Angiogenesis and cell proliferation are fundamental biological processes whose pathologic states represent two hallmarks of cancer. Central to controlling both processes is the TGF-β/BMP signaling pathway, for which the SMAD proteins serve as major downstream effector molecules. Upon ligand-binding, TGF-β or BMP type I/II receptor heterotetramers phosphorylate receptor-regulated SMADs (R-SMADs). TGF-β-receptor binding leads to SMAD2/3 phosphorylation, whereas BMP-receptor binding induces phosphorylation of SMADs 1/5/8. Phosphorylated SMADs (pSMADs) then form a complex with the co-SMAD SMAD4 at which point they undergo nuclear translocation, where they function as transcriptional modulators of target genes. The magnitude of SMAD phosphorylation and functional output (e.g., stimulated angiogenesis or attenuated cell proliferation) depends on both the ligand concentration, as well as the duration of exposure. In this study, we quantitatively evaluate the phosphorylation states of R-SMADs, as well as their downstream biological effects at three different biological scales: 1) biochemical, 2) cellular, and 3) tissue/3D models. At the biochemical level, the temporal and dose-dependent phosphorylation of R-SMADs in response to growth factor stimulation can be quantified using a quantitative ELISA approach. Growth factor stimulation can be quantified at the cellular level by high content imaging of SMAD phosphorylation and nuclear translocation, while simultaneously monitoring cell proliferation rates. Lastly, high-resolution confocal imaging can be employed to observe developmental consequences of phospho-SMAD signaling using a HUVEC-based 3D angiogenesis model system.
