Citations

▪ Abstract The assembly of the cystic fibrosis transmembrane regulator (CFTR) chloride channel is of interest from the broad perspective of understanding how ion channels and ABC transporters are formed as well as dealing with the mis-assembly of CFTR in cystic fibrosis. CFTR is functionally distinct from other ABC transporters because it permits bidirectional permeation of anions rather than vectorial transport of solutes. This adaptation of the ABC transporter structure can be rationalized by considering CFTR as a hydrolyzable-ligand-gated channel with cytoplasmic ATP as ligand. Channel gating is initiated by ligand binding when the protein is also phosphorylated by protein kinase A and made reversible by ligand hydrolysis. The two nucleotide-binding sites play different roles in channel activation. CFTR self-associates, possibly as a function of its activation, but most evidence, including the low-resolution three-dimensional structure, indicates that the channel is monomeric. Domain assembly and interaction within the monomer is critical in maturation, stability, and function of the protein. Disease-associated mutations, including the most common, ΔF508, interfere with domain folding and association, which occur both co- and post-translationally. Intermolecular interactions of mature CFTR have been detected primarily with the N- and C-terminal tails, and these interactions have some impact not only on channel function but also on localization and processing within the cell. The biosynthetic processing of the nascent polypeptide leading to channel assembly involves transient interactions with numerous chaperones and enzymes on both sides of the endoplasmic reticulum membrane.

AbstractThe etiology, prognosis, and optimal management of primary gastric carcinoids remain controversial. Records of 36 consecutive patients with gastric carcinoid (15 men) were reviewed retrospectively between 1975 and 1990. Follow‐up was complete in 97% of cases. Mean age at diagnosis was 58.4 years (range 24–82 years). The clinical presentations included anemia (72%), pain (69%), and carcinoid syndrome (11%). Associated autoimmune and endocrine abnormalities were common and included atrophic gastritis (67%), pernicious anemia (58%), hypothyroidism (39%), diabetes (19%), Addison's disease (6%), and hyperparathyroidism (6%). Lesions were nonantral in 78%, involving only the corpus in 42%, the fundus in 28%, and only the antrum in 8%; 42% were multiple. Urinary 5‐hydroxyindoleacetic acid (5‐HIAA) and serum gastrin levels were elevated in 17% and 50% of those tested, respectively. Histologic examination revealed that 28% of lesions were ≥2 cm, and 33% had liver metastases on presentation or developed them during follow‐up. Eight patients (22%) died of tumor with a median survival of 39 months. The presence of metastases, atypical histology, serosal involvement, and size > 2 cm were adverse prognostic factors. In patients without hypergastrinemia (n=6), 66% developed metastases, 60% had elevated 5‐HIAA, and 50% died of carcinoid tumor. In sharp contrast, those patients with hypergastrinemia and “typical” gastric carcinoids (n=15), metastases and death did not occur (p<0.003 and p < 0.005, respectively, compared with eugastrinemic patients). In the latter group (hypergastrinemia and typical histology), pernicious anemia was common (73%); solitary lesions and serosal penetration were seen comparatively less often (33% versus 100%, p<0.005 and 0% versus 33%, p<0.05, respectively); and no lesion measured > 2.0 cm compared to 66% in the group without elevated gastrin (p<0.002). No patient with hypergastrinaemia had elevated levels of 5‐HIAA. Overall survival at 5 and 10 years was 58% and 28%, respectively. Survival was 80% at 5 and 10 years in the hypergastrinemic group. Gastric carcinoid tumors that are histologically atypical, large (>2 cm), or present without elevated gastrin are potentially lethal and require aggressive therapy. In contrast, gastric carcinoids with typical histology and hypergastrinemia are rarely lethal, and conservative management with local excision and close observation is appropriate.

