Secreted cytokine-like protein. Inhibits cell growth in vitro. Homodimer; disulfide-linked. Highly expressed in lung and prostate (PubMed:11481438). Also found in mammary gland, spleen, pancreas, testis and liver (PubMed:11481438). Detected throughout the airway epithelium in lung, with highest expression in large airways (PubMed:12406855). Found in lung submucosal glands where it localizes to acinar and ductile cells (PubMed:12406855). Not detected in respiratory bronchioles, alveolar ducts or alveolar epithelium (PubMed:12406855). In mammary gland, specifically localizes to luminal epithelial cells (PubMed:11481438). Belongs to the secretoglobin family. UGRP subfamily.