Is Surgery Beneficial for MEN1 Patients with Small (≤2 cm), Nonfunctioning Pancreaticoduodenal Endocrine Tumor? An Analysis of 65 Patients from the GTE

Background: The management of small, nonfunctioning pancreaticoduodenal endocrine tumors (NFPET) in multiple endocrine neoplasia type 1 (MEN1) patients is still controversial. We therefore investigated the effect of surgery on survival and tumor progression in MEN1 patients with NFPET ≤2 cm by analyzing data from the Groupe des Tumeurs Endocrines (GTE) registry. Materials and Methods: Among 579 MEN1 patients in the registry, 65 had NFPET ≤ 2 cm. Fifteen (23%) underwent pancreatectomy, 9 at least segmental pancreatectomies and 6 biopsies or enucleations (the surgery group), and 50 (77%) were followed conservatively (the no surgery group). Age at MEN1 and NFPET diagnosis was similar in both groups, as was size of the primary tumor. Seven (10.8%) patients had metastases. Five metastases were synchronous, and 2 (one in each group) were metachronous. Tumor size was similar in patients with or without metastasis. Results: There was no perioperative mortality. The average follow-up time after NFPET diagnosis was 6.7 years in the surgery group and 3.3 years in the no surgery group. Three (4.6%) patients died during follow-up, 2 due to NFPET and 1 due to thymus tumor. The 2 patients who died of NFPET had undergone pancreatic surgery at the time of NFPET diagnosis. The 2 groups did not differ significantly with respect to tumor progression [5/15 (33%) vs 6/38 (16%), P = 0.16]. Overall life expectancy of patients with NFPET ≤2 cm was not different than that of the 229 MEN1 patients in the registry without any pancreaticoduodenal tumor (P = 0.33). Conclusions: This study suggests that surgery may not be beneficial for MEN1 patients with NFPET ≤2 c

Human Thyroperoxidase Is Largely Retained and Rapidly Degraded in the Endoplasmic Reticulum. Its N-Glycans Are Required for Folding and Intracellular Trafficking

International audienceHuman thyroperoxidase (hTPO), a type I transmembrane heme containing glycoprotein, catalyzes iodide organification and thyroid hormone synthesis and plays a major role in thyroid autoimmunity. Whereas hormonosynthesis occurs at the apical membrane of thyroid cells, TPO localizes mainly in the perinuclear membrane and the endoplasmic reticulum. To establish the intracellular trafficking and the structural characteristics of hTPO in the various cell compartments, hTPO was stably expressed in the Chinese hamster ovary cell line, and its folding was studied with two monoclonal antibodies (mAbs): mAb 47, recognizing a linear epitope; and mAb 15, recognizing a conformational epitope present in the mature protein. The results show that only 15-20% of hTPO molecules were able to acquire a conformation suitable for the recognition by mAb 15. On the other hand, only a part (approximately 15%) of the latter were able to reach the plasma membrane. The hTPO, unable to fold correctly, was more rapidly degraded than that recognized by mAb 15 (half-time, 2 h vs. 7 h). Study of the carbohydrate content of hTPO showed that N-glycans with complex-type structure were found only on hTPO at the cell surface, whereas intracellular hTPO bore high-mannose-type structures. Taken together, these data demonstrate that the intracellular pool of enzyme is formed of newly synthesized molecules and is not caused by recycling of mature hTPO from the cell surface. Complete inhibition of hTPO N-glycosylation with tunicamycin led to a 95% decrease in hTPO at the plasma membrane and, thus, to a decrease in enzymatic activity at the cell surface, emphasizing the role of N-glycans in the intracellular trafficking of hTPO. However, inhibition of formation of complex-type structures with deoxymannojirimycin and of O-glycans with phenyl-alpha-GalNAc did not influence the intracellular trafficking and enzymatic activity of hTPO

Role of Heme in Intracellular Trafficking of Thyroperoxidase and Involvement of H 2 O 2 Generated at the Apical Surface of Thyroid Cells in Autocatalytic Covalent Heme Binding

