Soluble frizzled-related proteins (sFRPS) function as modulators of Wnt signaling through direct interaction with Wnts. They have a role in regulating cell growth and differentiation in specific cell types (By similarity). SFRP4 plays a role in bone morphogenesis (By similarity). May also act as a regulator of adult uterine morphology and function (PubMed:12063187). May also increase apoptosis during ovulation possibly through modulation of FZ1/FZ4/WNT4 signaling (PubMed:12960062). Has phosphaturic effects by specifically inhibiting sodium-dependent phosphate uptake (By similarity). Expressed in the involuting mammary gland, ovarian corpus luteum and prostate. In ovaries, low levels found in granulosa cells. High levels in corpora lutea of pregnant animals. Expressed from day 9 of pregnant uterus. Highest level at day 12, specifically in the decidua and weakly, in the myometrium. Levels decline thereafter. Up-regulated 48 hours after estrogen treatment mainly in the uterine endometrial stroma (PubMed:12063187). Induced in ovarian granulosa cells after 12 hours treatment with chorionic gonadotrophin (CG). Further up-regulated in corpora lutea by the luteotrophic hormone PRL (PubMed:12960062). The FZ domain is involved in binding with Wnt ligands. Belongs to the secreted frizzled-related protein (sFRP) family.