highlighted as a critical protein that regulates numerous cell functions from proliferation/apoptosis to stressresistance and aging. FoxO3a has been found to be deregulated in several diseases and FoxO3a targeting approaches are currently underway to treat various types of cancers. This review will describe the current concept of FoxO3a's pathological role in various diseases and elucidate the regulatory mechanisms involved. It will also provide the clinical significance and strategies to target FoxO3a to limit the progression of human diseases.
INTRODUCTIONForkhead box O (FoxO) transcription factors are the human homologues of the C. elegans transcription factor DAF-16 and share a highly conserved 110-amino acid DNA binding domain, forkhead box or winged-helix domain [1,2] . Forkhead box proteins comprise more than 100 members in humans, classified from FOXA to FOXR [3][4][5] . Members of class O share the characteristic of being regulated by the insulin/PI3K/Akt signaling pathway [4] . Four principal members of the mammalian FoxO subfamily, FoxO1, FoxO3a, FoxO4 and FoxO6 have been previously described [3] . Although they seem to bind a common set of DNA sites, FoxO6 is mainly specific to neurons, while the other 3 FoxO family members are expressed in most tissues. These FoxO members are linked to cell survival, cellular proliferation and DNA damage repair response [5,6] . Among them, FoxO3a has recently been studied extensively as a crucial protein that is involved in the regulation of several essential cellular functions (see page 349). Prior studies have shown that FoxO3a functions as a tumor suppressor by regulating expression of genes in-
AbstractThe Forkhead box O (FoxO) family has recently been highlighted as an important transcriptional regulator of crucial proteins associated with the many diverse functions of cells. So far, FoxO1, FoxO3a, FoxO4 and FoxO6 proteins have been identified in humans. Although each FoxO family member has its own role, unlike the other FoxO families, FoxO3a has been extensively studied because of its rather unique and pivotal regulation of cell proliferation, apoptosis, metabolism, stress management and longevity. FoxO3a alteration is closely linked to the progression of several types of cancers, fibrosis and other types of diseases. In this review, we will examine the function of FoxO3a in disease progression and also explore FoxO3a's regulatory mechanisms. We will also discuss FoxO3a as a potential target for the treatment of several types of disease.