Significance: MicroRNAs (miRNAs) are small ∼22-nt RNAs that are important regulators of posttranscriptional gene expression. Since their initial discovery, they have been shown to be involved in many cellular processes, and their misexpression is associated with disease etiology. Currently, nearly 2,800 human miRNAs are annotated in public repositories. A key question in miRNA research is how many miRNAs are harbored by the human genome. To answer this question, we examined 1,323 short RNA sequence samples and identified 3,707 novel miRNAs, many of which are human-specific and tissue-specific. Our findings suggest that the human genome expresses a greater number of miRNAs than has previously been appreciated and that many more miRNA molecules may play key roles in disease etiology.

Maternally expressed gene 3 (MEG3) is a maternally expressed imprinted gene representing a large noncoding RNA in which microRNAs (miRNAs) and small nucleolar RNAs are also hosted. It is capable of interacting with cyclic AMP, p53, murine double minute 2 (MDM2) and growth differentiation factor 15 (GDF15) playing a role in cell proliferation control. MEG3 expression is under epigenetic control, and aberrant CpG methylation has been observed in several types of cancer. Moreover, gene copy number loss has been reported as additional mechanism associated with tumorigenesis. MEG3 deletion seems to upregulate the paternally expressed genes and on the other hand downregulate the expression of downstream maternally expressed genes and tumor suppressor miRNAs, although there are conflicting data on the topic. MEG3 could represent a tumor suppressor gene located in chromosome 14q32 and its association with tumorigenesis is growing every day.

Arginine deprivation, either by nutritional starvation or exposure to ADI-PEG20, induces adaptive transcriptional upregulation of ASS1 and ASL in glioblastoma multiforme ex vivo cultures and cell lines. This adaptive transcriptional upregulation is blocked by neoplasia-specific CpG island methylation in either gene, causing arginine auxotrophy and cell death. In cells with methylated ASS1 or ASL CpG islands, ADI-PEG20 initially induces a protective autophagic response, but abrogation of this by chloroquine accelerates and potentiates cytotoxicity. Concomitant methylation in the CpG islands of both ASS1 and ASL, observed in a subset of cases, confers hypersensitivity to ADI-PEG20. Cancer stem cells positive for CD133 and methylation in the ASL CpG island retain sensitivity to ADI-PEG20. Our results show for the first time that epigenetic changes occur in both of the two key genes of arginine biosynthesis in human cancer and confer sensitivity to therapeutic arginine deprivation. We demonstrate that methylation status of the CpG islands, rather than expression levels per se of the genes, predicts sensitivity to arginine deprivation. Our results suggest a novel therapeutic strategy for this invariably fatal central nervous system neoplasm for which we have identified robust biomarkers and which overcomes the limitations to conventional chemotherapy imposed by the blood/brain barrier.

Background: In HIV cohorts with access to highly active antiretroviral therapy (HAART), the incidence of Kaposi's sarcoma (KS) is falling; however, the incidence of multicentric Castleman's disease (MCD) in HIV has not previously been described. Methods: The incidence of HIV-associated MCD was calculated from a prospective HIV database with 56 202 patient-years of follow-up and compared with KS. Univariate and multivariate analyses were carried out to identify factors associated with MCD. Plasma human herpesvirus (HHV)-8 DNA levels were measured in HIV-seropositive individuals with newly diagnosed MCD (n = 24), KS (n = 72), HIV-associated lymphoma (n = 74) and HIV-positive controls (n = 53). Results: From 24 cases of HIV-associated MCD, the incidence measured 4.3/10 000 patient-years [95% confidence interval (CI) 2.7–6.4]. The incidence in the pre-HAART (1983–1996), early-HAART (1997–2001) and later HAART (2002–2007) eras were 2.3 (95% CI 0.02–4.2), 2.8 (95% CI 0.9–6.5) and 8.3 (95% CI 4.6–12.6), respectively, representing a statistically significant increase over time (P < 0.05). In contrast, from 1180 cases of KS, the incidence in this cohort decreased with time. Multivariate analysis demonstrated that a nadir CD4 count >200/mm³, increased age, no previous HAART exposure and non-Caucasian ethnicity were all associated with an increased risk of MCD. Plasma HHV-8 DNA levels were higher in patients with newly diagnosed MCD than with KS, lymphomas or HIV-positive controls (Mann–Whitney U-test, P < 0.0001). Conclusions: The incidence of HIV-associated MCD is increasing. It appears to occur more frequently in older HIV-positive individuals with well-preserved immune function.