Kallikrein-binding protein is induced by growth hormone in the dwarf rat.

Abstract

Rat kallikrein-binding protein (KBP), a member of the serpin family, is a tissue kallikrein inhibitor. It has been shown to be a potential pathogenic factor of diabetic retinopathy and may play a role in animal development and growth. To determine whether reduced KBP expression is involved in retarded animal growth, we examined the in vivo effect of growth hormone (GH) deficiency on the expression of KBP in the Lewis dwarf (dw/dw). We found that serum levels of functionally active KBP were reduced in the dwarf rat (P < 0.05) as determined by complex formation assay between serum KBP and (125)I-labeled rat tissue kallikrein. Enzyme-linked immunosorbent assay showed that KBP levels were significantly reduced in the serum of the dwarf rat compared to the Lewis rat (213.8 ng/ml vs. 413.8 ng/ml, n = 4, P < 0.01). The decreased KBP levels were confirmed by Western blot analysis. Moreover, treatment of the dwarf rat with recombinant human GH for 4 wk resulted in a significant increase in KBP activity (P < 0.01) and serum KBP levels compared with the untreated dwarf rat (549.8 ng/ml, n = 5, vs. 213.8 ng/ml, n = 4, P < 0.02). Northern blot analysis and densitometry showed that liver KBP mRNA levels were reduced by fivefold in the dwarf rat compared to the Lewis rat and the decrease was reversed by the GH treatment. These results indicate that the KBP levels are regulated at the RNA level. Furthermore, in vitro studies using cultured rat hepatocytes showed that GH may have a direct regulatory effect on KBP expression since KBP levels increased in the conditioned media of cells treated with GH. These results demonstrated that KBP is reduced in the genetic dwarf rat and is restored to normal by GH; therefore, KBP is a GH-dependent protein and may be a new target for studying the mechanism of pathological animal growth.