Yin and yang of the plasminogen activator inhibitor.

Plasminogen activator inhibitor type one (PAI-1) is involved in many biological processes, and depending on a disease its overexpression, deficiency or normal level can sometimes produce surprising outcomes. This paper reviews low, high, and normal levels of PAI-1 in relation to diseases, their incidents, and possible treatment. Also, a role of PAI-1 in cancer is discussed with attention to "PAI-1 paradox" and explanation of the possible therapeutic applications using this protein.