Regulator of telomere length 1 (RTEL1) is an essential DNA helicase that disassembles telomere loops (T loops) and suppresses telomere fragility to maintain the integrity of chromosome ends. We established that RTEL1 also associates with the replisome through binding to proliferating cell nuclear antigen (PCNA). Mouse cells disrupted for the RTEL1-PCNA interaction (PIP mutant) exhibited accelerated senescence, replication fork instability, reduced replication fork extension rates, and increased origin usage. Although T-loop disassembly at telomeres was unaffected in the mutant cells, telomere replication was compromised, leading to fragile sites at telomeres. RTEL1-PIP mutant mice were viable, but loss of the RTEL1-PCNA interaction accelerated the onset of tumorigenesis in p53-deficient mice. We propose that RTEL1 plays a critical role in both telomere and genome-wide replication, which is crucial for genetic stability and tumor avoidance.

BackgroundHLTF (Helicase-like Transcription Factor) is a DNA helicase protein homologous to the SWI/SNF family involved in the maintenance of genomic stability and the regulation of gene expression. HLTF has also been found to be frequently inactivated by promoter hypermethylation in human colon cancers. Whether this epigenetic event is required for intestinal carcinogenesis is unknown.ResultsTo address the role of loss of HLTF function in the development of intestinal cancer, we generated Hltf deficient mice. These mutant mice showed normal development, and did not develop intestinal tumors, indicating that loss of Hltf function by itself is insufficient to induce the formation of intestinal cancer. On the Apcmin/+ mutant background, Hltf- deficiency was found to significantly increase the formation of intestinal adenocarcinoma and colon cancers. Cytogenetic analysis of colon tumor cells from Hltf -/-/Apcmin/+ mice revealed a high incidence of gross chromosomal instabilities, including Robertsonian fusions, chromosomal fragments and aneuploidy. None of these genetic alterations were observed in the colon tumor cells derived from Apcmin/+ mice. Increased tumor growth and genomic instability was also demonstrated in HCT116 human colon cancer cells in which HLTF expression was significantly decreased.ConclusionTaken together, our results demonstrate that loss of HLTF function promotes the malignant transformation of intestinal or colonic adenomas to carcinomas by inducing genomic instability. Our findings highly suggest that epigenetic inactivation of HLTF, as found in most human colon cancers, could play an important role in the progression of colon tumors to malignant cancer.

A putative leucine-rich repeat receptor-like protein kinase (LRR-RLK) gene together with its 5′ and 3′ untranslated regions of jute (Corchorus olitorius L.) has been identified and sequenced. The gene is 3,371 bp long containing two exons and one intron. The coding sequence of the gene is 2,879 bp long encoding a peptide of 957 amino acids. The predicted protein contains several domains and motifs characteristic of a transmembrane protein kinase. It is complete with domains for an Nterminal leucine-rich repeat and a protein kinase core, an active site for serine/threonine protein kinase, an ATP binding conserved site and a transmembrane region.

Regulator of telomere length 1 (RTEL1) is a DNA helicase protein that has been demonstrated to be required for the maintenance of telomere length and genomic stability. It has also been found to be essential for DNA homologous recombination during DNA repairing. Human RTEL1 genomic locus (20q13.3) is frequently amplified in multiple types of human cancers, including hepatocellular carcinoma and gastrointestinal tract tumors, indicating that upregulated RTEL1 activity could be important for tumorigenesis. In this study, we have developed a conditional transgenic mouse model that overexpress mouse Rtel1 in a Cre-excision manner. By crossing with a ubiquitous Cre mouse line, we further demonstrated that these established Rtel1 conditional transgenic mice allow to efficiently and highly express a functional Rtel1 that is able to rescue the embryonic defects of Rtel1 null mouse allele. Furthermore, we demonstrated that more than 70% transgenic mice that widely overexpress Rtel1 developed liver tumors that recapitulate many malignant features of human hepatocellular carcinoma (HCC). Our work not only generated a valuable mouse model for determining the role of RTEL1 in the development of cancers, but also provided the first genetic evidence to support that amplification of RTEL1, as observed in several types of human cancers, is tumorigenic.