a major role in responses of cancer cells to stimulatory signals that are critical for the development of cancer. Accordingly, gene expression by degradation of transcription factors, such as p53, c-jun, c-Fos, NF-κB, c-Myc, HIF-1α, MATα2, STAT3, sterol-regulated element-binding proteins and androgen receptors are all controlled by the UPS and thus involved in the development of various malignancies. Moreover, the UPS regulates the degradation of tumor suppressor gene products such as adenomatous polyposis coli (APC) in colorectal cancer, retinoblastoma (Rb). and von Hippel–Lindau tumor suppressor (VHL), as well as a number of proto-oncogenes (Raf, Myc, Myb, Rel, Src, Mos, ABL). The UPS is also involved in the regulation of inflammatory responses. This activity is usually attributed to the role of proteasomes in the activation of NF-κB which further regulates the expression of pro inflammatory cytokines such as TNF-α, IL-β, IL-8, adhesion molecules (ICAM-1, VCAM-1, P-selectin) and prostaglandins and nitric oxide (NO). Additionally, the UPS also plays a role in inflammatory responses as regulators of leukocyte proliferation, mainly through proteolysis of cyclines and the degradation of CDK inhibitors. Lastly, autoimmune disease patients with SLE, Sjögren syndrome and rheumatoid arthritis (RA) predominantly exhibit circulating proteasomes which can be applied as clinical biomarkers. As genetic factors play an crucial role in the predisposition to cancer, genome-wide association studies (GWAS) have linked the chromosome 15q25.1 locus to the susceptibility of lung cancer and implicated the proteasome subunit alpha type-4 (PMSA4) as a candidate gene. A case-control study in lung cancer patients and controls in the Chinese Han population was investigated and suggested an association between PSMA4 and lung cancer. Furthermore, PMSA4 has also been implicated to be involved in the pathogenesis of ankylosing spondylitis (AS) and may therefore be a potential biomarker for clinical applications in AS. Interactions PSMA4 has been shown to interact with PLK1. References Further reading