Molecular cloning and characterization of two rat renal kallikrein genes

Kallikreins compose a multigene family coding for a subgroup of serine proteases, which are involved in the processing of bioactive peptides. Two rat kallikrein-related genes, RSKG-7 (rat submandibular gland kallikrein gene 7) and RSKG-3, have been cloned and their sequences analyzed. RSKG-7 is approximately 4200 bases in length and consists of five exons and four introns. The 5' end region contains the variant CATAT box and TTTAAA box; the 3' end region contains the polyadenylation signal AATAAA. This gene encodes a putative 28,935-dalton preproenzyme of 261 amino acids (aa). The active enzyme consists of 237 aa and is preceded by a deduced signal peptide of 18 aa and a profragment of 6 aa. RSKG-3 is highly homologous to RSKG-7 in terms of its sequence and structure; it encodes a 28,730-dalton prepropeptide consisting of a signal peptide of 18 aa, a profragment of 6 aa, and an active peptide of 235 aa. Sequence comparisons of RSKG-7, RSKG-3, and other kallikrein-related enzymes reveal the key amino acid residues needed for both serine protease activity (His/Asp/Ser) and kallikrein-like cleavage specificity at basic amino acids. Northern blot analyses using specific oligonucleotide probes demonstrate that, among the 12 tissues studied, RSKG-7 and RSKG-3 are expressed in the rat kidney and submandibular gland. Castration of male rats results in a decrease in submandibular gland RSKG-7 mRNA, which can be restored to the normal level by treatment with thyroxine or testosterone. On the other hand, neither castration nor hormonal manipulation affects RSKG-7 mRNA levels in the kidney.