Decreased stability of transforming growth factor beta type II receptor mRNA in RER+ human colon carcinoma cells

Differential regulation and predictive potential of MacroH2A1 isoforms in colon cancer

Histone variant macroH2A1 has two splice isoforms, macroH2A1.1 and macroH2A1.2, with tissue- and cell-specific expression patterns. Although macroH2A1.1 is mainly found in differentiated, nonproliferative tissues, macroH2A1.2 is more generally expressed, including in tissues with ongoing cell proliferation. Consistently, studies in breast and lung cancer have demonstrated a strong correlation between macroH2A1.1 levels and proliferation, which is not the case for macroH2A1.2. This is the first study to assess the differential regulation and predictive potential of macroH2A1 isoforms in colon cancer. We found that macroH2A1.1 mRNA was down-regulated in primary colorectal cancer samples compared to matched normal colon tissue, whereas macroH2A1.2 was up-regulated. At the protein level, down-regulation of macroH2A1.1 correlated significantly with patient outcome (P = 0.0012), and loss of macroH2A1.1 was associated with a worse outcome. Over the course of Caco-2 cell differentiation, macroH2A1.1 was up-regulated at both the RNA and protein levels, whereas macroH2A1.2 was slightly down-regulated at the RNA level and stable at the protein level. These changes were accompanied by an antiproliferative phenotype exhibiting features of cellular senescence. Loss of macroH2A1.1 in vitro was characterized by a phenotype associated with cell growth and metastasis. These data demonstrate that macroH2A1 isoforms are differentially regulated in colon cancer, reflecting the degree of cellular differentiation. Notably, macroH2A1.1 expression predicts survival in colon cancer, thus identifying macroH2A1.1 as a novel colon cancer biomarker.

Restoration of transforming growth factor-beta receptor II expression in colon cancer cells with microsatellite instability increases metastatic potential in vivo

Microsatellite instability (MSI), which occurs in 15% of colorectal cancer, has been shown to have a lower incidence of metastasis and better patient survival rates compared with microsatellite stable colorectal cancer. However, a mechanistic understanding of the basis for this difference is very limited. Here, we show that restoration of TGFβ signaling by re-expression of TGFβ receptor II in MSI colon cancer cells increased PI3K/AKT activation, conferred resistance to growth factor deprivation stress-induced apoptosis, and promoted cell motility in vitro. Treatment with a potent PI3K inhibitor (LY294002) blocked the prosurvival and promotility effects of TGFβ, indicating that TGFβ-mediated promotion of cell survival and motility is dependent upon activation of the PI3K/AKT pathway. Analysis of apoptotic effectors that are affected by TGFβ signaling indicated that Bim is an effector of TGFβ-mediated survival. In addition, TGFβ-induced down-regulation of E-cadherin contributed to the prosurvival effect of TGFβ, and restoration of TGFβ signaling in MSI colon cancer cells increased liver metastasis in an orthotopic model in vivo. Taken together, our results demonstrate that restoration of TGFβ signaling promotes cell survival, motility, and metastatic progression in MSI colon cancer cells and indicate that TGFβ receptor II mutations contribute to the favorable outcomes in colon cancer patients with MSI.

Transforming growth factor beta1 signaling via interaction with cell surface Hyal-2 and recruitment of WWOX/WOX1

