Fam49/CYRI interacts with Rac1 and locally suppresses protrusions.

Actin-based protrusions are reinforced through positive feedback, but it is unclear what restricts their size, or limits positive signals when they retract or split. We identify an evolutionarily conserved regulator of actin-based protrusion: CYRI (CYFIP-related Rac interactor) also known as Fam49 (family of unknown function 49). CYRI binds activated Rac1 via a domain of unknown function (DUF1394) shared with CYFIP, defining DUF1394 as a Rac1-binding module. CYRI-depleted cells have broad lamellipodia enriched in Scar/WAVE, but reduced protrusion-retraction dynamics. Pseudopods induced by optogenetic Rac1 activation in CYRI-depleted cells are larger and longer lived. Conversely, CYRI overexpression suppresses recruitment of active Scar/WAVE to the cell edge, resulting in short-lived, unproductive protrusions. CYRI thus focuses protrusion signals and regulates pseudopod complexity by inhibiting Scar/WAVE-induced actin polymerization. It thus behaves like a 'local inhibitor' as predicted in widely accepted mathematical models, but not previously identified in cells. CYRI therefore regulates chemotaxis, cell migration and epithelial polarization by controlling the polarity and plasticity of protrusions.

Fibroblast activation protein-α in fibrogenic disorders and cancer: more than a prolyl-specific peptidase?

INTRODUCTION: Fibroblast activation protein-α (FAP-α) belongs to the family of prolyl-specific serine proteases. FAP-α displays both exopeptidase and endopeptidase/gelatinase/collagenase activities. FAP-α protein and/or activity have been associated with fibrosis, inflammation and cancer, but the protein is undetectable in most normal tissues. FAP-α is selectively expressed at sites of tissue remodeling and repair and enhances tumor progression, suggesting that this protease may be a therapeutic target to treat human disorders associated with fibrotic dysregulation. Areas covered: In this review, we summarize the mechanisms driving tissue fibrosis and describe some of the enzymes involved in fibrosis, concentrating on FAP-α. We describe its enzymatic properties, discuss the tools developed to control its activity and the problem of selectivity toward the other proteases of the family and outline its potential biological substrates. We also consider non-enzymatic functions of this protein and suggest that repression of FAP-α expression may represent therapeutic options. Expert opinion: Questions remain regarding the biological functions of FAP-α, either dependent or independent of its enzyme activity. However, as progress is underway to develop FAP-α-specific inhibitors and therapeutic antibodies, its role in diseases associated with fibrosis is starting to emerge, ultimately leading to novel therapeutic options for inflammatory and oncologic diseases.

A host-factor interaction and localization map for a plant-adapted rhabdovirus implicates cytoplasm-tethered transcription activators in cell-to-cell movement.

To identify host factors that play critical roles in processes, including cell-to-cell movement of plant-adapted rhabdoviruses, we constructed and validated a high-resolution Nicotiana benthamiana yeast two-hybrid library. The library was screened with the putative movement protein (sc4), nucleocapsid (N), and matrix (M) proteins of Sonchus yellow net virus (SYNV). This resulted in identification of 31 potential host factors. Steady-state localization studies using autofluorescent protein fusions to full-length clones of interactors were conducted in transgenic N. benthamiana marker lines. Bimolecular fluorescence complementation assays were used to validate two-hybrid interactions. The sc4 interactor, sc4i21, localized to microtubules. The N interactor, Ni67, localized to punctuate loci on the endoplasmic reticulum. These two proteins are 84% identical homologues of the Arabidopsis phloem-associated transcription activator AtVOZ1, and contain functional nuclear localization signals. Sc4i17 is a microtubule-associated motor protein. The M interactor, Mi7, is a nuclear-localized transcription factor. Combined with a binary interaction map for SYNV proteins, our data support a model in which the SYNV nucleocapsids are exported from the nucleus and moved cell-to-cell by transcription activators tethered in the cytoplasm.