Recombinant Semliki Forest virus enhanced plasminogen activator inhibitor 1 expression and storage in the megakaryocytic cell line MEG-01

Thrombopoietin-induced Dami cells as a model for α-granule biogenesis

Megakaryocytic alpha-granules contain secretory proteins relevant to megakaryocyte and platelet functions. Understanding alpha-granule biogenesis is hampered because human primary megakaryocytes are difficult to manipulate. Existing promegakaryocytic cell lines do not spontaneously exhibit mature alpha-granules. Dami cells, transfected with the megakaryocytic platelet factor 4, fused to GFP (PF4-GFP), were induced in the presence of thrombopoietin (TPO), a megakaryocyte cytokine and PMA. Using confocal microscopy, PF4-GFP colocalized with von Willebrand Factor (vWF) in newly formed storage granules. Immunoelectron microscopy demonstrated alpha-granule-like features, including a dense core or parallel tubules and colocalization of PF4-GFP and vWF. Hence, TPO-treated Dami cells are a suitable model to study alpha-granules and their biogenesis.

Efficient gene expression in megakaryocytic cell line using nucleofection

To clarify the mechanism of platelet production from megakaryocytes, expression of target proteins by gene transfection was examined using various gene delivery techniques. Transfection into hematopoietic cells, including megakaryocytes, by conventional gene delivery techniques such as electroporation and lipofection are known to be difficult. In this study, in addition to electroporation and lipofection, we tested other gene-transfer methods (nucleofection, transfection using inactivated virus envelope, and transferrin-linked cationic polymer) with the green fluorescent protein (GFP) gene into the human megakaryocytic cell line MEG-01. We found that nucleofection, which uses a combination of special electrical parameters and specific solutions, was the best, judging from the expression ratio of GFP-positive cells (approximately 70% of cells) and low toxicity. The efficiency of GFP expression was not related to the amount of pDNA delivered into the MEG-01 cells. To verify the utility of nucleofection, the thrombopoietin (TPO) receptor c-mpl was transfected into MEG-01 cells. Transfected cells showed a higher responsiveness to TPO than mock-transfected MEG-01 cells. We propose that nucleofection is a useful method for transfecting target genes to megakaryocytic cells when addressing the mechanism of platelet production.

Effects of oxidized and glycated low-density lipoproteins on transcription and secretion of plasminogen activator inhibitor-1 in vascular endothelial cells

Plasminogen activator inhibitor-1 (PAI-1) is the major physiological inhibitor of fibrinolysis. Elevated levels of PAI-1 were frequently detected in patients with coronary artery disease (CAD) or diabetes. Low-density lipoprotein (LDL) is a classical risk factor of CAD. Oxidation and glycation increase the atherogenecity of LDL. Previous studies demonstrated that oxidized LDL (oxLDL) or glycated LDL (gly-LDL) increased the release of PAI-1 from endothelial cells (ECs). The present study examined the effects of oxLDL and gly-LDL on the transcription, expression, secretion, and subcellular distribution of PAI-1 in cultured human ECs. Treatment with LDL significantly increased the promoter activity, mRNA level, and the release of PAI-1 from ECs by two- to threefold compared to controls. Oxidation or glycation significantly enhanced the effects of LDL on PAI-1 production in ECs compared to LDL (four- to fivefold vs. controls). No significant differences were detected between the effects of oxLDL and gly-LDL. Abundant PAI-1 antigens were detected in the perinuclear region of ECs and overlapped with giantin, a marker of Golgi apparatus. Treatment with brefeldin A disturbed the stack structure of Golgi apparatus and almost completely inhibited the release of PAI-1 from ECs induced by the lipoproteins and at basal conditions. The results suggest that oxidation and glycation enhanced the effects of LDL on the production of PAI-1 in ECs through increasing the transcription of PAI-1. Intact Golgi apparatus is required for PAI-1 generation from ECs induced by LDL or its modified forms.

Semliki Forest virus vectors for rapid and high-level expression of integral membrane proteins

Semliki Forest virus (SFV) vectors have been applied for the expression of recombinant integral membrane proteins in a wide range of mammalian host cells. More than 50 G protein-coupled receptors (GPCRs), several ion channels and other types of transmembrane or membrane-associated proteins have been expressed at high levels. The establishment of large-scale SFV technology has facilitated the production of large quantities of recombinant receptors, which have then been subjected to drug screening programs and structure-function studies on purified receptors. The recent Membrane Protein Network (MePNet) structural genomics initiative, where 100 GPCRs are overexpressed from SFV vectors, will further provide new methods and technologies for expression, solubilization, purification and crystallization of GPCRs.