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Proteasome inhibitors induce apoptosis in some malignant cells, and we show here that these inhibitors induce apoptosis in rat pituitary MMQ and GH3 tumor cells but not in normal pituitary cells. Three proteasome inhibitors, PSI, MG-132, and lactacystin, but not the calpain inhibitor, ALLM, dose- and time-dependently caused apoptosis in these cells, and 10 microM PSI caused apoptosis in 70% of MMQ cells and in 25% of GH3 cells within 24 h. A lower PSI dose (10 nM) inhibited GH3 cell growth without causing significant apoptosis or affecting prolactin secretion. Primary rat pituitary cells were resistant to both PSI and MG-132 and did not undergo apoptosis. In MMQ cells, DNA synthesis was slowed (approximately 30%) after 6 h of 10 microM PSI treatment and a partial cell cycle block at G2/M was evident after 8 h. Colorimetric caspase substrate assay and Western blotting of caspase substrates showed that caspases 2 and 3 are activated by PSI while caspases 6 and 8 remained inactive. A broad-range caspase inhibitor, caspase inhibitor III, prevented apoptosis induced by PSI. The results show that proteasome inhibitors induce apoptosis in rat pituitary tumor cells by specific caspase activation. This novel group of drugs may potentially be used in treatment of aggressive pituitary tumors, especially as their action appears relative for tumor cells.

Neonatal overnutrition results in accelerated development of high-fat diet (HFD)-induced metabolic defects in adulthood. To understand whether the increased susceptibility was associated with aggravated inflammation and dysregulated lipid metabolism, we studied metabolic changes and insulin signaling in a chronic postnatal overnutrition (CPO) mouse model. Male Swiss Webster pups were raised with either three pups per litter to induce CPO or ten pups per litter as control (CTR) and weaned to either low-fat diet (LFD) or HFD. All animals were killed on the postnatal day 150 (P150) except for a subset of mice killed on P15 for the measurement of stomach weight and milk composition. CPO mice exhibited accelerated body weight gain and increased body fat mass prior to weaning and the difference persisted into adulthood under conditions of both LFD and HFD. As adults, insulin signaling was more severely impaired in epididymal white adipose tissue (WAT) from HFD-fed CPO (CPO–HFD) mice. In addition, HFD-induced upregulation of pro-inflammatory cytokines was exaggerated in CPO–HFD mice. Consistent with greater inflammation, CPO–HFD mice showed more severe macrophage infiltration than HFD-fed CTR (CTR–HFD) mice. Furthermore, when compared with CTR–HFD mice, CPO–HFD mice exhibited reduced levels of several lipogenic enzymes in WAT and excess intramyocellular lipid accumulation. These data indicate that neonatal overnutrition accelerates the development of insulin resistance and exacerbates HFD-induced metabolic defects, possibly by worsening HFD-induced inflammatory response and impaired lipid metabolism.

The regulated endocrine-specific protein, RESP18, first found in the rat pituitary, was thought to be regulated by dopaminergic drugs. Bioinformatics studies showed that RESP18 shares sequence homology with the luminal region of IA-2, a dense core vesicle (DCV) transmembrane protein involved in insulin secretion. The present study was initiated to examine the genomic structure and subcellular localization of RESP18 and the effect of glucose on its expression. Human RESP18 was isolated from a pancreas cDNA library and its subcellular localization was determined by immunoelectron microscopy. MIN6 cells and mouse islets were used to study the effect of glucose on RESP18 expression. Bioinformatics analysis revealed that RESP18 and IA-2 are tandemly arranged within a 45 kb region on human chromosome 2 and share common intron–exon boundaries. By confocal microscopy, RESP18 was found in α, β and δ cells in the pancreatic islets. Electron microscopy revealed that RESP18 is present in the lumen of DCVs. The expression of RESP18 in β cells is markedly increased following exposure to high glucose and also elevated in the islets of diabetic, but not non-diabetic, NOD mice. We conclude that RESP18 is a luminal protein of DCVs and its expression is regulated by exposure to glucose.