Schizosaccharomyces pombe cell division cycle under limited glucose requires Ssp1 kinase, the putative CaMKK, and Sds23, a PP2A‐related phosphatase inhibitor

Abstract

Calcium/calmodulin-dependent protein kinase (CaMK) is required for diverse cellular functions, and similar kinases exist in fungi. Although mammalian CaMK kinase (CaMKK) activates CaMK and also evolutionarily-conserved AMP-activated protein kinase (AMPK), CaMKK is yet to be established in yeast. We here report that the fission yeast Schizosaccharomyces pombe Ssp1 kinase, which controls G2/M transition and response to stress, is the putative CaMKK. Ssp1 has a CaM binding domain (CBD) and associates with 14-3-3 proteins as mammalian CaMKK does. Temperature-sensitive ssp1 mutants isolated are defective in the tolerance to limited glucose, and this tolerance requires the conserved stretch present between the kinase domain and CBD. Sds23, multi-copy suppressor for mutants defective in type 1 phosphatase and APC/cyclosome, also suppresses the ssp1 phenotype, and is required for the tolerance to limited glucose. We demonstrate that Sds23 binds to type 2A protein phosphatases (PP2A) and PP2A-related phosphatase Ppe1, and that Sds23 inhibits Ppe1 phosphatase activity. Ssp1 and Ppe1 thus seem to antagonize in utilizing limited glucose. We also show that Ppk9 and Ssp2 are the catalytic subunits of AMPK and AMPK-related kinases, respectively, which bind to common b-(Amk2) and g-(Cbs2) subunits.

Deletion of conserved protein phosphatases reverses defects associated with mitochondrial DNA damage inSaccharomyces cerevisiae

“…Sit4p and Pph21p/Pph22p are thought to be inhibited by the Sds23 family of proteins (19). We asked whether deletion of the two paralogous members of this family in S. cerevisiae, Sds23p and Sds24p, would reduce the proliferation of otherwise WT cells after mtDNA loss.…”

AMPK phosphorylation by Ssp1 is required for proper sexual differentiation in fission yeast

“…This feature resembles the mammalian AMPKrelated kinases MARK or BRSK, which are the substrates of LKB1 (Jaleel et al, 2006). Recently, Ssp1 has been described as the orthologue of CaMKK protein in S. pombe that contains the kinase domain and a putative CBD region (calmodulin-binding domain) (Hanyu et al, 2009). Interestingly, Ssp1 and Ssp2 were described originally to be required for growth polarity and actin localization in fission yeast (Matsusaka et al, 1995).…”

“…In S. pombe, ADP is also able to bind to the b-subunit, suggesting a possible role for ADP in regulating AMPK (Jin et al, 2007). Ssp2 (the a-subunit) contains the ubiquitin-associating UBA domain immediately adjacent to the kinase domain (Hanyu et al, 2009). This feature resembles the mammalian AMPKrelated kinases MARK or BRSK, which are the substrates of LKB1 (Jaleel et al, 2006).…”

“…Another catalytic subunit, Ppk9, has been described in Schizosaccharomyces pombe. Ppk9 also interacts with Amk2 and Cbs2 (Hanyu et al, 2009). In S. pombe, ADP is also able to bind to the b-subunit, suggesting a possible role for ADP in regulating AMPK (Jin et al, 2007).…”

Cellular stress induces cytoplasmic RNA granules in fission yeast

“…The S. pombe-specific protein Git1, with a role in cAMP signaling, possesses a C2 domain, which has also been in PKC, where it is required for association with phospholipids in a calcium-dependent way (Kao et al 2006). Ssp1 is a putative calmodulin-dependent kinase in S. pombe, and ssp1 mutants are defective in the tolerance to limited glucose (Hanyu et al 2009). We thus find it likely that the effects on RNA granules that we observe on calcium homeostasis perturbations are functionally linked to and funneled through the glucose-sensing system and PKA.…”