Phosphorylation of ser²⁴⁶ residue in integrin‐linked kinase 1 by serum‐ and glucocorticoid‐induced kinase 1 is required to form a protein‐protein complex with 14–3–3

Abstract

Integrin‐linked kinase 1 (ILK1) regulates several protein kinases, including PKB/Akt kinase and glycogen synthase kinase β. ILK1 is also involved distinctively in the cell morphological and structural functions by interacting with the components of the extracellular matrix or integrin. According to the information of serum‐ and glucocorticoid‐induced kinase 1 (SGK1) substrate specificity (R‐X‐R‐X‐X‐(S/T)‐ϕ; ϕ indicates a hydrophobic amino acid), two putative phosphorylation sites, Thr¹⁸¹ and Ser²⁴⁶, were found in ILK1. We showed that ILK1 fusion protein and two fluorescein‐labeled ILK1 peptides, FITC‐¹⁷⁴RTRPRNGTLN¹⁸³ and FITC‐²³⁹CPRLRIFSHP²⁴⁸, were phosphorylated by SGK1 in vitro. We also identified that 14–3–3 θ, ϵ and ζ among several 14–3–3 isotypes (β, γ, ϵ, η, σ, θ, τ and ζ) formed protein complex with ILK1 in COS‐1 cells. Furthermore, the phosphorylation of Ser²⁴⁶ by SGK1 induced the binding with 14–3–3. It was also demonstrated that 14–3–3‐bound ILK1 has reduced kinase activity. Thus, these data suggest that SGK1 phosphorylatesThr¹⁸¹ and Ser²⁴⁶ of ILK1 and the phosphorylation of its Ser²⁴⁶ makes ILK1 bind to 14–3–3, resulting in the inhibition of ILK1 kinase activity.

Key words:

• ILK1
• SGK1
• 14–3–3 isotypes
• protein phosphorylation
• protein‐protein interaction

Notes

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