Gaumann A, Groot M, Drexler H C, Breier G
Max-Planck-Institut für physiologische und klinische Forschung, Abteilung molekulare Zellbiologie, Bad Nauheim.
Verh Dtsch Ges Pathol. 2003;87:232-9.
The VEGF/VEGFR system is known to play an important role in the development of new blood vessels during tumor formation. There is evidence that VEGFRs are not only present on endothelial cells but also on tumor cells. Since VEGF is able to induce proliferation and migration via VEGFR-2 we have studied the expression of VEGFRs and related receptor tyrosine kinases (RTKs) in different tumor cell lines and the effect of growth factor stimulation.
RTK expression was investigated in 5 different human tumor cell lines on protein and mRNA levels. Tumor cell lines were exposed to growth factors such as VEGF and the phosphorylation of downstream molecules involved in proliferation, migration and apoptosis were assessed. Under comparable conditions proliferation and migration essays were performed. Endogenous production of VEGF and PDGF by the tumor cells was measured by ELISA of cell culture supernatants.
Most tested cell lines expressed all known VEGFR's, PDGFR-beta on protein and mRNA levels to a varying extent. 3 out of 5 cell lines could be stimulated after addition of VEGF reflected by an increased phosphorylation of MAPK, AKT/PKB and to a lesser extent of p38. This was underlined by an increased cell number and reduced number of apoptotic cells. After stimulation with PDGF-BB a stronger induction of MAPK and AKT/PKB phosphorylation than for VEGF could be seen. In contrast, no effect on tumor cell migration was detectable in all examined cell lines. The investigation of cell culture supernatants revealed that most cell lines do not produce VEGF or PDGF.
Tumor cell lines express RTKs and the receptor is stimulable after addition of growth factors such as VEGF. Thus, secretion of groth factors in the tumor microenvironment is not only able to stimulate proliferation and survival of endothelial cells but also tumor cells themselve. One cell line displayed high levels of endogenous VEGF which could explain the lack of an increased cell number after addition of VEGF. It remains obscure why another cell line could not be stimulated although receptors were present at the cellular surface. Further investigations should prove that RTK's could be influenced by therapeutic drugs in order to suppress cell proliferation and migration and induce apoptosis in tumor cell lines.
已知血管内皮生长因子（VEGF）/血管内皮生长因子受体（VEGFR）系统在肿瘤形成过程中新生血管的发育中起重要作用。有证据表明，VEGFR不仅存在于内皮细胞上，也存在于肿瘤细胞上。由于VEGF能够通过VEGFR-2诱导增殖和迁移，我们研究了不同肿瘤细胞系中VEGFR和相关受体酪氨酸激酶（RTK）的表达以及生长因子刺激的作用。
在5种不同的人肿瘤细胞系中研究RTK在蛋白质和mRNA水平上的表达。将肿瘤细胞系暴露于VEGF等生长因子，并评估参与增殖、迁移和凋亡的下游分子的磷酸化情况。在可比条件下进行增殖和迁移实验。通过对细胞培养上清液进行酶联免疫吸附测定（ELISA）来检测肿瘤细胞内源性VEGF和血小板衍生生长因子（PDGF）的产生。
大多数受试细胞系在蛋白质和mRNA水平上不同程度地表达所有已知的VEGFR、PDGFR-β。5种细胞系中有3种在添加VEGF后可被刺激，表现为丝裂原活化蛋白激酶（MAPK）、蛋白激酶B（AKT/PKB）磷酸化增加，p38磷酸化增加程度较小。细胞数量增加和凋亡细胞数量减少证明了这一点。在用血小板源性生长因子BB（PDGF-BB）刺激后，可观察到MAPK和AKT/PKB磷酸化的诱导作用比VEGF更强。相比之下，在所有检测的细胞系中均未检测到对肿瘤细胞迁移的影响。对细胞培养上清液的研究表明，大多数细胞系不产生VEGF或PDGF。
肿瘤细胞系表达RTK，添加VEGF等生长因子后受体可被激活。因此，肿瘤微环境中生长因子的分泌不仅能够刺激内皮细胞的增殖和存活，也能刺激肿瘤细胞本身。一个细胞系显示出高水平的内源性VEGF，这可以解释添加VEGF后细胞数量未增加的原因。尽管细胞表面存在受体，但另一个细胞系为何不能被刺激仍不清楚。进一步的研究应证明RTK可受治疗药物影响，从而抑制肿瘤细胞系中的细胞增殖和迁移并诱导凋亡。