Transforming growth factor beta (TGF-beta) initiates multiple signal pathways and activates many downstream kinases. Here, we determined that TGF-beta1 bound cell surface hyaluronidase Hyal-2 on microvilli in type II TGF-beta receptor-deficient HCT116 cells, as determined by immunoelectron microscopy. This binding resulted in recruitment of proapoptotic WOX1 (also named WWOX or FOR) and formation of Hyal-2.WOX1 complexes for relocation to the nuclei. TGF-beta1 strengthened the binding of the catalytic domain of Hyal-2 with the N-terminal Tyr-33-phosphorylated WW domain of WOX1, as determined by time lapse fluorescence resonance energy transfer analysis in live cells, co-immunoprecipitation, and yeast two-hybrid domain/domain mapping. In promoter activation assay, ectopic WOX1 or Hyal-2 alone increased the promoter activity driven by Smad. In combination, WOX1 and Hyal-2 dramatically enhanced the promoter activation (8-9-fold increases), which subsequently led to cell death (>95% of promoter-activated cells). TGF-beta1 supports L929 fibroblast growth. In contrast, transiently overexpressed WOX1 and Hyal-2 sensitized L929 to TGF-beta1-induced apoptosis. Together, TGF-beta1 invokes a novel signaling by engaging cell surface Hyal-2 and recruiting WOX1 for regulating the activation of Smad-driven promoter, thereby controlling cell growth and death.

Transforming growth factor beta induces apoptosis through repressing the phosphoinositide 3-kinase/AKT/survivin pathway in colon cancer cells

FET cells, derived from an early-stage colon carcinoma, are nontumorigenic in athymic mice. Stable transfection of a dominant-negative transforming growth factor beta (TGFbeta) type II receptor (DNRII) into FET cells that express autocrine TGFbeta shows loss of TGFbeta signaling and increased tumorigenicity in vivo indicating tumor suppressor activity of TGFbeta signaling in this model. The ability of tumorigenic cells to withstand growth factor and nutrient deprivation stress (GFDS) is widely regarded as a key attribute for tumor formation and progression. We hypothesized that increased tumorigenicity of FET/DNRII cells was due to loss of participation of autocrine TGFbeta in a "fail-safe" mechanism to generate cell death in response to this stress. Here, we document that loss of autocrine TGFbeta in FET/DNRII cells resulted in greater endogenous cell survival in response to GFDS due to activation of the phosphoinositide 3-kinase (PI3K)/Akt/survivin pathway. Treatment of FET DNRII cells with a PI3K inhibitor (LY294002) inhibited Akt phosphorylation and reduced survivin expression resulting in increased apoptosis in FET/DNRII cells. We also show that exogenous TGFbeta increased apoptosis in FET cells through repression of the PI3K/Akt/survivin pathway during GFDS. These results indicate that the PI3K/Akt/survivin pathway is blocked by TGFbeta signaling and that loss of autocrine TGFbeta leads to increased cell survival during GFDS through the novel linkage of TGFbeta-mediated repression of survivin expression. Inhibition of survivin function by dominant-negative approaches showed that this inhibitor of apoptosis family member is critical to cell survival in the FET/DNRII cells, thus indicating the importance of this target for TGFbeta-mediated apoptosis.

Deletion of Tgfbr2 in Prx1-cre expressing mesenchyme results in defects in development of the long bones and joints

In this study, we address the function of Transforming Growth Factor beta (TGF-beta) and its type II receptor (Tgfbr2) in limb development in vivo. Mouse embryos were generated in which the Tgfbr2 gene was deleted in early limb mesenchyme using Prx1Cre-mediated LoxP recombination. A high level of Tgfbr2 gene deletion was verified in limb mesenchyme by PCR between E9.5 and E10.5 days in Cre expressing mice. RT-PCR assays indicated a significant depletion of Tgfbr2 mRNA by E10.5 days as a result of Cre mediated gene deletion. Furthermore, limb mesenchyme from Cre(+);Tgfbr2(f/f) mice placed in micromass culture did not respond to exogenously added TGF-beta1 confirming the functional deletion of the receptor. However, there was an unexpected increase in the number and intensity of Alcian blue stained chondrogenic nodules in micromass cultures derived from Tgfbr2-deleted limbs relative to cultures from control limbs suggesting that Tgfbr2 normally limits chondrogenesis in vitro. In vivo, early limb development and chondrocyte differentiation occurred normally in Tgfbr2-depleted mice. Later in development, depletion of Tgfbr2 in limb mesenchyme resulted in short limbs and fusion of the joints in the phalanges. Alteration in the length of the long bones was primarily due to a decrease in chondrocyte proliferation after E13.5 days. In addition, the transition from prehypertrophic to hypertrophic cells was accelerated while there was a delay in late hypertrophic differentiation leading to a reduction in the length of the marrow cavity. In the joint, cartilage cells replaced interzone cells during development. Analysis of markers for joint development indicated that the joint was specified properly and that the interzone cells were initially formed but not maintained. The results suggest that Tgfbr2 is required for normal development of the skeleton and that Tgfbr2 can act to limit chondrogenesis in mesenchymal cells like the interzone.

