Alternative titles; symbols
HGNC Approved Gene Symbol: SPARCL1
Cytogenetic location: 4q22.1 Genomic coordinates (GRCh38) : 4:87,473,335-87,529,376 (from NCBI)
The cells in high endothelial venules (HEVs) in lymphoid tissues have a plump, almost cuboidal, appearance and support high levels of lymphocyte extravasation from blood, possibly due to the presence of desmosome-like junctions rather than tight junctions in the HEVs. Lymphocytes stick to HEVs through a process of rolling, activation, and strong adhesion, followed by transendothelial migration and the passage of lymphocytes through the HEV basement membrane. In chronic inflammation, the activated endothelium of nonlymphoid tissues acquires an HEV-like morphology and function. Hevin is highly expressed in HEV and is thought to contribute to the induction or maintenance of features of the HEV endothelium that facilitate lymphocyte migration (Girard and Springer, 1995).
By differential hybridization of a tonsillar high endothelial cell cDNA library, Girard and Springer (1995) obtained a cDNA encoding SPARCL1, which they termed Hevin. Sequence analysis predicted that Hevin is an evolutionarily conserved, 664-amino acid secreted protein. Hevin contains 7 potential N-linked glycosylation sites, an N-terminal signal peptide, a long acidic region rich in glu and asp, a cysteine-rich domain, and a C-terminal region with a 12-residue segment homologous to the calcium-binding loops of EF-hand structures in the calmodulin family of proteins (see CALM1; 114180). The 232 C-terminal amino acids of Hevin are 62% identical to the homologous portion of SPARC (182120). In situ hybridization analysis showed selective expression of Hevin in the cytoplasmic region of high endothelial cells. Northern blot analysis revealed high expression of a 2.7-kb Hevin transcript in lymph node, brain, heart, lung, skeletal muscle, ovary, small intestine, and colon, with lower levels in placenta, pancreas, testis, spleen, and thymus, and no expression in kidney, liver, and peripheral blood leukocytes. Unlike SPARC, Hevin is absent from flat umbilical vein endothelial cells. Girard and Springer (1995) proposed that Hevin may have antiadhesive properties similar to those of SPARC.
Girard, J.-P., Springer, T. A. Cloning from purified high endothelial venule cells of hevin, a close relative of the antiadhesive extracellular matrix protein SPARC. Immunity 2: 113-123, 1995. [PubMed: 7600298] [Full Text: https://doi.org/10.1016/1074-7613(95)90083-7]