A Novel Function of Plasminogen Activator Inhibitor-1 in Modulation of the AKT Pathway in Wild-type and Plasminogen Activator Inhibitor-1-deficient Endothelial Cells

Abstract

Cell proliferation, an event associated with angiogenesis, involves coordinated activities of a number of proteins. The role of plasminogen activator inhibitor-1 (PAI-1) in angiogenesis remains controversial. Utilizing proliferating PAI-1 ؊/؊ endothelial cells (EC), the impact of a host PAI-1 deficiency on Akt activation was evaluated. Hyperactivation of Akt(Ser(P) 473 ) was observed in PAI-1 ؊/؊ EC, and this was probably due to enhanced inactivation of tumor suppressor PTEN, thus rendering the cells resistant to apoptotic signals. Higher levels of inactivated caspase-9 in PAI-1 ؊/؊ EC led to lower levels of procaspase-3 and cleaved caspase-3, thereby promoting survival. These effects were reversed when recombinant PAI-1 was added to PAI-1 ؊/؊ EC. Additional studies demonstrated that regulation of proliferation is dependent on its interaction with low density lipoprotein receptor-related protein. Thus, PAI-1 is a negative regulator of cell growth, exerting its effect on the phosphatidylinositol 3-kinase/Akt pathway and allowing controlled cell proliferation.Angiogenesis is an important biological process involving the formation of new capillaries from preexisting blood vessels, and it occurs in normal as well as pathophysiological settings. It involves a highly orchestrated series of events, including the stimulation of endothelial cells (EC) 2 by growth factors, degradation of the extracellular matrix, migration and proliferation of EC, and formation of new capillary tubes (1, 2). Components of the fibrinolytic pathway have been implicated in the formation of angiogenic vessels, notably plasminogen activators, viz. urokinase-type plasminogen activator (uPA) and tissue-type plasminogen activator. The activation product, plasmin, a trypsin-like serine protease, facilitates degradation of the extracellular matrix, either directly or indirectly through activation of matrix metalloproteases. This process allows migration of EC and subsequent events leading to neovessel formation. However, specific inhibitors control proteolysis of the extracellular matrix, and PAI-1 is an important inhibitor of the plasminogen activation system (3, 4). Considering the important role of the plasminogen activator-PAI-1 system in angiogenesis and the availability of genetically engineered mice lacking various components of this system, several investigators have utilized transgenic approaches to establish the functional potential of components of the plasminogen activator-PAI-1 system in angiogenesis.The role of PAI-1 in angiogenesis and tumor formation has been extensively studied, but results were determined to be dependent on the experimental setting (5-8), the stage of cancer progression, and the origin of the cells (9 -13). It has been demonstrated that implanted malignant keratinocytes were unable to induce vascularization of tumors in PAI-1-deficient mice (PAI-1 Ϫ/Ϫ ) (5). Similarly, T241 fibrosarcoma tumor growth was suppressed in PAI-1 Ϫ/Ϫ mice relative to WT mice (6). In vitro studies demonstrated a lack of microvessel gen...

Inhibition of neutrophil apoptosis by PAI-1

“…Recent studies have reported that PAI-1 can induce pro-and antiapoptotic responses in nonmyeloid cell populations, including fibroblasts and endothelial cells (3,5,29). We have extended those observations and shown that exposure of neutrophils to PAI-1 diminished their progression to apoptotic cell death.…”

siRNA against plasminogen activator inhibitor-1 ameliorates bleomycin-induced lung fibrosis in rats

“…For example, the uPA-uPAR-PAI-1 complex interacts with integrins to induce focal adhesion kinase (FAK) and ERK activation [30] via low-density lipoprotein receptor-related protein (LRP-1). This complex also regulates ras-related C3 botulinum toxin substrate 1 (Rac1) and ERK activation [31] , the JAK-STAT signalling pathway, the ERK/MAPK and PI3K/AKT pathways [32] , and it modulates the AKT pathway in wild-type and PAI-1-deficient endothelial cells [33] . Therefore, it is possible that the ERK and AKT signalling pathways play an important role in IPF.…”

Focused PCR Screen Reveals p53 Dependence of Nitric Oxide-Induced Apoptosis and Up-Regulation of Maspin and Plasminogen Activator Inhibitor-1 in Tumor Cells

“…PAI-1 is an essential target of p53, and both are necessary for the induction of replicative senescence of normal fibroblasts, which is associated with down-regulation of the growthpromoting Akt kinase pathway (43,49). The restoration of the Akt pathway in PAI-1 -deficient fibroblast and endothelial cells may allow these cells to escape growth arrest or senescence (43,59,60). In conclusion, through a rigorous semiquantitative RT-PCR screening approach, we showed that both NO-induced apoptosis and the up-regulation of the serpins maspin and PAI-1 are dependent on p53.…”