UBE2I and head and neck squamous cell carcinoma: HPV E6 was shown to promote the degradation of the SUMO E2 enzyme UBC9, reducing global SUMOylation rates in keratinocytes [137]; however, more recent work has demonstrated that UBC9, SUMO1 and SUMO2/3 are over expressed in HPV+ cervical cancer and HNSCC [138].