Involvement of SH2-SH2-SH3 domain of phospholipase cgamma1 in NF-kappaB signaling

Phospholipase Cγ1 links inflammation and tumorigenesis in colitis-associated cancer

Colorectal cancer (CRC) is the third diagnosed cancer and the second leading cause of cancer-related deaths in the United States. Colorectal cancer is linked to inflammation and phospholipase Cγ1 (PLCγ1) is associated with tumorigenesis and the development of colorectal cancer; however, evidence of mechanisms connecting them remains unclear. The tight junctions (TJ), as intercellular junctional complexes, have an important role for integrity of the epithelial barrier to regulate the cellular permeability. Here we found that PLCγ1 regulated colitis and tumorigenesis in intestinal epithelial cells (IEC). To induce the colitis-associated cancer (CAC), we used the AOM/DSS model. Mice were sacrificed at 100 days (DSS three cycles) and 120 days (DSS one cycle). In a CAC model, we showed that the deletion of PLCγ1 in IEC decreased the incidence of tumors by enhancing apoptosis and inhibiting proliferation during tumor development. Accordingly, the deletion of PLCγ1 in IEC reduced colitis-induced epithelial inflammation via inhibition of pro-inflammatory cytokines and mediators. The PLCγ1 pathway in IEC accelerated colitis-induced epithelial damage via regulation of TJ proteins. Conclusions: Our findings suggest that PLCγ1 is a critical regulator of colitis and colorectal cancer and could further help in the development of therapy for colitis-associated cancer.

Overexpression of phospholipase C-gamma1 inhibits NGF-induced neuronal differentiation by proliferative activity of SH3 domain

Since the biological role of phospholipase C (PLC) gamma1 in neuronal differentiation still barely understood, here, we report that overexpression of PLC gamma1 inhibits neurite outgrowth and prolonged proliferation ability of PLC gamma1 contribute to the alteration of cell cycle regulatory proteins, subsequently exiting from cell growth arrest. Deletion of the SH3 or the entire SH223 domains, but not deletion of the N-SH2 or both the N-SH2 and C-SH2 domains expressing cells abolishes the differentiation-inhibitory effects of PLC gamma1, displaying depression of PCNA and elevation of cyclin D1. Moreover, these cells declined CDK1 and CDK2 expression and increased p21WAF-1, accompanying with G2/M accumulation. Some antiproliferative reagents are able to restore neurite outgrowth in PLC gamma1 cells, showing G2/M arrest. Our findings suggest that the proliferation activity of PLC gamma1 via its SH3 domain may be coupled with the flight from growth arrest by NGF, thereby inhibiting neuronal differentiation.

NF-kappaB and Hsp70 are involved in the phospholipase Cgamma1 signaling pathway in colorectal cancer cells

The majority of deaths from colorectal cancer are due to tumor invasion and metastasis. Induced migration of tumor cell is generally considered to be one critical step in cancer progression to the invasive and metastatic stage. Phospholipase Cgamma1 (PLCgamma1) is a key molecular switch in the process. But, the mechanism and function of PLCgamma1 in colorectal cancer motility are unclear. We showed first in this report that epidermal growth factor (EGF) stimulated the phosphorylation of PLCgamma1 in human colorectal cancer cell line LoVo. Inhibition of PLCgamma1 with the pharmacologic agent U73122 decreased the migration of LoVo cells in a dose-dependent manner while EGF treatment reversed it partially. PLCgamma1 signaling pathway also upregulated the activity of NF-kappaB. Furthermore, expression of Hsp70 was increased by treatment with U73122 or pyrrolidine dithiocarbamate (PDTC), a NF-kappaB inhibitor. These data indicated that PLCgamma1 played a pivotal role in the migration of human colorectal cancer cell and first demonstrated that upregulation of NF-kappaB binding activity and downregulation of Hsp70 expression were PLCgamma1-dependent in LoVo cells.

Oxidized low-density lipoprotein retards the growth of proliferating cells by inhibiting nuclear translocation of cell cycle proteins

OBJECTIVE

Our study tested the hypothesis that the mitogenic effect of oxidized low-density lipoprotein (oxLDL) on vascular cells may be further enhanced by the presence of cytokines and growth factors known to be present in the atherosclerotic environment.

