Interleukin 18 (IL18) was originally identified as an inflammation-induced cytokine that is secreted by immune cells. An increasing number of studies have focused on its non-immunological functions, with demonstrated functions for IL18 in energy homeostasis and neural stability. IL18 is reportedly required for lipid metabolism in the liver and brown adipose tissue. Furthermore, IL18 (Il18) deficiency in mice leads to mitochondrial dysfunction in hippocampal cells, resulting in depressive-like symptoms and cognitive impairment.
1. Introduction
Interleukin (IL) 18 was initially cloned in 1995 and identified as a proinflammatory cytokine that stimulates type 1 helper T cells to produce interferon (IFN)-γ
[1]. The 23-kDa precursor form of IL18 is activated by cleaved caspase-1 and secreted as an active, 18-kDa mature form
[2,3,4,5,6][2][3][4][5][6]. IL18 is secreted by hematopoietic lineages, such as macrophage cells
[1] and microglia
[7], as well as non-immune cells such as neural cells
[6]. IL18 plays multiple roles in immune function, energy metabolism, and psychiatric disorders
[1[1][8][9][10][11],
8,9,10,11], and is also a therapeutic target for cancer immunotherapy, inhibition of body weight gain, and cognitive impairment
[8,10,12][8][10][12].
2. IL18 and Cancer
An increasing number of studies have demonstrated a relationship between IL18 and cancer. In pancreatic ductal adenocarcinoma (PDA), serum and stromal IL18 is positively correlated with patient mortality
[20,21][13][14]. High expression of IL18 in PDA was associated with worse disease progression and poor survival
[22][15]. However, there is the other report that serum IL18 concentration was not correlated with patient survival of pancreatic adenocarcinoma
[23][16]. In oral squamous cell carcinoma (OSCC), the serum levels of IL18 increase during tumor growth
[24,25][17][18]. IL18 expression in peripheral blood mononuclear cells is also increased in OSCC patients compared with that in healthy individuals
[25][18]. In OSCC patients with lymph node metastasis and a severe TNM stage, serum IL18 levels were significantly higher than those in patients without lymph node metastasis or a severe TNM stage. This trend has also been observed in patients with other cancers
[25][18].
In clinical trials, systematic administration of IL18 significantly suppressed the growth of several kinds of carcinomas, such as melanoma and renal cell cancer, by stimulating the immune system
[26,27,28][19][20][21]. Furthermore, the effectiveness of cancer immunotherapy using IL18 to augment immune checkpoint inhibitors
[12]. Moreover, mutant IL18 engineered for resistance to inhibitory binding of the high-affinity IL-18 decoy receptor also promoted the activity of NK cells, resulting in the enhancement of anti-tumor effects in mouse tumor models
[29][22]. These results suggest the possibility that IL18 may be an important cytokine in cancer treatment.
3. Cancer-Related Genes in Il18−/− Mice
Among the DEGs identified in our microarray analysis of
Il18−/− mice, those with involvement in various cancers are listed in
Table 1.
Table 1.
Cancers and related genes with differential expression in liver, brown adipose tissue, and brain under IL18 deficiency.