Chromatin conformational changes at human satellite II contribute to the senescence phenotype in the tumor microenvironment

Cellular senescence and senescence-associated secretory phenotype (SASP) in stromal cells within the tumor microenvironment promote cancer progression. Although cellular senescence has been shown to induce changes in the higher-order chromatin structure and abnormal transcription of repetitive elements in the genome, the functional significance of these changes is unclear. In this study, we examined the human satellite II (hSATII) loci in the pericentromere to understand these changes and their functional significance. Our results indicated that the hSATII loci decompact during senescence induction, resulting in new DNA-DNA interactions in distinct genomic regions, which we refer to as DRISR (Distinctive Regions Interacted with Satellite II in Replicative senescent Fibroblasts). Interestingly, decompaction occurs before the expression of hSATII RNA. The DRISR with altered chromatin accessibility was enriched for motifs associated with cellular senescence and inflammatory SASP genes. Moreover, DNA-fluorescence in situ hybridization analysis of the breast cancer tissues revealed hSATII decompaction in cancer and stromal cells. Furthermore, we reanalyzed the single-cell assay for transposase-accessible chromatin with sequencing data and found increased SASP-related gene expression in fibroblasts exhibiting hSATII decompaction in breast cancer tissues. These findings suggest that changes in the higher-order chromatin structure of the pericentromeric repetitive sequences during cellular senescence might directly contribute to the cellular senescence phenotype and cancer progression via inflammatory gene expression.

Identification of Novel Senescent Markers in Small Extracellular Vesicles

Senescent cells exhibit several typical features, including the senescence-associated secretory phenotype (SASP), promoting the secretion of various inflammatory proteins and small extracellular vesicles (EVs). SASP factors cause chronic inflammation, leading to age-related diseases. Recently, therapeutic strategies targeting senescent cells, known as senolytics, have gained attention; however, noninvasive methods to detect senescent cells in living organisms have not been established. Therefore, the goal of this study was to identify novel senescent markers using small EVs (sEVs). sEVs were isolated from young and senescent fibroblasts using three different methods, including size-exclusion chromatography, affinity column for phosphatidylserine, and immunoprecipitation using antibodies against tetraspanin proteins, followed by mass spectrometry. Principal component analysis revealed that the protein composition of sEVs released from senescent cells was significantly different from that of young cells. Importantly, we identified ATP6V0D1 and RTN4 as novel markers that are frequently upregulated in sEVs from senescent and progeria cells derived from patients with Werner syndrome. Furthermore, these two proteins were significantly enriched in sEVs from the serum of aged mice. This study supports the potential use of senescent markers from sEVs to detect the presence of senescent cells in vivo.

0590 Reliability of Simple Sleep Evaluation Device at Split-Night Polysomnography

Introduction

Watch-PAT is a sleep evaluation device that measures the peripheral blood volume continuously with a probe attached to a fingertip and does not use an electroencephalogram or a nasal cannula. There has been no report on the usefulness of watch-PAT to determine the apnea diagnosis and continuous positive airway pressure (CPAP) use effects in split-night sleep study.

Methods

The consent of the study was obtained. Watch-PAT was simultaneously worn on a patient admitted for split-night polysomnography. The apnea-hypopnea index (AHI) obtained from PSG and the pAHI gained from the watch-PAT were measured when not using CPAP and when using CPAP respectively. And also we examined whether the reduction rates of AHI and pAHI could be correlated.

Results

38 subjects (32 men, age 55 ± 13 years old). BMI 28.3 ± 5.7 kg / m2. When CPAP was not used, AHI was 57.2 ± 23.3 / h and pAHI was 50.8 ± 20.3 / h (r = 0.93, p < 0.0001), when CPAP was used, AHI was 5.2 ± 4.5 /h and pAHI was 6.2 ± 4.5 h (r = 0.82, p < 0.0001), AHI reduction rate was 90.4 ± 8.0% and pAHI reduction rate was 85.4 ± 14.6% (r = 0.76, p < 0.0001).

