TIMP-1 regulation of cell cycle in human breast epithelial cells via stabilization of p27KIP1 protein

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Abstract
Increasing evidence suggests that tissue inhibitor of metalloproteinases-1 (TIMP-1) can directly regulate cell growth and apoptosis independent of its matrix metalloproteinases (MMPs)-inhibitory activity. While TIMP-1's antiapoptotic activity has been well demonstrated, conflicting data has been reported regarding TIMP-1's role in growth regulation. Here we show that TIMP-1 reduces the growth rate of human breast epithelial (MCF10A) cells by inducing cell cycle arrest at G1. TIMP-1-mediated cell cycle arrest is associated with its downregulation of cyclin D1 and upregulation of p27KIP1, resulting in inhibition of cyclin-dependent kinase activity necessary for phosphorylation of the tumor suppressor retinoblastoma protein. We further show that TIMP-1 modulation of cyclin D1 and p27KIP1 is achieved through TIMP-1-mediated differential regulation of protein stability independent of growth factor signaling. We also show that TIMP-1-mediated differential regulation of cyclin D1 and p27KIP1 is independent of cell adhesion signaling. Whereas approximately 50% of MCF10A cells with reduced TIMP-1 expression underwent cell death following loss of cell adhesion (anoikis), TIMP-1 overexpressing cells remained viable with prominent cell cycle arrest without detectable cell death. Taken together, we propose that TIMP-1-mediated cell survival independent of cell adhesion is accompanied with cell cycle arrest in human breast epithelial cells, although cell cycle regulation may not be a prerequisite for TIMP-1 regulation of apoptosis in general.