Human granzyme B (GrB) released from cytotoxic lymphocytes plays a key role in the induction of target cell apoptosis when internalized in the presence of perforin. Here we demonstrate that GrB also possesses a potent extracellular matrix remodeling activity. Both native and recombinant GrB caused detachment of immortalized and transformed cell lines, primary endothelial cells, and chondrocytes. Cell detachment by GrB induced endothelial cell death (anoikis). GrB also inhibited tumor cell spreading, migration, and invasion in vitro. Investigation into the underlying mechanism revealed that GrB efficiently cleaves three proteins involved in extracellular matrix structure and function: vitronectin, fibronectin, and laminin. In vitronectin, GrB cleaves after an Arg-Lys-Asp (RGD) motif, which is part of the integrin-binding site found in matrix proteins. We propose that targeting of the integrin-extracellular matrix interface by GrB may allow perforin-independent killing of target cells via anoikis, restrict motility of tumor cells, facilitate lymphocyte migration, or directly reduce virus infectivity. It may also contribute to tissue destruction in diseases in which extracellular GrB is evident, such as rheumatoid arthritis and atherosclerosis.

Most studies investigating laminins (LMs) in breast can1 Although there is considerable structural homology between LM isoforms 2 and overlap in receptors used, 3,4 they differ in their tissue distribution and functional properties and have different roles under normal and pathological conditions, including cancer.1,5-8 Alterations in the composition and level of expression of BM LMs and their receptors in breast cancer have been documented and shown to contribute to disease progression.9,10 In particular, the excessive proteolytic activity associated with cancer progression typically results in decreased LM deposition and dissolution of the BM, a hallmark of invasive breast tumors. [11][12][13] It is clear, however, that despite decreased BM deposition, some LM remains expressed in invasive breast tumor cells and contributes functionally to their motile and invasive phenotype.11,14 -16 Consistent with this, increased expression of several LM receptors has been reported in breast tumor cells and shown to be associated with metastatic progression and poor prognosis in breast cancer patients. 9,[17][18][19][20][21][22][23] Together, these studies suggest that production of LM by breast cancer cells most likely contributes to their metastatic dissemination through autocrine stimulation.Although the association between LMs and breast cancer progression is well supported, the critical LM isoform involved in the metastatic progression of breast tumors remains unclear. Most studies investigating the expression and function of LMs and their receptors in breast cancer have been interpreted as evidence for the role of LM-111 (␣1␤1␥1 trimer, previously known as laminin-1) or LM-332 (␣3␤3␥2 trimer, previously known as laminin-5) but did not take into account the lack of specificity of some of the LM antibodies 14,22,24,25 or the overlap in receptors used to bind these isoforms and the more recently identified LM-511/521 (␣5␤1␥1 and ␣5␤2␥1 trimers, previously known as laminin-10 and -11, respecSupported by the US Army Department of Defense (concept award no. W81XWH-04-1-0707 to N.P.).

Objective-The collagen VI muscular dystrophies, Bethlem myopathy and Ullrich congenital muscular dystrophy, form a continuum of clinical phenotypes. Glycine mutations in the triple helix have been identified in both Bethlem and Ullrich congenital muscular dystrophy, but it is not known why they cause these different phenotypes.Methods-We studied eight new patients who presented with a spectrum of clinical severity, screened the three collagen VI messenger RNA for mutations, and examined collagen VI biosynthesis and the assembly pathway.Results-All eight patients had heterozygous glycine mutations toward the N-terminal end of the triple helix. The mutations produced two assembly phenotypes. In the first patient group, collagen VI dimers accumulated in the cell but not the medium, microfibril formation in the medium was moderately reduced, and the amount of collagen VI in the extracellular matrix was not significantly altered. The second group had more severe assembly defects: some secreted collagen VI tetramers