Cholecystokinin stimulates the down-regulation of CTP:phosphocholine cytidylyltransferase in pancreatic acinar cells

Stimulation of rat pancreatic acinar cells with cholecystokinin (CCK) is known to result in a significant inhibition of CTP:phosphocholine cytidylyltransferase (CT), a rate-limiting enzyme in phosphatidylcholine biosynthesis. Immunoprecipitation of CT from 32P-labeled acinar cells revealed that CCK treatment also caused a marked reduction in CT phosphate levels. The effects of CCK were maximal over 60 min and dependent on concentration, exhibiting an EC50 of 800 pM. Other calcium mobilizing secretagogues such as carbamylcholine (100 microM) and bombesin (10 nM) also reduced CT phosphate levels to 20 and 39% of control, respectively. Treatment of cells with thapsigargin and/or 12-O-tetradecanoyl-phorbol-13-acetate established that a combination of increased intracellular Ca2+ and protein kinase C activation was necessary to decrease phosphorylated CT content. Conversely, secretin (10 nM) or 8-(4-chlorophenylthio)-cAMP (100 microM) added alone had no effects. Use of the compound JMV-180 indicated CCK was acting through the low affinity state of the CCKA receptor to reduce CT phosphate levels. Further, the decrease in phosphorylated CT caused by CCK was blocked by the phosphatase inhibitors okadaic acid (3 microM) and calyculin A (100 nM). Finally, immunoblotting from whole cell lysates revealed CT was partially degraded in response to CCK, providing a novel mechanism by which the inhibition of CT enzyme activity occurs in response to the hormone. Moreover, this degradation was also blocked by a phosphatase inhibitor. These data suggest that the dephosphorylation of either CT itself or some other regulatory molecule(s) which mediates the CCK-induced protease activation may play a central role in reducing CT enzyme levels in acinar cells.

Identification of the nuclear localization signal of rat liver CTP:phosphocholine cytidylyltransferase

CTP:phosphocholine cytidylyltransferase (CT) is a major regulatory enzyme in phosphatidylcholine synthesis in mammalian cells. CT is found in both soluble and particulate forms, both of which are nuclear. We report here the identification of a 21-residue sequence at the amino terminus of CT, 8KVNSRKRRKEVPGPNGATEED28, which was sufficient to direct beta-galactosidase into the cell nucleus. Further deletions from either end of this sequence greatly reduced the nuclear localization of beta-galactosidase. Deletions of amino acids within the nuclear localization signal or of the entire signal disrupted CT nuclear localization, but CT was not completely excluded from the nucleus. Clones of stable transfectants of the nuclear localization signal-deficient CT expressed in Chinese hamster ovary (CHO) 58 cells, which is temperature-sensitive for growth and CT activity, were isolated and characterized. The deletion mutants were active under the same conditions as the wild-type enzyme. Despite the difference in subcellular location from wild-type CT, the nuclear localization mutants were fully able to complement the CT-deficient cell line CHO 58 for both growth and choline incorporation into phosphatidylcholine at the nonpermissive temperature. The mobility of the mutant enzymes on SDS gels was altered relative to the mobility of wild-type CT; however, the extent of phosphorylation of the mutant enzymes was decreased only slightly. Thus, the distribution of CT in both cytoplasm and nucleus, rather than exclusively nucleus, has little effect on the ability of CT to function in growing CHO cells.

Protein ubiquitination and neuronal differentiation in chick embryos

Ubiquitin is a small highly conserved intracellular protein which is involved in a number of cellular functions including targeting proteins for degradation. We have studied the distribution of ubiquitin-protein conjugates and two enzymes involved in protein ubiquitination in chick embryos. Using immunocytochemical techniques, we have observed that chick neural crest cells and dorsal root ganglia acquire immunoreactivity in their nuclei and cytoplasm as they mature, both in vivo and in vitro, though they are not immunoreactive at early stages of development. Immunoreactivity for the ubiquitin activating enzyme (E1) and a carboxyl terminal hydrolase for ubiquitin (PGP 9.5) also appears in the nuclei of differentiating neurons at the same time as ubiquitin-protein conjugates. Our results provide evidence that the nuclear accumulation of ubiquitin-protein conjugates is closely associated with maturation of neurons towards a differentiated phenotype.

Complex branch renovascular disease: management options and late results

PURPOSE

The purpose of this report is to review management options and late results of complex renovascular disease managed over the last 22 years.

METHODS

Complex branch renal artery disease in 84 kidneys was repaired during 75 operations performed in 68 consecutive patients. There were 61 females (90%) and 7 males (10%) whose predominant pathologic diagnosis was fibromuscular dysplasia manifesting as either renovascular hypertension or aneurysmal degeneration. These patients underwent 15 in situ, 52 ex vivo, and 8 combined reconstructions. In situ repair primarily with use of the bifurcated internal iliac artery autograft was used for primary lesions of the proximal renal artery bifurcation (two branches). Ex vivo repairs, primarily with use of the multibranch internal iliac autograft and hypothermic perfusion preservation, were used for all other patterns of distal renal artery branch disease and reoperative problems.

RESULTS

Renovascular reconstruction was successful in salvaging 83 of 84 kidneys (98.8%) in 67 of 68 patients. There were no operative deaths. Two reconstructions thrombosed in the early postoperative period. One was due to severe aortic disease, the other to branch artery dissection after a failed balloon angioplasty. Both patients continued to have hypertension. Before hospital discharge 65 patients had 81 renal revascularizations proven patent by arteriography. Their renal function was assessed and blood pressure was determined in a follow-up extending to 20 years (mean 7.5 years, median 7.9 years). Late arteriograms were obtained in 30 patients (46%) an average of 52 months after operation (range 6 months to 18 years). They demonstrate stable renal artery repair with no evidence of late graft failure in each. Hypertension was cured or improved in 51 of 53 patients (96%) with a proven patent reconstruction. Aneurysms were successfully repaired in 11 patients. Renal function was improved in four patients with ex vivo repairs, unchanged in 59 patients (15 in situ, 44 ex vivo), and persistently worse in only three patients, all of whom had in situ repairs.

CONCLUSION

The branched arterial autograft allows the restoration of normal renal arterial anatomy and function when inserted to replace complex distal renovascular disease. This provides a durable repair, essential for younger patients affected by this pattern of disease who anticipate a normal life span after renovascular repair. Successful long-term correction of diastolic hypertension and aneurysmal disease was accomplished without significant morbidity.

An AIDS vaccine: a flickering light at the end of the tunnel

Ten years ago, federal officials predicted that an AIDS vaccine was just around the corner. Today--millions of dollars and scores of research trials later--AIDS researchers at the National Institutes of Health are deciding whether to test two promising AIDS vaccines. This time, officials aren't promising a quick fix.