Differential effects of interferon-γ on the expression of cyclooxygenase-2 in high-grade human gliomas versus primary astrocytes

Inhibition of cyclooxygenase-2 enhances immunotherapy against experimental brain tumors

Glioblastoma multiforme is the most common and aggressive malignant brain tumor in humans, and the prognosis is very poor despite conventional therapy. Immunotherapy represents a novel treatment approach, but the effect is often weakened by release of immune-suppressive molecules such as prostaglandins. In the current study, we investigated the effect of immunotherapy with irradiated interferon-γ (IFN-γ)-secreting tumor cells and administration of the selective cyclooxygenase-2 (COX-2) inhibitor parecoxib as treatment of established rat brain tumors. COX-2 inhibition and immunotherapy significantly enhanced the long-term cure rate (81% survival) compared with immunotherapy alone (19% survival), and there was a significant increase in plasma IFN-γ levels in animals treated with the combined therapy, suggesting a systemic T helper 1 immune response. COX-2 inhibition alone, however, did neither induce cure nor prolonged survival. The tumor cells were identified as the major source of COX-2 both in vivo and in vitro, and unmodified tumor cells produced prostaglandin E(2) in vitro, while the IFN-γ expressing tumor cells secreted significantly lower levels. In conclusion, we show that immunotherapy of experimental brain tumors is greatly potentiated when combined with COX-2 inhibition. Based on our results, the clinically available drug parecoxib may be added to immunotherapy against human brain tumors. Furthermore, the discovery that IFN-γ plasma levels can be used to determine the ongoing in vivo immune response has translational potential.

Astrocytoma cells upregulate expression of pro-inflammatory cytokines after co-culture with activated peripheral blood mononuclear cells

In this study, we investigated the effect of CD3/CD28-activated peripheral blood mononuclear cells (PBMCs) on two human astrocytoma cell lines (1321N1 and CCF-STTG1), with respect to the expression of cytokines and chemokines. We used an in vitro co-culture system in which the astrocytoma cells and PBMCs were separated by a membrane in a transwell system. Proliferation of T cells was quantified by a [(3) H]-thymidine incorporation assay. Differential gene expression of astrocytoma cells cultured alone or with PBMCs was identified using gene arrays. Protein expression of CCL3, CCL5, CXCL8, CXCL9, CXCL10, IL6, and IL1β was determined by Luminex. Co-culture of activated T cells and astrocytoma cells resulted in inhibition of T cell proliferation. Moreover, astrocytoma cells upregulated a number of pro-inflammatory genes including CCL3, CCL5, CXCL8, CXCL9, CXCL10, IL6, and IL1β upon co-culture with activated PBMCs. These results were confirmed on the protein level. Astrocytoma cells inhibited the proliferation of T cells, indicating that astrocytes may play an important role in controlling T cell mediated immune responses in the brain. Contrary to this, soluble factors derived from CD3/CD28-activated PBMCs affected the transcriptome of astrocytoma cells, which then upregulated several pro-inflammatory genes and proteins. This could be part of neuroinflammatory events and may play a role in neurodegenerative diseases.

STAT1-independent inhibition of cyclooxygenase-2 expression by IFNgamma; a common pathway of IFNgamma-mediated gene repression but not gene activation

Cyclooxygenase-2 (COX-2), the rate-limiting enzyme in the synthesis of prostaglandins, promotes the development of colorectal cancer, and is a key molecular target of non-steroidal anti-inflammatory drugs, compounds that reduce the relative risk of developing colon cancer. In this study, we showed that interferon gamma (IFNgamma) inhibits the expression of COX-2 protein in intestinal epithelial cells (IECs) through a pathway that requires Janus-activated kinase (JAK) activity. In contrast, we demonstrated that transcriptional inhibition of COX-2 by IFNbeta or IFNgamma occurs in cells with silenced signal transducer and activator of transcription 1 (STAT1) expression and that IFNs retained the ability to inhibit COX-2 transcription in cells with activated RasV12, in which IFNgamma failed to induce STAT1. Thus, unlike the activity of JAK, STAT1 is not required for the inhibition of COX-2 expression by IFNgamma. In contrast to COX-2, the activation of genes in response to IFNgamma, such as interferon regulatory factor-1, was severely impaired by both STAT1 silencing and by constitutive Ras signaling. To determine whether there is a general differential requirement for STAT1 in gene activation and gene repression in response to IFNgamma in intestinal cells, we performed genome-wide analysis of IFNgamma target genes in an IEC line in which STAT1 expression was silenced by small interfering RNA. The results confirmed that the activation of the majority of genes by IFNgamma required STAT1. In contrast, the repression of several genes, as we showed for COX-2 specifically, was largely unaffected in cells with silenced STAT1. Our results therefore demonstrate that in general gene activation by IFNgamma is more sensitive to STAT1 deficiency than gene repression, and suggest that IFNgamma activates and represses gene expression via distinct pathways that can be distinguished, at least in part, by their requirement for STAT1.