Cancer cells are able to proliferate at accelerated rates within the confines of a three-dimensional (3D) extracellular matrix (ECM) that is rich in type I collagen. The mechanisms used by tumor cells to circumvent endogenous antigrowth signals have yet to be clearly defined. We find that the matrix metalloproteinase, MT1-MMP, confers tumor cells with a distinct 3D growth advantage in vitro and in vivo. The replicative advantage conferred by MT1-MMP requires pericellular proteolysis of the ECM, as proliferation is fully suppressed when tumor cells are suspended in 3D gels of protease-resistant collagen. In the absence of proteolysis, tumor cells embedded in physiologically relevant ECM matrices are trapped in a compact, spherical configuration and unable to undergo changes in cell shape or cytoskeletal reorganization required for 3D growth. These observations identify MT1-MMP as a tumor-derived growth factor that regulates proliferation by controlling cell geometry within the confines of the 3D ECM.

The striking clinical benefit of PTH in osteoporosis began a new era of skeletal anabolic agents. Several studies have been performed, new studies are emerging out and yet controversies remain on PTH anabolic action in bone. This review focuses on the molecular aspects of PTH and PTHrP signaling in light of old players and recent advances in understanding the control of osteoblast proliferation, differentiation and function.

Prostate cancer almost exclusively metastasizes to skeletal sites, indicating that the bone provides a favorable microenvironment for its localization and progression. A natural yet understudied factor in bone that could facilitate tumor localization is elevated extracellular calcium (

p53 monitors genomic integrity at the G1 and G2/M cell cycle checkpoints. Cells lacking p53 may show gene ampli®cation as well as the polyploidy or aneuploidy typical of many tumors. The pathways through which this develops, however, are not well de®ned. We demonstrate here that the combination of p53 inactivation and c-myc overexpression in diploid cells markedly accelerates the spontaneous development of tetraploidy. This is not seen with either N-myc or L-myc. Tetraploidy is accompanied by signi®cantly higher levels of cyclin B and its associated cdc2 kinase activity. Mitotic spindle poisons accelerate the appearance of tetraploidy in cells either lacking functional p53 or overexpressing c-myc whereas the combination is additive. Restoration of p53 function in cells overexpressing c-myc causing rapid apoptosis, indicating that cells yet to become tetraploid have nonetheless suered irreversible genomic and/or mitotic spindle damage. In the face of normal p53 function, such damage would either be repaired or trigger apoptotis. We propose that loss of p53 and overexpression of c-myc permits the emergence and survival of cells with increasingly severe damage and the eventual development of tetraploidy.

Adenosine kinase catalyzes the phosphorylation of adenosine to AMP and hence is a potentially important regulator of extracellular adenosine concentrations. Despite extensive characterization of the kinetic properties of the enzyme, its primary structure has never been elucidated. Full-length cDNA clones encoding catalytically active adenosine kinase were obtained from lymphocyte, placental, and liver cDNA libraries. Corresponding mRNA species of 1.3 and 1.8 kb were noted on Northern blots of all tissues examined and were attributable to alternative polyadenylylation sites at the 3' end of the gene. The encoding protein consists of 345 amino acids with a calculated molecular size of 38.7 kDa and does not contain any sequence similarities to other wellcharacterized mammalian nucleoside kinases, setting it apart from this family of structurally and functionally related proteins. In contrast, two regions were identified with significant sequence identity to microbial ribokinase and fructokinases and a bacterial inosine/guanosine kinase. Thus, adenosine kinase is a structurally distinct mammalian nucleoside kinase that appears to be akin to sugar kinases of microbial origin.Adenosine kinase (AK; ATP:adenosine 5'-phosphotransferase, EC 2.7.1.20) is an abundant enzyme in mammalian tissues that catalyzes the transfer of the y-phosphate from ATP to adenosine, thereby serving as a potentially important regulator of concentrations of both extracellular adenosine and intracellular adenine nucleotides. Adenosine has widespread effects on the cardiovascular, nervous, respiratory, and immune systems (1) and it has been postulated that inhibitors of AK could play an important pharmacologic role in increasing intravascular adenosine concentrations and acting as antiinflammatory agents (2, 3). In addition, this enzyme is responsible for the phosphorylation and consequent clinical activity of several therapeutically useful nucleosides, including the antiviral drug ribavirin and the immunosuppressive drug mizoribine (4, 5). AK has been purified from a number of sources including rabbit liver (6), human placenta (7) and liver (5), murine leukemia cells (8), and Leischmania donovani (9) RNA was purified by the acid guanidine isothiocyanate procedure (1 1).AK Purification. AK was purified from the human Tlymphoblast cell line Molt-4 by a modification of the procedure previously described (7). Cytosol was passed over a 5'-AMPSepharose column equilibrated with 20 mM imidazole HCl, pH 7.6, containing 1 mM phenylmethylsulfonyl fluoride (PMSF) and 1 mM EGTA. The column was eluted with buffer containing 5 mM adenosine and the peak fractions were pooled in 20% (vol/vol) glycerol. Several 2-ml fractions were loaded onto a Superose 12 column (50 x 1.6 cm) previously equilibrated with 50 mM imidazolevHCl, pH 7.2/50 mM KCI/5 mM dithiothreitol (DTT)/1 mM ATP/1 mM MgCl2/5% glycerol. Fractions containing AK activity, assayed as described (7), were pooled, diluted into buffer containing 1 mM PMSF, and applied to a DE52 column. Fractions we...