The apoptotic v-cyclin-CDK6 complex phosphorylates and inactivates Bcl-2.
v-cyclin encoded by Kaposi's sarcoma herpesvirus/human herpesvirus 8 (KSHV or HHV8) associates with cellular cyclin-dependent kinase 6 (CDK6) to form a kinase complex that promotes cell-cycle progression, but can also induce apoptosis in cells with high levels of CDK6. Here we show that whereas HHV8-encoded v-Bcl-2 protects against this apoptosis, cellular Bcl-2 has lost its anti-apoptotic potential as a result of an inactivating phosphorylation in its unstructured loop region. Moreover, we identify Bcl-2 as a new substrate for v-cyclin-CDK6 in vitro, and show that it is present in a complex with CDK6 in cell lysates. A Bcl-2 mutant with a S70A S87A double substitution in the loop region is not phosphorylated and provides resistance to apoptosis, indicating that inactivation of Bcl-2 by v-cyclin-CDK6 may be required for the observed apoptosis. Furthermore, the identification of phosphorylated Bcl-2 in HHV8-positive Kaposi's sarcoma indicates that HHV8-mediated interference with host apoptotic signalling pathways may encourage the development of Kaposi's sarcoma.
Ojala
P M
PM
Haartman Institute & Biocentrum Helsinki, University of Helsinki, PO Box 21, Haartmaninkatu 3, 00014 Helsinki, Finland. Paivi.Ojala@helsinki.fi
Yamamoto
K
K
Castaños-Vélez
E
E
Biberfeld
P
P
Korsmeyer
S J
SJ
Mäkelä
T P
TP
D000818:Animals; D017209:Apoptosis; D019556:COS Cells; D002457:Cell Extracts; D002522:Chlorocebus aethiops; D051361:Cyclin-Dependent Kinase 6; D018844:Cyclin-Dependent Kinases; D016213:Cyclins / Q000235:genetics / Q000378:metabolism*; D016195:G2 Phase; D005982:Glutathione Transferase / Q000235:genetics; D019288:Herpesvirus 8, Human / Q000502:physiology; D006801:Humans; D048055:Mitogen-Activated Protein Kinase 8; D020928:Mitogen-Activated Protein Kinases / Q000378:metabolism; D008938:Mitosis; D010766:Phosphorylation; D017346:Protein Serine-Threonine Kinases / Q000235:genetics / Q000378:metabolism*; D019253:Proto-Oncogene Proteins c-bcl-2 / Q000378:metabolism*; D011993:Recombinant Fusion Proteins / Q000235:genetics / Q000378:metabolism; D012694:Serine / Q000378:metabolism; D013379:Substrate Specificity; D014407:Tumor Cells, Cultured; D014764:Viral Proteins
D002457:Cell Extracts; D016213:Cyclins; D019253:Proto-Oncogene Proteins c-bcl-2; D011993:Recombinant Fusion Proteins; D014764:Viral Proteins; D012694:Serine; D005982:Glutathione Transferase; D017346:Protein Serine-Threonine Kinases; C495911:CDK6 protein, human; D051361:Cyclin-Dependent Kinase 6; D018844:Cyclin-Dependent Kinases; D048055:Mitogen-Activated Protein Kinase 8; D020928:Mitogen-Activated Protein Kinases