellular concentration of Ca2+ leads to rapid translocation of eIF6 from the cytoplasm to the nucleus, an event that is blocked by specific calcineurin inhibitors cyclosporin A or FK520. Nuclear export of eIF6 is regulated by phosphorylation at Ser-174 and Ser-175 by the nuclear isoform of CK1. Mutation of eIF6 at the phosphorylatable Ser-174 and Ser-175 to alanine or treatment of cells with the CK1 inhibitor, D4476 inhibits nuclear export of eIF6 and results in nuclear accumulation of eIF6. Together, these results establish eIF6 as a substrate for calcineurin and suggest a novel paradigm for calcineurin function in 60 S ribosome biogenesis via regulating the nuclear accumulation of eIF6.

Original languageEnglish (US)
Pages (from-to)3129-3138
Number of pages10
JournalJournal of Biological Chemistry
Issue number4
StatePublished - Jan 28 2011


ASJC Scopus subject areas

  • Biochemistry
  • Molecular Biology
  • Cell Biology

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