Overexpression of c-fos inhibits down-regulation of a cyclin-dependent kinase-2 inhibitor p27Kip1 in splenic B cells activated by surface Ig cross-linking

Splenic B cells activated by surface Ig (sIg) cross-linking transiently express the c-fos gene within 0.5 h and then enter into S phase of the cell cycle within 48 h. To investigate a role of c-fos in cell cycle progression, we used splenic B cells from IFN-alphabeta-inducible c-fos transgenic mice (Mx-c-fos). In the absence of IFN, the cell cycle progression of Mx-c-fos B cells stimulated with anti-IgM Ab was similar to that in control B cells. The cell cycle was arrested in G1 phase when we added IFN to the culture within 12 h after anti-IgM Ab stimulation, suggesting that overexpression of c-fos until mid-G1 phase perturbs activation of the cell cycle regulatory machinery. In control B cells, cyclin E and cdk2 were induced within 24 to 48 h after stimulation, and this induction was accompanied by down-regulation of a cdk2 inhibitor p27Kip1. As a consequence of these activation processes, cdk2 kinase activity was induced in B cells in the late G1 phase. However, kinase activity was not detected in Mx-c-fos B cells, presumably because the down-regulation of p27 was perturbed. These data suggest that c-Fos can negatively control cell cycle regulatory machinery in sIg-stimulated B cells.

Overexpression of c-Fos induces apoptosis of CD43+ pro-B cells

The proto-oncogene product c-Fos, a component of the transcription factor AP-1, is induced in early B lineage cells. To investigate a role of c-Fos in early B cell development, fetal liver (FL) cells from transgenic mice carrying an IFN-alphabeta (IFN)-inducible c-fos gene (Mx-c-fosD) were cultured on a stromal cell layer with IL-7. Although B lineage cells normally developed in the Mx-c-fosD FL cell culture, the development was perturbed by the addition of IFN at the beginning of culture. When IFN was added in the FL culture after B lineage cells developed, pro-B (B220+,CD43+) cells were selectively dying by apoptosis within 48 h after IFN stimulation. This apoptosis was intrinsically induced in the pro-B cells that overexpressed c-fos when the Mx-c-fosD FL (H-2Kb) cells were cocultured with the normal C3H FL (H-2Kk) cells. The molecular basis of the apoptosis was investigated by examining expression of the genes that regulate apoptosis. The IFN stimulation did not modulate expression of Bcl-2 and Fas in early B lineage cells from the Mx-c-fosD FL culture. However, Rag-2 was down-regulated in these cells within 12 h after IFN stimulation. These results suggest that the c-Fos plays a causal role in deletion of pro-B cells with nonfunctional Ag receptor.

Overexpression of c-Fos induces apoptosis of CD43+ pro-B cells

The proto-oncogene product c-Fos, a component of the transcription factor AP-1, is induced in early B lineage cells. To investigate a role of c-Fos in early B cell development, fetal liver (FL) cells from transgenic mice carrying an IFN-alphabeta (IFN)-inducible c-fos gene (Mx-c-fosD) were cultured on a stromal cell layer with IL-7. Although B lineage cells normally developed in the Mx-c-fosD FL cell culture, the development was perturbed by the addition of IFN at the beginning of culture. When IFN was added in the FL culture after B lineage cells developed, pro-B (B220+,CD43+) cells were selectively dying by apoptosis within 48 h after IFN stimulation. This apoptosis was intrinsically induced in the pro-B cells that overexpressed c-fos when the Mx-c-fosD FL (H-2Kb) cells were cocultured with the normal C3H FL (H-2Kk) cells. The molecular basis of the apoptosis was investigated by examining expression of the genes that regulate apoptosis. The IFN stimulation did not modulate expression of Bcl-2 and Fas in early B lineage cells from the Mx-c-fosD FL culture. However, Rag-2 was down-regulated in these cells within 12 h after IFN stimulation. These results suggest that the c-Fos plays a causal role in deletion of pro-B cells with nonfunctional Ag receptor.

