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HMGA1 Inhibits the Function of p53 Family Members in Thyroid Cancer Cells

¹ Endocrinologia, Dipartimento di Medicina Interna, e Medicina Specialistica, Ospedale Garibaldi; ² Dipartimento di Scienze Biomediche, Istituto di Patologia Generale; ³ Dipartimento di Medicina Interna, e Medicina Specialistica, Servizio di Diabetologia, Ospedale Cannizzaro, Catania, Italy; ⁴ Dipartimento di Biochimica, Biofisica e Chimica delle Macromolecole, Università di Trieste; and ⁵ Laboratorio Nazionale CIB, Area Science Park, Trieste, Italy

Requests for reprints: Guidalberto Manfioletti, Dipartimento di Biochimica, Biofisica e Chimica delle Macromolecole, via Giorgieri, 1, 34127 Trieste, Italy. Phone: 39-40-558-3675; Fax: 39-40-558-3694; E-mail: manfiole{at}univ.trieste.it.

HMGA1 is an architectural transcription factor expressed at high levels in transformed cells and tumors. Several lines of evidence indicate that HMGA1 up-regulation is involved in the malignant transformation of thyroid epithelial cells. However, the mechanisms underlying the effect of HMGA1 on thyroid cancer cell phenotype are not fully understood. We now show that in thyroid cancer cells, HMGA1 down-regulation by small interfering RNA and antisense techniques results in enhanced transcriptional activity of p53, TAp63, TAp73, and, consequently, increased apoptosis. Coimmunoprecipitation and pull-down experiments with deletion mutants showed that the COOH-terminal oligomerization domain of p53 family members is required for direct interaction with HMGA1. Moreover, inhibition of HMGA1 expression in thyroid cancer cells resulted in increased p53 oligomerization in response to the DNA-damaging agent doxorubicin. Finally, electrophoretic mobility shift assay experiments showed that the p53-HMGA1 interaction results in reduced DNA-binding activity. These results indicate a new function of HMGA1 in the regulation of p53 family members, thus providing new mechanistic insights in tumor progression. (Cancer Res 2006; 66(6): 2980-89)

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