Regulation of p21Waf1 expression and TNFalpha biosynthesis by glutathione modulators in PMA induced-THP1 differentiation: involvement of JNK and ERK pathways

Pathways related to PMA-differentiated THP1 human monocytic leukemia cells revealed by RNA-Seq

Previous analyses have reported that the human monocytic cell line THP1 can be differentiated into cells with macrophage-like characteristics by phorbol 12-myristate 13-acetate (PMA). However, little is known about the mechanism responsible for regulating this differentiation process. Here, we performed high-throughput RNA-Seq analysis to investigate the genes differently expressed in THP1 cells treated with and without PMA and examined those that may be responsible for the PMA-induced differentiation of monocytes into macrophages. We found 3,000 genes to be differentially expressed after PMA treatment. Gene ontology analysis revealed that genes related to cellular processes and regulation of biological processes were significantly enriched. KEGG analysis also demonstrated that the differentially expressed genes (DEGs) were significantly enriched in the PI3K/AKT signaling pathway and phagosome pathway. Importantly, we reveal an important role of the PI3K/AKT pathway in PMA-induced THP1 cell differentiation. The identified DEGs and pathways may facilitate further study of the detailed molecular mechanisms of THP1 differentiation. Thus, our results provide numerous potential therapeutic targets for modulation of the differentiation of this disease.

Clusterin induces the secretion of TNF-α and the chemotactic migration of macrophages

Tumor associated macrophages are known to be closely linked with tumor progression and metastasis. On the other hand, clusterin is overexpressed in several tumor types and regarded as a putative tumor-promoting factor due to this overexpression and the subsequent induction of chemoresistance. In our previous study, clusterin was found to induce the expression of matrix metalloproteinase-9 (MMP-9) in macrophages, and MMP-9 is known to be essential for tumor cell migration and invasion via basement membrane breakdown. Because paracrine interactions between tumor cells and surrounding macrophages regulate metastasis, these findings raise the possibility that clusterin promotes the secretion of cytokines in macrophages in addition to MMP-9. Here, we demonstrate that clusterin upregulates the expressions of chemotactic cytokines, that is, monocyte chemotactic protein-1 (MCP-1), macrophage inflammatory protein-1β (MIP-1β), regulated upon activation, normal T cell expressed and secreted (RANTES), and tumor necrosis factor-α (TNF-α) in Raw264.7 macrophages. In particular, clusterin stimulated TNF-α secretion via the activations of ERK, JNK, and PI3K/Akt pathways in a time and dose-dependent manner. Furthermore, clusterin-induced TNF-α secretion was found to play a critical role in the chemotactic migration of Raw264.7 macrophages. It was also found that clusterin acts directly as a chemoattractant for macrophages. Together, these results suggest that clusterin stimulates the expression and secretion of TNF-α, which plays a critical role in promoting macrophage chemotaxis, via ERK, JNK, and PI3K/Akt pathways. Collectively, these findings describe a novel function for clusterin as an inducer of TNF-α in macrophages and their chemotactic migration, and suggest that clusterin has a tumor-promoting effect.

Distinct roles of MK2 and MK5 in cAMP/PKA- and stress/p38MAPK-induced heat shock protein 27 phosphorylation

Background

Classical mammalian mitogen-activated protein kinase (MAPK) pathways consist of a cascade of three successive phosphorylation events resulting in the phosphorylation of a variety of substrates, including another class of protein kinases referred to as MAPK-activating protein kinases (MAPKAPKs). The MAPKAPKs MK2, MK3 and MK5 are closely related, but MK2 and MK3 are the major downstream targets of the p38^MAPK pathway, while MK5 can be activated by the atypical MAPK ERK3 and ERK4, protein kinase A (PKA), and maybe p38^MAPK. MK2, MK3, and MK5 can phosphorylate the common substrate small heat shock protein 27 (HSP27), a modification that regulates the role of HSP27 in actin polymerization. Both stress and cAMP elevating stimuli can cause F-actin remodeling, but whereas the in vivo role of p38^MAPK-MK2 in stress-triggered HSP27 phosphorylation and actin reorganization is well established, it is not known whether MK2 is involved in cAMP/PKA-induced F-actin rearrangements. On the other hand, MK5 can phosphorylate HSP27 and cause cytoskeletal changes in a cAMP/PKA-dependent manner, but its role as HSP27 kinase in stress-induced F-actin remodeling is disputed. Therefore, we wanted to investigate the implication of MK2 and MK5 in stress- and PKA-induced HSP27 phosphorylation.

