Identification and functional analysis of novel inactivating thyrotropin receptor mutations in patients with thyrotropin resistance.

OBJECTIVE: We identified and analyzed novel thyrotropin (TSH) receptor mutations in three Japanese families with resistance to TSH. DESIGN: The TSH receptor gene was sequenced and the mutations were determined. The mutant TSH receptors were transfected into COS-7 cells, and their functions were analyzed. PATIENTS: The patients were compound-heterozygotes for the R450H mutation and novel mutations in the TSH receptor gene. The first patient was a compound-heterozygote for R450H and V473I. The second sibling possessed R450H and R519C. The third sibling had R450H and R519G. RESULTS: The R450H mutant exhibited moderately impaired receptor functions and a moderately decreased cell surface expression in agreement with previous results. The V473I mutant exhibited an almost normal TSH binding, a slightly decreased cyclic adenosine monophosphate (cAMP) response, a moderately decreased inositolphosphate (IP) response, and an almost normal cell surface expression. TSH binding and TSH stimulation of cAMP and IPs were markedly decreased in the R519C and R519G mutants. Cell surface expression was decreased in the R519C mutant and negligible in the R519G mutant. All of these mutants showed normal intracellular synthesis of TSH receptors. CONCLUSIONS: These novel inactivating mutations contribute to understanding of the structure-function relationship of the TSH receptor. To date, all of the patients with TSH resistance resulting from TSH receptor mutations identified in Japan possessed the R450H mutation at least in one allele. These observations suggest that the R450H mutation is a commonly observed TSH receptor mutation in patients with TSH resistance in Japan.     

Effects of 2 weeks of low-intensity cycle training with different pedaling rates on the work rate at lactate threshold

Purpose

This study examined (1) the effects of a single bout of exercise at different pedaling rates on physiological responses, pedal force, and muscle oxygenation, and (2) the effects of 2 weeks of training with different pedaling rates on work rate at lactate threshold (Work_LT).

Methods

Sixteen healthy men participated in the study. An incremental exercise test involving pedaling a cycling ergometer at 50 rpm was conducted to assess maximal oxygen consumption and Work_LT. The participants performed constant workload, submaximal exercise tests at Work_LT intensity with three different pedaling rates (35, 50, and 75 rpm). Oxygen consumption (\(\dot{V}\)O₂), blood pressure, heart rate (HR), blood lactate, and pedal force were measured and oxy-hemoglobin/myoglobin concentration (OxyHb/Mb) at vastus lateralis was monitored by near-infrared spectroscopy during exercise. The participants were then randomly assigned to cycling exercise training at Work_LT in either the low or high frequency pedaling rate (LFTr, 35 rpm or HFTr, 75 rpm) group. Each 60-min training session was performed five times/week.

Results

Despite maintaining the same work rate, \(\dot{V}\)O₂ and HR were significantly lower at 35 than 75 rpm. Conversely, integrated pedal force was significantly higher at 35 than 75 rpm. Peripheral OxyHb/Mb was significantly lower at 35 than 75 rpm. After 2 weeks of training, Work_LT normalized to body mass significantly increased in the LFTr, but not the HFTr group.

Conclusions

Pedaling rate and the corresponding pedal force and peripheral oxygenation during cycling exercise influence the effect of training at LT on Work_LT.

     

Carcinogenicity of dimethylarsinic acid in p53 heterozygous knockout and wild-type C57BL/6J mice

There is abundant epidemiological evidence that arsenic is an environmental carcinogen related to human cancers of the skin, lung, liver and urinary bladder, in particular. Dimethylarsinic acid (DMA) has also been reported to act as a carcinogen/or a promoter in rat models. To elucidate molecular mechanisms, we conducted an 18 month carcinogenicity study of DMA in p53 heterozygous (+/-) knockout mice, which are susceptible to early spontaneous development of various types of tumors, and wild-type (+/+) C57BL/6J mice. Totals of 88-90 males, 7-8 weeks of age, were divided into three groups each administered 0, 50 or 200 p.p.m. DMA in their drinking water for 18 months. Mice that were found moribund or died before the end of the study were autopsied to evaluate the tumor induction levels, as well as those killed at the end. Both p53(+/-) knockout and wild-type mice demonstrated spontaneous tumor development, but lesions were more prevalent in the knockout case. Carcinogenic effect of DMA was evident by significant early induction of tumors in both treated p53(+/-) knockout and wild-type mice, significant increase of the tumor multiplicity in 200 p.p.m.-treated p53(+/-) knockout mice, and by significant increase in the incidence and multiplicity of tumors (malignant lymphomas) in the treated wild-type mice. By the end of 80 weeks, tumor induction, particularly malignant lymphomas and sarcomas, were similar in treated and control p53(+/-) knockout mice. No evidence for organ-tumor specificity of DMA was obtained. Molecular analysis using PCR-SSCP techniques revealed no p53 mutations in lymphomas from either p53(+/-) knockout or wild-type mice. In conclusion, DMA primarily exerted its carcinogenic effect on spontaneous development of tumors with both of the animal genotypes investigated here.     

p53 null mutations detected by a p53 yeast functional assay predict a poor outcome in young esophageal carcinoma patients

The real cause of genetic instability, which is the hall-mark of most cancers, is poorly understood. Specific gene mutations and acquired aneuploidy have been implicated as the root causes of genetic instability. Here we propose and cite evidence for the hypothesis that genetic instability of cancer cells is caused by telomere dynamics, erosion and/or amplification of the TTAGGG repeat sequences present at chromosomal termini. Since telomeres determine the domain of individual chromosomes within a nucleus and protect them from internal and external challenges, their erosion will destabilize the cell karyotype. Our hypothesis predicts that telomere dynamics provides the single unifying mechanism playing a major role in speciation, aging and cancer development. It was found that metastatic cancers of different histologic phenotypes, as well as mammalian taxa with active speciation and larger numbers of species exhibit amplification of their telomeric DNA as compared to non-metastatic counterpart cancers and taxa with only a limited number of species. The dynamic nature of this DNA can be found not only in the cancer cells but also in the peripheral lymphocytes of cancer patients. Human syndromes such as Down, Turner, Bloom, Werner, Fanconi, ataxia and many others, show aneuploidy and also are prone to develop various malignancies and premature aging. We have found that of all these syndromes have a reduced amount of telomeric DNA associated with specific mitotic catastrophes as compared to cells of age- and sex-matched normal individuals. From these and additional data generated by our group concerning speciation, aging and cancer karyotypes, we conclude that aneuploidy, which is responsible for birth defects, cancer initiation and is a major player in natural speciation, is a consequence of telomere dynamics. Because telomere reduction is linked to the aging process, which is a risk factor for cancer development in the human population, our hypothesis offers a unifying mechanism for the initiation of both hematologic and solid cancers, as well as for the origin of new species.