S-Adenosylmethionine Decarboxylase Degradation by the 26 S Proteasome Is Accelerated by Substrate-mediated Transamination

Abstract

The short-lived enzyme S-adenosylmethionine decarboxylase uses a covalently bound pyruvoyl cofactor to catalyze the formation of decarboxylated S-adenosylmethionine, which then donates an aminopropyl group for polyamine biosynthesis. Here we demonstrate that S-adenosylmethionine decarboxylase is ubiquitinated and degraded by the 26 S proteasome in vivo, a process that is accelerated by inactivation of S-adenosylmethionine decarboxylase by substrate-mediated transamination of its pyruvoyl cofactor. Proteasome inhibition in COS-7 cells prevents the degradation of S-adenosylmethionine decarboxylase antigen; however, even brief inhibition of the 26 S proteasome caused substantial losses of S-adenosylmethionine decarboxylase activity despite accumulation of S-adenosylmethionine decarboxylase antigen. Levels of the enzyme's substrate (S-adenosylmethionine) increased rapidly after 26 S proteasome inhibition, and this increase in substrate level is consistent with the observed loss of activity arising from an increased rate of inactivation by substrate-mediated transamination. Evidence is also presented that this substrate-mediated transamination accelerates normal degradation of S-adenosylmethionine decarboxylase, as the rate of degradation of the enzyme was increased in the presence of AbeAdo (5 -([(Z)-4-amino-2-butenyl]methylamino]-5 -deoxyadenosine) (a substrate analogue that transaminates the enzyme); conversely, when the intracellular substrate level was reduced by methionine deprivation, the rate of degradation of the enzyme was decreased. Ubiquitination of S-adenosylmethionine decarboxylase is demonstrated by isolation of His-tagged AdoMetDC (S-adenosylmethionine decarboxylase) from COS-7 cells co-transfected with hemagglutinin-tagged ubiquitin and showing bands that were immunoreactive to both anti-AdoMetDC antibody and anti-hemagglutinin antibody. This is the first study to demonstrate that AdoMetDC is ubiquitinated and degraded by the 26 S proteasome, and substrate-mediated acceleration of degradation is a unique finding.

BSCTV C2 Attenuates the Degradation of SAMDC1 to Suppress DNA Methylation-Mediated Gene Silencing in Arabidopsis

“…Total protein from the whole inoculated plants was used for immunoblot with anti-myc antibody (top) and Ponceau S staining (bottom) of ribulose-1,5-bisphosphate carboxylase/ oxygenase (Rubisco) protein is shown as a loading control. Persson, 1993;Berntsson et al, 1999;Yerlikaya and Stanley, 2004). Our results of the wheat germ and Arabidopsis cell-free assays also indicated that Arabidopsis SAMDC1 is degraded in a similar 26S proteasome-dependent manner.…”

“…The PEST sequence has been reported to be located in some proteins with fast turnover rates and be essential for the interaction between SCF complex and target proteins, which consequently leads to ubiquitination/26S proteasome-mediated degradation (Kiernan et al, 2001;Berset et al, 2002;Blondel et al, 2005;Pal et al, 2007). Human SAMDC was reported to have a short half-life and is regulated at multiple levels, such as the transcriptional, translational, and posttranslational levels (Shantz et al, 1992;Stanley et al, 1994;Hanfrey et al, 2003;Yerlikaya and Stanley, 2004). Taking all the information above together, we wanted to ask whether the interaction with BSCTV C2 can affect with the stability of SAMDC1.…”

“…SAMDCs in many organisms are highly conserved, sharing a defined autocleavage recognition site and a PEST region enriched in Pro (P), Glu (E), Ser (S), and Thr (T) that is correlated with the protein's rapid turnover (Salama et al, 1994;Rechsteiner and Rogers, 1996;Berset et al, 2002;Blondel et al, 2005;Pal et al, 2007). SAMDC is expressed throughout the cell, and its expression is regulated at multiple levels, such as the transcriptional, translational, and posttranslational levels (Shantz et al, 1992;Stanley et al, 1994;Hanfrey et al, 2003;Yerlikaya and Stanley, 2004). Previous studies indicated that SAMDC is involved in diverse growth and developmental processes, including cell division, cell proliferation and differentiation, morphological development, and response to abiotic stress (Kumar et al, 1996;Frostesjö et al, 1997;Shibata et al, 1998;Wi et al, 2006).…”

Remaining Mysteries of Molecular Biology: The Role of Polyamines in the Cell

“…AdoMetDC turnover accelerates when concentrations of Spd and Spm are high [67]. Degradation of AdoMetDC by polyubiquitination via the proteasome is accelerated when its pyruvoyl group is transaminated and transformed into alanine by its substrate AdoMet [74]. This transformation is suggested to induce a conformational change in this enzyme, making its ubiquitination site more accessible and thus more prone for degradation [61,74].…”

Effects of dihydrotestosterone on skeletal muscle transcriptome in mice measured by serial analysis of gene expression

“…The ODC antizyme encoded by Oaz, as well as ribosomal proteins L34 and S20, inhibit ODC and arginine decarboxylases (Panagiotidis et al 1995). The ODC and SAMDC are degraded by the 26S proteasome (Yerlikaya & Stanley 2004) which is encoded by Psmc3 and Psmc5. The ODC antizyme also inhibits polyamine uptake and stimulates excretion (Sakata et al 2000).…”