Uteroglobin is a small, non-glycosylated secreted protein of the secretoglobin superfamily. It is produced by the non-ciliated, non-mucous secretory cells that predominate in lung bronchioles (Clara cells), and other non-ciliated epithelia that communicate with the external environment. Expression is induced by steroid hormones such as estrogen, and enhanced by the non-steroid hormone prolactin. Human Uteroglobin cDNA encodes a 21 amino acid (aa) signal sequence and a 70 aa mature protein. The mature protein forms a disulfide-linked head-to-tail homodimer of 16 kDa. This homodimer is thought to form a binding pocket that binds hydrophobic ligands such as phospholipids, progesterone and retinols. Binding of fibronectin to Uteroglobin in the kidney is thought to protect against nephropathy, while binding of the lipocalin-1 receptor has been reported to suppress cancer cell motility and invasion.