Altered transcription control is responsible for the increased level of proliferation-associated P120 in rapidly growing breast carcinoma

Human NOP2/NSUN1 regulates ribosome biogenesis through non-catalytic complex formation with box C/D snoRNPs

5-Methylcytosine (m⁵C) is a base modification broadly found on various RNAs in the human transcriptome. In eukaryotes, m⁵C is catalyzed by enzymes of the NSUN family composed of seven human members (NSUN1-7). NOP2/NSUN1 has been primarily characterized in budding yeast as an essential ribosome biogenesis factor required for the deposition of m⁵C on the 25S ribosomal RNA (rRNA). Although human NOP2/NSUN1 has been known to be an oncogene overexpressed in several types of cancer, its functions and substrates remain poorly characterized. Here, we used a miCLIP-seq approach to identify human NOP2/NSUN1 RNA substrates. Our analysis revealed that NOP2/NSUN1 catalyzes the deposition of m⁵C at position 4447 on the 28S rRNA. We also find that NOP2/NSUN1 binds to the 5′ETS region of the pre-rRNA transcript and regulates pre-rRNA processing through non-catalytic complex formation with box C/D snoRNAs. We provide evidence that NOP2/NSUN1 facilitates the recruitment of U3 and U8 snoRNAs to pre-90S ribosomal particles and their stable assembly into snoRNP complexes. Remarkably, expression of both WT and catalytically inactive NOP2/NSUN1 in knockdown background rescues the rRNA processing defects and the stable assembly of box C/D snoRNP complexes, suggesting that NOP2/NSUN1-mediated deposition of m⁵C on rRNA is not required for ribosome synthesis.

Engineering unnatural nucleotide specificity to probe G protein signaling

G proteins comprise approximately 0.5% of proteins encoded by mammalian genomes. To date, there exists a lack of small-molecule modulators that could contribute to their functional study. In this report, we present the use of H-Ras to develop a system that answers this need. Small molecules that allow for the highly specific inhibition or activation of the engineered G protein were developed. The rational design preserved binding of the natural substrates to the G protein, and the mutations were functionally innocuous in a cellular context. This tool can be used for isolating specific G protein effectors, as we demonstrate with the identification of Nol1 as a putative effector of H-Ras. Finally, the generalization of this system was confirmed by applying it to Rap1B, suggesting that this method will be applicable to other G proteins.

Efficacy of p120 antisense-mediated therapy for pancreatic cancer

p120 antisense oligodeoxynucleotides were used to determine whether they inhibited cell growth of MIA PaCa-2, a highly tumorigenic human pancreatic carcinoma cell line. Growth inhibition assays were determined in vitro by the ability of these oligomers to inhibit DNA synthesis and cell growth. For in vivo studies, nude mice were injected with cells and palpable tumors were found in 16 of 20 animals by day 14. Sixteen animals (8 in each group) were then treated daily (25 mg/kg intraperitoneally) for up to 40 days with nonsense control oligomers or p120 antisense oligomers. p120 Antisense oligomers inhibited the in vitro proliferation of MIA PaCa-2 cells in a dose-dependent manner, and optimal growth inhibition of greater than 90% was achieved at an antisense oligomer concentration of 100 micromol/L. The tumor volume was calculated for antisense- and nonsense-treated animals. Fifteen days after the beginning of treatment, control animals had a significantly greater (P=0.0035) tumor volume (425=244 mm3 above baseline) as compared to p120 antisense-treated animals (166+/-116 mm3). Seven of the eight control animals formed tumors that had a volume greater than 1200 mm3 45 days after treatment was begun, whereas only three of eight p120 antisense-treated animals had tumors that were this large. Two of the latter three animals had relatively large, palpable tumors (>150 mm3) prior to treatment. Twenty days after treatment was stopped (day 60), all animals had tumors larger than 1200 mm3. p120 Antisense oligomers were effective for inhibiting in vitro growth of the pancreatic cancer cell line MIA PaCa-2. In preliminary studies, p120 antisense oligomers appeared to inhibit the rate of growth in nude mice; however, no cures were achieved. The most effective response was seen in animals with initial low tumor burden.

Nucleolar p120 is expressed as a delayed early response gene and is inducible by DNA-damaging agents

Regulation of the expression of the growth-related nucleolar p120 protein was examined in serum-deprived and stimulated nontransformed and SV40-transformed WI-38 human fibroblasts. In quiescent cells, transcriptional activity of the p120 gene was very low or undetectable, and the steady-state levels of the p120 mRNA and the p120 protein were also negligible. The transient expression of the p120 gene in the cell cycle was detected in middle G1-phase after the expression of the early response genes and before the expression of the DNA-synthesis genes. Protein synthesis was required for the induction of p120 expression in serum-stimulated cells. The increased level of p120 mRNA in middle G1-phase was attributed to an increased transcription rate of the p120 gene, and not to a change in p120 mRNA stability. The calculated half-life of p120 mRNA was unchanged (1.8 +/- 0.2 hr) in all four cell conditions tested; i.e., in middle G1- or S-phase cells and in exponentially growing normal or transformed cells. Transcription rate of the p120 gene was correlated with the steady-state levels of either p120 protein or p120 mRNA. A sharp increase in p120 mRNA level occurred in both normal and transformed cells treated with actinomycin D used to examine p120 mRNA stability. This induction of p120 mRNA expression was seen in early G1-phase, but not in quiescent cells, or in middle to late G1-phase when cells expressed the highest level of p120 mRNA. The same expression pattern was seen by treatment with chlorambucil, another DNA-damaging agent. The conclusions of these studies are that the expression of p120 (1) is serum inducible in a fashion characteristic of the delayed early response gene products, (2) requires the presence of newly synthesized proteins, (3) is regulated transcriptionally, and (4) can be induced by DNA-damaging agents.