The Hace1 E3 Ligase Modulates the Activity of Multiple Tumor Suppressive CRL E3 Ligases by binding to CAND1

The Hace1 E3 ligase is a tumor suppressor in stressed cells. Through unknown mechanisms, Hace1 indirectly targets the cyclin D1 proto-oncogene for proteasomal degradation during nutrient depletion. We now show that Hace1 targets HIF1alpha for VHL-dependent degradation during hypoxia. To better understand these diverse actions we performed mass spectrometry to identify Hace1-interacting proteins. We show that Hace1 interacts with cullin-associated NEDD8-dissociated protein 1 (CAND1) under nutrient depletion and hypoxia. CAND1 binds cullins and prevents their entry into cullin ring E3 ligase (CRL) complexes, thus blocking CRL activity. Hace1 binding releases CUL1/2 from CAND1, facilitating assembly of CRL complexes to degrade cyclin D1 and HIF1alpha, respectively. These findings suggest a broad role for Hace1 in regulating tumor suppressive CRL E3 ligases. In this study, we used gene expression profiling to characterize how Hace1 overexpression affect the transcriptional response to hypoxic stress Using Affymetrix exon-level microarrays, we compared the expression profile of HEK293 cells overexpressing either Hace1 or MSCV vector alone, under hypoxia or normoxia