The effects of oestradiol-17beta on protein synthesis in the immature rat uterus

A number of previous studies have built up a picture of the early events in the oestrogenic response of the immature rat uterus. This consists of an overall growth and development of the tissue preparing it to support a pregnancy. The most important requirement in this chain of events is the massive increase in protein synthesis as the lining of the uterus differentiates and proliferates. This requires the synthesis of large numbers of new ribosomes. The evidence suggests that this synthesis is preceded by and is dependent on stimulated hnRNA synthesis which is detectable 30 minutes after giving the hormone. It is apparently vital that messenger sequences present in this hnRNA be translated before the stimulation of ribosomal RNA can occur. Hybridisation studies suggest that the proteins eliciting this response are encoded by a small number of moderately abundant messenger sequences, all of which appear in the polysome population between 2 and 4 hours after oestrogen administration. This project set out to detect and characterise these proteins by radio-labelling immature rat uteri in vitro after short periods of oestrogen stimulation in vivo and analysing the protein species by two dimensional gel electrophoresis and fluorography. The three approaches adopted were the labelling of whole uteri in vitro; the labelling of fractionated epithelial, stromal and myometrial cells in vitro; and the translation of uterine polysomes in cell free systems. These three methods yielded different information. Whole uteri labelled in vitro showed very little difference between the protein populations from control and stimulated animals, although analysis of their polysome profiles showed the translational statuses of the two groups of uteri to differ greatly. The study of fractionated cell type proteins revealed a differential response to the hormone. Epithelial cells showed relatively small quantitative differences between the control and hormone-treated uteri, but at least three new proteins were reproducibly detected as radioactive spots. Stromal protein synthesis was strongly stimulated after four hours of oestrogen treatment and in addition to the quantitative changes, some further qualitative changes were also detected. Nine new species were seen in response to oestrogen treatment and the labelling of a number of other species was strongly enhanced. Little data were collected on the response of the myometrium which showed lower levels of radioactive incorporation, and fewer protein species than the other two fractions examined. Cell-free translation revealed a number of changes in the protein population during the first four hours of stimulation. The synthesis of at least ten proteins was stimulated 2 hours after oestrogen administration although only five of these were totally reproducible. Further changes were observed by 4 hours after treatment. Unfortunately, none of the new proteins detected by cell-free protein synthesis could be identified with oestrogen-induced species in intact, isolated cells. However, the possible identity of some of the proteins synthesised in increased quantities by polysomes from oestrogen-treated rats was investigated. These experiments established the presence of actin and IP, an induced protein, in the uterine protein population. None of the stimulated uterine protein species comigrated with a number of other candidate proteins, including non-histone chromatin protein and hnRNP particle protein, however, the presence of low levels of ribosomal proteins was established. The results obtained by each method are assessed, discussed and compared with results from other systems. It is thought that the bulk of early induced proteins we sought to identify was present in quantities too small to be detected using the methods employed in this study