Results

Using HEK293 cells, we show that MK2, MK3, and MK5 are expressed in these cells, but MK3 protein levels are very moderate. Stress- and cAMP-elevating stimuli, as well as ectopic expression of active MKK6 plus p38^MAPK or the catalytic subunit of PKA trigger HSP27 phosphorylation, and specific inhibitors of p38^MAPK and PKA prevent this phosphorylation. Depletion of MK2, but not MK3 and MK5 diminished stress-induced HSP27 phosphorylation, while only knockdown of MK5 reduced PKA-induced phosphoHSP27 levels. Stimulation of the p38^MAPK, but not the PKA pathway, caused activation of MK2.

Conclusion

Our results suggest that in HEK293 cells MK2 is the HSP27 kinase engaged in stress-induced, but not cAMP-induced phosphorylation of HSP27, while MK5 seems to be the sole MK to mediate HSP27 phosphorylation in response to stimulation of the PKA pathway. Thus, despite the same substrate specificity towards HSP27, MK2 and MK5 are implicated in different signaling pathways causing actin reorganization.

Cortisol is a potent modulator of lipopolysaccharide-induced interferon signaling in macrophages

The effects of cortisol (CORT) on resting and lipopolysaccharide (LPS)-activated monocyte-derived THP-1 macrophages were investigated by proteomics. Forty-seven proteins were found to be modulated, 20 by CORT, 11 by LPS, and 16 by CORT and LPS. Cortisol-sensitive chaperones and cytoskeletal proteins were mostly repressed. HCLS1, MGN, and MX1 were new proteins identified to be under the transcriptional control of this steroid and new CORT-sensitive variants of MX1, SYWC and IFIT3 were found. FKBP51, a known CORT target gene, showed the strongest response to CORT and synergism with LPS. In resting THP-1 macrophages, 18 proteins were modulated by CORT, with 15 being down-regulated. Activation of macrophages by LPS was associated with enhanced expression of immune response and metabolic proteins. In activated macrophages, CORT had a more equilibrated effect and almost all metabolism-related proteins were up-regulated, whereas immune response proteins were mostly down-regulated. The majority of the LPS up-regulated immune response-related proteins are known interferon (IFN) target genes (IFIT3, MX1, SYWC, PSME2) suggesting activation of the IRF3 signaling pathway. They were all suppressed by CORT. This is the first proteomics study to investigate the effects of CORT on activated immune cells.

Inhibition of CDKS by roscovitine suppressed LPS-induced *NO production through inhibiting NFkappaB activation and BH4 biosynthesis in macrophages