The BCL6 gene is predominantly expressed in keratinocytes at their terminal differentiation stage

We analyzed the expression of the BCL6 gene in mouse tissues by in situ hybridization. The expression was strong in the upper layer but undetectable in the basal layer of epidermis from adult mice. When human keratinocytes were cultured with a high concentration of calcium ion, these cells stopped their proliferation and differentiated to their terminal stage. In these keratinocytes, BCL6 expression was induced after stimulation and progressively up-regulated. The kinetics was very similar to that of a cyclin dependent kinase inhibitor p21sdil/cip1/WAF1 in these cells. These results suggest that BCL6 plays a role in keratinocytes at terminal differentiation stage.

Essential requirement of an invariant V alpha 14 T cell antigen receptor expression in the development of natural killer T cells

NK1.1+ T [natural killer (NK) T] cells express an invariant T cell antigen receptor alpha chain (TCR alpha) encoded by V alpha 14 and J alpha 281 segments in association with a limited number of V betas, predominantly V beta 8.2. Expression of the invariant V alpha 14/J alpha 281, but not V alpha 1, TCR in transgenic mice lacking endogenous TCR alpha expression blocks the development of conventional T alpha beta cells and leads to the preferential development of V alpha 14 NK T cells, suggesting a prerequisite role of invariant V alpha 14 TCR in NK T cell development. In V beta 8.2 but not B beta 3 transgenic mice, two NK T cells with different CD3 epsilon expressions, CD3 epsilon(dim) and CD3 epsilon(high), can be identified. CD3 epsilon(high) NK T cells express surface V alpha 14/V beta 8 TCR, indicating a mature cell type, whereas CD3 epsilon(dim) NK T cells express V beta 8 without V alpha 14 TCR and no significant CD3 epsilon expression (CD3 epsilon(dim)) on the cell surface. However, the latter are positive for recombination activating gene (RAG-1 and RAG-2) mRNA, which are only expressed in the precursor or immature T cell lineage, and also possess CD3 epsilon mRNA in their cytoplasm, suggesting that CD3 epsilon(dim) NK T cells are the precursor of V alpha 14 NK T cells.

[Overexpression of c-Fos induces apoptosis of CD43+ pro-B cells]

The proto-oncogene product c-Fos, a component of the transcription factor AP-1, is induced in early B lineage cells. In order to investigate a role of the c-Fos in early B cell development, fetal liver (FL) cells from transgenic mice carrying an IFN-inducible c-fos gene (Mx-c-fos) were cultured on a stromal cell layer with IL-7. The development was perturbed by the addition of IFN at the beginning of culture. When IFN was added in the FL culture after B lineage cells developed, pro-B (B220+, CD43+) cells were selectively dying by apoptosis within 48 h after IFN stimulation. These results suggest that c-Fos plays a causal role in deletion of pro-B cells.

A regulatory role of c-Fos in the development of precursor B lymphocytes mediated by interleukin-7

The proto-oncogene product c-Fos, a component of the transcription factor AP-1, plays a critical role in the expression of genes required for cellular proliferation and differentiation. The c-Fos is induced in early B lineage cells developed in the interleukin-7-dependent bone marrow (BM) cell culture from normal mice. In order to investigate a role of the c-Fos in early B cell development, we have used BM cells from two different transgenic mice carrying the exogenous c-fos gene controlled by the promoter of the H-2Kb gene (H2-c-fos) or the interferon alpha/beta (IFN)-inducible Mx gene (Mx-c-fosD). Development of B lineage cells was retarded in the BM cell culture from H2-c-fos mice. Although B lineage cells normally developed in the BM cell culture from Mx-c-fosD mice without IFN stimulation, the development was completely blocked in the Mx-c-fosD culture when transgenic c-fos was induced in BM cells by IFN stimulation. Furthermore, the IL-7-dependent proliferation of B lineage cells in Mx-c-fosD BM cells was also suppressed by the induction of c-Fos. These results suggest that the c-Fos plays a role as a negative regulator in the early B cell development.