Conclusion

It was suggested that Watch-PAT had a good correlation with AHI at split night-sleep study.

Support

None

Ablation of the p16(INK4a) tumour suppressor reverses ageing phenotypes of klotho mice

The p16^INK4a tumour suppressor has an established role in the implementation of cellular senescence in stem/progenitor cells, which is thought to contribute to organismal ageing. However, since p16^INK4a knockout mice die prematurely from cancer, whether p16^INK4a reduces longevity remains unclear. Here we show that, in mutant mice homozygous for a hypomorphic allele of the α-klotho ageing-suppressor gene (kl^kl/kl), accelerated ageing phenotypes are rescued by p16^INK4a ablation. Surprisingly, this is due to the restoration of α-klotho expression in kl^kl/kl mice and does not occur when p16^INK4a is ablated in α-klotho knockout mice (kl^−/−), suggesting that p16^INK4a is an upstream regulator of α-klotho expression. Indeed, p16^INK4a represses α-klotho promoter activity by blocking the functions of E2Fs. These results, together with the observation that the expression levels of p16^INK4a are inversely correlated with those of α-klotho throughout ageing, indicate that p16^INK4a plays a previously unrecognized role in downregulating α-klotho expression during ageing.

The protein p16^INK4a promotes senescence in tissue stem cells and thereby contributes to organismal ageing. Here the authors reveal that p16^INK4a also downregulates expression of a-klotho, thereby revealing an additional ageing-promoting function of 16^INK4a that is independent from its role in senescence.

Crosstalk between the Rb pathway and AKT signaling forms a quiescence-senescence switch

Cell-cycle arrest in quiescence and senescence is largely orchestrated by the retinoblastoma (Rb) tumor-suppressor pathway, but the mechanisms underlying the quiescence-senescence switch remain unclear. Here, we show that the crosstalk between the Rb-AKT-signaling pathways forms this switch by controlling the overlapping functions of FoxO3a and FoxM1 transcription factors in cultured fibroblasts. In the absence of mitogenic signals, although FoxM1 expression is repressed by the Rb pathway, FoxO3a prevents reactive oxygen species (ROS) production by maintaining SOD2 expression, leading to quiescence. However, if the Rb pathway is activated in the presence of mitogenic signals, FoxO3a is also inactivated by AKT, thus reducing SOD2 expression and consequently allowing ROS production. This situation elicits senescence through irreparable DNA damage. We demonstrate that this pathway operates in mouse liver, indicating that this machinery may contribute more broadly to tissue homeostasis in vivo.

Bioluminescent system for dynamic imaging of cell and animal behavior

The current utility of bioluminescence imaging is constrained by a low photon yield that limits temporal sensitivity. Here, we describe an imaging method that uses a chemiluminescent/fluorescent protein, ffLuc-cp156, which consists of a yellow variant of Aequorea GFP and firefly luciferase. We report an improvement in photon yield by over three orders of magnitude over current bioluminescent systems. We imaged cellular movement at high resolution including neuronal growth cones and microglial cell protrusions. Transgenic ffLuc-cp156 mice enabled video-rate bioluminescence imaging of freely moving animals, which may provide a reliable assay for drug distribution in behaving animals for pre-clinical studies.

