Serpin family D member 1 (SERPIND1, Serpin D1) is also named heparin cofactor 2 (HC-II) and protease inhibitor leuserpin-2 (HLS2). It belongs to the serpin family. SERPIND1 can inhibit thrombin activity through interaction with heparin; hence, it is also known as heparin cofactor II (PMID: 15315969). SERPIND1 can also promote the release of leukocyte chemotactic factors and induce angiogenesis (PMID: 2713501, PMID: 22904320). SERPIND1 promoted the proliferation, migration, invasion, G1-to-S phase transition, and epithelial-mesenchymal transition of ovarian cancer cells and inhibited their apoptosis by promoting phosphorylation in the phosphoinositide 3-kinase/protein kinase B (PI3K/AKT) pathway (PMID: 31637210). It is a thrombin inhibitor activated by the glycosaminoglycans, heparin or dermatan sulfate. In the presence of the latter, HC-II becomes the predominant thrombin inhibitor in place of antithrombin III (AT-III). It also inhibits chymotrypsin, but in a glycosaminoglycan-independent manner (PMID: 1939083, PMID: 32827448).