Immune homeostasis depends on the proper function of regulatory T (Treg) cells. Compromised Treg cell suppressive activity leads to autoimmune disease, graft rejection and promotes anti-tumor immunity. Here we report the previously unrecognized requirement of the serine/threonine phosphatase Protein Phosphatase 2A (PP2A) for the function of Treg cells. Treg cells exhibited high PP2A activity and Treg cell-specific ablation of the PP2A complex resulted in a severe, multi-organ, lymphoproliferative autoimmune disorder. Mass spectrometric analysis revealed that PP2A associates with components of the mTOR pathway and suppresses mTORC1 activity. In the absence of PP2A, Treg cells altered their metabolic and cytokine profile and were unable to suppress effector immune responses. Therefore, PP2A is requisite for the function of Treg cells and the prevention of autoimmunity.

Despite the well-documented action of growth hormone-releasing hormone (GHRH) on the stimulation of production and release of growth hormone (GH), the effects of GHRH in peripheral tissues are incompletely explored. In this study, we show that GHRH plays a role in wound healing and tissue repair by acting primarily on woundassociated fibroblasts. Mouse embryonic fibroblasts (MEFs) in culture and wound-associated fibroblasts in mice expressed a splice variant of the receptors for GHRH (SV1). Exposure of MEFs to 100 nM and 500 nM GHRH or the GHRH agonist JI-38 stimulated the expression of α-smooth muscle actin (αSMA) based on immunoblot analyses as well as the expression of an αSMA-β-galactosidase reporter transgene in primary cultures of fibroblasts isolated from transgenic mice. Consistent with this induction of αSMA expression, results of transwellbased migration assays and in vitro wound healing (scratch) assays showed that both GHRH and GHRH agonist JI-38 stimulated the migration of MEFs in vitro. In vivo, local application of GHRH or JI-38 accelerated healing in skin wounds of mice. Histological evaluation of skin biopsies showed that wounds treated with GHRH and JI-38 were both characterized by increased abundance of fibroblasts during the early stages of wound healing and accelerated reformation of the covering epithelium at later stages. These results identify another function of GHRH in promoting skin tissue wound healing and repair. Our findings suggest that GHRH may have clinical utility for augmenting healing of skin wounds resulting from trauma, surgery, or disease.smooth muscle | actin | fibroblast proliferation | growth hormone G rowth hormone-releasing hormone (GHRH) is produced by the hypothalamus and acts on the pituitary, stimulating the production and release of growth hormone (GH) (1). Much evidence suggests that besides its hypophyseal action, GHRH plays a role in extrapituitary tissues and importantly in cancers stimulating tumor growth by paracrine and/or autocrine mechanisms (2, 3). Conversely, antagonistic analogs of GHRH potently inhibit the growth of various experimental human cancers in vitro and in vivo, suggesting that GHRH antagonists could serve as another specific class of anticancer agents (4).In addition to the hypothalamus, expression of GHRH has been reported in several nonhypothalamic tissues including placenta, ovaries, testes, lymphocytes, and others (5-14), but the physiological significance of this ectopic production of GHRH remains poorly elucidated. However, it has been suggested that locally produced GHRH promotes follicular maturation by paracrine modulation of the stimulatory action of follicle stimulating hormone on granulosa cell function (12), whereas in Leydig cells, GHRH contributes to spermatogenesis (9). Recent evidence also demonstrates that this neuropeptide can induce cardiac repair after myocardial infarction, by mechanisms involving a direct action on the cardiomyocytes (15, 16). Lately, it was also reported that GHRH agonists stimulate the proliferation...

BackgroundOur understanding of the multiple roles exosomes play during tumor progression is still very poor and the contribution of the normal tissue derived exosomes in distant seeding and tumor outgrowth has also not been widely appreciated.MethodsUsing our all-human liver microphysiological system (MPS) platform as a model to closely recapitulate the early metastatic events, we isolated exosomes from both tumor cells and liver microenvironment.ResultsWe observed that while priming of the hepatic niche (HepN) with MDA-231 breast cancer derived exosomes facilitated seeding of the cancer cells in the liver, subsequent tumor outgrowth was diminished; this was consistent with increased entry into dormancy. We found that hepatic niche (HepN) derived exosomes contribute significantly to the exosome pool and are distinguished from cancer derived exosomes based on their size, protein and miRNA content. By Ingenuity Pathway Analysis (IPA) of the miRNA content of the HepN, MDA-231/HepN and MDA-231 cells we showed that the HepN derived exosomes affect the breast cancer cells by suppressing pathways involved in cancer cell proliferation and invasion. More importantly exposure of MDA-231 and MDA-468 cells to purified normal HepN derived exosomes, induced changes in the cells consistent with a Mesenchymal to Epithelial reverting Transition (MErT). miRNA arrays performed on MDA-231 treated with Hum Hep/NPC derived exosomes showed significant changes in the levels of a select number of miRNAs involved in epithelial cell differentiation and miRNAs, such as miR186, miR23a and miR205, from our top and bottom bins have previously been reported to regulate E-cadherin transcription and MErT induction in various cancer types. Consistently HepN derived exosome treatment of breast and prostate cancer lines lead to a transient induction of E-cadherin and ZO-1 at the protein level and a more epithelial-like morphology of the cells.ConclusionsCollectively our data revealed a novel mechanism of regulation of the metastatic cascade, showing a well-orchestrated, timely controlled crosstalk between the cancer cells and the HepN and implicating for the first time the normal tissue/HepN derived exosomes in enabling seeding and entry into dormancy of the cancer cells at the metastatic site.Electronic supplementary materialThe online version of this article (10.1186/s12943-017-0740-6) contains supplementary material, which is available to authorized users.

The unfolded protein response (UPR) is triggered during stress of the endoplasmic reticulum (ER) and facilitates tissue homeostasis. Considering the role of p53 tumor suppressor gene in the interpretation of stress-inducing stimuli, in this study, we explored whether p53 modulates UPR. We found that p53 ablation resulted in a profound sensitivity to tunicamycin that was associated with liver dysfunction, ground glass hepatocyte (GGH) development and nuclear atypia/dysplasia. Binding immunoglobulin protein (BiP)/glucose-regulated protein 78 (GRP78) chaperone was readily detected in the cytoplasm of GGHs, confirming ER expansion. Tunicamycin administration induced BiP/GRP78 and GRP94 expression more potently in the p53-deficient mice than in controls and elevated phosphatidylcholine, the major lipid of ER, by a p53-dependent mechanism. Furthermore, alternative splicing of XBP1, the transcription factor that executes the UPR, was more efficient in cells which do not express p53. The cytoprotective effects of p53 were confirmed by cell viability studies, indicating that p53 deficiency conferred sensitivity against tunicamycin. Our findings show that p53 protects from the hepatotoxic effects of chronic ER stress. Stimulation of p53 activity when intense UPR is undesirable may possess therapeutic implications.