Cooperation between STAT5 and phosphatidylinositol 3-kinase in the IL-3-dependent survival of a bone marrow derived cell line

Cytokine-dependent activation of distinct signaling pathways is a common scheme thought to be required for the subsequent programmation into cell proliferation and survival. The PI 3-kinase/Akt, Ras/MAP kinase, Ras/NFIL3 and JAK/STAT pathways have been shown to participate in cytokine mediated suppression of apoptosis in various cell types. However the relative importance of these signaling pathways seems to depend on the cellular context. In several cases, individual inhibition of each pathway is not sufficient to completely abrogate cytokine mediated cell survival suggesting that cooperation between these pathways is required. Here we showed that individual inhibition of STAT5, PI 3-kinase or MEK activities did not or weakly affected the IL-3 dependent survival of the bone marrow derived Ba/F3 cell line. However, the simultaneous inhibition of STAT5 and PI 3-kinase activities but not that of STAT5 and MEK reduced the IL-3 dependent survival of Ba/F3. Analysis of the expression of the Bcl-2 members indicated that phosphorylation of Bad and Bcl-x expression which are respectively regulated by the PI 3-kinase/Akt pathway and STAT5 probably explain this cooperation. Furthermore, we showed by co-immunoprecipitation studies and pull down experiments with fusion proteins encoding the GST-SH2 domains of p85 that STAT5 in its phosphorylated form interacts with the p85 subunit of the PI 3-kinase. These results indicate that the activations of STAT5 and the PI 3-kinase by IL-3 in Ba/F3 cells are tightly connected and cooperate to mediate IL-3-dependent suppression of apoptosis by modulating Bad phosphorylation and Bcl-x expression.     

MAP kinase activation by interleukin-9 in lymphoid and mast cell lines

Interleukin-9 (IL-9) stimulates the proliferation of mast cells and lymphocytes. In the present study, we showed that IL-9 induced a transient phosphorylation of MEK, ERK2 and p90/RSK in murine lymphoid and mast cell lines. ERK2 in vitro kinase activity was also increased upon IL-9 stimulation. Similar results were obtained with IL-4, which had not been previously reported to activate these kinases in hematopoietic cells. Analysis of IL-9 receptor mutants showed that activation of the pathway was correlated with proliferation and with phosphorylation of the adaptor protein SHC, but not IRS2 or GAB2. The MEK inhibitor PD98059 reduced the mitogenic response to IL-4 and IL-9. In addition, expression of a dominant-negative RAS variant blocked ERK phosphorylation and significantly decreased Ba/F3 cell growth in the presence of IL-9, but did not affect expression of pim-1, a STAT target gene. In summary, these results indicate that IL-9 can transiently activate the mitogen-activated protein kinase pathway, which contributes to growth stimulation of hematopoietic cell lines.     

Autocrine-mediated ErbB-2 kinase activation of STAT3 is required for growth factor independence of pancreatic cancer cell lines

Pancreatic ductal adenocarcinoma (PDAC) cell lines, MIA PaCa-2, and UK Pan-1, were used to investigate the role of ErbB2 in PDAC oncogenesis. Both these cell lines exhibit exogenous growth factor-independent proliferation that was attributed to the production of autocrine growth factors and/or overexpression of growth factor receptors. The exogenous growth factor-independent phenotype displayed by these PDAC cell lines was dependent on ErbB2 kinase activity since treatment of cells with tyrphostin AG879 prevented serum-free media (SFM) induction of cell proliferation. We determined that ErbB2 kinase contributed to aberrant cell cycle regulation in PDAC through the induction of cyclin D1 levels and the suppression of p21(Cip1) and p27(Kip1). Inhibition of ErbB2 kinase led to cell cycle arrest marked by an increased association of p27(Kip1) with cdk2 and reduced levels of phosphorylated pRb. We further observed constitutive STAT3 activation in the PDAC cell lines and an increase in STAT3 activation upon stimulating quiescent cells with SFM. Inhibitors of ErbB2 kinase blocked STAT3 activation, whereas inhibition of EGFR kinase led to a slight reduction of STAT3 activation. STAT3 was coimmunoprecipitated with ErbB2. SFM stimulation caused an increase in the association of ErbB2 and STAT3, which was blocked by inhibition of ErbB2 kinase. Expression of a STAT3 dominant negative prevented SFM-stimulated cell proliferation of MIA PaCa-2 cells, suggesting that activation of STAT3 by ErbB2 is required for a growth factor-independent phenotype of these cells. Consistent with this observation in PDAC cell lines, we found that most PDAC tumor specimens (10 of 11) showed constitutive activation of STAT3 and that ErbB2 was readily detected in most of these tumors (nine of 11). We believe that these findings indicate a novel mechanism of oncogenesis in PDAC and may suggest future therapeutic strategies in the treatment of PDAC.     

