Low prevalence of Gs alpha mutations in śomatotroph adenomas of children and adolescents

MEG3 is associated with gsp oncogene regulation of growth hormone hypersecretion, proliferation and invasiveness of human GH-secreting adenomas

Overactivation of the Gs-mediated pathway by mutations of the G-protein α subunit (Gsα), a gsp oncogene, results in increased growth hormone (GH) hypersecretion and reduced tumor volume in patients with GH-secreting pituitary tumors. However, the mechanism underlying the clinical characteristics of gsp oncogene requires further investigation. Cyclic adenosine monophosphate-responsive element binding (CREB), as a downstream target gene of gsp oncogene, is implicated in activating maternally expressed gene 3 (MEG3). The present study proposes that gsp oncogene mediates MEG3-regulating GH hypersecretion, resulting in the small tumor size of GH-secreting tumors. Therefore, the present study detected Gsα mutations by polymerase chain reaction in GH-secreting tumors, and revealed that Gsα mutations were observed in 7/25 (28%) GH-secreting tumors. Gsp-positive tumors indicated significantly increased levels of phosphorylated p-CREB (P<0.0001) and MEG3 (P=0.039), compared with gsp-negative tumors. The results indicated that MEG3 levels were positively correlated with GH and IGF-1 levels, and negatively correlated with the tumor volume of GH-secreting tumors. The group with gsp-positive or with high MEG3 expression indicated a significantly reduced proportion of invasiveness and lower Ki-67 index, compared with the gsp-negative or low MEG3 expression group. In conclusion, gsp oncogene may mediate MEG3 by promoting GH hypersecretion, resulting in smaller tumors, as well as suppressing proliferation and invasiveness of GH-secreting pituitary tumors.

The curious case of Gαs gain-of-function in neoplasia

BACKGROUND

Mutations activating the α subunit of heterotrimeric Gs protein are associated with a number of highly specific pathological molecular phenotypes. One of the best characterized is the McCune Albright syndrome. The disease presents with an increased incidence of neoplasias in specific tissues.

MAIN BODY

A similar repertoire of neoplasms can develop whether mutations occur spontaneously in somatic tissues during fetal development or after birth. Glands are the most "permissive" tissues, recently found to include the entire gastrointestinal tract. High frequency of activating Gαs mutations is associated with precise diagnoses (e.g., IPMN, Pyloric gland adenoma, pituitary toxic adenoma). Typically, most neoplastic lesions, from thyroid to pancreas, remain well differentiated but may be a precursor to aggressive cancer.

CONCLUSIONS

Here we propose the possibility that gain-of-function mutations of Gαs interfere with signals in the microenvironment of permissive tissues and lead to a transversal neoplastic phenotype.

Pituitary gigantism: a retrospective case series

BACKGROUND

Pituitary gigantism (PG) is a rare pediatric disease with poorly defined long-term outcomes. Our aim is to describe the longitudinal clinical course in PG patients using a single-center, retrospective cohort study.

METHODS

Patients younger than 19 years diagnosed with PG were identified. Thirteen cases were confirmed based on histopathology of a GH secreting adenoma or hyperplasia and a height >2 SD for age and gender. Laboratory studies, initial pathology, and imaging were abstracted.

RESULTS

Average age at diagnosis was 13 years with an average initial tumor size of 7.4×3.8 mm. Initial transsphenoidal surgery was curative in 3/12 patients. Four of the nine patients who failed the initial surgery required a repeat procedure. Octreotide successfully normalized GH levels in 1/6 patients with disease refractory to surgery (1/6). Two out of five patients received pegvisomant after failing octreotide but only one patient responded to treatment. Five patients were ultimately treated with radiosurgery or radiation patients were followed for an average of 10 years.

CONCLUSIONS

PG is difficult to treat. In most patients, the initial transsphenoidal surgery failed to normalize GH levels. If the initial surgery was unsuccessful, repeat surgery was unlikely to control GH secretion. Treatment with octreotide or pegvisomant was successful in less than half the patients failing surgery. Radiosurgery was curative, but is not an optimal treatment for pediatric patients. Despite the small sample, our study suggests that the treatment outcome of pediatric PG may be different than adults.

Landscape of Familial Isolated and Young-Onset Pituitary Adenomas: Prospective Diagnosis in AIP Mutation Carriers

CONTEXT

Familial isolated pituitary adenoma (FIPA) due to aryl hydrocarbon receptor interacting protein (AIP) gene mutations is an autosomal dominant disease with incomplete penetrance. Clinical screening of apparently unaffected AIP mutation (AIPmut) carriers could identify previously unrecognized disease.

OBJECTIVE

To determine the AIP mutational status of FIPA and young pituitary adenoma patients, analyzing their clinical characteristics, and to perform clinical screening of apparently unaffected AIPmut carrier family members.

DESIGN

This was an observational, longitudinal study conducted over 7 years.

SETTING

International collaborative study conducted at referral centers for pituitary diseases.

