The enzymes of the ubiquitylation pathway play a pivotal role in a number of cellular processes including the regulated and targeted proteasome-dependent degradation of substrate proteins. Three classes of enzymes are involved in the process of ubiquitylation; activating enzymes (E1s), conjugating enzymes (E2s) and protein ligases (E3s). Hect, Uba, and Wwe Domains containing protein 1 (HUWE1) is a member of the Homologous to the E6AP Carboxyl Terminus (HECT) E3 protein ligase family and cloning of the human gene was first described by (Liu et al., 2005). HUWE1 ubiquitylates the Histone proteins, H1, H2A, H2B, H3 and H4 (Liu et al., 2005). PCR analysis of X chromosome-specific array comparative genomic hybridization has identified over expression of HUWE1 in the blood of individuals affected by nonsyndromic X-linked mental retardation (Froyen et al., 2008). HUWE1 catalyses K48 linked poly-ubiquitylation and proteasomal degradation of the transcription factor Miz1 (Myc-Interacting Zinc finger protein 1) (Yang et al., 2010). HUWE1 has also been shown to ubiquitylate Mcl1, p53, MyoD and cMyc (Zhong et al., 2005; Chen et al., 2005; Noy et al., 2012; Inoue et al., 2013). HUWE1 null mice display increased number and severity of skin tumors which can be reversed by concomitant genetic knockout of c-Myc (Inoue et al., 2013).
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