ABSENCE OF EXPRESSION OF TRANSFORMING GROWTH FACTOR-beta TYPE II RECEPTOR IS ASSOCIATED WITH AN AGGRESSIVE GROWTH PATTERN IN A MURINE RENAL CARCINOMA CELL LINE, RENCA

Role of Tissue Transglutaminase Catalytic and Guanosine Triphosphate-Binding Domains in Renal Cell Carcinoma Progression

Tissue transglutaminase (TG2) is a multifunctional protein that can act as a cross-linking enzyme, GTPase/ATPase, protein kinase, and protein disulfide isomerase. TG2 is involved in cell adhesion, migration, invasion, and growth, as well as epithelial-mesenchymal transition (EMT). Our previous findings indicate that the increased expression of TG2 in renal cell carcinoma (RCC) results in tumor metastasis with a significant decrease in disease- and cancer-specific survival outcome. Given the importance of the prometastatic activity of TG2 in RCC, in the present study, we aim to investigate the relative contribution of TG2's transamidase and guanosine triphosphate (GTP)-binding/GTPase activity in the cell migration, invasion, EMT, and cancer stemness of RCC. For this purpose, the mouse RCC cell line RenCa was transduced with wild-type-TG2 (wt-TG2), GTP-binding deficient-form TG2-R580A, transamidase-deficient form with low GTP-binding affinity TG2-C277S, and transamidase-inactive form TG2-W241A. Our results suggested that predominantly, GTP-binding activity of TG2 is responsible for cell migration and invasion. In addition, CD marker analysis and spheroid assay confirmed that GTP binding/GTPase activity of TG2 is important in the maintenance of mesenchymal character and the cancer stem cell profile. These findings support a prometastatic role for TG2 in RCC that is dependent on the GTP binding/GTPase activity of the enzyme.

P44/WDR77 restricts the sensitivity of proliferating cells to TGFβ signaling

We previously reported that a novel WD-40 domain-containing protein, p44/WDR77, drives quiescent epithelial cells to re-enter the cell cycle and plays an essential role for growth of lung and prostate cancer cells. Transforming growth factor beta (TGFβ) signaling is important in the maintenance of non-transformed cells in the quiescent or slowly cycling stage. However, both non-transformed proliferating cells and human cancer cells are non-responsive to endogenous TGFβ signaling. The mechanism by which proliferating cells become refractory to TGFβ inhibition is not well established. Here, we found that silencing p44/WDR77 increased cellular sensitivity to TGFβ signaling and that this was inversely correlated with decreased cell proliferation. Smad2 or 3 phosphorylation, TGFβ-mediated transcription, and TGFβ2 and TGFβ receptor type II (TβRII) expression were dramatically induced by silencing of p44/WDR77. These data support the hypothesis that p44/WDR77 down-regulates the expression of the TGFβ ligand and its receptor, thereby leading to a cellular non-response to TGFβ signaling. Finally, we found that p44/WDR77 expression was correlated with cell proliferation and decreased TGFβ signaling during lung tumorigenesis. Together, these results suggest that p44/WDR77 expression causes the non-sensitivity of proliferating cells to TGFβ signaling, thereby contributing to cellular proliferation during lung tumorigenesis.

Treatment of transforming growth factor-beta-insensitive mouse Renca tumor by transforming growth factor-beta elimination

OBJECTIVES

The mouse renal cell carcinoma line, Renca, is insensitive to transforming growth factor-beta (TGF-beta) in vitro. The present study was conducted to determine whether removal of TGF-beta from these tumor cells would inhibit tumor progression in vivo.

METHODS

TGF-beta elimination was accomplished either by administration of neutralizing TGF-beta antibody into mice receiving intravenous injection of Renca tumor cells or infection of TGF-beta antisense expression vector into these tumor cells before subcutaneous injection into recipient mice.

