Response from lieberman and colleagues

Respond on comments on Lieberman's article: Cyclosiloxanes Produce Fatal Liver and Lung Damage in Mice. Environ Health Perspect 107:161-165     

Histamine H2 receptor trafficking: role of arrestin, dynamin, and clathrin in histamine H2 receptor internalization

Agonist-induced internalization of G protein-coupled receptors (GPCRs) has been implicated in receptor desensitization, resensitization, and down-regulation. In the present study, we sought to establish whether the histamine H2 receptor (H2r) agonist amthamine, besides promoting receptor desensitization, induced H2r internalization. We further studied the mechanisms involved and its potential role in receptor resensitization. In COS7 transfected cells, amthamine induced H2r time-dependent internalization, showing 70% of receptor endocytosis after 60-min exposure to amthamine. Agonist removal led to the rapid recovery of resensitized receptors to the cell surface. Similar results were obtained in the presence of cycloheximide, an inhibitor of protein synthesis. Treatment with okadaic acid, an inhibitor of the protein phosphatase 2A (PP2A) family of phosphatases, reduced the recovery of both H2r membrane sites and cAMP response. Arrestin 3 but not arrestin 2 overexpression reduced both H2r membrane sites and H2r-evoked cAMP response. Receptor cotransfection with dominant-negative mutants for arrestin, dynamin, Eps15 (a component of the clathrin-mediated endocytosis machinery), or RNA interference against arrestin 3 abolished both H2r internalization and resensitization. Similar results were obtained in U937 cells endogenously expressing H2r. Our findings suggest that amthamine-induced H2r internalization is crucial for H2r resensitization, processes independent of H2r de novo synthesis but dependent on PP2A-mediated dephosphorylation. Although we do not provide direct evidence for H2r interaction with beta-arrestin, dynamin, and/or clathrin, our results support their involvement in H2r endocytosis. The rapid receptor recycling to the cell surface and the specific involvement of arrestin 3 in receptor internalization further suggest that the H2r belongs to class A GPCRs.     

E1A deregulates the centrosome cycle in a Ran GTPase-dependent manner

By means of the yeast two-hybrid system, we have discovered a novel physical interaction between the adenovirus E1A oncoprotein and Ran, a small GTPase which regulates nucleocytoplasmic transport, cell cycle progression, and mitotic spindle organization. Expression of E1A elicits induction of S phase and centrosome amplification in a variety of rodent cell lines. The induction of supernumerary centrosomes requires functional RCC1, the nucleotide exchange factor for Ran and, hence, a functional Ran network. The E1A portion responsible for the interaction with Ran is the extreme NH(2)-terminal region (amino acids 1-36), which is also required for the induction of centrosome amplification. In an in vitro assay with recombinant proteins, wild-type E1A interferes with nucleotide exchange on Ran, whereas an E1A mutant, deleted from the extreme NH(2)-terminal region, does not. In addition, we detected an in vitro interaction between Ran and HPV-16 E7 and SV40 large T antigen, two oncoproteins functionally related to E1A. These findings suggest a common pathway of these oncoproteins in eliciting virus-induced genomic instability.     

Prevention of radiotherapy-induced emesis

In this minireview the authors examine and discuss the radioprotective compounds and the new combination therapies for the prophylaxis of radiation-induced emesis. Radiation-induced emesis is an important secondary effect of this anticancer treatment and it represents one of the causes of therapy interruption and decay of life quality before the introduction of optimal control of radiation-induced emesis with new antiemetic drugs which ensure the continuance of radiotherapy and avoid time breaks, that could negatively influence the efficacy of anticancer treatment. The incidence, the severity or the latency of radiotherapy-induced nausea and vomiting are correlated both with the treatment features (fractions, total dose, irradiation site) and with the main clinical characteristics of the patients. In contrast to the very extensive literature on the prevention of chemotherapy-induced emesis, relatively few studies about the prevention of nausea and vomiting in patients submitted to radiotherapy have been published. Among antiemetic drugs for the prevention of emesis, benzamides and in particular metoclopramide, are widely used in clinical practice. The introduction of selective 5-HT3 antagonists in clinical practice produced an important improvement in control of chemotherapy induced emesis, but few published studies were aimed at evaluating the efficacy of these drugs in the prophylaxis of nausea and vomiting due to radiation exposure. We herewith present a brief summary of Clinical practice guidelines for the use of antiemetics in anticancer therapy recently published by ASCO (American Society of Clinical Oncology).     

Differential expression of the retinoblastoma gene family members in choroidal melanoma: prognostic significance.

We evaluated 55 samples of choroidal melanoma managed by enucleation. Knowing that the immunohistochemical expression of the retinoblastoma gene family members Rb/p105, p107, and pRb2/p130 was inversely correlated with the degree of malignancy in at least some histological types, we investigated the expression of these three proteins in choroidal melanoma. We focused on the relationship between patient survival and the immunohistochemical detection of the retinoblastoma proteins. No correlation with clinical outcome was found for Rb/p105 and p107. However, we found pRb2/p130 to be an independent prognostic factor correlating positively or directly with patient survival times and indirectly or inversely with the degree of malignancy. Demonstration of the prognostic value of the immunohistochemical expression of pRb2/p130 is of significance, even if additional studies are required to confirm these data and to compare the prognostic value of pRb2/p130 immunodetection to that of other recently proposed markers, such as p53.     

Colorectal carcinomas and PTEN/MMAC1 gene mutations.

PURPOSE: PTEN/MMAC1/TEP1 is a tumor suppressor gene encoding a dual-specificity protein phosphatase with homology to the cytoskeleton proteins, chicken tensin and bovine auxilin. PTEN mutations have been described in several types of human cancer. Recently, mutations at an (A)(6) repeat of PTEN exons 7 and 8 in colorectal cancer (CRC) patients with microsatellite instability have been detected. Moreover, an involvement of the transforming growth factor (TGF)-beta pathway in hereditary colorectal syndromes has been proposed. Experimental Design: In this study, we analyzed the frequency of PTEN gene mutations in 36 CRC patients and 5 colon cancer cell lines. Furthermore, in 16 of 36 patients, microsatellite instability and TGF-beta receptor II analysis was possible. The study was performed by PCR and automated sequencing of the entire coding region of the PTEN gene. RESULTS: About 17% of colon cancer patients and one of five (HSR 320) colon cancer cell lines had mutations. Mutations were detected only among patients with locally advanced or metastatic CRC. PTEN mutations were detected in three of five (60%) patients showing both microsatellite instability and TGF-beta receptor II mutations. These patients presented with advanced or metastatic CRC CONCLUSIONS: Overall, these results show that PTEN alteration together with TGF-beta pathway inactivation could contribute to tumorigenesis and metastatic spread of sporadic and microsatellite unstable CRC.     

Estimating impacts on developing countries of the decrease in U.S. training opportunities for foreign medical graduates.

Between 1973 and 1983, the number of foreign nationals from developing nations who entered the United States for graduate medical education decreased by approximately 90%. Many of those who would have studied in the United States if this decrease had not occurred would have returned home to serve their countries. To estimate the impact of this loss, a survey was conducted in six major cities in Latin America between 1983 and 1989. Selected local medical students interviewed 554 physicians who had returned home after U.S. training and 60 of their classmates who had not trained there. The findings indicate that the returned physicians had given approximately twice as much time to teaching, research, and medical administration as did those who had not left home. The authors maintain that this and related findings show how the curtailment of opportunities for training foreign nationals in the United States is detrimental to both the aspirations of developing nations and the influence of the United States in world affairs.