Loss of functional transforming growth factor (TGF)-beta type II receptor results in insensitivity to TGF-beta1-mediated apoptosis and Epstein-Barr virus reactivation

Transforming growth factor (TGF)-beta1 induces not only cell growth inhibition or apoptosis but also Epstein-Barr virus (EBV) reactivation in some Burkitt's lymphoma (BL) cell lines. The purpose of this study was to define the role of TGF-beta signaling molecules in response to TGF-beta1-mediated cell growth inhibition, apoptosis, and EBV reactivation in BL cell lines. First, we confirmed the effect of TGF-beta1 on the cell growth and EBV reactivation in six BL cell lines. TGF-beta1 induced cell growth inhibition and EBV reactivation in these cell lines but did not in Akata cells. To elucidate the mechanism of TGF-beta1 unresponsiveness in Akata cells, we studied the expression of TGF-beta receptors and the intracellular signaling molecules Smads. All cell lines expressed TGF-beta type I receptor, Smad2, Smad3, and Smad4. TGF-beta type II receptor (R-II) was expressed in all cell lines except Akata cells. Introduction of the TGF-beta R-II into Akata cells results in sensitivity to TGF-beta1-mediated growth inhibition, apoptosis, and EBV reactivation. In addition, to test a possibility to the transcriptional repression of the TGF-beta R-II gene in Akata cells, the effect of histone deacetylation (HDAC) inhibitor, trichostatin A (TSA) was examined. The expression of TGF-beta R-II in Akata cells was induced by TSA treatment. These results suggest that the lack of functional TGF-beta R-II impedes the progression of signals through TGF-beta1 and becomes a determinant of unresponsiveness to TGF-beta1-mediated growth inhibition and EBV reactivation.

Aberrant expression and mutations of TGF-beta receptor type II gene in endometrial cancer

OBJECTIVE

Transforming growth factor beta (TGF-beta) is a multifunctional cytokine that strongly inhibits epithelial cell growth. Disabling of TGF-beta signaling is thought to be involved in development of a variety of tumors in which abnormal expression or function of TGF-beta receptor plays critical roles. In the present study, we examined aberrant expression and mutation of the gene TGF-beta receptor type II (TbetaRII) in endometrial cancers of endometrioid subtype.

METHODS AND RESULTS

Real-time PCR analysis using surgical tissue specimens of 27 endometrial cancers and 24 normal endometria revealed that endometrial cancers had significantly decreased levels of TbetaRII mRNA expression (mean level 2.44 +/- 2.65), compared to normal endometria (mean level 7.23 +/- 6.07) (P < 0.001). Methylation status of TbetaRII promoter containing 30 CpGs was examined by bisulfite sequencing analysis, and 98% (51/52) of the patients were found to have unmethylated TbetaRII promoter, indicating that promoter hypermethylation is not the major cause of decreased expression of TbetaRII in endometrial cancers. Mutational analysis revealed that 15.1% (8/53) of endometrial cancers had frameshift mutations at polyadenine repeats in exon 3 of the TbetaRII gene. Notably, these mutations were preferentially accumulated in patients with MSI-H phenotype (7/19:37%) (P < 0.001) or with those with methylated MLH1 promoters (6/16:38%) (P < 0.01). Thus, it appears that the TbetaRII gene is a target of mismatch repair deficiency.

