Anticancer properties of the IL-12 family--focus on colorectal cancer.

The prominent role of interleukin (IL)-12 in inflammatory responses, especially in TH1 T cell differentiation, is well established. Moreover, in murine models of tumorigenesis, IL-12 displays remarkable antitumor properties that are mainly mediated by interferon (IFN)-γ secretion by CD4+, CD8+ T cells, natural killer (NK) or NK-T cells. Importantly, IL-12 through IFN- γ -dependent induction of the antiangiogenic factors interferon-inducible protein (IP) 10 and monokine induced by gamma interferon (MIG) contributes to tumor eradication. Recently, the structurally similar but functionally different cytokines IL-23 and IL-27 were discovered and related to the IL-12 family of cytokines. Each of those cytokines has its own specific effects on tumor growth. Similarly to IL12p70, antitumor effects of IL-27 are mediated via the IFN γ -IP10/MIG-axis and tumor-specific increase of cytotoxic T-lymphocyte activity. Additionally, IL-27 itself may mimic the function of IFN- γ due to the similarity in usage of JAK/STAT signalling molecules such as STAT1. The role of IL-23 in tumor growth to date is controversial. Whether IL-23 acts pro- or anticancerogenic seems to depend on a critical balance of STAT3 signalling in both the tumor and the immune cellular microenvironment of the tumor. At least for solid tumors the promising results from preclinical studies of systemic and on-site IL-12-based therapy did not prevail in clinical studies. In future combinatorial approaches using IL-12 together with other cytokines or antiangiogenic molecules have to be evaluated. This review focuses on anticancer effects of the IL-12 family in preclinical and clinical studies with an emphasis on colorectal cancer.

Intracellular localization of the p35 subunit of murine IL-12.

Production of interleukin-12 (IL-12), a heterodimer of p35 and p40 subunits, is limited by p35 expression. A long and a short murine p35 mRNA potentially encoding proteins differing in pre-sequence size are produced. Increased pre-sequence size could convert a cleaved signal peptide to an uncleaved signal peptide, raising the possibility that a membrane-bound form of p35 is produced. The intracellular localization of the p35 encoded by each mRNA isoform was determined by constructing cDNAs containing the long or short p35 cDNA isoform fused in-frame to a cDNA encoding green fluorescent protein (GFP). After transfection of a CV-1 African green monkey kidney cell line with the constructs, confocal microscopy and immunoblotting of extracted microsomal membranes demonstrated that the p35-GFP fusion protein encoded by the long or short mRNA accumulates in the Golgi apparatus as an endoglycosidase H-sensitive glycosylated integral membrane protein. In contrast, a p40-GFP fusion protein accumulates in the Golgi apparatus as a soluble protein. Since assembly of the p35 and p40 subunits to form bioactive IL-12 occurs in the ER, release of membrane-tethered IL-12 by proteolytic cleavage in a late Golgi or post-Golgi compartment may represent an as yet unidentified level at which bioactive IL-12 secretion is regulated.

A novel interleukin-12 p40-related protein induced by latent Epstein-Barr virus infection in B lymphocytes.

We have isolated a cDNA encoding a novel hematopoietin receptor family member related to the p40 subunit of interleukin-12 and to the ciliary neurotrophic factor receptor, whose expression is induced in B lymphocytes by Epstein-Barr virus (EBV) infection. This gene, which we have designated EBV-induced gene 3 (EBI3), encodes a 34-kDa glycoprotein which lacks a membrane-anchoring motif and is secreted. Despite the absence of a membrane-anchoring motif and of cysteines likely to mediate covalent linkage to an integral membrane protein, EBI3 is also present on the plasma membrane of EBV-transformed B lymphocytes and of transfected cells. Most newly synthesized EBI3 is retained in the endoplasmic reticulum in an endoglycosidase H-sensitive form associated with the molecular chaperone calnexin and with a novel 60-kDa protein. EBI3 is expressed in vivo by scattered cells in interfollicular zones of tonsil tissue, by cells associated with sinusoids in perifollicular areas of spleen tissue, and at very high levels by placental syncytiotrophoblasts. EBI3 expression in vitro is induced in EBV-negative cell lines by expression of the EBV latent infection membrane protein-1 and in peripheral blood mononuclear cells by pokeweed mitogen stimulation. EBI3 maps to chromosome 19p13.2/3, near genes encoding the erythropoietin receptor and the cytokine receptor-associated kinase, Tyk2. EBI3 synthesis by trophoblasts and by EBV-transformed cells and similarities to interleukin-12 p40 are compatible with a role for EBI3 in regulating cell-mediated immune responses.