TGF-beta1, WNT, and SHH signaling in tumor progression and in fibrotic diseases

Activation of resting fibroblasts to myofibroblasts characterizes several physiological and pathological conditions, from wound healing to aggressive metastatic cancers. In tissue damage, including wound healing, fibroblasts are activated in response to injury for a limited period of time to stimulate the healing process. Similar biological mechanisms are maintained in pathological conditions, e.g., scleroderma and cancer, where myofibroblasts persist in producing cytokines and growth factors to drive the development of fibrosis and the progression of disease. Studies characterizing the bi-directional signal transduction pathways between cancer cells and stromal cells have suggested novel druggable targets that may function in both the inhibition of fibrotic reactions in cancer stroma and in the inhibition of fibrotic diseases. In this review, we focus on transforming growth factor beta (TGF-beta), int/Wingless (WNT), and sonic hedgehog (SHH) signal transduction pathways and describe small molecule inhibitors that are used in phase I/II clinical trials to treat fibrosis or fibrotic cancers.

Extracellular superoxide dismutase regulates the expression of small gtpase regulatory proteins GEFs, GAPs, and GDI

Extracellular superoxide dismutase (SOD3), which catalyzes the dismutation of superoxide anions to hydrogen peroxide at the cell membranes, regulates the cellular growth in a dose-dependent manner. This enzyme induces primary cell proliferation and immortalization at low expression levels whereas it activates cancer barrier signaling through the p53-p21 pathway at high expression levels, causing growth arrest, senescence, and apoptosis. Because previous reports suggested that the SOD3–induced reduction in the rates of cellular growth and migration also occurred in the absence of functional p53 signaling, in the current study we investigated the SOD3-induced growth-suppressive mechanisms in anaplastic thyroid cancer cells. Based on our data, the robust over-expression of SOD3 increased the level of phosphorylation of the EGFR, ERBB2, RYK, ALK, FLT3, and EPHA10 receptor tyrosine kinases with the consequent downstream activation of the SRC, FYN, YES, HCK, and LYN kinases. However, pull-down experiments focusing on the small GTPase RAS, RAC, CDC42, and RHO revealed a reduced level of growth and migration signal transduction, such as the lack of stimulation of the mitogen pathway, in the SOD3 over-expressing cells, which was confirmed by MEK1/2 and ERK1/2 Western blotting analysis. Interestingly, the mRNA expression analyses indicated that SOD3 regulated the expression of guanine nucleotide-exchange factors (RHO GEF16, RAL GEF RGL1), GTPase-activating proteins (ARFGAP ADAP2, RAS GAP RASAL1, RGS4), and a Rho guanine nucleotide-disassociation inhibitor (RHO GDI 2) in a dose dependent manner, thus controlling signaling through the small G protein GTPases. Therefore, our current data may suggest the occurrence of dose-dependent SOD3–driven control of the GTP loading of small G proteins indicating a novel growth regulatory mechanism of this enzyme.

Brief report: Mesenchymal stromal cell atrophy in coculture increases aggressiveness of transformed cells

Mesenchymal stromal cells (MSCs) are able to influence the growth abilities of transformed cells. Here, we show that papillary thyroid cancer TPC1 and HEK 293T cells interact physically with human primary bone marrow-derived MSCs followed by evanescence of MSC cytoplasm. Interestingly, transformed cells were able to connect only to apoptotic MSCs that had lost their migration ability, whereas naïve MSCs avoided the direct contact. The interaction stimulated the proliferation of the cocultured transformed cells, activated mitogen and stress signaling, and increased resistance to cytotoxins. Consistent with in vitro data, the MSC interaction stimulated transformed cells had enhanced ability to grow and metastasize in vivo. The parental control cells showed mild tumorigenicity as compared to MSC interaction stimulated cells yielding measurable tumors in 31 days and 7 days, respectively. Our coculture model system describes how adjacent transformed cells absorb stromal cells thereby leading to the stroma-driven evolution of moderately carcinogenic cells to highly aggressive metastatic cells.

