An Interferon-Driven Oxysterol-Based Defense against Tumor-Derived Extracellular Vesicles

Tumor-derived extracellular vesicles (TEV) "educate" healthy cells to promote metastases. We found that melanoma TEV downregulated type I interferon (IFN) receptor and expression of IFN-inducible cholesterol 25-hydroxylase (CH25H). CH25H produces 25-hydroxycholesterol, which inhibited TEV uptake. Low CH25H levels in leukocytes from melanoma patients correlated with poor prognosis. Mice incapable of downregulating the IFN receptor and Ch25h were resistant to TEV uptake, TEV-induced pre-metastatic niche, and melanoma lung metastases; however, ablation of Ch25h reversed these phenotypes. An anti-hypertensive drug, reserpine, suppressed TEV uptake and disrupted TEV-induced formation of the pre-metastatic niche and melanoma lung metastases. These results suggest the importance of CH25H in defense against education of normal cells by TEV and argue for the use of reserpine in adjuvant melanoma therapy.

Inactivation of Interferon Receptor Promotes the Establishment of Immune Privileged Tumor Microenvironment

Refractoriness of solid tumors, including colorectal cancers (CRCs), to immunotherapies is attributed to the immunosuppressive tumor microenvironment that protects malignant cells from cytotoxic T lymphocytes (CTLs). We found that downregulation of the type I interferon receptor chain IFNAR1 occurs in human CRC and mouse models of CRC. Downregulation of IFNAR1 in tumor stroma stimulated CRC development and growth, played a key role in formation of the immune-privileged niche, and predicted poor prognosis in human CRC patients. Genetic stabilization of IFNAR1 improved CTL survival and increased the efficacy of the chimeric antigen receptor T cell transfer and PD-1 inhibition. Likewise, pharmacologic stabilization of IFNAR1 suppressed tumor growth providing the rationale for upregulating IFNAR1 to improve anti-cancer therapies.

Type 1 interferons contribute to the clearance of senescent cell

The major known function of cytokines that belong to type I interferons (IFN, including IFNα and IFNβ) is to mount the defense against viruses. This function also protects the genetic information of host cells from alterations in the genome elicited by some of these viruses. Furthermore, recent studies demonstrated that IFN also restrict proliferation of damaged cells by inducing cell senescence. Here we investigated the subsequent role of IFN in elimination of the senescent cells. Our studies demonstrate that endogenous IFN produced by already senescent cells contribute to increased expression of the natural killer (NK) receptor ligands, including MIC-A and ULBP2. Furthermore, neutralization of endogenous IFN or genetic ablation of its receptor chain IFNAR1 compromises the recognition of senescent cells and their clearance in vitro and in vivo. We discuss the role of IFN in protecting the multi-cellular host from accumulation of damaged senescent cells and potential significance of this mechanism in human cancers.

DNA-damage-induced type I interferon promotes senescence and inhibits stem cell function

Expression of type I interferons (IFNs) can be induced by DNA-damaging agents, but the mechanisms and significance of this regulation are not completely understood. We found that the transcription factor IRF3, activated in an ATM-IKKα/β-dependent manner, stimulates cell-autonomous IFN-β expression in response to double-stranded DNA breaks. Cells and tissues with accumulating DNA damage produce endogenous IFN-β and stimulate IFN signaling in vitro and in vivo. In turn, IFN acts to amplify DNA-damage responses, activate the p53 pathway, promote senescence, and inhibit stem cell function in response to telomere shortening. Inactivation of the IFN pathway abrogates the development of diverse progeric phenotypes and extends the lifespan of Terc knockout mice. These data identify DNA-damage-response-induced IFN signaling as a critical mechanism that links accumulating DNA damage with senescence and premature aging.

Type I interferon controls propagation of long interspersed element-1

Type I interferons (IFN) including IFNα and IFNβ are critical for the cellular defense against viruses. Here we report that increased levels of IFNβ were found in testes from mice deficient in MOV10L1, a germ cell-specific RNA helicase that plays a key role in limiting the propagation of retrotransposons including Long Interspersed Element-1 (LINE-1). Additional experiments revealed that activation of LINE-1 retrotransposons increases the expression of IFNβ and of IFN-stimulated genes. Conversely, pretreatment of cells with IFN suppressed the replication of LINE-1. Furthermore, the efficacy of LINE-1 replication was increased in isogenic cell lines harboring inactivating mutations in diverse elements of the IFN signaling pathway. Knockdown of the IFN receptor chain IFNAR1 also stimulated LINE-1 propagation in vitro. Finally, a greater accumulation of LINE-1 was found in mice that lack IFNAR1 compared with wild type mice. We propose that LINE-1-induced IFN plays an important role in restricting LINE-1 propagation and discuss the putative role of IFN in preserving the genome stability.

