PT  - JOURNAL ARTICLE
AU  - Budnar, Srikanth
AU  - Husain, Kabir B.
AU  - Gomez, Guillermo A.
AU  - Naghibosidat, Maedeh
AU  - Verma, Suzie
AU  - Hamilton, Nicholas A.
AU  - Morris, Richard G.
AU  - Yap, Alpha S.
TI  - Scaffolding of RhoA contractile signaling by anillin: a regulatory analogue of kinetic proofreading
AID  - 10.1101/282756
DP  - 2018 Jan 01
TA  - bioRxiv
PG  - 282756
4099  - http://biorxiv.org/content/early/2018/03/18/282756.short
4100  - http://biorxiv.org/content/early/2018/03/18/282756.full
AB  - Scaffolding is a fundamental principle of cell signaling commonly thought to involve multi-domain proteins that tether different components of a pathway together into a complex 1,2. We now report an alternative mechanism for scaffolding that is necessary for RhoA-mediated contractile signaling. We find that anillin binding stabilizes active, GTP-RhoA, and promotes contractility at both the epithelial zonula adherens (ZA) and the cytokinetic furrow. However, anillin does not conform to the classical picture of a multi-domain tether, since its RhoA-binding AH domain alone was sufficient to promote contractile signaling. Moreover, anillin competes with contractile effectors for a common site on RhoA, presenting the conundrum of how an inhibitory interaction can otherwise promote signaling. To explain this, we propose that inactivation of RhoA is non-Poissonian, having a rate that increases with time, unless the process is reset via transient binding to anillin. Repeated cycles of binding and un-binding therefore increase cortical residence times of non-sequestered GTP-RhoA and hence the probability of engaging contractile effectors. We identify the modification of the local lipid environment as a potential mechanism underlying such non-Poisson statistics, and demonstrate agreement with a minimal cellular system. Finally, we show that Myosin II anchors anillin at the cortex to form a feedback pathway that enhances RhoA signaling. This new paradigm of scaffolding is a regulatory analogue of kinetic proofreading and may be employed by other binding proteins that do not fit the classical picture.