PKR and PKR-like endoplasmic reticulum kinase induce the proteasome-dependent degradation of cyclin D1 via a mechanism requiring eukaryotic initiation factor 2alpha phosphorylation.
Cyclin D1 plays a critical role in controlling the G(1)/S transition via the regulation of cyclin-dependent kinase activity. Several studies have indicated that cyclin D1 translation is decreased upon activation of the eukaryotic initiation factor 2alpha (eIF2alpha) kinases. We examined the effect of activation of the eIF2alpha kinases PKR and PKR-like endoplasmic reticulum kinase (PERK) on cyclin D1 protein levels and translation and determined that cyclin D1 protein levels decrease upon the induction of PKR and PERK catalytic activity but that this decrease is not due to translation. Inhibition of the 26 S proteasome with MG132 rescued cyclin D1 protein levels, indicating that rather than inhibiting translation, PKR and PERK act to increase cyclin D1 degradation. Interestingly, this effect still requires eIF2alpha phosphorylation at serine 51, as cyclin D1 remains unaffected in cells containing a non-phosphorylatable form of the protein. This proteasome-dependent degradation of cyclin D1 requires an intact ubiquitination pathway, although the ubiquitination of cyclin D1 is not itself affected. Furthermore, this degradation is independent of phosphorylation of cyclin D1 at threonine 286, which is mediated by the glycogen synthase kinase 3beta and mitogen-activated protein kinase pathways as described in previous studies. Our study reveals a novel functional cross-talk between eIF2alpha phosphorylation and the proteasomal degradation of cyclin D1 and that this degradation is dependent upon eIF2alpha phosphorylation during short, but not prolonged, periods of stress.
Department of Oncology, Faculty of Medicine, McGill University, Montreal, Quebec H2W 1S6, Canada; Lady Davis Institute for Medical Research, Sir Mortimer B. Davis-Jewish General Hospital, Montreal, Quebec H3T 1E2, Canada.
Jennifer F
JF
Raven
Department of Oncology, Faculty of Medicine, McGill University, Montreal, Quebec H2W 1S6, Canada; Lady Davis Institute for Medical Research, Sir Mortimer B. Davis-Jewish General Hospital, Montreal, Quebec H3T 1E2, Canada.
Dionissios
D
Baltzis
Lady Davis Institute for Medical Research, Sir Mortimer B. Davis-Jewish General Hospital, Montreal, Quebec H3T 1E2, Canada.
Shuo
S
Wang
Department of Oncology, Faculty of Medicine, McGill University, Montreal, Quebec H2W 1S6, Canada; Lady Davis Institute for Medical Research, Sir Mortimer B. Davis-Jewish General Hospital, Montreal, Quebec H3T 1E2, Canada.
Zineb
Z
Mounir
Department of Oncology, Faculty of Medicine, McGill University, Montreal, Quebec H2W 1S6, Canada; Lady Davis Institute for Medical Research, Sir Mortimer B. Davis-Jewish General Hospital, Montreal, Quebec H3T 1E2, Canada.
Andreas I
AI
Papadakis
Lady Davis Institute for Medical Research, Sir Mortimer B. Davis-Jewish General Hospital, Montreal, Quebec H3T 1E2, Canada.
Hong Qing
HQ
Gao
Department of Oncology, Faculty of Medicine, McGill University, Montreal, Quebec H2W 1S6, Canada; Lady Davis Institute for Medical Research, Sir Mortimer B. Davis-Jewish General Hospital, Montreal, Quebec H3T 1E2, Canada. Electronic address: antonis.koromilas@mcgill.ca.
Antonis E
AE
Koromilas
D045744:Cell Line, Tumor; D019938:Cyclin D1 / Q000378:metabolism*; D015536:Down-Regulation; D004721:Endoplasmic Reticulum / Q000378:metabolism; D015852:Eukaryotic Initiation Factor-2 / Q000378:metabolism*; D005786:Gene Expression Regulation; D038362:Glycogen Synthase Kinase 3 / Q000378:metabolism; D000071679:Glycogen Synthase Kinase 3 beta; D006801:Humans; D010766:Phosphorylation; D046988:Proteasome Endopeptidase Complex / Q000737:chemistry / Q000378:metabolism; D012694:Serine / Q000737:chemistry; D025801:Ubiquitin / Q000737:chemistry; D019892:eIF-2 Kinase / Q000378:metabolism*
D019938:Cyclin D1; D015852:Eukaryotic Initiation Factor-2; D038362:Glycogen Synthase Kinase 3; D000071679:Glycogen Synthase Kinase 3 beta; D046988:Proteasome Endopeptidase Complex; D012694:Serine; D025801:Ubiquitin; D019892:eIF-2 Kinase; C000605506:GSK3B protein, human; C061553:ATP dependent 26S protease