RESULTS

Although a low dose of TGF-beta antibody (5 mg/kg every 3 days) was without any effect, a high dose of TGF-beta antibody (50 mg/kg every 3 days), administered to recipient mice, resulted in a significant reduction in lung metastasis and was accompanied by increased apoptosis in the tumor cells. When the tumor cells were transfected with a TGF-beta1 antisense expressing vector, a significant reduction occurred in the tumor incidence, as well as the tumor burden. However, in nude mice, cells with reduced TGF-beta1 production grew almost as well as did the unmodified Renca cells, suggesting that the host's immune system might play an antitumor role.

CONCLUSIONS

These results indicate that progression of Renca tumor can be inhibited by eliminating TGF-beta from the tumor cells. Our results also suggest that, although insensitive to TGF-beta under in vitro conditions, Renca tumors could be inhibited by TGF-beta removal through the systemic host environment.

Targeted therapy for renal cell carcinoma: a new therapeutic paradigm

Renal cell carcinoma is the most common tumor of the kidney. It has an unpredictable behavior and poor response to systemic therapy. Developing newer therapy for this disease is a priority considering the high recurrence rate and the small subset of patients who benefit from the use of cytokines such as interferon-alpha or interleukin-2. Identifying molecular targets and targeting various biomarkers has revolutionized the therapeutic approach to advanced and metastatic renal cell carcinoma. Although some of the antiangiogenic agents and receptor tyrosine kinase inhibitors appear promising, further understanding of their mechanism of action and the patient population who would benefit most from such agents is still being explored. As numerous targeted agents are entering the clinical investigation arena in a relatively short period of time, newer challenges in renal cell carcinoma therapeutics are emerging. Some of the future challenges in using targeted antineoplastic agents in renal cell carcinoma will include evaluating their long-term safety and benefit, using the particular drug in the appropriate patient population after appropriate stratification and studying the combination of some of these drugs for synergy or additive effects.

Molecular pathogenetics of renal cancer

Recent developments in genetics and molecular biology have led to an increased understanding of the pathobiology of renal cancer. Thorough knowledge of the molecular pathways associated with renal cancer is a prerequisite for novel potential therapeutic interventions. Studies are ongoing to evaluate novel anticancer agents that target specific molecular entities. This article reviews current knowledge on the genetics and molecular pathogenesis of sporadic and inherited forms of renal cancer.

Restoration of expression of transforming growth factor-beta type II receptor in murine renal cell carcinoma (renca) cells by 5-Aza-2'-deoxycytidine

The murine renal cell carcinoma (Renca) cells are insensitive to TGF-beta due to a lack of TGF-beta type II receptor (TbetaR-II). The objective of the present study is to determine the mechanism of this loss of sensitivity to TGF-beta in Renca cells. Renca cells were cultured and treated with 5-Aza-2'-Deoxycytidine (5-Aza), a specific inhibitor of methylation. Expression of TGF-beta type I receptor (TbetaRI) and TbetaRII was determined by RT-PCR and Western blot analysis before and after the treatment of Renca cells with 5-Aza. The expression of phosphorylated Smad2 (P-Smad2) was determined by Western blot analysis. TGF-beta levels in the conditioned medium were measured by ELISA. Renca cells did not express TbetaR-II prior to 5-Aza treatment. After 5-Aza treatment, these cells expressed TbetaR-II at both mRNA and protein levels, which corresponded to the restoration of sensitivity to TGF-beta by an increase in P-Smad2. Levels of TGF-beta1 were similar before and after 5-Aza treatment. Results of the present study indicated that, in Renca cells, the loss of sensitivity to TGF-beta is likely due to a promoter hypermethylation in the TbetaR-II gene.

An intronic variant of the TGFBR1 gene is associated with carcinomas of the kidney and bladder

