Mariko Shirota

Human PRL receptor cDNA clones from hepatoma (Hep G2) and breast cancer (T-47D) libraries were isolated by using a rat PRL receptor cDNA probe. The nucleotide sequence predicts a mature protein of 598 amino acids with a much longer cytoplasmic domain than the rat liver PRL receptor. Although this extended region has additional segments of localized sequence identity with the human GH receptor, there is no identity with any consensus sequences known to be involved in hormonal signal transduction. This cDNA will be a valuable tool to better understand the role of PRL in the development and growth of human breast cancer.

The screening of a size-selected cDNA library from the ovary revealed the existence of a second form of PRL receptor in the rat. The polypeptide sequence deduced from cDNAs has a much longer cytoplasmic domain (357 amino acids) than the form previously identified in the liver (57 amino acids). Nucleotide sequence analysis and comparison with rabbit, mouse, and human PRL receptor cDNAs suggests that the two forms of rat PRL receptor result from alternative splicing of a primary transcript. Complementary DNAs encoding the long form of the receptor were also found in a library prepared from estradiol-treated rat liver, although they represent a minor fraction of total PRL receptor cDNAs obtained from this tissue. DNA polymerase chain reaction amplification of cDNA confirmed the presence of the two receptor forms in both the ovary and liver. Northern analysis, using probes that specifically hybridize with either form of mRNA, indicates a major transcript of 1.8 kilobases (kb) in estradiol-treated liver, which encodes the receptor with a short cytoplasmic domain, while the long form of the receptor is encoded by mRNAs of 2.5 and 3 kb. In the ovary, a complex pattern of hybridization to multiple mRNAs (1.8-5.5 kb) is obtained with the probe specific to the long form, and essentially only a 5.5-kb mRNA is obtained with the probe specific to the short form. The predicted size of the mature form of the long PRL receptor (PRL-R2) is 591 amino acid residues.(ABSTRACT TRUNCATED AT 250 WORDS)

Influence of di-(2-ethylhexyl)phthalate (DEHP) on testicular development was studied by oral administration of DEHP at doses of 500 and 1000 mg/kg/day to pregnant rats on gestational days (G) 7 to 18. Ethinyl estradiol (EE) at dose levels of 0.25 and 0.5 mg/kg/day was used as a reference substance. Each 5-6 pregnant rats were sacrificed and their fetuses were examined on G12, 14, 16, 18 and 20. Fetal deaths averaging 20-36% were observed at every examination in the group receiving 1000 mg/kg of DEHP. Increases of fetal deaths over 50% were also observed in the reference group that received 0.5 mg/kg of EE. Microscopic examination of the fetal testis in groups treated with DEHP revealed degeneration of germ cells in G16 fetuses and localized proliferation or hyperplasia of interstitial cells in G18 and 20 fetuses. Germ cells having more than two nuclei were observed in a few cases including the control testes of G14 fetuses. These multinucleated cells were observed frequently in G20 fetuses treated with DEHP. Examination of testes of naturally delivered offspring of dams treated with 1000 mg/kg of DEHP at 7 weeks of age revealed scattered atrophy or dilatation of seminiferous tubules. Another experiment was carried out to confirm the dose of DEHP affecting testicular development and spermatogenesis. DEHP was given to pregnant rats at doses of 125, 250 and 500 mg/kg/day during G7-18. Similar histopathological changes were observed in fetal testes of the group exposed to 500 and 250 mg/kg of DEHP, but not in those exposed to 125 mg/kg. In postnatal examinations, however, no abnormality was found in the testes at 5 and 10 weeks after birth in any of the treated groups. Furthermore, no abnormal findings were observed in the function of sperm, sperm counts and sperm morphology in the offspring of the group treated with DEHP during the fetal period at 10 weeks of age. Thus, 125 mg/kg/day is considered the no-observed-effect-level of DEHP on testicular development of rats by exposure in utero during the period of organogenesis.