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Human neutrophils utilize a Rac/Cdc42-dependent MAPK pathway to direct intracellular granule mobilization toward
Bin Zhong1, Kun Jiang, Danielle L Gilvary
1Immunology Program, H. Lee Moffitt Cancer Center & Research Institute, University of South Florida College of Medicine, Department of Interdisciplinary Oncology, Tampa, 33612, USA.
Abstract:
Elevated levels of mitogen-activated protein kinase/extracellular regulatory kinase (MAPK/ERK) activity are frequently found in some cancer cells. In efforts to reduce tumor growth, attempts have been made to develop cancer therapeutic agents targeting the MAPK. Here, by use of biologic, biochemical, and gene manipulation methods in human polymorphonuclear neutrophils (PMNs), we have identified a key pathway important in normal cell function involving MAPK/ERK in PMNs for growth inhibition of Candida albicans. Contact with C albicans triggered MAPK/ERK activation in PMNs within 5 minutes, and blocking of MAPK/ERK activation, either by the pharmacologic reagent PD098059 or by dominant-negative MAPK kinase (MEK) expression via vaccinia viral delivery, suppressed antimicrobial activity. Rac and Cdc42, but not Ras or Rho, were responsible for this MAPK/ERK activation. Expression of dominant-negative Rac (N17Rac) or Cdc42 (N17Cdc42) eliminated not only C albicans- mediated ERK phosphorylation but also phagocytosis and granule migration toward the ingested microbes, whereas dominant-negative Ras (N17Ras) and Rho (N19Rho) did not. PAK1 (p21-activated kinase 1) activation is induced by C albicans, suggesting that PAK1 may also be involved in the Rac1 activation of MAPK/ERK. We conclude from these data that Rac/Cdc42-dependent activation of MAPK/ERK is a critical event in the immediate phagocytic response of PMNs to microbial challenge. Therefore, use of MAPK pharmacologic inhibitors for the treatment of cancer may result in the interruption of normal neutrophil function. A balance between therapeutic outcome and undesirable side effects must be attained to achieve successful and safe anticancer therapy.
Insights
Mitogen-activated protein kinase/extracellular signal-regulated kinase (MAPK/ERK) pathway activation in neutrophils is crucial for inhibiting Candida albicans growth. Targeting MAPK/ERK for cancer therapy may impair normal neutrophil function.
Area of Science:
- Immunology
- Cell Biology
- Molecular Biology
Background:
- Mitogen-activated protein kinase/extracellular signal-regulated kinase (MAPK/ERK) activity is elevated in certain cancers.
- Targeting MAPK/ERK is a strategy for developing cancer therapeutics.
- The role of MAPK/ERK in normal neutrophil function, particularly in antimicrobial responses, is not fully understood.
Purpose of the Study:
- To investigate the role of the MAPK/ERK pathway in human polymorphonuclear neutrophils (PMNs) during Candida albicans infection.
- To identify upstream regulators of MAPK/ERK activation in PMNs in response to microbial challenge.
- To assess the implications of targeting MAPK/ERK for potential cancer therapies on normal immune cell function.
Main Methods:
- Biologic, biochemical, and gene manipulation techniques were employed in human PMNs.
- MAPK/ERK activation was assessed upon contact with Candida albicans.
- Pharmacologic inhibitors (PD098059) and dominant-negative constructs (MEK, Rac, Cdc42, Ras, Rho) were used to block specific pathway components.
- Phagocytosis and granule migration were evaluated.
- PAK1 activation was assessed.
Main Results:
- Candida albicans triggered rapid MAPK/ERK activation in PMNs.
- Blocking MAPK/ERK activation suppressed antimicrobial activity against C. albicans.
- Rac and Cdc42, but not Ras or Rho, were responsible for MAPK/ERK activation.
- Inhibition of Rac/Cdc42 also impaired phagocytosis and granule migration.
- PAK1 activation was observed, suggesting its involvement in Rac1-mediated MAPK/ERK activation.
Conclusions:
- Rac/Cdc42-dependent activation of MAPK/ERK is critical for the immediate phagocytic response of PMNs to microbial challenge.
- Targeting MAPK/ERK pharmacologically, as pursued in cancer therapy, could interfere with essential neutrophil functions.
- Balancing therapeutic benefits against potential side effects on normal neutrophil function is necessary for safe and effective anticancer treatments.