Mutation analysis of the transforming growth factor-beta type II receptor in human cell lines resistant to growth inhibition by transforming growth factor-beta

Canonical BMP Signaling Executes Epithelial-Mesenchymal Transition Downstream of SNAIL1

Epithelial-mesenchymal transition (EMT) is a pivotal process in development and disease. In carcinogenesis, various signaling pathways are known to trigger EMT by inducing the expression of EMT transcription factors (EMT-TFs) like SNAIL1, ultimately promoting invasion, metastasis and chemoresistance. However, how EMT is executed downstream of EMT-TFs is incompletely understood. Here, using human colorectal cancer (CRC) and mammary cell line models of EMT, we demonstrate that SNAIL1 critically relies on bone morphogenetic protein (BMP) signaling for EMT execution. This activity requires the transcription factor SMAD4 common to BMP/TGFβ pathways, but is TGFβ signaling-independent. Further, we define a signature of BMP-dependent genes in the EMT-transcriptome, which orchestrate EMT-induced invasiveness, and are found to be regulated in human CRC transcriptomes and in developmental EMT processes. Collectively, our findings substantially augment the knowledge of mechanistic routes whereby EMT can be effectuated, which is relevant for the conceptual understanding and therapeutic targeting of EMT processes.

Transforming Growth Factor β Signaling in Colorectal Cancer Cells With Microsatellite Instability Despite Biallelic Mutations in TGFBR2

BACKGROUND & AIMS

Most colorectal cancer (CRC) cells with high levels of microsatellite instability (MSI-H) accumulate mutations at a microsatellite sequence in the gene encoding transforming growth factor β receptor II (TGFBR2). TGFβ signaling therefore is believed to be defective in these tumors, although CRC cells with TGFBR2 mutations have been reported to remain sensitive to TGFβ. We investigated how TGFβ signaling might continue in MSI-H CRC cells.

METHODS

We sequenced the 10-adenines microsatellite sequence in the TGFBR2 gene of 32 MSI-H colon cancer tissues and 6 cell lines (HCT116, LS180, LS411N, RKO, SW48, and SW837). Activation of TGFβ signaling was detected by SMAD2 phosphorylation and through use of a TGFβ-responsive reporter construct in all CRC cell lines. Transcripts of TGFBR2 were knocked-down in CRC cells using short hairpin RNA. Full-length and mutant forms of TGFBR2 were expressed in LS411N cells, which do not respond to TGFβ, and their activities were measured.

RESULTS

SMAD2 was phosphorylated in most MSI-H CRC tissues (strong detection in 44% and weak detection in 34% of MSI-H tumors). Phosphorylation of SMAD2 in MSI-H cells required TGFBR2—even the form encoding a frameshift mutation. Transcription and translation of TGFBR2 with a 1-nucleotide deletion at its microsatellite sequence still produced a full-length TGFBR2 protein. However, protein expression required preservation of the TGFBR2 microsatellite sequence; cells in which this sequence was replaced with a synonymous nonmicrosatellite sequence did not produce functional TGFBR2 protein.

CONCLUSION

TGFβ signaling remains active in some MSI-H CRC cells despite the presence of frameshift mutations in the TGFBR2 gene because the mutated gene still expresses a functional protein. Strategies to reactivate TGFβ signaling in colorectal tumors might not be warranted, and the functional effects of mutations at other regions of microsatellite instability should be evaluated.

Tumors as organs: biologically augmenting radiation therapy by inhibiting transforming growth factor β activity in carcinomas

Transforming growth factor β (TGFβ) plays critical roles in regulating a plethora of physiological processes in normal organs, including morphogenesis, embryonic development, stem cell differentiation, immune regulation, and wound healing. Though considered a tumor suppressor, TGFβ is a critical mediator of tumor microenvironment, in which it likewise mediates tumor and stromal cell phenotype, recruitment, inflammation, immune function, and angiogenesis. The fact that activation of TGFβ is an early and persistent event in irradiated tissues and that TGFβ signaling controls effective DNA damage response provides a new means to manipulate tumor response to radiation. Here we discuss preclinical studies unraveling TGFβ effects in cancer treatment and review TGFβ biology in lung cancer as an example of the opportunities for TGFβ pathway inhibition as a pharmaceutical approach to augment radiation therapy.

Lewis Y regulates signaling molecules of the transforming growth factor β pathway in ovarian carcinoma-derived RMG-I cells

LeY (Lewis Y) is a difucosylated oligosaccharide carried by glycoconjugates on the cell surface. Elevation of LeY is frequently observed in epithelial-derived cancers and is correlated to pathological staging and prognosis. To study the role of LeY on cancer cells, a stably LeY-overexpressing cell line, RMG-I-H, was developed previously by transfection of the α1,2-fucosyltransferase gene, a key enzyme that catalyzes the synthesis of LeY, into ovarian carcinoma-derived RMG-I cells. Our studies have shown that LeY is involved in the changes in biological behavior of RMG-I-H cells. However, the mechanism is still largely unknown. In this study, we determined the structural relationship and co-localization between LeY and TβRI/TβRII, respectively, and the potential cellular signaling mechanism was also investigated. We found that both TβRI and TβRII contain the LeY structure, and the level of LeY in TβRI and TβRII in RMG-I-H cells was significantly increased. Overexpression of LeY up-regulates the phosphorylation of ERK, Akt and down-regulates the phosphorylation of Smad2/3. In addition, the phosphorylation intensity was attenuated significantly by LeY monoantibody. These findings suggest that LeY is involved in the changes in biological behavior through TGF-β receptors via Smad, ERK/MAPK and PI3K/Akt signaling pathways. We suggest that LeY may be an important composition of growth factor receptors and could be an attractive candidate for cancer diagnosis and treatment.

Different initial steps of apoptosis induced by two types of antineoplastic drugs

O6-Methylguanine and O6-chloroethylguanine are primary DNA lesions produced by two types of antineoplastic drugs, 8-carbamoyl-3-methylimidazo[5,1-d]-1,2,3,5-tetrazin-4(3H)-one (temozolomide, TMZ) and 1-(4-amino-2-methyl-5-pyrimidinyl) methyl-3-(2-chloroethyl)-3-nitrosourea (ACNU), respectively. They can be repaired by O6-methylguanine-DNA methyltransferase, coded by the Mgmt gene. Otherwise, these two types of lesions induce apoptosis in different ways. O6-Chloroethylguanine blocks DNA replication thereby inducing apoptosis. On the other hand, O6-methylguanine does not block DNA replication and the resulting O6-methylguanine-thymine mispair is recognized by mismatch repair-related proteins, including MLH1, thereby inducing apoptosis. Reflecting this, mouse cells lacking both MGMT and MLH1 are resistant to TMZ, but not to ACNU. The translocation of phosphatidylserine in cell membrane as well as a change of mitochondrial transmembrane potentials occurred in an MLH1-dependent manner after treatment with TMZ, but no such MLH1 dependency was observed in the case of ACNU treatment. By using cell lines defective in both APAF-1 and MGMT, it was revealed that the APAF-1 function is required for execution of apoptosis induced by either TMZ or ACNU. There is almost 12h delay in occurrence of apoptosis-related mitochondrial depolarization in TMZ-treated cells in comparison to those of ACNU-treated cells, reflecting the fact that at least one cycle of DNA replication is required to trigger apoptosis in the former case, but not in the latter.

