In a human genome, we found dispersed repetitive sequences homologous to part of a human endogenous retrovirus termed HERV-K which resembled mouse mammary tumor virus. For elucidation of their structure and organization, we cloned some of these sequences from a human gene library. The sequence common to the cloned DNA was ca. 630 base-pairs (bp) in length with an A-rich tail at the 3' end and was found to be a SINE (short interspersed repeated sequence) type nonviral retroposon. In this retroposon, the 5' end had multiple copies of a 40 bp direct repeat very rich in GC content and about the next 510 nucleotides were homologous to the 3' long terminal repeat and its upstream flanking region of the HERV-K genome. This retroposon was thus given the name, SINE-R element since most of it derived from a retrovirus. SINE-R elements were present at 4,000 to 5,000 copies per haploid human genome. The nucleotide sequence was ca. 90% homologous among the cloned elements.

Expression of the human endogenous retrovirus genome HERV-K, homologous to mouse mammary tumor virus, was investigated in cultured human tumor cells. In several cell lines, the HERV-K genome was expressed as an 8.8-kilobase poly(A)+ RNA which appeared to be a full-size transcript of this genome. In the human breast cancer cell line T47D, stimulation of HERV-K genome expression by progesterone was observed after estradiol treatment.

Endogenous retrovirus-like sequences homologous to intracisternal type-A particle (IAP) genes, which are present in the inbred mouse (Mus musculus) genome, were cloned from a Syrian hamster gene library. A typical hamster IAP gene was 7 kb long and segments homologous to long terminal repeat (IAP) sequences present in Mus musculus IAP genes were located at both ends of the gene. Contrary to the pattern found in the Mus musculus IAP genes, the organization of the cloned hamster IAP genes was not markedly polymorphic and deletion was not observed among these cloned genes. A sequence about 0.8 kb long and located close to the 3' end of the hamster IAP gene was well conserved in both IAP gene families, although they showed less overall homology with one another. The reiteration frequency of the hamster IAP genes was calculated to be 950 copies per haploid genome. Since such IAP genes with the above properties were not found in the genome of the Chinese hamster, whose progenitors diverged from those of the Syrian hamster about 7.5 Myr ago, the integration of a huge number of Syrian hamster IAP genes must have occurred subsequent to such divergence.

By using a radioimmunoassay specific for endothelin-1 (ET-1), we studied whether ET-1-like immunoreactivity (LI) is present in human urine. Significant amounts of ET-1-LI were present in human urine, and the daily urinary excretion of ET-1-LI in 30 normal subjects was 67.6 ± 35.5 ng/day. The mean urinary excretion of ET-1-LI determined in spot urine was 82.8 ± 38.2 pg/mg creatinine (n = 30), while the mean plasma concentrations of ET-1-LI in the same individuals were 1.1 ± 0.5 pg/ml. There was no significant correlation between urinary ET-1-LI excretion and its plasma levels. Reverse-phase high-pressure liquid chromatography of human urine extract revealed a major ET-1-LI component coeluting with standard ET-1. The present study demonstrates the presence of ET-1-LI excreted in human urine, although its exact source and physiological significance in renal tissues remain to be determined.

Four patients with chronic subdural hematomas, all of which resolved spontaneously, were followed from the time of injury to resolution of the chronic subdural hematoma. Periodic computed tomographic (CT) scans showed spontaneous resolution 78, 174, 231, and 326 days after the development of the chronic subdural hematoma, respectively. Features of the CT scans and a possible mechanism of spontaneous resolution are discussed.