The Sonic hedgehog (Shh) pathway plays a critical role in hair follicle physiology and is constitutively active in basal cell carcinomas (BCCs), the most common human malignancy. Type 3 iodothyronine deiodinase (D3), the thyroid hormone-inactivating enzyme, is frequently expressed in proliferating and neoplastic cells, but its role in this context is unknown. Here we show that Shh, through Gli2, directly induces D3 in proliferating keratinocytes and in mouse and human BCCs. We demonstrate that Gli-induced D3 reduces intracellular active thyroid hormone, thus resulting in increased cyclin D1 and keratinocyte proliferation. D3 knockdown caused a 5-fold reduction in the growth of BCC xenografts in nude mice. Shh-induced thyroid hormone degradation via D3 synergizes with the Shh-mediated reduction of the type 2 deiodinase, the thyroxine-activating enzyme, and both effects are reversed by cAMP. This previously unrecognized functional cross-talk between Shh/Gli2 and thyroid hormone in keratinocytes is a pathway by which Shh produces its proliferative effects and offers a potential therapeutic approach to BCC.basal cell carcinoma ͉ thyroxine ͉ differentiation ͉ cancer T hyroid hormone action is regulated by the activity of the deiodinases. Type 2 deiodinase (D2) activates the prohormone thyroxine (T4) by converting it to thyroid hormone (T3), whereas D3, by inactivating T3, terminates thyroid hormone action (1). All vertebrates express D2 and D3 that, in adults, contribute to plasma T3 and T4 homeostasis by their concerted actions with the hypothalamic-pituitary feedback axis. This homeostatic mechanism is possible because the Dio3 gene is transcriptionally stimulated by T3, whereas D2 is inhibited by two thyroid hormone-mediated effects, a transcriptional downregulation of Dio2 as well as protein inactivation by ubiquitination (for review, see ref.2). During development, preprogrammed changes in D2 and D3 expression are thought to regulate intracellular T3 concentrations essential to the normal development of the central nervous system, including the retina and the inner ear (3-6). However, the signals governing the changes in D2 and D3 expression during these complex processes are largely unknown.New insight into the developmental regulation of deiodinase expression has recently been obtained in the chicken growth plate, where Indian hedgehog induces WSB-1, an E3 ubiquitin ligase adaptor that inactivates D2 (7). The hedgehog pathway, acting through the Gli family of transcription factors, determines patterns of cell growth and differentiation in a wide variety of developmental settings (8-13). Given that, in general, signals regulating D2 expression affect D3 in a reciprocal fashion (2), we hypothesized that hedgehog proteins could up-regulate D3 while suppressing D2 expression. To explore this possibility, we turned to skin, a system in which Sonic hedgehog (Shh) is known to play dominant physiological as well as pathological roles (14). Both D2 and D3 are present in skin, a well recognized target of thyroid hormone...

The sodium/iodide symporter (NIS) is a plasma membrane protein that mediates active iodide transport in thyroid and mammary cells. It is a prerequisite for radioiodide treatment of thyroid cancer and a promising diagnostic and therapeutic tool for breast cancer. We investigated the molecular mechanisms governing NIS expression in mammary cells. Here we report that Nkx-2.5, a cardiac homeobox transcription factor that is also expressed in the thyroid primordium, is a potent inducer of the NIS promoter. By binding to two specific promoter sites (N2 and W), Nkx-2.5 induced the rNIS promoter (about 50-fold over the basal level). Interestingly, coincident with NIS expression, Nkx-2.5 mRNA and protein were present in lactating, but not virgin, mammary glands in two human breast cancer samples and in all-trans retinoic acid (tRA)-stimulated MCF-7 breast cancer cells. A cotransfected dominant-negative Nkx-2.5 mutant abolished tRA-induced endogenous NIS induction, which shows that Nkx-2.5 activity is critical for this process. Remarkably, in MCF-7 cells, Nkx-2.5 overexpression alone was sufficient to induce NIS and iodide uptake. In conclusion, Nkx-2.5 is a novel relevant transcriptional regulator of mammary NIS and could thus be exploited to manipulate NIS expression in breast cancer treatment strategies.

Thyroid transcription factor gene 1 (TTF-1) is a homeobox-containing gene involved in thyroid organogenesis. During early thyroid development, the homeobox gene Nkx-2.5 is expressed in thyroid precursor cells coincident with the appearance of TTF-1. The aim of this study was to investigate the molecular mechanisms underlying thyroid-specific gene expression. We show that the Nkx-2.5 C terminus interacts with the TTF-1 homeodomain and, moreover, that the expression of a dominant-negative Nkx-2.5 isoform (N188K) in thyroid cells reduces TTF-1-driven transcription by titrating TTF-1 away from its target DNA. This process reduced the expression of several thyroid-specific genes, including pendrin and thyroglobulin. Similarly, down-regulation of TTF-1 by RNA interference reduced the expression of both genes, whose promoters are sensitive to and directly associate with TTF-1 in the chromatin context. In conclusion, we demonstrate that pendrin and thyroglobulin are downstream targets in vivo of TTF-1, whose action is a prime factor in controlling thyroid differentiation in vivo.

The use of recombinant human PTH (1-84) [rhPTH(1-84)] is approved as hormonal replacement therapy in patients with hypoparathyroidism not adequately controlled with conventional therapy. The objective of this study was to investigate the effects of 12 months of rhPTH (1-84) treatment in a cohort of patients selected according to the indications of recent hypoparathyroidism guidelines. It is a multicenter, observational, retro-prospective, open label study. Eleven Italian Endocrinological centers were involved. Fourteen adult subjects with chronic hypoparathyroidism treated with rhPTH (1-84) for 12 months were enrolled. Main outcome measures included serum and urinary parameters of mineral metabolism, renal function, oral calcium and vitamin D doses, and clinical manifestations. At 12 months, 61.5% of patients discontinued calcium supplement and 69.2% calcitriol. Mean serum calcium levels quickly normalized after initiation of rhPTH (1-84) treatment compared to baseline (p=0.009). Rare hypo-hypercalcemia episodes were reported. Renal function was maintained normal and no renal complications were reported. Serum and urinary phosphate and urinary calcium were maintained in the normal range. Mean phosphatemia levels linearly decreased from 3 months up to 12 months compared to baseline (p= 0.014). No severe adverse events were described. In conclusion, this study confirm the efficacy and safety of rhPTH (1-84) therapy.