Tuberin Nuclear Localization Can Be Regulated by Phosphorylation of Its Carboxyl Terminus

Abstract

Tuberin, the tuberous sclerosis 2 (TSC2) gene product, has been identified as a tumor suppressor protein genetically implicated in the pathology of tuberous sclerosis and the female-specific lung disease lymphangioleiomyomatosis. Tuberin and its predominant cytoplasmic binding partner hamartin have been shown to complex with a variety of intracellular signaling regulators and affect the processes of protein translation, cellular proliferation, cellular migration, and cellular transcription. In previous studies, we have presented evidence for tuberin binding to the calcium-dependent intracellular signaling protein calmodulin (CaM), overlap of tuberin CaM binding domain with a binding domain for estrogen receptor A, and the phosphorylation-associated nuclear localization of tuberin. In the study presented here, we expand our findings on the mechanism of tuberin nuclear localization to show that the CaM-estrogen receptor-A binding domain of tuberin can also serve as a tuberin nuclear localization sequence. Furthermore, we identify an Akt/p90 ribosomal S6 kinase-1 phosphorylation site within the carboxyl terminus of tuberin that can regulate tuberin nuclear localization and significantly affect the ability of tuberin to modulate estrogen genomic signaling events. These findings suggest a link between tuberin nuclear localization and a variety of intracellular signaling events that have direct implications with respect to the role of tuberin in the pathology of tuberous sclerosis and lymphangioleiomyomatosis. (Mol Cancer Res 2006;4(11):885 -97)

Evidence for Epigenetic Changes in the Estrogen Receptor Alpha Promoter in Lymphangioleiomyomatosis (LAM)~!2010-01-05~!2010-03-12~!2010-05-11~!

“…Previous studies from our laboratory and that of others have demonstrated that tuberin can directly impact ERmediated genomic and nongenomic signaling [39][40][41][42]. Cumulatively these data support the hypothesis that, if ER is present in a cell, disruption of tuberin/hamartin-associated signaling events can directly impact signaling pathways mediated by ER .…”

“…In the LAM-associated cell lines examined in these studies it was observed that transcription expression of the ER gene was actively being initiated from multiple ER promoters. Although these studies were limited to looking at steadystate levels of ER mRNA and therefore do not directly address transcription rates, our previously published studies demonstrating tuberin's ability to localize to the nucleus [40,42] and tuberin's ability to directly impact transcription regulation [30,41] would support a direct impact on ER mRNA transcription as opposed to ER mRNA degradation.…”

“…These include studies from our laboratory and others that demonstrate: a) tuberin can impact ER non-genomic signaling through its ability to modulate PDGF signaling [39,62], p90RSK/ERK signaling and RHEB/mTOR signaling [42,63]; b) tuberin can inhibit ER genomic signaling through its ability to directly bind ER , directly bind ER 's coregulatory protein calmodulin and to block ER DNA binding [41,42]; c) a study that demonstrates estrogen can promote the survival and pulmonary metastasis of tuberin-null cells [64]; d) a study that demonstrates nongenomic estrogen activities can regulate tuberin stability [65]; and e) a study that provides evidence for upregulation of ER protein expression in LAM lesions through a post-transcriptional-protein degradation mechanism [66]. Although some of these findings might appear to be somewhat contradictory, they most probably reflect the dedifferentiated state and complexities of LAM lesions.…”

Hamartin-Hsp70 Interaction Is Necessary for Akt-Dependent Tuberin Phosphorylation during Heat Shock

“…16,17) Heat shock resulted in activation of Akt, as indicated by modulation of Ser308, and was accompanied by phosphorylation of tuberin at Thr1462 (Fig. 4A).…”

Capacidade proliferativa in vitro de precursores neuro-gliais, telencefálicos e expressão dos genes 1 e 2 do Complexo da Esclerose Tuberosa (TSC1 e TSC2)

“…Segundo Soucek et al (1997), o complexo hamartina-tuberina pode regular negativamente a progressão do ciclo celular deixando-as em um estado quiescente G0/G1 ao antagonizar mTOR ou por ter a capacidade de interagir diretamente no núcleo com p27/p27 KIP1 impedindo a degradação ou ubiquitinação desta última. Tuberina é capaz de transitar entre o citoplasma celular (onde interage com a hamartina) e o núcleo celular quando há fosforilação de sua porção carboxi-terminal (resíduos 1351 e 1807, Lou et al, 2006;York et al, 2009). Essa redistribuição na fase tardia de G1 do ciclo celular, demonstrada em nossos dados, já foi evidenciada em linhagem celular de músculo liso de traqueia (Clements et al, 2007) e outras (Rosner et al, 2004).…”