Contradictory functions of NF-kappaB in liver physiology and cancer

Rudolf Virchow (1821-1902), one of the founding fathers of modern pathology, hypothesized that cancer and inflammatory processes are linked, due to the presence of leukocytes in the tumor tissue. Today, chronic inflammation is believed to be one of the major causes for cancer development, accounting for nearly 20% of cancer cases worldwide. Hepatocellular carcinoma (HCC) is the third leading cause of cancer mortality throughout the world, and its incidence is increasing in the United States. HCC is widely accepted to be the outcome of continuous injury and chronic inflammation, and thus provides a good model to gain insight into inflammatory related cancer processes. Nuclear Factor- kappa B (NF-kappaB) was first identified as an enhancer protein of the kappa light-chain gene in B lymphocytes. Later it was realized that there are five NF-kappaB transcription factors with important roles in inflammation, innate immunity, cancer and apoptosis aborting. Consequently, NF-kappaB was shown to link inflammation and cancer, but recent reports have revealed it to play a much more complex role, where in some disease processes it promotes cancer and in others it impedes carcinogenesis. In this review, we will focus on the seemingly contradictory role of NF-kappaB in liver homeostasis, as well as in liver cancer.