CONCLUSION

Taken together, we found that the decreased expression of TbetaRII as well as frameshift mutation of TbetaRII via mismatch repair deficiency frequently occurs in this tumor type, possibly causing loss of receptor function and unresponsiveness of TGF-beta signaling that may lead to endometrial carcinogenesis.

Manipulation of nonsense mediated decay identifies gene mutations in colon cancer Cells with microsatellite instability

Cancer cells showing microsatellite instability (MSI) demonstrate a high frequency of acquired frameshift mutations that result in the generation of nonsense mutations. RNA transcripts carrying these nonsense mutations are usually targeted for degradation through the nonsense mediated decay (NMD) pathway. Blocking this pathway with drugs such as emitine, results in the 'stabilization' of these mutant transcripts, which can now be detected on cDNA arrays. Unfortunately, emetine also induces a stress response that results in upregulation of additional transcripts which contribute to the analysis of the array. As a result, identifying which genes truly carry nonsense mutations is made more difficult. To overcome this, we have combined the emetine treatment with actinomycin D, which effectively prevents the upregulation of stress response genes while still stabilizing mutant transcripts. When we applied this modified approach to the analysis of MSI-positive colon cancer cells, we identified mutations in the UVRAG and p300 genes.

Transforming growth factor beta1 receptor II is downregulated by E1A in adenovirus-infected cells

Transforming growth factor beta1 (TGF-beta1) signaling is compromised in many tumors, thereby allowing the tumor to escape the growth-inhibitory and proapoptotic activities of the cytokine. Human adenoviruses interfere with a number of cellular pathways involved in cell cycle regulation and apoptosis, initially placing the cell in a "tumor-like" state by forcing quiescent cells into the cell cycle and also inhibiting apoptosis. We report that adenovirus-infected cells resemble tumor cells in that TGF-beta1 signaling is inhibited. The levels of TGF-beta1 receptor II (TbetaRII) in adenovirus-infected cells were decreased, and this decrease was mapped, by using virus mutants, to the E1A gene and to amino acids 2 to 36 and the C-terminal binding protein binding site in the E1A protein. The decrease in the TbetaRII protein was accompanied by a decrease in TbetaRII mRNA. The decrease in TbetaRII protein levels in adenovirus-infected cells was greater than the decrease in TbetaRII mRNA, suggesting that downregulation of the TbetaRII protein may occur through more than one mechanism. Surprisingly in this context, the half-lives of the TbetaRII protein in infected and uninfected cells were similar. TGF-beta1 signaling was compromised in cells infected with wild-type adenovirus, as measured with 3TP-lux, a TGF-beta-sensitive reporter plasmid expressing luciferase. Adenovirus mutants deficient in TbetaRII downregulation did not inhibit TGF-beta1 signaling. TGF-beta1 pretreatment reduced the relative abundance of adenovirus structural proteins in infected cells, an effect that was potentiated when cells were infected with mutants incapable of modulating the TGF-beta signaling pathway. These results raise the possibility that inhibition of TGF-beta signaling by E1A is a means by which adenovirus counters the antiviral defenses of the host.

Loss of Smad signaling in human colorectal cancer is associated with advanced disease and poor prognosis

PURPOSE

Based largely on in vitro investigations and animal studies, investigators believe that disruptions of transforming growth factor-beta (TGF-beta) signaling contribute to the development and progression of human colorectal cancer. The purpose of this study was to directly assess the status of the TGF-beta signaling pathway in colorectal cancer and determine the effects of its disruption on clinical behavior and outcome.

MATERIALS AND METHODS

Smad proteins are the principal intracellular components of the TGF-beta signaling pathway. We conducted a high-throughput analysis of the expression patterns of Smad2, phosphorylated (activated) Smad2 (pSmad2), and Smad4 in more than 600 human colorectal cancer specimens assembled in tissue microarrays.

