TGFbeta signaling and cancer

Targeted next generation sequencing of parotid gland cancer uncovers genetic heterogeneity

Salivary gland cancer represents a heterogeneous group of malignant tumors. Due to their low incidence and the existence of multiple morphologically defined subtypes, these tumors are still poorly understood with regard to their molecular pathogenesis and therapeutically relevant genetic alterations.

Performing a systematic and comprehensive study covering 13 subtypes of salivary gland cancer, next generation sequencing was done on 84 tissue samples of parotid gland cancer using multiplex PCR for enrichment of cancer related gene loci covering hotspots of 46 cancer genes.

Mutations were identified in 22 different genes. The most frequent alterations affected TP53, followed by RAS genes, PIK3CA, SMAD4 and members of the ERB family. HRAS mutations accounted for more than 90% of RAS mutations, occurring especially in epithelial-myoepithelial carcinomas and salivary duct carcinomas. Additional mutations in PIK3CA also affected particularly epithelial-myoepithelial carcinomas and salivary duct carcinomas, occurring simultaneously with HRAS mutations in almost all cases, pointing to an unknown and therapeutically relevant molecular constellation. Interestingly, 14% of tumors revealed mutations in surface growth factor receptor genes including ALK, HER2, ERBB4, FGFR, cMET and RET, which might prove to be targetable by new therapeutic agents. 6% of tumors revealed mutations in SMAD4.

In summary, our data provide novel insight into the fundamental molecular heterogeneity of salivary gland cancer, relevant in terms of tumor classification and the establishment of targeted therapeutic concepts.

Analysis of the SMAD4 gene in asthma

Considering the importance of the TGF-β signaling pathway for normal lung function and especially its roles in inflammation and tissue remodeling, key features of asthma pathology, it can be assumed that these molecules may harbor mutations in asthmatics. The aim of this study was to analyze the SMAD4 gene in patients with asthma. Analysis has encompassed exons 10, 11, 12 and 13 encoding the carboxy-terminal (MH2) domain of the SMAD4 protein, where mutations most frequently occur. The study included 50 patients (20 men and 30 women) with asthma aged between 17 and 73 years (average age 45.2±15.6 years). Polymerase chain reaction (PCR) was used to amplify exons 10, 11, 12 and 13 of the SMAD4 gene and the obtained PCR products were subjected to direct DNA sequencing. No nucleotide changes were found in any of the analyzed exons in either of the subjects. Based on the results of this study, it seems that mutations in the carboxy-terminal (MH2) domain of the SMAD4 are not present in asthmatic patients. Future research should be directed at the analysis of the complete gene, including regulatory elements, in order to resolve the exact role of SMAD4 in asthma.

Menin and bone metabolism

Menin, a product of the MEN1 gene, is related to the ontogeny of several cancers such as MEN1 and sporadic endocrine tumors, although it is considered to be a tumor suppressor. Many proteins interact with menin, and it is involved in various biological functions in several tissues. Menin plays some physiological and pathological roles related to transforming growth factor-beta (TGF-β) signaling pathway in the parathyroid, and it is implicated in the tumorigenesis of parathyroid tumors. In bone, the bone phenotype was observed in some menin-deleted mice. Menin is considered to support BMP-2- and Runx2-induced differentiation of mesenchymal cells into osteoblasts by interacting with Smad1/5, Runx2, β-catenin and LEF-1, although it has different effects on osteoblasts at later differentiation stages through TGF-β-Smad3 and AP-1 pathways. Further research is expected to shed more light on the role of menin in bone.

Overexpression of transforming growth factor β1 in malignant prostate cells is partly caused by a runaway of TGF-β1 auto-induction mediated through a defective recruitment of protein phosphatase 2A by TGF-β type I receptor

OBJECTIVES

To elucidate the mechanism of transforming growth factor (TGF)-β1 overexpression in prostate cancer cells.

METHODS

Malignant (PC3, DU145) and benign (RWPE1, BPH1) prostate epithelial cells were used. Phosphatase activity was measured using a commercial kit. Recruitment of the regulatory subunit, Bα, of protein phosphatase 2A (PP2A-Bα) by TGF-β type I receptor (TβRI) was monitored by coimmunoprecipitation. Blockade of TGF-β1 signaling in cells was accomplished either by using TGF-β-neutralizing monoclonal antibody or by transduction of a dominant negative TGF-β type II receptor retroviral vector.

