Biomedical subjects
Publications and source records attributed to R V Thampan.
Hormonal control of rat uterine collagenase activities which use collagen types I, III, and V as the substrates has been studied. The collagenases are shown to be regulated in general by estradiol as well as by progesterone. However, the enzyme activity that uses type III collagen as the substrate appears to have a preferential response to progesterone over estradiol.
The estrogen receptor activation factor (E-RAF)-mediated binding of the receptor-estrogen complex to uterine nuclei was found to involve at least two classes of nuclear macromolecules: (1) the DNA, and (2) a proteinacious component. Evidences are presented to show that at least a portion of (2) is represented by the nuclear RNA polymerases. The receptor-estrogen complex associated in vivo with the nuclear RNA polymerases existed in two distinct forms which sedimented at 3.8 S and 4.8 S on sucrose density gradients. Almost 2/3 of the total radioactivity was associated with the 3.8 S species. Saturation kinetics of the two forms showed that while the 4.8 S form displayed characteristics similar to the classical type I nuclear binding site, the features displayed by the 3.8 S form were closely similar to those of the nuclear type II site. The 4.8 S species is a DNA binding form while the 3.8 S form is non-DNA binding. Anti-E-RAF IIA IgG cross-reacted with both the binding components. Goat uterine E-RAF I, IIA and IIB were purified to homogeneity as described earlier. While E-RAF IIA and IIB destabilized the native DNA structure and induced separation of the DNA strands, E-RAF I performed the opposite function. The reactions required the presence of ATP; all three of them displayed DNA-dependent ATPase activity. In an in vitro transcription system which contained purified RNA polymerase B (rat liver enzyme) and goat uterine DNA, E-RAF IIA and IIB enhanced transcription 7-fold over the control while E-RAF I totally suppressed the transcription process, irrespective of whether it was stimulated earlier by the other two E-RAF forms or not. This E-RAF property remained unchanged even after its association with the 4 S receptor-estrogen complex forming 5 S complex.
The present investigation probes the intranuclear molecular changes that serve to link the nuclear binding of estradiol with the hormone-stimulated ribonucleoprotein (RNP) transport in the rat uterus. Within 2 min of in vitro exposure of isolated uterine nuclei to 10 nM 17 beta-estradiol a Mg2+-dependent nuclear ATPase becomes activated and reaches its peak activity. This is immediately followed by a phase of ATP resynthesis. This newly synthesized ATP serves as the substrate for the nuclear protein kinases. Cyclic AMP inhibits this ATP resynthesis and, as a consequence, prevents the estradiol-stimulated nuclear protein kinase activity and the exit of the RNP-estradiol complex from the nuclei. cGMP is stimulatory to the estradiol-mediated nuclear ribonucleoprotein transport.
Goat uterine estrogen receptor activation factor, a 62 kDa protein existing in three molecular forms, E-RAF I, E-RAF IIA and E-RAF IIB, has been purified to homogeneity. The three forms are immunologically identical, but differ among themselves in their molecular Stokes radii and the sedimentation coefficients. The purified protein combines with the 4 S receptor-estrogen complex of the rat uterine cytosol to produce a 5 S receptor species. The E-RAF IgG cross-reacts with the nuclear 5 S receptor of the rat uterus but not with the cytoplasmic 4 S receptor. The E-RAF competes with the 5 S receptor for the DNA binding sites.
An inverse relationship exists in the rat uterus between the endogenous estradiol concentration and the rate of accumulation within the nuclei of ribonucleoproteins (RNP) that bind estradiol. Exposure of the uterine nuclei to physiological concentrations of estradiol, either in vivo or in vitro, results in the hormone binding to the nuclear RNP and the transport of the RNP-estradiol complex from the nuclei. Evidences suggest that the RNP-estradiol complex, thus released upon in vivo exposure of the nuclei to estradiol, associates with the ribosomes forming polysomes. The polysome profiles show that the hormone-binding activity is mainly associated with the rapidly sedimenting polysomal fractions.
The present study examines the hormonal regulation of the syntheses of gap junction proteins and estrogen receptor activation factors in the rat uterus. Ovariectomy and the depletion of estradiol from the system exerted negative influence on the synthesis of both the proteins. At the same time exposure of the ovariectomized rats to exogenous estradiol resulted in the restoration of protein synthesis back to the control level. A transient peak in the synthesis of the two proteins was observed on day 2 following ovariectomy. This increased activity was not observed in rats subjected to adrenalectomy along with ovariectomy. Furthermore, exposure of the ovariectomized plus adrenalectomized rats to progesterone clearly emphasized the point that the increase in the protein synthesis observed on day 2 post-ovariectomy was due to progesterone released from the adrenals. The results are indicative of a bi-hormonal involvement in the control of the syntheses of the two proteins, estrogen receptor activation factors and gap junction proteins in the rat uterus.
Synthesis of gap junction proteins (GJPs) and of collagenases in the rat uterus has been studied under two physiological conditions: various stages of the estrus cycle, and the early pregnancy period. The synthesis has been studied by incubating uterine horns in a short-term tissue culture medium containing radioactively-labeled amino acids, followed by a double antibody immunoprecipitation of the labeled proteins. After exposure of the media to either anti-collagenase IgG(s) or anti-GJPs IgG(s), the final immunoprecipitation was achieved with the use of goat anti-rabbit IgG. Collagenase(s) synthesis was found to reach the peak, during the estrus cycle, at the proestrus stage, while GJP synthesis reached the maximum during the estrus stage. In the preimplantation, pregnant, rat uterus the syntheses of both the proteins reached the respective peak activities on day 4 of pregnancy, about 24 h before the expected time of ovum implantation. A study of the literature reveals that this time coincides with a spurt in exposure of the progesterone dominated uterus to estradiol.
The localization and abundance of the estrogen receptor activation factor (E-RAF) and a small nuclear ribonucleoprotein (snRNP) complex containing three proteins, p32, p55 and p60, which interact with the nuclear estrogen receptor II (nER II), have been studied in rat endometrial epithelial cells by means of immunofluorescence and high resolution quantitative immunocytochemistry. In the cytoplasm E-RAF is associated with the rough endoplasmic reticulum. In the nucleus it is mainly localized at the interchromatin space, and surrounding the clumps of compact or semi-condensed chromatin. Quantitative analyses show that the abundance of E-RAF in the nucleus increases after ovariectomy and decreases 3 minutes after estradiol administration. These results are in agreement with the currently available biochemical data. Double immunolocalizations demonstrate that p32, p55, p60 co-localize with other splicing-related protein. High resolution immunolocalization shows that p32, p55, p60 are associated with perichromatin fibrils (co-transcriptional splicing) and with clusters of interchromatin granules (storage of splicing-related molecules). The nuclear abundance of the snRNP complex decreases with ovariectomy, increases within 3 minutes after estradiol administration and remains higher than that in ovariectomized animals for 27 minutes. These results strongly support the previous data on the role of nER-II in the regulation of mRNA transcription and its export from the nucleus to the cytoplasm.