Tumor progression–dependent changes are seen in Spp1 expression and in other genes in the Spp1 network. (A) The time course of the mean expression level of Spp1, secreted phosphoprotein 1 (better known as osteopontin) in the PC samples of study 1 (left) and study 2 (right). In both studies, the expression of Spp1 in frank tumor cells (days 104/105) was significantly lower (P < .05) than in tumor precursors, regardless which time of tumor induction (days 7-49) was used for t test analysis. (B) Ingenuity pathways analysis (IPA) comparisons of the Spp1-dependent gene network from study 1 on days 7 vs 17 (top row, left), days 7 vs 33 (center), days 7 vs 46 (right) and days 7 vs 104 (bottom row, right). Spp1 and Spp1-regulated target genes are in the center and periphery of network diagrams, respectively. Spp1 targets that were significantly up-regulated when the relatively high Spp1 level on day 7 exhibited further incremental increases (days 17-46) are highlighted in red to the bottom left: Rock2, Cxcl3, Cxcl6, EGFR, MMP9 (P < .001, > 3-fold differences). Spp1 targets that were significantly down-regulated in accordance with the drop in Spp1 levels on day 104 are highlighted in green (P < .001, > 3-fold differences). Note that 3 genes found to be up-regulated in earlier comparisons (Cxcl3, Cxcl6, Rock2) are now found to be significantly down-regulated. Similar results were obtained when the Spp1 network in study 2 was analyzed (not shown).