Differential expression and processing of secretogranin II in relation to the status of pheochromocytoma: implications for the production of the tumoral marker EM66

Abstract

We have previously demonstrated that measurement of tissue concentrations of the secretogranin II (SgII or SCG2 as listed in the HUGO database)-derived peptide EM66 may help to discriminate between benign and malignant pheochromocytomas and that EM66 represents a sensitive plasma marker of pheochromocytomas. Here, we investigated the gene expression and protein production of SgII in 13 normal adrenal glands, and 35 benign and 16 malignant pheochromocytomas with the goal to examine the molecular mechanisms leading to the marked variations in the expression of EM66 in tumoral chromaffin tissue. EM66 peptide levels were 16-fold higher in benign than in malignant pheochromocytomas and had an area under the receiver-operating characteristic curve of 0 . 95 for the distinction of benign and malignant tumors. Q-PCR experiments indicated that the SgII gene was significantly underexpressed in malignant tumors compared with benign tumors. Western blot analysis using antisera directed against SgII and SgII-derived fragments revealed lower SgII protein and SgII-processing products in malignant tumors. Western blot also showed that low p-cAMP-responsive element-binding (CREB) concentrations seemed to be associated with the malignant status. In addition, the prohormone convertase PC1 and PC2 genes and proteins were overexpressed in benign pheochromocytomas compared with malignant pheochromocytomas. Low concentrations of EM66 found in malignant tumors are associated with reduced expression and production of SgII and SgII-derived peptides that could be ascribed to a decrease in SgII gene transcription, probably linked to p-CREB down-regulation, and to lower PC levels. These findings highlight the mechanisms leading to lower concentrations of EM66 in malignant pheochromocytoma and strengthen the notion that this peptide is a suitable marker of this neuroendocrine tumor.

Characterization and Plasma Measurement of the WE-14 Peptide in Patients with Pheochromocytoma

“…We additionally found that EM66 levels are significantly increased in the plasma of patients with pheochromocytomas [29]. We also demonstrated that low tissue concentrations of the peptide are associated with malignant differentiation of these neoplasms [30], [31]. Our data suggested that EM66 could potentially be a new diagnostic and prognostic marker of pheochromocytomas, and that, besides CgA, other granin-derived peptides, such as EM66, could represent valuable supplementary markers for the management and follow-up of these tumors.…”

Metastatic pheochromocytoma and paraganglioma

“…CgA is also used as a marker of tumour burden and relapse following treatment . Recently, EM66, a secretogranin II‐derived peptide, and neuron‐specific enolase (NSE) have been shown to be promising in distinguishing between benign and metastatic disease .…”

Molecular and Therapeutic Advances in the Diagnosis and Management of Malignant Pheochromocytomas and Paragangliomas

“…Although elevated levels of many granin-derived peptides are found in PCCs/PGLs, they rarely help to discriminate between benign and malignant tumors [80]. Recently, EM66, a secretogranin II-derived peptide present in chromaffin cells, has shown the most promise in early studies in distinguishing between benign and malignant disease [81,82]. Malignant disease demonstrated lower gene expression and protein transcription, but this has yet to translate into a measurable circulating biomarker.…”