The spectrum of endogenous human chromogranin A-derived peptides identified using a modified proteomic strategy.

The hypothesis that chromogranin A (CgA), a protein of neuroendocrine cell secretory granules, may be a precursor of biologically active peptides, rests on observed activities of peptide fragments largely produced by exogenous protease digestion of the bovine protein. Here we have adopted a modified proteomic strategy to isolate and characterise human CgA-derived peptides produced by endogenous prohormone convertases. Initial focus was on an insulinoma as previous studies have shown that CgA is rapidly processed in pancreatic beta cells and that tumours arising from these express appropriate prohormone convertases. Eleven novel peptides were identified arising from processing at both monobasic and dibasic sites and processing was most evident in the C-terminal domain of the protein. Some of these peptides were identified in endocrine tumours, such as mid-gut carcinoid and phaeochromocytoma, which arise from endocrine cells of different phenotype and in different anatomical sites. Two of the most interesting peptides, GR-44 and ER-37, representing the C-terminal region of CgA, were found to be amidated. These data would imply that the intact protein is C-terminally amidated and that these peptides are probably biologically active. The spectrum of novel CgA-derived peptides, described in the present study, should provide a basis for biological evaluation of authentic entities.

Bone marrow micrometastases and markers of angiogenesis in esophageal cancer.

BACKGROUND: Tumor angiogenesis is critical for metastasis development. The detection of bone marrow micrometastases may indicate a metastatic phenotype. We aim to establish if the detection of bone marrow micrometastases associates with elevated markers of angiogenesis and adverse histopathologic features of esophageal cancer. METHODS: Bone marrow aspirates from 49 patients with esophageal cancer were assessed and assigned to be positive or negative for micrometastases. Routine histologic assessment of the primary tumor was also undertaken. Circulating and tumor levels of the angiogenic cytokine vascular endothelial growth factor were determined in plasma and tumor homogenate. Intratumor microvessel density was evaluated by counting anti-CD34 positive neovessels. RESULTS: Twenty-two patients were positive for bone marrow micrometastases (44.9%). The detection of micrometastases was associated with advanced T stage (T3/4 vs T1/2; p = 0.023), circumferential margin involvement (p = 0.002) and lymphovascular invasion (p = 0.024). Plasma vascular endothelial growth factor was significantly more elevated in micrometastatic-positive patients than in those without micrometastases (p = 0.018). No difference was noted in tumor vascular endothelial growth factor expression. For adenocarcinomas alone, intratumor microvessel density was significantly higher in micrometastatic positive cases (p = 0.03). This was not the case for squamous cell carcinomas. CONCLUSIONS: The detection of bone marrow micrometastases is associated with esophageal tumors of advanced T stage and specifically for adenocarcinomas with tumor vascularity. Plasma vascular endothelial growth factor is elevated in micrometastatic positive cases and might be derived from sources other than the primary tumor.