Lack of expression of transforming growth factor-beta type II receptor associated with malignant progression in human salivary gland cell clones

Relationship between major and minor salivary gland mucoepidermoid carcinoma malignancy grading and presence of stromal myofibroblasts: immunohistochemical study

OBJECTIVE

Mucoepidermoid carcinoma (MEC) is the most common malignant salivary tumour, classified as low, intermediate and high grade. Myofibroblasts are the main stromal component and are included as prognostic factor in some tumours. The aim of this study was to evaluate the myofibroblasts in the stroma of MEC with possible relationship to malignancy grading.

METHODS

Twenty-five cases of MEC (six low grade, 11 intermediate grade, four high grade and four metastasis) were stained for vimentin, desmin and smooth muscle actin (SMA) for the identification of myofibroblasts. Transforming growth factors (TGFbeta1 and TGFbetaRII) were also assessed in our study.

RESULTS

Myofibroblasts were present in all cases, in amounts varying according to histological grading. TGFbeta1 was positive in squamous cells of intermediate grade tumours, and in the stroma of only four cases. TGFbetaRII was positive in most squamous and intermediate cells, regardless of malignancy grading.

CONCLUSIONS

Our study showed that the analysis of neoplastic stroma must be added to the studies of neoplastic cells to draw a better picture leading to tumour diagnosis and prognosis.

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.

Sex hormone-induced mammary carcinogenesis in female Noble rats: expression of TGF-beta1 and its receptors, TGF-alpha, and EGF-R in mammary carcinogenesis

We have established a Noble rat model to explore the mechanisms of hormonal mammary carcinogenesis, in which the role of androgen in promoting mammary carcinogenesis was highlighted. We have also established that stromal-epithelial interactions may be responsible for the promotional effects of testosterone in mammary carcinogenesis. Based on these understandings, in the present study we examined the expression of transforming growth factor beta-1 (TGF-beta1) and its receptors (TGF-beta RI, TGF-beta RII), transforming growth factor alpha (TGF-alpha), and epidermal growth factor receptor (EGF-R) in 'pre-malignant' mammary glands treated with different protocols of sex hormones, as well as in mammary cancers. We observed that TGF-beta1 was strongly expressed in most mammary tumors, whereas TGF-beta RI and TGF-beta RII were negative in most mammary tumor cells. The results from comparative study of 'pre-malignant' glands further showed that when the animals were treated with testosterone, either alone or in combination with 17beta-estradiol, the mammary gland epithelial cells expressed high levels of TGF-beta1. This over-expression of TGF-beta1 can be blocked by flutamide, indicating that testosterone may be responsible for the expression of TGF-beta1 in mammary glands. TGF-beta RI and TGF-beta RII were also expressed strongly in testosterone-treated mammary epithelial cells and only weakly detectable in 17beta-estradiol treated and control mammary epithelial cells. Furthermore, TGF-beta RI and TGF-beta RII were also expressed in stromal cells, both in mammary tumors and in hormone-treated mammary glands. These observations indicate that the mechanism of testosterone in mammary carcinogenesis may be through its regulation of expression of TGF-beta1 and its receptors. On the other hand, TGF-alpha was also expressed in all 39 mammary cancers, while only 81% of the cancers were EGF-R positive. TGF-alpha was also strongly expressed in stromal cells in all three experimental groups, but only moderately expressed in epithelial cells when treated with a combination of testosterone and 17beta-estradiol. By contrast, EGF-R was strongly expressed in epithelial cells in the three experimental groups but negative in stromal cells. Flutamide or tamoxifen was unable to block the expression of TGF-alpha induced by the combined sex hormone treatment. However, they were effective in blocking the expression of TGF-alpha when the animals were treated with testosterone or 17beta-estradiol alone, respectively. These results suggest that both testosterone and 17beta-estradiol may be required for the over-expression of TGF-alpha in the mammary carcinogenesis induced by sex hormones. To our knowledge, this is the first experimental study to explore the regulation of TGF-beta1, TGF-alpha, and their receptors by testosterone and 17beta-estradiol in mammary carcinogenesis.

TGF-beta1 inhibits NF-kappaB activity through induction of IkappaB-alpha expression in human salivary gland cells: a possible mechanism of growth suppression by TGF-beta1

Transforming growth factor (TGF)-beta is the prototype of a large superfamily of signaling molecules involved in the inhibition of proliferation of multiple epithelial cell types. Although accumulated evidence indicates the mechanisms of the antimitogenic effect of TGF-beta in a variety of cell types, the signal transduction mechanism underlying the regulation of NF-kappaB transcription factor by TGF-beta is largely unknown. Because NF-kappaB is not only involved in inflammatory responses but also mediates cell growth, we have investigated the effect of TGF-beta1 on the activity of NF-kappaB and the role of the inhibitory IkappaB-alpha protein in the growth of the human salivary gland cell clones NS-SV-AC, HSGc, and cl-1. NF-kappaB, which is usually maintained in an inactive state by protein-protein interaction with IkappaB, was found to be constitutively active in salivary gland cell lines. Upon treatment of cell clones with TGF-beta1, the NF-kappaB activity in NS-SV-AC and HSGc, but not in cl-1, which lacks the expression of TGF-beta type II receptor, was suppressed. In NS-SV-AC and HSGc, this inhibition was mediated by the induction of IkappaB-alpha at the mRNA and protein levels. The blocking of NF-kappaB subunit with a specific antisense oligonucleotide reduced the growth rate of all of the cell clones, including cl-1. Introduction of a mutated form of IkappaB-alpha cDNA into NS-SV-AC suppressed the growth rate of this cell clone. These results indicate that TGF-beta1 downregulates NF-kappaB activity through the induction of IkappaB-alpha expression in human salivary gland cells and that inhibition of NF-kappaB activity suppresses the growth rate of these cells.

Expression of integrin subunits in normal and malignant human salivary gland cell clones and its regulation by transforming growth factor-beta 1

In this study, we have examined the expression of integrin subunits in normal and malignant human salivary gland cell clones as well as its regulation by transforming growth factor-beta 1 (TGF-beta 1). By the analysis using immunofluorescence staining, an SV40 immortalized normal human salivary gland duct cell clone (NS-SVDC) with no tumorigenic ability by s.c. implantation into nude mice was identified to express the integrin beta 1, alpha 2, alpha 3 and alpha 6 subunits on the cell surface, while the expression of these subunits, except for beta 1 subunit, was reduced or completely diminished in a neoplastic human salivary gland duct cell clone (HSGc) with tumorigenic but not metastatic potential in nude mice and metastatic cell clones derived after in vitro exposure of HSGc to N-methyl-N-nitrosourea. In addition, immunoblot analysis also exhibited the same results as those obtained with immunofluorescence staining. The alpha 1 subunit was not demonstrable in any of the cell clones by both techniques. TGF-beta 1 augmented the expression of the beta 1 subunit in NS-SV-DC, while HSGc and metastatic cell clones demonstrated no changes in the expression of the beta 1 subunit in response to TGF-beta 1. These findings, therefore, suggest that there is an inverse relationship between the malignancy and the expression mode of integrin subunits, especially alpha 2 subunit, in human salivary gland cell clones with varying degrees of malignant potential, and that TGF-beta 1 is a positive regulatory factor in the expression of the beta 1 subunit in normal but not malignant cell clones.