Eliminative signaling by Janus kinases: role in the downregulation of associated receptors

Activation of cytokine receptor-associated Janus kinases (JAKs) mediates most, if not all, of the cellular responses to peptide hormones and cytokines. Consequently, JAKs play a paramount role in homeostasis and immunity. Members of this family of tyrosine kinases control the cytokine/hormone-induced alterations in cell gene expression program. This function is largely mediated through an ability to signal toward activation of the signal transducer and activator of transcription proteins (STAT), as well as toward some other pathways. Importantly, JAKs are also instrumental in tightly controlling the expression of associated cytokine and hormone receptors, and, accordingly, in regulating the cell sensitivity to these cytokines and hormones. This review highlights the enzymatic and non-enzymatic mechanisms of this regulation and discusses the importance of the ambidextrous nature of JAK as a key signaling node that integrates the combining functions of forward signaling and eliminative signaling. Attention to the latter aspect of JAK function may contribute to emancipating our approaches to the pharmacological modulation of JAKs.

Triggering ubiquitination of IFNAR1 protects tissues from inflammatory injury

Type 1 interferons (IFN) protect the host against viruses by engaging a cognate receptor (consisting of IFNAR1/IFNAR2 chains) and inducing downstream signaling and gene expression. However, inflammatory stimuli can trigger IFNAR1 ubiquitination and downregulation thereby attenuating IFN effects in vitro. The significance of this paradoxical regulation is unknown. Presented here results demonstrate that inability to stimulate IFNAR1 ubiquitination in the Ifnar1(SA) knock-in mice renders them highly susceptible to numerous inflammatory syndromes including acute and chronic pancreatitis, and autoimmune and toxic hepatitis. Ifnar1(SA) mice (or their bone marrow-receiving wild type animals) display persistent immune infiltration of inflamed tissues, extensive damage and gravely inadequate tissue regeneration. Pharmacologic stimulation of IFNAR1 ubiquitination is protective against from toxic hepatitis and fulminant generalized inflammation in wild type but not Ifnar1(SA) mice. These results suggest that endogenous mechanisms that trigger IFNAR1 ubiquitination for limiting the inflammation-induced tissue damage can be purposely mimicked for therapeutic benefits.

Pathogen recognition receptor signaling accelerates phosphorylation-dependent degradation of IFNAR1

An ability to sense pathogens by a number of specialized cell types including the dendritic cells plays a central role in host's defenses. Activation of these cells through the stimulation of the pathogen-recognition receptors induces the production of a number of cytokines including Type I interferons (IFNs) that mediate the diverse mechanisms of innate immunity. Type I IFNs interact with the Type I IFN receptor, composed of IFNAR1 and IFNAR2 chains, to mount the host defense responses. However, at the same time, Type I IFNs elicit potent anti-proliferative and pro-apoptotic effects that could be detrimental for IFN-producing cells. Here, we report that the activation of p38 kinase in response to pathogen-recognition receptors stimulation results in a series of phosphorylation events within the IFNAR1 chain of the Type I IFN receptor. This phosphorylation promotes IFNAR1 ubiquitination and accelerates the proteolytic turnover of this receptor leading to an attenuation of Type I IFN signaling and the protection of activated dendritic cells from the cytotoxic effects of autocrine or paracrine Type I IFN. In this paper we discuss a potential role of this mechanism in regulating the processes of innate immunity.

Prolactin stimulates ubiquitination, initial internalization, and degradation of its receptor via catalytic activation of Janus kinase 2

Prolactin (PRL) activates its receptor to initiate signal transduction pathways (including activation of Janus kinases, Jak) but also stimulates downregulation of this receptor to limit the magnitude and duration of signaling. Degradation of the long form of PRL receptor (PRLr) depends on its phosphorylation on Ser349 that is required to facilitate PRLr ubiquitination. Signaling events that mediate PRL-induced degradation of PRLr remain to be elucidated. Here, we investigated the role of Jak2 activity in ligand-triggered increase of PRLr phosphorylation on Ser349, PRLr ubiquitination, endocytosis, and degradation. Using Jak2 reconstitution in Jak2-null cells as well as pharmacologic approaches, we found that treatment with PRL (but not with PRLr antagonist) promotes phosphorylation of PRLr on Ser349 and accelerates endocytosis of PRLr. Furthermore, PRL-stimulated PRLr phosphorylation, endocytosis, and degradation in Jak2-null cells reconstituted with wild type but not with catalytically inactive Jak2. We discuss how Jak2-mediated signaling might be transduced into Ser349 phosphorylation of PRLr as well as its ubiquitination and endocytosis.

