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SMR1 is a male-specific, 19 kDa, in vitro translation product of Wistar rat submaxillary glands, which may be the precursor of a small hormone resembling the TRH. In Sprague-Dawley and Fischer rats, instead of SMR1, a male-specific 18 kDa polypeptide may be found. We have cloned the cDNA encoding the 18 kDa polypeptide. We show that the 19 and the 18 kDa polypeptides have the same sequence except for one amino acid change.

A mouse renin-1 gene promoter fragment, normally inactive in B-cells, becomes a potent promoter in these cells after insertion of the highly conserved decanucleotide (dc/cd sequence) of immunoglobulin heavy and light chain promoters [(1987) EMBO J. 6, 1685–1690]. We observe retarded complexes of the same electrophoretic mobility when the cd-containing renin promoter fragment or an authentic immunoglobulin heavy chain promoter fragment is incubated with a nuclear extract from myeloma cells, suggesting that the renin promoter is activated due to its acquired ability to bind a B-cell-specific positive factor. No retarded complexes are observed with the original renin promoter fragment thus questioning the presence of a repressor as an explanation for its lack of activity in B-cells.

Apart from kidney, where renin synthesis takes place in all mammals, the submaxillary gland (SMG) of most mouse strains constitutes an important source of an isoenzyme, renin-2, that is highly homologous to renal renin, but unglycosylated [(1982) Nature 298, 90–92]. This unique phenotype is due to the presence of an extra copy of the renin gene. A puzzling observation is that (pro)renin-2 cannot be detected in the kidney of these animals, although both mRNAs accumulate at similar levels [(1985) Proc. Natl. Acad. Sci. USA 82, 6196–6200]. In order to investigate whether (pro)renin-2 expression is detectable in mouse heterologous cell lines we transfected the renin-2 cDNA into AtT20 (pituitary corticotrope) and BTG9A (hepatoma) cells. Stable clones expressing renin were obtained in both cases. BTG9A cells secreted only prorenin while AtT20 cells secreted prorenin and active renin. In addition, in AtT20 cells the secretion of active renin was stimulated by 8-Br cAMP. Our results show that unglycosylated (pro)renin-2 can be expressed and secreted in two murine cell lines. Moreover, it is correctly processed to active renin and secreted upon stimulation in AtT20 cells.

Expression of the mouse renin genes (Ren1 and Ren2) in the submaxillary gland of female mice has been analyzed following administration of thyroxine (T4) or dihydrotestosterone (DHT). Both hormones appear to act independently on mRNA accumulation which increases about 5 fold over basal level. In vitro transcription assays in isolated nuclei demonstrate that both hormones act at the transcriptional level. The effects of DHT and T4 were also analyzed in transgenic mice obtained by microinjection of the Ren2 gene. We show that T4 is as efficient as DHT in promoting renin mRNA accumulation in these transgenic animals, in spite of their low basal level of Ren2 mRNA. Structural comparison of the Ren1 and Ren2 promoters with those of other genes regulated by T4 shows the conservation of two discrete regions.

The expression of a hybrid gene containing the promoter region of the mouse Ren-1 or Ren-2 genes and the chloramphenicol acetyl transferase (CAT) gene coding region was analysed in five cell lines that do not normally express the renin gene. The renin promoter is inactive in each of these cell lines unless the SV40 enhancer is also present in the construct. In the latter case, transcription initiates at the normal renin start site. This is in contrast to the situation observed in lymphoid cells where the renin promoter is inactive even when coupled to a functional enhancer [(1987) EMBO J. 6, 1685–1690]. Furthermore, 5′-flanking sequences of Ren-2, placed upstream of the thymidine kinase or SV40 early region promoters do not alter the activity of these promoters in three different cell lines. The results suggest that, except for B cells, the renin promoter is not tissue-specific but that its lack of activity in cells that do not express the gene is not the result of repression but may be due to the absence in these cells of one or several trans-acting positive factors.