Mcl-1 regulation and its role in multiple myeloma

Among the Bcl-2 family, myeloid cell leukemia-1 (Mcl-1) distinguishes itself from the other pro-survival proteins by its ability to oppose to a wide variety of pro-apoptotic stimuli, short half-life, and presence of polypeptide sequences enriched in proline (P), glutamic acid (E), serine (S) and threonine (T) domains (PEST). Moreover, Mcl-1 undergoes a complex transcriptional, post-transcriptional, and post-translational regulation process. This regulation modifies not only Mcl-1 expression, but also its function. Various extra-cellular stimuli, including cytokines, growth factors, 12-O-tetradecanoyl-phorbol 13-acetate (TPA) and IFN, activate pathways which regulate Mcl-1 expression. Furthermore, Mcl-1 can be alternatively spliced into a long (Mcl-1) or a short (Mcl-1S) form. Mcl-1 opposes pro-apoptotic proteins and can be either cleaved or phosphorylated at a post-translational level. Mcl-1-spliced products, Mcl-1-cleaved products, or phosphorylated Mcl-1 have either a pro or an anti-apoptotic function, highlighting the complexity and pivotal role of Mcl-1 regulation. Here we discuss the regulation and function of Mcl-1 in the pathophysiology of multiple myeloma.