Hembree J R, Agarwal C, Eckert R L
Department of Physiology and Biophysics, Case Western Reserve University School of Medicine, Cleveland, Ohio 44106-4970.
Cancer Res. 1994 Jun 15;54(12):3160-6.
Human ectocervical epithelial cells are a primary target for infection by oncogenic papillomaviruses, which are strongly implicated as causative agents in the genesis of cervical cancer. Growth factors have been implicated as agents that stimulate proliferation and enhance the possibility of malignant transformation. In the present study we utilize several human papillomavirus (HPV) type 16-immortalized ectocervical epithelial cell lines to investigate the effects of epidermal growth factor (EGF) and insulin-like growth factor I (IGF-I) on cell proliferation and the production of IGF binding proteins (IGFBPs). ECE16-1 cells, an HPV16-immortalized/nontumorigenic cell line, maintained in defined medium, produce and release high levels of IGFBP-3 (38/42 kDa) as well as smaller amounts of a 24-kDa IGFBP. Supplementation of defined medium with EGF causes a dose-dependent increase in cell growth and a concomitant decrease in the levels of IGFBP-3 released into the culture medium. EGF suppression of IGFBP-3 is maintained even when EGF-stimulated cell growth is suppressed 67% due to the simultaneous presence of 3 ng/ml of TGF beta 1, indicating that EGF suppression of IGFBP-3 levels is independent of EGF effects on cell growth. EGF suppression of IGFBP-3 production is correlated with a reduction in IGFBP-3 mRNA level. In the presence of EGF, the growth response of the cells to ng amounts of IGF-I is significantly enhanced. Moreover, the simultaneous presence of both EGF and IGF-I reduces the level of IGFBP-3 more efficiently than EGF alone. We also observe that the IGFBP-3 level is decreased and the 24-kDa IGFBP level is increased in HPV16-positive tumorigenic versus nontumorigenic cell lines. This is the first report of EGF acting as a positive regulator of IGF-I action via the IGFBPs. On the basis of these findings, we propose that EGF stimulates ECE16-1 cell growth via a dual-action mechanism by (a) stimulating growth directly via the EGF mitogenic pathway and (b) stimulating growth indirectly by reducing the levels of inhibitory IGFBPs and thereby potentiating the effects of IGF-I. In addition, the observation that more highly transformed cell types produce lower levels of IGFBP-3 and higher levels of 24-kDa IGFBP suggests that tumor cells in more advanced cervical cancers may have an altered response to IGF-I.
人宫颈外膜上皮细胞是致癌乳头瘤病毒感染的主要靶标，而致癌乳头瘤病毒被强烈认为是宫颈癌发生的病原体。生长因子被认为是刺激细胞增殖并增加恶性转化可能性的因子。在本研究中，我们利用几种人乳头瘤病毒16型永生化宫颈外膜上皮细胞系，来研究表皮生长因子（EGF）和胰岛素样生长因子I（IGF-I）对细胞增殖以及胰岛素样生长因子结合蛋白（IGFBPs）产生的影响。ECE16-1细胞是一种HPV16永生化/非致瘤性细胞系，在限定培养基中培养时，会产生并释放高水平的IGFBP-3（38/42 kDa）以及少量的24 kDa IGFBP。在限定培养基中添加EGF会导致细胞生长呈剂量依赖性增加，同时释放到培养基中的IGFBP-3水平降低。即使由于同时存在3 ng/ml的TGFβ1，EGF刺激的细胞生长被抑制了67%，EGF对IGFBP-3的抑制作用仍然存在，这表明EGF对IGFBP-3水平的抑制作用与EGF对细胞生长的影响无关。EGF对IGFBP-3产生的抑制作用与IGFBP-3 mRNA水平的降低相关。在EGF存在的情况下，细胞对纳克量IGF-I的生长反应显著增强。此外，EGF和IGF-I同时存在比单独使用EGF更有效地降低了IGFBP-3的水平。我们还观察到，与非致瘤性细胞系相比，HPV16阳性致瘤性细胞系中的IGFBP-3水平降低，24 kDa IGFBP水平升高。这是关于EGF通过IGFBPs作为IGF-I作用的正调节因子的首次报道。基于这些发现，我们提出EGF通过双重作用机制刺激ECE16-1细胞生长：（a）通过EGF促有丝分裂途径直接刺激生长；（b）通过降低抑制性IGFBPs的水平间接刺激生长，从而增强IGF-I的作用。此外，观察到转化程度更高的细胞类型产生较低水平的IGFBP-3和较高水平的24 kDa IGFBP，这表明更晚期宫颈癌中的肿瘤细胞可能对IGF-I有改变的反应。
