My note on paper: Aberrant Wnt/beta-catenin signaling can induce chromosomal instability in colon cancer

Paper: Aberrant Wnt/beta-catenin signaling can induce chromosomal instability in colon cancer
(doi:10.1073/pnas.0604206103)

Abstract:
Chromosomal instability (CIN+)
1. hallmark of most colon tumors
2. promote tumor progression by increasing rate of genetic aberration
3. occur from mitosis/spindle checkpoint defect

Gap:
Molecular mechanism is unk

Rational:
1. colon cancer develop majorly from mutation of APC (Anaphase-promoting complex)
2. malfunction of APC causes wnt/b-catenin activation --> activate conductin/AXIN2

Research results:
1.wnt/catenin activation causes CIN via up-regulation of conductin
2.human colon cancer with CIN - found conductin higher
3.conductin is higher during the mitosis
4.conductin is localized with mitotic spindle of colon cancer cells
5.conductin binds polo-like kinase 1
6.when APC is forcibly downreglated by iRNA - conductin is ectopic upregulated lead to CIN in chromosomal stable colon cancer
7.higher expression of conductin disrupt spindle checkpoint (anaphase) - requires localized polo-like kinase1
8.KD conductin in colon carcinoma clls/mouse embryo fibroblast caused the checkpoint 8.KD conductin in colon carcinoma clls/mouse embryo fibroblast caused the checkpoint activation

Introduction;
1.wnt binds to Frizzled (receptor) and LRP (coreceptor)
2.causing accumulation of b-catenin
3.b-catenin is degraded by APC, GSK3B, CK1 and scaffold protein Axin1 and conduction/Axin2 through phosphorylation to b-catenin
4.b-catenin binds transcription factors (TCF/LEF - T cell factor/lymphocyte enhancer factor) activate gene related to proliferation and survival
5. abnormal activation of wnt/b-catenin is CRC initiation
6.mutations of APC - earliest and most frequent in CRC
7.conductin negatively regulates Wnt signaling pw - promote degradation of b-catenin
8.overexpression conductin which found in tumor could not suppress the abnormal activation of wnt/b-catenin
9.conductin acts on mitotic spindle checkpoint and bind PLK1
10.APC(-/-) tumor - abnormal wnt/b-catenin -- lead to CIN through up-regulated conductin

Mitotic spindle checkpoint
1.prevent segregation errors at anaphase
2.effctor on the checkpoint -- anaphase-promoting cpx or cyclosome (APC/C)
3.E3 ubiquitin ligase promotes degradation of mitotic regulator (PLK1) -- anaphase initiation
4.APC/C is inhibited by checkpoint to make sure microtubule-kinetochore attachment

Results:
1. Conductin Is Highly Up-Regulated in CIN Human Colon Tumors

Showing the expression level of conductin in tumor and non-tumor tissue in different type of chromosomal structure; CIN+ (chromosomal instability) and CIN-(non-chromosomal instability); using real-time PCR to measure the level of expression

2. Overexpression of Conductin Causes CIN

3. Wnt/beta-Catenin Signaling Activation Causes CIN via Conductin and Conductin Is Up-Regulated During Mitosis and Binds to PLK1

4. Conductin Compromises the Mitotic Spindle Checkpoint

Discussion part:

1.molecular basis of CIN in colon cancer is unk

2. mutated APC --> dysregulation of wnt signaling pw --> with unk mechanism leading to CIN

3. mutated APC -->aberrant wnt/catenin transcriptional activity --> upregulated conductin --> negatively regulates mitotic spindle checkpoint --> CIN (this finding correlates with the expression level of conductin which is up in the CIN type compare to non-CIN colon cancer and normal mucosae.

4. conductin overexpression not affect integrity if spindle microtubules, not cause obvious defect in spindle orientation

5. conductin may regulate the mitotic spindle checkpoint through signaling --> suppress the spindle checkpoint

6. conductin is the upstream regulator for PLK1 which is the mitotic regulator

7. other Wnt pw components, APC, GSK3b, and b-catenin -- associated with spindle apparatus

8. molecular mechanism of Wnt pa components that related to spindle function is largely unclear

9.wnt signaling promotes G1/s transition of cell cycle by transcriptional activation of regulators -- cyclin D1 and c-myc

10.authors proposed wnt signaling controls late events of cell cycles by modulating mitosis

11.up-regulation of conductin -- modify mitotic spindle checkpoint -- allowing execution of mitosis under growth-promoting conditions (another safety mechanism)

SW480 -- colon cancer cell line with possessing weak spindle checkpoint, chromosomally unstable, express high level of conductin
HCT116 -- colon cancer cell line chromosomal stable, carry mutated  b-catenin, wt-APC, low expression of conductin