HOX genes promote cell proliferation and are potential therapeutic targets in adrenocortical tumours

Background

Understanding the pathways that drive adrenocortical carcinoma (ACC) is essential to the development of more effective therapies. This study investigates the role of the transcription factor HOXB9 and other HOX factors in ACC and its treatment.

Methods

We used transgenic mouse models to determine the role of Hoxb9 in adrenal tumour development. Patient transcriptomic data was analysed for the expression of HOX genes and their association with disease. Drug response studies on various adrenocortical models were done to establish novel therapeutic options.

Results

Our human ACC dataset analyses showed high expression of HOXB9, and other HOX factors, are associated with poorer prognosis. Transgenic overexpression of Hoxb9 in the adrenal cortex of mice with activated Ctnnb1 led to larger adrenal tumours. This phenotype was preferentially observed in male mice and was characterised by more proliferating cells and an increase in the expression of cell cycle genes, including Ccne1. Adrenal tumour cells were found to be dependent on HOX function for survival and were sensitive to a specific peptide inhibitor.

Conclusions

These studies show Hoxb9 can promote adrenal tumour progression in a sex-dependent manner and have identified HOX factors as potential drug targets, leading to novel therapeutic approaches in ACC.

Pten Regulates Epithelial Cytodifferentiation during Prostate Development

Gene expression and functional studies have indicated that the molecular programmes involved in prostate development are also active in prostate cancer. PTEN has been implicated in human prostate cancer and is frequently mutated in this disease. Here, using the Nkx3.1:Cre mouse strain and a genetic deletion approach, we investigate the role of Pten specifically in the developing mouse prostate epithelia. In contrast to its role in other developing organs, this gene is dispensable for the initial developmental processes such as budding and branching. However, as cytodifferentiation progresses, abnormal luminal cells fill the ductal lumens together with augmented epithelial proliferation. This phenotype resembles the hyperplasia seen in postnatal Pten deletion models that develop neoplasia at later stages. Consistent with this, gene expression analysis showed a number of genes affected that are shared with Pten mutant prostate cancer models, including a decrease in androgen receptor regulated genes. In depth analysis of the phenotype of these mice during development revealed that loss of Pten leads to the precocious differentiation of epithelial cells towards a luminal cell fate. This study provides novel insight into the role of Pten in prostate development as part of the process of coordinating the differentiation and proliferation of cell types in time and space to form a functional organ.

In vivo evidence for the crucial role of SF1 in steroid-producing cells of the testis, ovary and adrenal gland

Adrenal and gonadal steroids are essential for life and reproduction. The orphan nuclear receptor SF1 (NR5A1) has been shown to regulate the expression of enzymes involved in steroid production in vitro. However, the in vivo role of this transcription factor in steroidogenesis has not been elucidated. In this study, we have generated steroidogenic-specific Cre-expressing mice to lineage mark and delete Sf1 in differentiated steroid-producing cells of the testis, the ovary and the adrenal gland. Our data show that SF1 is a regulator of the expression of steroidogenic genes in all three organs. In addition, Sf1 deletion leads to a radical change in cell morphology and loss of identity. Surprisingly, sexual development and reproduction in mutant animals were not compromised owing, in part, to the presence of a small proportion of SF1-positive cells. In contrast to the testis and ovary, the mutant adult adrenal gland showed a lack of Sf1-deleted cells and our studies suggest that steroidogenic adrenal cells during foetal stages require Sf1 to give rise to the adult adrenal population. This study is the first to show the in vivo requirements of SF1 in steroidogenesis and provides novel data on the cellular consequences of the loss of this protein specifically within steroid-producing cells.

