Anna Coppa

Transforming growth factor-β1 enhances the invasiveness of human MDA-MB-231 breast cancer cells by up-regulating urokinase activity

Transforming growth factor‐beta (TGFβ1) enhances human MDA‐MB‐231 breast tumour cell invasion of reconstituted basement membrane in vitro but does not inhibit proliferation of this cell line. In contrast to basal invasion, which is plasmin‐, urokinase (uPA)‐, tissue‐type plasminogen activator (t‐PA)‐, matrix metalloproteinase (MMP)‐9‐ and TIMP‐1‐inhibitable MMP‐dependent, TGFβ1 enhanced‐invasion is dependent upon plasmin and uPA activity but does not appear to involve t‐PA‐, MMP9‐ or TIMP‐1‐inhibitable MMPs, as judged by inhibitor studies. Enhanced invasion is associated with increased u‐PA, UPAR, PAI‐1, MT‐MMP‐1, MMP‐9 and TIMP‐1 expression; with reduced t‐PA, MMP‐1 and MMP‐3 expression; and with the induction of membrane MMP‐9 association. The net result of these changes includes increased secreted, but not membrane‐associated, uPA levels and activity and reduced secreted levels of plasmin and APMA‐activatable gelatinolytic, collagenolytic and caseinolytic MMP activity but no change in membrane‐associated gelatinolytic activity, despite increased MT‐MMP‐1 expression and MMP‐9 membrane association. TGFβ1 does not induce MMP‐2 expression. Our data indicate that TGFβ1 can promote the malignant behaviour of MDA‐MB‐231 cells refractory to TGFβ1‐mediated proliferation control by enhancing their invasive capacity. We suggest that this results from the action of a uPA/plasmin‐dependent mechanism resulting from stimulation of uPA expression, secretion and subsequent activity, despite elevated PAI‐1 inhibitor levels. Int. J. Cancer 75:721–730, 1998.© 1998 Wiley‐Liss, Inc.

The p85 regulatory subunit of PI3K mediates TSH-cAMP-PKA growth and survival signals

Phosphatidylinositol 3-kinase (PI3K) is necessary for thyroid stimulating hormone (TSH)-induced cell cycle progression. To determine the molecular mechanism linking PI3K to TSH, we have identified a serine residue in p85αPI3K phosphorylated by protein kinase A (PKA) in vitro and in vivo. Expression of an alanine mutant (p85A) abolished cyclic AMP/TSH-induced cell cycle progression and was lethal in thyroid cells (FRTL-5). The aspartic version of the p85αPI3K (p85D) inhibited apoptosis following TSH withdrawal. The p85αPI3K wild type not the p85A bound PKA regulatory subunit RIIβ in cells stimulated with cAMP or TSH. The binding of the aspartic version of p85αPI3K to RIIβ was independent of cAMP or TSH stimulation. Similarly, binding of PI3K to p21Ras and activation of AKT, a downstream PI3K target, were severely impaired in cells expressing the p85A mutant. Finally, we found that the catalytic activity of PI3K was stimulated by TSH in cells expressing the wild-type p85αPI3K but not in cells expressing p85A. This latter mutant did not affect the epidermal growth factor-stimulated PI3K activity. We suggest that (1) TSH–cAMP-induced PKA phosphorylates p85αPI3K at serine 83, (2) phosphorylated p85αPI3K binds RIIβ-PKA and targets PKAII to the membrane, and (3) PI3K activity and p21Ras binding to PI3K increase and activate PI3K downstream targets. This pathway is essential for the transmission of TSH–cAMP growth signals.

A complex pattern of mutations and abnormal splicing of Smad4 is present in thyroid tumours

Sensitivity to transforming growth factor-β is impaired in thyroid tumours. Similar to Mad – Mother Against Decapentaplegic-(Smad)4 is frequently altered in cancers, but its involvement in this system is unknown. We analysed 56 thyroid tumours of various histotypes for Smad4 mutations by PCR-SSCP and sequencing, linking them to Smad4 reactivity as examined by immunohistochemistry (IHC), and 29 of them also for abnormalities in RNA expression due to alternative splicing. In all, 15/56 cases (27%), both benign and malignant lesions, harbour alterations of Smad4 coding sequence. We found several novel intragenic mutations (13 missense, two silent, one frameshift and one large insertion-deletion), with high incidence in the linker region. A subset of mutated tumours failed to express Smad4 protein by IHC. We have also detected four alternatively spliced tumour-associated Smad4 isoforms, lacking portions of the linker region, and three more due to unreported internal exon–exon rearrangements. Smad4 is both frequently mutated and deregulated by aberrant splicing in thyroid tumours and these alterations may contribute as an early event to thyroid tumorigenesis.

