Dose-response relationship for radiation carcinogenesis in the low-dose region

Evidence that low-level radiation substantially enhances the effectiveness of repair mechanisms is summarized. This finding destroys the theoretical basis (there is no other basis) for use of a linear-no threshold dose-response relationship to estimate the cancer risk of exposure to low-level radiation. Such a methodology will exaggerate the risk. This conclusion is further supported by epidemiological evidence and by studies of the effects of radon exposure in the home, which are reviewed.

Indoor radon maps of the United States

A recently published compilation of average radon levels in 1,729 U.S. counties with standard errors of approximately 20% is used to generate maps exhibiting these results and showing correlations over multicounty areas. Several large areas and numerous smaller areas with high radon levels are identified.

Tests of the linear-no threshold theory for lung cancer induced by exposure to radon

The linear theory used to extrapolate the cancer risk of radon exposure from high levels where direct data are available to low levels encountered in homes is tested by comparing lung cancer rates, m, and average radon levels, r, in numerous U.S. states and counties. It is shown that most problems normally associated with ecological studies do not apply here. The data show a very strong tendency for lung cancer rates, corrected for smoking prevalence (S), to decrease with increasing r, in sharp contrast to the opposite behavior predicted by the theory. It is shown that even a perfect negative r-S correlation cannot explain this discrepancy. Actual r-S correlations are only a few percent. Several other possible explanations for the discrepancy are explored, but none can reduce it by more than about 25%.

Relationship between exposure to radon and various types of cancer

Correlations are studied between average radon levels in 1600 U.S. counties and mortality rates in them from various types of cancer. By far the strongest correlation is with lung cancer, but the sign of the correlation is negative. When smoking prevalence is included in a multiple regression, the large negative correlation between radon and lung cancer is essentially unaffected.

Benefits to a life insurance company from providing radon tests for clients

If a life insurance company provided free radon tests to clients, clients' life expectancies would be extended and profits would thereby be increased. This effect is quantified and it is found that the direct monetary benefits to the company could be substantial. Several subsidiary advantages are also discussed.

High frequency expression of integrated proviruses derived from enhancer trap retroviruses

Since retroviruses integrate preferentially into transcriptionally active loci, the provirus may come under the control of regulatory elements of the gene into which it integrated and thus become a functional tag for that gene. In order to determine the frequency of retroviral integration near active endogenous enhancer elements, a retroviral enhancer trap vector was constructed. Lacking the long terminal repeat enhancer, expression of the neomycin resistance (neo) gene, used as a reporter, is dependent upon endogenous enhancer elements able to activate the long terminal repeat promoter. Infection of murine fibroblast cells indicated that a high proportion of the proviral copies expressed the neo gene. Infection of hematopoietic lines confirmed this high frequency of expression of integrated proviruses. Overall, between 43 and 74% of proviruses integrated into several different cell lines expressed the neo gene. These data suggest that retroviral integration is not only dependent upon transcriptional activity of the genomic target sites, but, more specifically, retroviruses preferentially integrate near active enhancer elements which are often associated with developmentally regulated genes.

How do retinoblastoma tumours form?

The causes of retinoblastoma (RB) can now be described with considerable accuracy, although many details are still unclear. Understanding the genetic changes leading to RB has provided an awareness of general mechanisms of cancer development and progression, previously only suspected. From the basic understanding have come new diagnostic technologies that are now ready to be applied directly to RB patients and their families, and a rational approach, based on this understanding, will help us to develop new therapies that avoid the severe complications of conventional treatment.