A novel de novo germ-line V292M mutation in the extracellular region of RET in a patient with phaeochromocytoma and medullary thyroid carcinoma: functional characterization

CONTEXT

In multiple endocrine neoplasia (MEN), rearranged during transfection (RET), gene testing has been extensively exploited to characterize tumour aggressiveness and optimize the diagnostic and clinical management.

OBJECTIVE

To report the underlying genetic alterations in an unusual case of MEN type 2 (MEN-2A).

DESIGN AND PATIENT

Occult medullary thyroid carcinoma (MTC) was diagnosed in a 44-year-old man who had presented with unilateral phaeochromcytoma. DNA extracted from the blood and tumour tissues was analysed for mutations in RET. The transforming potential and mitogenic properties of the identified RET mutation were investigated.

RESULTS

The patient carried a novel heterozygous germ-line RET mutation in exon 5 (Val292Met, GTG>ATG) (V292M/RET) with no evidence of additional somatic alterations. The mutation maps to the third cadherin-like domain of RET, which is usually not included in RET screening. Interestingly, MTC with concomitant phaeochromcytoma has never been associated with a RET mutation involving the extracellular cadherin-like domain. V292M/RET was absent in the only two relatives examined. In vitro assays indicate that the mutant has low-grade transforming potential.

CONCLUSIONS

Complete characterization and classification of all novel RET mutations are essential for extending genetic analysis in clinical practice. Our findings suggest that: (i) in all MEN-2 patients negative for RET hot-spot mutations, testing should be extended to all coding regions of the gene and (ii) the newly identified V292M/RET mutation is characterized by relatively weak in vitro transforming ability.

Extracellular superoxide dismutase is a thyroid differentiation marker down-regulated in cancer

Reactive oxygen species, specifically hydrogen peroxide (H(2)O(2)), have a significant role in hormone production in thyroid tissue. Although recent studies have demonstrated that dual oxidases are responsible for the H(2)O(2) synthesis needed in thyroid hormone production, our data suggest a pivotal role for superoxide dismutase 3 (SOD3) as a major H(2)O(2)-producing enzyme. According to our results, Sod3 is highly expressed in normal thyroid, and becomes even more abundant in rat goiter models. We showed TSH-stimulated expression of Sod3 via phospholipase C-Ca(2+) and cAMP-protein kinase A, a pathway that might be disrupted in thyroid cancer. In line with this finding, we demonstrated an oncogene-dependent decrease in Sod3 mRNA expression synthesis in thyroid cancer cell models that corresponded to a similar decrease in clinical patient samples, suggesting that SOD3 could be used as a differentiation marker in thyroid cancer. Finally, the functional analysis in thyroid models indicated a moderate role for SOD3 in regulating normal thyroid cell proliferation being in line with our previous observations.

Human embryonic stem cell-derived mesenchymal stromal cell transplantation in a rat hind limb injury model

BACKGROUND AIMS

Mesenchymal stromal cells (MSC) have been used in a wide variety of pre-clinical experiments and in an increasing number of human clinical trials. Although many of these studies have shown different levels of engraftment, the exact fate of MSC after transplantation and the tissue response to their engraftment have not been investigated in detail. In the present work we studied the distribution of human MSC in a rat hind limb ischemic injury model immediately after transplantation and also analyzed the recipient tissue response to transplanted cells.

METHODS

We tracked the in vivo fate of the transplanted MSC utilizing bioluminescence imaging, fluorescence microscopy and gene/protein expression analysis in a rat hind limb ischemia model. We also monitored the viability of transplanted cells by graft versus recipient expression analysis and determined the angiogenic and proliferative effect of transplantation by histologic staining.

