Bishop W P, Wen J T
Department of Pediatrics, University of Iowa, Iowa City 52242.
Am J Physiol. 1994 Nov;267(5 Pt 1):G892-900. doi: 10.1152/ajpgi.1994.267.5.G892.
The epidermal growth factor (EGF) receptor is an important mediator of intestinal epithelial cell proliferation. We studied cell-surface localization of this molecule in Caco-2 cells and characterized cellular responses to apical or basolateral EGF stimulation. 125I-labeled EGF bound almost exclusively to a 180-kDa molecule, existing as a single high-affinity population by Scatchard analysis. On basolateral membranes 13- to 15-fold more ligand binding was seen. Apical/basolateral differences were not significantly altered by incubation with either blocking antibody to EGF receptor or transforming growth factor-alpha (TGF-alpha) neutralizing antibody. Even though apical EGF receptors were demonstrated, only basolateral membrane stimulation with EGF increased tyrosine kinase activity and enhanced uptake of [3H]thymidine. Continuous exposure to EGF during culture significantly increased monolayer DNA content. These data demonstrate that Caco-2 cell proliferation is driven solely by basolateral membrane EGF receptor, despite the presence of lesser amounts of this molecule on the apical surface. Differences between apical and basolateral membrane receptor expression are not the result of polarized secretion of TGF-alpha or other EGF receptor ligands.
表皮生长因子（EGF）受体是肠上皮细胞增殖的重要介质。我们研究了该分子在Caco-2细胞中的细胞表面定位，并表征了细胞对顶端或基底外侧EGF刺激的反应。125I标记的EGF几乎只与一个180 kDa的分子结合，通过Scatchard分析其以单一高亲和力群体形式存在。在基底外侧膜上观察到的配体结合量多出13至15倍。用EGF受体阻断抗体或转化生长因子-α（TGF-α）中和抗体孵育后，顶端/基底外侧差异没有显著改变。尽管已证实存在顶端EGF受体，但只有基底外侧膜受到EGF刺激时，酪氨酸激酶活性才会增加，并且[3H]胸苷的摄取也会增强。在培养过程中持续暴露于EGF会显著增加单层细胞的DNA含量。这些数据表明，尽管顶端表面存在少量该分子，但Caco-2细胞的增殖仅由基底外侧膜EGF受体驱动。顶端和基底外侧膜受体表达的差异并非TGF-α或其他EGF受体配体极化分泌的结果。