Abstract 2655: Visualization of G1 arrest of cell cycle induced by inhibition of PI-3 kinase in cancer cells: in vitro evaluations

The phosphoinositide 3-kinase (PI3K) pathway is frequently activated in cancer, and is considered as a promising therapeutic target of cancer therapy. Since PI3K pathway mediates growth- and anti-apoptotic signals, inhibition of PI3K is expected to induce apoptosis and/or growth arrest in cancer cells. We previously developed Fluorescent Ubiquitination-based Cell Cycle Indicator (Fucci) system to enable real-time visualization of cell cycle progression in live cells. Taking advantage of Fucci system, we examined cell cycle progression after treatment of various PI3K inhibitors by using a time-lapse fluorescent microscope. As a result, we could visualize the induction of G1 arrest of cell cycle in breast cancer MCF-7 cells within 24 h after treatment with ZSTK474, and the G1 arrest lasted at least 48 h. Similar results were obtained after treatment with other PI3K inhibitors such as NVP-BEZ235 and GDC-0941. These results clearly indicate that PI3K inhibitors exert antitumor activity via a cytostatic mechanism by inducing G1 arrest of cell cycle.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr 2655. doi:10.1158/1538-7445.AM2011-2655

Abstract 2493: Inhibition of phosphoinositide 3-kinase suppressed growth of cancer cells with PIK3CA mutations or loss of PTEN expression via G0/G1 arrest of cell cycle but not apoptosis

Background: The phosphoinositide 3-kinase (PI3K) pathway is frequently activated in cancer by gain-of-function mutation of PIK3CA and loss of PTEN expression, and mediates growth- and anti-apoptotic signals. Therefore, PI3K is considered as a promising therapeutic target to inhibit growth and to induce apoptosis in such cancers. We previously developed a novel PI3K-specific inhibitor ZSTK474 with antitumor efficacy (Yaguchi et al, J. Natl. Cancer Inst. 98: 545-56, 2006; Kong and Yamori, Curr. Med. Chem. 16: 2839-54, 2009). In this study, we have examined the cellular mechanism by which ZSTK474 exerts its antitumor efficacy in human cancer cells with or without PIK3CA/PTEN aberrations.

Methods: We examined the antitumor effect of ZSTK474 on various human cancer cell lines with or without PIK3CA/PTEN aberration in vitro and in vivo. Protein expression and apoptosis in ZSTK474-treated and untreated tumor sections were analyzed by immunohistochemistry and TUNEL assay, respectively. Analysis of cell cycle in vitro was determined by flow cytometry and by Fucci (Fluorescent Ubiquitination-based Cell Cycle Indicator) system introduced to cancer cells. Induction of apoptosis in vitro was estimated by caspase activation using a substrate cleavage assay and by detection of subdiploid cells using flow cytometry.

Results: In vivo, ZSTK474 effectively inhibited the growth of human tumor xenograft derived from a PTEN-null prostate cancer cell line PC3. In parallel, ZSTK474 treatment suppressed the expression of phospho-Akt, suggesting effective PI3K inhibition, and also suppressed the expression of nuclear cyclin D1 and Ki67, both of which are hallmarks of proliferation. However, ZSTK474 treatment did not increase TUNEL-positive apoptotic cells. Similar result was obtained in another PTEN-negative cell line KM-12 and three PIK3CA-mutated cell lines HCT-15 (E545K), MKN1 (E545K) and SK-OV3 (H1047R). In vitro, ZSTK474 induced marked G0/G1 arrest accompanied by a decrease of nuclear cyclin D1, induction of p27kip1 and p15ink4b, and hypophosphorylation of pRB in PC-3 cells. However, ZSTK474 did not increase the subdiploid cells or activate caspase, both of which are hallmarks of apoptosis. Similar result was obtained other cell lines with or without PIK3CA /PTEN aberrations.

Conclusion: These results clearly indicated that ZSTK474 did not induce apoptosis but rather induced strong G0/G1 arrest in cancer cells with or without PIK3CA/PTEN aberrations, which might cause its therapeutic efficacy.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 2493.

