ROBO2 is a stroma suppressor gene in the pancreas and acts via TGF-ß signalling.

Whereas genomic aberrations in the SLIT-ROBO pathway are frequent in pancreatic ductal adenocarcinoma (PDAC), their function in the pancreas is unclear. Here we report that in pancreatitis and PDAC mouse models, epithelial Robo2 expression is lost while Robo1 expression becomes most prominent in the stroma. Cell cultures of mice with loss of epithelial Robo2 (Pdx1Cre;Robo2F/F) show increased activation of Robo1+ myofibroblasts and induction of TGF-ß and Wnt pathways. During pancreatitis, Pdx1Cre;Robo2F/F mice present enhanced myofibroblast activation, collagen crosslinking, T-cell infiltration and tumorigenic immune markers. The TGF-ß inhibitor galunisertib suppresses these effects. In PDAC patients, ROBO2 expression is overall low while ROBO1 is variably expressed in epithelium and high in stroma. ROBO2low;ROBO1high patients present the poorest survival. In conclusion, Robo2 acts non-autonomously as a stroma suppressor gene by restraining myofibroblast activation and T-cell infiltration. ROBO1/2 expression in PDAC patients may guide therapy with TGF-ß inhibitors or other stroma /immune modulating agents.

Hematopoietic plakophilin-3 regulates acute tissue-specific and systemic inflammation in mice.

Plakophilin-3 (PKP3) is a member of the armadillo protein family, which is important in cell-cell contacts and signaling during development and tumorigenesis. In conventional facilities, PKP3-deficient mice (PKP3(-/-)) develop spontaneous dermatitis, indicating a possible involvement of PKP3 in inflammatory responses. Here, we show that PKP3 deficiency sensitizes mice to irritant contact dermatitis induced by phorbol myristate acetate (PMA). This sensitization occurred in mice with PKP3 deficiency in the hematopoietic system (PKP3(-/-hem)), but not if the deficiency was specific to skin keratinocytes (PKP3(-/-ker)). In a model of dextran sulfate sodium induced colitis, ubiquitous PKP3 deletion, but not intestinal epithelial PKP3 deficiency (PKP3(-/-IEC)), impaired survival from disease. Interestingly, PKP3(-/-hem) mice also displayed increased sensitivity to dextran sulfate sodium induced colitis. Finally, PKP3(-/-) mice were more sensitive to the lethality of lipopolysaccharide (LPS) injection than wild-type (WT) mice, and this phenotype was associated with increased intestinal permeability. PKP3(-/-IEC) mice did not reproduce the enhanced endotoxin reactivity of PKP3(-/-) mice, in contrast to PKP3(-/-hem) mice. Finally, in vitro stimulation of WT neutrophils with LPS or PMA increased Pkp3 expression. In conclusion, our data highlight a novel role for hematopoietic PKP3 in the regulation of both locally and systemically induced immune responses. Nonetheless, further research is needed to unravel the underlying mechanism.

Plakophilin-3-deficient mice develop hair coat abnormalities and are prone to cutaneous inflammation.

We generated mice deficient in plakophilin-3 (PKP3), a member of the Armadillo-repeat family and a component of desmosomes and stress granules in epithelial cells. In these mice, several subsets of hair follicles (HFs) had morphological abnormalities, and the majority of awl and auchene hair shafts had fewer medullar air columns. Desmosomes were absent from the basal layer of the outer root sheath of HFs and from the matrix cells that are in contact with dermal papillae. In the basal layer of PKP3-null epidermis, densities of desmosomes and adherens junctions were remarkably altered. Compensatory changes in several junctional proteins were observed. PKP3-null mice housed in conventional facilities were prone to dermatitis. Our animal model provides in vivo evidence that PKP3 plays a critical role in morphogenesis of HFs and shafts and in limiting inflammatory responses in the skin.

Fragmin60 encodes an actin-binding protein with a C2 domain and controls actin Thr-203 phosphorylation in Physarum plasmodia and sclerotia.

We report the isolation of a cDNA clone encoding a 60-kDa protein termed fragmin60 that cross-reacts with fragmin antibodies. Unlike other gelsolin-related proteins, fragmin60 contains a unique N-terminal domain that shows similarity with C2 domains of aczonin, protein kinase C, and synaptotagmins. The fragmin60 C2 domain binds three calcium ions, one with nanomolar affinity and two with micromolar affinity. Actin binding by fragmin60 requires higher calcium concentrations than does binding of actin by a fragmin60 mutant lacking the C2 domain, suggesting that the C2 domain secures the actin binding moiety in a conformation preventing actin binding at low calcium concentrations. The fragmin60 C2 domain does not bind phospholipids but interacts with the endogenous homologue of Saccharomyces cerevisiae S-phase kinase-associated protein (Skp1), as shown by pull-down assays and co-expression in mammalian cells. Recombinant fragmin60 promotes in vitro phosphorylation of actin Thr-203 by the actin-fragmin kinase. We further show that in vivo phosphorylation of actin in the fragmin60-actin complex occurs in sclerotia, a dormant stage of Physarum development, as well as in plasmodia. Our findings indicate that we have cloned a novel type of gelsolin-related actin-binding protein that is involved in controlling regulation of actin phosphorylation in vivo.