The gamma subunit of the rod photoreceptor cGMP phosphodiesterase can modulate the proteolysis of two cGMP binding cGMP-specific phosphodiesterases (PDE6 and PDE5) by caspase-3

We have investigated whether the proteolysis of members of the cGMP binding phosphodiesterases (PDE6, PDE5A1, and PDE10A2) by caspase-3 is modulated b y they inhibitor subunit of PDE6. We show here that purified caspase-3 prot eolyses PDE6, an enzyme composed of two nonidentical catalytic subunits (te rmed alpha and beta) with molecular mass of 88 and 84 kDa. The proteolysis of PDE6 produced a single fragment with a molecular mass of 78 kDa. This co rresponds to the possible cleavage of the caspase-3 consensus DFVD site (am ino acids: 164-168) in the alpha subunit and leads to a 50% decrease in the cGMP hydrolysing activity of the enzyme. The addition of rod PDE gamma to the incubation completely blocked the cleavage of PDE6 by caspase-3. In con trast, rod PDE gamma converted PDE5A1 (molecular mass of 98 kDa) to a bette r substrate for caspase-3. This resulted in the formation of four major fra gments with molecular mass of 82-83, 67, 43, and 34 kDa. In addition, caspa se-3 induced an similar to 80% reduction in the activity of a partially pur ified preparation of PDE5A1 in the presence of rod PDE gamma. Caspase-3 als o cleaved PDE10A2 (molecular mass of 95 kDa) to a single 48-kDa fragment. T his was consistent with cleavage of the DLFD site (amino acids: 312-315) in PDE10A2. In contrast with both PDE6 and PDE5A1, rod PDE gamma was without effect on this enzyme. These data show that rod PDE gamma interacts with at least two members of the cGMP binding PDE family (PDE5A1 and PDE6) and can exert differential effects on the cleavage of these enzymes by caspase-3. (C) 2001 Elsevier Science Inc. All rights reserved.