Loss of betaglycan expression in ovarian cancer: role in motility and invasion

The transforming growth factor-beta (TGF-beta) superfamily members, TGF-beta, activin, and inhibin, all have prominent roles in regulating normal ovarian function. Betaglycan, or the type III TGF-beta receptor, is a coreceptor that regulates TGF-beta, activin, and inhibin signaling. Here, we show that betaglycan expression is frequently decreased or lost in epithelial derived ovarian cancer at both the mRNA and protein level, with the degree of loss correlating with tumor grade. Treatment of ovarian cancer cell lines with the methyltransferase inhibitor 5-aza-2-deoxycytidine and the histone deacetylase inhibitor trichostatin A resulted in significant synergistic induction of betaglycan message levels and increased betaglycan protein expression, indicating that epigenetic silencing may play a role in the loss of betaglycan expression observed in ovarian cancer. Although restoring betaglycan expression in Ovca429 ovarian cancer cells is not sufficient to restore TGF-beta-mediated inhibition of proliferation, betaglycan significantly inhibits ovarian cancer cell motility and invasiveness. Furthermore, betaglycan specifically enhances the antimigratory effects of inhibin and the ability of inhibin to repress matrix metalloproteinase levels in these cells. These results show, for the first time, epigenetic regulation of betaglycan expression in ovarian cancer, and a novel role for betaglycan in regulating ovarian cancer motility and invasiveness.

Disruption of transforming growth factor beta-Smad signaling pathway in head and neck squamous cell carcinoma as evidenced by mutations of SMAD2 and SMAD4

The role of the TGF-beta-Smad signaling pathway in the carcinogenesis of head and neck cancer has not been fully evaluated genetically. In this study, we screened for mutation in the five main members of the TGF-beta -Smad signaling pathway, TGF-beta type I receptor (TGFBRI), TGF-beta type II receptor (TGFBRII), SMAD2, SMAD3 and SMAD4, in eight human head and neck squamous cell carcinoma (HNSCC) cell lines. Two mutations with presumed loss of heterozygosity (LOH) were identified. A novel missense mutation of SMAD2, located in exon 8 at codon 276 TCG (ser) -->TTG (leu), was identified in cell line SCC-15. This is the first report of a biallelic mutation of the SMAD2 gene in HNSCC. A nonsense mutation of the SMAD4 gene in exon 5 codon 245 CAG (glut) -->TAG (stop) was found in cell line CAL27. Western blotting verified that this nonsense mutation gives rise to the complete loss of the Smad4 protein in the cells. While the down-regulation and loss of expressions of the TGF-beta-Smad signaling pathway have been described frequently in HNSCC, here we offer further genetic evidence that the pathway is directly targeted for mutation during the HNSCC tumorigenesis.

Intrahepatic cholangiocarcinoma escapes from growth inhibitory effect of transforming growth factor-beta1 by overexpression of cyclin D1

Transforming growth factor-beta1 (TGF-beta1) is involved in tumor progression by promoting angiogenesis or suppressing the immune system; yet TGF-beta1 also has a growth-inhibitory effect on epithelial cells including carcinoma cells. Several mechanisms of impaired TGF-beta1 responsiveness of carcinoma cells have been reported. In this study, we examined how TGF-beta1 participates in the development and progression of intrahepatic cholangiocarcinoma (ICC) associated with hepatolithiasis, and how ICC cells escape from growth inhibitory effect of TGF-beta1. A total of 40 cases of hepatolithiasis were studied, including 16 cases of ICC, and in vitro studies were conducted with cultured murine non-neoplastic biliary epithelial cells (MBEC) and three ICC cell lines. Immunohistochemically, TGF-beta1 was expressed in mononuclear cells and mesenchymal cells around the stone-containing bile ducts and invasive ICC, and also in biliary epithelial cells (hyperplastic and precursor lesions, and ICC). TGF-beta type II receptor (TbetaR-II) was constantly expressed on biliary epithelial cells irrespective of biliary lesions. In cell culture studies, TGF-beta1 significantly inhibited proliferation of MBEC via downregulation of cyclin D1, cdk4, and cdk6, while TGF-beta1 did not influence the proliferation of ICC cells. After suppression of cyclin D1 expression in one ICC cell line using cyclin D1 small interfering RNA, TGF-beta1 significantly inhibited the proliferation of ICC cells. In conclusion, high levels of TGF-beta1 around ICC or its precursors may be involved in development and progression of ICC in hepatolithiasis. ICC cells could escape the growth inhibitory effect of TGF-beta1 by overexpression of cyclin D1.

Killing and mutagenic actions of dacarbazine, a chemotherapeutic alkylating agent, on human and mouse cells: effects of Mgmt and Mlh1 mutations

Among various types of drugs designed for use in cancer chemotherapy, some have the potential for alkylation. After metabolic activation, these chemicals attack DNA and alkylate their bases, thereby preventing multiplication of rapidly growing tumor cells. Some of alkylated bases cause mutations, leading to untoward induction of tumors. To search for the rationale to separate lethal and mutagenic effects of alkylation drugs, we investigated actions of dacarbazine, a monofunctional triazene, on mouse and human cell lines defective in the Mgmt and/or the Mlh1 gene, the former encoding a DNA repair methyltransferase and the latter a protein involved in mismatch repair and induction of apoptosis. Mgmt-deficient cells are hypersensitive to the killing action of dacarbazine. On the other hand, cells defective in both Mgmt and Mlh1 genes are as resistant to the drug as are wild-type cells, in terms of survival, but do have many mutations after dacarbazine treatment. Thus, the killing and mutagenic actions of dacabazine can be dissociated by manipulating actions of these gene products.