RESULTS

Basal levels of TGF-β1 in malignant cells were significantly higher than those in benign cells. Blockade of TGF-β signaling resulted in a significant decrease in TGF-β1 expression in malignant cells, but not in benign cells. Upon TGF-β1 treatment (10 ng/mL), TGF-β1 expression was increased in malignant cells, but not in benign cells. This differential TGF-β1 auto-induction between benign and malignant cells correlated with differential activation of extracellular signal-regulated kinase (ERK). Following TGF-β1 treatment, the activity of serine/threonine phosphatase and recruitment of PP2A-Bα by TβRI increased in benign cells, but not in malignant cells. Inhibition of PP2A in benign cells resulted in an increase in ERK activation and in TGF-β1 auto-induction after TGF-β1 (10 ng/mL) treatment.

CONCLUSIONS

These results suggest that TGF-β1 overexpression in malignant cells is caused, at least in part, by a runaway of TGF-β1 auto-induction through ERK activation because of a defective recruitment of PP2A-Bα by TβRI.

Dysregulation of Dkk-3 expression in benign and malignant prostatic tissue

BACKGROUND

The Dickkopf (Dkk) family comprises four members Dkk-1, -2, -3, and -4. Dkk-3, the most divergent family member, unlike the others does not modulate Wnt signaling. Dkk-3 is proposed to function as a secreted tumor suppressor since it is downregulated in a number of cancer cells and prostate cancer tissue and thus may be a promising candidate molecule for therapeutic interference.

METHODS

The in situ tissue localization of Dkk-3 protein in normal prostate (NP), benign prostatic hyperplasia (BPH), and prostate carcinoma (PCa) was investigated by immunohistochemistry (IHC)/immunofluorescence. In addition, biological function of Dkk-3 in terms of proliferation and viability was evaluated in primary prostate basal epithelial cells (PrEC), stromal cells (PrSC), and established human PCa cell lines by treatment with recombinant protein or by overexpression.

RESULTS

Stimulation with purified recombinant protein and overexpression of Dkk-3 did not significantly alter in vitro cell proliferation in any primary or tumor cell line evaluated. Dkk-3 was expressed in both the basal and secretory epithelium of NP. In BPH expression was restricted to defined basal cells and was absent in tumor cells of high grade PCa. In contrast to normal prostatic tissue, Dkk-3 was upregulated in subglandular blood vessels of BPH and in the reactive stroma of PCa tissue.

CONCLUSIONS

Our results indicate that Dkk-3 expression in the normal epithelium of the prostate is lost during benign and malignant transformation and differentiation processes. The loss of expression seems to be counterbalanced by upregulation of Dkk-3 expression in the blood vessels of the remodeled tissue.

TGFbeta/BMP inhibits the bone marrow transformation capability of Hoxa9 by repressing its DNA-binding ability

Homeobox (Hox) gene mutations and their altered expressions are frequently linked to human leukemia. Here, we report that transforming growth factor beta (TGFbeta)/bone morphogenetic protein (BMP) inhibits the bone marrow transformation capability of Hoxa9 and Nup98-Hoxa9, the chimeric fusion form of Hoxa9 identified in human acute myeloid leukemia (AML), through Smad4, the common Smad (Co-Smad) in the TGFbeta/BMP signaling pathway. Smad4 interacts directly with the homeodomain of Hoxa9 and blocks the ability of Nup98-Hoxa9 to bind DNA, thereby suppressing its ability to regulate downstream gene transcription. Mapping data revealed that the amino-terminus of Smad4 mediates this interaction and overexpression of the Hoxa9 interaction domain of Smad4 was sufficient to inhibit the enhanced serial replating ability of primary bone marrow cells induced by Nup98-Hoxa9. These studies establish a novel mechanism by which TGFbeta/BMP regulates hematopoiesis and suggest that modification of Hox DNA-binding activity may serve as a novel therapeutic intervention for those leukemias that involve deregulation of Hox.

