SUMOylation regulates the SNF1 protein kinase

Abstract

The AMP-activated protein kinase (AMPK) is a major stress sensor of mammalian cells. AMPK's homolog in the yeast Saccharomyces cerevisiae, the SNF1 protein kinase, is a central regulator of carbon metabolism that inhibits the Snf3/Rgt2-Rgt1 glucose sensing pathway and activates genes involved in respiration. We present evidence that glucose induces modification of the Snf1 catalytic subunt of SNF1 with the small ubiquitin-like modifier protein SUMO, catalyzed by the SUMO (E3) ligase Mms21. Our results suggest that SUMOylation of Snf1 inhibits its function in two ways: by interaction of SUMO attached to lysine 549 with a SUMO-interacting sequence motif located near the active site of Snf1, and by targeting Snf1 for destruction via the Slx5-Slx8 (SUMO-directed) ubiquitin ligase. These findings reveal another way SNF1 function is regulated in response to carbon source.protein kinase regulation | protein modification | signal transduction G lucose is the preferred carbon source of most cells, including Saccharomyces cerevisiae, which ferments it to ethanol and CO 2 , producing only two ATPs, even when oxygen is available to drive production of much more ATP. This preference for fermentation (which cancer cells share), is known as the Crabtree or Warburg effect (1, 2). Because of the energetic inefficiency of fermentation, yeast cells must be adroit in sensing glucose. S. cerevisiae has three well-known glucose sensing pathways: (i) the Gpa1/2-Ras2-PKA pathway that regulates stress response (through Msn2/4) and other things; (ii) the SNF1 pathway, which regulates respiratory metabolism and other processes; and (iii) the Snf3/Rgt2-Rgt1 (SRR) pathway that regulates expression of genes encoding hexose transporters (3).The SRR (sensor/receptor-repressor) pathway begins at the cell surface with high-affinity (Snf3) (4) and low-affinity (Rgt2) glucose sensors (5) that are coupled to the casein kinases Yck1 and Yck2, which catalyze phosphorylation of the corepressor proteins Mth1 and Std1 (6), leading to their ubiquitinylation by SCF Grr1 (7,8). The subsequent destruction of Mth1 and Std1 inactivates the Rgt1 transcriptional repressor, resulting in derepression of HXT genes encoding hexose transporters (7, 9). In response to glucose, Yck1/2 also mediates inactivation and degradation of transporters of alternative carbon sources, such as maltose (Mal61) (10) and lactate/pyruvate/acetate (Jen1) (11). Achieving this glucose-induced switching of transporters seems to be the main purpose of the SRR pathway (12).The SNF1 protein kinase-the ortholog of the AMP-activated protein kinase (AMPK), a major stress-activated protein kinase in mammalian cells (13,14)-is a central regulator of carbon metabolism (15,16). This kinase is an activator of Adr1 and Cat8, which activate expression of genes involved in the diauxic shift, ethanol, and lactate uptake and catabolism, gluconeogenesis, and respiration (17-21), and is an inhibitor of the Mig1 repressor of glucose-repressed genes (22). SNF1 is a heterotrimer of the Snf1 catalytic subunit,...

Feedback Control of Snf1 Protein and Its Phosphorylation Is Necessary for Adaptation to Environmental Stress

“…Previous evidence suggested that Snf1 can be SUMOylated, which promotes the conjugation of ubiquitin for degradation. This may in turn cause a decrease of Snf1 activity (18,21). Our current findings reveal a novel layer of regulation of Snf1 activity, involving a feedback loop between Snf1 protein level and its phosphorylation.…”

“…SUMOylation can also regulate the stability and function of Snf1 (21). To examine the role of ubiquitylation in the reduction of Snf1 in ubp8⌬ ubp10⌬, we mutated the SUMOylation site (K549R) to inhibit SUMOylation-mediated recruitment of E3 ubiquitin ligases and subsequent degradation of Snf1.…”

“…We found that both Ubp8 and Ubp10 were reported to co-purify with Snf1, implying that Ubp8 and * The authors declare that they have no conflicts of interest with the contents of this article. 1 (18,21). However, the correlation between the control of Snf1 protein level and SNF1 protein kinase activity is still poorly understood.…”

The SNF1 Kinase Ubiquitin-associated Domain Restrains Its Activation, Activity, and the Yeast Life Span

“…Also conserved is acetylation and ubiquitination, recently reported for both mammalian AMPK and yeast SNF1 kinase complexes (23)(24)(25)(26), that appear to have inhibitory roles in regulation of the kinase. Similarly, SUMOylation has been shown to be a negative regulator of Snf1 (27), clearly adding to the complexity of regulation of this central energy-sensing switch.…”

The E3 SUMO ligase Nse2 regulates sumoylation and nuclear-to-cytoplasmic translocation of skNAC-Smyd1 in myogenesis

“…Finally, most recently and remarkably, Simpson-Lavy and Johnston (Simpson-Lavy and Johnston, 2013) have demonstrated that the yeast Nse2 homolog, Mms21, can sumoylate the SNF1 protein, which is the yeast homolog of mammalian AMPactivated protein kinase (AMPK), thereby inhibiting its catalytic activity. In mammalian skeletal muscle cells, AMPK is a central player in the regulation of cell metabolism and fiber type specification, and skNAC has been implicated in the control of fiber type specification (Yotov and St-Arnaud, 1996;Park et al, 2010) (J.B. and B.M, unpublished data), suggesting that there is an interesting link between Nse2/Mms21 and skeletal muscle plasticity.…”