Transforming growth factor-beta (TGF-beta) type I receptor/ALK5-dependent activation of the GADD45beta gene mediates the induction of biglycan expression by TGF-beta

We have recently shown that induction of biglycan (BGN) expression by transforming growth factor-beta1 (TGF-beta1) required sequential activation of both Smad and p38 mitogen-activated protein kinase signaling (Ungefroren, H., Lenschow, W., Chen, W.-B., and Kalthoff, H. (2003) J. Biol. Chem. 278, 11041-11049). Here, we have analyzed the receptors through which TGF-beta1 controls expression of BGN and GADD45beta, the latter of which is postulated to link early Smad signaling to delayed activation of p38. Ectopic expression of a dominant-negative mutant of the TGF-beta type II receptor in PANC-1 cells abrogated TGF-beta-induced BGN up-regulation. Similarly, inhibition of the TGF-beta type I receptor/ALK5 with either SB431542 or by enforced stable expression of a kinase-dead mutant greatly attenuated the TGF-beta effect on both BGN and GADD45beta expression in PANC-1 and MG-63 cells. The enhancing effect of ALK5 on TGF-beta-mediated GADD45beta and BGN expression and on GADD45beta promoter activity was also dependent on its ability to activate Smad signaling, because an ALK5 mutant defective in Smad activation (TbetaRImL45) but with an otherwise functional kinase domain failed to mediate these responses. The TGF-beta/ALK5 effect on p38 activation and BGN expression was mimicked by overexpression of GADD45beta alone (in the absence of TGF-beta stimulation) and suppressed upon antisense inhibition of GADD45beta expression. These results show that TGF-beta induces BGN expression through (the Smad-activating function of) ALK5 and GADD45beta and suggest that the sensitivity of MyD118 to activation by TGF-beta, which varies between tissues, ultimately determines the strength of the TGF-beta effect on BGN.

BMP-2 modulates the proliferation and differentiation of normal and cancerous gastric cells

Bone morphogenetic protein 2 (BMP-2), a member of the transforming growth factor beta super-family, has been shown to act as an antiproliferative agent for a variety of cell lines by activating signaling cascades that cause cell cycle arrest. However, the biological effect and mechanism of action of BMP-2 on gastric cells remain unknown. In the present study, we showed that recombinant human BMP-2 dose-dependently inhibited the growth of OUMS37 rat gastric cells and MKN74 human gastric cancer cells. The antiproliferation seems to be due to cell cycle arrest in the G1-phase, which was revealed by flow cytometric assays. BMP-2 increased the level of p21/WAF1/CIP1, suggesting that BMP-2-mediated inhibition of cell proliferation may be induced through p21/WAF1/CIP1. In addition, BMP-2 increased the expression of pepsinogen II, a differentiation marker of the stomach, in MKN74 cells. These results indicate that BMP-2 plays important roles in modulating the proliferation and differentiation of gastric epithelial cells.

Role of transforming growth factor β in breast carcinogenesis

Transforming growth factor (TGF) beta is a pre-eminent negative growth regulator that has antiproliferative effects on a range of epithelial cells. This ability has evoked interest in this growth factor as a tumour suppressor with potential clinical significance. In the early stages of breast carcinogenesis, a growth-inhibitory response to TGFbeta is maintained, which depends on an intact TGFbeta signalling pathway. Tumour development and progression of cells along a neoplastic continuum is accompanied by loss of this growth-inhibitory response to TGFbeta, which might instead promote tumour growth indirectly through a combination of permissive effects on stromal tissue, angiogenesis, and the immune system. This review discusses the complexity of functional pleiotropy and the continually changing roles of TGFbeta as a tumour evolves, along with competing therapeutic strategies. The boosting of local endogenous amounts of TGFbeta in conjunction with enhancement of cellular responsiveness might be appropriate in early malignant disease, and anti-TGFbeta approaches could yield a therapeutic gain in metastatic states.

Higher stromal expression of transforming growth factor-beta type II receptors is associated with poorer prognosis breast tumors

Transforming growth factor-beta (TGFB) is a potent inhibitor of normal epithelial cell proliferation, and may be one of the regulatory factors that are perturbed during tumor development. While many tumor cell lines no longer respond to the inhibitory effects of TGFB due to a reduction or absence of the type II receptor (TGFBR2), the role of TGFBR2 in tumors from patients with breast cancer is less clear. The objective of this study was to screen human breast tumors to determine if there was a TGFBR2 mutation and/or altered expression of TGFBR2 protein. Using 10 unique primers, SSCP-PCR was used to detect heterozygosity in the complete coding sequence from 72 tumors and normal DNA from 20 individuals. One region of the promoter was also examined. Expression of TGFBR2 in the same breast tumors was examined by immunohistochemistry. Sequence variations were identified among normal and tumor tissue samples by SSCP-PCR within coding regions of exon 4 (1/72 samples) and within non-coding regions of intron 2 (1/72), intron 3 (72/72), and intron 6 (1/72). A new polymorphism was identified in intron 3. Observed allele frequencies were consistent with Hardy-Weinberg equilibrium in both the tumors and normal DNA. TGFBR2 was expressed in the epithelium and stroma of tumor tissue. The percentage of cells expressing TGFBR2 in stroma was higher in patients that had a positive lymph node status and/or negative estrogen and progesterone receptor expression. There was no relationship between TGFBR2 expression in the epithelium and these variables.

Lack of correlation between growth inhibition by TGF-beta and the percentage of cells expressing type II TGF-beta receptor in human non-small cell lung carcinoma cell lines

To determine the mechanisms involved in the evasion from TGF-beta growth regulation in the small cell lung carcinoma (SCLC) cell lines and the non-small cell lung carcinoma (NSCLC) cell lines, we studied: (a) production of TGF-beta1 and TGF-beta2; (b) percentage of cells expressing TGF-beta RII; (c) responsiveness of the tumour cell lines to exogenous TGF-beta1 or TGF-beta2; and (d) presence of mRNA transcripts of the three TGF-beta isoforms and of the TGF-beta RII. Our results indicate that the SCLC cell lines do not synthesize the isoforms TGF-beta1 and TGF-beta2 nor the TGF-beta RII, thus avoiding inhibitory autocrine and paracrine TGF-beta actions. However, NSCLC cell lines express not only TGF-beta1, TGF-beta2 and TGF-beta RII mRNA transcripts, but also synthesize both isoforms and the TGF-beta RII. Although approximately 50% of the cells from the studied cell lines expressed the TGF-beta RII, different cell lines varied greatly in the sensitivity to the inhibitory action of TGF-beta. This could result from alterations in: (i) the structure of TGF-beta RII; (ii) the phosphorylation motif of TGF-beta RI; (iii) the molecules involved in the intracellular signalling pathway of TGF-beta; and (iv) cell cycle regulation.