Failure of RB1 to reverse the malignant phenotype of human tumor cell lines

In addition to retinoblastoma and osteosarcoma, mutation of both alleles of the RB1 gene occurs frequently in several other types of tumors. In order to evaluate the role of RB1 in cancer, the wild type RB1 gene was introduced into the RB1-deleted breast cancer cell line MDA-468-S4 and retinoblastoma cell lines WERI-Rb1 and Y-79. The RB1 complementary DNA was under control of the inducible murine metallothionein promoter in MDA-468-S4 and the thymidine kinase promoter in the retinoblastoma lines. The protein, p110RB1, produced from the exogenously introduced gene appeared normal by immunoprecipitation, Western blot analysis, and nuclear localization and also showed normal cell cycle-dependent phosphorylation and an ability to bind to E1a protein. No changes in growth rate or morphology were observed in either of the reconstituted cell types. Expression of p110RB1 in MDA-468-S4 did not affect anchorage-independent growth when measured by colony formation in soft agar. Although the ability of WERI-Rb1 cells expressing p110RB1 to form colonies in methylcellulose was reduced, the reconstituted retinoblastoma cell lines formed intraocular tumors in immunodeficient mice with the same efficiency as the RB1-negative parent cell lines and the tumors produced by the RB1-reconstituted cells continued to express p110RB1. These experimental results suggest that the malignant phenotype is little affected by the replacement of p110RB1 and that RB1 is a relatively weak tumor suppressor gene.

Variation of radon levels in U.S. homes correlated with house characteristics, location, and socioeconomic factors

Data are analyzed on measurements of Rn levels in numerous U.S. homes, accompanied by responses to questionnaires. Substantial (but far from complete) bias reduction was accomplished using questionnaire responses, leaving 37,000 measurements in living areas and 33,000 in basements for the analysis. Variables studied included: level with respect to ground where measurement was made, room type, age of house, recent weatherization actions, draftiness, location (urban, suburban, rural), air pollution, market value of house, annual household income, educational attainment of head of household, cigarette smoking, whether the house is rented or owner occupied, and geographic section of U.S. Geometric mean Rn levels were determined for each response to questionnaire items (correlations) and for each pair of responses (cross correlations). Many interesting correlations and cross correlations were found, and their explanation and consequences are discussed.

Hyperphosphorylation of the retinoblastoma gene product is determined by domains outside the simian virus 40 large-T-antigen-binding regions

With the murine retinoblastoma (RB) cDNA, a series of RB mutants were expressed in COS-1 cells and the pRB products were assessed for their ability (i) to bind to large T antigen (large T), (ii) to become modified by phosphorylation, and (iii) to localize in the nucleus. All point mutations and deletions introduced into regions previously defined as contributing to binding to large T abolished pRB-large T complex formation and prevented hyperphosphorylation of the RB protein. In contrast, a series of deletions 5' to these sites did not interfere with binding to large T. While some of the 5' deletion mutants were clearly phosphorylated in a cell cycle-dependent manner, one, delta Pvu, failed to be phosphorylated depsite binding to large T. pRB with mutations created at three putative p34cdc2 phosphorylation sites in the N-terminal region behaved similarly to wild-type pRB, whereas the construct delta P5-6-7-8, mutated at four serine residues C terminal to the large T-binding site, failed to become hyperphosphorylated despite retaining the ability to bind large T. All of the mutants described were also found to localize in the nucleus. These results demonstrate that the domains in pRB responsible for binding to large T are distinct from those recognized by the relevant pRB-specific kinase(s) and/or those which contain cell cycle-dependent phosphorylation sites. Furthermore, these data are consistent with a model in which cell cycle-dependent phosphorylation of pRB requires complex formation with other cellular proteins.

Emerging technologies in the field of healthcare: enhancing the interface to the medical professional

This paper reviews the latest technology either available or currently under development which will enhance the medical professional's ability to interface computer systems. This technology includes bar-coding, graphics, intelligent workstation, and expert system. Whenever possible, examples are given to illustrate the technology.

Ecological versus case-control studies for testing a linear-no threshold dose-response relationship

The two basic problems with ecological studies are (A) individuals studied are not necessarily the individuals who are at risk, and (B) they are very vulnerable to confounding factors. It is shown that where the study is designed to test a linear-no threshold dose-response theory, (A) does not apply. Where the ecological study deals with the average dose and response in a large number of US counties, the available data and computer capability for reducing effects of confounders are so powerful that (B) may be no more important for the ecological than for a case-control study. The migration problem is treated and found to be relatively unimportant.

