p63(TP63) elicits strong trans-activation of the MFG-E8/lactadherin/BA46 gene through interactions between the TA and DeltaN isoforms

C-terminal α Domain of p63 Binds to p300 to Coactivate β-Catenin

TP63 (p63), a member of the tumor suppressor TP53 (p53) gene family, is essential for ectodermal tissue development and suppresses malignant progression of carcinomas. The most abundant isoform, ΔNp63α (referred to as p63), lacks the N-terminal transactivation (TA) domain, and was originally characterized as a dominant-negative type suppressor against p53 family proteins. It also binds to TCF/LEF to inhibit β-catenin. Nevertheless, transcriptional activation by p63 has also been observed in varied systems. To understand the puzzling results, we analyzed the structure–function relationship of p63 in the control of β-catenin-dependent transcription. p63 acted as a suppressor of moderately induced β-catenin. However, when nuclear targeted S33Y β-catenin was applied to cause the maximum enhancer activation, p63 displayed a β-catenin-coactivating function. The DNA-binding domain of p63 and the target sequence facilitated it. Importantly, we newly found that, despite the absence of TA domain, p63 was associated with p300, a general adaptor protein and chromatin modifier causing transcriptional activation. C-terminal α domain of p63 was essential for p300-binding and for the coactivator function. These results were related to endogenous p63-p300 complex formation and Wnt/β-catenin-responsive gene regulation by p63 in squamous cell carcinoma lines. The novel p63-p300 interaction may be involved in positive regulation of gene expression in tissue development and carcinogenesis.

The Healing Effect of Human Milk Fat Globule-EGF Factor 8 Protein (MFG-E8) in A Rat Model of Parkinson's Disease

We searched for drugs that alleviate the reduction of dopaminergic neurons caused by the administration of lipopolysaccharide (LPS) to the substantia nigra of the rat brain. Human milk fat globule-EGF factor 8 protein (MFG-E8) is similar to MFG-E8-S, a short isoform, of the mouse MFG-E8. However, the function of MFG-E8-S was not clear. Rats with LPS-induced Parkinson’s disease were prepared and the effects of human MFG-E8 were examined. MFG-E8 improved the significant reduction in mesencephalic dopamine neurons induced by the administration of LPS. LPS was administered to human induced pluripotent stem cell (iPSC)-derived dopaminergic neurons to induce inflammation and the effect of MFG-E8 was examined. MFG-E8 showed no toxicity toward neurons. We reanalyzed the results using public microarray data. MFG-E8 mRNA was found to be expressed in all parts of the body, particularly by adipose-derived stem cells (ADSCs). Furthermore, we investigated the culture supernatant of ADSCs using the liquid chromatography-tandem mass spectrometry (LC–MS/MS) analysis method and successfully identified the peptide of the MFG-E8 F5/8 type C domain. The results suggested that MFG-E8-S may have a preventive effect against Parkinson’s disease.

Cross-contamination of the human salivary gland HSG cell line with HeLa cells: A STR analysis study

OBJECTIVES

The human salivary gland (HSG) cell line, labeled as a submandibular ductal cell line, is commonly used as in vitro models to study radiation therapy, Sjögren's syndrome, pleomorphic adenoma, mucocele, epithelial-to-mesenchymal transition, and epigenetics. However, the American Type Culture Collection (ATCC) has recently released a list of cross-contaminated cell lines that included HSG. Despite this notice, some research laboratories still use HSG as a salivary cell model. Therefore, this study examined the authenticity of HSG sampled from three different laboratories.

METHODS

DNA was extracted from HSG and additional salivary cell lines (NS-SV-AC, NS-SV-DC, A253, HSY) and submitted for cell line authentication with short tandem repeat (STR) analysis.

RESULTS

All HSG samples had STR profiles indicating >80% match with HeLa in both the ATCC and Deutsche Sammlung von Mikroorganismen und Zellkulturen (DSMZ) databases. This confirmed that HSG sampled from three different laboratories and HSY shared a common ancestry (host) with HeLa, whereas NS-SV-AC, NS-SV-DC, and A253 had unique STR profiles.