TGF-beta signaling is frequently perturbed in many human cancers, including renal cell carcinomas (RCCs) and transitional cell carcinomas (TCCs) of the bladder. Genetic alterations of the TGF-beta type 1 receptor (TGFBR1) may contribute to these perturbations. We therefore examined variations in the TGFBR1 gene by PCR, SSCP and RFLP in carcinomas of the urinary system and in tissues from noncancer, age-matched controls. A G-->A variant 24 bp downstream of the exon/intron 7 boundary of the TGFBR1 gene (Int7G24A) was evident in patients with RCC (46.5%, n = 86) and bladder and upper urinary tract TCC (49.2%, n = 65) significantly more frequently than in age-matched controls (28.3%, n = 113, p < 0.002 by chi2 test). Moreover, 8 homozygous variant carriers were found in the cancer groups, whereas not a single homozygous variant carrier was found in the control group. The Int7G24A allele (both heterozygous G/A and homozygous A/A carriers) was associated with increased RCC incidence (OR = 2.20, 95% CI 1.22-3.96) and TCC incidence (OR = 2.45, 95% CI 1.89-3.16). One somatic mutation of serine to phenylalanine at codon 57 of the TGFBR1 gene was confirmed in an upper urinary tract TCC. In conclusion, the Int7G24A variant in the TGFBR1 gene is significantly more frequent in patients with RCC and TCC than normal age-matched controls, suggesting that it may represent a risk factor for the development of kidney and bladder carcinomas.

Expression of transforming growth factor beta in renal cell carcinoma and matched non-involved renal tissue

TGFbeta1 is one of several cytokines produced by proximal tubular and renal cancer cells. Previous studies have been mainly focused on determining plasma or serum TGFbeta levels, its effect on RCC cultures, and the expression of TGFbeta mRNA. Cancerous and autologous normal kidney samples were obtained from 24 patients treated by radical nephrectomy. TGFbeta1 expression was determined using a semi quantitative Western blot analysis and immunohistochemistry. Blot densities and immunohistochemical expression intensities in normal and neoplastic tissue were compared, and subsequently correlated to tumor stage, histological type and nuclear grade. All tissue samples examined expressed TGFbeta1; mean tumor to non-involved kidney spot density ratio correlated with advancing stage and higher nuclear grade. The overexpression of TGFbeta1 in certain RCCs may partially explain their resistance to the growth suppression action of TGFbeta. The correlation with tumor stage and grade indicates a possible role in the development of metastatic potential as well as in host's immune response modulation.

Genomic profiling identifies alterations in TGFbeta signaling through loss of TGFbeta receptor expression in human renal cell carcinogenesis and progression

Renal cell carcinoma (RCC) is a major health issue. Whereas localized disease can be cured surgically, there is no effective therapy for metastatic disease. The development of an effective therapy will require an understanding of the pathways that are important in RCC carcinogenesis and progression. Using genomic profiling of patient-matched tissue, we have identified aberrations in the transforming growth factor beta (TGFbeta) signaling pathway in RCC. We observed loss of type III TGFbeta receptor (TBR3) expression in all RCC samples. This suggests that TBR3 loss is an early event in RCC carcinogenesis and plays a sentinel role in the acquisition of a tumorigenic phenotype. We also observed subsequent loss of type II TGFbeta receptor (TBR2) expression in metastatic RCCs. We propose that loss of TBR3 is necessary for RCC carcinogenesis, and that loss of TBR2 leads to acquisition of a metastatic phenotype. To this end, we have identified a human renal cell carcinoma line (UMRC6) that is representative of localized, nonmetastatic RCC, reflecting a loss of TBR3, but not TBR2 expression. Another cell line, UMRC3, is highly metastatic, having lost TBR3 and TBR2 expression. We demonstrate functional loss of TGFbeta responsiveness in these cell lines as observed through phenotypic and transcriptional responsiveness to exogenous TGFbeta. Restoring TBR2 and TBR3 expression in UMRC3 cells attenuates cell proliferation, completely restores TGFbeta-mediated transcriptional responses, and completely blocks anchorage independent-growth: while restoration of TBR2 partially restores TGFbeta-mediated signaling. Based on these data, we propose that dysregulation in TGFbeta signaling, through stepwise loss in receptor expression, plays a prominent role in RCC carcinogenesis and progression. In addition, these studies unequivocably demonstrate a link between loss of TBR3 and a human disease.

