Simultaneous downregulation of CDK inhibitors p18(Ink4c) and p27(Kip1) is required for MEN2A-RET-mediated mitogenesis

A Proposed Grading Scheme for Medullary Thyroid Carcinoma Based on Proliferative Activity (Ki-67 and Mitotic Count) and Coagulative Necrosis

We investigated the prognostic value of a range of histologic parameters in medullary thyroid carcinoma (MTC) to design a grading system to predict overall survival. We assessed 76 patients with MTCs undergoing primary tumor resection for age, sex, tumor size, vascular space invasion, lymph node metastasis, multiple endocrine neoplasia type 2 (MEN2) status, mitotic count, Ki-67 proliferative index, spindled morphology, sheet-like growth pattern, coagulative necrosis, incipient necrosis, nuclear grade, multinucleation, prominent nucleoli, fibrosis, and amyloid deposition. In addition to the clinical features of age and the diagnosis of MEN2, the only histologic features that significantly predicted reduced overall survival were Ki-67 proliferative index, mitotic count, and the presence of coagulative necrosis. Using a combination of these 3 variables, we propose a 3-tiered grading system based solely on proliferative activity (Ki-67 proliferative index and mitotic count) and necrosis. There were 62 (82%) low-grade MTCs (low proliferative activity, no necrosis), 9 (12%) intermediate grade (low proliferative activity and necrosis present, or intermediate proliferative activity and no necrosis), and 5 (7%) high grade (intermediate proliferative activity and necrosis present, or high proliferative activity with or without necrosis). The mean overall survival was 193, 146, and 45 months, respectively (P=0.0001) for the 3 grades. The grading system remained prognostic when controlled for other factors associated with survival including age and known MEN2 syndrome. We conclude that this proposed grading system, which uses only a combination of proliferative activity (Ki-67 index, mitotic count) and coagulative necrosis, is a strong predictor of overall survival in MTC.

Characterization of neuroendocrine tumors in heterozygous mutant MENX rats: a novel model of invasive medullary thyroid carcinoma

Rats affected by the MENX syndrome spontaneously develop multiple neuroendocrine tumors (NETs) including adrenal, pituitary and thyroid gland neoplasms. MENX was initially reported to be inherited as a recessive trait and affected rats were found to be homozygous for the predisposing Cdkn1b mutation encoding p27. We here report that heterozygous MENX-mutant rats (p27+/mut) develop the same spectrum of NETs seen in the homozygous (p27mut/mut) animals but with slower progression. Consequently, p27+/mut rats have a significantly shorter lifespan compared with their wild-type (p27+/+) littermates. In the tumors of p27+/mut rats, the wild-type Cdkn1b allele is neither lost nor silenced, implying that p27 is haploinsufficient for tumor suppression in this model. Transcriptome profiling of rat adrenal (pheochromocytoma) and pituitary tumors having different p27 dosages revealed a tissue-specific, dose-dependent effect of p27 on gene expression. In p27+/mut rats, thyroid neoplasms progress to invasive and metastatic medullary thyroid carcinomas (MTCs) accompanied by increased calcitonin levels, as in humans. Comparison of expression signatures of late-stage vs early-stage MTCs from p27+/mut rats identified genes potentially involved in tumor aggressiveness. The expression of a subset of these genes was evaluated in human MTCs and found to be associated with aggressive RET-M918T-positive tumors. Altogether, p27 haploinsufficiency in MENX rats uncovered a novel, representative model of invasive and metastatic MTC exploitable for translational studies of this often aggressive and incurable cancer.

Signaling pathways in medullary thyroid carcinoma: therapeutic implications

Medullary thyroid cancer (MTC) is the third most frequent thyroid cancer arising from thyroid parafollicular cells. Surgery is the first-line strategy in treatment of MTC but disease relapse and patient's death have been observed in approximately two out of three of MTC cases. Identification of molecular mechanisms and different signaling pathways has offered new insights for disease treatment. The development of tyrosine kinase inhibitors targeting these pathways has provided a promising landscape for prevention of progression in patients with advanced metastatic MTC. In this review article different altered molecular pathways implicated in the development of MTC and the therapeutic strategies based on targeting the identified signaling pathways have been summarized.