CONCLUSION

Short tandem repeat analysis revealed that HSG was contaminated by the HeLa cell line. Furthermore, because genotyping of the original HSG cell line was not performed during its establishment, it will be difficult to authenticate an uncontaminated sample of HSG.

NF-Y loss triggers p53 stabilization and apoptosis in HPV18-positive cells by affecting E6 transcription

The expression of the high risk HPV18 E6 and E7 oncogenic proteins induces the transformation of epithelial cells, through the disruption of p53 and Rb function. The binding of cellular transcription factors to cis-regulatory elements in the viral Upstream Regulatory Region (URR) stimulates E6/E7 transcription. Here, we demonstrate that the CCAAT-transcription factor NF-Y binds to a non-canonical motif within the URR and activates viral gene expression. In addition, NF-Y indirectly up-regulates HPV18 transcription through the transactivation of multiple cellular transcription factors. NF-YA depletion inhibits the expression of E6 and E7 genes and re-establishes functional p53. The activation of p53 target genes in turn leads to apoptotic cell death. Finally, we show that NF-YA loss sensitizes HPV18-positive cells toward the DNA damaging agent Doxorubicin, via p53-mediated transcriptional response.

Molecular Mechanisms Underlying the Regulation of the MFG-E8 Gene Promoter Activity in Physiological and Inflammatory Conditions

Milk fat globule-EGF factor 8 (MFG-E8) is expressed by macrophages and plays an important role in attenuating inflammation and maintaining tissue homeostasis. Previously, we and others found that lipopolysaccharide (LPS) inhibits MFG-E8 gene expression in macrophages. Here, we characterized the 5'-flanking region of the mouse MFG-E8 gene. To functionally analyze the upstream regulatory region of the MFG-E8 gene, a series of luciferase reporter gene constructs containing deleted or mutated regulatory elements were prepared. Using the luciferase assay, we revealed that Sp1 binding motifs within the proximal promoter region were necessary for full activity of the MFG-E8 promoter, whereas AP-1 like binding sequence at -372 played a role in governing the promoter activity at a homeostatic level. With chromatin immunoprecipitation assay, we showed that Sp1 and c-Jun physically interact with the MFG-E8 promoter region in vivo. In addition, Sp1 was found to regulate the MFG-E8 promoter activity positively and c-Jun negatively. Furthermore, we demonstrated that LPS inhibited MFG-E8 promoter activity via targeting Sp1 and AP-1-like motifs in the 5'-flanking region. Collectively, our data indicate that Sp1 and AP-1-related factors are involved in the regulation of MFG-E8 gene transcription by targeting their binding sites in the 5'-flanking region under physiological and inflammatory states.

Role of milk fat globule-epidermal growth factor 8 in colonic inflammation and carcinogenesis

BACKGROUND

Milk fat globule-epidermal growth factor 8 (MFG-E8) promotes phagocytic clearance of apoptotic cells to maintain normal tissue homeostasis. However, its functions in intestinal inflammation and carcinogenesis are unknown.

METHODS

Experimental colitis was induced in MFG-E8 knockout (KO) and wild-type (WT) mice by dextran sodium sulfate (DSS) administration. Colon tissues were used for assessments of colitis activity and epithelial proliferation. A mouse colitis-associated cancer (CAC) model was induced by intraperitoneal injection of azoxymethane (AOM) and then the animals were given a single administration of DSS. A sporadic colon cancer model was established by repeated intraperitoneal injections of AOM. The role of MFG-E8 in epithelial proliferation with or without treatment of siRNA targeting α(v)-integrin was examined in vitro using a WST-1 assay.

RESULTS

The severity of colitis in KO mice was greater than that in WT mice, while the proliferative potential of colonic epithelial cells in KO mice was lower during the regenerative phase. In both CAC and sporadic models, tumor size in KO was lower as compared to WT mice, while decreased tumor incidence was only found in the CAC model. In vitro findings showed that MFG-E8 promotes epithelial cell proliferation, and treatment with a siRNA targeting α(v)-integrin reduced the proliferation of Colon-26 cells stimulated with recombinant MFG-E8.