AbstractInsulinoma in patients with multiple endocrine neoplasia (MEN) is a rare condition that because of its usual multicentricity presents difficulties not encountered in sporadic patients. In contrast to gastrinoma, which is the most common pancreatic neoplasm associated with MEN I, malignancy and duodenal tumors are much less common for patients with insulinomas, and excellent palliative medication is not available. Accordingly, there is a much greater reliance on surgical therapy for this group of patients. Between 1970 and 1991 a total of 19 patients had surgical treatment of MEN I‐related insulinoma. Each patient had hyperinsulinemic hypoglycemia. One patient, with extensive metastases, had unresectable disease. Of the remaining 18, there were 16 (89%) multiple pancreatic tumors. Tumors were located in the neck, body, or tail in 17 cases, 10 of whom also had tumors in the head. Pancreatic resections performed were 1 total, 12 subtotal (7 also had enucleation of tumors from the pancreatic head), and 5 limited distal resections and/or enucleation (conservative resection). There was no operative mortality. One patient developed pancreatitis, fistula, and diabetes following subtotal resection and enucleation. Postoperative cure was achieved in 17 of 18 cases. Recurrent disease occurred in 2 of 5 conservative resections compared to 0 of 12 subtotal resections, with median follow‐up times of 10.4 and 10.3 years, respectively. During the follow‐up period, four patients died, possibly all due to MEN I‐related conditions. Hyperinsulinism in MEN I is associated with the occurrence of multiple, usually benign, pancreatic islet cell tumors, and surgery is an effective treatment modality. Surgical management should be guided by two principles: total removal of gross disease and safe prophylactic pancreatic resection. Acceptable morbidity, low recurrence rates, and a low risk of inducing diabetes lead us to recommend routine subtotal distal pancreatectomy. Meticulous evaluation of the pancreatic head using intraoperative ultrasonography to locate tumors and to locate the pancreatic duct, followed by precise enucleation of residual tumors, is essential to ensure cure.

The breakpoint cluster region protein (Bcr) is a large soluble oligomeric multidomain protein best known because of its involvement in chronic myelogenous leukemia (CML). A chromosomal translocation between its gene and that of the c-abl kinase (`Philadelphia chromosome') plays a major causative role in that malignancy. Thus most attention has been paid to the role of the protein in hemopoietic cells. However, Bcr is also expressed in other cell types including epithelia. Bcr is generally considered to be a cytoplasmic protein but in addition to its kinase and GTPase exchange and activating domains it contains potentially membrane-interacting pleckstrin homology and C2 domains as well as a PDZ-binding C terminus mediating an interaction with a PDZ-domain protein at intercellular junctions of epithelial cells. We have examined the ability of Bcr to interact with other epithelial PDZ proteins and found specific binding to both the apical PDZK1 protein and the Golgi-localized Mint3. The former is important in the organization of several apical functions and the latter in vesicular trafficking in the secretory pathway. Hence these findings extend the interactions and likely signaling impact of Bcr in epithelia from the cytosol to at least these two membrane compartments.

Purpose This multicenter, open-label, phase II study was undertaken to assess the antitumor activity and safety of the oral mitogen-activated extracellular signal regulated kinase kinase (MEK) inhibitor, CI-1040, in breast cancer, colon cancer, non-small-cell lung cancer (NSCLC), and pancreatic cancer. Patients and Methods Patients with advanced colorectal, NSCLC, breast, or pancreatic cancer received oral CI-1040 continuously at 800 mg bid. All patients had measurable disease at baseline, a performance status of 2 or less, and adequate bone marrow, liver, and renal function. Expression of pERK, pAkt, and Ki-67 was assessed in archived tumor specimens by quantitative immunohistochemistry. Results Sixty-seven patients with breast (n = 14), colon (n = 20), NSCLC (n = 18), and pancreatic (n = 15) cancer received a total of 194 courses of treatment (median, 2.0 courses; range, one to 14 courses). No complete or partial responses were observed. Stable disease (SD) lasting a median of 4.4 months (range, 4 to 18 months) was confirmed in eight patients (one breast, two colon, two pancreas, and three NSCLC patients). Treatment was well tolerated, with 81% of patients experiencing toxicities of grade 2 or less severity. Most common toxicities included diarrhea, nausea, asthenia, and rash. A mild association (P < .055) between baseline pERK expression in archived tumor specimens and SD was observed. Conclusion CI-1040 was generally well tolerated but demonstrated insufficient antitumor activity to warrant further development in the four tumors tested. PD 0325901, a second generation MEK inhibitor, has recently entered clinical development and, with significantly improved pharmacologic and pharmaceutical properties compared with CI-1040, it may better test the therapeutic potential of MEK inhibition in cancer.

