Enables CXCR4 chemokine receptor binding activity. Acts upstream of or within several processes, including negative regulation of gastric acid secretion; negative regulation of macrophage activation; and positive regulation of ERK1 and ERK2 cascade. Located in extracellular space. Is expressed in several structures, including alimentary system; genitourinary system; liver; skeleton; and thymus. Orthologous to human TFF2 (trefoil factor 2). [provided by Alliance of Genome Resources, Apr 2022]