Singh P, Lu X, Cobb S, Miller B T, Tarasova N, Varro A, Owlia A
Department of Anatomy and Neurosciences, University of Texas Medical Branch, Galveston, Texas 77555-1043, USA.
Am J Physiol Gastrointest Liver Physiol. 2003 Feb;284(2):G328-39. doi: 10.1152/ajpgi.00351.2002. Epub 2002 Oct 16.
Proliferation and carcinogenesis of the large intestinal epithelial cells (IEC) cells is significantly increased in transgenic mice that overexpress the precursor progastrin (PG) peptide. It is not known if the in vivo growth effects of PG on IEC cells are mediated directly or indirectly. Full-length recombinant human PG (rhPG(1-80)) was generated to examine possible direct effects of PG on IEC cells. Surprisingly, rhPG (0.1-1.0 nM) was more effective than the completely processed gastrin 17 (G17) peptide as a growth factor. Even though IEC cells did not express CCK(1) and CCK(2) receptors (-R), fluorescently labeled G17 and Gly-extended G17 (G-Gly) were specifically bound to the cells, suggesting the presence of binding proteins other than CCK(1)-R and CCK(2)-R on IEC cells. High-affinity (K(d) = 0.5-1.0 nM) binding sites for (125)I-rhPG were discovered on IEC cells that demonstrated relative binding affinity for gastrin-like peptides in the order PG >or= COOH-terminally extended G17 >or= G-Gly > G17 > CCK-8 ( significant difference; P < 0.05). In conclusion, our studies demonstrate for the first time direct growth effects of the full-length precursor peptide on IEC cells in vitro that are apparently mediated by the high-affinity PG binding sites that were discovered on these cells.
在过表达前体胃泌素（PG）肽的转基因小鼠中，大肠上皮细胞（IEC）的增殖和致癌作用显著增强。尚不清楚PG对IEC细胞的体内生长效应是直接介导还是间接介导。制备了全长重组人PG（rhPG(1-80)）以研究PG对IEC细胞可能的直接作用。令人惊讶的是，作为生长因子，rhPG（0.1 - 1.0 nM）比完全加工的胃泌素17（G17）肽更有效。尽管IEC细胞不表达CCK(1)和CCK(2)受体（-R），但荧光标记的G17和甘氨酸延伸的G17（G-Gly）能特异性结合到细胞上，这表明IEC细胞上存在除CCK(1)-R和CCK(2)-R之外的结合蛋白。在IEC细胞上发现了针对(125)I-rhPG的高亲和力（K(d) = 0.5 - 1.0 nM）结合位点，该位点对胃泌素样肽的相对结合亲和力顺序为PG≥羧基末端延伸的G17≥G-Gly＞G17＞*CCK-8（*显著差异；P＜0.05）。总之，我们的研究首次证明了全长前体肽对体外IEC细胞的直接生长作用，这显然是由在这些细胞上发现的高亲和力PG结合位点介导的。
