Study of purinosome assembly in cell-based model systems with de novo purine synthesis and salvage pathway deficiencies.

Veronika Baresova,Stanislav Kmoch,Olga Souckova,Marie Zikanova,Matyas Krijt,Vaclava Skopova,Pankaj K Singh

doi:10.1371/journal.pone.0201432

Abstract

BackgroundThe enzymes involved in de novo purine synthesis (DNPS), one of the basic processes in eukaryotic cells, transiently and reversibly form a dynamic multienzyme complex called the purinosome in the cytoplasm. The purinosome has been observed in a broad spectrum of cells, but some studies claim that it is an artefact of the constructs used for visualization or stress granules resulting from the exposure of cells to nutrient-reduced growth media. Both may be true depending on the method of observation. To clarify this point, we combined two previously used methods, transfection and immunofluorescence, to detect purinosomes in purinosome-free cells deficient in particular DNPS steps (CR-DNPS cells) and in cells deficient in the salvage pathway, which resulted in construction of the purinosome regardless of purine level (CR-HGPRT cells).Methods and findingsTo restore or disrupt purinosome formation, we transiently transfected CR-DNPS and CR-HGPRT cells with vectors encoding BFP-labelled wild-type (wt) proteins and observed the normalization of purinosome formation. The cells also ceased to accumulate the substrate(s) of the defective enzyme. The CR-DNPS cell line transfected with a DNA plasmid encoding an enzyme with zero activity served as a negative control for purinosome formation. No purinosome formation was observed in these cells regardless of the purine level in the growth medium.ConclusionIn conclusion, both methods are useful for the detection of purinosomes in HeLa cells. Moreover, the cell-based models prepared represent a unique system for the study of purinosome assembly with deficiencies in DNPS or in the salvage pathway as well as for the study of purinosome formation under the action of DNPS inhibitors. This approach is a promising step toward the treatment of purine disorders and can also provide targets for anticancer therapy.

Highlights

Purines, essential molecules for the synthesis of nucleic acids, universal carriers of chemical energy and components of signalling molecules in all living organisms, are synthesized in higher eukaryotes via 10 reaction steps catalysed by six enzymes, four of which are multifunctional
The enzymes involved in de novo purine synthesis (DNPS), one of the basic processes in eukaryotic cells, transiently and reversibly form a dynamic multienzyme complex called the purinosome in the cytoplasm
The cell-based models prepared represent a unique system for the study of purinosome assembly with deficiencies in DNPS or in the salvage pathway as well as for the study of purinosome formation under the action of DNPS inhibitors

Summary

Introduction

Essential molecules for the synthesis of nucleic acids, universal carriers of chemical energy and components of signalling molecules in all living organisms, are synthesized in higher eukaryotes via 10 reaction steps catalysed by six enzymes, four of which are multifunctional. Once synthesized, they are efficiently recycled by the enzymes of the salvage pathway and eventually removed from cells in the form of uric acid or allantoin (Fig 1). We combined two previously used methods, transfection and immunofluorescence, to detect purinosomes in purinosome-free cells deficient in particular DNPS steps (CR-DNPS cells) and in cells deficient in the salvage pathway, which resulted in construction of the purinosome regardless of purine level (CR-HGPRT cells)

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