Glycosylation of Active Human Renin Is Necessary for Secretion: Effect of Targeted Modifications of Asn-5 and Asn-75

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Abstract
Renin is a mammalian aspartic protease that is rate-limiting in the renin-angiotensin cascade. Preprorenin is the translational product of the human renin gene and is secreted as prorenin, an inactive zymogen, primarily from the juxtaglomerular cells of the kidney. It has previously been shown that the 46-amino-acid pro domain is not necessary for the secretion of fully active or mature renin from mammalian cells. Additionally, previous reports indicated that glycosylation of Asn-5 and Asn-75, the two potential sites of N-glycosylation in renin, is not necessary for the secretion of prorenin from mammalian cells. In the present study, the role of N-glycosylation in the secretion of mature renin was examined. Asn to Ser mutations at one or both of the glycosylation sites of mature renin were made and the expression of these constructs was examined in COS, CHO, and Sf9 insect cells. In the absence of the pro sequence, N-glycoylation at Asn-75 was essential for the secretion of active renin protein from all three cell types. The mutation at Asn-75 caused a more dramatic reduction in renin secretion than the mutation at Asn-5. This is in contrast to results previously reported for prorenin.