Before the development of DNA micro-array and SAGE approaches, the use of labelling of proteins synthesized in cell culture, before and after hormone stimulation, allowed us detection of several steroid hormone specific induced proteins, as defined by their molecular weight in SDS-PAGE, which could then be identified and studied in tumour samples to specify their significance in human carcinogenesis (16). Regarding progestins, using dose/response curves and anti-hormones, we could not discriminate between MPA and R5020 (promegestone) with respect to the induction of specific PR responses, such as the secreted 48 kD protein (16-17) and the cellular 250 kD protein, which were both inhibited by the anti-progestin RU486, but not by the anti-androgen flutamide (18 and D.Chalbos et unpublished).
The two progestins were also similarly active, but at higher concentrations, inducing a specific response to an androgen receptor such as that of a 43-kD androgen induced secreted protein (16), which has been identified as the glycoprotein (19). The weaker activity of progesterone on the cell lines was probably due to its high metabolism of inactive products, while R5020 has been shown to be more stable. Both MPA and R5020 are pregnane derivatives, and, supposedly, both are less androgenic than 19 nor-testosterone progestins.
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