Hamartin and tuberin interaction with the G2/M cyclin-dependent kinase CDK1 and its regulatory cyclins A and B

Tuberous sclerosis (TSC) is a multi-system disorder characterized by hamart omatous rumors and abnormal brain development, with multiple foci of disrup ted neuronal migration and giant dysmorphic neurons within cortical tubers. TSC is associated with mutations in 2 genes. TSC1 and TSC2, which encode h amartin and tuberin, respectively. The functions of these proteins have yet to he determined. Recently. the Drosophila homologue of TSC2. gigas, has b een shown to be required for the G2/M transition of the cell cycle. However . the mechanism of this action remains unknown. Because the cyclin-dependen t kinase CDK1 forms a complex with cyclin B1 to trigger the G2/M transition . we hypothesized that tuberin interacts with CDK1 to regulate its activity . In the study reported in this paper, we have used co-immunoprecipitation and confocal microscopy to demonstrate that tuberin interacts with and co-l ocalizes with CDK1 and its binding partner cyclin B1 in multiple cell types . We also demonstrate that hamartin interacts with CDK1 and cyclin B1. We f urther present evidence that tuberin interacts with the other regulatory su bunit of CDK1. cyclin A. These findings suggest a direct role fur tuberin a nd hamartin in modulating the activity of CDK1 during G2 and the G2/M trans ition. This is the first description of a role fur both tuberin and hamarti n in a common cellular function, providing a potential mechanism for the id entical clinicopathologic manifestations that result when either of these p roteins are inactivated.