B-cell activating factor (BAFF) is a crucial survival factor for B cells, and excess BAFF contributes to development of autoimmune diseases. Recent studies have shown that rapamycin can prevent BAFF-induced B-cell proliferation and survival, but the underlying mechanism remains to be elucidated. Here we found that rapamycin inhibited human soluble BAFF (hsBAFF)-stimulated cell proliferation by inducing G1-cell cycle arrest, which was through downregulating the protein levels of CDK2, CDK4, CDK6, cyclin A, cyclin D1, and cyclin E. Rapamycin reduced hsBAFF-stimulated cell survival by downregulating the levels of anti-apoptotic proteins (Mcl-1, Bcl-2, Bcl-xL and survivin) and meanwhile upregulating the levels of pro-apoptotic proteins (BAK and BAX). The cytostatic and cytotoxic effects of rapamycin linked to its attenuation of hsBAFF-elevated intracellular free Ca2+ ([Ca2+]i). In addition, rapamycin blocked hsBAFF-stimulated B-cell proliferation and survival by preventing hsBAFF from inactivating PTEN and activating the Akt-Erk1/2 pathway. Overexpression of wild type PTEN or ectopic expression of dominant negative Akt potentiated rapamycin's suppression of hsBAFF-induced Erk1/2 activation and proliferation/viability in Raji cells. Interestingly, PP242 (mTORC1/2 inhibitor) or Akt inhibitor X, like rapamycin (mTORC1 inhibitor), reduced the basal or hsBAFF-induced [Ca2+]i elevations. Chelating [Ca2+]i with BAPTA/AM, preventing [Ca2+]i elevation using EGTA, 2-APB or verapamil, inhibiting CaMKII with KN93, or silencing CaMKII strengthened rapamycin's inhibitory effects. The results indicate that rapamycin inhibits BAFF-stimulated B-cell proliferation and survival by blunting mTORC1/2-mediated [Ca2+]i elevations and suppressing Ca2+-CaMKII-dependent PTEN/Akt-Erk1/2 signaling pathway. Our finding underscores that rapamycin may be exploited for prevention of excessive BAFF-induced aggressive B-cell malignancies and autoimmune diseases.

中文翻译：

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雷帕霉素通过抑制正常和肿瘤性B淋巴样细胞中Ca2 + -CaMKII依赖的PTEN / Akt-Erk1 / 2信号通路，抑制B细胞激活因子（BAFF）刺激的细胞增殖和存活。

B细胞活化因子（BAFF）是B细胞的关键生存因子，过量的BAFF会导致自身免疫性疾病的发展。最近的研究表明，雷帕霉素可以预防BAFF诱导的B细胞增殖和存活，但其潜在机制尚待阐明。在这里我们发现雷帕霉素通过下调CDK2，CDK4，CDK6，cyclin A，cyclin D1和cyclin E的蛋白水平来诱导G1细胞周期停滞，从而抑制了人类可溶性BAFF（hsBAFF）刺激的细胞增殖。雷帕霉素降低了hsBAFF通过下调抗凋亡蛋白（Mcl-1，Bcl-2，Bcl-xL和survivin）的水平刺激细胞存活，同时上调促凋亡蛋白（BAK和BAX）的水平。雷帕霉素的抑制细胞生长活性和细胞毒性作用与其减弱hsBAFF升高的细胞内游离Ca2 +（[Ca2 +] i）有关。此外，雷帕霉素可通过防止hsBAFF失活PTEN和激活Akt-Erk1 / 2途径来阻断hsBAFF刺激的B细胞增殖和存活。野生型PTEN的过表达或显性负Akt增强的雷帕霉素异位表达可抑制Raji细胞中hsBAFF诱导的Erk1 / 2活化和增殖/存活。有趣的是，PP242（mTORC1 / 2抑制剂）或Akt抑制剂X，如雷帕霉素（mTORC1抑制剂），减少了基础或hsBAFF诱导的[Ca2 +] i升高。用BAPTA / AM螯合[Ca2 +] i，使用EGTA，2-APB或维拉帕米防止[Ca2 +] i升高，用KN93抑制CaMKII，或使CaMKII沉默可增强雷帕霉素的抑制作用。结果表明，雷帕霉素通过钝化mTORC1 / 2介导的[Ca2 +] i升高并抑制Ca2 + -CaMKII依赖性PTEN / Akt-Erk1 / 2信号通路来抑制BAFF刺激的B细胞增殖和存活。我们的发现强调了雷帕霉素可用于预防过度的BAFF诱导的侵袭性B细胞恶性肿瘤和自身免疫性疾病。