Upon encounter with Ag, B-lymphocytes undergo terminal differentiation into plasma cells, highly specialized Ab secretors that mediate humoral immune responses. Profound changes adapt cellular morphology and proteome to the new secretory functions. Although a massive secretory activity is expected to require an efficient ubiquitin-proteasome degradation system, we recently reported that in the late phases of plasma cell differentiation, when Ab production becomes maximal, the relative amount and proteolytic activity of proteasomes dramatically decrease, potentially contributing to plasma cell death (1). We challenged this paradigm in mouse models of plasma cell differentiation in vivo, and observed that proteasome activity decreases at even higher velocity and intensity than previously reported in vitro. This decrease is linked to enhanced apoptotic sensitivity to the potent anti-myeloma proteasome inhibitor PS-341. Accordingly, in vivo treatment with PS-341 decreases Ab titres in T-dependent and independent mouse immunization models. MATERIAL AND METHODS: C57Bl/6 mice were injected intraperitoneally with LPS. For proteasome assays B-lymphocytes were purified by immunomagnetic positive selection upon labelling with FITC-conjugated CD38 antibody. For in vitro apoptosis assays, B-lymphocytes were purified by immunomagnetic negative selection. Proteasome activities and expression levels were assessed by fluorimetric assays and western blots respectively. Apoptosis was assessed by Flow cytometry after staining of cells with with Annexin V-FITC and propidium iodide. Ig titres in serum of mice immunized with Ova or NP-ficoll were determined by Elisa. Taken together, our results demonstrate that a built-in plasma cell developmental program impairs the ubiquitin-proteasome disposal system, and offer a novel strategy to manipulate plasma cell lifespan and secretory activity, with potential implications for the physiology of the immune system and for different pathological conditions, in primis Ig-secreting tumors and autoimmune diseases. (1) Cenci S.*, Mezghrani A.*, Cascio P.* et al. Progressively impaired proteasomal capacity during terminal plasma cell differentiation. The EMBO Journal, 2006, 25: 1104-13. (*Joint first authors)
Proteasome decrease during plasma cell differentiation in vivo enables to blunt Ab responses with proteasome inhibitors
CASCIO, Paolo;CERRUTI, Fulvia;BRUNO, Renato;
2007-01-01
Abstract
Upon encounter with Ag, B-lymphocytes undergo terminal differentiation into plasma cells, highly specialized Ab secretors that mediate humoral immune responses. Profound changes adapt cellular morphology and proteome to the new secretory functions. Although a massive secretory activity is expected to require an efficient ubiquitin-proteasome degradation system, we recently reported that in the late phases of plasma cell differentiation, when Ab production becomes maximal, the relative amount and proteolytic activity of proteasomes dramatically decrease, potentially contributing to plasma cell death (1). We challenged this paradigm in mouse models of plasma cell differentiation in vivo, and observed that proteasome activity decreases at even higher velocity and intensity than previously reported in vitro. This decrease is linked to enhanced apoptotic sensitivity to the potent anti-myeloma proteasome inhibitor PS-341. Accordingly, in vivo treatment with PS-341 decreases Ab titres in T-dependent and independent mouse immunization models. MATERIAL AND METHODS: C57Bl/6 mice were injected intraperitoneally with LPS. For proteasome assays B-lymphocytes were purified by immunomagnetic positive selection upon labelling with FITC-conjugated CD38 antibody. For in vitro apoptosis assays, B-lymphocytes were purified by immunomagnetic negative selection. Proteasome activities and expression levels were assessed by fluorimetric assays and western blots respectively. Apoptosis was assessed by Flow cytometry after staining of cells with with Annexin V-FITC and propidium iodide. Ig titres in serum of mice immunized with Ova or NP-ficoll were determined by Elisa. Taken together, our results demonstrate that a built-in plasma cell developmental program impairs the ubiquitin-proteasome disposal system, and offer a novel strategy to manipulate plasma cell lifespan and secretory activity, with potential implications for the physiology of the immune system and for different pathological conditions, in primis Ig-secreting tumors and autoimmune diseases. (1) Cenci S.*, Mezghrani A.*, Cascio P.* et al. Progressively impaired proteasomal capacity during terminal plasma cell differentiation. The EMBO Journal, 2006, 25: 1104-13. (*Joint first authors)
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