Overexpression of transforming growth factor β-type II receptor reduces tumorigenicity and metastastic potential of K-ras-transformed thyroid cells

Expression of type II receptor of transforming growth factor beta (TbetaRII) is necessary for this factor to inhibit the growth of thyroid epithelial cells. In rat thyroid transformed cells, the resistance to transforming growth factor beta (TGFbeta) is associated with a decreased expression of TbetaRII mRNA and protein. Reduced TbetaRII expression has also been found in human thyroid differentiated and undifferentiated carcinomas. To investigate the role of TbetaRII in modulating the tumorigenic potential of k-ras-transformed thyroid cells, we transfected these cells with an expression vector carrying the human TbetaRII gene, regulated by an inducible promoter. Isolated clones, overexpressing TbetaRII, showed a reduction in the anchorage-dependent and -independent cell growth, compared with control k-ras-transformed cells. When transplanted in athymic nude mice, the transfected clones presented a decrease in tumorigenicity with respect to the highly malignant parental cells. Moreover, the diminished tumorigenic ability of the clones studied was accompanied by a statistically significant reduction in spontaneous and lung artificial metastases. Taken together, our data demonstrate that TbetaRII acts as a potent tumor suppressor gene when overexpressed in malignant thyroid cells.

TGF-β control of rat thyroid follicular cells differentiation

Abstract TGF-β1 is a potent inhibitor of growth and DNA synthesis in thyroid cells. It has also been shown that TGF-β1 inhibits thyrocyte function. The functional inhibition is represented by a downregulation of thyroid specific genes, such as Na + /I − symporter (NIS), thyroglobulin (TG) and thyroperoxidase (TPO). The transcriptional control of these genes is mediated by thyroid-specific transcription factors: thyroid transcription factor-1 (TTF-1) and PAX-8. It has been shown that Smad proteins play a pivotal role in the intracellular signal transduction of the TGF-β family members. In this paper, the functional relevance of Smad4, in the control of thyroid differentiation genes and thyroid-specific transcription factors, has been investigated. The data obtained provides, for the first time, evidence that D.N. Smad4-100T is capable of blocking TGF-β1 action in the regulation of thyroid-specific genes expression. Such action is possible by blocking nuclear translocation of Smad4 and Smad2.

Restored expression of transforming growth factor β type II receptor ink-ras-transformed thyroid cells, TGFβ-resistant, reverts their malignant phenotype

Transforming growth factor β1 (TGFβ1) inhibits the growth of normal rat epithelial thyroid cells (FRTL‐5 strain) by counteracting thyrotropin (TSH)‐stimulated DNA synthesis and by slowing the cells in the G1 phase of the cell cycle. Here, we have studied two clones of FRTL‐5 thyroid cell line transformed by the wild type (wt) v‐k‐ras oncogene (K.M.A1, K.M.A2) and one clone (A6) transformed by a temperature‐sensitive (ts) v‐k‐ras mutant. Anchorage‐dependent as well as anchorage‐independent growth of these k‐ras‐transformed cells was not inhibited by TGFβ1. TGFβ1 resistance appeared to be dependent by a functional p21 k‐ras, because A6 cell growth was partially inhibited at the nonpermissive temperature (39°C). To determine the basis for TGFβ1 resistance in k‐ras‐transformed thyroid cells, we looked for possible defects in the expression of type I (TβR‐I/ALK5) and type II TGFβ receptors (TβR‐II). Lower levels of type II receptors were present in all of the k‐ras‐transformed clones, as revealed by both Northern blot and cross‐linking experiments.