Two forms of Hox11 a T cell leukemia oncogene, are expressed in fetal spleen but not in primary lymphocytes

HOX11 is identified from the breakpoint of human T cell acute lymphoblastic leukemias with t(10;14). Since overexpression of HOX11 in T cells caused leukemias in transgenic mice, the endogenous HOX11 may play a role in proliferation and differentiation of T cells. In order to elucidate the role, we examined the expression of Hox11 in normal lymphocytes by a reverse transcriptase-polymerase chain reaction analysis. Two alternatively spliced Hox11 mRNAs were expressed in fetal spleens. However, lymphocytes did not express Hox11 mRNA during differentiation. Furthermore, it was not induced in primary lymphocytes after activation. These results suggest that ectopic expression of HOX11 in T cells is responsible for leukemogenesis.

The murine BCL6 gene is induced in activated lymphocytes as an immediate early gene

The chromosomal translocation involving 3q27 is often detected in human B-cell lymphomas, especially diffuse lymphomas with a large-cell component. The BCL6 gene has been isolated from the chromosomal breakpoint in these lymphomas. Here we cloned the murine BCL6 (mBCL6) cDNA from the muscle cDNA library using the human BCL6 (hBCL6) cDNA as a probe. The predicted amino acid sequence was 95% identical to that of hBCL6. It contains six repeats of the Krüppel-like zinc-finger motif that are completely identical to those of hBCL6, indicating that the BCL6 gene is well conserved between humans and mice. Expression of the mBCL6 gene was ubiquitously detected in adult mouse tissues including lymphatic organs. Furthermore, it was induced in lymphocytes activated with phorbol ester and Ca2+ ionophore within 30 min after stimulation. This induction was not inhibited by treatment of the cells with a protein synthesis inhibitor, cycloheximide. These results suggest that BCL6 plays a role in activated lymphocytes as an immediate early gene.

Inhibitory effect of c-fos overexpression on B cell proliferative responses to membrane IGM cross-linking

Constitutive expression of the c-fos gene perturbs the de novo synthesis of RNA and DNA in B cells stimulated by surface immunoglobulin (sIg) cross-linking. In order to examine kinetics of the regulatory effect on the activation process of B cells, we used splenic B cells from transgenic mice carrying the c-fos gene under the control of the interferon alpha/beta (IFN)-inducible Mx gene promoter (Mx-c-fos). In the absence of IFN, Mx-c-fos B cells proliferated well by anti-IgM stimulation. However, both RNA and DNA synthesis in the Mx-c-fos B cells were markedly reduced by the addition of IFN in the culture within 12 h after anti-IgM stimulation. These results suggest that this regulatory effect of c-Fos displays at the mid G1 phase of the cell cycle.

Deregulated c-Fos/AP-1 accelerates cell cycle progression of B lymphocytes stimulated with lipopolysaccharide

We implicated deregulated c-Fos/AP-1 in proliferative response of B lymphocytes stimulated with lipopolysaccharide (LPS) using splenic B cells from c-fos transgenic (Mx-c-fos) mice. Levels of DNA synthesis of the Mx-c-fos B cells were augmented in proportion to the amount of AP-1. Since the number of LPS-responding splenic B cells from Mx-c-fos mice was similar to that from control mice duplication time of the Mx-c-fos B cells (0.9 days) was much shorter than that of the control B cells (2.1 days), this augmentation is explained by the acceleration of cell cycle progression by deregulated c-Fos/AP-1. These results suggest that AP-1 is a major regulatory factor for cell cycle progression of B cells activated with LPS.

