Localized to zymogen granules, where it functions in trypsinogen activation (By similarity). May indirectly regulate cell motility, cell-cell and cell/extracellular matrix interactions (By similarity). Expressed predominantly in epithelium of uterus and oviduct. In uterus, strongly expressed at proestrus, declines at estrus and disappears at diestrus. In oviduct, strongly expressed at both proestrus and estrus but declines significantly at diestrus. In uterus, highly expressed on day 1 of pregnancy but declines dramatically on day 2 and is not detected between days 3 and 7. In oviduct, highly expressed on days 1 and 2 of pregnancy but declines significantly on days 3 and 4. By estrogen, tamoxifen and growth hormone. Repressed by progesterone and by the antiestrogen ICI 182780.