METHODS AND RESULTS

Quiescent fibroblasts and vascular smooth muscle cells were treated with 10 or 50 microg/mL minimally-oxidized LDL in combination with serum for 24 or 48 hours. Surprisingly, these cells showed inhibited release from growth arrest and a significant reduction in the number of cells completing the cell cycle when compared with cells treated with serum alone. This was not due to an induction of apoptosis. The antiproliferative effects were not closely associated with changes in the expression of cell cycle proteins. Instead, oxLDL inhibited the translocation of cell cycle proteins cell division cycle (Cdc) 2, cyclin-dependent kinase (Cdk) 2, Cdk 4, Cyclin A, Cyclin B1, Cyclin D1, and proliferative cell nuclear antigen (PCNA) into the nucleus, as compared with separate treatments with serum alone. Kinase activation associated with specific cell cycle proteins was also inhibited by oxLDL.

CONCLUSIONS

oxLDL, in the presence of serum, has a surprising inhibitory effect on cell proliferation that occurs through an inhibition of import of cell cycle proteins into the cell nucleus.

OxLDL stimulates cell proliferation through a general induction of cell cycle proteins

Oxidized low-density lipoprotein (oxLDL) may be involved in atherosclerosis by stimulating proliferation of cells in the vessel wall. The purpose of this study was to identify the mechanism by which oxLDL induces proliferation. Quiescent human fibroblasts and rabbit smooth muscle cells were treated with 0, 10, or 50 microg/ml oxLDL for 24-48 h. This resulted in significant increases in total cell counts at both concentrations of oxLDL, at both time points, for both types of cells. Western blot analysis revealed that oxLDL-stimulated cell proliferation was associated with significant increases in the expression of proteins that regulate entry into and progression through the cell cycle [cell division cycle 2, cyclin-dependent kinase (cdk) 2, cdk 4, cyclin B1, cyclin D1, and PCNA]. Surprisingly, the expression of cell cycle inhibitors (p21 and p27) was stimulated by oxLDL as well, but this was to a lesser extent than the effects on cell cycle-activating proteins. OxLDL also induced nuclear localization of all cell cycle proteins examined. The similar effects of oxLDL on the translocation and expression of both cell cycle-activating and -inhibiting proteins may explain the controlled proliferative phenomenon observed in atherosclerosis as opposed to the more rapid proliferative event characteristic of cancer.

Angiotensin II activates nuclear transcription factor-kappaB through AT1 and AT2 receptors

BACKGROUND

Recent evidence suggests that angiotensin II (Ang II) induces a variety of proinflammatory mediators including chemokines. Nuclear factor-kappaB (NF-kappaB) activation plays an important role in Ang II-mediated inflammation. The present study investigated which Ang II receptor subtype is involved in NF-kappaB activation. We focused particularly on the Ang II subtype 2 (AT2) receptor because we previously observed that Ang II-induction of the chemokine RANTES in vitro and in vivo is mediated through AT2 receptors.

METHODS

AT1 or AT2 receptors were selectively overexpressed in COS7 cells that normally do not express Ang II receptors. In addition, rat glomerular endothelial cells (GER) that express AT1 and AT2 receptors and PC12 cells that exclusively exhibit AT2 receptors were studied also. Ang II-receptor expression was confirmed by Western blots of membrane lysates. NF-kappaB DNA binding in vitro was detected by electrophoretic shift assays. In addition, in vivo transactivation of a reporter gene construct with kappa enhancer coupled to luciferase also was investigated. Expression of the inhibitor of kappaB alpha (IkappaB-alpha) was detected by Western blots.

RESULTS

In AT1 or AT2 receptor transfected cells, but not untransfected COS7 cells, 10-7 mol/L Ang II induced NF-kappaB DNA binding in vitro, as detected by electrophoretic shift assays and in vivo transactivation of a reporter gene construct. The AT2 receptor antagonist PD 123319 but not losartan attenuated Ang II-mediated NF-kappaB activation in COS7 cells transfected with AT2 receptors. While Ang II also induced NF-kappaB activation in PC12 cells, this activation was blocked by PD 123319. Finally, stimulation of GERs with Ang II led to the activation of NF-kappaB through both subtypes of Ang II receptors. Nuclear extracts from COS7 cells transfected with AT2 receptors and PC12 cells with NF-kappaB DNA-binding activity consisted of p50/p65 complexes. There was no difference in subunit composition of nuclear proteins from Ang II-stimulated AT1 receptor transfected COS7 cells. An artificial peptide (p-Amino-Phe6-Ang II) with a high affinity for the AT2 receptor also activated NF-kappaB. Ang II-induced activation of NF-kappaB was associated with degradation of IkappaB-alpha in all studied cell lines.

