Phylogenetic and functional analysis of sequence variation of human papillomavirus type 31 E6 and E7 oncoproteins.

High-risk human papillomaviruses (HPV) are the causative agents of cervical and other anogenital cancers as well as a subset of head and neck cancers. The E6 and E7 oncoproteins of HPV contribute to oncogenesis by associating with the tumour suppressor protein p53 and pRb, respectively. For HPV types 16 and 18, intratypic sequence variation was shown to have biological and clinical significance. The functional significance of sequence variation among HPV 31 variants was studied less intensively. HPV 31 variants belonging to different variant lineages were found to have differences in persistence and in the ability to cause high grade cervical intraepithelial neoplasia. In the present study, we started to explore the functional effects of natural sequence variation of HPV 31 E6 and E7 oncoproteins. The E6 variants were tested for their effects on p53 protein stability and transcriptional activity, while the E7 variants were tested for their effects on pRb protein level and also on the transcriptional activity of E2F transcription factors. HPV 31 E7 variants displayed uniform effects on pRb stability and also on the activity of E2F transcription factors. HPV 31 E6 variants had remarkable differences in the ability to inhibit the trans-activation function of p53 but not in the ability to induce the in vivo degradation of p53. Our results indicate that natural sequence variation of the HPV 31 E6 protein may be involved in the observed differences in the oncogenic potential between HPV 31 variants.

The C. elegans Homolog of RBBP6 (RBPL-1) regulates fertility through controlling cell proliferation in the germline and nutrient synthesis in the intestine.

RBBP6 (retinoblastoma binding protein 6, also known as PACT or P2P-R in humans) is a multi-domain protein that functions in multiple processes, such as mitosis, cell differentiation, and cell apoptosis. RBBP6 is evolutionarily conserved and is present in unicellular organisms to mammals. Studies of RBBP6 have mostly focused on its RB- and p53-binding domains, which are found exclusively in mammals. Here, we investigated the C. elegans homolog of RBBP6 to explore the functional roles of its other domains. We found that RBPL-1, the homolog of RBBP6 in C. elegans, is indispensable for worm development. RNAi silencing of rbpl-1 led to embryonic lethality, as well as defects in oocyte production and intestine development. rbpl-1 RNAi worms showed defects in germ cell proliferation, suggesting that RBPL-1 regulates mitosis. Moreover, RNAi silencing of rbpl-1 inhibited nutrient synthesis in the worm intestine. RBPL-1, as a nucleolus protein, was found to be expressed in diverse tissues and necessary for both germline and soma development. Using microarray analysis, we identified ≈700 genes whose expression levels were changed at least 10-fold in rbpl-1 worms. We propose that RBPL-1, like its yeast homolog, may regulate gene expression as an mRNA cleavage and polyadenylation factor. Taken together, the findings from this study reveal that RBPL-1 plays a pivotal role in C. elegans germline and soma development, suggesting that the functions of RBBP6 are conserved in diverse eukaryotic species.

Characterization of a novel WDR5-binding site that recruits RbBP5 through a conserved motif to enhance methylation of histone H3 lysine 4 by mixed lineage leukemia protein-1.

Histone modification is well established as a fundamental mechanism driving the regulation of transcription, replication, and DNA repair through the control of chromatin structure. Likewise, it is apparent that incorrect targeting of histone modifications contributes to misregulated gene expression and hence to developmental disorders and diseases of genomic instability such as cancer. The KMT2 family of SET domain methyltransferases, typified by mixed lineage leukemia protein-1 (MLL1), is responsible for histone H3 lysine 4 methylation, a marker of active genes. To ensure that this modification is correctly targeted, a multiprotein complex associates with the methyltransferase and directs activity. We have identified a novel interaction site on the core complex protein WD repeat protein-5 (WDR5), and we mapped the complementary site on its partner retinoblastoma-binding protein-5 (RbBP5). We have characterized this interaction by x-ray crystallography and show how it is fundamental to the assembly of the complex and to the regulation of methyltransferase activity. We show which region of RbBP5 contributes directly to mixed lineage leukemia activation, and we combine our structural and biochemical data to produce a model to show how WDR5 and RbBP5 act cooperatively to stimulate activity.