Cip1 tunes cell cycle arrest duration upon calcineurin activation

Abstract

Significance To ensure their survival, cells arrest the cell division cycle when they are exposed to environmental stress. The duration of this arrest is dependent upon the time it takes a cell to adapt to a particular environment. How cells adjust the amount of time they remain arrested is not known. This study investigates the role of the phosphatase calcineurin in controlling cell cycle arrest duration in yeast. We show that calcineurin lengthens arrest by prolonging Hog1-dependent activation of the poorly characterized cyclin-dependent kinase inhibitor Cip1. Cip1 only impacts cell cycle arrest in response to stressors that robustly activate calcineurin, suggesting that Cip1 is a context-specific regulator that differentially adjusts the length of arrest depending on the particular stressor.

Calcineurin promotes adaptation to chronic stress through two distinct mechanisms

“…To better understand the response to chronic stress, we monitored CN activity as cells grew in CaCl2 for 72 hours using a fluorescent reporter (CNR-C), which measures CN-dependent dephosphorylation and nuclear localization of a GFP-tagged, non-functional fragment of Crz1. Consistent with previous studies (Stathopoulos-Gerontides et al, 1999;Leech et al, 2020;Flynn and Benanti, 2022), we observed CN-dependent changes in CNR-C within 10 minutes of CaCl2 treatment and both wild-type and crz1D cells initially activated CN to similar extents, as shown by the rapid appearance of the higher mobility CNR-C species and increased nuclear signal (Figure 2, A and B). In wild-type cells, CN was inactivated within 3 hours after CaCl2 treatment as indicated by the reappearance of the phosphorylated, lower mobility CNR-C species and loss of nuclear signal (Figure 2, A and B).…”

“…CN is strongly activated within minutes of exposure to CaCl 2 and is subsequently inactivated as cells adapt (Stathopoulos-Gerontides et al ., 1999; Leech et al ., 2020; Flynn and Benanti, 2022). However, the timing of CN inactivation and adaptation during prolonged stress exposure is unclear.…”

“…In response to acute CaCl 2 stress, CN delays progression through multiple phases of the cell cycle in combination with the stress-activated MAPKs Hog1 and Mpk1 (Mizunuma et al ., 1998, 2001; Yokoyama et al ., 2006; Leech et al ., 2020; Flynn and Benanti, 2022). This suggested that the fitness defects of CN mutant cells (Figure 1, C and E) may be due to slowed cell cycle progression.…”

“…Crz1 target genes also include negative regulators of CN signaling, which shut off CN activity once cells have adapted (Yoshimoto et al, 2002). In addition to regulating the expression of genes important for adaptation, CN delays cell cycle progression in collaboration with the MAPKs Hog1 and Mpk1 (Mizunuma et al, 1998(Mizunuma et al, , 2001Yokoyama et al, 2006;Leech et al, 2020;Flynn and Benanti, 2022).…”