Lesions of ERBB2, PTEN, and PIK3CA activate the phosphatidylinositol 3-kinase (PI3K) pathway during cancer development by increasing levels of phosphatidylinositol-3,4,5-triphosphate (PIP 3 ). 3-Phosphoinositide-dependent kinase 1 (PDK1) is the first node of the PI3K signal output and is required for activation of AKT. PIP 3 recruits PDK1 and AKT to the cell membrane through interactions with their pleckstrin homology domains, allowing PDK1 to activate AKT by phosphorylating it at residue threonine-308. We show that total PDK1 protein and mRNA were overexpressed in a majority of human breast cancers and that 21% of tumors had five or more copies of the gene encoding PDK1, PDPK1. We found that increased PDPK1 copy number was associated with upstream pathway lesions (ERBB2 amplification, PTEN loss, or PIK3CA mutation), as well as patient survival. Examination of an independent set of breast cancers and tumor cell lines derived from multiple forms of human cancers also found increased PDK1 protein levels associated with such upstream pathway lesions. In human mammary cells, PDK1 enhanced the ability of upstream lesions to signal to AKT, stimulate cell growth and migration, and rendered cells more resistant to PDK1 and PI3K inhibition. After orthotopic transplantation, PDK1 overexpression was not oncogenic but dramatically enhanced the ability of ERBB2 to form tumors. Our studies argue that PDK1 overexpression and increased PDPK1 copy number are common occurrences in cancer that potentiate the oncogenic effect of upstream lesions on the PI3K pathway. Therefore, we conclude that alteration of PDK1 is a critical component of oncogenic PI3K signaling in breast cancer. [Cancer Res 2009;69(15):6299-306]

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Enhancer of zeste homolog 2 (EZH2) is a key epigenetic regulator that catalyzes the trimethylation of H3K27 and is modulated by post-translational modifications (PTMs). However, the precise regulation of EZH2 PTMs remains elusive. We, herein, report that EZH2 is acetylated by acetyltransferase P300/CBP-associated factor (PCAF) and is deacetylated by deacetylase SIRT1. We identified that PCAF interacts with and acetylates EZH2 mainly at lysine 348 (K348). Mechanistically, K348 acetylation decreases EZH2 phosphorylation at T345 and T487 and increases EZH2 stability without disrupting the formation of polycomb repressive complex 2 (PRC2). Functionally, EZH2 K348 acetylation enhances its capacity in suppression of the target genes and promotes lung cancer cell migration and invasion. Further, elevated EZH2 K348 acetylation in lung adenocarcinoma patients predicts a poor prognosis. Our findings define a new mechanism underlying EZH2 modulation by linking EZH2 acetylation to its phosphorylation that stabilizes EZH2 and promotes lung adenocarcinoma progression.

Pre-eclampsia is a pregnancy-related disease that may cause maternal, neonatal and fetal morbidity and mortality and exists in 3–5% of pregnancies worldwide. The discovery of dysregulated microRNAs and their roles in placental development has provided a new avenue for elucidating the mechanism involved in this pregnancy-specific disorder. Here, the roles of human miR-181a-5p, a microRNA that is increased in both the plasma and placenta of severe pre-eclamptic patients, in invasion and migration of trophoblasts were investigated. Ectopic-expression of miR-181a-5p impaired the invasion and migration of HTR-8/SVneo cells, whereas miR-181a-5p inhibition had the opposite effects. IGF2BP2, which harbors a highly conserved miR-181a-5p-binding site within its 3ʹ-UTR, was identified to be directly inhibited by miR-181a-5p. Moreover, siRNAs targeting IGF2BP2 imitated the effects of overexpressed miR-181a-5p on HTR-8/SVneo cell invasion and migration, whereas restoring IGF2BP2 expression by overexpressing a plasmid encoding IGF2BP2 partially reversed the studied inhibitory functions of miR-181a-5p. Thus, we demonstrated here that miR-181a-5p suppresses the invasion and migration of cytotrophoblasts, and its inhibitory effects were at least partially mediated by the suppression of IGF2BP2 expression, thus shedding new light on the roles of miR-181a-5p in the pathogenesis of severe pre-eclampsia.

Starch synthesis is a key process that influences crop yield and quality, though little is known about the regulation of this complex metabolic pathway. Here, we present the identification of ZmbZIP91 as a candidate regulator of starch synthesis via co-expression analysis in maize (Zea mays L.). ZmbZIP91 was strongly associated with the expression of starch synthesis genes. Reverse tanscription-PCR (RT-PCR) and RNA in situ hybridization indicated that ZmbZIP91 is highly expressed in maize endosperm, with less expression in leaves. Particle bombardment-mediated transient expression in maize endosperm and leaf protoplasts demonstrated that ZmbZIP91 could positively regulate the expression of starch synthesis genes in both leaves and endosperm. Additionally, the Arabidopsis mutant vip1 carried a mutation in a gene (VIP1) that is homologous to ZmbZIP91, displayed altered growth with less starch in leaves, and ZmbZIP91 was able to complement this phenotype, resulting in normal starch synthesis. A yeast one-hybrid experiment and EMSAs showed that ZmbZIP91 could directly bind to ACTCAT elements in the promoters of starch synthesis genes (pAGPS1, pSSI, pSSIIIa, and pISA1). These results demonstrate that ZmbZIP91 acts as a core regulatory factor in starch synthesis by binding to ACTCAT elements in the promoters of starch synthesis genes.