RET/Papillary Thyroid Carcinoma Oncogenic Signaling through the Rap1 Small GTPase

Falco, Valentina De; Castellone, Maria Domenica; Vita, Gabriella De; Cirafici, Anna Maria; Hershman, Jerome M.; Guerrero, Carmen; Fusco, Alfredo; Melillo, Rosa Marina; Santoro, Massimo

doi:10.1158/0008-5472.can-06-0981

Cited by 54 publications

(40 citation statements)

References 42 publications

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“…PKAindependent Epac activation of Rap1 by cAMP has been reported in other thyroid cells (20,(22)(23)(24)29). Surprisingly, in primary dog thyrocyte, apart from Rap1 activation, Epac action played no apparent role in any aspect of cAMP biology, including mitogenesis (30).…”

Section: Discussionmentioning

confidence: 97%

Epac, in Synergy with cAMP-dependent Protein Kinase (PKA), Is Required for cAMP-mediated Mitogenesis

Hochbaum

Hong

Barila

et al. 2008

Journal of Biological Chemistry

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cAMP stimulates proliferation in many cell types. For many years, cAMP-dependent protein kinase (PKA) represented the only known cAMP effector. PKA, however, does not fully mimic the action of cAMP, indicating the existence of a PKA-independent component. Since cAMP-mediated activation of the G-protein Rap1 and its phosphorylation by PKA are strictly required for the effects of cAMP on mitogenesis, we hypothesized that the Rap1 activator Epac might represent the PKAindependent factor. Here we report that Epac acts synergistically with PKA in cAMP-mediated mitogenesis. We have generated a new dominant negative Epac mutant that revealed that activation of Epac is required for thyroid-stimulating hormone or cAMP stimulation of DNA synthesis. We demonstrate that Epac's action on cAMP-mediated activation of Rap1 and cAMP-mediated mitogenesis depends on the subcellular localization of Epac via its DEP domain. Disruption of the DEP-dependent subcellular targeting of Epac abolished cAMP-Epac-mediated Rap1 activation and thyroid-stimulating hormone-mediated cell proliferation, indicating that an Epac-Rap-PKA signaling unit is critical for the mitogenic action of cAMP.cAMP stimulates proliferation in several model systems (1). Particularly in endocrine cells, in vitro and in vivo studies demonstrated a role for cAMP in mitogenesis (2), a concept further supported by the identification of mutant receptors and G-proteins causally linking constitutive cAMP signaling with hyperproliferative states (3, 4). For many years, PKA 2 represented the only known cAMP effector (5); however, although its activity is necessary, it is not sufficient for cAMP mitogenic action (6, 7). These studies indicated the existence of PKA independent effectors involved in cAMP-mediated proliferation.Epac (exchange protein activated by cAMP) is a new cAMPdependent, PKA-independent guanine nucleotide-exchange factor (GEF) for the small G-protein Rap (8,9). Newly developed cAMP analogs (10) capable of discriminating between Epac and PKA are starting to unravel Epac's role in diverse biological responses (11, 12). Epac's N-terminal regulatory domain includes a DEP module (Disheveled, Egl10, Pleckstrin) responsible for its membrane localization (13) and a cAMPbinding domain (CBD) that directly binds cAMP (K d ϳ 4 M) (13). The catalytic domain consists of a Ras exchange motif (REM), and the CDC25-like catalytic core, sufficient for GEF action (8). Biochemical (13-16) and crystallographic studies (17) unmasked a role for the regulatory domain in maintaining Epac in a basal autoinhibited state; deletion of its N terminus converted REM-cdc25-Epac to a constitutively active (cAMPindependent) Rap GEF. The addition of the N terminus in trans to the active C terminus was able to inhibit its GEF activity, and this inhibition could be relieved by cAMP. Mutation analysis indicated a role for the N terminus sequence 321 VLVLE 325 (as in Epac1) as part of this inhibitory domain, and accordingly, disruption of this domain by conversion of this sequence to 321 AAAAA 325...

