Identification of SIN Pathway Targets Reveals Mechanisms of Crosstalk between NDR Kinase Pathways

Abstract

Summary The Septum Initiation Network (SIN) regulates multiple functions during late mitosis to ensure successful completion of cytokinesis in S. pombe. One mechanism by which the SIN promotes cytokinesis is by inhibiting a competing polarity pathway called the MOR [1], which is required for initiation of polarized growth following completion of cytokinesis [2]. Mutual antagonism between the two NDR kinase pathways, SIN and MOR, is required to coordinate cytoskeletal rearrangements during the mitosis-interphase transition. To determine how the SIN regulates the MOR pathway, we developed a proteomics approach that allowed us to identify multiple substrates of the SIN effector kinase, Sid2, including the MOR pathway components Nak1 kinase and an associated protein Sog2. We show that Sid2 phosphorylation of Nak1 causes removal of Nak1 from the SPBs, which may both relieve Nak1 inhibition of the SIN, and block MOR signaling by preventing interaction of Nak1 with the scaffold protein Mor2. Because the SIN and MOR are conserved in mammalian cells (Hippo and Ndr1/2 pathways respectively), this work may provide important insight into how the activities of these essential pathways are coordinated.

Pombe's thirteen – control of fission yeast cell division by the septation initiation network

“…Recent systematic searches for Sid2p substrates have exploited the fact that phosphorylation of the Sid2p consensus site, RxxS (Mah et al, 2005), creates a binding site for 14-3-3 proteins. Comparison of the proteins that associate with Rad24p when the SIN is switched on or off, has generated a list of potential Sid2p targets (Gupta et al, 2013). Some of these, such as the spindle checkpoint protein Mph1p, might point to new roles for Sid2p and/or the SIN, whose biological significance will doubtless be tested soon.…”

“…Its main components are two protein kinase modules, the protein kinase Nak1p (Huang et al, 2003;Leonhard and Nurse, 2005) and its regulators Sog2p (also known as Lrp1p) (Gupta et al, 2013;Kume et al, 2013) and Pmo25p (Kanai et al, 2005;Kume et al, 2007;Mendoza et al, 2005), which act upstream of the kinase Orb6p (Verde et al, 1998) and its regulator Mob2p (Hou et al, 2003). MOR signalling also requires the scaffold protein Mor2p (Hirata et al, 2002).…”

“…Important for CAR assembly. Control of polarized growth Nak1p and Sog2p Gupta et al, 2014;Gupta et al, 2013;Ray et al, 2010 Proposed mutual inhibition between SIN and MOR prevents conflicts between polar growth and cytokinesis.…”

Analysis ofS. pombeSIN protein SPB-association reveals two genetically separable states of the SIN

“…Pom1p inhibits, and Rad24p promotes, the transition to SIN asymmetry Phosphorylation of the Sid2p consensus creates a 14-3-3-proteinbinding site (Gupta et al, 2013;Mah et al, 2005). Phosphorylation of Cdc11p by Sid2p helps promote Cdc7p-GFP asymmetry in anaphase (Feoktistova et al, 2012), and SPB localisation of the 14-3-3 protein Rad24p in mitosis is dependent on Cdc11p (Mishra et al, 2005).…”

Dma1-dependent degradation of Septation Initiation Network proteins during meiosis inSchizosaccharomyces pombe

“…However, there is no indication that significant numbers of dma1-D spores undergo inappropriate septation during the germination process (Krapp et al, 2010). Alternatively, the SIN might be silenced to prevent it from inhibiting the morphology network, which is required to establish polar growth (Gupta et al, 2013;Ray et al, 2010), in the germinating apolar spore. It is noteworthy that dma1-D spores are slow to germinate and resume polar growth (Krapp et al, 2010).…”