MP1: ProductsMEK Binding Partner 1 (MP1), also known as Late Endosomal/Lysosomal Adaptor, MAPK and MTOR Activator 3 (LAMTOR3), is a 124 amino acid (aa) scaffold protein with a predicted molecular weight of 13.5 kDa. Human MP1 shares 97% and 96% aa sequence identity with the mouse and rat orthologs, respectively. MP1 is expressed in the heart, brain, lung, liver, muscle, kidney, spleen, and testis. Within the cytoplasm it is recruited to endosomes via the adaptor proteins p14 and p18, where it acts as a scaffold in the Raf-MEK-ERK signaling pathway. MP1 is degraded via the 26S Proteasome in the absence of p14, suggesting that p14 may also be required to stabilize MP1. MP1 has also been reported to function in the PAK1 and Akt signaling pathways. It has been implicated in a number of cellular processes as a part of these signaling pathways, including cell proliferation, cell motility, and differentiation. Additionally, MP1 may be important during development, since it has been shown to function in developing fly wings. MP1 also mediates pro-survival signaling in ER-positive breast cancer cells, suggesting that it may have an oncogenic role in cancer.