Stasimon/Tmem41b is required for cell proliferation and adult mouse survival.

Stasimon/Tmem41b is a transmembrane protein with phospholipid scrambling activity that resides in the endoplasmic reticulum and has been implicated in autophagy, lipid metabolism, and viral replication. Stasimon/Tmem41b has also been linked to the function of sensory-motor circuits and the pathogenesis of spinal muscular atrophy. However, the early embryonic lethality of constitutive knockout in mice has hindered the analysis of spatial and temporal requirements of Stasimon/Tmem41b in vivo. To address this, we developed a novel mouse line harboring a conditional knockout allele of the Stasimon/Tmem41b gene in which exon 4 has been flanked by loxP sites (Stas/Tmem41bCKO). Cre-mediated recombination of Stas/Tmem41bCKO generates a functionally null allele (Stas/Tmem41bΔ4) resulting in loss of protein expression and embryonic lethality in the homozygous mouse mutant. Here, using a ubiquitously expressed, tamoxifen inducible Cre recombinase in the homozygous Stas/Tmem41bCKO mice, we demonstrate that postnatal depletion of Stasimon/Tmem41b rapidly arrests weight gain in adult mice and causes motor dysfunction and death approximately three weeks after tamoxifen treatment. Moreover, we show that depletion of Stasimon/Tmem41b severely affects cell proliferation in mouse embryonic fibroblasts. This study provides new insights into the essential requirement of Stasimon/Tmem41b for cellular and organismal fitness and expands the experimental toolkit to investigate its functions in the mammalian system.

Neuromuscular denervation and deafferentation but not motor neuron death are disease features in the Smn2B/- mouse model of SMA.

Spinal muscular atrophy (SMA) is a neurodegenerative disease characterized by loss of motor neurons and skeletal muscle atrophy which is caused by ubiquitous deficiency in the survival motor neuron (SMN) protein. Several cellular defects contribute to sensory-motor circuit pathology in SMA mice, but the underlying mechanisms have often been studied in one mouse model without validation in other available models. Here, we used Smn2B/- mice to investigate specific behavioral, morphological, and functional aspects of SMA pathology that we previously characterized in the SMNΔ7 model. Smn2B/- SMA mice on a pure FVB/N background display deficits in body weight gain and muscle strength with onset in the second postnatal week and median survival of 19 days. Morphological analysis revealed severe loss of proprioceptive synapses on the soma of motor neurons and prominent denervation of neuromuscular junctions (NMJs) in axial but not distal muscles. In contrast, no evidence of cell death emerged from analysis of several distinct pools of lumbar motor neurons known to be lost in the disease. Moreover, SMA motor neurons from Smn2B/- mice showed robust nuclear accumulation of p53 but lack of phosphorylation of serine 18 at its amino-terminal, which selectively marks degenerating motor neurons in the SMNΔ7 mouse model. These results indicate that NMJ denervation and deafferentation, but not motor neuron death, are conserved features of SMA pathology in Smn2B/- mice.

NR2F1 Is a Barrier to Dissemination of Early-Stage Breast Cancer Cells.

Cancer cells can disseminate during very early and sometimes asymptomatic stages of tumor progression. Though biological barriers to tumorigenesis have been identified and characterized, the mechanisms that limit early dissemination remain largely unknown. We report here that the orphan nuclear receptor nuclear receptor subfamily 2, group F, member 1 (NR2F1)/COUP-TF1 serves as a barrier to early dissemination. NR2F1 expression was decreased in patient ductal carcinoma in situ (DCIS) samples. High-resolution intravital imaging of HER2+ early-stage cancer cells revealed that loss of function of NR2F1 increased in vivo dissemination and was accompanied by decreased E-cadherin expression, activation of wingless-type MMTV integration site family, member 1 (WNT)-dependent ß-catenin signaling, disorganized laminin 5 deposition, and increased expression of epithelial-mesenchymal transition (EMT) genes such as twist basic helix-loop-helix transcription factor 1 (TWIST1), zinc finger E-box binding homeobox 1 (ZEB1), and paired related homeobox 1 (PRRX1). Furthermore, downregulation of NR2F1 promoted a hybrid luminal/basal phenotype. NR2F1 expression was positively regulated by p38α signaling and repressed by HER2 and WNT4 pathways. Finally, early cancer cells with NR2F1LOW/PRRX1HIGH staining were observed in DCIS samples. Together, these findings reveal the existence of an inhibitory mechanism of dissemination regulated by NR2F1 in early-stage breast cancer cells. SIGNIFICANCE: During early stages of breast cancer progression, HER2-mediated suppression of NR2F1 promotes dissemination by inducing EMT and a hybrid luminal/basal-like program.

'Reduced malignancy as a mechanism for longevity in mice with adenylyl cyclase type 5 disruption'.

Disruption of adenylyl cyclase type 5 (AC5) knockout (KO) is a novel model for longevity. Because malignancy is a major cause of death and reduced lifespan in mice, the goal of this investigation was to examine the role of AC5KO in protecting against cancer. There have been numerous discoveries in genetically engineered mice over the past several decades, but few have been translated to the bedside. One major reason is that it is difficult to alter a gene in patients, but rather a pharmacological approach is more appropriate. The current investigation employs a parallel construction to examine the extent to which inhibiting AC5, either in a genetic knockout (KO) or by a specific pharmacological inhibitor protects against cancer. This study is unique, not only because a combined genetic and pharmacological approach is rare, but also there are no prior studies on the extent to which AC5 affects cancer. We found that AC5KO delayed age-related tumor incidence significantly, as well as protecting against mammary tumor development in AC5KO × MMTV-HER-2 neu mice, and B16F10 melanoma tumor growth, which can explain why AC5KO is a model of longevity. In addition, a Food and Drug Administration approved antiviral agent, adenine 9-ß-D-arabinofuranoside (Vidarabine or AraAde), which specifically inhibits AC5, reduces LP07 lung and B16F10 melanoma tumor growth in syngeneic mice. Thus, inhibition of AC5 is a previously unreported mechanism for prevention of cancers associated with aging and that can be targeted by an available pharmacologic inhibitor, with potential consequent extension of lifespan.