Cyclic AMP-regulated Synthesis of the Tissue Inhibitors of Metalloproteinases Suppresses the Invasive Potential of the Human Fibrosarcoma Cell Line HT1080

Tissue inhibitors of metalloproteinases (TIMPs) play an important role in regulating the activity of matrix metalloproteinases (MMPs). Tumor cell invasion and metastasis closely correlate with the activities of two members of MMPs, MMP2 and MMP9, both of which degrade type IV collagen in basement membranes. We herein report that the treatment of HT1080 cells with 8-bromo-cAMP and other chemicals that activate cyclic adenylase activity induces the expression of TIMP1 and TIMP2 both at the mRNA and the protein levels and that this induction of TIMPs correlates with suppression of invasive phenotypes of HT1080 cells. Treatment with various cAMP-elevating reagents induced the expression of TIMPs and MMP2 in HT1080 cells, whereas the expression of MMP9 was not significantly affected. The protein amounts of TIMP1, TIMP2, and MMP2 secreted into the medium from HT1080 cells treated with 1 mM 8-bromo-cAMP were 7.9-, 9.3-, and 8.5-fold higher than those secreted from untreated cells, respectively. Induction of these mRNAs by 8-bromo-cAMP was blocked by HA1004, a protein kinase A inhibitor, but not by calphostin C, a protein kinase C inhibitor. Cycloheximide abolished the induction of TIMPs and MMP2 mRNAs by 8-bromo-cAMP, indicating that the induction depends on a newly synthesized protein(s) whose expression may be regulated by cAMP. Type IV collagenolytic activity and the invasiveness of HT1080 cells, both of which were suppressed by 8-bromo-cAMP, were efficiently restored when the cells were exposed to anti-TIMP antibodies, demonstrating the importance of the increased levels of TIMP1 and TIMP2 proteins for the cAMP-mediated suppression of both type IV collagenolytic activity and the invasiveness of HT1080 cells.