International audienceThyroperoxidase (TPO) is a glycosylated hemoprotein that plays a key role in thyroid hormone synthesis. We previously showed that in CHO cells expressing human TPO (hTPO) only 2% of synthesized hTPO reaches the cell surface. Herein, we investigated the role of heme moiety insertion in the exit of hTPO from the endoplasmic reticulum. Peroxidase activity at the cell surface and cell surface expression of hTPO were decreased by approximately 30 and approximately 80%, respectively, with succinyl acetone, an inhibitor of heme biosynthesis, and were increased by 20% with holotransferrin and aminolevulinic acid, precursors of heme biosynthesis. Results were similar with holotransferrin plus aminolevulinic acid or hemin, but hemin increased cell surface activity more efficiently (+120%) relative to the control. It had been suggested (DePillis, G., Ozaki, S., Kuo, J. M., Maltby, D. A., and Ortiz de Montellano, P. R. (1997) J. Biol. Chem. 272, 8857-8960) that covalent attachment of heme to mammalian peroxidases could be an H2O2-dependent autocatalytic processing. In our study, heme associated intracellularly with hTPO, and we hypothesized that there was insufficient exposure to H2O2 in Chinese hamster ovary cells before hTPO reached the cell surface. After a 10-min incubation, 10 microM H2O2 led to a 65% increase in cell surface activity. In contrast, in thyroid cells, H2O2 was synthesized at the apical cell surface and allowed covalent attachment of heme. Two-day incubation of primocultures of thyroid cells with catalase led to a 30% decrease in TPO activity at the cell surface. In conclusion, we provide compelling evidence for an essential role of 1) heme incorporation in the intracellular trafficking of hTPO and of 2) H2O2 generated at the apical pole of thyroid cells in the autocatalytic covalent heme binding to the TPO molecule

Alternatively spliced form of human thyroperoxidase, TPOzanelli: activity, intracellular trafficking, and role in hormonogenesis.

International audienceThyroperoxidase (TPO), a type I transmembrane heme containing glycoprotein, catalyzes iodide organification and thyroid hormone synthesis. One of the two main alternatively spliced forms of this enzyme, TPOzanelli, which is present in Graves's disease thyroid tissue, has a cytoplasmic domain completely modified. In the first stage of this study, the results of RT-PCR experiments showed that the TPOzanelli mRNA is present in normal thyroid tissue. We then generated CHO cell lines expressing the wild-type TPO (TPO1) and the alternatively spliced form TPOzanelli. Upon investigating a panel of 12 mAbs directed against the extracellular domain of TPO1 and sera from patients with a high titer of TPO autoantibodies, we observed that (i) the three-dimensional structure of this domain is similar in both isoforms; (ii) the autoantibodies recognize TPOzanelli as well as TPO1. The results of pulse chase and cell surface biotinylation experiments showed that the TPOzanelli has a shorter half-life (7 versus 11 h) and is expressed at the cell surface in lesser amounts than TPO1 (7 versus 15%). The total enzymatic activity and cell surface activity were determined in CHO cells expressing TPO1 and TPOzanelli, and TPO1 and TPOzanelli were found to have similar levels of activity. It was established that approximately 20% of the TPO purified from a Graves' disease thyroid gland was precipitated by polyclonal antibodies directed against a specific part of the cytoplasmic tail of TPOzanelli. This confirmed that the protein corresponding to the mRNA is present in the thyroid tissue. All in all, these results indicate that TPOzanelli can be expected to play a role in thyroid hormone synthesis and in thyroid autoimmunity

Is surgery beneficial for MEN1 patients with small (< or = 2 cm), nonfunctioning pancreaticoduodenal endocrine tumor? An analysis of 65 patients from the GTE.

The management of small, nonfunctioning pancreaticoduodenal endocrine tumors (NFPET) in multiple endocrine neoplasia type 1 (MEN1) patients is still controversial. We therefore investigated the effect of surgery on survival and tumor progression in MEN1 patients with NFPET < or = 2 cm by analyzing data from the Groupe des Tumeurs Endocrines (GTE) registry

Epidemiology data on 108 MEN 1 patients from the GTE with isolated nonfunctioning tumors of the pancreas

To analyze the penetrance and clinical course of isolated nonfunctioning tumors of the pancreas (NFTP) in MEN 1 patients, and to propose a strategy for managing them