Chinese tree shrews (Tupaia belangeri chinensis) possess many features valuable in animals used as experimental models in biomedical research. Currently, there are numerous attempts to employ tree shrews as models for a variety of human disorders: depression, myopia, hepatitis B and C virus infections, and hepatocellular carcinoma, to name a few. Here we present a publicly available annotated genome sequence for the Chinese tree shrew. Phylogenomic analysis of the tree shrew and other mammalians highly support its close affinity to primates. By characterizing key factors and signalling pathways in nervous and immune systems, we demonstrate that tree shrews possess both shared common and unique features, and provide a genetic basis for the use of this animal as a potential model for biomedical research.

KLF5 (Kruppel-like factor 5) is a basic transcription factor binding to GC boxes at a number of gene promoters and regulating their transcription. KLF5 is expressed during development and, in adults, with higher levels in proliferating epithelial cells. The expression and activity of KLF5 are regulated by multiple signaling pathways, including Ras/MAPK, PKC, and TGFbeta, and various posttranslational modifications, including phosphorylation, acetylation, ubiquitination, and sumoylation. Consistently, KLF5 mediates the signaling functions in cell proliferation, cell cycle, apoptosis, migration, differentiation, and stemness by regulating gene expression in response to environment stimuli. The expression of KLF5 is frequently abnormal in human cancers and in cardiovascular disease-associated vascular smooth muscle cells (VSMCs). Due to its significant functions in cell proliferation, survival, and differentiation, KLF5 could be a potential diagnostic biomarker and therapeutic target for cancer and cardiovascular diseases.

Accumulating evidence suggests that E3 ubiquitin ligases play important roles in cancer development. In this article, we provide a comprehensive summary of the roles of the Nedd4-like family of E3 ubiquitin ligases in human cancer. There are nine members of the Nedd4-like E3 family, all of which share a similar structure, including a C2 domain at the N-terminus, two to four WW domains in the middle of the protein, and a homologous to E6-AP COOH terminus domain at the C-terminus. The assertion that Nedd4-like E3s play a role in cancer is supported by the overexpression of Smurf2 in esophageal squamous cell carcinoma, WWP1 in prostate and breast cancer, Nedd4 in prostate and bladder cancer, and Smurf1 in pancreatic cancer. Because Nedd4-like E3s regulate ubiquitin-mediated trafficking, lysosomal or proteasomal degradation, and nuclear translocation of multiple proteins, they modulate important signaling pathways involved in tumorigenesis like TGFbeta, EGF, IGF, VEGF, SDF-1, and TNFalpha. Additionally, several Nedd4-like E3s directly regulate various cancer-related transcription factors from the Smad, p53, KLF, RUNX, and Jun families. Interestingly, multiple Nedd4-like E3s show ligase independent function. Furthermore, Nedd4-like E3s themselves are frequently regulated by phosphorylation, ubiquitination, translocation, and transcription in cancer cells. Because the regulation and biological output of these E3s is such a complex process, study of the role of these E3s in cancer development poses some challenges. However, understanding the oncogenic potential of these E3s may facilitate the identification and development of biomarkers and drug targets in human cancer.