Deregulated c-Fos/AP-1 modulates expression of the cyclin and the cdk gene in splenic B cells stimulated with lipopolysaccharide

Overexpression of c-Fos/AP-1 augments proliferation of splenic B cells stimulated with lipopolysaccharide (LPS). To elucidate mechanisms of the augmentation by c-Fos/AP-1, a cell cycle of the LPS-activated B cells from c-fos transgenic mice was analyzed. Cell cycle progression into the S phase was accelerated in the c-fos B cells. Expression of genes related to the cell cycle progression was examined in these B cells. Amount of cyclin D3 and cdk4 mRNA increased in the c-fos B cells at 6 h earlier than that in the control B cells, indicating that the kinetics of these mRNA expressions correlate with the acceleration of cell cycle progression. Furthermore, cyclin D1 and cyclin E mRNA were detected in the c-fos B cells but not in the control B cells. These results indicate that deregulated c-Fos/AP-1 modulates expression of the cyclin and the cdk gene in splenic B cells stimulated with LPS. These modulations may accelerate cell cycle progression and augment proliferation of the B cells.

p53 controls proliferation of early B lineage cells by a p21 (WAF1/Cip1)-independent pathway

We examined a role of p53 in early B cell development using fetal liver (FL) cells from p53 deficient (-/-) mice. Expression of p53 was detected in early B lineage (pre-B) cells developed in the stromal cell-dependent FL cell culture. Proliferation of the pre-B cells from the p53(-/-) mice was augmented, suggesting that p53 negatively regulates proliferation of pre-B cells. Although p21 (WAF1/Cip1) is a downstream effector of p53 and mediates growth arrest by inhibiting the action of cyclin-dependent kinases, expression of p21 was also induced in the pre-B cells from p53(-/-) mice. These results indicate that expression of the p21 in pre-B cells is independent of p53 and that the regulatory effect of p53 on proliferation of pre-B cells is mediated by a p21-independent pathway.

Analysis of IL-2 gene regulation in c-fos transgenic mice. Evidence for an enhancement of IL-2 expression in splenic T cells stimulated via TCR/CD3 complex

Effects of the deregulated c-fos gene product on IL-2 expression were studied in splenic T cells from c-fos transgenic (H2-c-fos) mice. IL-2 gene expression and IL-2 production by H2-c-fos T cells stimulated with immobilized anti-CD3 Abs were enhanced and prolonged as compared with those by control T cells. Activator protein-1 activity in nuclear extract from the H2-c-fos T cells was also higher than that from the control cells. There was no significant difference in the activity of other transcription factors including IL-2 kappa B, NFAT, and Oct-1, between the H2-c-fos and the control T cells. However, activity of a negative regulatory element binding factor (NRE-A) in the H2-c-fos T cells was much lower than that in the control cells. These results suggest that c-Fos/activator protein-1 is a major regulatory factor for IL-2 gene expression in splenic T cells activated through the TCR/CD3 complex.

Analysis of IL-2 gene regulation in c-fos transgenic mice. Evidence for an enhancement of IL-2 expression in splenic T cells stimulated via TCR/CD3 complex

Effects of the deregulated c-fos gene product on IL-2 expression were studied in splenic T cells from c-fos transgenic (H2-c-fos) mice. IL-2 gene expression and IL-2 production by H2-c-fos T cells stimulated with immobilized anti-CD3 Abs were enhanced and prolonged as compared with those by control T cells. Activator protein-1 activity in nuclear extract from the H2-c-fos T cells was also higher than that from the control cells. There was no significant difference in the activity of other transcription factors including IL-2 kappa B, NFAT, and Oct-1, between the H2-c-fos and the control T cells. However, activity of a negative regulatory element binding factor (NRE-A) in the H2-c-fos T cells was much lower than that in the control cells. These results suggest that c-Fos/activator protein-1 is a major regulatory factor for IL-2 gene expression in splenic T cells activated through the TCR/CD3 complex.