RESULTS

According to imaging analysis only a small portion of cells persisted for an extended period of time at the site of injury. Interestingly, recipient versus graft expression studies showed increased synthesis of rat-origin angiogenic factors and no human-origin mRNA or protein synthesis in transplanted tissues. More importantly, despite the lack of robust engraftment or growth factor secretion the transplantation procedure exerted a significant pro-angiogenic and pro-proliferative effect, which was mediated by angiogenic and mitogenic signaling pathways.

CONCLUSIONS

Our results show an immediate temporal tissue effect in response to MSC transplantation that may represent a novel indirect paracrine mechanism for the beneficial effects of cell transplantation observed in injured tissues.

SOD3 reduces inflammatory cell migration by regulating adhesion molecule and cytokine expression

Inflammatory cell migration characteristic of ischemic damages has a dual role providing the tissue with factors needed for tissue injury recovery simultaneously causing deleterious development depending on the quality and the quantity of infiltrated cells. Extracellular superoxide dismutase (SOD3) has been shown to have an anti-inflammatory role in ischemic injuries where it increases the recovery process by activating mitogen signal transduction and increasing cell proliferation. However, SOD3 derived effects on inflammatory cytokine and adhesion molecule expression, which would explain reduced inflammation in vascular lesions, has not been properly characterized. In the present work the effect of SOD3 on the inflammatory cell extravasation was studied in vivo in rat hind limb ischemia and mouse peritonitis models by identifying the migrated cells and analyzing SOD3-derived response on inflammatory cytokine and adhesion molecule expression. SOD3 overexpression significantly reduced TNFalpha, IL1alpha, IL6, MIP2, and MCP-1 cytokine and VCAM, ICAM, P-selectin, and E-selectin adhesion molecule expressions in injured tissues. Consequently the mononuclear cell, especially CD68+ monocyte and CD3+ T cell infiltration were significantly decreased whereas granulocyte migration was less affected. According to our data SOD3 has a selective anti-inflammatory role in ischemic damages preventing the migration of reactive oxygen producing monocyte/macrophages, which in excessive amounts could potentially further intensify the tissue injuries therefore suggesting potential for SOD3 in treatment of inflammatory disorders.

Gene expression changes in a patient presenting nonleukaemic nasal granulocytic sarcoma to acute myelogenous leukaemia using 40 K cDNA microarray

This is a case report of granulocytic sarcoma occurring as a nasal lesion prior to the onset of acute myelogenous leukaemia (AML). To understand this case in more detail, we used 40,000 human cDNA microarray to identify the gene expression patterns of nonleukaemic stage bone marrow (BM), AML stage BM and AML stage peripheral blood cells and subsequently define the molecular basis of this disease progression. Of significance, we have tracked the expression profile of BM samples during the course of nonleukaemic to leukaemic progression, and identified a number of genes that may account for the growth potential of leukaemia cells and indicate poor prognosis of this case.

Regulation of the transcriptional activity of c-Fos by ERK. A novel role for the prolyl isomerase PIN1

The activation of the activating protein-1 (AP-1) family of transcription factors, including c-Fos and c-Jun family members, is one of the earliest nuclear events induced by growth factors that stimulate extracellular signal-regulated kinases (ERKs). In the case of c-Fos, the activation of ERK leads to an increased expression of c-fos mRNA. In turn, we have recently shown that ERK phosphorylates multiple residues within the carboxylterminal transactivation domain (TAD) of c-Fos, thus resulting in its increased transcriptional activity. However, how ERK-dependent phosphorylation regulates c-Fos function is still poorly understood. In this regard, it has been recently observed that the prolyl isomerase Pin1 can interact with proteins phosphorylated on serine or threonine residues that precede prolines (pS/T-P), such as the transcription factors p53 and c-Jun, thereby controlling their activity by promoting the cis-trans isomerization of these pS/T-P bonds. Here, we found that Pin1 binds c-Fos through specific pS/T-P sites within the c-Fos TAD, and that this interaction results in an enhanced transcriptional response of c-Fos to polypeptide growth factors that stimulate ERK. Our findings suggest that c-Fos represents a novel target for the isomerizing activity of Pin1 and support a role for Pin1 in the mechanism by which c-Jun and c-Fos can cooperate to regulate AP-1-dependent gene transcription upon phosphorylation by mitogen-activated kinase (MAPK) family members.

