Cell cycle-regulated phosphorylation of hamartin, the product of the tuberous sclerosis complex 1 gene, by cyclin-dependent kinase 1/cyclin B.
Tuberous sclerosis complex is a tumor suppressor gene syndrome whose manifestations can include seizures, mental retardation, and benign tumors of the brain, skin, heart, and kidneys. Hamartin and tuberin, the products of the TSC1 and TSC2 genes, respectively, form a complex and inhibit signaling by the mammalian target of rapamycin. Here, we demonstrate that endogenous hamartin is threonine-phosphorylated during nocodazole-induced G2/M arrest and during the G2/M phase of a normal cell cycle. In vitro assays showed that cyclin-dependent kinase 1 phosphorylates hamartin at three sites, one of which (Thr417) is in the hamartin-tuberin interaction domain. Tuberin interacts with phosphohamartin, and tuberin expression attenuates the phosphorylation of exogenous hamartin. Hamartin with alanine mutations in the three cyclin-dependent kinase 1 phosphorylation sites increased the inhibition of p70S6 kinase by the hamartin-tuberin complex. These findings support a model in which phosphorylation of hamartin regulates the function of the hamartin-tuberin complex during the G2/M phase of the cell cycle.
Astrinidis
Aristotelis
A
Fox Chase Cancer Center, Philadelphia, Pennsylvania 19111, USA.
Senapedis
William
W
Coleman
Thomas R
TR
Henske
Elizabeth Petri
EP
D001665:Binding Sites; D016203:CDC2 Protein Kinase / Q000378:metabolism; D002460:Cell Line; D019926:Cyclin B / Q000378:metabolism; D016195:G2 Phase; D006801:Humans; D007399:Interphase; D016297:Mutagenesis, Site-Directed; D010766:Phosphorylation; D011485:Protein Binding; D011506:Proteins / Q000235:genetics / Q000378:metabolism* / Q000502:physiology; D012097:Repressor Proteins / Q000378:metabolism; D014162:Transfection; D014402:Tuberous Sclerosis / Q000235:genetics*; D000077004:Tuberous Sclerosis Complex 1 Protein; D000077005:Tuberous Sclerosis Complex 2 Protein; D025521:Tumor Suppressor Proteins
D019926:Cyclin B; D011506:Proteins; D012097:Repressor Proteins; C000624650:TSC1 protein, human; C000624653:TSC2 protein, human; D000077004:Tuberous Sclerosis Complex 1 Protein; D000077005:Tuberous Sclerosis Complex 2 Protein; D025521:Tumor Suppressor Proteins; D016203:CDC2 Protein Kinase