Establishment and characterisation of six human biliary tract cancer cell lines

Human cell lines established from biliary tract cancers are rare, and only five have been reported previously. We report the characterisation of six new six biliary tract cancer cell lines (designated SNU-245, SNU-308, SNU-478, SNU-869, SNU-1079 and SNU-1196) established from primary tumour samples of Korean patients. The cell lines were isolated from two extrahepatic bile duct cancers (one adenocarcinoma of common bile duct, one hilar bile duct cancer), two adenocarcinomas of ampulla of Vater, one intrahepatic bile duct cancer (cholangiocarcinoma), and one adenocarcinoma of the gall bladder. The cell phenotypes, including the histopathology of the primary tumours and in vitro growth characteristics, were determined. We also performed molecular characterisation, including DNA fingerprinting analysis and abnormalities of K-ras, p15, p16, p53, hMLH1, hMSH2, DPC4, beta-catenin, E-cadherin, hOGG1, STK11, and TGF-betaRII genes by PCR-SSCP and sequencing analysis. In addition, we compared the genetic alterations in tumour cell lines and their corresponding tumour tissues. All lines grew as adherent cells. Population doubling times varied from 48-72 h. The culture success rate was 20% (six out of 30 attempts). All cell lines showed (i) relatively high viability; (ii) absence of mycoplasma or bacteria contamination; and (iii) genetic heterogeneity by DNA fingerprinting analysis. Among the lines, three lines had p53 mutations; and homozygous deletions in both p16 and p15 genes were found three and three lines, respectively; one line had a heterozygous missense mutation in hMLH1; E-cadherin gene was hypermethylated in two lines. Since the establishment of biliary tract cancer cell lines has been rarely reported in the literature, these newly established and well characterised biliary tract cancer cell lines would be very useful for studying the biology of biliary tract cancers, particularly those related to hypermethylation of E-cadherin gene in biliary tract cancer.

Systematic analysis of the TGF-beta-Smad signaling pathway in gastrointestinal cancer cells

The transforming growth factor-beta (TGF-beta)-Smad signaling pathway has an important role in carcinogenesis. To study the frequency and mechanism of functional impairment of this pathway in human gastrointestinal cancers, we used a reporter assay to examine the response of 38 cell lines (11 colorectal, 9 pancreatic, 10 gastric, and 8 hepatic cancers) to TGF-beta. We then analyzed TGF-beta type II receptor (T beta RII) gene, immunoblots of Smad4, and restoration of the pathway by rescuing T beta R or Smad. We observed impaired signaling in 91% of colorectal, 67% of pancreatic, and 40% of gastric cancer cell lines, but in none of the hepatic cancer cells. We suggest that this pathway does not function as a tumor suppressor in hepatic carcinogenesis. The impairment is due to inactivation of T beta RII and Smad4 in colorectal and pancreatic cancers. However, because the signal was not recovered by rescuing T beta R or Smad genes in TGF-beta-response-defective gastric cancer cell lines, we suggest that novel molecules or mechanisms are involved in the impaired pathway in some gastric cancers.

Identification of genetic alterations in the TGFbeta type II receptor gene promoter

Modifications in the control sequences of tumor suppressor genes have been found to play a role in the activation or inactivation of these genes and may play an important role in tumorigenesis. For example, hypermethylation of CpG islands and promoter polymorphisms have been found to be involved in transcriptional repression. A decrease in the levels of expression of one such tumor suppressor gene, the TGFbeta type II receptor (TbetaR-II), has been associated with increased tumorigenicity in a number of human tumors. Genetic alterations have been described in several tumor types in the coding region of this gene. However, no comprehensive search for genetic alterations in the TbetaR-II promoter has been reported. Genetic alterations in the promoter of the TbetaR-II gene could inhibit binding of putative regulatory factors. For example, we have reported a A-364-G alteration in the TbetaR-II promoter, which results in decreased transcriptional activity. In this study, we analyzed the 1.0kb region upstream of the TbetaR-II transcriptional start site and found genetic alterations in 46% of the head and neck squamous cell carcinoma (SqCC) samples examined. The most frequent alteration was a G-875-A alteration, present in 41.6% of the samples. Analysis of normal healthy individuals showed a similar frequency of this alteration, suggesting that alterations within the TbetaR-II promoter are unlikely to account for the decreased expression of TbetaR-II in head and neck SqCC.

Microsatellite instability in transforming growth factor-beta 1 type II receptor gene in alveolar lining epithelial cells of idiopathic pulmonary fibrosis

It has been reported that transforming growth factor (TGF)-beta, which plays an integral role in the pathogenesis of idiopathic pulmonary fibrosis (IPF), suppresses proliferation of alveolar epithelial cells in vitro. Although hyperplastic lesions of alveolar lining epithelial cells (ALECs) are characteristic pathologic features of IPF, the mechanism of their involvement in the pathogenesis has not yet been extensively studied. On the assumption that the hyperplastic ALECs have escaped from the growth-inhibitory effects of TGF-beta, we searched for mutations in the microsatellite of the TGF-beta receptor type II (T beta RII) gene. To detect a deletion in the polyadenine tract in exon 3 of the T beta RII gene, cells were isolated by microdissection from lung sections of IPF patients, and DNA was extracted from these cells and amplified by high-fidelity polymerase chain reaction. A total of 121 sites of hyperplastic ALECs from 11 IPF patients were analyzed, and a one-base-pair deletion was detected in nine sites from five patients. The mutation was also detected in smooth muscle-like cells of the thickened pulmonary artery. In some tissue areas where the deletion was detected, low T beta RII expression was confirmed by immunohistochemical staining. These data suggest that microsatellite instability in the T beta RII gene occurred in some lesions of hyperplastic ALECs in IPF, although at a low incidence, and that this genetic disorder might play a partial role in the pathologic changes of IPF.

Microsatellite instability is an independent indicator of recurrence in sporadic stage I-II endometrial adenocarcinoma

PURPOSE

The aim of this study was to define the prognostic role of microsatellite status in 65 stage I-II primary sporadic endometrioid endometrial adenocarcinoma (EEA) patients.

PATIENTS AND METHODS

Familiarity for neoplasia was ascertained in all patients on the basis of a questionnaire. Microsatellite status was assessed by matching normal and tumoral DNA probed for five dinucleotide repeats and one mononucleotide repeat marker. Microsatellite status was analyzed in relation to clinicopathologic characteristics of the patients and length of disease-free survival (DFS).

RESULTS

Eleven tumors (17%) of 65 had instability at two or more loci and were considered as unstable or microsatellite instability (MI). Tumors with no instability or instability at one locus were classified as microsatellite stable (MS). The percentage of MI was significantly higher in poorly than in well to moderately differentiated tumors (50% v 9%; P =.003). The 5-year DFS rate of MI patients was 63% (95% confidence interval [CI], 35% to 91%) versus 96% (95% CI, 91% to 101%) of MS patients (P =.0004). In multivariate analysis, only the presence of MI, stage II of disease, and depth of myometrial invasion greater than 50% retained independent prognostic roles.

CONCLUSION

The assessment of microsatellite status may provide useful information for preoperative prognostic characterization of stage I-II primary sporadic EEA patients in which more individualized treatment options can be attempted.