Site-specific ubiquitination exposes a linear motif to promote interferon-alpha receptor endocytosis

Ligand-induced endocytosis and lysosomal degradation of cognate receptors regulate the extent of cell signaling. Along with linear endocytic motifs that recruit the adaptin protein complex 2 (AP2)–clathrin molecules, monoubiquitination of receptors has emerged as a major endocytic signal. By investigating ubiquitin-dependent lysosomal degradation of the interferon (IFN)-α/β receptor 1 (IFNAR1) subunit of the type I IFN receptor, we reveal that IFNAR1 is polyubiquitinated via both Lys48- and Lys63-linked chains. The SCF^βTrcp (Skp1–Cullin1–F-box complex) E3 ubiquitin ligase that mediates IFNAR1 ubiquitination and degradation in cells can conjugate both types of chains in vitro. Although either polyubiquitin linkage suffices for postinternalization sorting, both types of chains are necessary but not sufficient for robust IFNAR1 turnover and internalization. These processes also depend on the proximity of ubiquitin-acceptor lysines to a linear endocytic motif and on its integrity. Furthermore, ubiquitination of IFNAR1 promotes its interaction with the AP2 adaptin complex that is required for the robust internalization of IFNAR1, implicating cooperation between site-specific ubiquitination and the linear endocytic motif in regulating this process.

p21 loss cooperates with INK4 inactivation facilitating immortalization and Bcl-2-mediated anchorage-independent growth of oncogene-transduced primary mouse fibroblasts

The INK4 and CIP cyclin-dependent kinase (Cdk) inhibitors (CKI) activate pocket protein function by suppressing Cdk4 and Cdk2, respectively. Although these inhibitors are lost in tumors, deletion of individual CKIs results in modest proliferation defects in murine models. We have evaluated cooperativity between loss of all INK4 family members (using cdk4r24c mutant alleles that confer resistant to INK4 inhibitors) and p21(Waf1/Cip1) in senescence and transformation of mouse embryo fibroblasts (MEF). We show that mutant cdk4r24c and p21 loss cooperate in pRb inactivation and MEF immortalization. Our studies suggest that cdk4r24c mediates resistance to p15(INK4B)/p16(INK4A) that accumulates over passage, whereas loss of p21 suppresses hyperoxia-induced Cdk2 inhibition and pRb dephosphorylation on MEF explantation in culture. Although cdk4r24c and p21 loss cooperate in H-ras(V12)/c-myc-induced foci formation, they are insufficient for oncogene-induced anchorage-independent growth. Interestingly, p21(-/-); cdk4r24c MEFs expressing H-ras(V12) and c-myc display detachment-induced apoptosis and are transformed by c-myc, H-ras(V12), and Bcl-2. We conclude that the INK4 family and p21 loss cooperate in promoting pRb inactivation, cell immortalization, and H-ras(V12)/c-myc-induced loss of contact inhibition. In addition, absence of pRb function renders H-ras(V12) + c-myc-transduced fibroblasts prone to apoptosis when deprived of the extracellular matrix, and oncogene-induced anchorage-independent growth of pocket protein-deficient cells requires apoptotic suppression.

Mutant p53 protein overexpression in women with ipsilateral breast tumor recurrence following lumpectomy and radiation therapy

BACKGROUND

The p53 tumor suppressor gene encodes a nuclear phosphoprotein that is thought to be important to cell cycle regulation and DNA repair and that also may regulate induction of apoptosis by ionizing radiation. Somatic p53 gene mutations occur in 30-50% of breast carcinomas and are associated with poor prognosis. Mutations in the p53 gene result in prolonged stability of the protein that can be detected by immunohistochemical techniques. In a matched case-control study of breast carcinoma patients with ipsilateral breast tumor recurrence (IBTR) following lumpectomy and radiation therapy, the authors investigated the frequency and prognostic significance of somatic p53 mutations as well as the clinical characteristics of patients with these mutations.

METHODS

Between 1973 and 1995, there were 121 breast carcinoma patients with IBTR following lumpectomy and radiation therapy, and the authors identified 47 patients in whom the paraffin embedded tissue blocks from the primary breast tumors were available for further molecular analysis. Forty-seven control breast carcinoma patients from the breast carcinoma data base were individually matched to the index cases who did not have IBTR for age, treatment date, follow-up, histology, margin status, radiation dose, and adjuvant treatment. Immunohistochemistry using a monoclonal antibody to mutant p53 protein was used to determine mutant p53 protein overexpression in breast tumors and appropriately scored.

