Gut bacteria require neutrophils to promote mammary tumorigenesis.

Recent studies suggest that gastrointestinal tract microbiota modulate cancer development in distant non-intestinal tissues. Here we tested mechanistic hypotheses using a targeted pathogenic gut microbial infection animal model with a predilection to breast cancer. FVB-Tg(C3-1-TAg)cJeg/JegJ female mice were infected by gastric gavage with Helicobacter hepaticus at three-months-of-age putting them at increased risk for mammary tumor development. Tumorigenesis was multifocal and characterized by extensive infiltrates of myeloperoxidase-positive neutrophils otherwise implicated in cancer progression in humans and animal models. To test whether neutrophils were important in etiopathogenesis in this bacteria-triggered model system, we next systemically depleted mice of neutrophils using thrice weekly intraperitoneal injections with anti-Ly-6G antibody. We found that antibody depletion entirely inhibited tumor development in this H. hepaticus-infected model. These data demonstrate that host neutrophil-associated immune responses to intestinal tract microbes significantly impact cancer progression in distal tissues such as mammary glands, and identify gut microbes as novel targets for extra-intestinal cancer therapy.

A cell-intrinsic role for CaMKK2 in granulocyte lineage commitment and differentiation.

Granulocytes serve a critical function in host organisms by recognizing and destroying invading microbes, as well as propagating and maintaining inflammation at sites of infection. However, the molecular pathways underpinning the development of granulocytes are poorly understood. Here, we identify a role for CaMKK2 in the restriction of granulocytic fate commitment and differentiation of myeloid progenitor cells. Following BMT, engraftment by Camkk2(-/-) donor cells resulted in the increased production of mature granulocytes in the BM and peripheral blood. Similarly, Camkk2(-/-) mice possessed elevated numbers of CMP cells and exhibited an accelerated granulopoietic phenotype in the BM. Camkk2(-/-) myeloid progenitors expressed increased levels of C/EBPα and PU.1 and preferentially differentiated into Gr1(+)Mac1(+) granulocytes and CFU-G in vitro. During normal granulopoiesis in vivo or G-CSF-induced differentiation of 32D myeloblast cells in vitro, CaMKK2 mRNA and protein were decreased as a function of time and were undetectable in mature granulocytes. Expression of ectopic CaMKK2 in Camkk2(-/-) CMPs was sufficient to rescue aberrant granulocyte differentiation and when overexpressed in 32D cells, was also sufficient to impede granulocyte differentiation in a kinase activity-dependent manner. Collectively, our results reveal a novel role for CaMKK2 as an inhibitor of granulocytic fate commitment and differentiation in early myeloid progenitors.

Gfer inhibits Jab1-mediated degradation of p27kip1 to restrict proliferation of hematopoietic stem cells.

Growth factor erv1-like (Gfer) is an evolutionarily conserved sulfhydryl oxidase that is enriched in embryonic and adult stem cells and plays an essential prosurvival role in pluripotent embryonic stem cells. Here we show that knockdown (KD) of Gfer in hematopoietic stem cells (HSCs) compromises their in vivo engraftment potential and triggers a hyper-proliferative response that leads to their exhaustion. KD of Gfer in HSCs does not elicit a significant alteration of mitochondrial morphology or loss of cell viability. However, these cells possess significantly reduced levels of the cyclin-dependent kinase inhibitor p27(kip1). In contrast, overexpression of Gfer in HSCs results in significantly elevated total and nuclear p27(kip1). KD of Gfer results in enhanced binding of p27(kip1) to its inhibitor, the COP9 signalosome subunit jun activation-domain binding protein 1 (Jab1), leading to its down-regulation. Conversely, overexpression of Gfer results in its enhanced binding to Jab1 and inhibition of the Jab1-p27(kip1) interaction. Furthermore, normalization of p27(kip1) in Gfer-KD HSCs rescues their in vitro proliferation deficits. Taken together, our data demonstrate the presence of a novel Gfer-Jab1-p27(kip1) pathway in HSCs that functions to restrict abnormal proliferation.