Activation of the cyclin D1 gene by the EPA-associated protein p300 through AP-1 inhibits cellular apoptosis

The adenovirus E1A protein interferes with regulators of apoptosis and grow th by physically interacting with cell cycle regulatory proteins including the retinoblastoma tumor suppressor protein and the coactivator proteins p3 00/CBP (where CBP is the CREB-binding protein). The p300/CBP proteins occup y a pivotal role in regulating mitogenic signaling and apoptosis, The mecha nisms by which cell cycle control genes are directly regulated by p300 rema in to be determined. The cyclin D1 gene, which is overexpressed in many dif ferent tumor types, encodes a regulatory subunit of a holoenzyme that phosp horylates and inactivates PRE. In the present study E1A12S inhibited the cy clin D1 promoter Fia the amino-terminal p300/CBP binding domain in human ch oriocarcinoma JEG-3 cells. p300 induced cyclin D1 protein abundance, and p3 00, but not CBP, induced the cyclin DI promoter. cyclin D1 or p300 overexpr ession inhibited apoptosis in JEG-3 cells. The CH3 region of p300, which wa s required for induction of cyclin D1, was also required for the inhibition of apoptosis. p300 activated the cyclin D1 promoter through an activator p rotein-1 (AP-1) site at -954 and was identified within a DNA-bound complex with c-Jun at the AP-1 site. Apoptosis rates of embryonic fibroblasts deriv ed from mice homozygously deleted of the cyclin D1 gene (cyclin D1(-/-)) we re increased compared with wild type control on several distinct matrices. p300 inhibited apoptosis in cyclin D1(+/+) fibroblasts but increased apopto sis in cyclin D1(-/-) cells. The anti-apoptotic function of cyclin D1, demo nstrated by sub-G(1) analysis and annexin V staining, may contribute to its cellular transforming and cooperative oncogenic properties.