A serum factor stimulating cathepsin D-release from erythrocytes or ghosts

Area of Science:

• Biochemistry
• Cell Biology

Background:

• Cathepsin D is an aspartic protease involved in various cellular processes.
• Erythrocytes, or red blood cells, are known to release certain enzymes under specific conditions.

Purpose of the Study:

• To identify and characterize a serum factor that induces cathepsin D release from blood cells.
• To elucidate the mechanism by which this serum factor affects erythrocytes.

Main Methods:

• Purification of a serum factor from bovine serum.
• Incubation of rat blood cells (erythrocytes, leucocytes, lymphocytes) with the purified factor.
• Investigation of the effects of various reagents (Ca2+, SH-blocking agents, protease inhibitors, calmodulin inhibitors) and EGTA-pretreatment on cathepsin D release.

Main Results:

• A purified serum factor stimulated cathepsin D release from erythrocytes in a concentration-dependent manner.
• Leucocytes and lymphocytes were unresponsive to the factor.
• The release mechanism appears to involve activation of the Ca2+-calmodulin system and a calmodulin-dependent SH-protease in the erythrocyte plasma membrane.

Conclusions:

• The serum factor, proposed to be named "calciferin", triggers cathepsin D release from erythrocytes.
• The mechanism involves calcium mobilization, calmodulin activation, and subsequent protease activity at the erythrocyte membrane.
• This finding sheds light on erythrocyte enzyme release regulation.