The Multifaceted Role of TNF-Alpha in Cancer
Introduction
Tumor Necrosis Factor (TNF) is a trimeric type II transmembrane protein composed of approximately 80 amino acids. It features a proline-rich cytoplasmic domain that plays a role in membrane trafficking and in reverse signaling triggered by receptor binding. This domain is followed by a single transmembrane segment and an extracellular domain that contains the defining TNF homology domain (THD). The THD is connected to the transmembrane region by a stalk segment (Figure 1) (Bodmer et al., 2002). Activated immune cells—particularly macrophages and T lymphocytes—are the main producers of TNF. However, a range of other cell types, such as fibroblasts and tumor cells, are also capable of synthesizing it (Wajant et al., 2003). The biological actions of TNF are mainly mediated via two receptors—TNFR1 and TNFR2. TNFR1, containing a death domain, can initiate apoptosis or necrosis but also activates pro-survival pathways such as NFkB. TNFR2 lacks a death domain and tends to promote cell survival and proliferation through NFkB signaling. Both receptors interact with different adaptor proteins and signaling cascades, influencing cellular outcomes (apoptosis, survival, proliferation, inflammation).
Figure 1: Human TNF. Amino acid numbering refers to the mature receptors and processed soluble TNF, respectively. Myristylated lysine residues in TNF are indicated (Wajant, 2009).
Role of TNF in Tumor Suppression and Promotion
Antitumoral effects
Initially, TNF was characterized as a cytokine capable of killing tumor cells and was used therapeutically in isolated limb perfusion with melphalan for soft tissue sarcomas (van Horssen et al. 2006). In this application, TNF increases vascular permeability, facilitating immune cell infiltration and tumor destruction. TNF can also stimulate immune responses that promote tumor cell clearance, with systemic administration showing some antitumor activity in preclinical models (van Horssen et al. 2006).
Pro-tumoral effects
Conversely, TNF plays significant roles in tumor promotion and progression. Numerous experimental models demonstrate that TNF contributes to carcinogenesis: it promotes inflammation conducive to tumor initiation (e.g., in skin carcinogenesis with DMBA/TPA treatment), supports preneoplastic oval cell proliferation in the liver, and fosters tumor progression by activating pro-survival and pro-inflammatory pathways like NFkB in tumor and stromal cells (Arnott et al. 2002).
TNF in specific types and stages of cancer
Gastrointestinal cancers: In gastric cancer, inflammation involving TNF and other cytokines facilitates carcinogenesis, often triggered by Helicobacter pylori infection. TNF increases tumour infiltration and promotes angiogenesis, contributing to tumour growth (Popivanova et al. 2008).
Liver and skin cancers: In hepatocarcinogenesis, TNF-induced NFkB activation in hepatocytes promotes cell proliferation and inhibits apoptosis, contributing to early tumor development. Similar mechanisms are involved in models of skin carcinogenesis (Pikarsky et al. 2004).
Metastasis and EMT: TNF promotes metastasis in models such as colon and pancreatic cancers by inducing EMT, increasing invasiveness and altering the tumour microenvironment to promote dissemination (Chuang et al. 2008).
TNF and tumor-associated symptoms
Beyond its role in tumor growth, TNF is implicated in tumor-related symptoms such as cachexia, cancer-associated pain, and bone destruction. It influences osteoclastogenesis leading to bone degradation and activates neurons involved in pain signaling, contributing to cancer pain syndromes. TNF also suppresses differentiation of muscle cells, contributing to muscle wasting and fatigue common in cancer patients.
TNF's role in cancer is highly complex—capable of both suppressing and promoting tumor growth depending on various factors such as receptor engagement, cellular context, and the tumor microenvironment. Therapeutic strategies aim to harness its beneficial effects while mitigating its tumor-promoting activities, highlighting the importance of precise modulation within the cancer microenvironment.
References
Bodmer, J.L., Schneider, P. and Tschopp, J., 2002. The molecular architecture of the TNF superfamily. Trends in biochemical sciences, 27(1), pp.19-26.
Wajant, H., 2009. The role of TNF in cancer. Death Receptors and Cognate Ligands in Cancer, pp.1-15.
Wajant, H., Pfizenmaier, K. and Scheurich, P., 2003. Tumor necrosis factor signaling. Cell Death & Differentiation, 10(1), pp.45-65.
Van Horssen, R., Ten Hagen, T.L. and Eggermont, A.M., 2006. TNF-α in cancer treatment: molecular insights, antitumor effects, and clinical utility. The oncologist, 11(4), pp.397-408.
Popivanova BK , Kitamura K , Wu Y , Kondo T , Kagaya T , Kaneko S , Oshima M , Fujii C , Mukaida N (2008) . Blocking TNF-alpha in mice reduces colorectal carcinogenesis associated with chronic colitis . J Clin Invest 118 : 560 – 570
Pikarsky, E., Porat, R.M., Stein, I., Abramovitch, R., Amit, S., Kasem, S., Gutkovich-Pyest, E., Urieli-Shoval, S., Galun, E. and Ben-Neriah, Y., 2004. NF-κB functions as a tumour promoter in inflammation-associated cancer. Nature, 431(7007), pp.461-466.