Alteration of cell growth and morphology by overexpression of transforming growth factor beta type II receptor in human lung adenocarcinoma cells

TGF-beta is a potent inhibitory regulator of cell growth, which is transduced through interaction between type I (RI) and type II (RII) receptors that form heteromeric kinase complexes. Abnormal expression of these receptors has been identified in several human epithelial cancers and has been shown to be highly associated with resistance to TGF-beta. In this study, we investigated the expression of RI and RII in 13 human non-small cell lung cancer cell lines (NSCLCs) and demonstrated decreased or loss of RII expression in five lung cancer cell lines, but not of RI. Of these cell lines, the role of RII in NCI-H358 adenocarcinoma, which lacks RII and is insensitive to TGF-beta, was investigated by transducing this cell line with a recombinant retrovirus expressing full-length TGF-beta RII. Stably transfected cells showed significant increase in RII mRNA and protein expression. These cells responded to exogenous TGF-beta1 with suppressed proliferation in a dose-dependent manner and G1 arrest accompanied by morphological change distinct from control cells. We also investigated whether overexpression of dominant-negative RII (dnRII) in NCI-H441 adenocarcinoma, which is sensitive but expresses low levels of RII, could block signaling through the receptor complex. The overexpression of this kinase-domain-truncated RII by expressing the retroviral dnRII construct led to loss of the ability to respond to TGF-beta1 and an exhibition of uncontrolled growth. These results suggest a close association between the loss of the expression of wild-type TGF-beta RII and carcinogenesis in human lung cancer cells.

Activin A and activin receptors in thyroid cancer

Proliferation is controlled by a network of mitogenic and growth inhibitory factors. Transforming growth factor-beta1 (TGF-beta1) and activin A are the most important growth inhibitors of benign follicular epithelial cells of the human thyroid. The effects of these substances on malignant primary thyrocytes are not known. We have examined the growth regulatory effects of activin A and TGF-beta1 in primary cultures derived from four papillary cancers, two follicular thyroid cancers, and three benign thyroid tissues. Malignant cells demonstrated resistance to activin and TGF-beta1 or reversal to a weak but significant mitogenic effect (p < 0.001). We also evaluated the activin receptor transcription pattern. Isoforms alk4-1, 4-2, and 4-3 were found in benign (n = 12) and malignant (n = 22) tissues. Two subtypes of type I and type II activin receptors were demonstrated. Semiquantitative reverse transcription-polymerase chain reaction (RT-PCR) demonstrated a significant threefold downregulation of alk4-1 receptors in papillary (n = 25) and follicular (n = 18) thyroid cancers as compared to normal thyroids (n = 12) (p < 0.001). To our knowledge these are the first data to demonstrate reversal of activin and TGF-beta1 effects in thyroid malignancy and to demonstrate changes of the type Ib activin receptor expression in thyroid malignancy.

TGF-beta signaling in mammary gland development and tumorigenesis

Ligands of the TGF-beta superfamily are unique in that they signal through transmembrane receptor serine-threonine kinases, rather than tyrosine kinases. The receptor complex couples to a signal transduction pathway involving a novel family of proteins, the Smads. On phosphorylation, Smads translocate to the nucleus where they modulate transcriptional responses. However, TGF-betas can also activate the mitogen-activated protein kinase (MAPK)4 pathway, and the different biological responses to TGF-beta depend to varying degrees on activation of either or both of these two pathways. The Smad pathway is a nexus for cross-talk with other signal transduction pathways and for modulation by many different interacting proteins. Despite compelling evidence that TGF-beta has tumor suppressor activity in the mammary gland, neither TGF-beta receptors nor Smads are genetically inactivated in human breast cancer, though receptor expression is reduced. Possible reasons are discussed in relation to the dual role of TGF-beta as tumor suppressor and oncogene.

Mutation analysis of the gene encoding the human mannose 6-phosphate/insulin-like growth factor 2 receptor (M6P/IGF2R) in human cell lines resistant to growth inhibition by transforming growth factor beta(1) (TGF-beta(1))

The mannose 6-phosphate/insulin-like growth factor 2 receptor (M6P/IGF2R) is involved in activating the transforming growth factor beta(1) (TGF-beta(1)), an inhibitor of the cell proliferation, and limiting the insulin-like growth factor 2 mediated-growth stimulation. The M6P/IGF2R gene has been reported to be mutated and deleted in various cancers, and is a candidate tumor suppressor gene. We studied the genomic structure of the M6P/IGF2R gene and designed the intron primers to detect mutations in the M6P/IGF2R gene of genomic DNA samples. The M6P/IGF2R gene consists of 48 exons. The previously reported 23 mutations of the M6P/IGF2R gene in human cancers, liver, breast, and gastrointestinal tumors, are located in five exons, exon 27, 28, 31, 40, 48. Using the intron primers designed in this study, polymerase chain reaction-single strand conformation polymorphism (PCR-SSCP) analysis, and direct sequencing, we performed an initial analysis of the complete coding sequences of the M6P/IGF2R gene in 21 human cell lines resistant to growth inhibition by TGF-beta(1). An adenine-to-guanine transition, resulting in an asparagine-to-serine amino acid substitution, was found in one lung adenocarcinoma cell line at exon 40 where the mutation has been previously reported in human cancers. This is the first report of a mutation of the M6P/IGF2R gene in lung tumor. These results indicated that the mutation in M6P/IGF2R may be involved in human lung cancinogenesis.

Transforming growth factor-β: pleiotropic role in the regulation of hematopoiesis

Hematopoiesis is a remarkable cell-renewal process that leads to the continuous generation of large numbers of multiple mature cell types, starting from a relatively small stem cell compartment. A highly complex but efficient regulatory network is necessary to tightly control this production and to maintain the hematopoietic tissue in homeostasis. During the last 3 decades, constantly growing numbers of molecules involved in this regulation have been identified. They include soluble cytokines and growth factors, cell–cell interaction molecules, and extracellular matrix components, which provide a multifunctional scaffolding specific for each tissue. The cloning of numerous growth factors and their mass production have led to their possible use for both fundamental research and clinical application.

Transforming growth factor-β: pleiotropic role in the regulation of hematopoiesis

Hematopoiesis is a remarkable cell-renewal process that leads to the continuous generation of large numbers of multiple mature cell types, starting from a relatively small stem cell compartment. A highly complex but efficient regulatory network is necessary to tightly control this production and to maintain the hematopoietic tissue in homeostasis. During the last 3 decades, constantly growing numbers of molecules involved in this regulation have been identified. They include soluble cytokines and growth factors, cell–cell interaction molecules, and extracellular matrix components, which provide a multifunctional scaffolding specific for each tissue. The cloning of numerous growth factors and their mass production have led to their possible use for both fundamental research and clinical application.