RESULTS

The vast majority (93.8%; 95% CI: 92%-96%) of colorectal cancers expressed phosphorylated Smad2, indicating the ability of the tumors to survive and proliferate within a microenvironment that contains bioactive TGF-beta. Twelve of 633 (1.9%; 95% CI: 1%-3%) cases failed to express Smad2, and 15 of 641 (2.3%; 95% CI: 1%-4%) cases failed to express Smad4. Moreover, 29 of 615 (4.7%; 95% CI: 3%-7%) of cases expressed Smad2 but not its activated form (pSmad2), suggesting the presence of a TGF-beta receptor defect. Based on an analysis of 577 cases for which clinical outcome information was available, failure to express Smad2, pSmad2, or Smad4 was associated with advanced-stage disease, the presence of lymph node metastases, and a significantly shorter overall survival (median survival: 35 vs 58 months).

DISCUSSION

Loss of Smad activation and/or expression occurs in approximately 10% of colorectal cancers. This subset has a poor prognosis because of its association with advanced disease and the presence of lymph node metastases at diagnosis.

Autocrine TGFbeta signaling mediates vitamin D3 analog-induced growth inhibition in breast cells

In this study, we address whether TGFbeta signaling mediates vitamin D3 analog-induced growth inhibition in nonmalignant and malignant breast cells. Normal mammary epithelial cells (184), immortalized nonmalignant mammary epithelial cells (184A1 and MCF10A), and breast cancer cells (early passage MCF7: MCF7E) were sensitive to the inhibitory effects of vitamin D3 analogs (EB1089 and MC1288) while late passage MCF7 breast cancer (MCF7L) cells were relatively resistant. A similar pattern of sensitivity to TGFbeta was observed with these cells. Thus, the sensitivity to the vitamin D3 analogs correlated with the sensitivity to TGFbeta. MCF7L TGFbetaRII-transfected cells, which have autocrine TGFbeta activity, were more sensitive to EB1089 than MCF7L cells. TGFbeta neutralizing antibody was found to block the inhibitory effects of these analogs. These results are consistent with the idea that autocrine TGFbeta signaling mediates the anti-proliferative effects of the vitamin D3 analogs in these cells. The expression of TGFbeta isoforms and/or TGFbeta receptors was induced by the analogs in the vitamin D3 and TGFbeta sensitive cells. Vitamin D3 analogs did not induce TGFbeta or TGFbeta receptor expression in the resistant MCF7L cells. Therefore, EB1089 induces autocrine TGFbeta activity through increasing expression of TGFbeta isoforms and/or TGFbeta receptors. In addition, EB1089 induced nuclear VDR protein levels in the sensitive 184A1 cells but not in the resistant MCF7L cells. 184A1 cells were more sensitive to EB1089-induced VDR-dependent transactivation than MCF7L cells as measured by a luciferase reporter construct containing the VDRE, indicating a defect of VDR signaling in MCF7L cells. Smad3, a TGFbeta signaling mediator, coactivated VDR-dependent transactivation in 184A1 cells but not in MCF7L cells. These results indicate that Smad3 coactivates VDR to further enhance TGFbeta signaling and vitamin D3 signaling in the sensitive 184A1 cells. The results also indicate that Smad3 is not of itself sufficient to coactivate VDR in TGFbeta/vitamin D3 resistant MCF7L cells and other factors are required. We found that the PI 3-kinase pathway inhibitor LY29004 inhibited the synergy of TGFbeta and EB1089 on VDR-dependent transactivation activity. This indicates that the crosstalk between TGFbeta and vitamin D signaling is also PI 3-kinase pathway dependent.

