ODCp, a brain- and testis-specific ornithine decarboxylase paralogue, functions as an antizyme inhibitor, although less efficiently than AzI1

Abstract

ODC (ornithine decarboxylase), the first enzyme in the polyamine biosynthesis pathway in mammalian cells, is a labile protein. ODC degradation is stimulated by Az (antizyme), a polyamine-induced protein, which in turn is regulated by an ODC-related protein termed AzI (Az inhibitor). Recently, another ODCp (ODC paralogue) was suggested to function as AzI, on the basis of its ability to increase ODC activity and inhibit Az-stimulated ODC degradation in vitro. We show in the present study that ODCp is indeed capable of negating Az functions, as reflected by its ability to increase ODC activity and polyamine uptake and by its ability to provide growth advantage in stably transfected cells. However, ODCp is less potent than AzI1 in stimulating ODC activity, polyamine uptake and growth rate. The superiority of AzI1 to ODCp in inhibiting the Az-stimulated ODC degradation is also demonstrated using an in vitro degradation assay. We show that the basis for the inferiority of ODCp as an AzI is its lower affinity towards Az (Az1 and Az3). Further, we show here that ODCp, like AzI, is degraded in a ubiquitin-dependent manner, in a reaction that does not require either interaction with Az or the integrity of its C-terminus. Interaction with Az actually stabilizes ODCp by interfering with its ubiquitination. This results in sequestration of Az into a stable complex with ODCp, which is the central feature contributing to the ability of ODCp to function as AzI.

High expression of antizyme inhibitor 2, an activator of ornithine decarboxylase in steroidogenic cells of human gonads

“…We identiWed and cloned the cDNA of a novel human ODC-like protein called ODC paralogue (ODC-p) (Pitkanen et al 2001), and recently, we demonstrated that ODC-p is indeed a novel form of AZIN (Kanerva et al 2008). Our Wndings were conWrmed by Snapir et al (2008). Moreover, Lopez-Contreras et al (2006) reported that also the murine paralogue of ODC-p acts as an AZIN.…”

Antizyme Inhibitor 2 (AZIN2/ODCp) Stimulates Polyamine Uptake in Mammalian Cells

“…Our results on COS7 cells also support that AZIN1 increases polyamine uptake, at least as efficiently as AZIN2. Recently, Snapir et al (42) found that AZIN2, stably transfected into NIH 3T3 cells, exerted a modest increase on the spermidine uptake rate (less than 20%), when compared with the effect of AZIN1 (about 100%), concluding that AZIN2 is less potent than AZIN1 in regulating polyamine uptake. The higher increase in polyamine uptake rate produced by both AZINs (about 300%) in our system in comparison with that observed in stably transfected cells could be related with a lower AZs/AZINs ratio.…”

Antizyme and antizyme inhibitor, a regulatory tango

“…ODCp was demonstrated to lack ornithine decarboxylase and arginine decarboxylase activity, but is able to rescue ODC from degradation and to inhibit the antizyme-mediated inhibition of polyamine uptake; therefore, it was termed antizyme inhibitor 2 [109][110][111][112][113]. Like antizyme inhibitor 1, antizyme inhibitor 2 is also rapidly degraded in a ubiquitin-dependent manner [111,113]; it stimulates ODC activity, polyamine uptake and cellular proliferation although less efficiently than antizyme inhibitor 1 [113]. Antizyme inhibitor 2 and antizyme 3 are both expressed in the haploid germinal cells, a location different from that of ODC mRNA, which localizes predominantly to the outer part of the seminiferous tubules.…”