Release from quiescence of primitive human hematopoietic stem/progenitor cells by blocking their cell-surface TGF-beta type II receptor in a short-term in vitro assay

Genetic alterations of the signaling cascade of transforming growth factor-beta (TGF-beta) are often associated with neoplastic transformation of primitive cells. This demonstrates the key role for this pleiotropic factor in the control of quiescence and cell proliferation in vivo. In the high proliferative potential-quiescent cell (HPP-Q) in vitro assay, the use of TGF-beta1 blocking antibodies (anti-TGF-beta1) allows the detection within two to three weeks of primitive hematopoietic cells called HPP-Q, which otherwise would not grow. However, the possibility of triggering cell proliferation by blocking the cell-surface TGF-beta receptors has not been investigated until now. We have tested here the efficiency of a blocking antibody against TGF-betaRII (anti-TGF-betaRII) on CD34(+)CD38(-) hematopoietic cells, a subpopulation enriched in primitive stem/progenitor cells, and compared its effect with that of anti-TGF-beta1. About twice as many HPP colony-forming cells were detected in the presence of anti-TGF-beta1 or anti-TGF-betaRII, compared to the control (p < 0.02). Moreover, anti-TGF-betaRII was as efficient as anti-TGF-beta1 for activating multipotent HPP-granulocyte erythroid macrophage megakaryocyte and HPP-Mix, bipotent HPP-granulocyte-macrophage (GM) and unipotent HPP-G, HPP-M and HPP-BFU-E. We therefore propose the use of anti-TGF-betaRII to release primitive cells from quiescence in the HPP-Q assay. This strategy could be extended to nonhematopoietic tissues, as TGF-beta1 may be a pleiotropic regulator of somatic stem cell quiescence.

Ras-mediated suppression of TGFbetaRII expression in intestinal epithelial cells involves Raf-independent signaling

Ras-transformed intestinal epithelial cells are resistant to the growth inhibitory actions of TGFbeta and have a marked decrease in expression of the TGFbeta type II receptor (TGFbetaRII). Rat intestinal epithelial cells (RIE) were stably transfected with activated Ras, Sos and Raf constructs and tested for expression of TGFbetaRII and sensitivity to growth inhibition by TGFbeta. The parental RIE line and the RIE-Raf cells were non-transformed in morphology and were sensitive to TGFbeta (70-90% inhibited). In contrast, the RIE-Ras and RIE-Sos lines were transformed, resistant to TGFbeta and expressed 5- to 10-fold decreased levels of the TGFbetaRII mRNA and protein. Cyclin D1 protein expression was repressed by TGFbeta treatment in parental RIE and RIE-Raf cells, whereas levels of cyclin D1 in RIE-Ras and RIE-Sos cells remained unchanged. Treatment of RIE-Ras cells with 25 microM farnesyl transferase inhibitor, FTI L739,749, for 48 hours restored expression of TGFbetaRII to levels equivalent to control cells. In addition, treatment of RIE-Ras cells for 48 hours with PD-98059, a specific MAPKK inhibitor, also increased expression of TGFbetaRII to control levels. Collectively these results suggest that downregulation of TGFbetaRII and loss of sensitivity to growth inhibition by TGFbeta in Ras-transformed intestinal epithelial cells is not mediated exclusively by the conventional Ras/Raf/MAPKK/MAPK pathway. However, activation of MAPK, perhaps by an alternate Ras effector pathway, appears to be necessary for Ras-mediated downregulation of TGFbetaRII.

Disrupted transforming growth factor-beta signaling and deregulated growth in human biliary tract cancer cells

Biliary tract carcinoma is a common neoplasm in Japan, and its treatment is difficult because it tends to promote fibrosis and easily invades surrounding tissues. To better characterize the biological features of this carcinoma, we investigated abnormalities in the transforming growth factor-beta (TGF-beta) signaling pathway in five human biliary tract cancer cell lines: RBE, KMBC, SK-ChA-1, Mz-ChA-1, and Mz-ChA-2. We stably transfected into these cells the luciferase reporter plasmid carrying promoter of the plasminogen activator inhibitor-1 gene, the expression of which is stimulated by TGF-beta1. Treating the KMBC and Mz-ChA-1 cells with TGF-beta1 neither inhibited cell growth nor stimulated luciferase activity. In contrast, the RBE and Mz-ChA-2 cells responded well to TGF-beta1 treatment. TGF-beta1-treated SK-ChA-1 cells exhibited attenuated luciferase activity and their growth was not inhibited. Smad4 mRNA was not detected in SK-ChA-1 and Mz-ChA-1 cells by Northern blot analysis. Genetic analysis disclosed a nonsense mutation in the Mad homologue 2a domain of the Smad4 gene in the SK-ChA-1 cells and a heterozygous deletion in the TGF-beta type II receptor gene in the KMBC cells. Expression of the exogenous Smad4 gene in the Mz-ChA-1 cells by transient transfection restored their luciferase activity. When these TGF-beta1-insensitive and less-TGF-beta1-sensitive cell lines were xenografted into nude mice, they developed tumors that had more prominent, intervening fibrosis (desmoplasia) than the tumors caused by TGF-beta1-sensitive cells. Thus, a tight correlation between disruption of the TGF-beta signaling pathway and deregulated growth of cancer cells has been demonstrated in biliary tract carcinoma. This seems to be a critical event in this carcinoma and may also be correlated with stromal cell reaction in cancer invasion.

Loss of transforming growth factor-beta (TGF-beta) receptor type I mediates TGF-beta resistance in human papillomavirus type 16-transformed human keratinocytes at late stages of in vitro progression

Human keratinocytes (HKc) immortalized by human papillomavirus type 16 DNA (HKc/HPV16) progress toward malignancy through growth factor-independent (HKc/GFI) and differentiation-resistant stages (HKc/DR). This progression is associated with a loss of sensitivity to growth inhibition by both all-trans-retinoic acid (RA) and transforming growth factor-beta (TGF-beta). In the accompanying article (Borger et al., 2000, Virology 270, 397-407), we demonstrate that RA resistance in HKc/HPV16 arises despite functional nuclear retinoid receptors and that TGF-beta mediates growth inhibition by RA. To investigate the basis for the loss of TGF-beta sensitivity during in vitro progression of HKc/HPV16, we explored the expression of TGF-beta receptors type I and type II in independently derived HKc/HPV16 lines and their corresponding HKc/GFI and HKc/DR derivatives. While TGF-beta receptor type II mRNA levels were unchanged during progression, mRNA levels for TGF-beta receptor type I decreased dramatically as the cells became TGF-beta resistant. At the HKc/DR stage, loss of TGF-beta receptor type I mRNA, compared to low-passage cells, ranged from 55 to 87% in four HKc/HPV16 lines examined. Immunohistochemistry, using anti-TGF-beta receptor type I antibodies, confirmed a loss of TGF-beta receptor type I expression in HKc/DR. Reintroduction of the TGF-beta-receptor type I into TGF-beta-resistant HKc/DR completely restored growth inhibition by TGF-beta. Southern blot analysis of DNA extracted from normal HKc, HKc/HPV16, and HKc/DR ruled out any gross changes in the TGF-beta receptor type I gene. The activity of the TGF-beta receptor type I promoter, cloned upstream of a luciferase reporter gene, was decreased in HKc/DR, to an extent comparable to the decrease in mRNA levels for the TGF-beta receptor type I. Thus, TGF-beta resistance at late stages of HPV16-mediated transformation of HKc is the result of a loss of expression of TGF-beta receptor type I.

