The small heat-shock protein alpha B-crystallin promotes FBX4-dependent ubiquitination.
AlphaB-crystallin is a small heat-shock protein in which three serine residues (positions 19, 45, and 59) can be phosphorylated under various conditions. We describe here the interaction of alphaB-crystallin with FBX4, an F-box-containing protein that is a component of the ubiquitin-protein isopeptide ligase SCF (SKP1/CUL1/F-box). The interaction with FBX4 was enhanced by mimicking phosphorylation of alphaB-crystallin at both Ser-19 and Ser-45 (S19D/S45D), but not at other combinations. Ser-19 and Ser-45 are preferentially phosphorylated during the mitotic phase of the cell cycle. Also alphaB-crystallin R120G, a mutant found to co-segregate with a desmin-related myopathy, displayed increased interaction with FBX4. Both alphaB-crystallin S19D/S45D and R120G specifically translocated FBX4 to the detergent-insoluble fraction and stimulated the ubiquitination of one or a few yet unknown proteins. These findings implicate the involvement of alphaB-crystallin in the ubiquitin/proteasome pathway in a phosphorylation- and cell cycle-dependent manner and may provide new insights into the alphaB-crystallin-induced aggregation in desmin-related myopathy.
den Engelsman
John
J
Department of Biochemistry, Nÿmegen Center for Molecular Life Sciences, University of Nijmegen, 6500 HB Nijmegen, The Netherlands.
Keijsers
Vivian
V
de Jong
Wilfried W
WW
Boelens
Wilbert C
WC
D002453:Cell Cycle / Q000502:physiology; D006367:HeLa Cells; D006801:Humans; D016297:Mutagenesis, Site-Directed; D010453:Peptide Synthases / Q000378:metabolism*; D011485:Protein Binding; D044843:SKP Cullin F-Box Protein Ligases; D015398:Signal Transduction; D025801:Ubiquitin / Q000378:metabolism*; D038203:alpha-Crystallin B Chain / Q000235:genetics / Q000378:metabolism*
D025801:Ubiquitin; D038203:alpha-Crystallin B Chain; D044843:SKP Cullin F-Box Protein Ligases; D010453:Peptide Synthases