A role for intracellular pH in membrane IgM-mediated cell death of human B lymphomas
R Marches1, E S Vitetta, J W Uhr
1Cancer Immunobiology Center, Department of Microbiology, University of Texas Southwestern Medical Center, Dallas, TX 75390, USA. radu.marches@utsouthwestern.edu
Insights
Anti-IgM stimulation triggers cell death in B lymphoma cells via intracellular acidification, regulated by the Na+/H+ exchanger 1 (NHE1). Calcineurin inhibition prevents this by modulating NHE1 activity and maintaining cell viability.
Area of Science:
- Immunology
- Cell Biology
- Biochemistry
Background:
- B cell antigen receptor (BCR) signaling is crucial for B cell function and survival.
- Dysregulation of BCR signaling is implicated in B cell malignancies like lymphoma.
- Intracellular pH regulation plays a role in cellular processes, including apoptosis.
Purpose of the Study:
- To investigate the role of intracellular pH (pH(i)) in anti-IgM-induced cell death in human B lymphoma cell lines.
- To elucidate the involvement of the Na+/H+ exchanger isoform 1 (NHE1) and calcineurin in regulating pH(i) and cell fate during anti-IgM stimulation.
Main Methods:
- Utilized human B lymphoma cell lines (B104 and Daudi).
- Stimulated cells with anti-IgM antibody.
- Measured intracellular pH (pH(i)) changes and cell viability.
- Assessed NHE1 phosphorylation status as an indicator of its activation.
- Employed calcineurin inhibitor (cyclosporin A) and NHE1 inhibitor (5-(N,N-hexamethylene)amiloride).
Main Results:
- Anti-IgM induced cell death, intracellular acidification, and cell shrinkage in B104 cells.
- Daudi cells, less susceptible to BCR-mediated death, showed increased pH(i) upon anti-IgM stimulation.
- Changes in pH(i) correlated with differential activation of NHE1.
- Cyclosporin A abrogated anti-IgM-induced cell death and acidification in B104 cells, increasing NHE1 phosphorylation.
- NHE1 inhibition in Daudi cells affected cell viability, confirming the role of pH(i).
Conclusions:
- Intracellular pH regulation, controlled by NHE1, is a critical determinant of B lymphoma cell fate following anti-IgM stimulation.
- Calcineurin plays a key role in regulating pH(i) and cell viability by influencing NHE1 activity.
- Inactivation of NHE1 leads to intracellular acidification, triggering or amplifying cell death in anti-IgM-stimulated B cells.
Abstract:
We show that anti-IgM-induced cell death in a human B lymphoma cell line, B104, is associated with early intracellular acidification and cell shrinkage. In contrast, another human B cell lymphoma line, Daudi, less susceptible to B cell antigen receptor-mediated cell death, responded to anti-IgM with an early increase in intracellular pH (pH(i)). The anti-IgM-induced changes of pH(i) were associated with different levels of activation of the Na(+)/H(+) exchanger isoform 1 (NHE1) as judged by its phosphorylation status. Prevention of anti-IgM-induced cell death in B104 cells by the calcineurin phosphatase inhibitor, cyclosporin A, abrogated both intracellular acidification and cell shrinkage and was associated with an increase in the phosphorylation level of NHE1 within the first 60 min of stimulation. This indicates a key role for calcineurin in regulating pH(i) and cell viability. The potential role of pH(i) in cell viability was confirmed in Daudi cells treated with an Na(+)/H(+) exchanger inhibitor 5-(N,N-hexamethylene)amiloride. These observations indicate that the outcome of the anti-IgM treatment depends on NHE1-controlled pH(i). We suggest that inactivation of the NHE1 in anti-IgM-stimulated cells results in intracellular acidification and subsequently triggers or amplifies cell death.
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