FUNCTIONAR ROFE OF C-FOS IN DIFFERENTIATION AND PROLIFERATION OF MATURE B CELLS

c-Fos诱导老年中心B细胞凋亡我们使用携带c-fos基因的转基因小鼠检测了c-Fos在成熟B细胞分化为产生IgG的细胞中的作用，所述转基因小鼠在IFN-α/b诱导型Mx启动子（Mx-c-fos）或组成型H-2 B启动子（H2-c-fos）的控制下。用LPS和rIL-4培养Mx-c-fos小鼠的脾B细胞，第3天后培养物中产生IgG 1 ^+ B细胞。从第2天开始加入IEN-a/B，24 h内IgG 1 ^+ B细胞的发育受到干扰，凋亡细胞数量增加，表明c-Fos诱导Ig类转换B细胞凋亡。为证实c-Fos对B细胞分化的影响，用DNP-OVA免疫H2-c-fos小鼠，小鼠血清中产生抗DNP-Ab的IgM抗体，但不产生IgG抗体，脾脏中不能产生生发中心。通过将H2-c-fos小鼠与携带bcl-2基因的转基因小鼠交配， ...更多信息 -2基因与IG启动子的同源性。然而，在双转基因小鼠中，初级IgG 1抗DNP Ab的产生仍然受到抑制，这表明Bcl-2可以延迟c-Fos诱导的IG类转换B细胞凋亡的时间，但不能挽救死亡。由于c-Fos在与Ags反应的成熟B细胞中被诱导，并且生发中心中自身反应性B细胞的克隆缺失对Bcl-2不敏感，c-fos基因的表达延长抑制骨髓造血干细胞的细胞周期进入原癌基因c-fos在原始造血干细胞中表达短暂上调（Lin ^-Sca-1 ^+）细胞，用干细胞因子、白细胞介素-3和白细胞介素-6刺激。为了研究c-fos在造血干细胞中的作用，我们使用了来自携带c-fos基因的转基因小鼠的骨髓（BM）细胞和来自c-fos缺陷小鼠的胎肝细胞，所述转基因小鼠在干扰素-a/B诱导型Mx启动子（Mx-c-fos）的控制下。Lin ^-Sca-1 ^+ BM细胞中c-fos的长期表达通过将基质细胞层保持在细胞周期的G0/G1期来抑制因子依赖性集落形成和造血。当外源性c-fos下调时，这些基质层上的Lin ^-Sca-1 ^+ BM细胞进入细胞周期。然而，当Lin ^-Sca-1 ^+ BM细胞进入细胞周期后，异位c-fos并不干扰其集落形成。此外，内源性c-fos对造血干细胞的细胞周期进程不是必需的，因为来自c-fos缺陷小鼠的Lin ^-Sca-1 ^+胎肝细胞的因子依赖性和基质依赖性造血没有受损。这些结果表明，在原始造血干细胞中诱导的c-fos负性控制细胞周期进程，并维持它们处于休眠状态。少

c-Fos Induces Apoptosis in Germinal Center B CellsWe examined a role of c-Fos in differentiation of mature B cells into IgG producing cells using transgenic mice carrying the c-fos gene under the control of the IFN-a/b-inducible Mx promoter (Mx-c-fos) or the constitutive H-2^b promoter (H2-c-fos). Splenic B cells from Mx-c-fos mice were cultured with LPS and rlL-4, and IgG1^+ B cells were developed in the culture after d 3. When IEN-a/b was added in the culture from d 2, development of IgG1^+ B cells was perturbed and the number of apoptotic cells increased within 24 h, suggesting that c-Fos induces apoptosis in Ig class-switching B cells. To confirm the effect of c-Fos on the B cell differentiation in vivo, H2-c-fos mice were immunized with DNP-OVA.The mice produced primary IgM but not IgG anti-DNP Ab in sera and failed to generate germinal centers in spleen. The perturbation of germinal center formation in H2-c-fos mice was rescued by mating them with transgenic mice carrying the bcl … More -2 gene with the Ig promoter. However, primary IgG1 anti-DNP Ab production was still suppressed in doubly transgenic mice, suggesting that Bcl-2 can delay time of c-Fos-induced apoptosis in Ig class-switching B cells but cannot rescue the death. Since c-Fos is induced in mature B cells reacted with Ags and clonal deletion of self-reactive B cells in germinal centers is insensitive to Bcl-2, these results suggest that c-Fos plays a causal role in clonal deletion of germinal center B cells.Prolonged Expression of c-fos Suppresses Cell Cycle Entry of Dormant Hematopoietic Stem CellsThe proto-oncogene c-fos was transiently up-regulated in primitive hematopoietic stem (Lin^-Sca-1^+) cells stimulated with stem cell factor, interleukin-3, and interleukin-6. To investigate a role of the c-fos in hematopoietic stem cells, we used bone marrow (BM) cells from transgenic mice carrying the c-fos gene under the control of the interferon-a/b inducible Mx-promoter (Mx-c-fos), and fetal liver cells from c-fos-deficient mice. Prolonged expression of the c-fos in Lin^- Sca-1^+ BM cells inhibited factor dependent colony formation and hematopoiesis on a stromal cell layer by keeping them at G0/G1 phase of the cell cycle. These Lin^- Sca-1^+ BM cells on a stromal layer entered into the cell cycle whenever exogenous c-fos was down-regulated. However, ectopic c-fos did not perturb colony formation by Lin^- Sca-1^+ BM cells after they entered the cell cycle. Furthermore, endogenous c-fos is not essential to cell cycle progression of hematopoietic stem cells since the factor dependent and the stroma dependent hematopoiesis by Lin^- Sca-1^+ fetal liver cells from c-fos-deficient mice were not impaired. These results suggest that the c-fos induced in primitive hematopoietic stem cells negatively controls cell cycle progression and maintains them in a dormant state. Less