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Basement membranes are important for epithelial differentiation, cell survival, and normal and metastatic cell migration. Much is known about their breakdown and remodeling, yet their positive regulation is poorly understood. Our previous analysis of a fibroblast growth factor (FGF) receptor mutation raised the possibility that protein kinase B (Akt͞PKB) activated by FGF is connected to the expression of certain laminin and type IV collagen isotypes. Here we test this hypothesis and demonstrate that constitutively active Akt͞PKB, an important downstream element of phosphoinositide 3-kinase signaling, induces the synthesis of laminin-1 and collagen IV isotypes and causes their translocation to the basement membrane. By using promoter-reporter constructs, we show that constitutively active phosphoinositide 3-kinase-p110 or Akt͞PKB activates, whereas dominant negative Akt͞PKB inhibits, transcription of laminin ␤1 and collagen IV ␣1 in differentiating C2 myoblast-and insulin-induced Chinese hamster ovary-T cell cultures. These results suggest that Akt͞PKB activated by receptor tyrosine kinases is involved in the positive regulation of basement membrane formation. The possible role of Akt͞PKB-induced laminin and collagen IV synthesis in cell survival and differentiation will be discussed.transcription ͉ extracellular matrix ͉ receptor kinases ͉ P13K ͉ signal transduction S ecreted laminin and type IV collagen chains form heterotrimers because of their mutual affinity and assemble into the basement membrane's (BM's) protein network, where they associate with additional proteins such as nidogens and heparan sulfate proteoglycans (HSPG) (1). Collagen IV and laminin isotypes bind to the cell membrane through integrin or dystroglycan receptors and induce cytoskeletal rearrangements, which contribute to the BM's final mat-like structure (2). They initiate signaling pathways through both their receptors (3) and HSPGs associated with them. HSPGs bind and present a number of polypeptide growth factors to cellular receptors (3, 4). Thus, the BM provides a platform for multiple signaling mechanisms, which may explain its importance in epithelial differentiation, cell migration, and morphogenesis. BMs are also involved in cell survival and metastasis formation, and their thickening is typical of late-stage diabetes. Therefore, the assembly (1, 5) and distribution of multiple BM components (6) and their breakdown by metalloproteinases (7) attracted extensive interest. Yet the positive regulation of BM components is poorly understood, although there is evidence for their de novo synthesis during development. Laminins (8) and their receptors (9, 10) are required in early embryogenesis and branching organogenesis (11-13). Because receptor tyrosine kinases are major inducers of cell differentiation and morphogenesis, we were interested whether they are involved in the positive regulation of BM components.We were led to the analysis of these questions by recent results with embryonic stem (ES) cell-derived embryoid bodies. Dominant ne...

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