Lefty inhibits receptor-regulated Smad phosphorylation induced by the activated transforming growth factor-beta receptor

Transforming growth factor-beta (TGF-beta) is a pleiotropic cytokine that regulates growth and differentiation of diverse types of cells. TGF-beta actions are directed by ligand-induced activation of TGF-beta receptors with intrinsic serine/threonine kinase activity that trigger phosphorylation of receptor-regulated Smad (R-Smad) protein. Phosphorylated R-Smad proteins bind to Smad4, and the complexes formed move into the nucleus, where they act as components of a transcriptional complex. Here, we show that TGF-beta signaling is inhibited by lefty, a novel member of the TGF-beta superfamily. Lefty perturbed TGF-beta signaling by inhibiting the phosphorylation of Smad2 following activation of the TGF-beta receptor. Moreover, lefty inhibited the events that lie downstream from R-Smad phosphorylation, including heterodimerization of R-Smad proteins with Smad4 and nuclear translocation of the R-Smad.Smad4 complex. Lefty repressed TGF-beta-induced expression of reporter genes for the p21, cdc25, and connective tissue growth factor promoters and of a reporter gene driven by the Smad-binding element. Similarly, lefty inhibited both BMP-mediated Smad5 phosphorylation and gene transcription. The action of lefty does not appear to depend on protein synthesis, including synthesis of inhibitory Smad proteins. Thus, lefty provides a repressed state of TGF-beta- or BMP-responsive genes and participates in negative modulation of TGF-beta and BMP signaling by inhibition of phosphorylation of R-Smad proteins.

Role of transforming growth factor beta in cancer

Transforming growth factor beta (TGF-beta) is an effective and ubiquitous mediator of cell growth. The significance of this cytokine in cancer susceptibility, cancer development and progression has become apparent over the past few years. TGF-beta plays various roles in the process of malignant progression. It is a potent inhibitor of normal stromal, hematopoietic, and epithelial cell growth. However, at some point during cancer development the majority of transformed cells become either partly or completely resistant to TGF-beta growth inhibition. There is growing evidence that in the later stages of cancer development TGF-beta is actively secreted by tumor cells and not merely acts as a bystander but rather contributes to cell growth, invasion, and metastasis and decreases host-tumor immune responses. Subtle alteration of TGF-beta signaling may also contribute to the development of cancer. These various effects are tissue and tumor dependent. Identifying and understanding TGF-beta signaling pathway abnormalities in various malignancies is a promising avenue of study that may yield new modalities to both prevent and treat cancer. The nature, prevalence, and significance of TGF-beta signaling pathway alterations in various forms of human cancer as well as potential preventive and therapeutic interventions are discussed in this review.

Captopril restores transforming growth factor-beta type II receptor and sensitivity to transforming growth factor-beta in murine renal cell cancer cells

PURPOSE

Captopril is known to inhibit the growth of renal cancer but the mechanism involved has been unclear. The current study elucidates the mechanism of captopril induced inhibition of the growth of the Renca mouse renal cancer cell line involving transforming growth factor-beta, which is known to be a growth inhibitory cytokine in epithelial cells and tissues.

MATERIALS AND METHODS

Transforming growth factor-beta in conditioned medium was measured by bioassay. Levels of transforming growth factor-beta and transforming growth factor-beta type II receptor expression messenger RNA were determined by reverse transcriptase-polymerase chain reaction and flow cytometry. Cell viability was determined by bromodeoxyuridine (BrdU) incorporation and tetrazolium bromide assay.

RESULTS

Captopril (0.01 to 1 mM.) showed no significant effect on transforming growth factor-beta synthesis or transforming growth factor-beta messenger RNA in Renca cells. On the other hand, 1 mM. captopril significantly inhibited Renca cell growth. Reverse transcriptase-polymerase chain reaction and flow cytometry showed that 1 mM. captopril up-regulated type II receptor expression.

CONCLUSIONS

These findings suggest that captopril restores transforming growth factor-beta type II receptor expression and inhibits the growth of Renca cells by increasing their sensitivity to transforming growth factor-beta.

