van der Burg B, Isbrücker L, van Selm-Miltenburg A J, de Laat S W, van Zoelen E J
Hubrecht Laboratory, Netherlands Institute for Developmental Biology, Utrecht.
Cancer Res. 1990 Dec 15;50(24):7770-4.
Insulin-like growth factor I (IGF-I) is the most potent growth factor for estrogen (E2)-dependent breast cancer cell lines. It has been reported that such cell lines produce an immunoreactive IGF-I-related protein in an E2-dependent fashion, while autonomously growing cell lines constitutively produce these factors, indicating that they might be involved in autocrine growth stimulation of breast cancer cells. We have studied the role of IGFs in autocrine growth stimulation of the E2-dependent breast cancer cell line MCF7 by using IGF-binding proteins (BPs) that were able to neutralize completely the mitogenic effect of IGF-I on this cell line. These BPs, however, did not have any inhibitory effect on E2-induced mitogenesis, suggesting that secretion of autocrine IGFs is not involved in growth stimulation by E2. To exclude the possibility that variants of IGF are produced by the cells that are not recognized by the BPs, we also studied the production of biologically active IGF using the same MCF7 cell line in a sensitive bioassay in which the various forms of IGF and insulin can be detected. Although the conditioned medium (CM) of human fibroblasts used as a control showed IGF-like activity in this assay, no such activity was detected in CM of both untreated and E2-stimulated MCF7 cells, while the CM of the E2-independent cell lines BT20 and Hs578T had only slight mitogenic activity or was even growth inhibitory, respectively. These data show that no significant secretion of biologically active IGFs by human breast cancer cells could be detected and do not support a possible autocrine function of IGFs in the proliferation of such cells. Because E2-dependent cells strongly react to externally added IGF-like factors produced by human fibroblasts, a role for IGFs in paracrine regulation of proliferation is suggested.
胰岛素样生长因子I（IGF-I）是雌激素（E2）依赖的乳腺癌细胞系中最有效的生长因子。据报道，此类细胞系以E2依赖的方式产生一种免疫反应性IGF-I相关蛋白，而自主生长的细胞系则组成性地产生这些因子，这表明它们可能参与了乳腺癌细胞的自分泌生长刺激。我们通过使用能够完全中和IGF-I对该细胞系促有丝分裂作用的IGF结合蛋白（BPs），研究了IGFs在E2依赖的乳腺癌细胞系MCF7自分泌生长刺激中的作用。然而，这些BPs对E2诱导的有丝分裂没有任何抑制作用，这表明自分泌IGFs的分泌不参与E2的生长刺激。为了排除细胞产生不被BPs识别的IGF变体的可能性，我们还使用相同的MCF7细胞系在一种敏感的生物测定中研究了生物活性IGF的产生，在该测定中可以检测到各种形式的IGF和胰岛素。尽管用作对照的人成纤维细胞的条件培养基（CM）在此测定中显示出IGF样活性，但在未处理和E2刺激的MCF7细胞的CM中均未检测到此类活性，而E2非依赖细胞系BT20和Hs578T的CM分别仅具有轻微的促有丝分裂活性或甚至具有生长抑制作用。这些数据表明，未检测到人乳腺癌细胞有显著分泌生物活性IGFs的情况，也不支持IGFs在此类细胞增殖中可能的自分泌功能。由于E2依赖的细胞对人成纤维细胞产生的外部添加的IGF样因子有强烈反应，提示IGFs在旁分泌调节增殖中起作用。