Estrogen inhibits transforming growth factor beta signaling by promoting Smad2/3 degradation

Estrogen is a growth factor that stimulates cell proliferation. The effects of estrogen are mediated through the estrogen receptors, ERalpha and ERbeta, which function as ligand-induced transcription factors and belong to the nuclear receptor superfamily. On the other hand, TGF-beta acts as a cell growth inhibitor, and its signaling is transduced by Smads. Although a number of studies have been made on the cross-talk between estrogen/ERalpha and TGF-beta/Smad signaling, whose molecular mechanisms remain to be determined. Here, we show that ERalpha inhibits TGF-beta signaling by decreasing Smad protein levels. ERalpha-mediated reductions in Smad levels did not require the DNA binding ability of ERalpha, implying that ERalpha opposes the effects of TGF-beta via a novel non-genomic mechanism. Our analysis revealed that ERalpha formed a protein complex with Smad and the ubiquitin ligase Smurf, and enhanced Smad ubiquitination and subsequent degradation in an estrogen-dependent manner. Our observations provide new insight into the molecular mechanisms governing the non-genomic functions of ERalpha.

SKI and MEL1 cooperate to inhibit transforming growth factor-beta signal in gastric cancer cells

Chromosomal amplification occurs frequently in solid tumors and is associated with poor prognosis. Several reports demonstrated the cooperative effects of oncogenic factors in the same amplicon during cancer development. However, the functional correlation between the factors remains unclear. Transforming growth factor (TGF)-beta signaling plays important roles in cytostasis and normal epithelium differentiation, and alterations in TGF-beta signaling have been identified in many malignancies. Here, we demonstrated that transcriptional co-repressors of TGF-beta signaling, SKI and MDS1/EVI1-like gene 1 (MEL1), were aberrantly expressed in MKN28 gastric cancer cells by chromosomal co-amplification of 1p36.32. SKI and MEL1 knockdown synergistically restored TGF-beta responsiveness in MKN28 cells and reduced tumor growth in vivo. MEL1 interacted with SKI and inhibited TGF-beta signaling by stabilizing the inactive Smad3-SKI complex on the promoter of TGF-beta target genes. These findings reveal a novel mechanism where distinct transcriptional co-repressors are co-amplified and functionally interact, and provide molecular targets for gastric cancer treatment.

Bone morphogenetic protein signaling enhances invasion and bone metastasis of breast cancer cells through Smad pathway

Transforming growth factor (TGF)-beta is known to promote tumor invasion and metastasis. Although bone morphogenetic proteins (BMPs), members of the TGF-beta family, are expressed in a variety of human carcinoma cell lines, their roles in tumor progression have not been fully clarified. In this study, we sought to determine the roles of BMPs in the progression of breast cancer bone metastasis using human breast cancer samples and a mouse xenograft model. Immunohistochemical analysis of samples from breast cancer patients as well as a mouse xenograft model of MDA-231-D, highly metastatic human breast cancer cells, revealed phospho-Smad2 and phospho-Smad1/5/8 staining in the nuclei of cancer cells in primary tumor and/or bone metastasis. Using a functional in vivo bioluminescence imaging system, we showed that TGF-beta- and BMP-induced transcriptional pathways are active in bone metastatic lesions in vivo. In addition, both TGF-beta3 and BMP-2 promoted the motility and invasiveness of the MDA-231-D cells in vitro. Moreover, expression of dominant-negative receptors for TGF-beta and/or BMPs in the MDA-231-D cells inhibited invasiveness in vitro and bone metastasis in the xenograft model. These results suggest that BMPs as well as TGF-beta promote invasion and bone metastasis of breast cancer.

[TGF-beta signaling during bone metastasis of breast cancer and in-vivo imaging]

Transforming growth factor (TGF)-beta is a potent growth inhibitor of various types of cells, whereas it stimulates deposition of extracellular matrix proteins and induction of epithelial-to-mesenchymal transition (EMT). TGF-beta thus plays two distinct and opposing roles in cancer progression. In the present study, we have developed a useful method that enables monitoring of tumor and its TGF-beta signaling within the same animal using in vivo bioluminescent imaging.

