New player in endosomal trafficking: Differential roles of Smad Anchor for Receptor Activation (SARA) protein.

The development and maintenance of multicellular organisms require specialized coordination between external cellular signals and the proteins receiving stimuli and regulating responses. A critical role in the proper functioning of these processes is played by endosomal trafficking, which enables the transport of proteins to targeted sites as well as their return to the plasma membrane through its essential components, the endosomes. During this trafficking, signaling pathways controlling functions related to the endosomal system are activated both directly and indirectly. Although there are a considerable number of molecules participating in these processes, some are more known than others for their specific functions.Toward the end of the 90s, SARA protein was described as controlling and facilitating the localization of Smads to TGFβ-receptors during TGFβ signaling activation and, strikingly, SARA was also identified as one of the proteins that bind to early endosomes (EE) participating in membrane trafficking in several cell models. The purpose of this review is to analyze the state of the art of the contribution of SARA in different cell types and cellular contexts, focusing on the biological role of SARA in two main processes: trafficking and cellular signaling, both necessary for intercellular coordination, communication and development.