Cdk2 associates with MAP kinase in vivo and its nuclear translocation is dependent on MAP kinase activation in IL-2-dependent Kit 225 T lymphocytes

Cell proliferation is controlled by cdk2 which in association with cyclin E and A regulates G1/S transition and S phase progression. cdk2 activation is dependent on its localization in the nucleus where regulatory mediators are found. We report that activation of cdk2 is associated with the formation of cdk2/MAP Kinase complexes. cdk2 associates with both inactive and activated MAP Kinase. Prevention of MAP Kinase activation by the MEK inhibitor PD98059 inhibits both activation and nuclear localization of cdk2 and S phase entry. These findings indicate that the nuclear translocation of cdk2 is associated with the formation of molecular complexes containing active MAP Kinase and is dependent on MAP Kinase activation. Oncogene (2000) 19, 4184 - 4189     

白细胞介素-6/信号转导和转录激活因子3信号通路在大细胞肺癌NL9980细胞系增殖中的作用及机制

背景与目的：白细胞介素-6/信号转导和转录激活因子3(IL-6/STAT3)信号通路在很多恶性肿瘤中存在过度激活及表达,包括白血病、头颈部鳞状细胞癌多发性黑色素瘤、乳腺癌以及前列腺癌等,但其在大细胞肺癌中的研究少见。该研究旨在探索大细胞肺癌NL9980细胞系中IL-6/STAT3信号通路在细胞增殖中的作用及其机制。方法：将外源性IL-6设立5个浓度梯度(终浓度分别为0、1.0、5.0、10.0和20.0 ng/mL),分别对NL9980细胞系进行干预。运用噻唑蓝(MTT)法观察细胞增殖活力改变,并确立IL-6干预的最佳浓度。采用RT-PCR技术检测IL-6/STAT3相关基因及其下游调控基因Bcl-2、VEGF和CYCD1的mRNA表达量,并将IL-6/STAT3相关基因与下游基因做相关性分析。结果：外源性IL-6可促进NL9980细胞系的增殖,其最佳干预浓度为5 ng/mL(F=8.11,P<0.05)。信号通路相关基因IL-6及STAT3的mRNA表达量均以5 ng/mL组最高,分别为4.78±0.09和5.17±0.05(P<0.05);下游调控基因中,Bcl-2、VEGF及CYCD1的mRNA表达量均在5 ng/mL组最高,分别为4.52±0.14、4.12±0.12和3.98±0.17,其余浓度组与对照组相比,差异无统计学意义(P>0.05)。相关性分析表明,下游基因中Bcl-2、VEGF、CYCD1与IL-6(r=0.952,r=0.836,r=0.880)和STAT3(r=0.995,r=0.746,r=0.800)呈正相关性。结论：IL-6可促进大细胞肺癌NL9980细胞系的增殖,其机制可能是通过活化IL-6/STAT3信号通路并上调相关基因Bcl-2、VEGF和CYCD1的表达来实现的。     

Expression and function of Flt3/flk2 in human tumor cell lines

The receptor tyrosine kinase Flt3 is expressed on the blasts of a high proportion of AML cases. We were interested in the expression and function of Flt3 on various human tumors. human tumor cell lines were tested for Flt3 expression by northern blot analysis and RT-PCR using head/neck (n=3), breast (n=4), ovarian (n=4), small cell lung (n=2), non-small cell lung (n=2), gastric (n=1), colon (n=3), pancreatic (n=1) and prostate carcinoma (n=1), choriocarcinoma (n=1), glioblastoma (n=5), neuroblastoma (n=1), melanoma (n=3), lymphoma (n=1), Hodgkin's disease (n=2), and leukemic (n=6) cell lines. With no expression on the other cell samples, 3 of 6 leukemic cell lines showed expression of Flt3 mRNA. The cDNA region corresponding to the juxtamembrane domain did not show any mutation as determined by sequence analysis. In all 3 positive cell lines, protein expression was verified by immunoprecipitation followed by immunoblot analysis. Although Flt3 is functional in these cell lines, as judged by ligand-dependent receptor autophosphorylation, it only mediates a proliferative response in 2 of the 3 cell lines. In conclusion, Flt3 is expressed exclusively in hematopoietic malignancies. Although early signalling events are detectable in all Flt3-positive cell lines tested, the expression of Flt3 does not predict a proliferative response of the cell lines. No internal tandem duplication of the juxtamembrane domain can be observed.     

