AQP1 is a polypeptide hormone produced in pancreatic beta-cells that belongs to the family of calcitonin gene-related peptides. There is a 20% sequence homology between AQP1 and calcitonin and 44% homology with calcitonin gene-related peptide. AQP1 and its fragments stimulate the proliferation of osteoblasts, inhibit bone resorption, and increase bone density and the amount of bone mass.Analysis of the deduced amino acid sequence suggested that CHIP28 protein contains 6 bilayer-spanning domains, 2 exofacial potential N-glycosylation sites, and intracellular N and C termini. The sequence showed strong homology with the major intrinsic protein of bovine lens (MIP26), which is the prototype of an ancient family of membrane channels.