Characterization of integrin beta6 and thrombospondin-1 double-null mice

To identify overlapping and non-overlapping functions for TSP-1 and alphavbeta6, we crossed TSP-1-null and beta6-null mice and compared the phenotype of the double-null mice with those of wild-type and single-null mice. The double-null mice exhibited focal acute and organizing pneumonia that was more severe than the wild-type and single-null mice as well as a significantly higher incidence of inflammation in tissues other than the lung. The TSP-1-null and beta6-null mice exhibited a five to eight-fold increase in granulocyte recruitment to the lung three days after exposure to lipopolysaccharide. They also had abnormalities that were infrequently observed in the wild-type and single-null mice, including heart degeneration (8.35% in wild-type and 28.1% in double-null mice), hyperplasia of the glandular of the stomach (2.8% in wild-type and 21.1% in double-null mice) and endometrial hyperplasia (0% in wild-type and 38.5% in double-null females). Furthermore, the beta6-null and double-null mice displayed a significant elevation in benign and malignant cancers. Stomach papillomas, squamous cell carcinomas of the ear and stomach, and adenocarcinomas of the lungs, vagina/cervix and colon were observed with the highest frequency. These data demonstrate that TSP-1 and alphavbeta6 are involved in regulation of the immune system and epithelial homeostasis. They also indicate that alphavbeta6 functions as a tumor suppressor gene and that activation of TGFbeta by TSP-1 and alphavbeta6 contributes to normal tissue architecture and function.

Menin inactivation leads to loss of transforming growth factor beta inhibition of parathyroid cell proliferation and parathyroid hormone secretion

Primary hyperparathyroidism is a common endocrine disorder caused by parathyroid gland enlargement and excessive parathyroid hormone (PTH) secretion. However, the precise mechanisms of tumorigenesis of the parathyroids are unknown. Here we have investigated the roles of transforming growth factor (TGF)-beta and menin, the product of the multiple endocrine neoplasia type 1 (Men1) gene, in the proliferation and PTH production of parathyroid cells from either patients with secondary hyperparathyroidism or Men1. TGF-beta was expressed in the parathyroid endocrine cells. Addition of TGF-beta to parathyroid cells from patients with secondary hyperparathyroidism inhibited their proliferation and PTH secretion. These responses to TGF-beta were lost when menin was specifically inactivated by antisense oligonucleotides. Moreover, TGF-beta did not affect the proliferation and PTH production of parathyroid cells from a Men1 patient. These results indicate that menin is required for TGF-beta action in the parathyroid. We conclude that TGF-beta is an important autocrine/paracrine negative regulator of parathyroid cell proliferation and PTH secretion and that loss of TGF-beta signaling due to menin inactivation contributes to parathyroid tumorigenesis.

Transforming growth factor-beta signaling in normal and malignant hematopoiesis

Transforming growth factor-beta (TGF-beta) is perhaps the most potent endogenous negative regulator of hematopoiesis. The intracellular signaling events mediating the effects of TGF-beta are multiple, involving extensive crosstalk between Smad-dependent and MAP-kinase-dependent pathways. We are only beginning to understand the importance of the balance between these cascades as a determinant of the response to TGF-beta, and have yet to determine the roles that disruption in TGF-beta signaling pathways might play in leukemogenesis. This review summarizes current knowledge regarding the function of TGF-beta in normal and malignant hematopoiesis. The principal observations made by gene targeting studies in mice are reviewed, with an emphasis on how a disruption of this pathway in vivo can affect blood cell development and immune homeostasis. We overview genetic alterations that lead to impaired TGF-beta signaling in hematopoietic neoplasms, including the suppression of Smad-dependent transcriptional responses by oncoproteins such as Tax and Evi-1, and fusion proteins such as AML1/ETO. We also consider mutations in genes encoding components of the core cell cycle machinery, such as p27(Kip1) and p15(INK4A), and emphasize their impact on the ability of TGF-beta to induce G1 arrest. The implications of these observations are discussed, and opinions regarding important directions for future research on TGF-beta in hematopoiesis are provided.

TGFbeta1 signaling via alphaVbeta6 integrin

BACKGROUND

Transforming growth factor beta1 (TGFbeta1) is a potent inhibitor of epithelial cell growth, thus playing an important role in tissue homeostasis. Most carcinoma cells exhibit a reduced sensitivity for TGFbeta1 mediated growth inhibition, suggesting TGFbeta1 participation in the development of these cancers. The tumor suppressor gene DPC4/SMAD4, which is frequently inactivated in carcinoma cells, has been described as a key player in TGFbeta1 mediated growth inhibition. However, some carcinoma cells lacking functional SMAD4 are sensitive to TGFbeta1 induced growth inhibition, thus requiring a SMAD4 independent TGFbeta1 pathway.

