Cell-surface CD74 initiates a signaling cascade leading to cell proliferation and survival

CD74 is an integral membrane protein that was thought to function mainly as an MHC class 11 chaperone. However, CD74 was recently shown to have a role as an accessory-signaling molecule. Our studies demonstrated that CD74 regulates B-cell differentiation by inducing a pathway leading to the activation of transcription mediated by the NF-kappa B p65/RelA homodimer and its coactivator, TAF(vertical bar vertical bar)105. Here, we show that CD74 stimulation with anti-CD74 antibody leads to an induction of a signaling cascade resulting in NF-kappa B activation, entry of the stimulated cells into the S phase, elevation of DNA synthesis, cell division, and augmented expression of BCL-XL. These studies therefore demonstrate that surface CD74 functions as a survival receptor.