CONCLUSIONS

MFG-E8 promotes tumor growth regardless of the presence or absence of colonic inflammation, whereas colon tumor development is initiated by MFG-E8 under inflammatory conditions. These MFG-E8 functions may be dependent on integrin-mediated cellular signaling.

MFG-E8 activates proliferation of vascular smooth muscle cells via integrin signaling

An accumulation of milk fat globule EGF-8 protein (MFG-E8) occurs within the context of arterial wall inflammatory remodeling during aging, hypertension, diabetes mellitus, or atherosclerosis. MFG-E8 induces VSMC invasion, but whether it affects VSMC proliferation, a salient feature of arterial inflammation, is unknown. Here, we show that in the rat arterial wall in vivo, PCNA and Ki67, markers of cell cycle activation, increase with age between 8 and 30 months. In fresh and early passage VSMC isolated from old aortae, an increase in CDK4 and PCNA, an increase in the acceleration of cell cycle S and G2 phases, decrease in the G1/G0 phase, and an increase in PDGF and its receptors confer elevated proliferative capacity, compared to young VSMC. Increased coexpression and physical interaction of MFG-E8 and integrin αvβ5 occur with aging in both the rat aortic wall in vivo and in VSMC in vitro. In young VSMC in vitro, MFG-E8 added exogenously, or overexpressed endogenously, triggers phosphorylation of ERK1/2, augmented levels of PCNA and CDK4, increased BrdU incorporation, and promotes proliferation, via αvβ5 integrins. MFG-E8 silencing, or its receptor inhibition, or the blockade of ERK1/2 phosphorylation in these cells reduces PCNA and CDK4 levels and decelerates the cell cycle S phase, conferring a reduction in proliferative capacity. Collectively, these results indicate that MFG-E8 in a dose-dependent manner coordinates the expression of cell cycle molecules and facilitates VSMC proliferation via integrin/ERK1/2 signaling. Thus, an increase in MFG-E8 signaling is a mechanism of the age-associated increase in aortic VSMC proliferation.

Activation of the long terminal repeat of human endogenous retrovirus K by melanoma-specific transcription factor MITF-M

The human and Old World primate genomes possess conserved endogenous retrovirus sequences that have been implicated in evolution, reproduction, and carcinogenesis. Human endogenous retrovirus (HERV)-K with 5'LTR-gag-pro-pol-env-rec/np9-3'LTR sequences represents the newest retrovirus family that integrated into the human genome 1 to 5 million years ago. Although a high-level expression of HERV-K in melanomas, breast cancers, and teratocarcinomas has been demonstrated, the mechanism of the lineage-specific activation of the long terminal repeat (LTR) remains obscure. We studied chromosomal HERV-K expression in MeWo melanoma cells in comparison with the basal expression in human embryonic kidney 293 (HEK293) cells. Cloned LTR of HERV-K (HML-2.HOM) was also characterized by mutation and transactivation experiments. We detected multiple transcriptional initiator (Inr) sites in the LTR by rapid amplification of complementary DNA ends (5' RACE). HEK293 and MeWo showed different Inr usage. The most potent Inr was associated with a TATA box and three binding motifs of microphthalmia-associated transcription factor (MITF). Both chromosomal HERV-K expression and the cloned LTR function were strongly activated in HEK293 by transfection with MITF-M, a melanocyte/melanoma-specific isoform of MITF. Coexpression of MITF and the HERV-K core antigen was detected in retinal pigmented epithelium by an immunofluorescence analysis. Although malignant melanoma lines MeWo, G361, and SK-MEL-28 showed enhanced HERV-K transcription compared with normal melanocytes, the level of MITF-M messenger RNA persisted from normal to transformed melanocytes. Thus, MITF-M may be a prerequisite for the pigmented cell lineage-specific function of HERV-K LTR, leading to the high-level expression in malignant melanomas.

