– Serpins are the largest and most diverse family of serine protease inhibitors which are involved in a number of fundamental biological processes such as blood coagulation, complement activation, fibrinolysis, angiogenesis, inflammation and tumor suppression and are expressed in a cell-specific manner. Serpins are a group of proteins with similar structures that were first identified as a set of proteins able to inhibit proteases. The acronym serpin was originally coined because many serpins inhibit chymotrypsin-like serine proteases (serine protease inhibitors). Over 1 serpins have been identified.Mouse SerpinB1, also known as Peptidase inhibitor 1, PI-1, Bomapin and SERPINB1, is a nucleus and cytoplasm protein that belongs to the serpin family and Ov-serpin subfamily. SerpinB1 is expressed specifically in the bone marrow. SerpinB1 is a protease inhibitor that may play a role in the regulation of protease activities during hematopoiesis and apoptosis induced by TNF. SerpinB1 is a redox-sensitive nuclear serpin that augments proliferation or apoptosis of leukaemia cells, depending on growth factors availability. SerpinB1 may regulate protease activities in the cytoplasm and the nucleus.