cIAP1/2 Are Direct E3 Ligases Conjugating Diverse Types of Ubiquitin Chains to Receptor Interacting Proteins Kinases 1 to 4 (RIP1–4)
Figure 2
cIAP1 and cIAP2 are direct E3 ubiquitin ligases for RIP1–4 proteins.
(A) In vitro ubiquitination assays were performed on in vitro-transcribed and -translated RIP1–4 proteins labeled with 35S-methionine. GST, GST-XIAP, GST-cIAP1, or GST-cIAP2 was used as E3 component, UbcH5a as the E2 component, and using wild-type ubiquitin. RIP ubiquitination was revealed by autoradiography and appears as a smear in the figure. (B) HEK293T cells were transfected with VSV-tagged RIP3 and RIP4 plasmids in the absence or presence of a Myc-tagged cIAP2 plasmid. cIAP2 was immunoprecipitated in NP-40 buffer using anti-Myc antibody and coimmunoprecipitated ubiquitinated RIP3 and RIP4 were revealed by immunoblotting with anti-VSV and anti-ubiquitin antibodies. Protein expression in the lysates is shown. (C) HEK293T cells were transfected with VSV-tagged RIP3 plasmid in the absence or presence of a cIAP2 plasmid. RIP3 was immunoprecipitated in RIPA buffer using anti-VSV antibody and ubiquitinated RIP3 was revealed by immunoblotting with anti-VSV and anti-ubiquitin antibodies. Protein expression in the lysates is shown.