TGFB1 and neoplasm: Tumor cells induced positive staining of Smad2/3 in HUVECs, especially localized in the cell nuclei (Figure 4D and Figure 4E for HUVECs co-cultured with A549 and A375, respectively), confirming the above observation on the expression of the upstream tumor-derived TGF-β1 (Figure 3F).