PARTICIPANTS

FIPA families (n 216) and sporadic young-onset (30 y) pituitary adenoma patients (n 404) participated in the study.

INTERVENTIONS

We performed genetic screening of patients for AIPmuts, clinical assessment of their family members, and genetic screening for somatic GNAS1 mutations and the germline FGFR4 p.G388R variant.

MAIN OUTCOME MEASURE(S)

We assessed clinical disease in mutation carriers, comparison of characteristics of AIPmut positive and negative patients, results of GNAS1, and FGFR4 analysis.

RESULTS

Thirty-seven FIPA families and 34 sporadic patients had AIPmuts. Patients with truncating AIPmuts had a younger age at disease onset and diagnosis, compared with patients with nontruncating AIPmuts. Somatic GNAS1 mutations were absent in tumors from AIPmut-positive patients, and the studied FGFR4 variant did not modify the disease behavior or penetrance in AIPmut-positive individuals. A total of 164 AIPmut-positive unaffected family members were identified; pituitary disease was detected in 18 of those who underwent clinical screening.

CONCLUSIONS

A quarter of the AIPmut carriers screened were diagnosed with pituitary disease, justifying this screening and suggesting a variable clinical course for AIPmut-positive pituitary adenomas.

Impact of gsp oncogene on the mRNA content for somatostatin and dopamine receptors in human somatotropinomas

INTRODUCTION

It has been reported in some series that gsp+ somatotropinomas are more sensitive to somatostatin analogues (SA) and dopamine's actions which may be related to their somatostatin receptor (SSTR) and dopamine receptor (DR) profile. No previous studies have been undertaken to evaluate the SSTR and DR profile related with the gsp status in somatotropinomas.

OBJECTIVES

To determine if (1) gsp status is correlated with response to octreotide LAR (LAR) and tumor expression patterns of SSTR1-5 and DR1-5 and (2) cAMP level can directly modulate SSTR and DR mRNA levels.

METHODS

Response to SA was evaluated by GH and IGF-I percent reduction after 3 and 6 months of treatment with LAR. Conventional PCR and sequencing were used to identify gsp+ tumors. Quantitative real-time PCR was used to determine SSTR and DR tumor expression. Primary pituitary cell cultures of primates were used to study whether SSTR and DR expression is regulated by forskolin.

RESULTS

The response to LAR did not significantly differ between patients with gsp+ and gsp- tumors; however, gsp+ tumors expressed higher levels of SSTR1, SSTR2, DR2 and a lower level of SSTR3. Forskolin increased SSTR1, SSTR2, DR1 and DR2 expression in cell cultures.

CONCLUSION

Elevated SSTR1, SSTR2, and DR2 tumor expression may help improve responsiveness to SA and DA therapy; however, this study may not have been appropriately powered to observe significant effects in the clinical response. Elevated cAMP levels could be directly responsible for the upregulation in SSTR1, SSTR2 and DR2 mRNA levels observed in gsp+ patients.

Prevalence of gsp oncogene in somatotropinomas and clinically non-functioning pituitary adenomas: our experience

The purpose of the present study is to evaluate the prevalence of the gsp oncogene in Brazilian patients harboring somatotropinomas and non-functioning pituitary adenomas (NFPA). Patients and methods Deoxyribonucleic acid was extracted from 54 somatotropinomas and 14 NFPA. Exons 8 and 9 (including codons 201 and 227, respectively) of the GNAS gene were amplified by polymerase chain reaction (PCR). The PCR products were then purified and sequenced using the same primers. Results The gsp oncogene was found in nine tumors (eight somatotropinomas). The prevalence among somatotropinomas was 15% and among NFPA was 7%. The mutation was found in codon 201 in eight tumors and in codon 227 in one tumor (a somatotropinoma). No differences were found in age, sex, GH, and IGF-I levels or tumor volume at diagnosis between gsp+ and gsp- patients. Conclusion We found a lower than expected prevalence of gsp mutations in somatotropinomas and a similar prevalence in NFPA compared to previous studies from other countries.

McCune-Albright syndrome and disorders due to activating mutations of GNAS1

It has been more than seven decades since Drs. Fuller Albright and Donovan McCune published the first reports on individuals with McCune-Albright syndrome (MAS). Since then, the classic triad of precocious puberty, café-aulait spots, and polyostotic bone dysplasia continues to define the syndrome. However, having gathered a better picture of the pathophysiology of MAS, the way this condition is understood has changed. Isolated activating mutations of the alpha subunit of the G protein (GNAS1) have been found in different tissues, including pituitary adenomas, thyroid adenomas, ovarian cysts, monostotic bone dysplasia, and the adrenal glands, to name a few. For this reason, we have added 'and disorders due to activating mutations of GNAS1' to the title of this review. We discuss here the clinical consequences of GNAS1 activating mutations in different body systems and organs, the diagnostic approach to MAS, and the current therapeutic recommendations.