Brain Tumors and the Lynch Syndrome

Lynch syndrome (LS) (MIM No. 120435-6), previously known as hereditary nonpolyposis colorectal cancer (HNPCC) (Boland, 2005), is an autosomal dominant disorder caused by germline mutation in one of the DNA mismatch repair (MMR) genes. LS is among the most prevalent cancer syndromes in man and is estimated to account for 1-6% of all colorectal cancers (Lynch & de la Chapelle, 2003)

Molecular mechanisms of cancer predisposition in HNPCC/Lynch syndrome

Hereditary non-polyposis colorectal carcinoma (HNPCC; Lynch syndrome) is among the most common hereditary cancers in man and a model of cancers arising through deficient DNA mismatch repair (MMR). It is inherited in a dominant manner with predisposing germline mutations in the MMR genes, mainly MLH1, MSH2, MSH6 and PMS2. Both copies of the MMR gene need to be inactivated for cancer development. Since Lynch syndrome family members are born with one defective copy of one of the MMR genes in their germline, they only need to acquire a so called second hit to inactivate the MMR gene. Hence, they usually develop cancer at an early age. MMR gene inactivation leads to accumulation of mutations particularly in short repeat tracts, known as microsatellites, causing microsatellite instability (MSI). MSI is the hallmark of Lynch syndrome tumors, but is present in approximately 15% of sporadic tumors as well. There are several possible mechanisms of somatic inactivation (i.e. the second hit ) of MMR genes, for instance deletion of the wild-type copy, leading to loss of heterozygosity (LOH), methylation of promoter regions necessary for gene transcription, or mitotic recombination or gene conversion. In the Lynch syndrome tumors carrying germline mutations in the MMR gene, LOH was found to be the most frequent mechanism of somatic inactivation in the present study. We also studied MLH1/MSH2 deletion carriers and found that somatic mutations identical to the ones in the germline occurred frequently in colorectal cancers and were also present in extracolonic Lynch syndrome-associated tumors. Chromosome-specific marker analysis implied that gene conversion, rather than mitotic recombination or deletion of the respective gene locus accounted for wild-type inactivation. Lynch syndrome patients are predisposed to certain types of cancers, the most common ones being colorectal, endometrial and gastric cancer. Gastric cancer and uroepithelial tumors of bladder and ureter were observed to be true Lynch syndrome tumors with MMR deficiency as the driving force of tumorigenesis. Brain tumors and kidney carcinoma, on the other hand, were mostly MSS, implying the possibility of alternative routes of tumor development. These results present possible implications in clinical cancer surveillance. In about one-third of families suspected of Lynch syndrome, mutations in MMR genes are not found, and we therefore looked for alternative mechanisms of predisposition. According to our results, large genomic deletions, mainly in MSH2, and germline epimutations in MLH1, together explain a significant fraction of point mutation-negative families suspected of Lynch syndrome and are associated with characteristic clinical and family features. Our findings have important implications in the diagnosis and management of Lynch syndrome families.Tjock- och ändtarmscancer (kolorektalcancer) är en av de vanligaste cancerformerna i Finland. Dödligheten är högre än för både bröst- och prostatacancer och utgör efter lungcancer den nästvanligaste orsaken till morbiditet och mortalitet till följd av cancer. Hereditär nonpolyposis kolorektalcancer (HNPCC; Lynch syndrom) hör till de vanligast förekommande ärftliga formerna av cancer, och är samtidigt en modell för canceruppkomst till följd av defekt i gener med DNA repareringsfunktion (MMR; mismatch repair). Båda kopiorna av MMR genen skall vara ur funktion för cancerutveckling. Individer som tillhör familjer där Lynch syndrom har konstaterats föds med en defekt kopia av MMR genen i groddbanan, d.v.s. det krävs bara att den återstående normala kopian slås ur funktion för att cancer ska uppstå. Därför får individer med Lynch syndrom cancer vid ung ålder jämfört med den övriga befolkningen. Defekt MMR gen leder till ansamling av mutationer i arvsmassan, speciellt i repetitiva sekvenser, även kallat mikrosatellit instabilitet. Denna form av instabilitet är kännetecknande för Lynch syndrom, men förekommer även hos individer med sporadisk cancer i mindre utsträckning. Inaktivering av den kvarstående normala kopian hos individer med Lynch syndrom kan ske på flera sätt, bl.a. genom deletion, eller epimutationer (reversibla förändringar i DNA som inte förändrar i DNAts nukleotidsekvens) eller mitotisk rekombination/genkonversion (utbyte av DNA mellan kromosomerna i ett kromosompar). I vår studie var deletion den vanligaste formen av MMR geninaktivering hos patienter med Lynch syndrom. Vi fann också att genkonversion, istället för mitotisk rekombination, ledde till inaktivering av den normala kopian hos en del patienter. Individer med Lynch syndrom har en ärftlig benägenhet för vissa typer av cancer, främst kolorektal-, livmoder- och magsäckscancer. Våra resultat tyder på att magsäckscancer och cancer i urinblåsa och urinledare tillhör tumörspektrat vid Lynch syndrom, i och med att dessa cancertyper påvisades uppstå genom defekt MMR funktion. Hjärntumörer och njurcancer, å andra sidan, trots MMR mutation i groddbanan, saknade de övriga kännetecknen för tumörer vid Lynch syndrom, därmed antas dessa cancerformer uppstå genom andra mekanismer. En tredjedel av alla familjer som misstänks ha Lynch syndrom påvisar inga mutationer i MMR generna, och därför sökte vi efter alternativa mekanismer för cancerbenägenheten. Vi fann att omfattande genomiska deletioner och epimutationer i groddbanan tillsammans förklarade en signifikant andel av fallen där Lynch syndrom misstänktes och de konstaterades vara förknippade med typiska kliniska och familjära särdrag. Dessa fynd har viktig innebörd vid diagnostisering och behandling av Lynch syndrom familjer

