Maurice M, Rogier E, Cassio D, Feldmann G
Institut National de la Santé et de la Recherche Médicale, Unité 24, Laboratoire de Biologie Cellulaire, Faculté de Médecine Xavier-Bichat, Paris, France.
J Cell Sci. 1988 May;90 ( Pt 1):79-92. doi: 10.1242/jcs.90.1.79.
In vivo, proteins of the hepatocyte plasma membrane are asymmetrically distributed, making it possible to distinguish a sinusoidal, a lateral and a canalicular domain. The conditions that determine hepatocyte plasma membrane polarity have been investigated in vitro, using three monoclonal antibodies directed against integral membrane proteins, which were characteristic of each domain. The localization of the three antigens was studied by immunolabelling of hepatocytes isolated from adult rat liver, primary monolayer cultures and rat hepatoma cell lines. When hepatocytes were isolated, the three antigens spread over the entire cell surface. The lateral antigen redistributed at lateral sites as soon as cell-cell contacts were established, 4 h after the beginning of primary culture. The sinusoidal and canalicular antigens became asymmetrically distributed after 48 h of primary culture, after the formation of bile canaliculus-like structures. In most of the hepatoma lines studied, the three antigens were expressed, except that the canalicular antigen was fully expressed in differentiated clones only. The lateral antigen was always distributed on the contiguous membranes of clustered hepatoma cells, whereas the sinusoidal and canalicular antigens were localized on the entire plasma membrane. However, in a few cells of some clones in which bile canaliculus-like structures were observed, the canalicular membranes were strongly labelled only with the canalicular antibody. In the absence of bile canalicular formations, in both primary culture and cell lines, the canalicular antigen and, to a lesser extent, the sinusoidal antigen accumulated in the Golgi apparatus, suggesting that their transport to the cell surface was altered in the absence of a bile pole. These results show that in hepatic cells, polarization of the plasma membrane is determined by: (1) the existence of cell-cell contacts, which is correlated with the domain-specific localization of the lateral antigen; and (2) the formation of bile canaliculi, which would trigger the development of an asymmetrical distribution of the sinusoidal and canalicular antigens.
在体内，肝细胞质膜蛋白呈不对称分布，从而能够区分窦状、侧面和胆小管结构域。利用三种针对整合膜蛋白的单克隆抗体，在体外研究了决定肝细胞质膜极性的条件，这三种抗体分别是每个结构域的特征性抗体。通过对从成年大鼠肝脏分离的肝细胞、原代单层培养细胞和大鼠肝癌细胞系进行免疫标记，研究了这三种抗原的定位。当肝细胞被分离时，这三种抗原分布在整个细胞表面。原代培养开始4小时后，一旦细胞间接触建立，侧面抗原就会重新分布到侧面位点。原代培养48小时后，在胆小管样结构形成后，窦状和胆小管抗原开始不对称分布。在大多数研究的肝癌细胞系中，这三种抗原都有表达，只是胆小管抗原仅在分化的克隆中完全表达。侧面抗原总是分布在聚集的肝癌细胞的相邻膜上，而窦状和胆小管抗原则定位在整个质膜上。然而，在一些观察到胆小管样结构的克隆的少数细胞中，胆小管膜仅被胆小管抗体强烈标记。在原代培养和细胞系中，在没有胆小管形成的情况下，胆小管抗原以及在较小程度上的窦状抗原会在高尔基体中积累，这表明在没有胆小极的情况下它们向细胞表面的转运发生了改变。这些结果表明，在肝细胞中，质膜的极化由以下因素决定：（1）细胞间接触的存在，这与侧面抗原的结构域特异性定位相关；（2）胆小管的形成，这将触发窦状和胆小管抗原不对称分布的发展。
