SPP1 and neoplasm: To address the function of the RGD domain in tumor-derived OPN for different splice forms and in the different human tumor cell lines, we overexpressed (1) wild type OPN (WT), (2) OPN with mutations in the RGD domain (RAA), or (3) OPN with the RGD deleted (NoRGD) for the two different splice forms: OPN-A and OPN-B.