Molecular Basis of Mismatch Repair Protein Deficiency in Tumors from Lynch Suspected Cases with Negative Germline Test Results

Some 10–50% of Lynch-suspected cases with abnormal immunohistochemical (IHC) staining remain without any identifiable germline mutation of DNA mismatch repair (MMR) genes. MMR proteins form heterodimeric complexes, giving rise to distinct IHC patterns when mutant. Potential reasons for not finding a germline mutation include involvement of an MMR gene not predicted by the IHC pattern, epigenetic mechanism of predisposition, primary mutation in another DNA repair or replication-associated gene, and double somatic MMR gene mutations. We addressed these possibilities by germline and tumor studies in 60 Lynch-suspected cases ascertained through diagnostics (n = 55) or research (n = 5). All cases had abnormal MMR protein staining in tumors but no point mutation or large rearrangement of the suspected MMR genes in the germline. In diagnostic practice, MSH2/MSH6 (MutS Homolog 2/MutS Homolog 6) deficiency prompts MSH2 mutation screening; in our study, 3/11 index individuals (27%) with this IHC pattern revealed pathogenic germline mutations in MSH6. Individuals with isolated absence of MSH6 are routinely screened for MSH6 mutations alone; we found a predisposing mutation in MSH2 in 1/7 such cases (14%). Somatic deletion of the MSH2-MSH6 region, joint loss of MSH6 and MSH3 (MutS Homolog 3) proteins, and hindered MSH2/MSH6 dimerization offered explanations to misleading IHC patterns. Constitutional epimutation hypothesis was pursued in the MSH2 and/or MSH6-deficient cases plus 38 cases with MLH1 (MutL Homolog 1)-deficient tumors; a primary MLH1 epimutation was identified in one case with an MLH1-deficient tumor. We conclude that both MSH2 and MSH6 should be screened in MSH2/6- and MSH6-deficient cases. In MLH1-deficient cases, constitutional epimutations of MLH1 warrant consideration

3'-UTR Poly(T/U) tract deletions and altered expression of EWSR1 are a hallmark of mismatch repair-deficient cancers

The genome-wide accumulation of DNA replication errors known as microsatellite instability (MSI) is the hallmark lesion of DNA mismatch repair (MMR)-deficient cancers. Although testing for MSI is widely used to guide clinical management, the contribution of MSI at distinct genic loci to the phenotype remains largely unexplored. Here, we report that a mononucleotide (T/U)16 tract located in the 3' untranslated region (3'-UTR) of the Ewing sarcoma breakpoint region 1 (EWSR1) gene is a novel MSI target locus that shows perfect sensitivity and specificity in detecting mismatch repair-deficient cancers in two independent populations. We further found a striking relocalization of the EWSR1 protein from nucleus to cytoplasm in MMR-deficient cancers and that the nonprotein-coding MSI target locus itself has a modulatory effect on EWSR1 gene expression through alternative 3' end processing of the EWSR1 gene. Our results point to a MSI target gene-specific effect in MMR-deficient cancers. Cancer Res; 74(1); 224-34. ©2013 AACR

Genome-wide meta-analysis of phytosterols reveals five novel loci and a detrimental effect on coronary atherosclerosis

Correction: Volume13, Issue1 Article Number1122 DOI 10.1038/s41467-022-28863-y Published FEB 25 2022Phytosterol serum concentrations are under tight genetic control. The relationship between phytosterols and coronary artery disease (CAD) is controversially discussed. We perform a genome-wide meta-analysis of 32 phytosterol traits reflecting resorption, cholesterol synthesis and esterification in six studies with up to 9758 subjects and detect ten independent genomewide significant SNPs at seven genomic loci. We confirm previously established associations at ABCG5/8 and ABO and demonstrate an extended locus heterogeneity at ABCG5/8 with different functional mechanisms. New loci comprise HMGCR, NPC1L1, PNLIPRP2, SCARB1 and APOE. Based on these results, we perform Mendelian Randomization analyses (MR) revealing a risk-increasing causal relationship of sitosterol serum concentrations and CAD, which is partly mediated by cholesterol. Here we report that phytosterols are polygenic traits. MR add evidence of both, direct and indirect causal effects of sitosterol on CAD.Peer reviewe

The β-tail domain (βTD) regulates physiologic ligand binding to integrin CD11b/CD18

Crystallographic and electron microscopy studies revealed genuflexed (bent) integrins in both unliganded (inactive) and physiologic ligandbound (active) states, suggesting that local conformational changes are sufficient for activation. Herein we have explored the role of local changes in the contact region between the membrane-proximal β-tail domain (βTD) and the ligand-binding βA domain of the bent conformation in regulating interaction of integrin CD11b/CD18 (αMβ2) with its physiologic ligand iC3b. We replaced the βTD CD loop residues D658GMD of the CD18 (β2) subunit with the equivalent D672SSG of the β3 subunit, with AGAA or with NGTD, expressed the respective heterodimeric receptors either transiently in epithelial HEK293T cells or stably in leukocytes (K562), and measured their ability to bind iC3b and to conformation-sensitive mAbs. In the presence of the physiologic divalent cations Ca(2+) plus Mg(2+) (at 1 mM each), the modified integrins showed increased (in HEK293) or constitutive (in K562) binding to iC3b compared with wild-type receptors. K562 expressing the βTD-modified integrins bound in Ca(2+)Mg(2+) to the βA-directed high-affinity reporter mAb 24 but not to mAb KIM127, a reporter of the genu-straightened state. These data identify a role for the membrane proximal βTD as an allosteric modulator of integrin activation