Author Archives: Marjaana E Pussila

Reduced mismatch repair gene expression and functional deficiency as indicators of Lynch syndrome

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Mariann Kasela, M.Sc. will defend the doctoral dissertation entitled “Reduced mismatch repair gene expression and functional deficiency as indicators of Lynch syndrome” in the Faculty of Biological and Environmental Sciences, University of Helsinki, on 26 June 2020 at 12:00. The public examination will take place at the following address: Porthania, P673, Yliopistonkatu 3.

Professor Karl Heinimann, University of Basel, Switzerland, will serve as the opponent, and Professor Minna Nyström as the custos.

The dissertation will be published in the series Dissertationes Scholae Doctoralis Ad Sanitatem Investigandam Unviersitatis Helsinkiensis.

The dissertation is also available in electronic form through the E-thesis service.

Western diet enhances intestinal tumorigenesis in Min/+ mice, associating with mucosal metabolic and inflammatory stress and loss of Apc heterozygosity.

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Niku M, Pajari AM, Sarantaus L, Päivärinta E, Storvik M, Heiman-Lindh A, Suokas S, Nyström M, Mutanen M.

Western-type diet (WD) is a risk factor for colorectal cancer, but the underlying mechanisms are poorly understood. We investigated the interaction of WD and heterozygous mutation in the Apc gene on adenoma formation and metabolic and immunological changes in the histologically normal intestinal mucosa of ApcMin/+ (Min/+) mice. The diet used was high in saturated fat and low in calcium, vitamin D, fiber and folate. The number of adenomas was twofold higher in the WD mice compared to controls, but adenoma size, proliferation or apoptosis did not differ. The ratio of the Min to wild-type allele was higher in the WD mice, indicating accelerated loss of Apc heterozygosity (LOH). Densities of intraepithelial CD3ε+ T lymphocytes and of mucosal FoxP3+ regulatory T cells were higher in the WD mice, implying inflammatory changes. Western blot analyses from the mucosa of the WD mice showed suppressed activation of the ERK and AKT pathways and a tendency for reduced activation of the mTOR pathway as measured in phosphoS6/S6 levels. The expression of pyruvate dehydrogenase kinase 4 was up-regulated in both mRNA and protein levels. Gene expression analyses showed changes in oxidation/reduction, fatty acid and monosaccharide metabolic pathways, tissue organization, cell fate and regulation of apoptosis. Together, our results suggest that the high-risk Western diet primes the intestine to tumorigenesis through synergistic effects in energy metabolism, inflammation and oxidative stress, which culminate in the acceleration of LOH of the Apc gene.

J Nutr Biochem. 2016

Human DNA polymerase α interacts with mismatch repair proteins MSH2 and MSH6

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Itkonen HM, Kantelinen J, Vaara M, Parkkinen S, Schlott B, Grosse F, Nyström M, Syväoja JE, Pospiech H.

The high fidelity of genome duplication is ensured by cooperation of the proofreading and mismatch repair (MMR) activities of DNA polymerases. Here, we show that human mismatch recognizing proteins MutS homologue 2 (MSH2) and MSH6 co-purify and interact with replicative Pol α, the replicative primase which replicates DNA with poor fidelity. We show that MSH2 associates with known human replication origins with different dynamics than Pol α. Furthermore, we explored the potential functional role of Pol α in the mismatch repair reaction by using an in vitro mismatch repair assay and observed that Pol α promotes mismatch repair. Taken together, we show that human Pol α interacts with MSH2-MSH6 complex and propose that this interaction occurs during the mismatch repair reaction.

FEBS Letters, 2016

 

Assessment of the InSiGHT interpretation criteria for the clinical classification of 24 MLH1 and MSH2 gene variants

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Tricarico R, Kasela M, Mareni C, Thompson BA, Drouet A, Staderini L, Gorelli G, Crucianelli F, Ingrosso V, Kantelinen J, Papi L, De Angioletti M, Berardi M, Gaildrat P, Soukarieh O, Turchetti D, Martins A, Spurdle AB, Nyström M, Genuardi; InSiGHT Variant Interpretation Committee.

 

Pathogenicity assessment of DNA variants in disease genes to explain their clinical consequences is an integral component of diagnostic molecular testing. The International Society for Gastrointestinal Hereditary Tumors (InSiGHT) has developed specific criteria for the interpretation of mismatch repair (MMR) gene variants. Here, we performed a systematic investigation of 24 MLH1 and MSH2 variants. The assessments were done by analyzing population frequency, segregation, tumor molecular characteristics, RNA effects, protein expression levels, and in vitro MMR activity. Classifications were confirmed for 15 variants and changed for three, and for the first time determined for six novel variants. Overall, based on our results, we propose the introduction of some refinements to the InSiGHT classification rules. The proposed changes have the advantage of homogenizing the InSIGHT interpretation criteria with those set out by the Evidence-based Network for the Interpretation of Germline Mutant Alleles (ENIGMA) consortium for the BRCA1/BRCA2 genes. We also observed that the addition of only few clinical data was sufficient to obtain a more stable classification for variants considered as “likely pathogenic” or “likely nonpathogenic.” This shows the importance of obtaining as many as possible points of evidence for variant interpretation, especially from the clinical setting.

Hum Mutat. 2016