Influence of mitogen-activated protein kinase (MAPK) signaling on mast cell differentiation and histone acetylation modifiers

Introduction: Mechanisms directing mast cell differentiation are incompletely defined. Epigenetic modifications by promoter methylation have been identified as key modulators of locus-specific chromatin accessibility during mast cell differentiation, but the role of histone acetylation (HA) has not been explored. Resultant changes in gene accessibility support a trajectory of lineage-specific gene expression as unique cell types mature from pluripotent progenitor hematopoietic stem cells. The MAPK signaling pathway contributes to regulating differentiation and proliferation and directly influences HA modifiers in a host of contexts. We aim to measure how the MAPK signaling pathway influences histone modifiers during mast cell differentiation in vitro toward the identification of potential key contributors. Methods: Mast cell differentiation was initiated from cultures of isolated murine bone marrow and samples were collected throughout differentiation. Quantitative polymerase chain reaction (qPCR) measurement of the RNA level, western blotting assessment of the protein level, and flow cytometry assessment of cell-surface receptor phenotype were conducted for HDACs, HATs and key mast cell-specific markers and transcription factors. Results: The MAPK signaling pathway significantly affected the expression of histone acetyltransferases, histone deacetylases and histone H3 post-translational modification. The inhibition of ERK (SCH772984) differently influenced the differentiation of mast cells through increased HDAC4 and increased PCAF gene expression. This was accompanied with changes in Histone H3 acetylation (K9) and phosphorylation (S10) and increased FcεRIα surface receptor presence with ERK inhibition. The inhibition of p38 (Losmapimod) showed a reduction in mast cell differentiation through decreased mast cell specific transcription factors and enzymes, MITF, Tpsb2, Cpa3 and Cma1, while decreasing FcεRIα receptor presence on the cell surface. The inhibition of JNK (JNK-IN-8) had no effect on mast cell differentiation. Conclusion: This work demonstrates the differential and dynamic importance of the ERK and p38 MAPK signaling pathways in mast cell differentiation and suggests links between the mast cell lineage program and epigenetic modifications via HA. Activation of the p38 MAPK signaling pathway is shown to drive mast cell differentiation, while ERK activation hinders HSC mast cell differentiation