Peroxiredoxin 2 nuclear levels are regulated by circadian clock synchronization in human keratinocytes

Circadian rhythms are highly conserved time tracking systems regulating important biological processes at both systemic and cellular levels. The present study was aimed to identify proteins and biological functions circadian regulated in human keratinocytes. HaCaT keratinocytes were entrained by temperature cycles, and a proteomic study was performed on cell fractions isolated under free running conditions at constant temperature. Bioinformatics analysis revealed that molecular clock entrainment was associated with changes in molecular components regulating cell proliferation, energy metabolism, transcription, translation and redox balance. Nuclear levels of the antioxidant enzyme Peroxiredoxin 2 (PRDX2) were found to oscillate rhythmically over two entire 24h long cycles. Donwregulation of PRDX2 resulted in upregulation of the mitochondrion-specific Peroxiredoxin 3 (PRDX3), all other members of the Peroxiredoxin family remained unaltered. Furthermore, PRDX2 knockdown increased intracellular levels of reactive oxygen species (ROS) and impaired cell cycle progression and proliferation. HaCaT cells transduced with a scramble shRNA were used as control. Our work is the first to show that nuclear levels of PRDX2 display circadian oscillation participating in the regulation of human keratinocytes redox balance.

Role of reduced expression of SMAD4 in papillary thyroid carcinoma.

It has been demonstrated that transforming growth factor-β (TGFβ) and other members of TGFβ superfamily play an important role in thyroid proliferative diseases. The deficiencies of SMAD4 are responsible to accelerate the malignant progression of neoplastic lesions in several types of tumors. Therefore, the objective of the present study was to determine the functional role of reduced expression of SMAD4 in human papillary thyroid carcinogenesis. For this purpose, we examined the TGFβ response in two cell lines, TPC-1 and BCPAP. Our data demonstrated for the first time that these cells showed a strong reduction in the level of SMAD4 protein, which was responsible for an alteration of TGFβ signaling and for some of the TGFβ-mediated biological effects. The overexpression of SMAD4, restoring TGFβ transduction, determined a significant increase of antiproliferative response to TGFβ, and reduced the invasive behavior of these cells. Therefore, our data indicated that reduction of SMAD4 may play a significant role in thyroid carcinogenesis.

A novel human Smad4 mutation is involved in papillary thyroid carcinoma progression

Smad proteins are the key effectors of the transforming growth factor β (TGFβ) signaling pathway in mammalian cells. Smad4 plays an important role in human physiology, and its mutations were found with high frequency in wide range of human cancer. In this study, we have functionally characterized Smad4 C324Y mutation, isolated from a nodal metastasis of papillary thyroid carcinoma. We demonstrated that the stable expression of Smad4 C324Y in FRTL-5 cells caused a significant activation of TGFβ signaling, responsible for the acquisition of transformed phenotype and invasive behavior. The coexpression of Smad4 C324Y with Smad4 wild-type determined an increase of homo-oligomerization of Smad4 with receptor-regulated Smads and a lengthening of nuclear localization. FRTL-5 clones overexpressing Smad4 C324Y showed a strong reduction of response to antiproliferative action of TGFβ1, acquired the ability to grow in anchorage-independent conditions, showed a fibroblast-like appearance and a strong reduction of the level of E-cadherin, one crucial event of the epithelial-mesenchymal transition process. The acquisition of a mesenchymal phenotype gave the characteristics of increased cellular motility and a significant reduction in adhesion to substrates such as fibronectin and laminin. Overall, our results demonstrate that the Smad4 C324Y mutation plays an important role in thyroid carcinogenesis and can be considered as a new prognostic and therapeutic target for thyroid cancer.

The role of peroxiredoxins in cancer (Review)

Peroxiredoxins (PRDXs) are a ubiquitously expressed family of small (22–27 kDa) non-seleno peroxidases that catalyze the peroxide reduction of H2O2, organic hydroperoxides and peroxynitrite. They are highly involved in the control of various physiological functions, including cell growth, differentiation, apoptosis, embryonic development, lipid metabolism, the immune response, as well as cellular homeostasis. Although the protective role of PRDXs in cardiovascular and neurological diseases is well established, their role in cancer remains controversial. Increasing evidence suggests the involvement of PRDXs in carcinogenesis and in the development of drug resistance. Numerous types of cancer cells, in fact, are characterized by an increase in reactive oxygen species (ROS) production, and often exhibit an altered redox environment compared with normal cells. The present review focuses on the complex association between oxidant balance and cancer, and it provides a brief account of the involvement of PRDXs in tumorigenesis and in the development of chemoresistance.