Transforming growth factor-b (TGF-b) superfamily members signal via membrane-bound heteromeric serinethreonine kinase receptor complexes. Upon ligand-binding, receptor activation leads to phosphorylation of cytoplasmic protein substrates of the Smad family. Following phosphorylation and oligomerization, the latter move into the nucleus to act as transcription factors to regulate target gene expression. TGF-b responses are not solely the result of the activation Smad cascade, but are highly cell-type specific and dependent upon interactions of Smad signaling with a variety of other intracellular signaling mechanisms, initiated or not by TGF-b itself, that may either potentiate, synergize, or antagonize, the rather linear TGF-b/Smad pathway. These include, (a), regulation of Smad activity by mitogen-activated protein kinases (MAPKs), (b), nuclear interaction of activated Smads with transcriptional cofactors, whether coactivators or corepressors, that may be themselves be regulated by diverse signaling mechanisms, and (c), negative feedback loops exerted by inhibitory Smads, transcriptional targets of the Smad cascade. This review focuses on how MAPKs modulate the outcome of Smad activation by TGF-b, and how cross-signaling mechanisms between the Smad and MAPK pathways may take place and affect cell fate in the context of carcinogenesis.

Members of the transforming growth factor-beta (TGF-beta) superfamily are pleiotropic cytokines that have the ability to regulate numerous cell functions, including proliferation, differentiation, apoptosis, epithelial-mesenchymal transition, and production of extracellular matrix, allowing them to play an important role during embryonic development and for maintenance of tissue homeostasis. Three TGF-beta isoforms have been identified in mammals. They propagate their signal via a signal transduction network involving receptor serine/threonine kinases at the cell surface and their substrates, the SMAD proteins. Upon phosphorylation and oligomerization, the latter move into the nucleus to regulate transcription of target genes. This review will summarize recent advances in the understanding of the mechanisms underlying SMAD modulation of extracellular matrix gene expression in the context of wound healing and tissue fibrosis.

Summary There is growing evidence that the metastatic spread of melanoma is driven not by a linear increase in tumorigenic aggressiveness, but rather by switching back and forth between two different phenotypes of metastatic potential. In vitro these phenotypes are respectively defined by the characteristics of strong proliferation/weak invasiveness and weak proliferation/strong invasiveness. Melanoma cell phenotype is tightly linked to gene expression. Taking advantage of this, we have developed a gene expression–based tool for predicting phenotype called Heuristic Online Phenotype Prediction. We demonstrate the predictive utility of this tool by comparing phenotype‐specific signatures with measurements of characteristics of melanoma phenotype‐specific biology in different melanoma cell lines and short‐term cultures. We further show that 86% of 536 tested melanoma lines and short‐term cultures are significantly associated with the phenotypes we describe. These findings reinforce the concept that a two‐state system, as described by the phenotype switching model, underlies melanoma progression.

Melanoma has a propensity to metastasize to bone, where it is exposed to high concentrations of transforming growth factor-B (TGF-B). Because TGF-B promotes bone metastases from other solid tumors, such as breast cancer, we tested the role of TGF-B in melanoma metastases to bone. 1205Lu melanoma cells, stably transfected to overexpress the natural TGF-B/Smad signaling inhibitor Smad7, were studied in an experimental model of bone metastasis whereby tumor cells are inoculated into the left cardiac ventricle of nude mice. All mice bearing parental and mock-transfected 1205Lu cells developed osteolytic bone metastases 5 weeks post-tumor inoculation. Mice bearing 1205Lu-Smad7 tumors had significantly less osteolysis on radiographs and longer survival compared with parental and mock-transfected 1205Lu mice. To determine if the reduced bone metastases observed in mice bearing 1205Lu-Smad7 clones was due to reduced expression of TGF-B target genes known to enhance metastases to bone from breast cancer cells, we analyzed gene expression of osteolytic factors, parathyroid hormone-related protein (PTHrP) and interleukin-11 (IL-11), the chemotactic receptor CXCR4, and osteopontin in 1205Lu cells. Quantitative reverse transcription-PCR analysis indicated that PTHrP, IL-11, CXCR4, and osteopontin mRNA steady-state levels were robustly increased in response to TGF-B and that Smad7 and the TBRI small-molecule inhibitor, SB431542, prevented such induction. In addition, 1205Lu-Smad7 bone metastases expressed significantly lower levels of IL-11, connective tissue growth factor, and PTHrP. These data suggest that TGF-B promotes osteolytic bone metastases due to melanoma by stimulating the expression of prometastatic factors via the Smad pathway. Blockade of TGF-B signaling may be an effective treatment for melanoma metastasis to bone. [Cancer Res 2007;67(5):2317-24]