Differential expression of cell cycle regulators in CDK5-dependent medullary thyroid carcinoma tumorigenesis

Medullary thyroid carcinoma (MTC) is a neuroendocrine cancer of thyroid C-cells, for which few treatment options are available. We have recently reported a role for cyclin-dependent kinase 5 (CDK5) in MTC pathogenesis. We have generated a mouse model, in which MTC proliferation is induced upon conditional overexpression of the CDK5 activator, p25, in C-cells, and arrested by interrupting p25 overexpression. Here, we identify genes and proteins that are differentially expressed in proliferating versus arrested benign mouse MTC. We find that downstream target genes of the tumor suppressor, retinoblastoma protein, including genes encoding cell cycle regulators such as CDKs, cyclins and CDK inhibitors, are significantly upregulated in malignant mouse tumors in a CDK5-dependent manner. Reducing CDK5 activity in human MTC cells down-regulated these cell cycle regulators suggesting that CDK5 activity is critical for cell cycle progression and MTC proliferation. Finally, the same set of cell cycle proteins was consistently overexpressed in human sporadic MTC but not in hereditary MTC. Together these findings suggest that aberrant CDK5 activity precedes cell cycle initiation and thus may function as a tumor-promoting factor facilitating cell cycle protein expression in MTC. Targeting aberrant CDK5 or its downstream effectors may be a strategy to halt MTC tumorigenesis.

New Insights Into the Mechanism of COP9 Signalosome-Cullin-RING Ubiquitin-Ligase Pathway Deregulation in Urological Cancers

Urological cancers are a very common type of cancer worldwide and have alarming high incidence and mortality rates, especially in kidney cancers, illustrate the urgent need for new therapeutic targets. Recent publications point to a deregulated COP9 signalosome (CSN)-cullin-RING ubiquitin-ligase (CRL) pathway which is here considered and investigated as potential target in urological cancers with strong focus on renal cell carcinomas (RCC). The CSN forms supercomplexes with CRLs in order to preserve protein homeostasis and was found deregulated in several cancer types. Examination of selected CSN-CRL pathway components in RCC patient samples and four RCC cell lines revealed an interesting deregulated p27(Kip1)-Skp2-CAND1 axis and two p27(Kip1) point mutations in 786-O cells; p27(Kip1)V109G and p27(Kip1)I119T. The p27(Kip1) mutants were detected in patients with RCC and appear to be responsible for an accelerated growth rate in 786-O cells. The occurrence of p27(Kip1)V109G and p27(Kip1)I119T in RCC makes the CSN-CRL pathway an attractive therapeutic target.

Polymorphisms of cell cycle control genes influence the development of sporadic medullary thyroid carcinoma

BACKGROUND

The role of key cell cycle regulation genes such as, CDKN1B, CDKN2A, CDKN2B, and CDKN2C in sporadic medullary thyroid carcinoma (s-MTC) is still largely unknown.

METHODS

In order to evaluate the influence of inherited polymorphisms of these genes on the pathogenesis of s-MTC, we used TaqMan SNP genotyping to examine 45 s-MTC patients carefully matched with 98 controls.

RESULTS

A multivariate logistic regression analysis demonstrated that CDKN1B and CDKN2A genes were related to s-MTC susceptibility. The rs2066827*GT+GG CDKN1B genotype was more frequent in s-MTC patients (62.22%) than in controls (40.21%), increasing the susceptibility to s-MTC (OR=2.47; 95% CI=1.048-5.833; P=0.038). By contrast, the rs11515*CG+GG of CDKN2A gene was more frequent in the controls (32.65%) than in patients (15.56%), reducing the risk for s-MTC (OR=0.174; 95% CI=0.048-0.627; P=0.0075). A stepwise regression analysis indicated that two genotypes together could explain 11% of the total s-MTC risk. In addition, a relationship was found between disease progression and the presence of alterations in the CDKN1A (rs1801270), CDKN2C (rs12885), and CDKN2B (rs1063192) genes. WT rs1801270 CDKN1A patients presented extrathyroidal tumor extension more frequently (92%) than polymorphic CDKN1A rs1801270 patients (50%; P=0.0376). Patients with the WT CDKN2C gene (rs12885) presented larger tumors (2.9±1.8 cm) than polymorphic patients (1.5±0.7 cm; P=0.0324). On the other hand, patients with the polymorphic CDKN2B gene (rs1063192) presented distant metastases (36.3%; P=0.0261).

