悪性リンパ腫におけるMALT1とBCL10蛋白の核内発現の意義

原著

目的:Extranodal marginal zone B-cell lymphoma of mucosa-associated lymphoid tissue(MALT リンパ腫),濾胞性リンパ腫(follicular lymphoma:FL),びまん性大細胞型リンパ腫(diffuse large B-cell lymphoma:DLBCL),末梢性T 細胞性リンパ腫(peripheral T-cell lymphoma:PTCL)の症例におけるMALT1とB-cell lymphoma leukemia 10(BCL10)蛋白の細胞内局在を解析する.さらに,核内におけるMALT1とBCL10 両分子の発現頻度や染色パターンを各種病型で比較検討し,悪性リンパ腫(malignant lymphoma:ML)発症機構におけるMALT1 とBCL10 両分子の核内発現の意義を考察する.対象および方法:正常リンパ装置8 例およびMALT リンパ腫30 例,FL 25 例,DLBCL 44 例,PTCL 16 例におけるMALT1 とBCL10 蛋白の細胞内局在を蛍光二重染色で解析した.さらにML 細胞株を用いてウエスタンブロット法を施行して細胞内局在における両蛋白の発現量を細胞レベルで検討した.結果:MALT リンパ腫では両蛋白は細胞質のみで発現頻度が高かった.しかしFL やDLBCL では核と細胞質の両者で発現頻度が増加し,特にDLBCL では形態学的に両蛋白が核内で粗大顆粒状を呈していた.しかしPTCL では核と細胞質ともにMALT1 蛋白の発現頻度が高度に減少していた.培養細胞ではDLBCL細胞株において細胞内のBCL10 およびnuclear factor-kappa B(NF-κB)p-65 の有意な増加がみられ,同時に核内でもBCL10 発現増加が確認された.結論:MALT リンパ腫と比較してFL やDLBCL ではMALT1 とBCL10 蛋白の核内発現が増加しており,両蛋白の核内発現メカニズムとして従来提唱されたMALT 関連染色体転座以外のメカニズムの関与が示唆された.ウエスタンブロット法による結果から,ML,特にDLBCL における両分子の核内発現は余剰な細胞質内BCL10 量を反映し,この余剰な細胞質内BCL10 はNF-κB 活性化の亢進に寄与していることが示唆された.Background: Nuclear expression of MALT1 and B-cell lymphoma/leukemia 10 (BCL10) was identified in extranodal marginal zone B-cell lymphoma of mucosa-associated tissue (MALT lymphoma) associated with translocation of t (1; 14) or (11; 18). Recently, aberrant nuclear expression of BCL10 was found in a subset of malignant lymphoma not including MALT lymphomas. However, the significance of nuclear expression of these 2 proteins in the pathogenesis of lymphoma cells remains to be elucidated.Methods: Subcellular localization of the MALT1 and BCL10 proteins was examined in various types of lymphoma cells, including 30 cases of MALT lymphoma, 25 cases of follicular lymphoma (FL), 44 cases of dif-fuse large B-cell lymphoma (DLBCL), and 16 cases of peripheral T-cell lymphoma (PTCL). We also assessed protein levels of MALT1, BCL10, CARMA1, and NF-κB p65 in whole-cell and nuclear fractions of cultured lymphoma cells.Results: Nuclear and cytoplasmic expression of MALT1 and BCL10 was identified in MALT lymphoma, DLBCL, and FL, and the number of cases that were positive for both proteins was markedly higher for DLBCL and FL than for MALT lymphoma. DLBCL and FL displayed spotty nuclear staining with irregu-larly shaped granules that were positive for both proteins. Cultured DLBCL cells had significantly increased expressions of MALT1, BCL10, and NF-κB p65 in whole-cell lysate and markedly increased BCL10 expres-sion in nuclear fractions.Conclusions: The marked difference between DLBCL and MALT lymphoma in positive rates ofMALT1 and BCL10 nuclear expression indicates that there is no significant correlation between the nuclear expres-sions of these proteins and MALT lymphoma-associated translocation. Thepositive relationship in BCL10 expression between whole-cell and nuclear fractions of cultured DLBCL cells suggests that BCL10 nuclear expression is mediated by its level in cytoplasm. This might represent theactivation status of NF-κB, which is mediated by the formation of the CARMA1-BCL10-MALT1 signalosome.