Localised inhibition of FGF signalling in the third pharyngeal pouch is required for normal thymus and parathyroid organogenesis

The thymus and parathyroid glands are derived from the third pharyngeal pouch endoderm. The mechanisms that establish distinct molecular domains in the third pouch and control the subsequent separation of these organ primordia from the pharynx are poorly understood. Here, we report that mouse embryos that lack two FGF feedback antagonists, Spry1 and Spry2, display parathyroid and thymus hypoplasia and a failure of these organ primordia to completely separate from the pharynx. We show that FGF ligands and downstream reporter genes are expressed in highly regionalised patterns in the third pouch and that sprouty gene deletion results in upregulated FGF signalling throughout the pouch endoderm. As a consequence, the initiation of markers of parathyroid and thymus fate is altered. In addition, a normal apoptotic programme that is associated with the separation of the primordia from the pharynx is disrupted, resulting in the maintenance of a thymus-pharynx attachment and a subsequent inability of the thymus to migrate to its appropriate position above the heart. We demonstrate that the sprouty genes function in the pharyngeal endoderm itself to control these processes and that the defects in sprouty-deficient mutants are, at least in part, due to hyper-responsiveness to Fgf8. Finally, we provide evidence to suggest that parathyroid hypoplasia in these mutants is due to early gene expression defects in the third pouch, whereas thymus hypoplasia is caused by reduced proliferation of thymic epithelial cells in the thymus primordium.

Sprouty1 is a candidate tumor-suppressor gene in medullary thyroid carcinoma

Medullary thyroid carcinoma (MTC) is a malignancy derived from the calcitonin-producing C-cells of the thyroid gland. Oncogenic mutations of the Ret proto-oncogene are found in all heritable forms of MTC and roughly one half of the sporadic cases. However, several lines of evidence argue for the existence of additional genetic lesions necessary for the development of MTC. Sprouty (Spry) family of genes is composed of four members in mammals (Spry1-4). Some Spry family members have been proposed as candidate tumor-suppressor genes in a variety of cancerous pathologies. In this work, we show that targeted deletion of Spry1 causes C-cell hyperplasia, a precancerous lesion preceding MTC, in young adult mice. Expression of Spry1 restrains proliferation of the MTC-derived cell line, TT. Finally, we found that the Spry1 promoter is frequently methylated in MTC and that Spry1 expression is consequently decreased. These findings identify Spry1 as a candidate tumor-suppressor gene in MTC.

Biallelic expression of Tbx1 protects the embryo from developmental defects caused by increased receptor tyrosine kinase signaling

BACKGROUND

22q11.2 deletion syndrome (22q11DS) is the most common microdeletion syndrome in humans, characterized by cardiovascular defects such as interrupted aortic arch, outflow tract defects, thymus and parathyroid hypo- or aplasia, and cleft palate. Heterozygosity of Tbx1, the mouse homolog of the candidate TBX1 gene, results in mild defects dependent on genetic background, whereas complete inactivation results in severe malformations in multiple tissues.

RESULTS

The loss of function of two Sprouty genes, which encode feedback antagonists of receptor tyrosine kinase (RTK) signaling, phenocopy many defects associated with 22q11DS in the mouse. The stepwise reduction of Sprouty gene dosage resulted in different phenotypes emerging at specific steps, suggesting that the threshold up to which a given developmental process can tolerate increased RTK signaling is different. Tbx1 heterozygosity significantly exacerbated the severity of all these defects, which correlated with a substantial increase in RTK signaling.

CONCLUSIONS

Our findings suggest that TBX1 functions as an essential component of a mechanism that protects the embryo against perturbations in RTK signaling that may lead to developmental defects characteristic of 22q11DS. We propose that genetic factors that enhance RTK signaling ought to be considered as potential genetic modifiers of this syndrome.

SF-1 expression during adrenal development and tumourigenesis

SF-1 is a master regulator of steroidogenesis whose expression is critical for normal adrenal and gonadal organogenesis. Strict maintenance of SF-1 levels is essential, and mutations causing under- or overexpression result in congenital adrenal and gonadal defects or hyperplasia, respectively. Data from transgenic mouse models points to a network of transcription factors responsible for stringent regulation of Sf-1 expression during development, which bind to intronic enhancer elements in addition to the basal promoter to specifically modulate transcription in each Sf-1-expressing tissue. Furthermore, analysis of the role of SF-1 in adrenal tumourigenesis implies that improper developmental regulation of Sf-1 expression may have postnatal consequences separate from the well-documented developmental defects.