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Section: Discussionmentioning

confidence: 97%

Epac, in Synergy with cAMP-dependent Protein Kinase (PKA), Is Required for cAMP-mediated Mitogenesis

Hochbaum

Hong

Barila

et al. 2008

Journal of Biological Chemistry

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“…Rap1, a member of the RAS family of small GTPases, has been implicated in the regulation of mitogenic and oncogenic pathways in thyroid (7)(8)(9), and biochemical studies showed its role in regulating the ERK cascade and specifically its requirement for the RET/PTC-induced activation of BRAF-MEK-ERK (9)(10)(11). Like other small GTPases, Rap1 functions as a molecular switch, which cycles between an inactive GDP-bound and active GTP-bound form.…”

Section: Introductionmentioning

confidence: 99%

Downregulation of Rap1GAP through Epigenetic Silencing and Loss of Heterozygosity Promotes Invasion and Progression of Thyroid Tumors

Zuo

Gandhi²,

Edreira³

et al. 2010

Cancer Research

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Thyroid cancer is the most common type of endocrine malignancy, encompassing tumors with various levels of invasive growth and aggressiveness. Rap1GAP, a Rap1 GTPase-activating protein, inhibits the RAS superfamily protein Rap1 by facilitating hydrolysis of GTP to GDP. In this study, we analyzed 197 thyroid tumor samples and showed that Rap1GAP was frequently lost or downregulated in various types of tumors, particularly in the most invasive and aggressive forms of thyroid cancer. The downregulation was due to promoter hypermethylation and/or loss of heterozygosity, found in the majority of thyroid tumors. Treatment with demethylating agent 5-aza-deoxycytidine and/or histone deacetylation inhibitor trichostatin A induced gene reexpression in thyroid cells. A genetic polymorphism, Y609C, was seen in 7% of thyroid tumors but was not related to gene downregulation. Loss of Rap1GAP expression correlated with tumor invasiveness but not with specific mutations activating the mitogen-activated protein kinase pathway. Rap1GAP downregulation was required in vitro for cell migration and Matrigel invasion. Recovery of Rap1GAP expression inhibited thyroid cell proliferation and colony formation. Overall, our findings indicate that epigenetic or genetic loss of Rap1GAP is very common in thyroid cancer, where these events are sufficient to promote cell proliferation and invasion. Cancer Res; 70(4); 1389-97. ©2010 AACR.

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“…1A, the PI3K inhibitor LY294002 (LY) or the MEK1/2 inhibitor U0126 (U0) did not disrupt early transcriptional induction of MCP1 or IL6 by RP3. As a control for protein expression, RP3 K284M , which is devoid of all kinase activity (37,38), was examined and demonstrated no increase in AKT, ERK, or proinflammatory cytokine activity. Furthermore, RP3-transfected cells treated with LY or U0 and cells transfected with RP3 K284M exhibited less cell scattering, indicative of increased cell mobilization and less transformation when phenotypically compared with cells transfected with RP3…”

Section: Resultsmentioning

confidence: 99%

Identification of Functionally Distinct TRAF Proinflammatory and Phosphatidylinositol 3-Kinase/Mitogen-activated Protein Kinase/Extracellular Signal-regulated Kinase Kinase (PI3K/MEK) Transforming Activities Emanating from RET/PTC Fusion Oncoprotein

Wixted

Rothstein

Eisenlohr

2012

Journal of Biological Chemistry

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Background: Follicular cell-derived thyroid carcinomas harboring RET/PTC oncoproteins are immunostimulatory and highly curable, despite activating RAS/BRAF/MEK/ERK and PI3K/AKT. Results: RET/PTC oncoproteins associate with TRAFs to mediate cytokine production but not transformation. Conclusion:The RET/PTC-TRAF pathway is functionally separable from the RET/PTC-induced MEK/ERK and PI3K/AKT pathways. Significance: Understanding RET/PTC-mediated immunostimulation could provide new strategies for treating more aggressive forms of thyroid carcinoma.

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RET/Papillary Thyroid Carcinoma Oncogenic Signaling through the Rap1 Small GTPase

Cited by 54 publications

References 42 publications

Epac, in Synergy with cAMP-dependent Protein Kinase (PKA), Is Required for cAMP-mediated Mitogenesis

Epac, in Synergy with cAMP-dependent Protein Kinase (PKA), Is Required for cAMP-mediated Mitogenesis

Downregulation of Rap1GAP through Epigenetic Silencing and Loss of Heterozygosity Promotes Invasion and Progression of Thyroid Tumors

Identification of Functionally Distinct TRAF Proinflammatory and Phosphatidylinositol 3-Kinase/Mitogen-activated Protein Kinase/Extracellular Signal-regulated Kinase Kinase (PI3K/MEK) Transforming Activities Emanating from RET/PTC Fusion Oncoprotein

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