Induction of ΔNp63 by the newly identified keratinocyte-specific transforming growth factor β Signaling Pathway with Smad2 and IκB Kinase α in squamous cell carcinoma

The expression of p63 (TP63/p51) occurs in the basal cells of stratified epithelia and is strongly enhanced at the early stages of squamous cell carcinomas (SCCs) of the head and neck, skin, cervix, and others. We analyzed a promoter/enhancer region (2kΔN) that drives the predominant expression of ΔNp63 for sensitivity to Smad signaling pathways. Reporter assays in HepG2 cells showed a moderate activation of 2kΔN by Smad2 and IκB kinase α (IKKα), partners of the newly identified keratinocyte-specific transforming growth factor β (TGF-β) signaling, but not by other Smad molecules. In A431 cells, 2kΔN was activated by Smad2 and IKKα, for which a Smad binding element (SMD2) at -204 was essential. Binding of Smad2 to the chromosomal SMD2 site was detectable. The association of Smad2 with IKKα was evident in the nucleus of A431, accounting for the enhancement of ΔNp63 expression by TGF-β. Moreover, both ΔNp63 and IKKα were necessary to maintain the noninvasive phenotype of this cell line. FaDu, an invasive, Smad4-deficient SCC, also allowed 2kΔN transactivation by transfected Smad2 in the presence of endogenous IKKα. Reflecting the lack of chromosomal SMD2-Smad2 association and the absence of nuclear IKKα, however, endogenous ΔNp63 was not controlled by TGF-β or IKKα in FaDu. SCC tissue arrays showed nuclear accumulation of IKKα and p63 intensification in well-differentiated noninvasive lesions. This study indicates that p63 is a target gene of the proposed keratinocyte-specific TGF-β signal pathway for suppression of the malignant conversion of SCC.

The integrin alpha(v)beta(3-5) ligand MFG-E8 is a p63/p73 target gene in triple-negative breast cancers but exhibits suppressive functions in ER(+) and erbB2(+) breast cancers

The progression from preinvasive lesion to invasive carcinoma is a critical step contributing to breast cancer lethality. We identified downregulation of milk fat globule-EGF factor 8 (MFG-E8) as a contributor to breast cancer progression using microarray analysis of laser capture microdissected (LCM) tissues. We first identified MFG-E8 downregulation in invasive lesions in transgenic mammary tumor models, which were confirmed in LCM-isolated human invasive ductal carcinomas compared with patient-matched normal tissues. In situ analyses of MFG-E8 expression in estrogen receptor (ER) positive cases confirmed its downregulation during breast cancer progression and small inhibitory MFG-E8 RNAs accelerated ER(+) breast cancer cell proliferation. MFG-E8 also decreased in erbB2(+) human cancers and erbB2 transgenic mice lacking MFG-E8 showed accelerated tumor formation. In contrast, MFG-E8 expression was present at high levels in triple-negative (ER(-), PgR(-), erbB2(-)) breast cancers, cell lines, and patient sera. Knockdown, chromatin immunoprecipitation, and reporter assays all showed that p63 regulates MFG-E8 expression, and MFG-E8 knockdowns sensitized triple-negative breast cancers to cisplatin treatment. Taken together, our results show that MFG-E8 is expressed in triple-negative breast cancers as a target gene of the p63 pathway, but may serve a suppressive function in ER(+) and erbB2(+) breast cancers. Its potential use as a serum biomarker that contributes to the pathogenesis of triple-negative breast cancers urges continued evaluation of its differential functions.