RESULTS

A total of 12 of 47 tumor specimens (26%) from index patients with breast tumor relapses demonstrated mutant p53 protein overexpression, whereas only 4 of 47 specimens from controls (9%) demonstrated high mutant p53 immunoreactivity (P = 0.02). The authors found that 9 of 23 patients (39%) with early breast tumor recurrences (recurrences within 4 years of diagnosis) had overexpression of mutant p53 protein, whereas only 1 of 23 control cases (4%) had high mutant p53 protein immunoreactivity (P = 0.003). In contrast, index cases from patients with late breast tumor relapses (more than 4 years after diagnosis), which are more likely to represent de novo breast tumors, and control cases from the breast carcinoma data base without IBTR had similar levels of mutant p53 protein overexpression (P = not significant). The 10-year distant disease free survival for patients with mutant p53 protein was 48%, compared with 67% for breast carcinoma patients without detection of mutant p53 protein (P = 0. 08). The authors found that 13 of 14 primary breast tumors (93%) with mutant p53 protein overexpression were estrogen receptor negative (P = 0.01) and 11 of 14 (79%) were progesterone receptor negative (P = not significant).

CONCLUSIONS

In a matched case-control study, overexpression of mutant p53 protein has prognostic significance with respect to IBTR following lumpectomy and radiation therapy. Breast tumors with p53 mutations are generally estrogen receptor negative and are associated with compromised distant disease free survival.

Elevated frequency and functional activity of a specific germ-line p53 intron mutation in familial breast cancer

Previous studies have determined that the frequency of germ-line p53 mutations in familial breast cancer patients is 1% or less, but these reports have not investigated the importance of polymorphic intron base changes in the p53 gene. Therefore, we investigated the frequency of both exon and intron germ-line p53 base changes in 42 breast cancer patients with a strong family history of breast cancer. The mean age of presentation of these patients was 44.0 years (range, 29-69), and 12 of 42 (29%) were of known Ashkenazi ancestry. Purified DNA obtained from the 42 index cases was screened for germ-line p53 mutations in exons 2-11 and surrounding introns using a combination of intron based primers for PCR-single strand conformation polymorphism analysis, direct sequencing, and microarray sequencing using the Affymetrix p53 gene chip methodology. Morphological analysis of apoptosis and cell survival determination were performed on EBV-immortalized lymphoblastoid cell lines from two patients with the p53 intron 6 mutation. A germ-line mutation in the p53 gene at nucleotide 13964 with a G to C base change (13964GC) was identified in 3 of 42 (7.1%) hereditary breast cancer patients. Two patients were heterozygous for this mutation, and one patient had a homozygous mutation. In comparison, 0 of 171 (0%) of sporadic breast cancer patients had the p53 13964GC mutation (P = 0.0003). We found that 0 of 42 (0%) of these hereditary breast cancer patients had other germ-line p53 mutation in exons 2-11. However, pedigree analysis demonstrated that all three patients had strong family histories of multiple types of cancers consistent with Li-Fraumeni syndrome but with late age of onset. Comprehensive BRCA1 and BRCA2 nucleotide analysis from patients with the p53 13964GC mutation revealed no concomitant deleterious BRCA1 or BRCA2 mutations, although they were found in the other hereditary breast cancer patients. Functional analysis of two immortalized lymphoblastoid cell lines derived from patients with the p53 13964GC mutation demonstrated prolonged in vitro survival in response to cisplatinum treatment and showed decreased chemotherapy-induced apoptosis. Immunohistochemical analysis of breast tumors from these patients revealed high levels of mutant p53 protein, suggesting a functional mutation in the p53 gene. In summary, we have identified a single p53 intron mutation in familial breast cancer patients that is present at elevated frequency and has functional activity.

14-3-3Gamma interacts with and is phosphorylated by multiple protein kinase C isoforms in PDGF-stimulated human vascular smooth muscle cells

It has recently been demonstrated that some members of the 14-3-3 protein family play an important role in signal transduction leading to cellular proliferation. We have previously shown that expression of 14-3-3gamma is induced by growth factors in human vascular smooth muscle cells (VSMC). In this study, we cloned the human homolog of 14-3-3gamma and observed many potential phosphorylation sites, suggesting the potential for post-translational modification. In VSMC treated with platelet-derived growth factor (PDGF), 14-3-3gamma protein was expressed and phosphorylated in an activation-dependent manner. Platelet-derived growth factor-induced phosphorylation could be inhibited by phosphokinase C (PKC) inhibitory compounds, and 14-3-3gamma could be phosphorylated in the absence of PDGF by compounds that activate PKC. We also demonstrated interaction between 14-3-3gamma and several PKC isoforms (alpha, beta, gamma, theta, and delta), implicating these PKC family isoforms as the kinases responsible for PDGF-induced 14-3-3gamma phosphorylation. We found that 14-3-3gamma interacted with the signal transduction protein Raf-1, suggesting that 14-3-3gamma provides a link between this protein and PKC. Thus, 14-3-3gamma may represent a signal transduction protein that is regulated transcriptionally and post-transcriptionally by growth factors.