Unraveling mysteries of the multifunctional protein SPARC.

The matricellular protein SPARC (secreted protein acidic and rich in cysteine) has diverse functions in melanoma cells. Because this secreted protein is produced not only in tumor cells but also in stromal cells, the question has been asked whether paracrine effects of stroma-derived SPARC contribute to melanoma progression. In this issue, Prada et al. (2007) begin to answer this question by demonstrating that SPARC produced by melanoma, but not stromal cells, is essential to regulate melanoma cell growth.