CONCLUSION

In summary, we demonstrated that CDKN1B and CDKN2A genes are associated with susceptibility, whereas the inherited genetic profile of CDKN1A, CDKN2B, and CDKN2C is associated with aggressive features of tumors. This study suggests that profiling cell cycle genes may help define the risk and characterize s-MTC aggressiveness.

Key roles for MYC, KIT and RET signaling in secondary angiosarcomas

Background:

Angiosarcomas may develop as primary tumours of unknown cause or as secondary tumours, most commonly following radiotherapy to the involved field. The different causative agents may be linked to alternate tumorigenesis, which led us to investigate the genetic profiles of morphologically indistinguishable primary and secondary angiosarcomas.

Methods:

Whole-genome (18k) c-DNA-mediated annealing, selection, extension and ligation analysis was used to genetically profile 26 primary and 29 secondary angiosarcomas. Key findings were thereafter validated using RT–qPCR, immunohistochemistry and validation of the gene signature to an external data set.

Results:

In total, 103 genes were significantly deregulated between primary and secondary angiosarcomas. Secondary angiosarcomas showed upregulation of MYC, KIT and RET and downregulation of CDKN2C. Functional annotation analysis identified multiple target genes in the receptor protein tyrosine kinase pathway. The results were validated using RT–qPCR and immunohistochemistry. Further, the gene signature was applied to an external data set and, herein, distinguished primary from secondary angiosarcomas.

Conclusions:

Upregulation of MYC, KIT and RET and downregulation of CDKN2C characterise secondary angiosarcoma, which implies possibilities for diagnostic application and a mechanistic basis for therapeutic evaluation of RET-kinase-inhibitors in these highly aggressive tumours.

Cell cycle regulation by long non-coding RNAs

The mammalian cell cycle is precisely controlled by cyclin-dependent kinases (CDKs) and related pathways such as the RB and p53 pathways. Recent research on long non-coding RNAs (lncRNAs) indicates that many lncRNAs are involved in the regulation of critical cell cycle regulators such as the cyclins, CDKs, CDK inhibitors, pRB, and p53. These lncRNAs act as epigenetic regulators, transcription factor regulators, post-transcription regulators, and protein scaffolds. These cell cycle-regulated lncRNAs mainly control cellular levels of cell cycle regulators via various mechanisms, and may provide diversity and reliability to the general cell cycle. Interestingly, several lncRNAs are induced by DNA damage and participate in cell cycle arrest or induction of apoptosis as DNA damage responses. Therefore, deregulations of these cell cycle regulatory lncRNAs may be involved in tumorigenesis, and they are novel candidate molecular targets for cancer therapy and diagnosis.

Cellular signaling pathway alterations and potential targeted therapies for medullary thyroid carcinoma

Parafollicular C-cell-derived medullary thyroid cancer (MTC) comprises 3% to 4% of all thyroid cancers. While cytotoxic treatments have been shown to have limited efficacy, targeted molecular therapies that inhibit rearranged during transfection (RET) and other tyrosine kinase receptors that are mainly involved in angiogenesis have shown great promise in the treatment of metastatic or locally advanced MTC. Multi-tyrosine kinase inhibitors such as vandetanib, which is already approved for the treatment of progressive MTC, and cabozantinib have shown distinct advantages with regard to rates of disease response and control. However, these types of tyrosine kinase inhibitor compounds are able to concurrently block several types of targets, which limits the understanding of RET as a specific target. Moreover, important resistances to tyrosine kinase inhibitors can occur, which limit the long-term efficacy of these treatments. Deregulated cellular signaling pathways and genetic alterations in MTC, particularly the activation of the RAS/mammalian target of rapamycin (mTOR) cascades and RET crosstalk signaling, are now emerging as novel and potentially promising therapeutic treatments for aggressive MTC.