Deregulated expression of c-fos disturbs proliferative responses of B cells to sIg cross-linking

B cell activation by surface immunoglobulin (sIg) cross-linking is accompanied by transient expression of the c-fos protooncogene. This expression is strictly controlled in the B cells. To investigate a biological implication of the c-fos expression in the process of B cell activation by sIg cross-linking, we examined the proliferation of splenic B cells from H2-c-fos transgenic mice. Constitutive expression of the c-fos gene perturbs de novo synthesis of RNA and DNA in the B cells stimulated with anti-IgM antibody. Early events of signal transduction such as an increase in intracellular free calcium level and an induction of the endogenous immediate early genes (c-fos and c-myc) were apparently intact in those B cells. When the sIg stimulation of B cells was mimicked by the costimulation with 12-O-tetradecanoylphorbol 13-acetate and ionomycin, H2-c-fos B cells required higher concentrations of ionomycin for the optimal proliferative responses, suggesting that calcium-dependent signal transduction pathways are disturbed in those B cells. These results demonstrate a novel regulatory effect of c-fos protein on the proliferation of B cells mediated by sIg cross-linking.

c-fos and jun gene expression in murine precursor B lymphocytes developed in the interleukin-7-dependent bone marrow cell culture

We analyzed the expression of c-fos and jun family gene in murine pre-B cells developed in the interleukin-7-(IL-7) dependent bone marrow cell culture. The c-fos gene was expressed in the pre-B cells. The c-fos RNA became undetectable after IgM+ B cells were developed in the culture. The c-fos expression in the pre-B cells was IL-7-dependent. However, the c-fos RNA was not induced when the pre-B cells cultured without IL-7 for 6 h were restimulated with IL-7. The expression of c-jun RNA was slightly induced in the restimulated pre-B cells. The junB and junD RNA were the steady state level in the cells. These gene products formed AP-1 molecule in the pre-B cells. These results suggest that the AP-1 plays a role in the IL-7-dependent pre-B cell development.

Deregulated c-fos modulates IgG2b production of B cells mediated by lipopolysaccharide

We have examined effects of the deregulated c-fos protein on IgG2b production of B cells cultured with lipopolysaccharide (LPS) using splenic B cells from a transgenic line carrying the mouse c-fos gene under the control of the interferon alpha/beta (IFN) inducible Mx promoter (Mx-c-fosD). High c-fos expression was induced in the Mx-c-fosD B cells during the first two days of culture. DNA synthesis and IgG2b production were augmented in the culture. When IFN was added together with LPS, the high c-fos expression was prolonged until day 3 of culture. IgG2b production was remarkably suppressed. However, the production was not suppressed by upregulation of c-fos via exogenous IFN on day 4 of culture. These results suggest a regulatory effect of the c-fos protein on the differentiation of B cells to IgG2b producing cells at a distinct period.

Deregulated c-fos modulates B cell responses to switch mediators

We examined effects of deregulated c-fos on the proliferation and differentiation of B cells in vitro, using splenic B cells from H2-c-fos transgenic mice. When these cells were cultured with lipopolysaccharide (LPS) plus recombinant interleukin 4 (rIL-4) (10(4) U/ml), the proliferative response of the B cells was augmented with any dose of LPS used. This augmented proliferation resulted in an increase in IgG1 production in the culture, at the lower concentrations of LPS (< 2.5 micrograms/ml). However, H2-c-fos B cells did not produce IgG1 in the culture at higher concentrations of LPS (> 5 micrograms/ml) probably due to the perturbation of B cell differentiation to antibody-forming cells. These results suggest that the deregulated expression of c-fos modulates the proliferation and differentiation of B cells stimulated with LPS plus rIL-4.

Regulation of class II MHC gene expression by the inducible anti-sense RNA in transgenic mice

We have established a gene regulatory system in mice by the inducible anti-sense RNA. We have generated transgenic mice carrying the anti-sense DNA composed of the class II MHC gene under the control of the human metallothionein IIa gene promoter. The detectable amount of anti-sense RNA was constitutively produced in spleen and bone marrow from transgenic mice and the amount in spleen was increased about fivefold by the stimulation of mice with heavy metal ions. We have previously reported that the reduction of class II MHC molecules on early B lineage cells by the anti-sense RNA results in delay of their development in the bone marrow culture. The early B cell development was slightly delayed in the culture from the transgenic mice. This delay was augmented in the culture by the addition of heavy metal ions in proportion to its concentration. These results suggest that the inducible anti-sense RNA reduces the expression of class II MHC molecules on B lineage cells.