RESULTS

Here we report that mature TGFbeta1 is a ligand for the integrin alphaVbeta6, independent of the common integrin binding sequence motif RGD. After TGFbeta1 binds to alphaVbeta6 integrin, different signaling proteins are activated in TGFbeta1-sensitive carcinoma cells, but not in cells that are insensitive to TGFbeta1. Among others, interaction of TGFbeta1 with the alphaVbeta6 integrin resulted in an upregulation of the cell cycle inhibitors p21/WAF1 and p27 leading to growth inhibition in SMAD4 deleted as well as in SMAD4 wildtype carcinoma cells.

CONCLUSIONS

Our data provide support for the existence of an alternate TGFbeta1 signaling pathway that is independent of the known SMAD pathway. This alternate pathway involves alphaVbeta6 integrin and the Ras/MAP kinase pathway and does not employ an RGD motif in TGFbeta1-sensitive tumor cells. The combined action of these two pathways seems to be necessary to elicit a complete TGFbeta1 signal.

CD103+ intraepithelial lymphocytes--a unique population in microsatellite unstable sporadic colorectal cancer

Colorectal cancers with microsatellite instability (MSI) typically show increased numbers of intraepithelial lymphocytes (IEL) in comparison to microsatellite stable (MSS) cancers. The aim of this study was to determine the phenotype of this unique lymphocyte population in MSI and MSS colorectal cancers. Twenty-four individuals with sporadic colorectal cancer (17 MSI, 7 MSS) were included in this study. Intraepithelial and stromal lymphocytes were detected using immunohistochemistry with anti-CD8 and anti-CD103 antibodies, and two observers independently quantified the numbers of lymphocytes. CD103+ (alpha E beta 7+) IELs detected within tumour tissue co-expressed CD8+ while the stromal lymphocytes were phenotypically heterogeneous, with respect to CD8+ and CD103+ expression. MSI colorectal cancers harboured increased numbers of CD8+ CD103+ IELs, as well as CD8+ CD103- and CD8+ CD103+ stromal lymphocytes, when compared with MSS colorectal cancers. CD103+ IELs were found at 27-fold greater numbers in the tumour epithelium than in normal epithelium from the same patient (P = 0.001, Wilcoxon matched pairs test). From our findings, we have proposed a mechanism for the homing of these alpha E beta 7+ lymphocytes to tumour tissue in MSI and MSS colorectal cancers.

Levels of phospho-Smad2/3 are sensors of the interplay between effects of TGF-beta and retinoic acid on monocytic and granulocytic differentiation of HL-60 cells

We have investigated the role of Smad family proteins, known to be important cytoplasmic mediators of signals from the transforming growth factor-beta (TGF-beta) receptor serine/threonine kinases, in TGF-beta-dependent differentiation of hematopoietic cells, using as a model the human promyelocytic leukemia cell line, HL-60. TGF-beta-dependent differentiation of these cells to monocytes, but not retinoic acid-dependent differentiation to granulocytes, was accompanied by rapid phosphorylation and nuclear translocation of Smad2 and Smad3. Vitamin D(3) also induced phosphorylation of Smad2/3 and monocytic differentiation; however the effects were indirect, dependent on its ability to induce expression of TGF-beta1. Simultaneous treatment of these cells with TGF-beta1 and all-trans-retinoic acid (ATRA), which leads to almost equal numbers of granulocytes and monocytes, significantly reduced the level of phospho-Smad2/3 and its nuclear accumulation, compared with that in cells treated with TGF-beta1 alone. TGF-beta1 and ATRA activate P42/44 mitogen-activated protein (MAP) kinase with nearly identical kinetics, ruling out its involvement in these effects on Smad phosphorylation. Addition of the inhibitor-of-protein serine/threonine phosphatases, okadaic acid, blocks the ATRA-mediated reduction in TGF-beta-induced phospho-Smad2 and shifts the differentiation toward monocytic end points. In HL-60R mutant cells, which harbor a defective retinoic acid receptor-alpha (RAR-alpha), ATRA is unable to reduce levels of TGF-beta-induced phospho-Smad2/3, coincident with its inability to differentiate these cells along granulocytic pathways. Together, these data suggest a new level of cross-talk between ATRA and TGF-beta, whereby a putative RAR-alpha-dependent phosphatase activity limits the levels of phospho-Smad2/3 induced by TGF-beta, ultimately reducing the levels of nuclear Smad complexes mediating the TGF-beta-dependent differentiation of the cells to monocytic end points.

