SPARC, an extracellular matrix protein with tumor-suppressing activity in human ovarian epithelial cells.

SPARC, also termed osteonectin, BM-40 and 43K protein, is an acidic, cysteine-rich component of the extracellular matrix that has been shown to be directly regulated by progesterone and dexamethasone and indirectly by cytokines. By RNA fingerprinting technique, we cloned a SPARC homolog from the normal human ovarian surface epithelial (HOSE) cells and demonstrated that it is expressed at high levels in the normal HOSE cells but at much lower levels in ovarian carcinoma cells in vitro and in vivo. Subsequently, we transfected the full length SPARC cDNA into an ovarian carcinoma cell line SKOV3 and showed that it reduced the growth rate of the cancer cell line in culture and reduced the cell's ability to induce tumours in nude mice. These results suggest that SPARC may play an important role in growth and and differentiation of the HOSE cells and support the hypothesis that SPARC functions as a tumor suppressor.