Identification of the secretogranin II-derived peptide EM66 in pheochromocytomas as a potential marker for discriminating benign versus malignant tumors.

EM66 is a novel secretogranin II-derived peptide present in chromaffin cells of the human adrenal gland. The aim of the present study was to investigate the possible occurrence of EM66 in benign and malignant pheochromocytomas. Immunohistochemical labeling using specific antibodies revealed intense staining in both benign and malignant tumors. Coincubation of pheochromocytoma slices with EM66 and tyrosine hydroxylase antibodies showed that the immunostaining was restricted to chromaffin cells. RIA experiments indicated that serial dilutions of extracts of benign and malignant tumors generated displacement curves that were parallel to those produced by recombinant EM66. RIA quantification revealed concentrations of EM66 immunoreactivity ranging from 3.2-210 ng/mg protein (median = 25.6 ng/mg protein) in benign pheochromocytomas, and from 2.9-6.3 ng/mg protein (median = 3.8 ng/mg protein) in malignant tumors. The EM66-like immunoreactivity contained in the pheochromocytoma extracts was characterized by HPLC analysis combined with RIA detection. All of the benign and malignant tumors examined exhibited a single immunoreactive peak coeluting with recombinant EM66. These data indicate that the secretogranin II-derived peptide EM66 is generated in human tumoral chromaffin tissue. The significant difference in EM66 concentrations observed between benign and malignant pheochromocytomas suggests that measurement of EM66 levels may help identifying patients with higher risk of progression of such tumors.