Murine models and cell lines for the investigation of pheochromocytoma: applications for future therapies?

Pheochromocytomas (PCCs) are slow-growing neuroendocrine tumors arising from adrenal chromaffin cells. Tumors arising from extra-adrenal chromaffin cells are called paragangliomas. Metastases can occur up to approximately 60% or even more in specific subgroups of patients. There are still no well-established and clinically accepted "metastatic" markers available to determine whether a primary tumor is or will become malignant. Surgical resection is the most common treatment for non-metastatic PCCs, but no standard treatment/regimen is available for metastatic PCC. To investigate what kind of therapies are suitable for the treatment of metastatic PCC, animal models or cell lines are very useful. Over the last two decades, various mouse and rat models have been created presenting with PCC, which include models presenting tumors that are to a certain degree biochemically and/or molecularly similar to human PCC, and develop metastases. To be able to investigate which chemotherapeutic options could be useful for the treatment of metastatic PCC, cell lines such as mouse pheochromocytoma (MPC) and mouse tumor tissue (MTT) cells have been recently introduced and they both showed metastatic behavior. It appears these MPC and MTT cells are biochemically and molecularly similar to some human PCCs, are easily visualized by different imaging techniques, and respond to different therapies. These studies also indicate that some mouse models and both mouse PCC cell lines are suitable for testing new therapies for metastatic PCC.

Cyclin dependent kinase inhibitors differentially modulate synergistic cytokine responsiveness of hematopoietic progenitor cells

Cyclin dependent kinase inhibitors (CDKIs) influence proliferation of hematopoietic progenitor cells (HPCs), but little is known of how they influence proliferative responsiveness of HPCs to colony stimulating factors (CSFs), alone and in combination with other hematopoietically active factors, such as the potent co-stimulating cytokine stem cell factor (SCF), or inhibition by myelosuppressive chemokines. Using mice with deletions in p18(INK4c), p21(CIP1/WAF1), or p27(KIP1) genes, and in mice with double gene deletions for either p18/p21 or p18/p27, we determined effects of absence of these CDKIs and their interactions on functional HPC numbers in vivo, and HPC proliferative responsiveness in vitro. There is a decrease in bone marrow HPC proliferation in p18(-/-) mice commensurate with decreased numbers of HPC, suggesting a positive role for p18 on HPC in vivo, similar to that for p21. These positive effects of p18 dominate negative effects of p27 gene deletion. Moreover, the CDKIs differentially regulate responsiveness of granulocyte macrophage (GM) progenitors to synergistic cell proliferation in response to GM-CSF plus SCF, which is considered important for normal hematopoiesis. Responsiveness of HPCs to inhibition by myelosuppressive chemokines is directly related to the capacity of HPCs to respond to synergistic stimulation, and their cell cycle status. P18(INK4c) gene deletion rescued the loss of chemokine suppression of synergistic proliferation due to deletion of p21(CIP1/WAF1). These findings underscore the complex interplay of cell cycle regulators in HPC, and demonstrate that loss of one can sometimes be compensated by loss of another CDKI in both, a pro- or anti-proliferative context.