The cell line secretome, a suitable tool for investigating proteins released in vivo by tumors: application to the study of p53-modulated proteins secreted in lung cancer cells

Malignant processes such as metastasis, invasion, or angiogenesis are tightly dependent on the composition of the extracellular medium, which is itself affected by the release of proteins by the tumor cells. p53, a major tumor suppressor protein very frequently mutated and/or inactivated in cancer cells, is known to modulate the release of proteins by the tumor cells; however, while p53-modulated intracellular proteins have been extensively studied, little is known concerning their extracellular counterparts. Here, we characterized the p53-dependent secretome of a lung tumor model in vitro (H358 human nonsmall cell lung adenocarcinoma cell line with a homozygous deletion of p53) and demonstrate that the modulation of exported proteins can also be detected in vivo in the plasma of tumor-bearing mice. We used a clone of H358, stably transfected with a tetracycline-inducible wild-type p53-expressing vector. With the use of iTRAQ labeling and LC-MALDI-MS/MS analysis, we identified 909 proteins released in vitro by the cells, among which 91 are p53-modulated. Three proteins (GDF-15, FGF-19, and VEGF) were also investigated in H358/TetOn/p53 xenograft mice. The ELISA dosage on total tumor protein extracts confirmed the influence of p53 on the release of these proteins in vivo. Moreover, the GDF-15 concentration was measured in the plasma and its p53-dependent modulation was confirmed. To our knowledge, this is the first report establishing that the in vitro cell line secretome is reliable and reflects the extracellular release of proteins from tumor cells in vivo and could be used to identify putative tumor markers.

Milk fat globule EGF-8 promotes melanoma progression through coordinated Akt and twist signaling in the tumor microenvironment

The pathogenesis of malignant melanoma involves the interplay of tumor cells with normal host elements, but the underlying mechanisms are incompletely understood. Here, we show that milk fat globule EGF-8 (MFG-E8), a secreted protein expressed at high levels in the vertical growth phase of melanoma, promotes disease progression through coordinated alpha(v)beta(3) integrin signaling in the tumor microenvironment. In a murine model of melanoma, MFG-E8 enhanced tumorigenicity and metastatic capacity through Akt-dependent and Twist-dependent pathways. MFG-E8 augmented melanoma cell resistance to apoptosis, triggered an epithelial-to-mesenchymal transition (EMT), and stimulated invasion and immune suppression. In human melanoma cells, MFG-E8 knockdown attenuated Akt and Twist signaling and thereby compromised tumor cell survival, EMT, and invasive ability. MFG-E8-deficient human melanoma cells also showed increased sensitivity to small molecule inhibitors of insulin-like growth factor I receptor and c-Met. Together, these findings delineate pleiotropic roles for MFG-E8 in the tumor microenvironment and raise the possibility that systemic MFG-E8 blockade might prove therapeutic for melanoma patients.

Milk fat globule EGF factor 8 in the serum of human patients of systemic lupus erythematosus

Mouse milk fat globule epidermal growth factor 8 (MFG-E8), which is secreted by a subset of activated macrophages, binds to apoptotic cells by recognizing phosphatidylserine and promotes their engulfment. Many apoptotic cells are left unengulfed in the germinal centers of the spleen in MFG-E8(-/-) mice, and these mice develop an autoimmune disease resembling human systemic lupus erythematosus (hSLE). Here, we report that hMFG-E8 bound to phosphatidylserine and an integrin alpha(v)beta(3) complex. Increasing concentrations of MFG-E8 generated a bell-shaped response curve for the efficiency of phagocytosis. That is, in NIH3T3 and MFG-E8(-/-) thioglycollate-elicited peritoneal macrophages that do not express MFG-E8, hMFG-E8 enhanced engulfment at low concentrations but inhibited it at high concentrations. On the other hand, hMFG-E8 dose-dependently inhibited the engulfment of apoptotic cells by MFG-E8(+/+) thioglycollate-elicited peritoneal macrophages, indicating that an excess of MFG-E8 has an inverse effect on the engulfment of apoptotic cells. To investigate the role of MFG-E8 in human disease, we generated two mAb against MFG-E8 and screened human blood samples for MFG-E8 using an ELISA. We found that some childhood-onset and adult SLE patients carried a significant level of MFG-E8 in their blood samples. These results suggested that the aberrant expression of MFG-E8 is involved in the pathoetiology of some cases of hSLE.