Joan Massagué

Mechanisms of TGF-β Signaling from Cell Membrane to the Nucleus

TGF-β signaling controls a plethora of cellular responses and figures prominently in animal development. Recent cellular, biochemical, and structural studies have revealed significant insight into the mechanisms of the activation of TGF-β receptors through ligand binding, the activation of Smad proteins through phosphorylation, the transcriptional regulation of target gene expression, and the control of Smad protein activity and degradation. This article reviews these latest advances and presents our current understanding on the mechanisms of TGF-β signaling from cell membrane to the nucleus.

Cancer Metastasis: Building a Framework

Metastasis occurs when genetically unstable cancer cells adapt to a tissue microenvironment that is distant from the primary tumor. This process involves both the selection of traits that are advantageous to cancer cells and the concomitant recruitment of traits in the tumor stroma that accommodate invasion by metastatic cells. Recent conceptual and technological advances promote our understanding of the origins and nature of cancer metastasis.

TGFβ in Cancer

The transforming growth factor beta (TGFbeta) signaling pathway is a key player in metazoan biology, and its misregulation can result in tumor development. The regulatory cytokine TGFbeta exerts tumor-suppressive effects that cancer cells must elude for malignant evolution. Yet, paradoxically, TGFbeta also modulates processes such as cell invasion, immune regulation, and microenvironment modification that cancer cells may exploit to their advantage. Consequently, the output of a TGFbeta response is highly contextual throughout development, across different tissues, and also in cancer. The mechanistic basis and clinical relevance of TGFbetas role in cancer is becoming increasingly clear, paving the way for a better understanding of the complexity and therapeutic potential of this pathway.

TGFβ Signaling in Growth Control, Cancer, and Heritable Disorders

We are grateful to members of the Massague laboratory for insightful discussions. R. S. L. would like to thank S. H. Roan for all her help. R. S. L is supported by an NIH Medical Scientist Training Program (MSTP) grant. S. W. B. is a Special Fellow of the Leukemia and Lymphoma Society. J. M. is an investigator of the Howard Hughes Medical Institute.

Genes that mediate breast cancer metastasis to lung

By means of in vivo selection, transcriptomic analysis, functional verification and clinical validation, here we identify a set of genes that marks and mediates breast cancer metastasis to the lungs. Some of these genes serve dual functions, providing growth advantages both in the primary tumour and in the lung microenvironment. Others contribute to aggressive growth selectively in the lung. Many encode extracellular proteins and are of previously unknown relevance to cancer metastasis.

Cloning of p27Kip1, a cyclin-dependent kinase inhibitor and a potential mediator of extracellular antimitogenic signals

We cloned p27Kip1, a cyclin-dependent kinase inhibitor implicated in G1 phase arrest by TGF beta and cell-cell contact. p27Kip1 associates with cyclin E-Cdk2 complexes in vivo and in vitro, prevents their activation, and inhibits previously activated complexes, and p27Kip1 overexpression obstructs cell entry into S phase. p27Kip1 potently inhibits Rb phosphorylation by cyclin E-Cdk2, cyclin A-Cdk2, and cyclin D2-Cdk4. p27Kip1 is highly conserved and broadly expressed in human tissues, and its mRNA levels are similar in proliferating and quiescent cells. p27Kip1 has a region of sequence similarity to p21Cip1/WAF1, the Cdk inhibitor whose transcription is stimulated by p53. A p27Kip1 peptide corresponding to this region retains Cdk inhibitory activity. We suggest that cell contact, TGF beta, and p53 all restrain cell proliferation through related Cdk inhibitors.

A multigenic program mediating breast cancer metastasis to bone

We investigated the molecular basis for osteolytic bone metastasis by selecting human breast cancer cell line subpopulations with elevated metastatic activity and functionally validating genes that are overexpressed in these cells. These genes act cooperatively to cause osteolytic metastasis, and most of them encode secreted and cell surface proteins. Two of these genes, interleukin-11 and CTGF, encode osteolytic and angiogenic factors whose expression is further increased by the prometastatic cytokine TGF beta. Overexpression of this bone metastasis gene set is superimposed on a poor-prognosis gene expression signature already present in the parental breast cancer population, suggesting that metastasis requires a set of functions beyond those underlying the emergence of the primary tumor.

Transcriptional control by the TGF‐β/Smad signaling system

The deployment of a cells genetic program in a multicellular organism must be tightly controlled for the sake of the organism as a whole. Over the past 20 years the transforming growth factor‐β (TGF‐β) family of secretory polypeptides has emerged as a major source of signals exerting this type of control. This family includes various forms of TGF‐β, the bone morphogenetic proteins (BMPs), the Nodals, the Activins, the anti‐Mullerian hormone, and many other structurally related factors in vertebrates, insects and nematodes (Massague, 1998). Produced by diverse cell types, these factors regulate cell migration, adhesion, multiplication, differentiation and death throughout the life span of the organism. Many of these responses result from changes in the expression of key target genes. Hence, transcriptional control by the TGF‐β family has become a subject of intense investigation in recent years. The present knowledge of these mechanisms is reviewed here. One basic concept concerning the role of the TGF‐β family as hormonally active agents warrants mention at the outset. Unlike classical hormones, whose actions are few and concrete, the members of the TGF‐β family have many different effects depending on the type and state of the cell. For example, in the same healing wound TGF‐β may stimulate or inhibit cell proliferation depending on whether the target is a fibroblast or a keratinocyte (Ashcroft et al ., 1999); in mammary epithelial cells TGF‐β will cause growth arrest or metastatic behavior depending on the level of oncogenic Ras activity present in the cell (Oft et al ., 1996); and human BMP4 and its Drosophila ortholog, DPP, can signal dorsalization in the fly (Padgett et al ., 1993) yet bone formation in a vertebrate (Sampath et al ., 1993). TGF‐β family members are multifunctional hormones, the nature of their effects depending on what has been called ‘the cellular context’. It was plausible …

How cells read TGF-|[beta]| signals

Cell proliferation, differentiation and death are controlled by a multitude of cell?cell signals, and loss of this control has devastating consequences. Prominent among these regulatory signals is the transforming growth factor-β (TGF-β) family of cytokines, which can trigger a bewildering diversity of responses, depending on the genetic makeup and environment of the target cell. What are the networks of cell-specific molecules that mould the TGF-β response to each cells needs?

Metastasis: from dissemination to organ-specific colonization

Metastasis to distant organs is an ominous feature of most malignant tumours but the natural history of this process varies in different cancers. The cellular origin, intrinsic properties of the tumour, tissue affinities and circulation patterns determine not only the sites of tumour spread, but also the temporal course and severity of metastasis to vital organs. Striking disparities in the natural progression of different cancers raise important questions about the evolution of metastatic traits, the genetic determinants of these properties and the mechanisms that lead to the selection of metastatic cells.