Activation of Polyamine Catabolism Profoundly Alters Tissue Polyamine Pools and Affects Hair Growth and Female Fertility in Transgenic Mice Overexpressing Spermidine/SpermineN 1-Acetyltransferase

Abstract

We have generated a transgenic mouse line that overexpresses the rate-controlling enzyme of polyamine catabolism, spermidine/spermine N 1 -acetyltransferase. Tissues of these mice showed markedly distorted polyamine pools, which in most cases were characterized by the appearance of N 1 -acetylspermidine, not normally found in mouse tissues, a massive accumulation of putrescine, and decreases in spermidine and/or spermine pools. The most striking phenotypic change was permanent hair loss at the age of 3 to 4 weeks which was typified histologically by the appearance of extensive follicular cysts in the dermis. The effect seemed attributable to putrescine interference with hair development, possibly with differentiation/proliferation of epidermal cells located in hair follicles. Female members of the transgenic line were found to be infertile apparently due to ovarian hypofunction and hypoplastic uteri. The findings demonstrate the utility of spermidine/spermine N 1 -acetyltransferase overexpression as an effective means for genetically modulating total tissue polyamine pools in transgenic animals and examining the developmental and oncogenic consequences.The well recognized association of polyamines with cell growth (1-3) is best illustrated by findings related to the key polyamine biosynthetic enzyme, ornithine decarboxylase (ODC).1 Although ODC is sharply but transiently increased by growth stimuli, it is constitutively activated during cell transformation induced by carcinogens, viruses, or oncogenes. Overexpression of ODC has been correlated with increased proliferative potential (4), tissue invasiveness (5), and in certain cell types, with oncogene-like transforming capabilities (6 -8). Thus far, ODC appears to be the only growth-related gene activated by the transcription factors c-myc (9 -11) and n-myc (12), suggesting a critical role for the enzyme in growth control. However, as indicated below, findings obtained in cell culture may not be directly applicable to conditions prevailing in vivo.To define the role of polyamines in proliferative processes associated with the whole animal, we have generated a number of transgenic mouse and rat lines that overexpress ODC and/or other polyamine biosynthetic enzymes. Given the importance of polyamine biosynthetic activity to cell growth, the phenotypic changes were unexpectedly mild. In transgenic mice overexpressing ODC, the most marked effect was inhibition of meiotic DNA synthesis during spermatogenesis (13) ultimately leading to male infertility (14). It is also noteworthy that lifelong overexpression of ODC in mouse tissues did not seem to increase the incidence of spontaneous tumors (15). The absence of more profound phenotypic changes in these mice may be attributable to the relatively minor changes observed in higher polyamine pools. Despite severalfold increases in ODC activity, polyamine pool disturbances were mainly confined to putrescine accumulation, and the pools of those polyamines considered to be more significantly involved in cell growth, spermidi...

Activated Polyamine Catabolism Depletes Acetyl-CoA Pools and Suppresses Prostate Tumor Growth in TRAMP Mice

“…Consistent with SSAT gene overexpression prostatic enzyme activity in both SSAT and TRAMP/SSAT mice was elevated by ϳ18-fold. SSAT mRNA in liver of SSAT and TRAMP/SSAT mice was increased 20-and 30-fold over wild-type mice, but unlike the prostate, enzyme activities were only increased 3-and 2-fold, presumably due to tissue-specific differences in translational control (24). The data confirm that overexpression of SSAT occurs in the prostate of transgene-bearing mice.…”

“…We previously generated mice that systemically overexpressed SSAT under its endogenous murine gene promoter (24). These SSAT transgenic mice, in the CD2F1 genetic background (24), were backcrossed for Ͼ8 generations into C57BL/6, the same genetic background as the TRAMP mouse.…”

“…These SSAT transgenic mice, in the CD2F1 genetic background (24), were backcrossed for Ͼ8 generations into C57BL/6, the same genetic background as the TRAMP mouse. The SSAT transgenic mice are characterized by pronounced hair loss by 3-4 weeks of age (24), making genotyping unnecessary.…”

“…These SSAT transgenic mice, in the CD2F1 genetic background (24), were backcrossed for Ͼ8 generations into C57BL/6, the same genetic background as the TRAMP mouse. The SSAT transgenic mice are characterized by pronounced hair loss by 3-4 weeks of age (24), making genotyping unnecessary. Since female SSAT transgenic mice are infertile and male mice have normal reproductive capabilities, the latter were cross-bred with female TRAMP mice to generate the bigenic mice used in this study.…”

A Polyamine Metabolon Involving Aminopropyl Transferase Complexes in Arabidopsis

“…Spermidine plays an important role as an aminobutyryl donor in post-translational modification of a lysyl residue of eukaryotic translation factor eIF-5A (Coffino, 2001). Although the levels of spermidine seem to be regulated primarily through its recycling to putrescine by acetyltransferases in animals (Pietilä et al, 1997), spermidine production correlates with the tissue-specific regulation of SAMDC and SPDS in plants (Malmberg et al, 1998). A coordinated reduction of spermidine, SAMDC, and SPDS levels during stress suggests that the regulation of SPDS activity plays an important role in the proper adjustment of plant polyamine levels (Yamanoha and Cohen, 1985;Tiburcio et al, 1993).…”