Frameshift peptide-derived T-cell epitopes: a source of novel tumor-specific antigens

Microsatellite instability (MSI) caused by defective DNA mismatch repair (MMR) is a hallmark of hereditary nonpolyposis colorectal cancers (HNPCC) but also occurs in about 15% of sporadic tumors. If instability affects microsatellites in coding regions, translational frameshifts lead to truncated proteins often marked by unique frameshift peptide sequences at their C-terminus. Since MSI tumors show enhanced lymphocytic infiltration and our previous analysis identified numerous coding mono- and dinucleotide repeat-bearing candidate genes as targets of genetic instability, we examined the role of frameshift peptides in triggering cellular immune responses. Using peptide pulsed autologous CD40-activated B cells, we have generated cytotoxic T lymphocytes (CTL) that specifically recognize HLA-A2.1-restricted peptides derived from frameshift sequences. Among 16 frameshift peptides predicted from mutations in 8 different genes, 3 peptides conferred specific lysis of target cells exogenously loaded with cognate peptide. One peptide derived from a (-1) frameshift mutation in the TGFbetaIIR gene gave rise to a CTL bulk culture capable of lysing the MSI colorectal cancer cell line HCT116 carrying this frameshift mutation. Given the huge number of human coding microsatellites and assuming only a fraction being mutated and encoding immunologically relevant peptides in MSI tumors, frameshift protein sequences represent a novel subclass of tumor-specific antigens. It is tempting to speculate that a frameshift peptide-directed vaccination approach not only could offer new treatment modalities for existing MSI tumors but also might benefit asymptomatic at-risk individuals in HNPCC families by a prophylactic vaccination strategy.

Resistance to TGF-beta1 correlates with a reduction of TGF-beta type II receptor expression in Burkitt's lymphoma and Epstein-Barr virus-transformed B lymphoblastoid cell lines

The pleiotropic cytokine TGF-beta1 is a member of a large family of related factors involved in controlling cell proliferation, differentiation and apoptosis. TGF-beta ligands interact with a complex of type I and type II transmembrane serine/threonine kinases and they transmit their signals to the nucleus via a family of Smad proteins. A panel of over 20 Burkitt's lymphoma (BL) cell lines has been compiled including those that are Epstein-Barr virus (EBV) negative, those that carry EBV with a restricted pattern of EBV latent gene expression (group I) and those that express the full range of latent EBV genes (group III), together with selected EBV-transformed lymphoblastoid cell lines (LCLs). Most of the EBV-negative and group I BL cell lines underwent apoptosis or a G(1) arrest in response to TGF-beta1 treatment. In contrast, group III cell lines and LCLs were completely refractory to these effects of TGF-beta1. All of the cell lines expressed the TGF-beta pathway Smads and the TGF-beta type I receptor. Lack of responsiveness to TGF-beta1 appears to correlate with a down-regulation of TGF-beta type II receptor expression. Studies of EBV-converted and stably transfected BL cell lines demonstrated that the EBV gene LMP-1 is neither necessary nor sufficient to block the TGF-beta1 response.

The role of Sp1 in the differential expression of transforming growth factor-beta receptor type II in human breast adenocarcinoma MCF-7 cells

Progression of MCF-7 cells from early passage (MCF-7E, <200 passage) to late passage (MCF-7L, >500 passage) correlates with a loss of sensitivity to exogenous TGFbeta1. We have previously shown that loss of TGFbeta sensitivity is due to decreased expression of the transforming growth factor receptor type II (TbetaRII) and is associated with increased tumorigenicity in nude mice. Reduced TbetaRII expression in MCF-7L cells is caused by decreased TbetaRII promoter activity in this cell line. Our previous studies using 5' deletion constructs of this promoter revealed that MCF-7L cells were unable to support transcription of the minimal promoter (-47 to +2) to the same levels as the MCF-7E cells. This region of the promoter contains an Sp1 element at position -25 from the major transcription start site. In this study, we investigated the role of Sp1 in TbetaRII transcription. Mutation of the Sp1 site resulted in decreased transcription of TbetaRII in MCF-7E and MCF-7L cells, indicating that this site played a role in transcription of this promoter. Gel shift assays using the proximal Sp1 site from the TbetaRII promoter showed enhanced DNA:protein complex formation with nuclear proteins isolated from MCF-7E cells compared with MCF-7L cells. Supershift analysis identified this binding activity as Sp1. Western blot analysis of Sp1 levels demonstrated that MCF-7E cells contain increased Sp1 protein compared with MCF-7L cells, paralleling the increased binding activity. Differential Sp1 activity was also demonstrated by higher levels of transcription of an Sp1-dependent insulin-like growth factor II promoter construct in MCF-7E cells compared with MCF-7L cells. Co-transfection of an Sp1 expression vector with a TbetaRII promoter construct in MCF-7L cells induced the expression from the promoter-CAT constructs and resulted in an increase of endogenous TbetaRII protein levels. These results demonstrate that the transcriptional repression of TbetaRII in MCF-7L cells is caused, in part, by lower Sp1 levels.