Transforming growth factor-beta and breast cancer: Transforming growth factor-beta/SMAD signaling defects and cancer

Transforming growth factor-beta (TGF-beta) is a tumor suppressor, the function of which is compromised in many types of human cancer, including breast cancer. The tumor suppressive effects of TGF-beta are caused by potent inhibition of cell proliferation due to cell cycle arrest in the G1 phase. Such antiproliferative responses are mediated by a signaling system that includes two types of cell surface receptors and intracellular signal transducers, the SMAD proteins. Different molecular mechanisms can lead to loss of antiproliferative TGF-beta responses in tumor cells, including mutations in components of the signaling system and inhibition of the SMAD signaling pathway by aberrant activities of various regulatory molecules. Some of these mechanisms will be discussed, with emphasis on their potential involvement in breast tumorigenesis.

TGF-beta and cancer

The relationships between transforming growth factor-beta (TGF-beta) and cancer are varied and complex. The paradigm that is emerging from the experimental evidence accumulated over the past decade or so is that TGF-beta can play two different and opposite roles with respect to the process of malignant progression. During early stages of carcinogenesis, TGF-beta acts predominantly as a potent tumor suppressor and may mediate the actions of chemopreventive agents such as retinoids and nonsteroidal anti-estrogens. However, at some point during the development and progression of malignant neoplasms, bioactive TGF-betas make their appearance in the tumor microenvironment and the tumor cells escape from TGF-beta-dependent growth arrest. In many cases, this resistance to TGF-beta is the consequence of loss or mutational inactivation of the genes that encode signaling intermediates. These include the types I and II TGF-beta receptors, as well as receptor-associated and common-mediator Smads. The stage of tumor development or progression at which TGF-beta-resistant clones come to dominate the tumor cell population in different types of neoplasm remains to be defined. The phenotypic switch from TGF-beta-sensitivity to TGF-beta-resistance that occurs during carcinogenesis has several important implications for cancer prevention and treatment.

Mutations in hMSH6 alone are not sufficient to cause the microsatellite instability in colorectal cancer cell lines

Microsatellite instability (MSI) at simple repeated sequences characterises a distinct mechanism of carcinogenesis in hereditary nonpolyposis colorectal cancer (HNPCC), as well as sporadic colorectal cancers displaying MSI. Such MSI is associated with mutations of hMSH2 and hMLH1, and somatic frameshift mutations in TGF-beta RII, IGFIIR, BAX, hMSH3 and hMSH6 at simple repeated sequences in coding regions. The aim of this study was to look for a correlation between mutations in mismatch repair genes and frameshift mutations in colorectal cancer cell lines with MSI. Using 22 colorectal cancer cell lines, we examined the MSI status at mononucleotide repeat microsatellite markers and mutations in hMSH2 and hMLH1, TGF-beta RII, IGFIIR, BAX, hMSH3 and hMSH6. Thirteen of 22 lines (59%) displayed MSI. In these 13 lines showing MSI, 10 lines (77%) had mutations in TGF-beta RII, nine lines (69%) in BAX, seven lines (54%) in hMSH6, and six lines (46%) in hMSH3, while mutations in the IGFIIR gene were identified in only two lines (15%). Of the 13 lines with MSI, six lines (46%) harboured mutations/deletions in hMSH2 (two nonsense mutations, three deletions and one no expression of transcripts) and three of these cell lines (50%) had mutations both in the hMSH2 and hMSH3 genes. Two cell lines (15%) had mutations/deletions in hMLH1 (one missense mutation and one deletion) and these two cell lines also had mutations in hMSH3. One line had a mutation in hMSH3 only, although this line showed MSI and had mutations in TGF-beta RII, IGFIIR and BAX. All lines with mutations in hMLH1, hMSH2, TGF-beta RII, IGFIIR, BAX and hMSH3 genes showed MSI. However, of the nine lines without MSI, two (22%) had homozygous mutations in hMSH6. In these two cell lines, no mutations were identified in hMLH1, hMSH2, TGF-beta RII, IGFIIR, BAX and hMSH3. Our results indicate that mutations in hMLH1, hMSH2 and hMSH3 are associated with MSI, but mutations in hMSH6 are not. We conclude that mutations in hMSH6 alone are not sufficient to cause MSI, although protein functional effects of these mutations should still be examined.

Inactivation of the transforming growth factor beta type II receptor in human small cell lung cancer cell lines

Transforming growth factor beta (TGF-beta) exerts a growth inhibitory effect on many cell types through binding to two types of receptors, the type I and II receptors. Resistance to TGF-beta due to lack of type II receptor (RII) has been described in some cancer types including small cell lung cancer (SCLC). The purpose of this study was to examine the cause of absent RII expression in SCLC cell lines. Northern blot analysis showed that RII RNA expression was very weak in 16 of 21 cell lines. To investigate if the absence of RII transcript was due to mutations, we screened the poly-A tract for mutations, but no mutations were detected. Additional screening for mutations of the RII gene revealed a GG to TT base substitution in one cell line, which did not express RII. This mutation generates a stop codon resulting in predicted synthesis of a truncated RII of 219 amino acids. The nature of the mutation, which has not previously been observed in RII, has been linked to exposure to benzo[a]-pyrene, a component of cigarette smoke. Since RII has been mapped to chromosome 3p22 and nearby loci are often hypermethylated in SCLC, it was examined whether the lack of RII expression was due to hypermethylation. Southern blot analysis of the RII promoter did not show altered methylation patterns. The restriction endonuclease pattern of the RII gene was altered in two SCLC cell lines when digested with Smal. However, treatment with 5-aza-2'-deoxycytidine did not induce expression of RII mRNA. Our results indicate that in SCLC lack of RII mRNA is not commonly due to mutations and inactivation of RII transcription was not due to hypermethylation of the RII promoter or gene. Thus, these data show that in most cases of the SCLC cell lines, the RII gene and promoter is intact in spite of absent RII expression. However, the nature of the mutation found could suggest that it was caused by cigarette smoking.

