Smorodinsky N, Weiss M, Hartmann M L, Baruch A, Harness E, Yaakobovitz M, Keydar I, Wreschner D H
Department of Cell Research and Immunology, George S. Wise Faculty of Life Sciences, Tel Aviv University, Ramat Aviv, Israel.
Biochem Biophys Res Commun. 1996 Nov 1;228(1):115-21. doi: 10.1006/bbrc.1996.1625.
Although MUC1 proteins are known to be secreted by breast cancer cells, the mechanism of their release from the cell is still obscure. Our previously reported MUC1 cDNA sequences suggested the existence of a secreted MUC1 isoform, MUC1/SEC, that includes a sequence of intron 2, and terminates prematurely at a stop codon within this intron. It is thus devoid of a transmembrane domain. As no formal evidence for MUC1/SEC expression at the protein level had been provided, we generated monoclonal antibodies (mAbs) against a peptide sequence (sec peptide) that is unique for the MUC1/SEC protein. Two anti-sec peptide mAbs were obtained which reacted strongly with (a) the immunizing peptide, (b) recombinant MUC1/SEC protein, and (c) MUC1 proteins secreted from breast cancer cells. The immunoreactivity of the anti-sec peptide mAbs with MUC1 proteins secreted by breast cancer cells was specifically inhibited by the sec peptide-it was completely unaffected by a peptide sequence that represents a MUC1 repeat motif. Significantly, the anti-sec peptide mAbs also detected MUC1/SEC protein in sera of breast cancer patients. We have established here that these mAbs recognize the MUC1/SEC isoform via a peptide sequence which is unique for the MUC1/SEC protein. Our studies thus demonstrate that the MUC1/SEC protein is a bona-fide MUC1 isoform and that its expression may contribute to the secretion of MUC1 proteins by secretory epithelial cells in general and breast cancer cells in particular.
虽然已知MUC1蛋白由乳腺癌细胞分泌，但其从细胞中释放的机制仍不清楚。我们之前报道的MUC1 cDNA序列提示存在一种分泌型MUC1异构体MUC1/SEC，它包含内含子2的一段序列，并在该内含子内的一个终止密码子处提前终止。因此它没有跨膜结构域。由于尚未提供MUC1/SEC在蛋白质水平表达的正式证据，我们针对MUC1/SEC蛋白特有的一段肽序列（sec肽）制备了单克隆抗体（mAb）。获得了两种抗sec肽单克隆抗体，它们与（a）免疫肽、（b）重组MUC1/SEC蛋白以及（c）乳腺癌细胞分泌的MUC1蛋白发生强烈反应。抗sec肽单克隆抗体与乳腺癌细胞分泌的MUC1蛋白的免疫反应性被sec肽特异性抑制，而代表MUC1重复基序的肽序列对其完全没有影响。重要的是，抗sec肽单克隆抗体还在乳腺癌患者血清中检测到了MUC1/SEC蛋白。我们在此证实，这些单克隆抗体通过MUC1/SEC蛋白特有的一段肽序列识别MUC1/SEC异构体。我们的研究因此表明，MUC1/SEC蛋白是一种真正的MUC1异构体，其表达可能有助于一般分泌上皮细胞尤其是乳腺癌细胞分泌MUC1蛋白。