Role of transforming growth factor beta in cancer

Transforming growth factor beta (TGF-beta) is an effective and ubiquitous mediator of cell growth. The significance of this cytokine in cancer susceptibility, cancer development and progression has become apparent over the past few years. TGF-beta plays various roles in the process of malignant progression. It is a potent inhibitor of normal stromal, hematopoietic, and epithelial cell growth. However, at some point during cancer development the majority of transformed cells become either partly or completely resistant to TGF-beta growth inhibition. There is growing evidence that in the later stages of cancer development TGF-beta is actively secreted by tumor cells and not merely acts as a bystander but rather contributes to cell growth, invasion, and metastasis and decreases host-tumor immune responses. Subtle alteration of TGF-beta signaling may also contribute to the development of cancer. These various effects are tissue and tumor dependent. Identifying and understanding TGF-beta signaling pathway abnormalities in various malignancies is a promising avenue of study that may yield new modalities to both prevent and treat cancer. The nature, prevalence, and significance of TGF-beta signaling pathway alterations in various forms of human cancer as well as potential preventive and therapeutic interventions are discussed in this review.

Generation of active TGF-beta by prostatic cell cocultures using novel basal and luminal prostatic epithelial cell lines

Two prostatic epithelial lines, one of basal origin and one of luminal origin, were established from the dorsolateral prostates of p53 null mice. The cell lines are nontumorigenic when inoculated subcutaneously under the renal capsule or intraprostatically in syngeneic mice. The luminal cell line (PE-L-1) expresses cytokeratins 8 and 18 and the basal cell line (PE-B-1) expresses cytokeratins 5 and 14. The basal cells require serum for growth, whereas the luminal cells grow only in serum-free medium. Both cell lines require the presence of growth factors for optimal growth in culture, with EGF and FGF-2 having the greatest effect on the growth rate. Both lines express androgen receptor (AR) mRNA and protein. Androgen stimulates growth of the basal cell line, indicating that the ARs are functional, whereas growth of the luminal cells is unaffected by androgens. The luminal line is significantly inhibited by exogenous TGF-beta and produces low levels of endogenous TGF-beta. In contrast, the basal cell line produces significant amounts of TGF-beta and its growth is not influenced by this cytokine. Coculture of luminal cells with prostatic smooth muscle cells results in the generation of increased levels of biologically active TGF-beta, indicating a paracrine mechanism of TGF-beta activation that may be involved in the maintenance of normal prostatic function. To our knowledge this is the first report describing both basal and luminal prostatic cell lines from a single inbred animal species and the first indication that prostatic epithelial and stromal cells interact to generate the biologically active form of TGF-beta. These lines will provide an important model for determining basal/luminal interactions in both in vitro and in vivo assays.

Transforming growth factor-beta type II receptor confers tumor suppressor activity in murine renal carcinoma (Renca) cells

OBJECTIVES

To demonstrate that the introduction of the transforming growth factor-beta (TGF-beta) type II receptor (TbetaR-II) decreases tumorigenicity in an aggressive murine renal carcinoma line, Renca. These cells do not express TbetaR-II. Because the presence of TbetaR-II in benign epithelial cells is ubiquitous, the ability to restore tumor suppressor activity in the Renca cell line with its introduction would elucidate the role of TbetaR-II as a tumor suppressor gene.

METHODS

Renca cells were stably transfected with a retrovirus-mediated TbetaR-II expression vector. In vitro sensitivity to growth inhibitory effect of TGF-beta was assessed by the 3H-thymidine incorporation assay. For in vivo testing, xenograft tumors were produced by subcutaneous injection of tumor cells into immunodeficient nude mice. The tumorigenicity of these TbetaR-II transfected cells was tested. Wild-type Renca cells and cells transfected with the control vector were also tested for comparison.

RESULTS

Expression of TbetaR-II mRNA was evident in Renca cells after transfection with the TbetaR-II construct. In vitro sensitivity to the growth inhibitory effect of TGF-beta was restored. This effect of TGF-beta was reversible with a neutralizing antibody specific for the extracellular domain of TbetaR-II. Xenografts grown from TbetaR-II transfected cells were significantly smaller, weighed less, and developed tumors later than those developed from wild-type Renca cells and those transfected with the control vector.

CONCLUSIONS

We conclude that TbetaR-II is a central mediator of tumorigenicity in Renca cells. As with other tumor suppressor genes, the loss of TbetaR-II expression allows for the development of an aggressive phenotype.