Distribution of SPARC in normal and neoplastic human tissue

SPARC (Secreted Protein, Acidic and Rich in Cysteine)/osteonectin is a secreted glycoprotein that exhibits restricted expression in routine adult and embryonic tissues and is associated with cell migration, matrix mineralization, steroid hormone production, cell cycle regulation, and angiogenesis. We produced a monoclonal antibody, MAb SSP2, against a Ca²⁺- binding region of SPARC and evaluated the immunoreactivity of normal and malignant tissue from 118 human samples. In normal tissue we found restricted and moderate reactivity with SSP2 in steroidogenic cells, chondrocytes, placental trophoblasts, vascular smooth muscle cells, and endothelial cells. Strong reactivity was found in fibrocytes and endothelial cells involved in tissue repair and in invasive malignant tumors, including those of the gastrointestinal tract, breast, lung, kidney, adrenal cortex, ovary, and brain. We conclude that SSP2 is a useful reagent for detection of SPARC in human tissue. Given the broad reactivity of malignant tissues, we propose that SPARC expression might contribute to some aspects of tumor progression.