Activation of Ras overcomes B-cell tolerance to promote differentiation of autoreactive B cells and production of autoantibodies.
Newly generated immature B cells are selected to enter the peripheral mature B-cell pool only if they do not bind (or bind limited amount of) self-antigen. We previously suggested that this selection relies on basal extracellular signal-regulated kinase (Erk) activation mediated by tonic B-cell antigen receptor (BCR) signaling and that this signal can be replaced by an active rat sarcoma (Ras), which are small GTPase proteins. In this study we compared the activity of Ras and Erk in nonautoreactive and autoreactive immature B cells and investigated whether activation of Ras can break tolerance. Our results demonstrate lower levels of active Erk and Ras in autoreactive immature B cells, although this is evident only when these cells display medium/high avidity for self-antigen. Basal activation of Erk in immature B cells is proportional to surface IgM and dependent on sarcoma family kinases, whereas it is independent of B-cell activating factor, IFN, and Toll-like receptor signaling. Ectopic expression of the constitutively active mutant Ras form N-RasD12 in autoreactive cells raises active Erk, halts receptor editing via PI3 kinase, and promotes differentiation via Erk, breaking central tolerance. Moreover, when B cells coexpress autoreactive and nonautoreactive BCRs, N-RasD12 leads also to a break in peripheral tolerance with the production of autoantibodies. Our findings indicate that in immature B cells, basal activation of Ras and Erk are controlled by tonic BCR signaling, and that positive changes in Ras activity can lead to a break in both central and peripheral B-cell tolerance.
['Teodorovic|Lenka S|LS|', 'Babolin|Chiara|C|', 'Rowland|Sarah L|SL|', 'Greaves|Sarah A|SA|', 'Baldwin|David P|DP|', 'Torres|Raul M|RM|', 'Pelanda|Roberta|R|']
D000818:Animals D001323:Autoantibodies D001402:B-Lymphocytes D001854:Bone Marrow Cells D002454:Cell Differentiation D002478:Cells, Cultured D048049:Extracellular Signal-Regulated MAP Kinases D007108:Immune Tolerance D019869:Phosphatidylinositol 3-Kinases D051381:Rats D011947:Receptors, Antigen, B-Cell D015398:Signal Transduction D018631:ras Proteins
BAFF Src