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
RØYRVIK ET AL.2plastic properties. Colorectal tumors develop through waves of clonal expansionfollowing events that confer a growth advantage upon a cell. 3-5 Some sort ofpronounced genetic or epigenetic instability is usually considered to be a prerequisitefor the development of tumors. 4,6 Sporadic cases of colorectal cancer canbe sub-classified according to their molecular phenotypes: one referred to aschromosomally unstable (CIN), and the other unstable in microsatellites (MSI),representing 85% and 15% of all cases, respectively. 7 The former type is characterizedby its widespread aneuploidy, 8 which may be a result of the instability, 9and is largely overlapping with the category of tumors designated as microsatellitestable (MSS). The MSI-type carcinoma, the focus of this review, is usuallydiploid or near-diploid, but exhibits instability in microsatellites, short DNA sequencesconsisting of a stretch of small repetitive units (1-6 nucleotides) flankedby unique sequences. MSI tumors are also prone to lymphocyte infiltration, havea higher incidence of proximal colonic location, and have poorer differentiationthan MSS tumors. 10-17 The largely proximal location of these tumors may be significantin that this area of the colon is of a different embryological provenancethan the distal portion, the proximal originating from the midgut and the distalfrom the hindgut. 18 In addition, there are differences in blood supply, metabolism,bacterial flora, antigenic profile, and gene expression between the two sections ofthe normal colon. 18-20 All of the above have led to the assumption that there are atleast two distinct pathways which may lead to colon cancer – each with their ownset of preferential, though not absolute, molecular alterations and locations. Athird pathway of colorectal tumorigenesis has been proposed, the CpG island methylatorphenotype (CIMP), based on concurrent promoter hypermethylation ofmultiple genes in a given tumor. 21 However, the existence of this phenotype iscontroversial, and no consensus regarding it has been reached.In the progression from adenoma to carcinoma, both the MSI and MSS phenotypesoften display early mutations in either the CRC “gatekeeper” genes APC(at a frequency as high as 80% 22 ) or CTNNB1 (-catenin), and in KRAS for thedevelopment of adenomas, but their genetic and epigenetic profiles diverge moresignificantly when they start to approach malignancy (Fig. 1). 4 Though subsequentgene targets may be disparate, mutations frequently affect the same pathwaysin MSI and MSS tumors, as is the case with the TGFRII-SMADs pairinginvolved in proliferation repression and TP53-BAX in apoptotic promotion (Fig.2). Signaling pathways such as MAPK, WNT, TGF, AKT, and the TP53 networkare affected in most CRCs, and they are all implicated in cell cycle control.Some common targets in these pathways are illustrated in Figure 2; their alterationsare the result of both genetic and epigenetic mechanisms.II. IDENTIFICATION OF THE INSTABILITY OF TUMORSThe hereditary non-polyposis colorectal cancer syndrome (HNPCC) accounts forless than 5% of all CRC. The position of a gene co-segregating with this disease230
TARGET GENES OF MSI COLORECTAL CANCERFIGURE 1. Adenoma-carcinoma sequence. Changes affecting CIN tumors in blue, MSItumors in red; those common to both are in green.FIGURE 2. Signaling pathways commonly affected in colorectal tumorigenesis. Proteins inred indicate genes often affected in MSI tumors due either to mutations or epigeneticevents; those in blue are genes targeted by other mutational or epigenetic mechanisms inMSS tumors.231
- Page 114 and 115: strands. Proc Natl Acad Sci U S A 1
- Page 116 and 117: concomitant absence of transcript a
- Page 119 and 120: Volume 10 Number 7 July 2008 pp. 68
- Page 121 and 122: 682 RAS Signaling in Colorectal Car
- Page 123 and 124: 684 RAS Signaling in Colorectal Car
- Page 125 and 126: 686 RAS Signaling in Colorectal Car
- Page 127: Table W2. Detailed Somatic Events o
- Page 131 and 132: Identification of RCC2 as a prognos
- Page 133 and 134: INTRODUCTIONMicrosatellite instabil
- Page 135 and 136: unselected series of primary tumors
- Page 137 and 138: specificity, i.e. that they only am
- Page 139 and 140: On the assumption that DNA repair a
- Page 141 and 142: In order to ensure that gene mutati
- Page 143 and 144: Figure 2. Mutation frequency differ
- Page 145 and 146: and TAF1B (0.50), ACVR2A and ASTE1
- Page 147 and 148: Multivariate analysesA multivariate
- Page 149 and 150: When comparing our findings of muta
- Page 151 and 152: The test series included a low numb
- Page 153 and 154: entering M-phase remains to be seen
- Page 155 and 156: 12. Duval A, Reperant M, Hamelin R
- Page 157 and 158: 34. Martineau-Thuillier S, Andreass
- Page 159: AppendicesAppendix I:List of abbrev
- Page 163: Critical Reviews TM in Oncogenesis,
- Page 167 and 168: TARGET GENES OF MSI COLORECTAL CANC
- Page 169 and 170: TARGET GENES OF MSI COLORECTAL CANC
- Page 171 and 172: TARGET GENES OF MSI COLORECTAL CANC
- Page 173 and 174: TARGET GENES OF MSI COLORECTAL CANC
- Page 175 and 176: TARGET GENES OF MSI COLORECTAL CANC
- Page 177 and 178: TARGET GENES OF MSI COLORECTAL CANC
- Page 179 and 180: TARGET GENES OF MSI COLORECTAL CANC
- Page 181 and 182: TARGET GENES OF MSI COLORECTAL CANC
- Page 183 and 184: TARGET GENES OF MSI COLORECTAL CANC
- Page 185 and 186: TARGET GENES OF MSI COLORECTAL CANC
- Page 187 and 188: TARGET GENES OF MSI COLORECTAL CANC
- Page 189 and 190: TARGET GENES OF MSI COLORECTAL CANC
- Page 191: TARGET GENES OF MSI COLORECTAL CANC
TARGET GENES OF MSI COLORECTAL CANCERFIGURE 1. Ade<strong>no</strong>ma-carc<strong>in</strong>oma sequence. Changes affect<strong>in</strong>g CIN tumors <strong>in</strong> blue, MSItumors <strong>in</strong> red; those common to both are <strong>in</strong> green.FIGURE 2. Signal<strong>in</strong>g pathways commonly affected <strong>in</strong> colorectal tumorigenesis. Prote<strong>in</strong>s <strong>in</strong>red <strong>in</strong>dicate genes often affected <strong>in</strong> MSI tumors due either to mutations or epi<strong>genetic</strong>events; those <strong>in</strong> blue are genes targeted by other mutational or epi<strong>genetic</strong> mechanisms <strong>in</strong>MSS tumors.231