Dikov M M, Oyama T, Cheng P, Takahashi T, Takahashi K, Sepetavec T, Edwards B, Adachi Y, Nadaf S, Daniel T, Gabrilovich D I, Carbone D P
The Vanderbilt Cancer Center and Department of Medicine, Vanderbilt University School of Medicine, Nashville, Tennessee 37232-6838, USA.
Cancer Res. 2001 Mar 1;61(5):2015-21.
Vascular endothelial growth factor (VEGF) inhibits of the activation of transcription factor nuclear factor-kappaB (NF-kappaB) in hematopoietic progenitor cells (HPCs), and this is associated with alterations in the development of multiple lineages of hematopoietic cells and defective immune induction in tumor-bearing animals. Antibodies to VEGF have been shown to abrogate this effect. The mechanism by which VEGF antagonizes the induction of NF-kappaB was investigated in this study. Using supershift electrophoretic mobility shift analysis, we found that although tumor necrosis factor alpha (TNF-alpha) induced the nuclear translocation and DNA binding of p65-containing complexes, VEGF alone induced nuclear translocation and DNA binding of the complexes containing RelB. These results were confirmed by immunofluorescence confocal microscopy. VEGF effectively blocked TNF-alpha-induced NF-kappaB activation in HPCs from RelB-/- mice, however, similar to the effect observed in HPCs obtained from RelB+/- and RelB+/+ mice. This suggests that RelB is not required for VEGF to inhibit NF-kappaB activation. However, although TNF-alpha induced rapid activation of IkappaB kinase (IKK) as expected, this activity was substantially reduced in the presence of VEGF. This decreased IKK activation correlated with the inhibition of IkappaB alpha phosphorylation and degradation of IkappaB alpha and IkappaB epsilon in HPCs. VEGF alone, however, did not have any effect on phosphorylation of IkappaB alpha or degradation of IkappaB alpha and other inhibitory molecules IkappaB beta, IkappaB epsilon, or Bcl-3. SU5416, a potent inhibitor of the VEGF receptor I (VEGFR1) and VEGFR2 receptor tyrosine kinases, did not abolish the inhibitory effect of VEGF, indicating that the VEGF effect is mediated by a mechanism unrelated to VEGFR1 or VEGFR2 tyrosine kinase activity. Thus, VEGF appears to inhibit TNF-alpha-induced NF-kappaB activation by VEGFR kinase-independent inhibition of IKK. Therapeutic strategies aimed at overcoming VEGF-mediated defects in immune induction in tumor-bearing hosts will need to target this kinase-independent pathway.
血管内皮生长因子（VEGF）可抑制造血祖细胞（HPC）中转录因子核因子-κB（NF-κB）的激活，这与造血细胞多个谱系发育的改变以及荷瘤动物免疫诱导缺陷有关。已证实抗VEGF抗体可消除这种效应。本研究探讨了VEGF拮抗NF-κB诱导的机制。通过超迁移电泳迁移率变动分析，我们发现尽管肿瘤坏死因子α（TNF-α）诱导含p65复合物的核转位和DNA结合，但单独的VEGF诱导含RelB复合物的核转位和DNA结合。这些结果通过免疫荧光共聚焦显微镜得到证实。VEGF有效地阻断了RelB基因敲除小鼠的HPC中TNF-α诱导的NF-κB激活，然而，这与在RelB杂合子和RelB野生型小鼠获得的HPC中观察到的效应相似。这表明RelB对于VEGF抑制NF-κB激活并非必需。然而，尽管TNF-α如预期诱导IκB激酶（IKK）快速激活，但在VEGF存在的情况下，这种活性显著降低。这种IKK激活的降低与HPC中IκBα磷酸化的抑制以及IκBα和IκBε的降解相关。然而，单独的VEGF对IκBα的磷酸化或IκBα以及其他抑制分子IκBβ、IκBε或Bcl-3的降解没有任何影响。SU5416是VEGF受体I（VEGFR1）和VEGFR2受体酪氨酸激酶的强效抑制剂，并未消除VEGF的抑制作用，表明VEGF的效应是由与VEGFR1或VEGFR2酪氨酸激酶活性无关的机制介导的。因此，VEGF似乎通过VEGFR激酶非依赖性抑制IKK来抑制TNF-α诱导的NF-κB激活。旨在克服荷瘤宿主中VEGF介导的免疫诱导缺陷的治疗策略将需要针对这种激酶非依赖性途径。