How to Treat a Signal? Current Basis for RET-Genotype-Oriented Choice of Kinase Inhibitors for the Treatment of Medullary Thyroid Cancer

The significance of RET in thyroid cancer comes from solid evidence that, when inherited, an RET activating mutation primes C-cells to transform into medullary carcinomas. Moreover, environmental exposure to radiation also induces rearranged transforming RET “isoforms” that are found in papillary thyroid cancer. The RET gene codes for a tyrosine kinase receptor that targets a diverse set of intracellular signaling pathways. The nature of RET point mutations predicts differences in the mechanisms by which the receptor becomes activated and correlates with different forms of clinical presentation, age of onset, and biological aggressiveness. A number of RET-targeting Tyrosine Kinase Inhibitors (TKIs) are currently undergoing clinical trials to evaluate their effectiveness in the treatment of thyroid cancer, and it is conceivable that the RET genotype may also influence response to these compounds. The question that now emerges is whether, in the future, the rational for treatment of refractory thyroid cancer will be based on the management of an abnormal RET signal. In this paper we address the RET-targeting TKIs and review studies about the signaling properties of distinct RET mutants as a means to predict response and design combinatorial therapies for the soon to be available TKIs.

p27kip1: a new multiple endocrine neoplasia gene?

Multiple endocrine neoplasias (MEN) are autosomal dominant disorders characterized by the occurrence of tumors in at least two endocrine glands. Two types of MEN syndromes have long been known: MEN type 1 (MEN1) and MEN type 2 (MEN2), associated with a different spectrum of affected organs. MEN1 and MEN2 are caused by germline mutations in the MEN1 tumor suppressor gene and the RET proto-oncogene, respectively. Lately, a new type of MEN was identified (named MEN4) which is due to mutations in the CDKN1B gene, encoding for p27kip1 (p27), a cyclin-dependent kinase (Cdk) inhibitor that regulates the transition of cells from G1 to S phase. p27 is a non-canonical tumor suppressor since it is usually not somatically mutated in human cancers but it is often downregulated by post-translational mechanisms. The discovery of MEN4 has defined a new role for CDKN1B as a tumor susceptibility gene for multiple endocrine tumors. To date, six germline CDKN1B mutations have been found in patients with a MEN1-like phenotype but negative for MEN1 mutations. Due to the limited number of patients so far identified, the phenotypic features of MEN4 are not clearly defined. Here, we review the clinical and molecular characteristics of the MEN4 syndrome and summarize the main functions of p27 to better comprehend how their alteration can predispose to neuroendocrine tumors.

N-Myc is a downstream target of RET signaling and is required for transcriptional regulation of p18(Ink4c) by the transforming mutant RET(C634R)

Inherited activating mutations in RET predispose humans to Multiple Endocrine Neoplasia type-2 (MEN2). The MEN2A-specific mutation RET(C634R), RET2A, has been shown to simultaneously downregulate the CDKIs p18 and p27, and upregulate cyclin D1. Importantly, the loss of p18 is necessary and sufficient for RET2A-mediated hyperproliferation. The loss of N-Myc in mice results in embryonic lethality due to a lack of neuronal progenitor cells that fail to proliferate, correlate with accumulation of p18 and p27. Therefore, N-Myc may regulate expression of both CDKIs. Also, N-Myc is expressed predominantly in neuroendocrine cells that give rise to the primary cell types affected in MEN2A. Together these studies suggest that N-Myc is a downstream target of RET2A signaling that prevents accumulation of p18 and/or p27. We report that MAPK activation by RET2A leads to a transient induction of N-Myc mRNA and protein levels, and that N-Myc induction is required to maintain low p18 and p27 levels. Induced N-Myc levels correlate with increased binding of N-Myc to an initiator consensus binding site in the p18 promoter, and this binding is essential for RET2A-mediated transcriptional regulation of p18. Finally, loss of N-Myc induction prevents RET2A-mediated hyperproliferation. Our results demonstrate for the first time that N-Myc is a downstream target of RET2A signaling, and propose that induction of N-Myc by RET2A is a key step leading to lower p18 levels during MEN2A tumorigenesis.