Transforming growth factor-beta promotes survival of mammary carcinoma cells through induction of antiapoptotic transcription factor DEC1

Transforming growth factor-beta (TGF-beta) signaling facilitates tumor growth and metastasis in advanced cancer. In the present study, we identified differentially expressed in chondrocytes 1 (DEC1, also known as SHARP2 and Stra13) as a downstream target of TGF-beta signaling, which promotes the survival of breast cancer cells. In the mouse mammary carcinoma cell lines JygMC(A) and 4T1, the TGF-beta type I receptor kinase inhibitors A-44-03 and SB431542 induced apoptosis of cells under serum-free conditions. Oligonucleotide microarray and real-time reverse transcription-PCR analyses revealed that TGF-beta induced DEC1 in these cells, and the increase of DEC1 was suppressed by the TGF-beta type I receptor kinase inhibitors as well as by expression of dominant-negative TGF-beta type II receptor. Overexpression of DEC1 prevented the apoptosis of JygMC(A) cells induced by A-44-03, and knockdown of endogenous DEC1 abrogated TGF-beta-promoted cell survival. Moreover, a dominant-negative mutant of DEC1 prevented lung and liver metastasis of JygMC(A) cells in vivo. Our observations thus provide new insights into the molecular mechanisms governing TGF-beta-mediated cell survival and metastasis of cancer.

Ki26894, a novel transforming growth factor-beta type I receptor kinase inhibitor, inhibits in vitro invasion and in vivo bone metastasis of a human breast cancer cell line

Transforming growth factor (TGF)-beta signaling has been shown to promote tumor growth and metastasis in advanced cancer. Use of inhibitors of TGF-beta signaling may thus be a novel strategy for treatment of patients with such cancers. In this study, we investigated the effects of a novel TGF-beta type I receptor (TbetaR-I) kinase inhibitor, Ki26894, on bone metastasis of a highly bone-metastatic variant of human breast cancer MDA-MB-231 cells, termed MDA-MB-231-5a-D (MDA-231-D). Ki26894 blocked TGF-beta signaling in MDA-231-D cells, as detected by suppression of phosphorylation of Smad2 and inhibition of TGF-beta-responsive reporter activity. Moreover, Ki26894 decreased the motility and the invasion of MDA-231-D cells induced by TGF-beta in vitro. Ki26894 also suppressed transcription of plasminogen activator inhibitor-1 (PAI-1), parathyroid hormone-related protein (PTHrP), and interleukin-11 (IL-11) mRNA of MDA-231-D cells, which were stimulated by TGF-beta. X-ray radiography revealed that systemic Ki26894 treatment initiated 1 day before the inoculation of MDA-231-D cells into the left ventricle of BALB/cnu/nu female mice resulted in decreased bone metastasis of breast cancer cells. Moreover, Ki26894 prolonged the survival of mice inoculated with MDA-231-D cells compared to vehicle-treated mice. These findings suggest that TbetaR-I kinase inhibitors such as Ki26894 may be useful for blocking the progression of advanced cancers.

The ALK-5 inhibitor A-83-01 inhibits Smad signaling and epithelial-to-mesenchymal transition by transforming growth factor-beta

Transforming growth factor (TGF)-beta signaling facilitates tumor growth and metastasis in advanced cancer. Use of inhibitors of TGF-beta signaling may thus be a novel strategy for the treatment of patients with such cancer. In this study, we synthesized and characterized a small molecule inhibitor, A-83-01, which is structurally similar to previously reported ALK-5 inhibitors developed by Sawyer et al. (2003) and blocks signaling of type I serine/threonine kinase receptors for cytokines of the TGF-beta superfamily (known as activin receptor-like kinases; ALKs). Using a TGF-beta-responsive reporter construct in mammalian cells, we found that A-83-01 inhibited the transcriptional activity induced by TGF-beta type I receptor ALK-5 and that by activin type IB receptor ALK-4 and nodal type I receptor ALK-7, the kinase domains of which are structurally highly related to those of ALK-5. A-83-01 was found to be more potent in the inhibition of ALK5 than a previously described ALK-5 inhibitor, SB-431542, and also to prevent phosphorylation of Smad2/3 and the growth inhibition induced by TGF-beta. In contrast, A-83-01 had little or no effect on bone morphogenetic protein type I receptors, p38 mitogen-activated protein kinase, or extracellular regulated kinase. Consistent with these findings, A-83-01 inhibited the epithelial-to-mesenchymal transition induced by TGF-beta, suggesting that A-83-01 and related molecules may be useful for preventing the progression of advanced cancers.

