Spermidine/spermine N¹-acetyltransferase overexpression in kidney epithelial cells disrupts polyamine homeostasis, leads to DNA damage, and causes G₂ arrest

Abstract

Expression of spermidine/spermine N(1)-acetyltransferase (SSAT) increases in kidneys subjected to ischemia-reperfusion injury (IRI). Increased expression of SSAT in vitro leads to alterations in cellular polyamine content, depletion of cofactors and precursors of polyamine synthesis, and reduced cell proliferation. In our model system, a >28-fold increase in SSAT levels in HEK-293 cells leads to depletion of polyamines and elevation in the enzymatic activities of ornithine decarboxylase and S-adenosylmethionine decarboxylase, suggestive of a compensatory reaction to increased polyamine catabolism. Increased expression of SSAT also led to DNA damage and G(2) arrest. The increased DNA damage was primarily due to the depletion of polyamines. Other factors such as increased production of H(2)O(2) due to polyamine oxidase activity may play a secondary role in the induction of DNA lesions. In response to DNA damage the ATM/ATR --> Chk1/2 DNA repair and cell cycle checkpoint pathways were activated, mediating the G(2) arrest in SSAT-expressing cells. In addition, the activation of ERK1 and ERK2, which play integral roles in the G(2)/M transition, is impaired in cells expressing SSAT. These results indicate that the disruption of polyamine homeostasis due to enhanced SSAT activity leads to DNA damage and reduced cell proliferation via activation of DNA repair and cell cycle checkpoint and disruption of Raf --> MEK --> ERK pathways. We propose that in kidneys subjected to IRI, one mechanism through which increased expression of SSAT may cause cellular injury and organ damage is through induction of DNA damage and the disruption of cell cycle.

Elevated Ornithine Decarboxylase Levels Activate Ataxia Telangiectasia Mutated–DNA Damage Signaling in Normal Keratinocytes

“…Whereas elevated ODC activity provides a strong proliferative stimulus, it can also induce the expression of inhibitory proteins such as p53, p21 WAF1 , and p27 KIP1 as well as evidence of apoptosis in nontumor-bearing skin of K6/ODC transgenic mice (1). Conversely, polyamine depletion via inhibition of ODC or the induction of polyamine catabolic enzymes leads to enhanced expression of inhibitory proteins and inhibition of cell proliferation as well (4)(5)(6). These observations support the little understood view that tightly regulated intracellular levels of polyamines are required to maintain cell growth and normal cellular homeostasis.…”

“…The induction of polyamine catabolic pathways leads to the production of H 2 O 2 and cytotoxic aldehydes (6,21). The back conversion of the polyamines spermine and spermidine can be mediated by two pathways, both involving oxidases that generate H 2 O 2 (22)(23)(24)(25).…”

Depletion of cellular polyamines, spermidine and spermine, causes a total arrest in translation and growth in mammalian cells

“…The effects of overexpression of SAT1 were previously reported by others using cell lines overexpressing SAT1 stably or in an inducible manner (22)(23)(24)33), SAT1 transgenic mice (34)(35)(36), and a SAT1 adenovirus (37,38). Although retardation of growth and decreases in spermidine and spermine were consistently associated with SAT1 overexpression, the degree of growth inhibition and polyamine depletion were much lower than those reported in this study.…”

“…SAT1 overexpression (22)(23)(24) is often accompanied by a compensatory induction of ODC and S-adenosylmethionine decarboxylase (AdoMetDC) resulting in an accelerated metabolic cycling of polyamine biosynthesis and catabolism (25), an increased oxidative stress from hydrogen peroxide generated by the APAO reaction and the consumption of acetyl CoA. However, two inhibitors of APAO, MDL72521 (N 1 -methyl-N 2 -(2,3-butadienyl)-1,4-diaminobutane) and MDL72527 (N 1 ,N 4 -bis(2,3-butadienyl)-1,4-diaminobutane), did not restore GFP expression in cells overexpressing SAT1 (Fig.…”

Histone Deacetylase Inhibitor Enhances Recovery after AKI

“…12,13 Recent studies have also shown that a significant proportion of surviving, proliferating RTECs undergo G2/M arrest after injury, which delays recovery and promotes postinjury fibrosis. [14][15][16] This finding suggests that G2/M arrest plays an important role in limiting regenerative capacity of surviving RTECs and that therapies that drive cell cycle progression might accelerate recovery and reduce postinjury fibrosis after AKI.…”