Regulation of Hsf4b nuclear translocation and transcription activity by phosphorylation at threonine 472

• Hsf4b's nuclear translocation is regulated by T472 phosphorylation.
• Phosphorylation of T472 regulates Hsf4b's association with importin beta and Hsc70.
• Hsf4b conformation and protein stability are modulated by T472 phosphorylation.
• MEK6 contributes T472 phosphorylation in Hsf4b.

Hsf4b, a key regulator of postnatal lens development, is subjected to posttranslational modifications including phosphorylation. However, the phosphorylation sites in Hsf4b and their biological effects on the transcription activity of Hsf4b are poorly understood. Here we examined 17 potential phosphorylation residues in Hsf4b with alanine-scanning assays and found that a T472A mutation diminished Hsf4b-mediated expression of Hsp25 and αB-crystallin. In contrast, the phosphomimetic mutation of T472D enhanced their expression. Further investigation demonstrated that Hsf4b could interact with nuclear-transporter importin β-1 and Hsc70 via amino acids 246–320 and 320–493, respectively. T472A mutation reduced Hsf4b's interaction with importin β-1, while enhancing its interaction with Hsc70, resulting in Hsf4b cytosolic re-localization, protein instability and transcription activity attenuation. At the upstream, MEK6 was found to interact with Hsf4b and enhance Hsf4b's nuclear translocation and transcription activity, probably by phosphorylation at sites such as T472. Taken together, our results suggest that phosphorylation of Hsf4b at T472 by protein kinases such as MEK6 regulates Hsf4b interaction with the importin β-1-Hsc70 complex, resulting in blockade of its nuclear translocation and transcriptional activity of Hsf4b.