Role Played by Microphthalmia Transcription Factor Phosphorylation and Its Zip Domain in Its Transcriptional Inhibition by PIAS3

Abstract

Mutation of microphthalmia transcription factor (MITF) results in deafness, bone loss, small eyes, and poorly pigmented eyes and skin. A search for MITF-associated proteins, using a mast cell library that was screened with a construct that encodes the basic helix-loop-helix leucine zipper (Zip) domain of MITF, resulted in the isolation of the STAT3 inhibitor, PIAS3. PIAS3 functions in vivo as a key molecule in suppressing the transcriptional activity of MITF. Here, we report that the Zip domain is the region of MITF that is involved in the direct interaction between MITF and PIAS3. Additionally, we investigated the effect of phosphorylation of MITF on its interaction with PIAS3. We found that phosphorylation of MITF on serines in positions 73 and 409 plays an important role in its association with PIAS3. This effect was profound with phosphorylation on Ser409, which significantly reduced the inhibitory effect of PIAS3 on MITF and also modulated the transcriptional activity of MITF. Thus, phosphorylation of MITF could be considered a fine, and alternative, tuning of its transcriptional machinery.

A Specific Epitope of Protein Inhibitor of Activated STAT3 Is Responsible for the Induction of Apoptosis in Rat Transformed Mast Cells

“…For instance, the ring finger domain has been shown to be important for PIAS3's activity as a sumo-E3 ligase (21,23). We have found that PIAS3 functions in vivo as a key molecule in suppressing the transcriptional activity of both MITF and STAT3 (10,24,25). More specifically, we demonstrated that following cellular activation, PIAS3 is released from MITF and binds to STAT3 (25).…”

Protein Inhibitor of Activated STAT 3 Modulates Osteoclastogenesis by Down-Regulation of NFATc1 and Osteoclast-Associated Receptor

“…In the nucleus of resting cells, unphosphorylated Mitf is inactivated by association with PIAS3. Activation of the gp130 receptor or c-Kit receptor in melanoma and mast cells induces Mitf phosphorylation and results in the release of PIAS3, which then binds STAT3 (37,38). This indicates that the phosphorylation and dephosphorylation of Mitf is a key step in the regulation of interaction between Mitf, PIAS3, and STAT3.…”

The cleavage of microphthalmia-associated transcription factor, MITF, by caspases plays an essential role in melanocyte and melanoma cell apoptosis

“…Within this fragment resides the Ser 409 residue; phosphorylation of this Ser 409 residue by RSK1 controls MITF targeting to proteasome (Wu et al 2000) and interaction with PIAS3 (Levy et al 2003).…”