Mitogenic effects of certain cathepsins and calciferin on the intact liver in vivo

Calciferin, a new parathyroid hormone stimulating the release of cathepsins D and L (but not B) from isolated lysosomes, or the release of cathepsin D from erythrocytes or ghosts in vitro, elevated free cathepsin D in the blood, and at the same time stimulated DNA synthesis in the intact liver when it was injected into mice. Both calciferin and free cathepsin D in the blood (rats) were elevated concomitantly soon after 70% hepatectomy, reaching a peak around 5 hr. The cathepsin D-elevation was almost proportional to fractional hepatectomies. Cathepsin L (but not B), when injected intraperitoneally into mice, stimulated DNA synthesis and mitosis in the intact liver much like cathepsin D, the effect of which was reported earlier. In contrast to the mitogenic effects of calciferin or cathepsins (D and L) in vivo, only cathepsin L (but not cathepsin D or calciferin) in low concentrations appeared to stimulate DNA synthesis in the cultured liver cells, and also stimulated adenylate cyclase of isolated liver plasma membranes in vitro. Dibutyryl-cyclic AMP in concentrations lower than 10(-5) M also stimulated DNA synthesis in cultured liver cells.