Elevated serum levels of transforming growth factor-beta1 in patients with colorectal carcinoma: its association with tumor progression and its significant decrease after curative surgical resection

BACKGROUND

Transforming growth factor-beta1 (TGF-beta1) acts as a potent inhibitor of cell growth and tumor progression but loss of this negative regulation can contribute to tumor development. Some studies have reported an association between disease progression and TGF-beta1 expression in patients with colorectal carcinoma, but their results were not always consistent.

METHODS

Serum levels of TGF-beta1 were measured using an enzyme-linked immunoadsorbent assay in 121 consecutive patients with colorectal carcinoma and compared with TGF-beta1 serum levels in 31 healthy volunteers. Serum levels of TGF-beta1 also were measured in 50 patients who underwent curative surgical resection (part of the 121 preoperative patients) to compare their levels with preoperative serum levels of TGF-beta1.

RESULTS

Serum levels of TGF-beta1 in patients with colorectal carcinoma (45+/-15 ng/mL) (mean+/-the standard deviation) were significantly higher than those in the healthy control group (32+/-4 ng/mL) (P = 0.001). Serum levels of TGF-beta1 increased with increasing tumor stage (P < 0.01). Serum levels of TGF-beta1 were correlated significantly with depth of tumor invasion, lymph node metastasis, distant metastasis, and serum levels of carcinoembryonic antigen (CEA). Serum levels of TGF-beta1 tended to increase with increasing CEA (correlation coefficient = 0.21; P < 0.05). The mean serum level of TGF-beta1 in patients with colorectal carcinoma before surgery (45+/-14 ng/mL) (n = 50) significantly decreased to 34+/-7 ng/mL, which was within the normal range (32+/-4 ng/mL), after curative surgical resection of the tumor (P = 0.0000). Serum levels of TGF-beta1 after tumor resection decreased more significantly in patients with higher preoperative levels of TGF-beta1 (from 53+/-12 ng/mL to 36+/-6 ng/mL) (n = 30).

CONCLUSIONS

The results of the current study suggest that serum levels of TGF-beta1 in colorectal carcinoma patients may be associated with disease progression and may be used as a biomarker in the management of colorectal carcinoma patients. The authors believe further studies with a large number of patients for a longer follow-up period are necessary to conclude whether serum levels of TGF-beta1 carry significant clinical relevance.

Elevated serum levels of transforming growth factor-beta1 in patients with colorectal carcinoma: its association with tumor progression and its significant decrease after curative surgical resection

BACKGROUND

Transforming growth factor-beta1 (TGF-beta1) acts as a potent inhibitor of cell growth and tumor progression but loss of this negative regulation can contribute to tumor development. Some studies have reported an association between disease progression and TGF-beta1 expression in patients with colorectal carcinoma, but their results were not always consistent.

METHODS

Serum levels of TGF-beta1 were measured using an enzyme-linked immunoadsorbent assay in 121 consecutive patients with colorectal carcinoma and compared with TGF-beta1 serum levels in 31 healthy volunteers. Serum levels of TGF-beta1 also were measured in 50 patients who underwent curative surgical resection (part of the 121 preoperative patients) to compare their levels with preoperative serum levels of TGF-beta1.