CONCLUSIONS

Our results clearly demonstrate in various cell lines that Ang II induces NF-kappaB activation through AT2 receptors. These data may have important therapeutic consequences, because potential Ang II-mediated proinflammatory renal and cardiovascular effects may not be totally antagonized by the currently increased clinical use of AT1 receptor antagonists.

The role of phosphatidylinositol 3-kinase and the mitogen-activated protein kinases in insulin-like growth factor-I-mediated effects in vascular endothelial cells

Despite an improved understanding of the molecular mechanisms of insulin-like growth factor-I (IGF-I) signaling and the recognition that IGF-I mediates many effects in endothelial cells, some of which may be important for atherosclerosis, little is known about the signal transduction pathways that mediate the effects of IGF-I in endothelial cells. To that end, we examined the signaling pathways activated by IGF-I in endothelial cells and their contribution to IGF-I-stimulated endothelial cell migration and nuclear factor (NF)-kappaB-dependent transcription. Treatment of bovine pulmonary artery endothelial cells (PAEC) with IGF-I activated the mitogen-activated protein kinases extracellular signal-regulated kinase (ERK)1/2 and ERK5. In contrast, IGF-I had no effect on either c-Jun amino-terminal kinase or p38 kinase activity. IGF-I also activated phosphatidylinositol (PI) 3-kinase, as reflected by increased phosphorylation of AKT: There was no evidence of cross-talk between the ERK and PI 3-kinase pathways in PAEC. In PAEC transiently transfected with pTK81-NFkappaB-Luc, which contained four copies of the NF-kappaB DNA binding site 5' to a minimal promoter and the luciferase gene, treatment with 50 ng/ml IGF-I increased luciferase activity 1.8-fold. Inhibition of ERK activity using PD98059 and PI 3-kinase activity with LY 294002 abrogated the induction of NF-kappaB-dependent transcription by IGF-I, suggesting that both pathways contribute to the effect of IGF-I on NF-kappaBdependent transcription. In contrast to the effect of tumor necrosis factor-alpha on NF-kappaB activation, Western blot analyses demonstrated that IGF-I had no effect on IkappaB phosphorylation and degradation or nuclear translocation and DNA binding of NF-kappaB. These data suggest a direct of effect of IGF-I on nuclear NF-kappaB. IGF-I also increased endothelial cell migration approximately 2-fold, as demonstrated using a Boyden chamber apparatus. IGF-I-induced endothelial cell migration was inhibited, in part, by LY 294002 but not PD98059. Together, these studies demonstrate that IGF-I activates multiple signaling pathways in endothelial cells with little evidence for cross-talk between the pathways. Moreover, these pathways appear to mediate both overlapping and distinct effects in that activation of both PI 3-kinase and the ERKs contributed to the stimulation of NF-kappaB-dependent transcription by IGF-I, whereas only PI 3-kinase mediated IGF-I-stimulated endothelial cell migration.

Hematopoietic cell-specific adapter proteins, SLP-76 and BLNK, effectively activate NF-AT as well as NF-kappaB by Syk and Tec PTKs in non-lymphoid cell lines

To investigate the roles of various hematopoietic cell-specific adapter proteins in T cell receptor (TCR)-signaling leading to nuclear factor of activated T cell (NF-AT) and nuclear factor of kappaB (NF-kappaB) activation, we reconstituted TCR-signaling with CD8/zeta, various protein tyrosine kinases (PTKs), and adapter proteins in a non-lymphoid cell line, 293T. We show that SLP-76 and BLNK, but not LAT, effectively co-operated with Syk and Tec family PTKs to activate NF-AT and NF-kappaB. We also show that Tec family PTKs enhanced endogenous phospholipase C (PLC)-gamma1 phosphorylation induced by CD8/zeta and Syk in 293T cells. These results imply that PLC-gamma1 may play a critical role in a hematopoietic cell-specific adapter protein-mediated NF-AT and NF-kappaB activation in a non-lymphoid cell.