Frequent aberration of the transforming growth factor-beta receptor II gene in cell lines but no apparent mutation in pre-invasive and invasive carcinomas of the uterine cervix

The type II transforming growth factor-beta (TGF-beta) receptor (RII) gene located at 3p22 plays an important role in regulating growth and differentiation of epithelium, including that of the uterine cervix. Loss-of-function mutations of RII have frequently been found in gastrointestinal cancers, with a replication-error (RER) phenotype characterized by the presence of microsatellite instability (MI). In this study, genomic PCR, SSCP and DNA sequencing were conducted to investigate the coding sequences of the RII gene in cell lines (n = 5) and tissues (n = 15) of squamous carcinomas of the uterine cervix. Intragenic deletions were noted in 2 of 5 cervical-cancer cell lines (ME180 and HeLa cells). However, no mutation, other than DNA polymorphisms, was found in 15 cervical cancers with either alleleic loss at 3p22 (n = 11) or MI (n = 4). Further analysis of squamous intraepithelial lesions (SIL) with (n = 12) or without (n = 4) MI for the (A)10 change, a prototypic mutation found in over 90% of RER-positive colon cancers, also showed no aberration. Our study concludes that the RII gene is frequently disrupted in cervical-cancer cell lines, but is rarely mutated in CC and SIL tissues, including those showing MI or alleleic loss at 3p22. The underlined mechanism of genomic instability in CC and SIL may thus differ from that of colorectal cancer. The allelic loss at 3p22-24 in CC does not involve the coding sequence of the RII gene. The non-coding sequence of RII or an unidentified gene may be responsible for it.

No mutations of the Smad2 gene in human sporadic gastric carcinomas

BACKGROUND

The majority of cancer cells escape from TGF-beta-mediated growth control. However, the mechanism of resistance to the growth inhibitory effects by TGF-beta is not clear. TGF-beta signaling is initiated when the type I receptor phosphorylates the SMAD proteins, Smad2 and Smad3. Recently, mutations of Smad2 have been detected in human colon and lung cancers. Mutation of coding sequences of Smad2 in gastric carcinomas has not yet been elucidated adequately.

METHODS

PCR-SSCP analysis of the entire coding region of Smad2 in 35 human sporadic gastric cancers and eight gastric cancer cell lines was performed using 11 sets of intron-based primers.

RESULTS

No mutations of Smad2 were detected in any tumor or cell line.

CONCLUSIONS

The results suggest that mutation of Smad2 does not play a key role in human stomach carcinogenesis.

Genetic integrity of transforming growth factor beta (TGF-beta) receptors in cervical carcinoma cell lines: loss of growth sensitivity but conserved transcriptional response to TGF-beta

Transforming growth factor beta (TGF-beta) exerts an inhibitory effect on the growth of most epithelial cell types, and the loss of responsiveness to this growth inhibition has been implicated in the development of a variety of human cancers. The genetic alteration of TGF-beta receptors is known to play a critical role in this escape from growth regulation. We asked whether there is a correlation between TGF-beta sensitivity and the genetic status of TGF-beta type I and type II receptors (RI and RII, respectively) in human cervical carcinoma cell lines. Among 8 cell lines examined, 3 (ME-180, C-33A and HeLaS3) showed resistance to TGF-beta and 3 (SiHa, CaSki and HeLa229) showed minimal response to the growth inhibitory effect of TGF-beta; the other cell lines (HeLa and HT-3) were sensitive. Northern blot analysis revealed that the RII mRNA was not expressed in 2 TGF-beta-resistant cell lines (ME-180 and C-33A) but was expressed in the other cell lines. Southern blot analysis of RI and RII revealed a homozygous deletion of the entire TGF-beta RII gene in the cell line ME-180. We then asked whether the other TGF-beta-resistant or refractory cell lines had microsatellite instability and/or poly-adenine tract mutations of RII. We also checked for point mutations in the individual exons of the entire RII using polymerase chain reaction-single-strand conformational polymorphism (PCR-SSCP). Although C-33A exhibited poly-adenine microsatellite instability, its RII gene showed no signs of mutation. The molecular integrity of the TGF-beta, receptors in all cell lines, except ME-180 and C-33A, could be confirmed by examining the distinct transcriptional induction of plasminogen activator inhibitor-1 (PAI-1), p21(WAF1/CIP1) and, in some cases, the accompanying downregulation of c-myc in response to TGF-beta. Our observations, taken together, indicate that inactivation of the RII contributes to the resistance to TGF-beta of some cervical carcinoma cell lines. Loss of or attenuated sensitivity to TGF-beta growth inhibition in other cells may be attributed to the disruption of distal components in the TGF-beta signal pathway, but not to the receptor system.

High proliferative potential-quiescent cells: a working model to study primitive quiescent hematopoietic cells

Human adult hematopoietic stem cells are mostly quiescent or slow cycling. We have previously demonstrated that blocking of transforming growth factor-beta1 (TGF-beta1) is able to activate, in the presence of cytokines, primitive quiescent hematopoietic multipotent progenitors which could not grow in a two week semi-solid culture assay (short term culture). We have also shown that anti-TGF-beta1 can up-modulate c-KIT, the receptor of the stem cell factor (steel factor). To elucidate whether TGF-beta1 plays a central role in controlling the quiescence of hematopoietic primitive cells, it was necessary to demonstrate, as detailed in this study, that: (1) whatever the cytokine combination tested, addition of anti-TGF-beta1 releases from quiescence multipotent progenitors with a significantly higher hematopoietic potential than those activated by cytokines alone. (2) Other important cytokine receptors controlling the most primitive hematopoietic cells such as FLT3 and the IL6 receptor (IL6-R) are down-modulated by TGF-beta1 but rapidly up-modulated by anti-TGF-beta1. (3) Anti-TGF-beta1-sensitive multipotent and high proliferative potential progenitors express these cytokine receptors at a low level (FLT3(low) and IL6-Rlow). According to these results, we propose the working model of ‘High Proliferative Potential-Quiescent cells’ to refer to these primitive hematopoietic multipotent progenitors that are highly sensitive to the growth inhibitory effect of TGF-beta1. This model could be valid not only to study the human hematopoietic quiescent progenitors but also for other somatic stem cell systems.

Lack of transforming growth factor-beta type II receptor expression in human retinoblastoma cells

Retinoblastoma cells are resistant to transforming growth factor-beta (TGF-beta) activity due to the absence of TGF-beta binding. To further elucidate the mechanism of TGF-beta resistance, we studied the expression of the TGF-beta receptors and SMADs by using the Y79 and WERI-Rb-1 retinoblastoma cell lines. Binding of 125I-TGF-beta1 to serine/threonine kinase receptor type II (TbetaR-II) and TbetaR-I was not seen in the retinoblastoma cells. TbetaR-II mRNA was not expressed in these cells, but TbetaR-I mRNA was detected. Mutation analysis revealed no mutation in the coding region of the TbetaR-II gene, and TbetaR-II mRNA could be induced after the differentiation of Y79 cells. Smad2, Smad3, and Smad4, which are involved in TGF-beta signaling, were expressed in the retinoblastoma cells. Transcriptional activation of the TGF-beta-responsive genes was not seen by the transfection of either receptor cDNA alone but could be induced by transfection of both TbetaR-II and TbetaR-I. These data suggest that the defect in the TGF-beta response is caused by the lack of TbetaR-II in the retinoblastoma cells. In addition, TbetaR-I may be functionally inactivated in these cell lines.