COL1A1 and posterior cortical atrophy: Unexpectedly, we observed higherexpression of stemness marker SOX2 after 7 days ofcoculture with PCa cells, indicatinga less differentiated state (Figure 4E).67 We then tested threebone matrix protein genes, COL1A1 (Collagen typeI alpha 1), SPP1 (Osteopontin), and BGLAP (Osteocalcin),68 whose gene expressionwas consistently lower in bone cells after coculture with PCa cells(Figure 4F).