MicroRNAs are small noncoding 18- to 24-nt RNAs that are predicted to regulate expression of as many as 30% of protein-encoding genes. In prostate adenocarcinoma, 39 microRNAs are up-regulated, and six microRNAs are down-regulated. Production and function of microRNA requires coordinated processing by proteins of the microRNA machinery. Dicer, an RNase III endonuclease, is an essential component of the microRNA machinery. From a gene array analysis of 16 normal prostate tissue samples, 64 organ-confined, and four metastatic prostate adenocarcinomas, we identified an up-regulation of major components of the microRNA machinery, including Dicer, in metastatic prostate adenocarcinoma. Immunohistochemical studies on a tissue microarray consisting of 232 prostate specimens confirmed up-regulation of Dicer in prostatic intraepithelial neoplasia and in 81% of prostate adenocarcinoma. The increased Dicer level in prostate adenocarcinoma correlated with clinical stage, lymph node status, and Gleason score. Western blot analysis of benign and neoplastic prostate cell lines further confirmed Dicer up-regulation in prostate adenocarcinoma. Dicer up-regulation may explain an almost global increase of microRNA expression in prostate adenocarcinoma. The presence of up-regulated microRNA machinery may predict the susceptibility of prostate adenocarcinoma to RNA interference-based therapy.

Differential microRNA (miR) expression is described in nonsmall cell lung carcinoma. miR biogenesis requires a set of proteins collectively referred to as the miR machinery. In the proposed multistep carcinogenesis model, peripheral adenocarcinoma of the lung develops from noninvasive precursor lesions known as atypical adenomatous hyperplasia (AAH) and bronchioloalveolar carcinoma (BAC). The gene array analysis of BAC and adenocarcinoma showed a transient upregulation of Dicer (a key effector protein for small interfering RNA and miR function) and PACT along with down-regulation of most genes encoding miR machinery proteins. Immunohistochemically, Dicer was up-regulated in AAH and BAC and down-regulated in areas of invasion and in advanced adenocarcinoma. A fraction of adenocarcinomas lose Dicer as a result of deletions at the Dicer locus. Expanded immunohistochemical and Western blot analysis showed higher Dicer level in squamous cell carcinoma (SCC) of the lung when compared with adenocarcinoma. Other proteins of the RNAinduced silencing complex (RISC; SND1, PACT, and FXR1) were also present at higher levels in a SCC cell line when compared with an adenocarcinoma cell line. In conclusion, the stoichiometry of miR machinery and RISC depends on histologic subtype of lung carcinoma, varies along the AAH-BACadenocarcinoma sequence, and might explain the observed abnormal miR profile in lung cancer. The status of the endogenous miR machinery in various histologic subtypes and stages of lung cancer may help to predict the toxicity of and susceptibility to future RNA interference-based therapy.

Base excision repair (BER) protein expression is important for resistance to DNA damage-induced cytotoxicity. Conversely, BER imbalance [DNA polymerase β (Polβ) deficiency or repair inhibition] enhances cytotoxicity of radiation and chemotherapeutic DNA-damaging agents. Whereas inhibition of critical steps in the BER pathway result in the accumulation of cytotoxic DNA double-strand breaks, we report that DNA damage-induced cytotoxicity due to deficiency in the BER protein Polβ triggers cell death dependent on poly(ADP-ribose) (PAR) polymerase activation yet independent of PAR-mediated apoptosis-inducing factor nuclear translocation or PAR glycohydrolase, suggesting that cytotoxicity is not from PAR or PAR catabolite signaling. Cell death is rescued by the NAD + metabolite β-nicotinamide mononucleotide and is synergistic with inhibition of NAD + biosynthesis, showing that DNA damage-induced cytotoxicity mediated via BER inhibition is primarily dependent on cellular metabolite bioavailability. We offer a mechanistic justification for the elevated alkylation-induced cytotoxicity of Polβ-deficient cells, suggesting a linkage between DNA repair, cell survival, and cellular bioenergetics.