Tuberin: a stimulus-regulated tumor suppressor protein controlled by a diverse array of receptor tyrosine kinases and G protein-coupled receptors

Novel role of lncRNAs regulatory network in papillary thyroid cancer

Papillary thyroid cancer (PTC) is the most common endocrine malignancy. The incidence of PTC has increased annually worldwide. Thus, PTC diagnosis and treatment attract more attention. Noncoding RNAs (lncRNAs) play crucial roles in PTC progression and act as prognostic biomarkers. Moreover, microRNAs (miRNAs) and epithelial-mesenchymal transition (EMT)-associated proteins have potential biomarkers for diagnosing and treating PTC. However, the correlation of lncRNAs with miRNAs and EMT-associated proteins needs further clarification. The present review highlights the recent advances of lncRNAs in PTC. We significantly summarized the two molecular regulatory mechanisms in PTC progress, including lncRNAs-miRNAs-protein signaling axes and lncRNAs-EMT pathways. This review will help our understanding of the association between lncRNAs and PTC and may assist us in evaluating the prognosis for PTC patients. Taken together, targeting the lncRNAs regulatory network has promising applications in diagnosing and treating PTC.

Genetics and molecular biology of tuberous sclerosis complex

Tuberous Sclerosis Complex is a multisystem disorder exhibiting a wide range of manifestations characterized by tumour-like lesions called hamartomas in the brain, skin, eyes, heart, lungs and kidneys. Tuberous Sclerosis Complex is genetically determined with an autosomal dominant inheritance and is caused by inactivating mutations in either the TSC1 or TSC2 genes. TSC1/2 genes play a fundamental role in the regulation of phosphoinositide 3-kinase (PI3K) signalling pathway, inhibiting the mammalian target of rapamycin (mTOR) through activation of the GTPase activity of Rheb. Mutations in TSC1/2 genes impair the inhibitory function of the hamartin/tuberin complex, leading to phosphorylation of the downstream effectors of mTOR, p70 S6 kinase (S6K), ribosomal protein S6 and the elongation factor binding protein 4E-BP1, resulting in uncontrolled cell growth and tumourigenesis.

Despite recent promising genetic, diagnostic, and therapeutic advances in Tuberous Sclerosis Complex, continuing research in all aspects of this complex disease will be pivotal to decrease its associated morbidity and mortality. In this review we will discuss and analyse all the important findings in the molecular pathogenesis of Tuberous Sclerosis Complex, focusing on genetics and the molecular mechanisms that define this multisystemic disorder.

The Rheb-mTOR pathway is upregulated in reactive astrocytes of the injured spinal cord

Astrocytes in the CNS respond to tissue damage by becoming reactive. They migrate, undergo hypertrophy, and form a glial scar that inhibits axon regeneration. Therefore, limiting astrocytic responses represents a potential therapeutic strategy to improve functional recovery. It was recently shown that the epidermal growth factor (EGF) receptor is upregulated in astrocytes after injury and promotes their transformation into reactive astrocytes. Furthermore, EGF receptor inhibitors were shown to enhance axon regeneration in the injured optic nerve and promote recovery after spinal cord injury. However, the signaling pathways involved were not elucidated. Here we show that in cultures of adult spinal cord astrocytes EGF activates the mTOR pathway, a key regulator of astrocyte physiology. This occurs through Akt-mediated phosphorylation of the GTPase-activating protein Tuberin, which inhibits Tuberin's ability to inactivate the small GTPase Rheb. Indeed, we found that Rheb is required for EGF-dependent mTOR activation in spinal cord astrocytes, whereas the Ras-MAP kinase pathway does not appear to be involved. Moreover, astrocyte growth and EGF-dependent chemoattraction were inhibited by the mTOR-selective drug rapamycin. We also detected elevated levels of activated EGF receptor and mTOR signaling in reactive astrocytes in vivo in an ischemic model of spinal cord injury. Furthermore, increased Rheb expression likely contributes to mTOR activation in the injured spinal cord. Interestingly, injured rats treated with rapamycin showed reduced signs of reactive gliosis, suggesting that rapamycin could be used to harness astrocytic responses in the damaged nervous system to promote an environment more permissive to axon regeneration.

G protein-coupled receptor-induced Akt activity in cellular proliferation and apoptosis

Akt (also known as protein kinase B) plays an integral role in many intracellular signaling pathways activated by a diverse array of extracellular signals that target several different classes of membrane-bound receptors. Akt plays a particularly prominent part in signaling networks that result in the modulation of cellular proliferation, apoptosis and survival. Thus, the overexpression of Akt subtypes has been measured in a number of cancer types, and dominant-negative forms of Akt can trigger apoptosis and reduce the survival of cancer cells. G protein-coupled receptors act as cell-surface detectors for a diverse spectrum of biological signals and are able to activate or inhibit Akt via several direct and indirect means. In this review, we shall document how G protein-coupled receptors are able to control Akt activity and examine the resulting biochemical and physiological changes, with particular emphasis on cellular proliferation, apoptosis and survival.