STK40 (Serine/threonine-protein kinase 40), also known as Sugen kinase 495, is a 435 amino acid protein kinase that may be a negative regulator of NFκB and p53-mediated gene expression. Localized to both the cytoplasm and the nucleus, STK40 is ubiquitously expressed. STK40 has a central serine/threonine protein kinase domain and is homologous to TRB-3, a protein that regulates activation of MAP kinases and inhibits NFκB-mediated gene transcription. Similarly, overexpression of STK40 inhibits NFκB activation triggered by TNF and also inhibits p53-mediated transcription. There are four named isoforms of STK40 that are produced as a result of alternative splicing.