Melanoma represents approximately 4% of human skin cancers, yet accounts for approximately 80% of deaths from cutaneous neoplasms (1). Although progress has been made in understanding the genetics of the molecular events underlying melanoma oncogenesis (2-4), the clinical challenge remains enormous. A genetic hallmark of melanoma is the presence of activating mutations in the oncogenes BRAF and NRAS, which are present in 70% and 15% of melanomas, respectively, and lead to constitutive activation of mitogen-activated protein kinase pathway signaling (3,5). However, molecules that inhibit mitogen-activated protein kinase pathway-associated kinases, like BRAF and MEK, have shown only limited efficacy in the treatment of metastatic melanoma (6). Thus, a deeper understanding of the cross talk between signaling networks and the complexity of melanoma progression should lead to more effective therapy.Hedgehog (HH) signaling is controlled at the cell surface by two transmembrane proteins, the tumor suppressor Patched-1 (PTCH1), which acts as a HH receptor, and the oncoprotein Smoothened (SMO). In the absence of HH, PTCH1 maintains SMO in an inactive state. In the presence of any of the three HH ligands (Sonic, Indian, or Desert HH), inhibition of SMO by PTCH1 is alleviated and a signal is transduced that leads to the nuclear translocation and activation of GLI family transcription factors (7,8). GLIs are often overexpressed in cancers and contribute to the progression of a variety of neoplasms via regulation of cell cycle progression and apoptosis (9,10). One recent study (11) Article

Melanoma often metastasizes to bone where it is exposed to high concentrations of TGF-b. Constitutive Smad signaling occurs in human melanoma. Because TGF-b promotes metastases to bone by several types of solid tumors including breast cancer, we hypothesized that pharmacologic blockade of the TGF-b signaling pathway may interfere with the capacity of melanoma cells to metastasize to bone. In this study, we tested the effect of a small molecule inhibitor of TGF-b receptor I kinase (TbRI), SD-208, on various parameters affecting the development and progression of melanoma, both in vitro and in a mouse model of human melanoma bone metastasis. In melanoma cell lines, SD-208 blocked TGF-b induction of Smad3 phosphorylation, Smad3/4-specific transcription, Matrigel invasion and expression of the TGF-b target genes PTHrP, IL-11, CTGF, and RUNX2. To assess effects of SD-208 on melanoma development and metastasis, nude mice were inoculated with 1205Lu melanoma cells into the left cardiac ventricle and drug was administered by oral gavage on prevention or treatment protocols. SD-208 (60 mg/kg/d), started 2 days before tumor inoculation prevented the development of osteolytic bone metastases compared with vehicle. In mice with established bone metastases, the size of osteolytic lesions was significantly reduced after 4 weeks treatment with SD-208 compared with vehicle-treated mice. Our results demonstrate that therapeutic targeting of TGF-b may prevent the development of melanoma bone metastases and decrease the progression of established osteolytic lesions. Cancer Res; 71(1); 175-84. Ó2010 AACR.

SummaryTransforming growth factor-b (TGF-b) plays a complex role during carcinogenesis. It may either act as a tumor suppressor through its broad antiproliferative potential or as a tumor promoter either via direct effects on tumor cell aggressiveness or indirectly by modulating stromal responses, angiogenesis and immune surveillance. Increased production of TGF-b by cancer cells is often associated with tumor grade. Melanoma cells largely escape cell cycle arrest normally induced by TGF-b in normal melanocytes, yet produce active TGF-b and are capable of efficient transcriptional responses to the growth factor. In this review, we summarize the current knowledge about the role played by TGF-b in melanoma progression and hypothesize about the appropriateness of targeting TGF-b signaling for therapeutic intervention.

The Hedgehog (Hh) and Transforming Growth Factor-β (TGF-β) signaling pathways represent essential regulators of cell proliferation and differentiation during embryogenesis. Pathway deregulation is a characteristic of various cancers. Recently, evidence for a convergence of these pathways at the level of the GLI2 transcription factor in the context of tumor initiation and progression to metastasis has emerged. This short review summarizes recent knowledge about GLI2 function and mechanisms of action downstream of TGF-β in cancer.