Functional expression of the CXCR4 chemokine receptor is induced by RET/PTC oncogenes and is a common event in human papillary thyroid carcinomas

To identify genes involved in the transformation of thyroid follicular cells, we explored, using DNA oligonucleotide microarrays, the transcriptional response of PC Cl3 rat thyroid epithelial cells to the ectopic expression of the RET/PTC oncogenes. We found that RET/PTC was able to induce the expression of CXCR4, the receptor for the chemokine CXCL12/SDF-1alpha/beta. We observed that CXCR4 expression correlated with the transforming ability of the oncoprotein and depended on the integrity of the RET/PTC-RAS/ERK signaling pathway. We found that CXCR4 was expressed in RET/PTC-positive human thyroid cancer cell lines, but not in normal thyroid cells. Furthermore, we found CXCR4 expression in human thyroid carcinomas, but not in normal thyroid samples by immunohistochemistry. Since CXCR4 has been recently implicated in tumor proliferation, motility and invasiveness, we asked whether treatment with SDF-1alpha was able to induce a biological response in thyroid cells. We observed that SDF-1alpha induced S-phase entry and survival of thyroid cells. Invasion through a reconstituted extracellular matrix was also supported by SDF-1alpha and inhibited by a blocking antibody to CXCR4. Taken together, these results suggest that human thyroid cancers bearing RET/PTC rearrangements may use the CXCR4/SDF-1alpha receptor-ligand pathway to proliferate, survive and migrate.

Tyrosine kinase oncoprotein, RET/PTC3, induces the secretion of myeloid growth and chemotactic factors

Differentiated thyroid carcinomas are the most frequent endocrine neoplasms, but account for few cancer-related deaths. Although the indolent growth of these cancers correlates well with longevity, the biological basis for this good prognosis is not known. In contrast, two of the most frequent autoimmune diseases involve the thyroid suggesting a high propensity for this organ to invoke destructive immunity. Unfortunately, the mechanism linking malignancy and autoimmunity is not clear, although the expression of the oncogenic fusion protein RET/PTC3 (RP3) in both of these disorders may provide a clue. Interestingly, the signaling caused by activated RET kinase involves overlapping pathways and some common to the inflammatory response. Accordingly, we analyzed the function of RP3 and a mutant RP3 molecule to induce proinflammatory pathways in thyroid epithelial cells. Indeed, we find that RP3 alone causes increases in nuclear NF-kappaB activity and secretion of MCP-1 and GM-CSF. Finally, transfer of RP3-expressing thyrocytes into mice in vivo attracted dense macrophage infiltrates, which lead to rapid thyroid cell death. Further, cytokine synthesis and inflammation was largely abrogated by mutation of RP3 Tyr588; an important protein-binding site for downstream signaling. Together, these studies implicate oncogene-induced cytokine-signaling pathways in a new mechanism linking inflammation with cancer.

RET/PTC1 oncogene signaling in PC Cl 3 thyroid cells requires the small GTP-binding protein Rho