Analytical- and preparative-scale separation of molecular variants of alpha-fetoprotein by anion-exchange chromatography on Monobead resins

A rapid and reliable purification procedure is described that is useful for both analytical detection and quantitative recovery of milligram amounts of individual molecular variants of mouse alpha-fetoprotein (AFP). The appropriate separation conditions were developed with an analytical-size Mono Q anion-exchange column linked to an automated Fast Protein Liquid Chromatography system. Effective separations of fetal-derived AFP variants was accomplished within 20 min under mild conditions with an L-histidine buffer. Employing the optimal separation conditions established on the Mono Q HR 5/5 column we upscaled the procedure by using a preparative Mono Q HR 16/10 column in order to obtain milligram quantities of each molecular variant of AFP. Seven distinct isomeric forms of AFP could be recovered on the preparative anion exchanger in a highly reproducible manner. Each of the seven protein peaks eluted from the Mono Q column were confirmed to be distinct isoforms of AFP by isoelectric focusing and Western blotting developed with monospecific anti-AFP antisera. This method in its scaled up version offers the benefit of providing milligram quantities of immunochemically pure AFP isomers for structure and function studies.

Isolation and characterization of a distinct immunoregulatory isoform of alpha-fetoprotein produced by the normal fetus

In this report, we examine the functional significance of the molecular microheterogeneity of alpha-fetoprotein (AFP). In doing so, we have taken the direct approach of purifying the naturally occurring isomeric forms of fetal-derived AFP using a preparative anion exchange column linked to an automated fast protein liquid chromatography (FPLC) system followed by parallel testing of each isolated molecular variant for in vitro immunoregulatory activity. The data obtained demonstrate the presence of seven distinct variants of AFP as defined by their retention volumes on FPLC elution profiles, by their pIs on analytical IEF gels, and by Western blot analysis. Molecular mass determination by SDS-PAGE showed each isomer to be equivalent in size to 69,000-dalton native unfractionated AFP molecules. All the immunosuppressive activity of AFP was localized to a single variant representing only 6% of the total composition of native AFP. The immunoregulating isomer termed AFP-1 was the least acidic of the seven isolated variants with a pI of 5.1 and displayed a sialic acid content of 1 mol/mol of protein. The inhibitory activity of AFP-1 could be readily measured on T cell-dependent antibody synthesis, Con A-induced stimulation of Lyt-1+23- thymocyte DNA synthesis, and lymphokine-activated NK cell activity. All other isomers were without effect in these test systems. The immunosuppressive AFP-1 isomer also displayed the strongest growth-promoting influence on cultured bone marrow lymphocytes. There was no correlation between functional activity and degree of expression of sialic acid residues on the AFP molecules. These findings demonstrate that the immunoregulating function of AFP is confined to a distinct and relatively small subpopulation of native AFP molecules and should therefore contribute to the resolution of outstanding questions regarding the structure/function relationship of this onco-fetal glycoprotein.

Gamete intrafallopian tube transfer (GIFT): making laparoscopy more than "diagnostic"

Diagnostic laparoscopy is commonly performed on patients as part of a complete infertility investigation. Recently published protocols have investigated the efficacy of using empiric ovulation induction, intrauterine insemination, or both before beginning in vitro fertilization. Because many patients enrolled in these protocols will be exposed to both ovulation induction and diagnostic laparoscopy, the authors reasoned that it would be more effective to begin ovulation induction at the time of the proposed diagnostic laparoscopy in order to allow gamete intrafallopian tube transfer (GIFT) at the same time. Twenty-five nulliparous patients underwent diagnostic GIFT. There were eight continuing pregnancies in this group (32%). Diagnostic GIFT is a more effective use of the opportunity provided by laparoscopy than diagnostic laparoscopy alone.