STAT5B leukemic mutations, altering SH2 tyrosine 665, have opposing impacts on immune gene programs

Area of Science:

• Immunology
• Molecular Biology
• Genetics

Background:

• Signal transducer and activator of transcription 5B (STAT5B) is crucial for lymphocyte function.
• Mutations in STAT5B are implicated in T-cell leukemias, but their functional impact is not fully understood.

Purpose of the Study:

• To investigate the functional consequences of two specific STAT5B mutations (Y665F and Y665H) found in human T-cell leukemias.
• To elucidate the molecular mechanisms underlying altered STAT5B function in disease contexts.

Main Methods:

• In silico modeling to predict the effects of mutations on STAT5B homodimerization.
• In vitro studies using primary T cells to assess STAT5B activity.
• Generation and analysis of knock-in mouse models carrying the STAT5B mutations.

Main Results:

• STAT5B^Y665F exhibited gain-of-function, leading to increased CD8+ effector/memory and CD4+ regulatory T cells in mice, altering T cell ratios.
• STAT5B^Y665H demonstrated loss-of-function, with diminished CD8+ effector/memory and CD4+ regulatory T cells.
• The Y665F variant showed enhanced STAT5 phosphorylation, DNA binding, and transcriptional activity compared to wild-type STAT5B, while Y665H behaved as a null.

Conclusions:

• The study successfully characterized the distinct functional outcomes (gain-of-function vs. loss-of-function) of two STAT5B mutations.
• Combining in silico and in vivo approaches provides deep insights into disease-associated variants and their structural determinants.
• Identified a gain-of-function STAT5B variant that alters T cell populations without directly causing hematopoietic malignancy.