B cell development is perturbed in bone marrow from c-fos/v-jun doubly transgenic mice

c-fos and c-jun gene products form a heterodimeric complex (AP-1) that regulates target gene expression by binding to a specific DNA sequence motif. In order to study a role of AP-1 (Fos/Jun) in growth and differentiation of immature B lineage cells, we have established and mated two independent transgenic mice carrying the mouse c-fos gene or the viral v-jun gene fused to the H-2K promoter. IL-7 dependent bone marrow cell culture from doubly transgenic (H2-fos/jun) mice demonstrated severe delay of early B cell development. Proliferation of pre-B cells in the fresh bone marrow from H2-fos/jun mice to IL-7 stimulation was very low. These results suggest that the deregulated production of AP-1 perturbs IL-7 mediated proliferation and differentiation of immature B cells.

Deregulated c-fos augments cell proliferation of B cells mediated by lipopolysaccharide

We have examined effects of the deregulated c-fos protein on the lipopolysaccharide (LPS)-mediated B cell responses using splenic B cells from transgenic lines carrying the mouse c-fos gene under the control of the H-2K (H2-c-fos) and the inducible Mx promoter (Mx-c-fosD). High c-fos expression was induced in Mx-c-fosD B cells by LPS stimulation. DNA synthesis of the B cells from both lines was augmented depending on the amount of exogenous c-fos. This augmentation resulted in the increase of IgM and IgG2b productions in the culture. These results suggest a functional role of c-fos protein in cell cycle progression of the activated B cells.

[A dissociation of thresholds between Goldmann kinetic perimetry and high-pass resolution perimetry in retinitis pigmentosa]

The authors studied the differences between the automated static perimetry of high-pass resolution perimeter (HRP) and the kinetic perimetry of the Goldmann perimeter in 12 patients with retinitis pigmentosa. In a total of 10 eyes of 6 patients, we found 19 quadrants in which the patients were not able to recognize the largest ring target even when the target was within the isopter of the Goldmann perimetry. Also, there were 10 quadrants in which the largest target was not recognized in a total of 6 eyes of 4 patients even though their visual field showed symmetrical isopter in upper and lower or right and left quadrants in the Goldmann perimetry. As a result, it was suggested that the causes of the dissocation were a greater decrease in sensitivity for the low spatial frequency target than the high spatial frequency target and/or a greater decrease in resolution sensitivity than light sensitivity in retinitis pigmentosa.

Role of I-A molecules in early stages of B cell maturation

The role of the Ia molecule in the early phase of B cell development remains controversial. In contrast to previous studies, we have detected minute amounts of Ia (I-A) molecule on early B lineage (B220+IgM-) cells from normal bone marrow, using ELISA. The presence of the I-A molecule even on pro-B cells was deduced from experiments in which a monoclonal anti-I-A antibody completely blocked the generation of pre-B cells from B progenitor (B220-) cells in stromal cell-dependent B cell culture. Inasmuch as this antibody did not inhibit the maturation of pre-B cells to IgM+ B cells in culture, the I-A molecule on early B lineage cells probably plays a role in their maturation. We also examined the role of the I-A molecule in early B cell development, using transgenic mice harboring the antisense DNA to I-A beta-chain gene. The amount of I-A molecule on splenic B cells from the young transgenic mice decreased in the presence of abundant amounts of the antisense RNA. B cell development was perturbed in spleen from the transgenic mice. Stromal cell-dependent B cell cultures from these mice clearly showed that the maturation of B lineage cells was delayed at a very early stage of development (B220- to B220+). We propose that the I-A molecule on early B lineage cells may play an essential role in their maturation.