Novel genetic and epigenetic alterations in ... - Ous-research.no
Novel genetic and epigenetic alterations in ... - Ous-research.no Novel genetic and epigenetic alterations in ... - Ous-research.no
Introductioninasmuch as 80% of colorectal tumors [64]. Activation of the proto-oncogene KRAS is alsoconsidered an early event, and is present in 35% of colorectal carcinomas ** . TP53, called “theguardian of the genome”[66] is a critical component in sensing DNA damage and stresssignals, and is the most frequently altered tumor suppressor gene in human cancer in general.In colorectal cancer it is not altered until late in the development, in advanced carcinomas,and close to 50% of all CRC have mutations in TP53 at this stage †† . According to this model,microsatellite instability is a late event as it is only seen in advanced adenomas andsubsequent stages[64].Compelling evidence in recent years have questioned this paradigm and turned the scaletowards adenomas giving rise only to chromosome instable and CIMP-negative tumors,while the previously “ignored” hyperplastic polyps (HPs) have re-established their malignantpotential, as a subgroup of these, the sessile serrated polyps, are likely to give rise to MSI andCIMP tumors[67-70]. An equivalent to the adenoma-carcinoma sequence has now beensuggested and includes the development from normal mucosa via HPs and serrated lesionsto MSI-carcinomas. Typical for these cancers is that mutation in the proto-oncogene BRAFis considered the “gatekeeper”, and that the dysregulation of the methylation machineryoccurs before microsatellite instability (Figure 10)[71].Hypermethylation in normal-appearing colorectal mucosa adjacent to the primary tumorshas gained interest lately. This abnormality is thought to be the initiating event intumorigenesis, as it presents a field in which the cells are especially susceptible for additionalalterations. With a sufficing amount of alterations, the tumorigenesis is initiated. Thisphenomenon is called “field effect” or “field cancerization”, and several genes have beensuggested to generate such[72-75].** Catalogue of Somatic Mutations in Cancer database – http://www.sanger.ac.uk/genetics/CGP/cosmic/†† IARC TP53 Mutation Database (Release 12) - http://www-p53.iarc.fr/26
IntroductionFigure 10. Molecular pathways to colorectal cancer. Colorectal cancer develops through several distincthistopathological steps, each of which is associated with different kind of alterations. It is now believed thatMSI (in red) and CIN tumors (in blue) develop through two distinct pathways, the sessile serrated pathway,giving rise to MSI-tumors in the proximal colon, and the traditional adenoma-carcinoma pathway, giving rise toCIN tumors in the distal colon. While APC is considered to be the initiating event in the initiating event forCIN tumors, BRAF is one of the earliest recognized changes among the MSI precursors. The geneticcomplexity increases throughout CIN tumorigenesis due to the chromosomal instability, while CIMP leads toepigenetic instability among the MSI precursors, eventually affecting MLH1, which then causes MSI. With MSI,genes carrying repetitive units within their coding region are especially susceptible for mutations.27
- Page 1 and 2: Novel genetic and epigenetic altera
- Page 3 and 4: TABLE OF CONTENTSACKNOWLEDGEMENTS .
- Page 5 and 6: ACKNOWLEDGEMENTSThe present work ha
- Page 7 and 8: Prefacetechnology[3]. This new tech
- Page 10 and 11: SummaryThe subgroup of carcinomas w
- Page 12 and 13: Introduction“Epigenetic inheritan
- Page 14 and 15: Introductionamino acid change it is
- Page 16 and 17: Introductionmethylation during embr
- Page 18 and 19: IntroductionDNA is most of the time
- Page 20 and 21: IntroductionFigure 5. DNA methylati
- Page 22 and 23: IntroductionFigure 6. Incidence rat
- Page 24 and 25: IntroductionFigure 8. Tumor staging
- Page 28 and 29: IntroductionInstabilities involved
- Page 30 and 31: Introductionthere seems to be a fid
- Page 32 and 33: Introductionsevere alterations are
- Page 34 and 35: Introductionpopulation-wide screeni
- Page 36 and 37: IntroductionFigure 12. Present and
- Page 38 and 39: RESULTS IN BRIEFPaper Ia. “DNA hy
- Page 40 and 41: Results in Briefinstability, and se
- Page 42 and 43: Results in BriefUnivariate survival
- Page 44 and 45: Discussionseveral factors, and full
- Page 46 and 47: Discussionlow threshold, we increas
- Page 48 and 49: DiscussionIt may seem like unnecess
- Page 50 and 51: Discussionthan 96% DHPLC do not sta
- Page 52 and 53: DiscussionFigure 13. Mutation detec
- Page 54 and 55: DiscussionClinical impact of molecu
- Page 56 and 57: Discussionmarkers with a very high
- Page 58 and 59: Discussionchromosomes in metaphase[
- Page 60 and 61: DiscussionThese examples underline
- Page 62 and 63: Discussiongenes. One is based on mu
- Page 64 and 65: CONCLUSIONSWe have identified novel
- Page 66 and 67: Future PerspectivesMolecular risk a
- Page 68 and 69: REFERENCES1. Breasted J (1930) The
- Page 70 and 71: References29. Deng G, Chen A, Pong
- Page 72 and 73: References57. Al-Sukhni W, Aronson
- Page 74 and 75: References84. Kunkel TA (1993) Nucl
IntroductionFigure 10. Molecular pathways to colorectal cancer. Colorectal cancer develops through several dist<strong>in</strong>cthistopathological steps, each of which is associated with different k<strong>in</strong>d of <strong>alterations</strong>. It is <strong>no</strong>w believed thatMSI (<strong>in</strong> red) <strong>and</strong> CIN tumors (<strong>in</strong> blue) develop through two dist<strong>in</strong>ct pathways, the sessile serrated pathway,giv<strong>in</strong>g rise to MSI-tumors <strong>in</strong> the proximal colon, <strong>and</strong> the traditional ade<strong>no</strong>ma-carc<strong>in</strong>oma pathway, giv<strong>in</strong>g rise toCIN tumors <strong>in</strong> the distal colon. While APC is considered to be the <strong>in</strong>itiat<strong>in</strong>g event <strong>in</strong> the <strong>in</strong>itiat<strong>in</strong>g event forCIN tumors, BRAF is one of the earliest recognized changes among the MSI precursors. The <strong>genetic</strong>complexity <strong>in</strong>creases throughout CIN tumorigenesis due to the chromosomal <strong>in</strong>stability, while CIMP leads toepi<strong>genetic</strong> <strong>in</strong>stability among the MSI precursors, eventually affect<strong>in</strong>g MLH1, which then causes MSI. With MSI,genes carry<strong>in</strong>g repetitive units with<strong>in</strong> their cod<strong>in</strong>g region are especially susceptible for mutations.27
Change language