CUL5 and lung cancer: In order to explain the differential regulation of HIF-1α after treatment with Hsp90 inhibitors in H1339 and EPLC-272H lung cancer cells, we investigated the expression of Cullin 5 E3 ubiquitin ligase (Cul5), receptor of activated protein C kinase (RACK1) and Copper Metabolism MURR1 Domain containing 1 protein (COMMD1) which have been described to regulate the degradation of HIF-1α upon Hsp90 inhibition [16]–[18].