Bryostatin-1 and IL-2 Synergize to Induce IFN-γ Expression in Human Peripheral Blood T Cells: Implications for Cancer Immunotherapy

Abstract

Bryostatin-1 (Bryo-1), a protein kinase C modulator with antineoplastic activity, may exert some of its antitumor activity through activation of the immune response. Studies in tumor-bearing hosts have indicated that the T cell response, particularly IFN-γ production, is impaired. To evaluate whether Bryo-1 plus IL-2 may affect the activation pattern of T cells, we investigated the expression of IFN-γ mRNA and protein in human primary T cells. Northern blot analysis and ELISAs demonstrated that Bryo-1 and IL-2 synergized to induce both IFN-γ mRNA and protein expression. This synergistic induction was seen within 3 h of treatment and with as little as 10 U/ml IL-2 and 1.0 ng/ml Bryo-1. In vitro transcription assays revealed that Bryo-1 plus IL-2 induced transcriptional activation of the IFN-γ gene. Furthermore, mRNA stability studies indicated that this treatment also enhanced the IFN-γ mRNA half-life. Both CD4+ and CD8+ T cells responded to the treatment with IFN-γ expression. The induction of the IFN-γ expression was decreased by a specific p38 mitogen-activated protein kinase inhibitor, but not by a protein kinase C inhibitor. Our results demonstrate for the first time that Bryo-1 in combination with IL-2 control IFN-γ gene expression at both the transcriptional and post-transcriptional levels through a p38 mitogen-activated protein kinase-dependent process. Given the pivotal role that IFN-γ plays in the orchestration of an effective Th1 type of response, our results suggest that Bryo-1 plus IL-2 may be a valuable combined therapy for cancer treatment.

Enhanced Expression of CD20 in Human Tumor B Cells Is Controlled through ERK-Dependent Mechanisms

“…As a consequence, BI has a short-lived effect on ERK-1/2 phosphorylation (1-3 h) that is overcome after 6 -12 h of treatment with bryostatin-1, the time needed for the optimal induction of CD20 mRNA in NHL cells. Bryostatin-1 can induce gene expression also through p38 MAPK signaling pathway (32). Our results indicated that the effects of bryostatin-1 on CD20 mRNA expression or ERK-1/2 phosphorylation were not mediated by p38 MAPK (Figs.…”

“…The effects of bryostatin-1 are mediated through numerous pathways, including PKC, p38 MAPK, ERK-1/2, and others (32,59,65,66). It has been shown that bryostatin-1 activates the MEK/ ERK pathway (65,66).…”

“…Bryostatin-1 may control mRNA expression through both transcriptional and post-transcriptional mechanisms (29,31,32,60). In an attempt to determine whether message stabilization was one of the mechanisms responsible for the enhanced CD20 expression by bryostatin-1, the half-life of the mRNA was studied.…”

“…Furthermore, bryostatin-1 synergizes with IL-2 to induce the expression and secretion of IFN-␥ in human T cells (32). The in vivo mechanisms of antitumor action of bryostatin-1 are not completely understood.…”

Post-transcriptional control of the interferon system

“…In almost all cases, this increased stability was shown to be dependent upon p38 mitogen activated protein kinase (p38 MAPK) activity, as the stability was not observed when inhibitors of this pathway were included in the assay. These various stimulations include: treatment of T and NK cells with IL-2 + IL-12 [28][29][30][31][32]; IL-12 + IL-18 treatment of NK cells [32]; anti-CD3 + anti-CD28 or anti-CD2 treatment of T cells [33] with a similar study comparing cells obtained from old and young mice [34]; CD4+ memory T cells activated by OX40L [35]; treatment of both CD4+ and CD8+ T cells with IL-2 and bryostatin [36]; and stimulation of Jurkat T cells with anti-LFA1 and anti-CD3 [37]. In addition, our laboratory (H.A.Y.)…”