Dual loss of rb1 and Trp53 in the adrenal medulla leads to spontaneous pheochromocytoma

Using a Cre/loxP system, we have determined the phenotypic consequences attributable to in vivo deletion of both Rb1 and Trp53 in the mouse adrenal medulla. The coablation of these two tumor suppressor genes during embryogenesis did not disrupt adrenal gland development but resulted in the neoplastic transformation of the neural crest-derived adrenal medulla, yielding pheochromocytomas (PCCs) that developed with complete penetrance and were inevitably bilateral. Despite their typically benign status, these PCCs had profound ramifications on mouse vitality, with effected mice having a median survival of only 121 days. Evaluation of these PCCs by both immunohistochemistry and electron microscopy revealed that most Rb1(-/-):Trp53(-/-) chromaffin cells possessed atypical chromagenic vesicles that did not seem capable of appropriately storing synthesized catecholamines. The structural remodeling of the heart in mice harboring Rb1(-/-):Trp53(-/-) PCCs suggests that the mortality of these mice may be attributable to the inappropriate release of catecholamines from the mutated adrenal chromaffin cells. On the basis of the collective data from Rb1 and Trp53 knockout mouse models, it seems that the conversion of Rb1 loss-driven adrenal medulla hyperplasia to PCC can be greatly enhanced by the compound loss of Trp53, whereas the loss of Trp53 alone is generally ineffectual on adrenal chromaffin cell homeostasis. Consequently, the Trp53 tumor suppressor gene is an efficient genetic modifier of Rb1 loss in the development of PCC, and their compound loss in the adrenal medulla has a profound impact on both cellular homeostasis and animal vitality.

MEN-4 and other multiple endocrine neoplasias due to cyclin-dependent kinase inhibitors (p27(Kip1) and p18(INK4C)) mutations

Cyclin-dependent kinase inhibitors (CDKIs) are known targets to become deregulated in various tumour types, including endocrine tumours. Typically, these cell cycle regulators are somatically inactivated in sporadic endocrine tumours. Recently, it became known that certain CDKI genes cause inherited susceptibility to endocrine neoplasia. Multiple endocrine neoplasia type 4 (MEN4) emerged as a novel form of multiple endocrine neoplasia, caused by mutations in the CDKI gene CDKN1B/p27(Kip1). The MEN4 phenotype remains unclear, but all MEN4 patients identified thus far present with parathyroid involvement, and less typically with pituitary adenomas and other endocrine features. Moreover, the CDKI gene CDKN2C/p18(INK4C) has been also implicated in endocrine neoplasia susceptibility. This review presents the recent advances in these novel MEN-related states and summarises the current knowledge of how these CDKIs may be implicated in endocrine neoplasia. In addition, it briefly presents data from Cdkn1b/p27(Kip1) and Cdkn2c/p18(INK4C) murine models, which strongly support the protective role of these inhibitors against endocrine tumourigenesis.

The MENX syndrome and p27: relationships with multiple endocrine neoplasia

In the past 3 years new insight into the etiopathogenesis of hereditary endocrine tumors has emerged from studies conducted on MENX, a rat multiple endocrine neoplasia (MEN) syndrome. MENX spontaneously developed in a rat colony and was discovered by serendipity when these animals underwent complete necropsy, as they were found to consistently develop multiple endocrine tumors with a spectrum similar to both MEN type 1 (MEN1) and MEN2 human syndromes. Genetic studies identified a germline mutation in the Cdkn1b gene, encoding the p27 cell cycle inhibitor, as the causative mutation for the MENX syndrome. Capitalizing on these findings, we and others identified heterozygous germline mutations in the human homologue, CDKN1B, in patients with multiple endocrine tumors. As a consequence of these observations a novel human MEN syndrome, named MEN4, was recognized which is caused by mutations in p27. Altogether these studies identified Cdkn1b/CDKN1B as a novel tumor susceptibility gene for multiple endocrine tumors in both rats and humans. In this chapter we present the MENX syndrome and its phenotype, and we compare it to the human MEN syndromes; we discuss the current state of knowledge regarding the genes associated to inherited MEN, with a particular focus on CDKN1B; we present recent clinical and basic findings about the MEN4 syndrome and the functional characterization of the CDKN1B mutations identified. These findings are placed in the broader context of how p27 dysregulation might affect neuroendocrine cell function and trigger tumorigenesis.

