Modulated binding of SATB1, a matrix attachment region protein, to the AT-rich sequence flanking the major breakpoint region of BCL2.

in Molecular and cellular biology by M Ramakrishnan, W M Liu, P A DiCroce, A Posner, J Zheng, T Kohwi-Shigematsu, T G Krontiris

TLDR

  • The study investigates how a specific part of a gene called the major breakpoint region (MBR) in human follicular lymphoma is controlled. The MBR is a region in the gene that is important for the gene to work properly. The study found that a specific part of the MBR called the 87MBR is important for DNA-protein interactions, which help control the gene. The study also found that a protein called SATB1 is important for these interactions and helps control the gene. The study suggests that the MBR is important for the development and progression of follicular lymphoma and that future research should investigate how MARs, which are regions in the genome that help control gene expression, might be used to treat this type of cancer.

Abstract

The t(14,18) chromosomal translocation that occurs in human follicular lymphoma constitutively activates the BCL2 gene and disrupts control of apoptosis. Interestingly, 70% of the t(14,18) translocations are confined to three 15-bp clusters positioned within a 150-bp region (major breakpoint region or [MBR]) in the untranslated portion of terminal exon 3. We analyzed DNA-protein interactions in the MBR, as these may play some role in targeting the translocation to this region. An 87-bp segment (87MBR) immediately 3' to breakpoint cluster 3 was essential for DNA-protein interaction monitored with mobility shift assays. We further delineated a core binding region within 87MBR: a 33-bp, very AT-rich sequence highly conserved between the human and mouse BCL2 gene (37MBR). We have purified and identified one of the core factors as the matrix attachment region (MAR) binding protein, SATB1, which is known to bind to AT-rich sequences with a high propensity to unwind. Additional factors in nuclear extracts, which we have not yet characterized further, increased SATB1 affinity for the 37MBR target four- to fivefold. Specific binding activity within 37MBR displayed cell cycle regulation in Jurkat T cells, while levels of SATB1 remained constant throughout the cell cycle. Finally, we demonstrated in vivo binding of SATB1 to the MBR, strongly suggesting the BCL2 major breakpoint region is a MAR. We discuss the potential consequences of our observations for both MBR fragility and regulatory function.

Overview

  • The study investigates the role of DNA-protein interactions in the major breakpoint region (MBR) of the t(14,18) chromosomal translocation in human follicular lymphoma. The MBR is a 150-bp region containing three 15-bp breakpoint clusters in the untranslated portion of terminal exon 3. The study aims to identify the core factors involved in DNA-protein interactions in the MBR and their potential role in targeting the translocation to this region. The primary objective is to understand the regulatory function of the MBR and its potential consequences on MBR fragility and cell cycle regulation. The study uses Jurkat T cells and in vivo binding assays to investigate the role of DNA-protein interactions in the MBR.

Comparative Analysis & Findings

  • The study compares the outcomes observed under different experimental conditions, specifically the role of DNA-protein interactions in the MBR of the t(14,18) chromosomal translocation. The study identifies an 87-bp segment (87MBR) immediately 3' to breakpoint cluster 3 as essential for DNA-protein interaction monitored with mobility shift assays. The study further delineates a core binding region within 87MBR: a 33-bp, very AT-rich sequence highly conserved between the human and mouse BCL2 gene (37MBR). The study purifies and identifies one of the core factors as the matrix attachment region (MAR) binding protein, SATB1, which is known to bind to AT-rich sequences with a high propensity to unwind. Additional factors in nuclear extracts, which the study has not yet characterized further, increase SATB1 affinity for the 37MBR target four- to fivefold. The study demonstrates in vivo binding of SATB1 to the MBR, strongly suggesting the BCL2 major breakpoint region is a MAR. The key findings of the study suggest that DNA-protein interactions in the MBR play a crucial role in targeting the t(14,18) translocation to this region and regulating cell cycle progression. The study also highlights the potential consequences of MBR fragility and regulatory function on the development and progression of follicular lymphoma.

Implications and Future Directions

  • The study's findings have significant implications for the field of research and clinical practice. The study identifies a potential therapeutic target for follicular lymphoma by targeting the DNA-protein interactions in the MBR. The study also highlights the importance of understanding the regulatory function of the MBR and its potential consequences on MBR fragility and cell cycle regulation. The study suggests future research directions, such as identifying additional factors involved in DNA-protein interactions in the MBR and exploring their potential role in follicular lymphoma pathogenesis and treatment. The study also suggests future research directions to investigate the role of MARs in regulating chromosomal translocations and their potential as therapeutic targets in other cancers.
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