Mitochondrial stress-induced calcium signaling, phenotypic changes and invasive behavior in human lung carcinoma A549 cells

We have investigated mechanisms of mitochondrial stress-induced phenotypic changes and cell invasion in tumorigenic but poorly invasive human pulmonary carcinoma A549 cells that were partly depleted of mitochondrial DNA (mtDNA). Depletion of mtDNA (genetic stress) caused a markedly lower electron transport-coupled ATP synthesis, loss of mitochondrial membrane potential, elevation of steady state [Ca(2+)](c), and notably induction of both glycolysis and gluconeogenic pathway enzymes. Markers of tumor invasion, cathepsin L and TGFbeta1, were overexpressed; calcium-dependent MAP kinases (ERK1 and ERK2) and calcineurin were activated. The levels of anti-apoptotic proteins Bcl2 and Bcl-X(L) were increased, and the cellular levels of pro-apoptotic proteins Bid and Bax were reduced. Both mtDNA-depleted cells (genetic stress) and control cells treated with carbonyl cyanide m-chlorophenylhydrazone (metabolic stress) exhibited higher invasive behavior than control cells in a Matrigel basement membrane matrix assay system. MtDNA-depleted cells stably expressing anti-sense cathepsin L RNA, TGFbeta1 RNA, or treated with specific inhibitors showed reduced invasion. Reverted cells with 80% of control cell mtDNA exhibited marker protein levels, cell morphology and invasive property closer to control cells. Our results suggest that the mitochondria-to-nucleus signaling pathway operating through increased [Ca(2+)](c) plays an important role in cancer progression and metastasis.

Ultraviolet irradiation alters transforming growth factor beta/smad pathway in human skin in vivo

Solar ultraviolet irradiation damages human skin and causes premature skin aging and skin cancer. As transforming growth factor beta plays an important role in regulating cell growth and extracellular matrix synthesis, we investigated expression of transforming growth factor beta isoforms, transforming growth factor beta receptors, and transforming growth factor beta regulated Smad transcription factors following irradiation with an ultraviolet B source and solar-simulated ultraviolet irradiation of human skin in vivo. Full-thickness, sun-protected adult human skin expressed transforming growth factor beta1, beta2, and beta3 transcripts in a ratio of 1:5:3, as determined by quantitative real-time reverse transcription polymerase chain reaction. Northern analysis demonstrated that the ultraviolet irradiation (2 minimal erythema dose) caused moderate (2-3-fold) gradual increases of transforming growth factor beta1 and beta3 mRNA expression during 3 d post exposure. In contrast, expression of transforming growth factor beta2 mRNA, the predominant form of transforming growth factor beta in human skin, decreased within 4 h after ultraviolet irradiation. In situ hybridization revealed transforming growth factor beta1, beta2, and beta3 mRNA expression in cells throughout the epidermis and the dermis in nonirradiated skin. Following ultraviolet or solar-simulated ultraviolet irradiation, transforming growth factor beta1 and beta3 mRNA were increased and transforming growth factor beta2 mRNA was reduced throughout the epidermis and dermis. No significant changes were observed in transforming growth factor beta type I receptor mRNA expression after ultraviolet irradiation. In contrast, transforming growth factor beta type II receptor mRNA expression was reduced 60% within 4 h following ultraviolet exposure in human skin in vivo. Transforming growth factor beta type II receptor mRNA levels remained reduced for 8 h and recovered by 24 h post ultraviolet. In situ hybridization revealed that ultraviolet or solar-simulated ultraviolet irradiation caused loss of transforming growth factor beta type II receptor mRNA in basal and suprabasal cells in the epidermis and dermal cells. In addition, no significant changes were observed in Smad2, Smad3, and Smad4 expression after ultraviolet irradiation. In contrast, ultraviolet and solar-simulated ultraviolet irradiation rapidly induced gene expression of Smad7, which antagonizes the actions of the transforming growth factor beta/Smad pathway. Smad7 mRNA induction occurred throughout the epidermis and dermal cells as determined by in situ hybridization. Ultraviolet irradiation also caused reduced DNA binding of Smad3/4 in human skin in vivo. Reduced Smad3/4 DNA binding was observed within 4 h following irradiation. Taken together, these results demonstrate that ultraviolet and solar-simulated ultraviolet irradiation alter the transforming growth factor beta/Smad pathway in human skin in vivo. Ultraviolet induction of Smad7 and reduction of transforming growth factor beta2 and transforming growth factor beta type II receptor should diminish transforming growth factor beta signaling, and probably contribute to the decrease of transforming growth factor beta regulated type I and type III procollagen gene expression observed in ultraviolet and solar-simulated ultraviolet irradiated human skin in vivo.