Studies through the years have reported that changes in intracellular arginylation levels correlate with such fundamental physiological processes as aging (Kaji et al., 1980
; Lamon and Kaji, 1980
), stress (Lamon et al., 1980
), rat liver regeneration (Tanaka and Kaji, 1974
), temperature sensitivity and heat shock (Bongiovanni et al., 1999
; Rao and Kaji, 1977b
), nerve regeneration (Chakraborty and Ingoglia, 1993
; Wang and Ingoglia, 1997
; Xu et al., 1993
), and protein degradation in skeletal muscle (Solomon et al., 1998
). A breakthrough in these studies came with the identification of arginyltransferases in multiple species (Kwon et al., 1999
) and characterization of the mouse Ate1 gene (Kwon et al., 2002
; Kwon et al., 1999
). It was found that mouse Ate1 knockout results in embryonic lethality and defects in cardiovascular development and angiogenesis – a discovery that showed for the first time that arginylation plays an essential physiological role. Follow-up studies demonstrated that mammalian Ate1 can serve as a nitric oxide sensor that controls the levels of multiple biological regulators (Hu et al., 2005
; Hu et al., 2008
), and that arginylation regulates neural crest morphogenesis (Kurosaka et al., 2010
), cardiac contractility (Rai et al., 2008
), and gametogenesis (Leu et al., 2009
). Postnatal deletion of Ate1 results in loss of fat and increased metabolic rates and affects spermatogenesis and the nervous system (Brower and Varshavsky, 2009
). Thus, it became evident that arginylation is not only essential, but also takes part in a number of highly diverse physiological pathways. The currently known developmental processes regulated by arginylation in mice are summarized in and .
Mouse Ate1 knockout phenotypes
Schematic representation of the major organogenic defects resulting from Ate1 knockout in mice.
Studies in other organisms have shown that the essential role of arginylation is not confined to mammals. In Arabidopsis thaliana
arginylation knockout causes delayed leaf senescence (Lim et al., 2007
; Yoshida et al., 2002
), abnormal shoot and leaf development (Graciet et al., 2009
) and defects in seed germination (Holman et al., 2009
). In Drosophila, high throughput genomic studies demonstrated that Ate1 knockout results in embryonic lethality (). Interestingly, such studies also demonstrated that Ate1 gene is non-essential for survival in C. elegans
(), suggesting that the evolutionary boundary defining the global importance of arginyltransferases for an organism’s viability manifests only in species evolutionarily higher than worms.
Several of the identified Ate1 substrates have been implicated in exerting these biological effects. Proteins of the RGS family, which become metabolically unstable upon arginylation (Davydov and Varshavsky, 2000
; Lee et al., 2005
), are known regulators of cardiovascular development and are implicated in cell motility and related responses. Conceivably, lack of arginylation can lead to accumulation of these proteins, facilitating some of the developmental defects seen in Ate1 knockout mice. Another striking example concerns arginylation of non-muscle beta actin and actin cytoskeleton proteins (Karakozova et al., 2006
; Wong et al., 2007
), which have been functionally linked to impaired lamella formation (Karakozova et al., 2006
), defective cell adhesion, and a dramatic reduction of actin polymer level in cells (Saha et al., 2010
) – the effects that likely underlie the impairments in cell migration and adhesion seen in vivo. Given the large list of identified arginylation targets, it is only a matter of time before the researchers uncover more molecular links and identify the role of arginylation in regulation of the specific functions of individual proteins.
In summary, multiple studies show that arginylation is a global physiological regulator that modifies many proteins in vivo to modulate their functions in many critical pathways during embryogenesis and adulthood.