Identification and characterization of the type-IVA cyclic AMP-specific phosphodiesterase RD1 as a membrane-bound protein expressed in cerebellum

Abstract

An antiserum was generated against a dodecapeptide whose sequence is found at the C-terminus of a cyclic AMP (cAMP)-specific, type-IVA phosphodiesterase encoded by the rat 'dunc-like' cyclic AMP phosphodiesterase (RD1) cDNA. This antiserum identified a single approximately 73 kDa protein species upon immunoblotting of cerebellum homogenates. This species co-migrated upon SDS/PAGE with a single immunoreactive species observed in COS cells transfected with the cDNA for RD1. Native RD1 in cerebellum was found to be predominantly (approximately 93%) membrane-associated and could be found in isolated synaptosome populations, in particular those enriched in post-synaptic densities. Fractionation of lysed synaptosomes on sucrose density gradients identified RD1 as co-migrating with the plasma membrane marker 5'-nucleotidase. Laser scanning confocal and digital deconvolution immunofluorescence studies done on intact COS cells transfected with RD1 cDNA showed RD1 to be predominantly localized to plasma membranes but also associated with the Golgi apparatus and intracellular vesicles. RD1-specific antisera immunoprecipitated phosphodiesterase activity from solubilized cerebellum membranes. This activity had the characteristics expected of the type-IV cAMP phosphodiesterase RD1 in that it was cAMP specific, exhibited a low Km cAMP of 2.3 microM, high sensitivity to inhibition by 4-[3-(cyclopentoxyl)-4-methoxyphenyl]-2-pyrrolidone (rolipram) (Ki approximately 0.7 microM) and was unaffected by Ca2+/calmodulin and low concentrations of cyclic GMP. The phosphodiesterase activities of RD1 solubilized from both cerebellum and transfected COS cell membranes showed identical first-order thermal denaturation kinetics at 50 degrees C. Native RD1 from cerebellum was shown to be an integral protein in that it was solubilized using the non-ionic detergent Triton X-100 but not by either re-homogenization or high NaCl concentrations. The observation that hydroxylamine was unable to cause the release of RD1 from either cerebellum or COS membranes and that [3H]palmitate was not incorporated into the RD1 protein immunoprecipitated from COS cells transfected with RD1 cDNA, indicated that RD1 was not anchored by N-terminal acylation. The engineered deletion of the 25 residues forming the unique N-terminal domain of RD1 caused both a profound increase in its activity (approximately 2-fold increase in Vmax) and a profound change in intracellular distribution. Thus, immunofluorescence studies identified the N-terminal truncated species as occurring exclusively ion the cytosol of transfected COS cells. The cDNA for RD1 thus appears to encode a native full-length type-IVA phosphodiesterase that is expressed in cerebellum.(ABSTRACT TRUNCATED AT 400 WORDS)

Effects of Repeated Antidepressant Treatment on Type 4A Phosphodiesterase (PDE4A) in Rat Brain

“…3), as labeled by antibody C-PDE4A (batch 271). Again, they are known to be PDE4A5 and PDE4A1, respectively (Shakur et al, 1995;Ye et al, 1997). In addition, there was a minor, 102-kDa band that has been shown previously to be a presently uncharacterized PDE4A variant termed PDE4AX (Ye et al, 1997).…”

“…1), as labeled by the PDE4A-selective antibody. Based on the results of previous studies, these are identified as PDE4A5 and PDE4A1, respectively (Shakur et al, 1995;Ye et al, 1997).…”

Characterization of five different proteins produced by alternatively spliced mRNAs from the human cAMP-specific phosphodiesterase PDE4D gene

“…These were performed as described previously [21,24,35]. Briefly, increasing concentrations of high-speed pellet protein from COS cells, transfected with various PDE-expressing plasmids, were analysed by immunoblotting.…”

“…To define K m values, data from PDE assays were analysed by computer fitting to the hyperbolic form of the Michaelis-Menten equation using an iterative least-squares procedure (Ultrafit ; with Marquardt algorithm, robust fit, experimental errors supplied ; Biosoft). Relative V max values could be calculated using the Michaelis equation and the experimentally derived K m values, as described previously [35].…”

Subcellular Localization of Cyclic Nucleotide Phosphodiesterase Type 10A Variants, and Alteration of the Localization by cAMP-dependent Protein Kinase-dependent Phosphorylation

“…For example, whereas phosphorylation of the amino terminus of the PDE4D3 variant by PKA increases its activity (21)(22)(23), PDE4D3 is inactivated by extracellular signal-regulated kinase-mediated phosphorylation in vivo (24). PDE4A1, PDE4D, and PDE2A are localized in the Golgi apparatus (25)(26)(27)(28)(29)(30)(31), and PDE3B is associated with the endoplasmic reticulum via its amino-terminal hydrophobic domain (32). Thus, it is intriguing that alterations of the cyclic nucleotide-hydrolyzing activity of PDEs by the phosphorylation and compartmentalization of several signaling molecules such as PDEs, AKAPs, and PKA would be involved in the modulation of the subcellular signaling of cyclic nucleotides.…”