**2.8 CRABPs (cellular retinoic acid-binding proteins)**

CRABP1 (Cellular Retinoic Acid Binding Protein 1) and CRABP2 (Cellular Retinoic Acid Binding Protein 2) are paralogous genes that encode cellular RA binding proteins. These proteins transport RA to the nucleus and function to regulate the access of RA to the nuclear RA receptors. Specifically, CRABPs are cytosol-to-nuclear shuttling proteins, which facilitate RA binding to its cognate receptor complex and nuclear transfer. These activities in the retinoid signaling pathway play an important role in RA-mediated differentiation and proliferation processes. CRABPs are structurally similar to the cellular retinol-binding proteins, but CRABPs only bind RA, which contributes to RA-directed differentiation in epithelial tissue. Diseases associated with CRABPs include embryonal carcinomas.