Arkadia amplifies TGF-beta superfamily signalling through degradation of Smad7

Arkadia was originally identified as a protein that enhances signalling activity of Nodal and induces mammalian nodes during early embryogenesis; however, the mechanisms by which Arkadia affects transforming growth factor-beta (TGF-beta) superfamily signalling have not been determined. Here we show that Arkadia is widely expressed in mammalian tissues, and that it enhances both TGF-beta and bone morphogenetic protein (BMP) signalling. Arkadia physically interacts with inhibitory Smad, Smad7, and induces its poly-ubiquitination and degradation. In contrast to Smurf1, which interacts with TGF-beta receptor complexes through Smad7 and degrades them, Arkadia fails to associate with TGF-beta receptors. In contrast to Smad7, expression of Arkadia is down-regulated by TGF-beta. Silencing of the Arkadia gene resulted in repression of transcriptional activities induced by TGF-beta and BMP, and accumulation of the Smad7 protein. Arkadia may thus play an important role as an amplifier of TGF-beta superfamily signalling under both physiological and pathological conditions.

SB-431542 and Gleevec inhibit transforming growth factor-beta-induced proliferation of human osteosarcoma cells

Transforming growth factor-beta (TGF-beta) has growth-stimulating effects on mesenchymal cells and several tumor cell lines. The signaling pathway for this effect is, however, not well understood. We examined how TGF-beta stimulates proliferation of MG63 human osteosarcoma cells. Two distinct type I receptors for TGF-beta, ALK-1 and ALK-5, were expressed and functional in MG63 cells. Of these two receptors, ALK-5 appears to be responsible for the growth stimulation because expression of constitutively active ALK-5, but not ALK-1, stimulated proliferation of MG63 cells. SB-431542 (0.3 microM), a novel inhibitor of ALK4/5/7 kinase, suppressed TGF-beta-induced growth stimulation. DNA microarray analysis as well as quantitative real-time PCR analysis of RNAs from TGF-beta-treated cells demonstrated that several growth factors, including platelet-derived growth factor AA, were induced in response to TGF-beta in MG63 cells. Gleevec (1 microM) as well as AG1296 (5 microM) inhibited TGF-beta-induced growth stimulation of MG63 cells, suggesting that platelet-derived growth factor AA was mainly responsible for the growth-stimulatory effect of TGF-beta. We also examined the mechanisms of perturbation of growth-suppressing signaling in MG63 cells. We found that expression of c-Myc, which is down-regulated by TGF-beta in many other cells, was up-regulated in MG63 cells, suggesting that up-regulation of c-Myc expression may be the mechanism canceling growth-suppressing signaling of TGF-beta in MG63 cells.

The N domain of Smad7 is essential for specific inhibition of transforming growth factor-beta signaling

