Heterozygous APC germline mutations impart predisposition to colorectal cancer.

Familial adenomatous polyposis (FAP) is an inherited syndrome caused by a heterozygous adenomatous polyposis coli (APC) germline mutation, associated with a profound lifetime risk for colorectal cancer. While it is well accepted that tumorigenic transformation is initiated following acquisition of a second mutation and loss of function of the APC gene, the role of heterozygous APC mutation in this process is yet to be discovered. This work aimed to explore whether a heterozygous APC mutation induces molecular defects underlying tumorigenic transformation and how different APC germline mutations predict disease severity. Three FAP-human embryonic stem cell lines (FAP1/2/3-hESC lines) carrying germline mutations at different locations of the APC gene, and two control hESC lines free of the APC mutation, were differentiated into colon organoids and analyzed by immunohistochemistry and RNA sequencing. In addition, data regarding the genotype and clinical phenotype of the embryo donor parents were collected from medical records. FAP-hESCs carrying a complete loss-of-function of a single APC allele (FAP3) generated complex and molecularly mature colon organoids, which were similar to controls. In contrast, FAP-hESCs carrying APC truncation mutations (FAP1 and FAP2) generated only few cyst-like structures and cell aggregates of various shape, occasionally with luminal parts, which aligned with their failure to upregulate critical differentiation genes early in the process, as shown by RNA sequencing. Abnormal disease phenotype was shown also in non-pathological colon of FAP patients by the randomly distribution of proliferating cells throughout the crypts, compared to their focused localization in the lower part of the crypt in healthy/non-FAP patients. Genotype/phenotype analysis revealed correlations between the colon organoid maturation potential and FAP severity in the carrier parents. In conclusion, this study suggest that a single truncated APC allele is sufficient to initiate early molecular tumorigenic activity. In addition, the results hint that patient-specific hESC-derived colon organoids can probably predict disease severity among FAP patients.

LIN28: A Stem Cell Factor with a Key Role in Pediatric Tumor Formation.

Differentiation and development are normally unidirectional processes in which progenitor/stem cells differentiate into more mature cells. Transformation of adult cells into cancer cells is accompanied in many cases by dedifferentiation of the adult cell, while differentiation failure of progenitor cells can result in the formation of unique type of cancers called pediatric cancer. LIN28A and its paralog LIN28B are pluripotent genes that are expressed mainly in stem/progenitor cells. Since the first identification of LIN28 in mammals, numerous studies demonstrated the general oncogenic features of these genes. In this review, we emphasize the unique role of LIN28 in pediatric tumor formation. We show, based on comprehensive literature screen and analysis of published microarray data, that LIN28 expression in pediatric tumors is even more common than in adult tumors, and discuss the possibility that in the case of pediatric cancers, LIN28 acts by preventing normal development/differentiation rather than by transformation of mature cells into cancer cells. Overall, this review highlights the role of LIN28 as a bridge point between embryonic development, stem cell biology, and cancer.

Multiple regulatory layers of SREBP1/2 by SIRT6.

The NAD(+)-dependent protein deacetylase SIRT6 regulates genome stability, cancer, and lifespan. Mice overexpressing SIRT6 (MOSES) have lower low-density lipoprotein cholesterol levels and are protected against the physiological damage of obesity. Here, we examined the role of SIRT6 in cholesterol regulation via the lipogenic transcription factors SREBP1 and SREBP2, and AMP-activated protein kinase (AMPK). We show that SIRT6 represses SREBP1 and SREBP2 by at least three mechanisms. First, SIRT6 represses the transcription levels of SREBP1/SREBP2 and that of their target genes. Second, SIRT6 inhibits the cleavage of SREBP1/SREBP2 into their active forms. Third, SIRT6 activates AMPK by increasing the AMP/ATP ratio, which promotes phosphorylation and inhibition of SREBP1 by AMPK. Reciprocally, the expression of miR33a and miR33b from the introns of SREBP2 and SREBP1, respectively, represses SIRT6 levels. Together, these findings explain the mechanism underlying the improved cholesterol homeostasis in MOSES mice, revealing a relationship between fat metabolism and longevity.

An outbreak of achromobacter xylosoxidans associated with ultrasound gel used during transrectal ultrasound guided prostate biopsy.

PURPOSE: We describe an outbreak of Achromobacter xylosoxidans after transrectal ultrasound guided prostate biopsy at a urology unit at a tertiary care center as well as clinical and microbiological investigation, and intervention. MATERIALS AND METHODS: In September 2008, several days after undergoing transrectal ultrasound guided prostate biopsy, 4 patients were hospitalized with fever. We reviewed the procedure and infection control practices in the urology service. Environmental cultures were obtained from equipment and materials used for the procedure. Isolates were identified by routine laboratory procedures with molecular confirmation and characterized by pulsed field gel electrophoresis. RESULTS: A. xylosoxidans was isolated from the urine of 2 patients, of whom 1 also had a positive blood culture. Review of transrectal ultrasound guided prostate biopsy revealed that the lubricant gel used in the procedure, which the biopsy needle passes through, was held in a plastic container that was repeatedly refilled from a large bag. A. xylosoxidans was isolated from this container. Pulsed field gel electrophoresis showed that the isolates obtained from patients and the gel were identical. CONCLUSIONS: Contaminated lubricant gel was the cause of this outbreak. The practice of repeatedly refilling gel containers with nonsterile gel was replaced by the use of individual sterile gel sachets in each patient. No further cases occurred. During an invasive procedure involving a sterile body site, such as transrectal ultrasound guided prostate biopsy, using sterile gel is essential. Our experience emphasizes the crucial need to review all invasive procedures from an infection control perspective.

Cluster of pseudoinfections with Burkholderia cepacia associated with a contaminated washer-disinfector in a bronchoscopy unit.

In December 2008, bronchoalveolar lavage fluid samples obtained from 3 patients were positive for Burkholderia cepacia complex on culture. Samples obtained from bronchoscopes and rinse-water samples obtained from the washer-disinfector were found to be positive for B. cepacia complex. The cause of this pseudo-outbreak was that the washer-disinfector was installed without the required antibacterial filter.