Glass W F, Kreisberg J I
Department of Pathology, University of Texas Health Science Center at San Antonio.
J Cell Physiol. 1993 Nov;157(2):296-306. doi: 10.1002/jcp.1041570212.
Cyclic AMP (cAMP) elevation causes diverse types of cultured cells to round partially and develop arborized cell processes. Renal glomerular mesangial cells are smooth, muscle-like cells and in culture contain abundant actin microfilament cables that insert into substratum focal contacts. cAMP elevation causes adhesion loss, microfilament cable fragmentation, and shape change in cultured mesangial cells. We investigated the roles of the classical vitronectin (alpha V beta 3 integrin) and fibronectin (alpha 5 beta 1 integrin) receptors in these changes. Mesangial cells on vitronectin-rich substrata contained microfilament cables that terminated in focal contacts that stained with antibodies to vitronectin receptor. cAMP elevation caused loss of focal contact and associated vitronectin receptor. Both fibronectin and its receptor stained in a fibrillary pattern at the cell surface under control conditions but appeared aggregated along the cell processes after cAMP elevation. This suggested that cAMP elevation caused loss of adhesion mediated by vitronectin receptor but not by fibronectin receptor. We plated cells onto fibronectin-coated slides to test the effect of ligand immobilization on the cellular response to cAMP. On fibronectin-coated slides fibronectin receptor was observed in peripheral focal contacts where actin filaments terminated, as seen with vitronectin receptor on vitronectin-coated substrata, and in abundant linear arrays distributed along microfilaments as well. Substratum contacts mediated by fibronectin receptor along the length of actin filaments have been termed fibronexus contacts. After cAMP elevation, microfilaments fragmented and fibronectin receptor disappeared from peripheral focal contacts, but the more central contacts along residual microfilament fragments appeared intact. Also, substratum adhesion was maintained after cAMP elevation on fibronectin--but not on vitronectin-coated surfaces. Although other types of extracellular matrix receptors may also be involved, our observations suggest that cAMP regulates adhesion at focal contacts but not at fibronexus-type extracellular matrix contacts.
环磷酸腺苷（cAMP）水平升高会使多种培养细胞部分变圆并形成树突状细胞突起。肾小球系膜细胞呈光滑的肌肉样细胞，在培养过程中含有丰富的肌动蛋白微丝束，这些微丝束插入到基质粘着斑中。cAMP水平升高会导致培养的系膜细胞失去黏附、微丝束断裂和形态改变。我们研究了经典的玻连蛋白（αVβ3整合素）和纤连蛋白（α5β1整合素）受体在这些变化中的作用。富含玻连蛋白的基质上的系膜细胞含有微丝束，这些微丝束终止于用玻连蛋白受体抗体染色的粘着斑处。cAMP水平升高导致粘着斑和相关玻连蛋白受体的丧失。在对照条件下，纤连蛋白及其受体在细胞表面呈纤维状染色，但在cAMP水平升高后，它们沿着细胞突起聚集。这表明cAMP水平升高导致由玻连蛋白受体介导的黏附丧失，而不是由纤连蛋白受体介导的黏附丧失。我们将细胞接种到纤连蛋白包被的载玻片上，以测试配体固定对细胞对cAMP反应的影响。在纤连蛋白包被的载玻片上，在肌动蛋白丝终止的外周粘着斑中观察到纤连蛋白受体，就像在玻连蛋白包被的基质上观察到的玻连蛋白受体一样，并且在沿着微丝分布的丰富线性阵列中也观察到纤连蛋白受体。沿着肌动蛋白丝长度由纤连蛋白受体介导的基质接触被称为纤维连接接触。cAMP水平升高后，微丝断裂，纤连蛋白受体从外周粘着斑消失，但沿着残留微丝片段的更中央的接触似乎完好无损。此外，在纤连蛋白包被的表面上，cAMP水平升高后基质黏附得以维持，但在玻连蛋白包被的表面上则不然。尽管其他类型的细胞外基质受体也可能参与其中，但我们的观察结果表明，cAMP调节粘着斑处的黏附，但不调节纤维连接型细胞外基质接触处的黏附。
