Matrix metalloproteinases: they're not just for matrix anymore!

The matrix metalloproteinases (MMPs) have been viewed as bulldozers, destro ying the extracellular matrix to permit normal remodeling and contribute to pathological tissue destruction and tumor cell invasion. More recently, th e identification of specific matrix and non-matrix substrates for MMPs and the elucidation of the biological consequence of cleavage indicates that pe rhaps MMPs should be viewed more as pruning shears, playing sophisticated r oles in modulating normal cellular behavior, cell-cell communication and tu mor progression.