Meta-Biol

• Pathways

CTDNEP1:CNEP1R1 serine/threonine protein phosphatase complex consists of the catalytic subunit CTDNEP1 (Dullard) and the regulatory subunit CNEP1R1 (TMEM188) and is evolutionarily conserved from yeast to mammals (Kim et al. 2007, Han et al. 2012). CTDNEP1:CNEP1R1 and its yeast counterpart NEM1:SPO7 localize to the nuclear envelope and the endoplasmic reticulum membrane. CTDNEP1:CNEP1R1 dephosphorylates lipins (LPIN1, LPIN2 and LPIN3), which act as phosphatidate phosphatases, dephosphorylating phosphatidate (PA) and converting it to diacylglycerol (DAG). The yeast NEM1:SPO7 complex dephosphorylates yeast lipin orthologue PAH1 (SMP2, PAP1). CTDNEP1:CNEP1R1 shows a preference for the phosphorylated serine S106 of lipins. S106 phosphorylation is insulin-induced, and could be mediated by CDK1, as it is proline-directed (Wu et al. 2011). CDC28, a yeast homolog of CDK1, was shown to phosphorylate PAH1, while NEM1:SPO7 removes CDC28-introduced phosphate groups. Lipin phosphorylation regulates lipin localization, with phosphorylated lipins being soluble and dephosphorylated lipins being membrane-bound (Grimsey et al. 2008, Choi et al. 2011). The association of lipins with the nuclear envelope brings lipins in proximity to its substrate, PA, thereby enabling lipin catalytic activity (Karanasios et al. 2010). Catalytic activity of PAH1 regulates the morphology and dynamics of endoplasmic reticulum and nuclear membranes in yeast. In C. elegans and in human cell lines, lipin catalytic activity is needed for mitotic progression as it facilitates depolymerization of the nuclear lamina and nuclear envelope breakdown (Santos-Rosa et al. 2005, Kim et al. 2007, Gorjanacz et al. 2009, Golden et al. 2009, Choi et al. 2011, Mall et al. 2012).