Inhibitory Smads (I-Smads) repress signaling by cytokines of the transforming growth factor-beta (TGF-beta) superfamily. I-Smads have conserved carboxy-terminal Mad homology 2 (MH2) domains, whereas the amino acid sequences of their amino-terminal regions (N domains) are highly divergent from those of other Smads. Of the two different I-Smads in mammals, Smad7 inhibited signaling by both TGF-beta and bone morphogenetic proteins (BMPs), whereas Smad6 was less effective in inhibiting TGF-beta signaling. Analyses using deletion mutants and chimeras of Smad6 and Smad7 revealed that the MH2 domains were responsible for the inhibition of both TGF-beta and BMP signaling by I-Smads, but the isolated MH2 domains of Smad6 and Smad7 were less potent than the full-length Smad7 in inhibiting TGF-beta signaling. The N domains of I-Smads determined the subcellular localization of these molecules. Chimeras containing the N domain of Smad7 interacted with the TGF-beta type I receptor (TbetaR-I) more efficiently, and were more potent in repressing TGF-beta signaling, than those containing the N domain of Smad6. The isolated N domain of Smad7 physically interacted with the MH2 domain of Smad7, and enhanced the inhibitory activity of the latter through facilitating interaction with TGF-beta receptors. The N domain of Smad7 thus plays an important role in the specific inhibition of TGF-beta signaling.

Intracellular signaling of the TGF-beta superfamily by Smad proteins

TGF-beta is a potent inhibitor of cell growth, and accumulating evidence suggests that perturbation of the TGF-beta signaling pathway leads to tumorigenesis. Smads are recently identified proteins that mediate intracellular signaling of the TGF-beta superfamily. Smads 2 and 3 are phosphorylated by the TGF-beta type I receptor. Smad4 was originally identified as a candidate tumor suppressor gene in pancreatic cancers. Smads 2 and 3 form complexes with Smad4 upon TGF-beta stimulation. The heteromeric Smad complexes translocate into the nucleus, where they activate expression of target genes. Our recent study demonstrated that Smads exist as monomers in the absence of TGF-beta. Smads 2 and 3 form homo- as well as hetero-oligomers with Smad4 upon ligand stimulation. Both homo-oligomers and hetero-oligomers directly bind to DNA, suggesting that the signaling pathway of Smads may be multiplex. Smads 2 and 3 associate with transcriptional coactivators such as p300 in a ligand-dependent manner, p300 enhances transactivation by TGF-beta, suggesting that coactivators link Smads to the basal transcriptional machinery. A missense mutation of Smad2 identified in colorectal and lung cancers was introduced to Smad3. The mutant, Smad3(DE), blocked the activation of wild-type Smad2 and Smad3. Thus, the missense mutation not only disrupts the function of the wild-type Smad but also creates a dominant-negative Smad, which could actively contribute to oncogenesis.

Effects of transforming growth factor beta on corneal epithelial and stromal cell function in a rat wound healing model after excimer laser keratectomy

BACKGROUND

Transforming growth factor beta (TGF-beta) regulates extracellular matrix deposition, cell proliferation, and migration, and is expressed in cornea. TGF-beta is thought to be involved in the corneal wound healing process.

METHODS

The central corneal area (3 mm in diameter) of Lewis rats was ablated using PTK mode excimer laser and the wound healing process was observed at 12 and 24 h and 2, 5, 10, and 30 days after treatment. The expression of TGF-beta 1, -beta 2 and -beta 3, TGF-beta type I and type II receptors, alpha 3, alpha 5, beta 4 integrin subunits, laminin and fibronectin was studied immunohistochemically. Antibody neutralizing TGF-beta 1, -beta 2 and -beta 3 was administered intraperitoneally, 50 micrograms daily, for 5 days after the laser treatment to investigate the effects of TGF-beta function blockade.

RESULTS

At the leading edge of the regenerating epithelium, no TGF-beta type I and type II receptors and beta 4 integrin subunits were expressed after 24 h. Regenerating epithelium covered the ablated area after 2 days. An abnormal fibrotic layer was formed in the subepithelial area. This layer contained round-shaped cells in the stroma in the early stage (2-5 days after laser ablation) and spindle-shaped fibroblast-like keratocytes after 10 days. Laminin and fibronectin expression increased in the fibrotic layer. The increased stromal cells expressed TGF-beta isoforms and TGF-beta receptors. Neutralizing TGF-beta inhibited the stromal cell increase in the laser ablated area after 5 days.