Balance between activated-STAT and MAP kinase regulates the growth of human bladder cell lines after treatment with epidermal growth factor.

Epidermal growth factor (EGF) is a potent mitogen, and its action is mediated by MAP kinase (MAPK). Reportedly EGF activates STAT, induces the expression of p21waf1, and subsequently inhibits the growth of several types of cancer cells. In this study, we used human bladder cancer cells (T24 and RT4), immortalized non-tumorigenic human urothelial cells (1T-1, 1T-2, and 1T-3), and epidermal carcinoma cells (A431). EGF inhibited the growth of T24 and A431, and stimulated the growth of 1T-1, 1T-3 and 1T-2, but did not affect the growth of RT4. EGF activated MAPK strongly in 1T-1, and slightly in A431, T24, 1T-2, and 1T-3 but marginally in RT4. We detected the activation of STAT in T24, 1T-3 and A431 after EGF treatment. EGF enhanced the expression of p21waf1 mRNA in T24, 1T-2, 1T-3 and A431, and activated the p21waf1 promoter in T24 cells. These results suggest that i) EGF inhibits the growth of T24 cells via induction of p21waf1 mediated by STAT, and ii) the balance between the STAT-induced p21waf1 and MAPK activities regulates the growth of human bladder cells after EGF treatment.     

Transfection of a factor-dependent cell line with the murine interleukin-3 (IL-3) cDNA results in autonomous growth and tumorigenesis

The factor dependent murine myeloid line 32D c15 was transfected by electroporation with a murine interleukin-3 (IL-3) cDNA expression plasmid bearing the murine metallothionein-I promoter element. Factor-independent cell growth was readily obtained, and was shown to be accompanied by the production of biologically active IL-3. Three cell lines, growing autonomously and secreting IL-3 activity into their supernatants were established. S-1 nuclease analysis was employed to demonstrate that the introduced plasmid and not the endogenous IL-3 gene was the source of the IL-3 in one of these lines. The transfected IL-3 secreting cell lines, but not the parental factor-dependent 32D c15 cells, were uniformly able to induce tumors in syngeneic mice. These results indicate that the conversion to a malignant phenotype of a “partially transformed” cell line may be achieved by one additional dominant genetic event, such as the acquisition of autocrine growth factor secretion.     

Protein kinase WNK3 increases cell survival in a caspase-3-dependent pathway

The subfamily of WNK (with no K= lysine) protein kinases has four human members and germline mutations in the WNK1 and WNK4 genes were recently found to cause pseudohypoaldosteronism type II, a familial hypertension disease. Here, we describe cloning and functional analysis of a further WNK member, human WNK3. Endogenous WNK3 protein is an active protein kinase when immunoprecipitated from cells and its overexpression increases the survival of HeLa cells by delaying the onset of apoptosis. Suppression of endogenous WNK3 protein by RNA interference accelerates the apoptotic response and promotes the activation of caspase-3. The mechanism of WNK3 action involves interaction with procaspase-3 and heat-shock protein 70. These results demonstrate a role for WNK3 in promoting cell survival and suggest a mechanism at the level of procaspase-3 activation.     

Retinoic acid inhibits IL-6-dependent but not constitutive STAT3 activation in Epstein-Barr virus-immortalized B lymphocytes

IL-6-mediated B-cell growth promotion is involved in the pathogenesis of EBV+ lymphoproliferative disorders of immunosuppressed patients. Since retinoic acid (RA) inhibits the proliferation of EBV-immortalized lymphoblastoid B-cell lines (LCLs), we have investigated the effects of RA on IL-6 signaling in these cells. RA down-regulated IL-6-receptor components with IL-6 agonist activity (membrane and soluble gp80) and increased the levels of soluble gp130, an IL-6 antagonist. These changes, however, were not related to the enhanced production of endogenous IL-6 induced by RA in LCLs. RA-induced modulation of IL-6 receptor components did not abolish IL-6-mediated phosphorylation of gp130, whereas JAK1 and STAT3 phosphorylation and activation induced by IL-6 were markedly inhibited. Overall, the effects of RA resulted in the induction of a complete resistance of LCLs to IL-6-mediated growth promotion. Conversely, RA did not inhibit the constitutive activation of JAK1, TYK2, STAT3 and ERK1/2, ruling out that the JAK/STAT and MAPK pathways may mediate the antiproliferative activity of RA. The finding that RA severely impairs IL-6-dependent signalings in LCLs and inhibits their growth despite the presence of constitutively active JAK/STAT and MAPK cascades provide additional support for a role of RA in the prevention and treatment of EBV-related lymphoproliferative disorders of immunosuppressed patients.     