Multiple endocrine neoplasia type 2

Multiple endocrine neoplasia type 2 (MEN 2) is an autosomal dominantly inherited tumor syndrome subclassified into three distinct syndromes: MEN 2A, MEN 2B and familial medullary thyroid carcinoma. In MEN 2 families, medullary thyroid carcinoma, pheochromocytomas and parathyroid adenomas occur with a variable frequency, also depending on the specific genetic defect involved. In 1993, the responsible MEN2 gene was identified. The genetic defect in these disorders involves the RET proto-oncogene on chromosome 10. The germline RET mutations result in a gain-of-function of the RET protein. Extensive studies on large families revealed that there is a strong genotype-phenotype correlation. In this review, guidelines for early diagnosis, including MEN2 gene mutation analysis, and treatment, including preventive surgery, periodic and clinical monitoring, have been formulated, enabling improvement of life expectancy and quality of life. Identification of the RET protein has also provided new insights into its function, and the specific pathways it effects involved in cell proliferation, migration, differentiation and survival. In the near future, identification of biological tumor markers will enable target-directed intervention and may prevent and/or delay progression of both primary and residual tumor growth.

Beyond RET: potential therapeutic approaches for advanced and metastatic medullary thyroid carcinoma

Medullary thyroid carcinoma (MTC) is a rare calcitonin-producing neuroendocrine tumour that originates from the parafollicular C-cells of the thyroid gland. The RET proto-oncogene encodes the RET receptor tyrosine kinase, which has essential roles in cell survival, differentiation and proliferation. Activating mutations of RET are associated with the pathogenesis of MTC and have been demonstrated in nearly all hereditary and in 30-50% of sporadic MTC cases, making this receptor an excellent target for small-molecule inhibitors for this tumour. Clinical trials of small organic inhibitors of tyrosine kinase receptors (TKIs) targeting the RET receptor have shown efficacy for treatment of metastatic MTC with 30-50% of patients responding to these agents. Despite the importance of the RET receptor in MTC, it is clear that other signal transduction pathways, tyrosine kinase receptors, and tumour suppressor genes are involved in MTC tumourigenesis and progression. A better understanding of molecular cross-talk between these signal pathways and the RET receptor may lead to combinatorial therapy that will improve outcomes beyond what is currently possible with RET-directed TKIs. Finally, there is evidence that immunological-based therapy using dendritic cell vaccination strategies have been effective for reducing tumour mass in a small number of patients. The identification of additional MTC-specific tumour antigens and a better understanding of specific epitopes in these tumour antigens may lead to improvement of response rates.

Medullary thyroid cancer: management guidelines of the American Thyroid Association

BACKGROUND

Inherited and sporadic medullary thyroid cancer (MTC) is an uncommon and challenging malignancy. The American Thyroid association (ATA) chose to create specific MTC Clinical Guidelines that would bring together and update the diverse MTC literature and combine it with evidence-based medicine and the knowledge and experience of a panel of expert clinicians.

METHODS

Relevant articles were identified using a systematic PubMed search and supplemented with additional published materials. Evidence-based recommendations were created and then categorized using criteria adapted from the United States Preventive Services Task Force, Agency for Healthcare Research and Quality.

RESULTS

Clinical topics addressed in this scholarly dialog included: initial diagnosis and therapy of preclinical disease (including RET oncogene testing and the timing of prophylactic thyroidectomy), initial diagnosis and therapy of clinically apparent disease (including preoperative testing and imaging, extent of surgery, and handling of devascularized parathyroid glands), initial evaluation and treatment of postoperative patients (including the role of completion thyroidectomy), management of persistent or recurrent MTC (including the role of tumor marker doubling times, and treatment of patients with distant metastases and hormonally active metastases), long-term follow-up and management (including the frequency of follow-up and imaging), and directions for future research.

CONCLUSIONS

One hundred twenty-two evidence-based recommendations were created to assist in the clinical care of MTC patients and to share what we believe is current, rational, and optimal medical practice.