CONCLUSION

TGF-beta may be involved in epithelial cell migration and stromal cell reaction during the corneal wound healing process after excimer laser ablation in rat models.

Smad proteins exist as monomers in vivo and undergo homo- and hetero-oligomerization upon activation by serine/threonine kinase receptors

Smad proteins are signal transducers for the members of the transforming growth factor-beta (TGF-beta) superfamily. Here we show that, in the absence TGF-beta stimulation, Smads exist as monomers in vivo. Smad2 and Smad3 form homo-oligomers upon phosphorylation by the constitutively active TGF-beta type I receptor, and this oligomerization does not require Smad4. Major portions of Smad4, Smad6 and Smad7 are also present as monomers in vivo. Analysis using a cross-linking reagent suggested that the Smad2 oligomer induced by receptor activation is a trimer. Studies by gel chromatography demonstrated that the Smad2-Smad4 heteromer is not larger than the Smad2 homomer. Moreover, overexpression of Smad4 prevented Smad2 from forming a homo-oligomer. These findings suggest that Smad2 may form a homotrimer, or heterotrimers with Smad4, which are probably composed of two and one, or one and two molecules of Smad2 and Smad4, respectively, depending on the amount of each protein. Gel-mobility shift assay revealed that the Smad3 homomer and Smad3-Smad4 heteromer constitute DNA-binding complexes. Transition of the Smad proteins from monomers to oligomers is thus a critical event in the signal transduction of the TGF-beta superfamily members.

Characterization of the MADH2/Smad2 gene, a human Mad homolog responsible for the transforming growth factor-beta and activin signal transduction pathway

The transforming growth factor beta (TGF-beta) superfamily is a family of multifunctional cytokines that transduce signals via serine/threonine kinase receptors. Recent studies revealed that Mothers against dpp (Mad) in Drosophila and its homologs play important roles in the intracellular signal transduction of the serine/threonine kinase receptors. In mammals, one of the Mad homologs, MADH2 (also termed Smad2), was reported to be a mediator of TGF-beta and activin signaling and was found mutated in some of the colon and lung cancer cases. We describe here the genomic organization of the human MADH2 gene. The gene is composed of 12 exons; 2 exons 1, i.e., exon 1a and 1b, are used separately or in conjunction to form exon 1a-exon 1b-exon 2 alternatively spliced mRNA. The 2 exons 1 are closely located, and the MADH2 mRNAs are transcribed from two promoters in one CpG island. The promoter activity in the 5' upstream sequence was confirmed by the luciferase assay. The 3' end of the mRNA is heterogenous, and we found several polyadenylation signals. Northern blot analysis revealed high expression of the MADH2 mRNA, e.g., in skeletal muscle, heart, and placenta. RT-PCR assay using primers in exons 2 and 4 and direct nucleotide sequencing proved that exon 3 is spliced out in about 10% of MADH2 in human placenta. These data will be valuable for studying the MADH2 function in both normal cells and cancer cells.

Growth/differentiation factor-5 induces angiogenesis in vivo

Bone morphogenetic proteins (BMPs) are multifunctional cytokines, which induce bone and cartilage formation and exert various other effects on many tissues. Since angiogenesis is involved in the bone formation process, certain members in the BMP family may induce angiogenesis. We examined the in vivo angiogenic activity of BMP family members, i.e., growth/differentiation factor (GDF)-5 and BMP-2. GDF-5 induced angiogenesis in both chick chorioallantoic membrane and rabbit cornea assays. In contrast, BMP-2 did not induce angiogenesis. In order to elucidate the mechanism of angiogenesis, we examined the effects of GDF-5 on cultured bovine aortic endothelial cells (BECs). GDF-5 induced plasminogen activator activity and accelerated the migration of BECs in a chemotactic fashion, which may contribute to the process of angiogenesis in vivo. These results suggest that GDF-5 is one of the molecules which induce angiogenesis in the bone formation process.