p53 and Functions
Activated p53 mediates apoptosis, cell cycle arrest, senescence, DNA repair, or metabolism (Lane and Levine, 2010). The primary structures of p53 and its isoforms are depicted (Figure 2). p53 induces cell cycle arrest by transactivating genes such as cyclin-dependent kinase inhibitor p21, or microRNA miR34. p53 induces apoptosis by transactivating proapoptotic genes such as BAX, PUMA, SCOTIN, and FAS, and inhibiting the antiapoptotic gene BCL-2 (Lane and Levine, 2010). p53 triggers pro-survival or cell death response, depending upon cell types, the intensity of the stress signal, and the extent of cellular damage (Menendez et al., 2009). Also, p53 plays a role in controlling cell motility via regulating the expression of smooth muscle α-actin (Comer et al., 1998), collagens IIα1 and VIα1 (Sun et al., 1999), and many others.
Figure 2  p53 and WWOX in GBM cell apoptosis. (A) Full-length p53 possesses two N-terminal transactivation acidic domains, a proline-rich domain, a central DNA-binding region, and a C-terminal domain, containing a nuclear localization signal, an oligomerization domain, and a basic region. N-terminal deletion mutants of p53 are also shown. (B) Three likely scenarios are proposed for WWOX and p53 to regulate GBM cell death. First, ectopic WWOX fails to induce apoptosis of GBM cells expressing endogenous wild type p53. It appears that ectopic WWOX binds and functionally antagonizes p53, and both proteins nullify each other’s function in inducing apoptosis. Second, no physical interactions between mutant p53 proteins and WWOX are expected in GBM cells. Thus, ectopic WWOX induce apoptosis in mutant p53-expressing cells. Finally, whether WWOX binds p53 isoforms is unknown. Also, whether ectopic WWOX induction of apoptosis in GBM cells expressing p53 isoforms remains to be established. TAD, transactivation domain; PrD, proline domain; NLS, nuclear localization signal; OD, oligomerization domain; BR, basic region.