Aberrant Function of Pathogenic STAT3 Mutant Proteins Is Linked to Altered Stability of Monomers and Homodimers

Authors

Moses M Kasembeli
Efiyenia Kaparos
Uddalak Bharadwaj
Ahmad Allaw
Alain Khouri
Bianca Acot
David J Tweardy

Publication Date

3-23-2023

Journal

Blood

Abstract

STAT3 mutations, predominantly in the DNA-binding domain (DBD) and Src-homology 2 domain (SH2D), cause rare cases of immunodeficiency, malignancy, and autoimmunity. The exact mechanisms by which these mutations abrogate or enhance STAT3 function are not completely understood. Here, we examined how loss-of-function (LOF) and gain-of-function (GOF) STAT3 mutations within the DBD and SH2D affect monomer and homodimer protein stability as well as their effect on key STAT3 activation events, including recruitment to phosphotyrosine (pY) sites within peptide hormone receptors, tyrosine phosphorylation at Y705, dimerization, nuclear translocation, and DNA binding. The DBD LOF mutants showed reduced DNA binding when homodimerized, whereas the DBD GOF mutants showed increased DNA binding. DBD LOF and GOF mutants showed minimal changes in other STAT3 functions or in monomer or homodimer protein stability. However, SH2D LOF mutants demonstrated reduced conformational stability as either monomers or homodimers, leading to decreased pY-peptide recruitment, tyrosine phosphorylation, dimerization, nuclear localization, and DNA binding. In contrast, cancer-causing SH2D GOF mutants showed increased STAT3 homodimer stability, which increased their DNA binding. Of note, a small-molecule inhibitor of STAT3 that targets the tyrosine phosphopeptide-binding pocket within the STAT3 SH2D potently inhibited cell proliferation driven by STAT3 SH2D GOF mutants. These findings indicate that the stability of STAT3 protein monomer and homodimer is critical for the pathogenesis of diseases caused by SH2D LOF and GOF mutations and suggest that agents that modulate STAT3 monomer and/or homodimer protein stability may have therapeutic value in diseases caused by these mutations.

Keywords

STAT3 Transcription Factor, Mutation, src Homology Domains, DNA, Tyrosine

DOI

10.1182/blood.2021015330

PMID

36240433

PMCID

PMC10651785

PubMedCentral® Posted Date

10-18-2022

PubMedCentral® Full Text Version

Post-print

Published Open-Access

yes