The influence of lysophosphatidic acid on the immunophenotypic differentiation of human monocytes into dendritic cells.

Lysophosphatidic acid (LPA), a naturally occurring phospholipid, has been suggested to have an immunoregulatory role. We investigated the effect of LPA on differentiation of human monocytes into dendritic cells (DC). We found that LPA affects DC differentiation from monocytes by blocking the expression of CD1a molecules on their surface in a dose-dependent manner.

Influence of pertussis toxin on CD1a isoform expression in human dendritic cells.

Pertussis toxin (PTX) is an exotoxin produced by Bordetella pertussis. It is known to exert adjuvant activities inducing Th1-launched immune responses. In this study, we show that PTX can selectively block the expression of CD1a isoform during the differentiation of human monocytes into dendritic cells. In fact, dendritic cells differentiated from monocytes in the presence of PTX do not express CD1a on their surface, unlike CD1b and CD1c isoforms, which are normally regulated. The impaired CD1a expression on cell membrane depends, at least partially, on decreased mRNA transcription and does not affect cellular capability to respond to other maturation stimuli. Since CD1a(+) dendritic cells are involved in the early steps of primary immune response, the interference of PTX in the CD1a expression may be relevant for its employment as adjuvant.

Hepatocyte growth factor effects on mesenchymal stem cells: proliferation, migration, and differentiation.

Hepatocyte growth factor (HGF), a pleiotropic cytokine of mesenchymal origin promoting migration, proliferation, and survival in a wide spectrum of cells, can also modulate different biological responses in stem cells, but the mechanisms involved are not completely understood so far. In this context, we show that short-term exposure of mesenchymal stem cells (MSCs) to HGF can induce the activation of its cognate Met receptor and the downstream effectors ERK1/2, p38MAPK, and PI3K/Akt, while long-term exposure to HGF resulted in cytoskeletal rearrangement, cell migration, and marked inhibition of proliferation through the arrest in the G1-S checkpoint. When added to MSCs, the K252A tyrosine kinase inhibitor prevented HGF-induced responses. HGF's effect on MSC proliferation was reversed by p38 inhibitor SB203580, while the effects on cell migration were abrogated by PI3K inhibitor Wortmannin, suggesting that HGF acts through different pathways to determine its complex effects on MSCs. Prolonged treatment with HGF induced the expression of cardiac-specific markers (GATA-4, MEF2C, TEF1, desmin, alpha-MHC, beta-MHC, and nestin) with the concomitant loss of the stem cell markers nucleostemin, c-kit, and CD105.

Atrial natriuretic peptide effects on intracellular pH changes and ROS production in HEPG2 cells: role of p38 MAPK and phospholipase D.

AIMS: The present study was performed to evaluate Atrial Natriuretic Peptide (ANP) effects on intracellular pH, phospholipase D and ROS production and the possible relationship among them in HepG2 cells. Cancer extracellular microenvironment is more acidic than normal tissues and the activation of NHE-1, the only system able to regulate pHi homeostasis in this condition, can represent an important event in cell proliferation and malignant transformation. METHODS: The ANP effects on pHi were evaluated by fluorescence spectrometry. The effects on p38 MAPK and ROS production were evaluated by immunoblots and analysis of DCF-DA fluorescence, respectively. RT-PCR analysis and Western blotting were used to determine the ANP effect on mRNA NHE-1 expression and protein levels. PLD-catalyzed conversion of phosphatidylcholine to phosphatydilethanol (PetOH), in the presence of ethanol, was monitored by thin layer chromatography. RESULTS: A significant pHi decrease was observed in ANP-treated HepG2 cells and this effect was paralleled by the enhancement of PLD activity and ROS production. The ANP effect on pHi was coupled to an increased p38 MAPK phosphorylation and a down-regulation of mRNA NHE-1 expression and protein levels. Moreover, the relationship between PLD and ROS production was demonstrated by calphostin-c, a potent inhibitor of PLD. At the same time, all assessed ANP-effects were mediated by NPR-C receptors. CONCLUSION: Our results indicate that ANP recruits a signal pathway associated with p38 MAPK, NHE-1 and PLD responsible for ROS production, suggesting a possible role for ANP as novel modulator of ROS generation in HepG2 cells.