EXPRESSION OF IL-3 cDNA IN MURINE BONE MARROW CELLS RESULTS IN AUTONOMOUS GROWTH

Infection of murine bone marrow cells with retrovirus, containing the interleukin 3(IL-3) coding sequence and the newmyecine resistant gene, resulted In the ggeneration of factor-independent, G418 resistant, and Immortalized cell line E001. The established cell line has unique cytochemistry character, two marker chromosomes, and the Robertsonian translocation of chromosome 10th. The cell needs a stromal-dependent Mage before Us autonomous growth. The E001 cells secrete IL-3 which supports the growth of factor-dependent cell line 32D. The E001 cell growth is not influenced by its own conditioned medium and the cell density. These data Indicate that the autocrine stimulating mechanism may be one of the promary events In the cell transformation, white the expression of IL-3 and/or the retrovirus Insertion may respond to the phenotype of me E001 cells. The stromal layer may also be necessary In the cell transforming process.     

Differences in phosphorylation of the IL-2R associated JAK/STAT proteins between HTLV-I(+), IL-2-independent and IL-2-dependent cell lines and uncultured leukemic cells from patients with adult T-cell lymphoma/leukemia

To determine activation status of the IL-2R-associated (Jak/STAT) pathway in the HTLV-I infected cells, we examined tyrosine phosphorylation of Jak3, STAT3, and STAT5 in several HTLV-I(+) T-cell lines and in uncultured leukemic T cells isolated from patients with adult T-cell lymphoma/leukemia (ATLL). Constitutive basal phosphorylation of Jak3 and, usually, STAT3 and STAT5 was detected in all four IL-2-independent cell lines tested, but in none of the three IL-2-dependent cell lines. Similarly, there was no detectable basal phosphorylation of Jak3 and STAT5 in the leukemic cells from ATLL patients (0/8 and 0/3, respectively). However, stimulation with IL-2 resulted in Jak3 and STAT5 phosphorylation in both leukemic ATLL cells and IL-2-dependent lines. Furthermore, expression of SHP-1 phosphatase which is a negative regulator of cytokine receptor signaling, was lost in most IL-2 independent cell lines (3/4) but not in the leukemic ATLL cells (0/3). Finally, the HTLV-I(+) T-cell lines (313) but not the control, HTLV-I(-) T-cell lines were resistant to rapamycin and its novel analog RAD. We conclude that (1) HTLV-I infection per se does not result in a constitutive phosphorylation of the Jak3, STAT3, and STAT5 proteins; (2) malignant transformation in at least some cases of ATLL does not require the constitutive, but may require IL-2-induced, activation of the IL-2R Jak/STAT pathway; and (3) there are major differences in T-cell immortalization mechanism(s) which appear to involve SHP-1 and target molecules for rapamycin and RAD.     

Inhibition of Akt/FOXO3a signaling by constitutively active FOXO3a suppresses growth of follicular thyroid cancer cell lines

Akt-dependent FOXO3a cytoplasmic translocation is an important tumorigenic mechanism for escaping from apoptosis in cancer cells. In the present study, we examined whether non-phosphorylatable FOXO3a can inhibit cell growth of various follicular thyroid carcinoma (FTC) cell lines. Adenovirus carrying the FOXO3a-triple mutant (TM) sequence including point mutations at three Akt phosphorylation sites (Ad-FOXO3a-TM) was generated and transduced to the cells to mimic inhibition of Akt/FOXO3a signal. Transduction of Ad-FOXO3a-TM to FTC133 cells induced cell cycle arrest and apoptosis. Injection of Ad-FOXO3a-TM suppressed the growth of xenograft tumors in athymic mice. Consequently, our results indicate that gene therapy based on Ad-FOXO3a-TM has therapeutic potential for FTC.