UV-damaged DNA-binding proteins are targets of CUL-4A-mediated ubiquitination and degradation.
Cul-4A, which encodes a member of the cullin family subunit of ubiquitin-protein ligases, is expressed at abnormally high levels in many tumor cells. CUL-4A can physically associate with the damaged DNA-binding protein (DDB), which is composed of two subunits, p125 and p48. DDB binds specifically to UV-damaged DNA and is believed to play a role in DNA repair. We report here that CUL-4A stimulates degradation of p48 through the ubiquitin-proteasome pathway, resulting in an overall decrease in UV-damaged DNA binding activity. The R273H mutant of p48 identified from a xeroderma pigmentosium (group E) patient is not subjected to CUL-4A-mediated proteolysis, consistent with its inability to bind CUL-4A. p125 is also an unstable protein, and its ubiquitination is stimulated by CUL-4A. However, the abundance of p125 is not dramatically altered by Cul-4A overexpression. UV irradiation inhibits p125 degradation, which is temporally coupled to the UV-induced translocation of p125 from the cytoplasm into the nucleus. CUL-4A is localized primarily in the cytoplasm. These findings identify DDB subunits as the first substrates of the CUL-4A ubiquitination machinery and suggest that abnormal expression of Cul-4A results in reduced p48 levels, thus impairing the ability of DDB in lesion recognition and DNA repair in tumor cells.
Chen
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X
Department of Pathology, Weill Medical College and Graduate School of Medical Sciences, Cornell University, New York, New York 10021, USA.
Zhang
Y
Y
Douglas
L
L
Zhou
P
P
D000818:Animals; D002460:Cell Line; D006224:Cricetinae; D044842:Cullin Proteins; D003593:Cytoplasm / Q000378:metabolism; D004268:DNA-Binding Proteins / Q000528:radiation effects*; D006801:Humans; D006868:Hydrolysis; D009363:Neoplasm Proteins / Q000378:metabolism*; D025801:Ubiquitin / Q000378:metabolism*; D014466:Ultraviolet Rays
C114234:CUL4A protein, human; D044842:Cullin Proteins; C117669:DDB2 protein, human; D004268:DNA-Binding Proteins; D009363:Neoplasm Proteins; D025801:Ubiquitin