No abstract

MicroRNAs (miRNAs) play key roles in regulation of cellular processes in response to changes in environment. In this study, we examined alterations in miRNA profiles in peripheral blood from 25 male medical students two months and two days before the National Examination for Medical Practitioners. Blood obtained one month after the examination were used as baseline controls. Levels of seven miRNAs (miR-16, -20b, -26b, -29a, -126, -144 and -144*) were significantly elevated during the pre-examination period in association with significant down-regulation of their target mRNAs (WNT4, CCM2, MAK, and FGFR1 mRNAs) two days before the examination. State anxiety assessed two months before the examination was positively and negatively correlated with miR-16 and its target WNT4 mRNA levels, respectively. Fold changes in miR-16 levels from two days before to one month after the examination were inversely correlated with those in WNT4 mRNA levels over the same time points. We also confirmed the interaction between miR-16 and WNT4 3′UTR in HEK293T cells overexpressing FLAG-tagged WNT4 3′UTR and miR-16. Thus, a distinct group of miRNAs in periheral blood may participate in the integrated response to chronic academic stress in healthy young men.

Ultraconserved regions (UCRs) are >200 bp genomic segments with perfect human-to-rodent sequence identity. Transcribed UCRs constitute a new category of noncoding RNAs whose functions remain poorly understood. The human transformer 2β (TRA2B) gene contains a 419-bp UCR spanning the 276-bp exon 2 and its neighboring introns. TRA2B exon 2 has premature stop codons, whereas an exon 2-containing splice variant (TRA2β4) was expressed preferentially in the nuclei of human colon cancer cells. TRA2β4 knockdown p53-independently stimulated CDKN1A transcription and increased p21, resulting in the appearance of senescent cells. Biotin pull-down and RNA immunoprecipitation assays revealed that TRA2β4 interacted with Sp1 through a Sp1-binding sequence (485-GGGG-488) in a stem-loop structure of exon 2. Mutation of this sequence (485-AAGG-488) disrupted the stem-loop structure, blocked the interaction with Sp1 and increased CDKN1A transcription. Overexpression of TRA2β4 significantly decreased CDKN1A mRNA levels and accelerated cell growth, but the introduction of the mutation in the Sp1-binding sequence completely canceled these effects. Taken together, TRA2β4 may sequester Sp1 from occupying promoters of target genes including CDKN1A, promoting cell growth by interrupting the senescence-related gene expression program. This novel function of TRA2β4 may uncover an oncogenic function of transcribed UCRs.

Homeodomain-interacting protein kinase 2 (HIPK2) is a potential tumor suppressor that has a crucial role in the DNA damage response (DDR) by regulating cell-cycle checkpoint activation and apoptosis. However, it is unclear whether HIPK2 exerts distinct roles in DNA damage repair. The aim of this study was to identify novel target molecule(s) of HIPK2, which mediates HIPK2-dependent DNA damage repair. HIPK2-knockdown human colon cancer cells (HCT116) or hipk1/hipk2 double-deficient mouse embryonic fibroblasts could not remove histone H2A.X phosphorylated at Ser139 (γH2A.X) after irradiation with a sublethal dose (10 J/m(2)) of ultraviolet (UV)-C, resulting in apoptosis. Knockdown of HIPK2 in p53-null HCT116 cells similarly promoted the UV-C-induced γH2A.X accumulation and apoptosis. Proteomic analysis of HIPK2-associated proteins using liquid chromatography-tandem mass spectrometry identified heterochromatin protein 1γ (HP1γ) as a novel target for HIPK2. Immunoprecipitation experiments with HCT116 cells expressing FLAG-tagged HIPK2 and one of the HA-tagged HP1 family members demonstrated that HIPK2 specifically associated with HP1γ, but not with HP1α or HP1β, through its chromo-shadow domain. Mutation of the HP1box motif (883-PTVSV-887) within HIPK2 abolished the association. HP1γ knockdown also enhanced accumulation of γH2A.X and apoptosis after sublethal UV-C irradiation. In vitro kinase assay demonstrated an HP1γ-phosphorylating activity of HIPK2. Sublethal UV-C irradiation phosphorylated HP1γ. This phosphorylation was absent in endogenous HIPK2-silenced cells with HIPK2 3'UTR siRNA. Overexpression of FLAG-HIPK2, but not the HP1box-mutated or kinase-dead HIPK2 mutant, in the HIPK2-silenced cells increased HP1γ binding to trimethylated (Lys9) histone H3 (H3K9me3), rescued the UV-C-induced phosphorylation of HP1γ, triggered release of HP1γ from histone H3K9me3 and suppressed γH2A.X accumulation. Our results suggest that HIPK2-dependent phosphorylation of HP1γ may participate in the regulation of dynamic interaction between HP1γ and histone H3K9me3 to promote DNA damage repair. This HIPK2/HP1γ pathway may uncover a new functional aspect of HIPK2 as a tumor suppressor.

Serine/arginine-rich splicing factor 3 (SRSF3) is a member of the SR protein family and plays wide-ranging roles in gene expression. The human SRSF3 gene generates two alternative splice transcripts, a major mRNA isoform (SRSF3-FL) encoding functional full-length protein and a premature termination codon (PTC)-containing isoform (SRSF3-PTC). The latter is degraded through nonsense-mediated mRNA decay (NMD). Treatment of a human colon cancer cell line (HCT116) with 100 μM sodium arsenite increased SRSF3-PTC mRNA levels without changing SRSF3-FL mRNA levels. A chemiluminescence-based NMD reporter assay system demonstrated that arsenite treatment inhibited NMD activity and increased SRSF3-PTC mRNA levels in the cytoplasm, facilitating translation of a truncated SRSF3 protein (SRSF3-TR) from SRSF3-PTC mRNA. SRSF3-TR lacked two-thirds of the Arg/Ser-rich (RS) domain whose phosphorylation state is known to be crucial for subcellular distribution. SRSF3-FL was localized in the nucleus, while overexpressed SRSF3-TR was diffusely distributed in the cytoplasm and the nucleus. A part of SRSF3-TR was also associated with stress granules in the cytoplasm. Interestingly, treatment of HCT116 cells with a small interference RNA specifically targeting SRSF3-PTC mRNA significantly attenuated arsenite-stimulated induction of c-JUN protein, its binding activity to the AP-1 binding site (-126 to 120 bp) in the interleukin (IL)-8 gene promoter, and AP-1 promoter activity, resulting in significant reduction of arsenite-stimulated IL-8 production. Our results suggest that SRSF3-TR may function as a positive regulator of oxidative stress-initiated inflammatory responses in colon cancer cells.