P18 is a tumor suppressor gene involved in human medullary thyroid carcinoma and pheochromocytoma development

In multiple endocrine neoplasia syndrome Type 2 (MEN2), medullary thyroid carcinoma (MTC) and pheochromocytoma (PC) are associated with hereditary activating germ-line mutations in the RET proto-oncogene. Also in a large percentage of sporadic MTCs and PCs, somatic RET mutations appear to be involved in tumor formation. In one single MEN2 family an extensive variety in disease expression may be observed, indicating that additional genetic events are responsible for progression of the disease towards a more aggressive phenotype. However, these additional mutations in both hereditary and sporadic MTC and PC development are largely unknown. Here, we show for the first time the presence of somatic mutations in the cell cycle regulator P18 in human RET-associated MTCs and PCs. Each of these mutations causes an amino acid substitution in the cyclin dependent kinase-interacting region of P18(INK4C). Since these mutations partly inhibited P18(INK4C) function and reduced its stability, our findings implicate P18 as a tumor suppressor gene involved in human MTC and PC development.

Expression of p18(INK4C) is down-regulated in human pituitary adenomas

Cyclin-dependent kinase inhibitors represented by the INK4 family comprising p16(INK4A), p15(INK4B), p18(INK4C), and p19(INK4D) are regulators of the cell cycle shown to be aberrant in many types of cancer. Mice lacking p18(Ink4c) exhibit a series of phenotypes including the development of widespread organomegaly and pituitary adenomas. The objective of our study is to examine the role of p18(INK4C) in the pathogenesis of human pituitary tumors. The protein and mRNA levels of p18(INK4C) were examined by immunohistochemistry and real-time reverse transcription-polymerase chain reaction, respectively. The methylation status of the p18(INK4C) gene promoter and somatic mutations of the p18(INK4C) gene were also investigated. p18(INK4C) protein expression was lost or significantly reduced in 64% of pituitary adenomas compared with levels in normal pituitary glands. p18(INK4C) mRNA levels were low in all ACTH adenomas and non-functioning (NF)-FSH and in 42%, 70% and 66% of GH, PRL, and subtype 3 adenomas, respectively. p18(INK4C) mRNA levels were significantly associated with p18(INK4C) protein levels. Neither methylated promoters in pituitary adenomas, except in one NF-FSH adenoma, nor somatic mutations of the p18(INK4C) gene in any pituitary adenomas were detected. The down-regulation of p18(INK4C) expression may contribute to the tumorigenesis of pituitary adenomas.

Repression of Ah receptor and induction of transforming growth factor-beta genes in DEN-induced mouse liver tumors

The aryl hydrocarbon receptor (AHR) is a ligand-activated transcription factor that mediates the biologic and toxic effects of its xenobiotic ligands. In recent years it has become evident that in the absence of ligand the AHR promotes cell cycle progression and that its activation by high-affinity ligands results in interactions with the retinoblastoma protein (RB) that lead to perturbation of the cell cycle, G0/G1 arrest, diminished capacity for DNA replication and inhibition of cell proliferation. Hence, the AHR has diametrically opposed pro-proliferative and anti-proliferative functions that have yet to be reconciled at the molecular level. Work from our own and from other laboratories suggests that the AHR may function as a tumor suppressor gene that becomes silenced in the process of tumor formation. To develop preliminary support for a more thorough examination of this hypothesis we characterized the expression levels of various tumor suppressor genes, transforming growth factor-beta (Tgfb) genes and the Ahr gene in liver tumor samples from mice with a liver-specific RB ablation and their wild-type littermates. In tumors arising in RB-positive livers, Cdkn2d and Tgfb1 were repressed and Cdkn2c, Tgfb2, Tgfb3 and Pai1 were induced, whereas in RB-negative tumors, only Cdkn2c and Tgfb3 were induced. Ahr was significantly repressed in tumors from both sets of mice, supporting the concept that Ahr silencing may be associated with cancer progression.