Continual signaling is responsible for constitutive ERK phosphorylation in B-1a cells

• Published in: Molecular immunology Vol. 46; no. 15; pp. 3029 - 3036
• Main Authors: Holodick, Nichol E., Tumang, Joseph R., Rothstein, Thomas L.
• Format: Journal Article
• Language: English
• Published: England Elsevier Ltd 01-09-2009
• Subjects: Animals; B cells; B-Lymphocytes - drug effects; B-Lymphocytes - metabolism; B7-2 Antigen - drug effects; B7-2 Antigen - metabolism; CD5 Antigens - metabolism; Enzyme Inhibitors - pharmacology; Extracellular Signal-Regulated MAP Kinases - antagonists & inhibitors; Extracellular Signal-Regulated MAP Kinases - metabolism; Intracellular Signaling Peptides and Proteins - antagonists & inhibitors; Intracellular Signaling Peptides and Proteins - metabolism; Male; Mice; Mice, Inbred BALB C; Phosphatidylinositol 3-Kinases - antagonists & inhibitors; Phosphatidylinositol 3-Kinases - metabolism; Phospholipase C gamma - antagonists & inhibitors; Phospholipase C gamma - metabolism; Phosphoric Monoester Hydrolases - antagonists & inhibitors; Phosphoric Monoester Hydrolases - metabolism; Phosphorylation - drug effects; Phosphorylation - physiology; Protein kinases/phosphatases; Protein-Tyrosine Kinases - antagonists & inhibitors; Protein-Tyrosine Kinases - metabolism; Rodent; Signal transduction; Signal Transduction - drug effects; Signal Transduction - physiology; src-Family Kinases - antagonists & inhibitors; src-Family Kinases - metabolism; Syk Kinase; Vanadates - pharmacology; Signal transduction; B cells; Protein kinases/phosphatases; Rodent
• ISSN: 0161-5890; 1872-9142
• DOI: 10.1016/j.molimm.2009.06.011

B-1a cells constitutively express phosphorylated, activated ERK, but the origin of pERK in B-1 cells has not been determined. To address this issue, we examined specific mediators of intracellular signaling in unmanipulated B-1a cells. We found that constitutive pERK was rapidly lost from B-1a cells following addition of metabolic inhibitors that block src kinase, Syk, PI-3K, and PLC function. We examined Syk and PLC in more detail and found rapid accumulation of phosphorylated forms of these molecules in B-1a cells, but not B-2 cells, when phosphatase activity was inhibited, and this change occurred in the majority of B-1a cells. Further, we showed that inhibition of src kinase activity eliminated “downstream” pSyk and pPLC accumulation in phosphatase-inhibited B-1a cells, indicating a pathway connection. CD86 expression is greater on B-1 than B-2 cells and plays a role in antigen presentation by B-1 cells to T cells. We found that when Syk or PI-3K was inhibited, CD86 expression was diminished in a reversible fashion. All together, these results indicate that continual activation of intracellular signaling leads to constitutive activation of ERK in B-1 cells, with attendant consequences for co-stimulatory molecule expression.