The 13q21 tumor suppressor locus, as defined by chromosomal deletion, harbors the KLF5 transcription factor which may have tumor suppressor function. To investigate whether KLF5 plays a role in breast cancer, we evaluated all genes and/or expressed sequence tags (ESTs) within a 3.3 Mb common region of deletion at 13q21. Of these, only KLF5 mRNA was expressed at high levels in non-neoplastic breast epithelial cells and in normal human mammary tissue, but at lower levels in various breast cancer cell lines. Using the real time TaqMan PCR assay, hemizygous deletion at KLF5 was detected in 13 out of 30, or 43% of breast cancer cell lines tested, and various degrees of loss of expression were detected in 21 out of 30, or 70% of these cell lines. Each of the cases with hemizygous deletion also exhibited loss of KLF5 expression, suggesting that loss of expression can result from chromosomal deletion, and that KLF5 may undergo haploinsufficiency during carcinogenesis. Only one of the 30 breast cancer cell lines tested exhibited a mutation in KLF5, and neither promoter methylation nor homozygous deletion was detected in any of the cell lines. In contrast, loss of heterozygosity (LOH) was frequently detected at KLF5. Re-expression of wild-type KLF5 in T-47D breast cancer cells significantly inhibited colony formation in these cells. Of the KLF5-transfected clones that did form colonies, none were found to express KLF5 mRNA. These findings suggest that loss of function by deletion and/or loss of expression frequently occurs at KLF5, and KLF5 suppresses tumor cell growth in breast cancer.

Cancer often results from the accumulation of multiple genetic alterations. Although most malignancies are sporadic, only a small number of genes have been shown to undergo frequent mutations in sporadic cancers. The long arm of chromosome 16 is frequently deleted in human cancers, but the target gene for this deletion has not been identified. Here we report that ATBF1, which encodes a transcription factor that negatively regulates AFP and MYB but transactivates CDKN1A, is a good candidate for the 16q22 tumor-suppressor gene. We narrowed the region of deletion at 16q22 to 861 kb containing ATBF1. ATBF1 mRNA was abundant in normal prostates but more scarce in approximately half of prostate cancers tested. In 24 of 66 (36%) cancers examined, we identified 22 unique somatic mutations, many of which impair ATBF1 function. Furthermore, ATBF1 inhibited cell proliferation. Hence, loss of ATBF1 is one mechanism that defines the absence of growth control in prostate cancer.

Frequent genomic deletion and loss of expression as well as cell growth suppression indicate that KLF5 is a reasonable candidate for the tumor suppressor gene at 13q21 in prostate cancer. Mutation and promoter methylation are not common mechanisms for the inactivation of KLF5 in prostate cancer.

KLF5 is a transcription factor that plays important roles in multiple physical and pathological processes, including cell growth, cell cycle regulation, and angiogenesis. To better characterize KLF5 function in bladder carcinogenesis, we established stable TSU-Pr1 cell clones expressing different levels of KLF5. These clones were then characterized for cell growth, cell cycle progression, tumorigenesis, and alteration in gene expression. Overexpression of KLF5 promoted tumorigenesis of the TSU-Pr1 cancer cells in mice. Consistently, KLF5 increased G1 to S phase transition, which was accompanied by the upregulation of cyclin D1, phosphorylation of MAPK and Akt, and reduced protein levels for CDK inhibitors p27 and p15. Microarray analysis combined with expression verification in different cell systems identified a number of additional genes that are potentially regulated by KLF5, including HBP17, ITGA6, and RAIG1. These findings suggest that the KLF5 transcription factor plays an oncogenic role in the TSU-Pr1 bladder cancer cell line through the regulation of a subset of genes. ' 2005 Wiley-Liss, Inc.

The transcription factor KLF5 plays an important role in human carcinogenesis. In epithelial cells, the KLF5 protein is tightly regulated by the ubiquitin-proteasome pathway. To better understand the mechanisms for the regulation of KLF5 protein, we identified and characterized an E3 ubiquitin ligase for KLF5, i.e. WWP1. We found that WWP1 formed a protein complex with KLF5 in vivo and in vitro. Furthermore, WWP1 mediated the ubiquitination and degradation of KLF5, and the catalytic cysteine residue of WWP1 is essential for its function. A PY motif in a transactivation domain of KLF5 is necessary for its interaction with WWP1. Finally, WWP1 was amplified and overexpressed in some cancer cell lines from the prostate and breast, which negatively regulated the function of KLF5 in gene regulation. These findings not only established WWP1 as an E3 ubiquitin ligase for KLF5, they also further implicated the KLF5 pathway in human carcinogenesis.