HTLV-1 bZIP factor impairs DNA mismatch repair system

Area of Science:

• Oncology
• Virology
• Molecular Biology

Background:

• Adult T-cell leukemia (ATL) is a peripheral T-cell malignancy linked to human T-cell leukemia virus type 1 (HTLV-1).
• Microsatellite instability (MSI), a hallmark of DNA mismatch repair (MMR) deficiency, is observed in ATL, but the underlying MMR defects remain unclear.
• The HTLV-1 bZIP factor (HBZ) is implicated in ATL pathogenesis, interacting with host transcription factors.

Purpose of the Study:

• To investigate the effect of HBZ on the MMR pathway in normal cells.
• To determine if HBZ can induce MSI and affect MMR factor expression.
• To elucidate the mechanism by which HBZ might compromise MMR, focusing on its interaction with transcription factors.

Main Methods:

• Ectopic expression of HBZ in MMR-proficient cells.
• Assessment of MSI and MMR factor expression.
• Luciferase reporter assays to evaluate the effect of HBZ and nuclear respiratory factor 1 (NRF-1) on the MSH2 promoter.
• Identification of NRF-1 binding sites in the MSH2 promoter.

Main Results:

• Ectopic HBZ expression in MMR-proficient cells induced MSI and suppressed the expression of several MMR factors.
• HBZ was found to interfere with NRF-1, a transcription factor crucial for MSH2 expression.
• NRF-1 enhanced MSH2 promoter activity, an effect reversed by HBZ co-expression, indicating HBZ inhibits NRF-1-mediated MSH2 transcription.

Conclusions:

• HBZ directly causes MMR deficiency by suppressing the transcription of the essential MMR gene MSH2 through inhibition of NRF-1.
• This HBZ-induced MMR impairment represents a novel mechanism of oncogenesis in HTLV-1-associated ATL.
• Targeting HBZ or the MMR pathway could offer new therapeutic strategies for ATL.