The regulation of cell proliferation in Tuberous Sclerosis

Tuberous sclerosis (TSC) is an autosomal dominant disease with an estimated prevelance of about 1 in 6000. This disease is characterized by mental retardation, epilepsy, and mostly non-malignant tumors of the skin, retina, kidney, and brain. Linkage studies in families with TSC show that about 50% are associated with a loss of functional TSCI gene, while TSC2 is implicated in the remainder. TSC2 has been cloned in 1993. Since then it has been shown that the TSC2 gene product, tuberin, has GTPase accelerating protein (GAP) activity against Rapla and Rab5. Recent data of our laboratory demonstrated that tuberin plays an important role in the regulation of the eukaryotic cell cycle. Currently, a more detailed understanding of the role of TSC2 in cell cycle control and transformation is missing. In the course of the submitted project we want to detaily investigate the mechanism of the effects of modulated tuberin expression on cell cycle control and anchorage-independent growth and investigate whether its GAP activity is necessary for these effects. Other results of our laboratory showed that tuberin is an essential regulator of the process of neuronal differentiation. As a logical consequence, we will now analyse the role of tuberin in the development of neuroectodermal tumors and the role of tuberin`s GAP activities in mediating these effects. Half a year ago, TSCI has been cloned. So far no biochemical or biological properties of its gene product, hamartin, have been reported. Since the clinical features of TSCI- and TSC2-associated TSC are identical, it is likely that tuberin and hamartin participate in the same pathways of cellular growth/differentiation control. Accordingly, we will analyse the effects of modulated hamartin expression on the regulation of cell cycle control, anchorage-independent growth and neuronal differentiation. The mechanisms of cellular effects upon modulated hamartin expression will detaily be investigated. Furthermore, to get more insights into the functions of hamartin we will search for hamartin-interacting proteins using the two hybrid screen. lt is the hope of tuberous sclerosis patients and investigators alike that a better understanding of the cellular role of the two proteins, tuberin and hamartin, will allow the development of specific therapies to both prevent and treat the manifestations of TSC. The submitted project was designed with an eye toward these goals.