RESULTS

Serum levels of TGF-beta1 in patients with colorectal carcinoma (45+/-15 ng/mL) (mean+/-the standard deviation) were significantly higher than those in the healthy control group (32+/-4 ng/mL) (P = 0.001). Serum levels of TGF-beta1 increased with increasing tumor stage (P < 0.01). Serum levels of TGF-beta1 were correlated significantly with depth of tumor invasion, lymph node metastasis, distant metastasis, and serum levels of carcinoembryonic antigen (CEA). Serum levels of TGF-beta1 tended to increase with increasing CEA (correlation coefficient = 0.21; P < 0.05). The mean serum level of TGF-beta1 in patients with colorectal carcinoma before surgery (45+/-14 ng/mL) (n = 50) significantly decreased to 34+/-7 ng/mL, which was within the normal range (32+/-4 ng/mL), after curative surgical resection of the tumor (P = 0.0000). Serum levels of TGF-beta1 after tumor resection decreased more significantly in patients with higher preoperative levels of TGF-beta1 (from 53+/-12 ng/mL to 36+/-6 ng/mL) (n = 30).

CONCLUSIONS

The results of the current study suggest that serum levels of TGF-beta1 in colorectal carcinoma patients may be associated with disease progression and may be used as a biomarker in the management of colorectal carcinoma patients. The authors believe further studies with a large number of patients for a longer follow-up period are necessary to conclude whether serum levels of TGF-beta1 carry significant clinical relevance.

The molecular basis of colorectal carcinogenesis

The development of colorectal neoplasms can be characterized by an ordered series of events that are referred to as the dysplasia-carcinoma sequence. These histologic changes occur as a result of genetic alterations in proto-oncogenes and tumor-suppressor genes. This review emphasizes important studies characterizing the role of four genes, APC, Cox-2, DCC/Smad4, and the mismatch repair genes, in colorectal carcinogenesis.

Accumulated clonal genetic alterations in familial and sporadic colorectal carcinomas with widespread instability in microsatellite sequences

A subset of hereditary and sporadic colorectal carcinomas is defined by microsatellite instability (MSI), but the spectra of gene mutations have not been characterized extensively. Thirty-nine hereditary nonpolyposis colorectal cancer syndrome carcinomas (HNPCCa) and 57 sporadic right-sided colonic carcinomas (SRSCCa) were evaluated. Of HNPCCa, 95% (37/39) were MSI-positive as contrasted with 31% (18/57) of SRSCCa (P < 0.000001), but instability tended to be more widespread in SRSCCa (P = 0.08). Absence of nuclear hMSH2 mismatch repair gene product by immunohistochemistry was associated with germline hMSH2 mutation (P = 0.0007). The prevalence of K-ras proto-oncogene mutations was similar in HNPCCa and SRSCCa (30% (11/37) and 30% (16/54)), but no HNPCCa from patients with germline hMSH2 mutation had codon 13 mutation (P = 0.02), and two other HNPCCa had multiple K-ras mutations attributable to subclones. 18q allelic deletion and p53 gene product overexpression were inversely related to MSI (P = 0.0004 and P = 0.0001, respectively). Frameshift mutation of the transforming growth factor beta type II receptor gene was frequent in all MSI-positive cancers (85%, 46/54), but mutation of the E2F-4 transcription factor gene was more common in HNPCCa of patients with germline hMSH2 mutation than in those with germline bMLH1 mutation (100% (8/8) versus 40% (2/5), P = 0.04), and mutation of the Bax proapoptotic gene was more frequent in HNPCCa than in MSI-positive SRSCCa (55% (17/31) versus 13% (2/15), P = 0.01). The most common combination of mutations occurred in only 23% (8/35) of evaluable MSI-positive cancers. Our findings suggest that the accumulation of specific genetic alterations in MSI-positive colorectal cancers is markedly heterogeneous, because the occurrence of some mutations (eg, ras, E2F-4, and Bax genes), but not others (eg, transforming growth factor beta type II receptor gene), depends on the underlying basis of the mismatch repair deficiency. This genetic heterogeneity may contribute to the heterogeneous clinical and pathological features of MSI-positive cancers.