As cancer cells traverse collagen-rich extracellular matrix (ECM) barriers and intravasate, they adopt a fibroblast-like phenotype and engage undefined proteolytic cascades that mediate invasive activity. Herein, we find that fibroblasts and cancer cells express an indistinguishable pericellular collagenolytic activity that allows them to traverse the ECM. Using fibroblasts isolated from gene-targeted mice, a matrix metalloproteinase (MMP)–dependent activity is identified that drives invasion independently of plasminogen, the gelatinase A/TIMP-2 axis, gelatinase B, collagenase-3, collagenase-2, or stromelysin-1. In contrast, deleting or suppressing expression of the membrane-tethered MMP, MT1-MMP, in fibroblasts or tumor cells results in a loss of collagenolytic and invasive activity in vitro or in vivo. Thus, MT1-MMP serves as the major cell-associated proteinase necessary to confer normal or neoplastic cells with invasive activity.

Genomic imprinting is an epigenetic modification that results in expression from only one of the two parental copies of a gene. Differences in methylation between the two parental chromosomes are often observed at or near imprinted genes. Beckwith-Wiedemann syndrome (BWS), which predisposes to cancer and excessive growth, results from a disruption of imprinted gene expression in chromosome band 11p15.5. One third of individuals with BWS lose maternal-specific methylation at KvDMR1, a putative imprinting control region within intron 10 of the KCNQ1 gene, and it has been proposed that this epimutation results in aberrant imprinting and, consequently, BWS1, 2. Here we show that paternal inheritance of a deletion of KvDMR1 results in the de-repression in cis of six genes, including Cdkn1c, which encodes cyclin-dependent kinase inhibitor 1C. Furthermore, fetuses and adult mice that inherited the deletion from their fathers were 20-25% smaller than their wildtype littermates. By contrast, maternal inheritance of this deletion had no effect on imprinted gene expression or growth. Thus, the unmethylated paternal KvDMR1 allele regulates imprinted expression by silencing genes on the paternal chromosome. These findings support the hypothesis that loss of methylation in BWS patients activates the repressive function of KvDMR1 on the maternal chromosome, resulting in abnormal silencing of CDKN1C and the development of BWS.

Integrin ␣1␤1 is a collagen receptor abundantly expressed on microvascular endothelial cells. As well as being the only collagen receptor able to activate the Ras͞Shc͞mitogen-activated protein kinase pathway promoting fibroblast cell proliferation, it also acts to inhibit collagen and metalloproteinase (MMP) synthesis. We have observed that in integrin ␣1-null mice synthesis of MMP7 and MMP9 was markedly increased compared with that of their wildtype counterparts. As MMP7 and MMP9 have been shown to generate angiostatin from circulating plasminogen, and angiostatin acts as a potent inhibitor of endothelial cell proliferation, we determined whether tumor vascularization was altered in the ␣1-null mice. Tumors implanted into ␣1-null mice showed markedly decreased vascularization, with a reduction in capillary number and size, which was accompanied by an increase in plasma levels of angiostatin due to the action of MMP7 and MMP9 on circulating plasminogen. In vitro analysis of ␣1-null endothelial cells revealed a marked reduction of their proliferation on both integrin ␣1-dependent (collagenous) and independent (noncollagenous) substrata. This reduction was prevented by culturing ␣1-null cells with plasma derived from plasminogen-null animals, thus omitting the source from which to generate angiostatin. Plasma from tumor-bearing ␣1-null animals uniquely inhibited endothelial cell growth, and this inhibition was relieved by the coaddition of either MMP inhibitors, or antibody to angiostatin. Integrin ␣1-deficient mice thus provide a genetically characterized model for enhanced angiostatin production and serve to reveal an unwanted potential side effect of MMP inhibition, increased tumor angiogenesis.