Thyroid tumors represent the most common endocrine malignancy in humans. Thyrocyte-derived tumors present as distinct types (follicular adenoma, papillary, follicular and anaplastic carcinoma, and their variants) and it is not clear how they can be generated from a single terminally differentiated cell type, or whether they have a monoclonal or polyclonal origin. Our recent identification of thyroid stem cells and an in vitro characterization of the stem-thyrocyte differentiation program will allow us to address whether thyroid tumors originate by de-differentiation of a terminal thyrocyte or from stem/progenitor cells with some self-renewal properties. TSH, via cAMP, is a key component in thyroid proliferation, involving both PKA-dependent and independent events;however, the main effectors of TSH-cAMP action still remain elusive. Agonists that increase intracellular cAMP are able to rapidly phosphorylate and activate Rap1b, and we have recently shown that the Rap-GEF Epac, in synergy with PKA, is required for TSH-dependent mitogenesis. Consistent with this, constitutively active G12V-Rap1b expression in the thyroid gland triggered a goitrogen (i.e. TSH-cAMP)- dependent tumorigenic phenotype. Increasing evidence supports an active role for bone-marrow and inflammation in tumorigenesis; specifically in the thyroid model we have recently demonstrated the presence of extrathyroideal cells that are recruited upon goitrogenesis. Among them, a population of Sca1+ stem cells was recently identified. Since Rap1 is known to modulate the release of proinflammatory and chemoattractant factors in several cell types, and it was recently demonstrated to be critical for the TPA-mediated inflammatory phase in skin carcinogenesis, we hypothesized that goitrogenic treatment triggers in the thyroid an inflammatory-like response mediated by the Rap1-dependent recruitment of extrathyroideal cells required for the process of tumorigenesis. We have developed a novel reporter line amenable for clonality determination and lineage tracing studies. The system relies on its ability to generate a random biallelic distribution, red or green fluorescence, utilizing the CRE/Lox technology. The ability to irreversibly tag specific cell types allows for lineage-tracing experiments to monitor recruitment/homing of fluorescently red-labeled cells into a green fluorescent compartment. This new line will be exploited in this proposal to assess the above-mentioned unresolved issues related to tumor clonality and the potential role of bone-marrow derived cells in the process of thyroid tumorigenesis. Successful completion of the proposed studies will provide new mechanisms involved in the process of goitrogenesis.

Public Health Relevance

Thyroid tumors are the most common endocrine malignancies in humans. Thyroid nodular transformation is a hallmark of thyroid goitrogenesis. Almost 20% of the population (with prevalence in women) will present thyroid nodules during their lifetime. However, the mechanisms involved are unknown. Originally thought as a cumulative process of mutations targeting the terminally differentiated thyroid cells, current models proposed that thyroid transformation is a stem-cell disease. These two alternative models have distinct predictions, if appropriate models could be developed. We have developed a novel strategy to address some of these issues that should provide new mechanistic aspects of the complex process of tumorigenesis.

Agency
National Institute of Health (NIH)
Institute
National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK)
Type
Research Project (R01)
Project #
5R01DK063069-08
Application #
8284469
Study Section
Molecular and Cellular Endocrinology Study Section (MCE)
Program Officer
Malozowski, Saul N
Project Start
2002-12-01
Project End
2014-06-30
Budget Start
2012-07-01
Budget End
2014-06-30
Support Year
8
Fiscal Year
2012
Total Cost
$322,956
Indirect Cost
$109,784
Name
University of Pittsburgh
Department
Pharmacology
Type
Schools of Medicine
DUNS #
004514360
City
Pittsburgh
State
PA
Country
United States
Zip Code
15213
Kelly, Lindsey M; Barila, Guillermo; Liu, Pengyuan et al. (2014) Identification of the transforming STRN-ALK fusion as a potential therapeutic target in the aggressive forms of thyroid cancer. Proc Natl Acad Sci U S A 111:4233-8
Zuo, Hui; Gandhi, Manoj; Edreira, Martin M et al. (2010) Downregulation of Rap1GAP through epigenetic silencing and loss of heterozygosity promotes invasion and progression of thyroid tumors. Cancer Res 70:1389-97
Edreira, Martin M; Li, Sheng; Hochbaum, Daniel et al. (2009) Phosphorylation-induced conformational changes in Rap1b: allosteric effects on switch domains and effector loop. J Biol Chem 284:27480-6
Ribeiro-Neto, Fernando; Leon, Angelica; Urbani-Brocard, Julie et al. (2004) cAMP-dependent oncogenic action of Rap1b in the thyroid gland. J Biol Chem 279:46868-75