Thyroid papillary carcinomas are characterized by RET/PTC rearrangements that cause the tyrosine kinase domain of the RET receptor to fuse with N-terminal sequences encoded by heterologous genes. This results in the aberrant expression of a ligand-independent and constitutively active RET kinase. We analysed actin reorganization induced by the RET/PTC1 oncogene in PC Cl 3 rat thyroid epithelial cells. Differently from oncogenes Src, Ras and Raf, RET/PTC1 caused actin filaments to form prominent stress fibers. Moreover, stress fibers were identified in human thyroid papillary carcinoma cell lines harboring RET/PTC1 rearrangements but not in thyroid carcinoma cells negative for RET/PTC rearrangements. RET/MEN 2A, a constitutively active but unrearranged membrane-bound RET oncoprotein, did not induce stress fibers in PC Cl 3 cells. Induction of stress fibers by RET/PTC1 was restricted to thyroid cells; it did not occur in NIH3T3 fibroblasts or MCF7 mammary cells. RET/PTC1-mediated stress fiber formation depended on Rho but not Rac small GTPase activity. In addition, inhibition of Rho, but not of Rac, caused apoptosis of RET/PTC1-expressing thyroid cells. We conclude that Rho is implicated in the actin reorganization and cell survival mediated by the chimeric RET/PTC1 oncogene in thyroid epithelial cells, both phenotypes being cell type- and oncogene type-specific.

Tyrosine 1062 of RET-MEN2A mediates activation of Akt (protein kinase B) and mitogen-activated protein kinase pathways leading to PC12 cell survival

The RET tyrosine kinase is a functional receptor for neurotrophic ligands of the glial cell line-derived neurotrophic factor (GDNF) family. Loss of function of RET is associated with congenital megacolon or Hirschsprung's disease, whereas germ-line point mutations causing RET activation are responsible for multiple endocrine neoplasia type 2 (MEN2A, MEN2B, and familial medullary thyroid carcinoma) syndromes. Here we show that the expression of a constitutively active RET-MEN2A oncogene promotes survival of rat pheochromocytoma PC12 cells upon growth factor withdrawal. Moreover, we show that the RET-MEN2A-mediated survival depends on signals transduced by the phosphoinositide 3-kinase (PI3K) and mitogen-activated protein kinase (MAPK) cascades. Thus, in PC12 cells, RET-MEN2A associates with the PI3K regulatory subunit p85 and promotes activation of Akt (also referred to as protein kinase B) in a PI3K-dependent fashion; in addition, RET-MEN2A promotes MAPK activation. PI3K recruitment and Akt activation as well as MAPK activation depend on RET-MEN2A tyrosine residue 1062. As a result, tyrosine 1062 of RET-MEN2A is essential for RET-MEN2A-mediated survival of PC12 cells cultured in growth factor-depleted media.

Akt/protein kinase B promotes survival and hormone-independent proliferation of thyroid cells in the absence of dedifferentiating and transforming effects

The Akt/protein kinase B serine/threonine kinase is a downstream effector of phosphoinositide 3-kinase (PI3K). Akt is an important component of mitogenic and antiapoptotic signaling pathways and is implicated in neoplastic transformation. Thyroid cells in culture retain a differentiated phenotype consisting of epithelial cell morphology and the expression of several tissue-specific genes. The survival and proliferation of these cells depend on thyrotropin and a mixture of five additional hormones that includes insulin. The regulation of proliferation and the expression of the thyroid differentiation program are intimately connected processes. As a result, oncogenes that induce hormone-independent proliferation invariably impair the expression of the thyroid-specific differentiation markers. Given that thyrotropin and insulin stimulate Akt activation in thyroid cells, we set out to determine the effects of Akt on thyroid cell proliferation, survival, and differentiation. To this end, we expressed constitutively active myristylated Akt (myrAkt) in PC Cl 3 thyroid cells. The myrAkt-expressing cells continued to proliferate, even in the absence of hormones, and they were resistant to programmed cell death induced by starvation. These effects were paralleled by the induction of the G1 cyclins D3 and E and by the inhibition of induction of the proapoptotic Fas, Fas ligand, and BAD genes in starved cells. However, in marked contrast with several other oncogenes, myrAkt did not interfere with the expression of thyroid differentiation functions. These results unveil the existence of an Akt-triggered thyroid cell pathway that modulates proliferation and survival without affecting the expression of the thyroid cell differentiated phenotype.