SPP1 and renal carcinoma: In a separate study of the Caki-1 renal carcinoma cell line, siRNA silencing of OPN resulted in induction of apoptotic peptidase activating factor 1, activation of caspase-3, decrease in b-cell lymphoma-2 (Bcl-2), and increase in Bcl-2-associated X protein [132], although the precise mechanism of this silencing of mitochondrial function is still under investigation.