In inflammatory diseases, tissue damage is critically associated with nitric oxide ((*)NO) and cytokines, which are overproduced in response to cellular release of endotoxins. Here we investigated the inhibitory effect of roscovitine, a selective inhibitor of cyclin-dependent kinases (CDKs) on (*)NO production in mouse macrophages. In RAW264.7 cells, we found that roscovitine abolished the production of (*)NO induced by lipopolysaccharide (LPS). Moreover, roscovitine significantly inhibited LPS-induced inducible nitric oxide synthase (iNOS) mRNA and protein expression. Our data also showed that roscovitine attenuated LPS-induced phosphorylation of IkappaB kinase beta (IKKbeta), IkappaB, and p65 but enhanced the phosphorylation of ERK, p38, and c-Jun NH(2)-terminal kinase (JNK). In addition, roscovitine dose dependently inhibited LPS-induced expression of cyclooxygenase-2 (COX)-2, IL-1beta, and IL-6 but not tumor necrosis factor (TNF)-alpha. Tetrahydrobiopterin (BH(4)), an essential cofactor for iNOS, is easily oxidized to 7,8-dihydrobiopterin (BH(2)). Roscovitine significantly inhibited LPS-induced BH(4) biosynthesis and decreased BH(4)-to-BH(2) ratio. Furthermore, roscovitine greatly reduced the upregulation of GTP cyclohydrolase-1 (GCH-1), the rate-limiting enzyme for BH(4) biosynthesis. Using other CDK inhibitors, we found that CDK1, CDK5, and CDK7, but not CDK2, significantly inhibited LPS-induced (*)NO production in macrophages. Similarly, in isolated peritoneal macrophages, roscovitine strongly inhibited (*)NO production, iNOS, and COX-2 upregulation, activation of NFkappaB, and induction of GCH-1 by LPS. Together, our data indicate that roscovitine abolishes LPS-induced (*)NO production in macrophages by suppressing nuclear factor-kappaB activation and BH(4) biosynthesis, which might be mediated by CDK1, CDK5, and CDK7. Our results also suggest that roscovitine may inhibit inflammation and that CDKs may play important roles in the mechanisms by which roscovitine attenuates inflammation.

Plasma membrane glutathione transporters and their roles in cell physiology and pathophysiology

Reduced glutathione (GSH) is critical for many cellular processes, and both its intracellular and extracellular concentrations are tightly regulated. Intracellular GSH levels are regulated by two main mechanisms: by adjusting the rates of synthesis and of export from cells. Some of the proteins responsible for GSH export from mammalian cells have recently been identified, and there is increasing evidence that these GSH exporters are multispecific and multifunctional, regulating a number of key biological processes. In particular, some of the multidrug resistance-associated proteins (Mrp/Abcc) appear to mediate GSH export and homeostasis. The Mrp proteins mediate not only GSH efflux, but they also export oxidized glutathione derivatives (e.g., glutathione disulfide (GSSG), S-nitrosoglutathione (GS-NO), and glutathione-metal complexes), as well as other glutathione S-conjugates. The ability to export both GSH and oxidized derivatives of GSH, endows these transporters with the capacity to directly regulate the cellular thiol-redox status, and therefore the ability to influence many key signaling and biochemical pathways. Among the many processes that are influenced by the GSH transporters are apoptosis, cell proliferation, and cell differentiation. This report summarizes the evidence that Mrps contribute to the regulation of cellular GSH levels and the thiol-redox state, and thus to the many biochemical processes that are influenced by this tripeptide.

Protein tyrosine phosphorylation and protein tyrosine nitration in redox signaling

Reversible phosphorylation of protein tyrosine residues by polypeptide growth factor-receptor protein tyrosine kinases is implicated in the control of fundamental cellular processes including the cell cycle, cell adhesion, and cell survival, as well as cell proliferation and differentiation. During the last decade, it has become apparent that receptor protein tyrosine kinases and the signaling pathways they activate belong to a large signaling network. Such a network can be regulated by various extracellular cues, which include cell adhesion, agonists of G protein-coupled receptors, and oxidants. It is well documented that signaling initiated by receptor protein tyrosine kinases is directly dependent on the intracellular production of oxidants, including reactive oxygen and nitrogen species. Accumulated evidence indicates that the intracellular redox environment plays a major role in the mechanisms underlying the actions of growth factors. Oxidation of cysteine thiols and nitration of tyrosine residues on signaling proteins are described as posttranslational modifications that regulate, positively or negatively, protein tyrosine phosphorylation (PTP). Early observations described the inhibition of PTP activities by oxidants, resulting in increased levels of proteins phosphorylated on tyrosine. Therefore, a redox circuitry involving the increasing production of intracellular oxidants associated with growth-factor stimulation/cell adhesion, oxidative reversible inhibition of protein tyrosine phosphatases, and the activation of protein tyrosine kinases can be delineated.