The OncoPPi network also revealed prominent PPI hubs with novel connectivity (Fig. 3a) exposing potentially critical biological insights for cancer genes such as MYC, STK11, RASSF1 and CDK4. To assess experimentally the physical connectivity of PPIs in the OncoPPi network with an orthogonal approach, we selected two major hubs for confirmation with a conventional GST-pull down assay, the oncogene CDK4 and the tumour suppressor RASSF1 (Fig. 3b,c). The gene discussed is CDK4; the disease is cancer.