Novel Interaction of Ornithine Decarboxylase with Sepiapterin Reductase Regulates Neuroblastoma Cell Proliferation

Abstract

Ornithine decarboxylase (ODC) is the sentinel enzyme in polyamine biosynthesis. Both ODC and polyamines regulate cell division, proliferation, and apoptosis. Sepiapterin reductase (SPR) catalyzes the last step in the biosynthesis of tetrahydrobiopterin (BH4), an essential cofactor of nitric oxide synthase (NOS), and has been implicated in neurological diseases but not yet in cancer. In this study, we present compelling evidence that native ODC and SPR physically interact, and we defined the individual amino acid residues involved in both enzymes using in silico protein-protein docking simulations. The resulting heterocomplex is a surprisingly compact structure, featuring two energetically and structurally equivalent binding modes both in monomer and dimer conformations. The novel interaction between ODC and SPR proteins was confirmed under physiological conditions by co-immunoprecipitation and co-localization in neuroblastoma (NB) cells. Importantly, we showed that siRNA-mediated knock-down of SPR expression significantly reduced endogenous ODC enzyme activity in NB cells, thus demonstrating the biological relevance of the ODC-SPR interaction. Finally, in a cohort of 88 human NB tumors we found that high SPR mRNA expression correlated significantly with poor survival prognosis using a Kaplan-Meier analysis (Logrank test P = 5 • 10−4), suggesting an oncogenic role for SPR in NB tumorigenesis. In conclusion, we showed that ODC binds SPR and thus propose a new concept in which two well-characterized biochemical pathways converge via the interaction of two enzymes. We identified SPR as a novel regulator of ODC enzyme activity, and based on clinical evidence present a model in which SPR drives ODC-mediated malignant progression in NB.

Expression of polyamine metabolism-related genes during the development of prehierarchical follicles in the Zi geese (Ansercygnoides)

“…Zhao et al (2008) found that ODC was highly expressed at the implantation site in the mouse uterus during the peri-implantation period. There exists well-documented literature about AOZS as negative feedback control regulators of cellular polyamine content (Lange et al 2014). The OAZ2 gene expressed in the prehierarchical follicles had the tendency of decliningrising-declining-rising presenting W-shaped pattern in changes.…”

Sepiapterin reductase promotes hepatocellular carcinoma progression via FoxO3a/Bim signaling in a nonenzymatic manner

“…Previous reports have illustrated that SPR functions as regulator in NB [12][13][14] . However, the role of SPR in HCC has not been reported as far as we know.…”

“…In addition, it has been reported that BH 4 plays a key role in the growth, angiogenesis, and migration of tumors [8][9][10] . Sepiapterin reductase (SPR), which is an important regulator in the biosynthesis of BH 4 11 , has been demonstrated to be significantly correlated with survival of human neuroblastoma (NB) 12 . Although NB cells treated with SPR small interfering RNA (siRNA) or an enzymatic inhibitor showed a significant decrease in growth, the underlying mechanism has not been fully elucidated [12][13][14] , and the biological functions and molecular mechanisms of SPR in most types of tumors remain unknown.…”

“…Sepiapterin reductase (SPR), which is an important regulator in the biosynthesis of BH 4 11 , has been demonstrated to be significantly correlated with survival of human neuroblastoma (NB) 12 . Although NB cells treated with SPR small interfering RNA (siRNA) or an enzymatic inhibitor showed a significant decrease in growth, the underlying mechanism has not been fully elucidated [12][13][14] , and the biological functions and molecular mechanisms of SPR in most types of tumors remain unknown. Among them, hepatocellular carcinoma (HCC) is a malignancy with poor prognosis, and is one of the leading causes of cancer death in China.…”

“…The effects of SPR inhibitors on cancer progression depend on the type of tumor. For instance, sulfasalazine, an inhibitor of SPR enzymatic activity, suppressed the proliferation of NB cells and exerted synergistic anti-proliferative effects in combination with α-difluoromethylornitine 12 . However, the depletion of BH 4 using a SPR inhibitor had no effects on MOLT-4 and MCF-7 cancer cell growth 19 .…”