Volume 12 Issue 7, July 2010

Adherens junctions, the sites of cadherin-dependent cell–cell adhesion, are also important for dynamic tension sensing, force transduction and signalling. Different myosin motors contribute to adherens junction assembly and versatility in distinct ways.

Rab GTPases regulate the dynamics of transport carriers by participating in their translocation across the cytoplasm, and in their docking and fusion with acceptor compartments. An interaction between Golgi-associated Rab6 and myosin II has now been shown to regulate the fission of Rab6-positive carriers, illuminating a previously unappreciated role for Rab6 and the actomyosin system in carrier biogenesis.

Recognition of apoptotic cells by phagocytic cells in Caenorhabditis elegans has been something of a mystery. A secreted transthyretin-like protein, TTR-52, has been identified as a bridging molecule between apoptotic cells and CED-1 on the phagocytic cells that engulf them.

The importin-β-like transport receptors and RanGTP govern selective transport of proteins into the nucleus. It has now been shown that importin-β2 (alternatively called transportin1) also selectively targets the motor protein Kif17 to primary cilia. In analogy to the nucleus, RanGTP in the intraciliary compartment mediates dissociation of Kif17 from its transport receptor and thereby completes import.

Tumour suppressors of the Forkhead box O (FoxO) family are proposed to limit tumour growth through direct transcriptional regulation. Cytosolic FoxO1 can also suppress tumour growth by triggering autophagy and ultimately cell death in a transcription-independent manner.

The non-processive motor, myosin II, is shown to be an effector of the Golgi-associated Rab6 GTPase. The acto-myosin machinery is involved in the fission of transport carriers from Golgi membranes.

Recognition of apoptotic cells by phagocytes is not fully understood. In C. elegans, the transthyretin-like protein, TTR-52, is secreted by the endoderm and clusters around apoptotic cells, inducing their engulfment through the CED-1/6/7 pathway.

Autophagy is involved in tumour suppression. Cytoplasmic FoxO1 is acetylated in response to stress and binds the autophagy regulator Atg7 to promote autophagy, cell death and tumour suppression, independently of its transcriptional activity.

During wound healing, the matricellular protein, CCN1, through its adhesion receptors α₆β₁ and heparan sulphate proteoglycans, activates senescence in fibroblasts by activation of p53. Senescence induced by CCN1 prevents fibrosis during tissue repair.

The stress-activated kinase, JNK, is regulated by the anaphase promoting complex (APC) ubiquitin ligase. Conversely, JNK also negatively controls the APC by directly phosphorylating the Cdh1 component of the APC and decreasing its affinity for the APC core subunits.

Different myosin II isoforms have distinct roles at adherens junctions: myosin IIa and IIb localization to junctions is regulated by unique upstream signals and they control specific aspects of junction adhesion and linkage to the actin cytoskeleton.

How factors are targeted to cilia remains largely unknown. A ciliary localization signal targets the KIF17 motor, important for intraflagellar transport, to cilia through importin-β2 and RanGTP.

How cell shape influences cell fate decisions is unclear. Epidermal stem cell fate is regulated by cell shape through the actin cytoskeleton and SRF transcriptional activity.

POGZ is identified as a binding partner for HP1 (Heterochomatin Protein 1) and as a regulator of mitotic progression. It mediates the activation of Aurora B and the dissociation of both HP1 and Aurora B from chromosome arms during mitosis.