Cystic fibrosis (CF) is a childhood hereditary disease in which the most common mutant form of the CF transmembrane conductance regulator (CFTR) ΔF508 fails to exit the endoplasmic reticulum (ER). Export of wild-type CFTR from the ER requires the coat complex II (COPII) machinery, as it is sensitive to Sar1 mutants that disrupt normal coat assembly and disassembly. In contrast, COPII is not used to deliver CFTR to ER-associated degradation. We find that exit of wild-type CFTR from the ER is blocked by mutation of a consensus di-acidic ER exit motif present in the first nucleotide binding domain. Mutation of the code disrupts interaction with the COPII coat selection complex Sec23/Sec24. We propose that the di-acidic exit code plays a key role in linking CFTR to the COPII coat machinery and is the primary defect responsible for CF in ΔF508-expressing patients.

AbstractAlthough useful palliation can often be achieved when external beam irradiation and chemotherapy are used to treat locally advanced gastrointestinal malignancies, local control and long‐term survival are infrequent in view of the limited tolerance of surrounding organs and tissues. In view of dose limitations of external beam irradiation, intraoperative irradiation (IORT) with electrons has been used as a supplement to external treatment in an attempt to improve the therapeutic ratio of local control versus complications. An IORT dose of 10 to 20 Gy has been combined with fractionated external beam doses of 45 to 55 Gy in 1.8 Gy fractions in studies performed in the United States, Japan, Europe, and Scandinavian countries. In this paper the indications for and the results of aggressive combined techniques that include IORT are discussed. Results obtained with external beam techniques alone or with chemotherapy and resection are presented by site to demonstrate the need for higher doses of irradiation. When results from IORT series are compared to standard treatment with regard to disease control and survival, local control appears better with locally advanced colorectal, gastric, and pancreatic cancer; and survival appears better with colorectal ± biliary cancers. With pancreatic cancer, improvements in local control do not translate into increased survival in view of the high incidence of subsequent liver and peritoneal failures. Implications for future strategies in all sites are discussed.

Abstract Inhaled glucocorticosteroids (ICS) are commonly prescribed for chronic obstructive pulmonary disease. No adverse effect on bone mineral density (BMD) has been proven. In a randomized double-blind, placebo-controlled trial at seven centers in North America, we recruited 412 current smokers or recent quitters with mild to moderate chronic obstructive pulmonary disease. They used inhaled triamcinolone acetonide, 600 mcg, or placebo, twice daily. We measured femoral neck and lumbar spine BMD at baseline and after 1 and 3 years, and serum osteocalcin at baseline, 3 months, 1 year, and 3 years. After 3 years, BMD at the femoral neck decreased 1.78% more with ICS than with placebo (p &lt; 0.001). More participants in the ICS group experienced 6% or more loss of femoral neck BMD (p = 0.002). Lumbar spine BMD increased in the placebo group by 0.98% but decreased by 0.35% in the ICS group (a difference of 1.33%, p = 0.007). Changes in osteocalcin did not correlate with changes in BMD. Fractures, lost height, or osteoporosis diagnoses were not increased among ICS users compared with placebo users. In summary, the use of inhaled triamcinolone acetonide was associated with loss of BMD at the femoral neck and lumbar spine after 3 years of treatment.