Colon cancer is the second leading cause of cancer deaths in the U.S. Polyps, the first stage In tumor development

Colorectal cancer 150,000 cases diagnosed per year (i.e., your chances are 1/18) > 50,000 deaths (2nd to lung cancer) Early detection key >90% 5 year survival with early detection 60% if it has spread locally <10% if it has metastasized Data from ACS

Colorectal cancer treatment 1. Surgical removal of tumor 2.This can be followed by either Radiation or chemotherapy (fluorouracil) 3. Chemotherapy also used to slow the progress of metastatic disease Data from ACS

HNPCC 3% of all cases. Defects in mismatch repair. Familial adenomatous polyposis (FAP) 1% of all colon cancers Caused by mutation in a single gene = APC Colon cancer genetics 95% of cases sporadic (no genetic history)

Familial Adenomatous Polyposis (FAP)

polyps by age % risk of colon cancer by age 40 Inheriting an APC mutation dramatically increases Your risk of developing colorectal cancer

Treatment with an aspirin-like drug called celecoxib (a COX2 inhibitor) led to a 25% reduction in polyp number, and the remaining polyps shrank. The hope is this will allow doctors to Delay surgery till later in life Steinbeck et al. New England Journal of Medicine 342, 1946 (2000). Until recently the only treatment Was to surgically remove the colon

colon polyps Adenomatous Polyposis Coli (APC) tumor suppressor mutated in FAP and in 70% of sporadic cases of colon cancer

APC mutations are the earliest event in the development of the tumor

APC To find clues to APC’s function they went fishing for partners Cell extract

APC Armadillo (ß-catenin) When they went fishing with APC, they pulled out Armadillo

Eric Wieschaus and Christiane Nüsslein-Volhard used genetics to identify proteins that set up the embryonic body plan

The mighty fruit fly

How is the body plan specified? Egg ---> animal in 24 hours!

Wieschaus and Nüsslein-Volhard removed single genes and looked for effects on the body plan

Wingless signaling specifies cell fates in the ventral epidermis arm mutantwild type

Wingless signal influences the fates of neighboring cells

Artist’s conception of an Armadillo

Epithelial cells at work

Elaine Fuch’s Hair Club for Men Rub ß-catenin here! BeforeAfter

Level of Wg signal Wingless signaling modulates the stability of Armadillo protein Armadillo

Wild-type APC mutant In the absence of APC, levels of Armadillo/ß-catenin rise dramatically

Our current model for Wnt signaling

Phosphorylation of Armadillo/ß-catenin By GSK3 creates a binding site for an E3 ubiquitin ligase

Arm Repeats APC is a complex protein 15 AA rpts Arm repeats protein-protein interaction motif also found in Arm !5 and 20 amino acids repeats bind to Arm SAMP repeats bind Axin 20 AA rpts SAMP rpts

Arm Repeats APC is a complex protein 15 AA rpts All tumors carry one allele that makes A truncated APC protein And truncations almost always occur in the “mutation cluster region” (MCR) 20 AA rpts SAMP rpts Arm Repeats MCR

Activated Wnt signaling triggers colon cancer

Crypt Villus Differentiated cells Proliferating cells A quick look at colon architecture

Begin with colon cancer cell line in which the Wnt pathway is ON Add an inducible dominant negative form of TCF4 that turns the Wnt pathway OFF Look for genes whose transcription is regulated by Wnt signaling Hans Clevers

Gene turned ON by WntGene turned OFF by Wnt signal The genes turned ON by Wnt signaling are expressed in crypts and those that are turned OFF are expressed in villi

Gene turned ON by WntGene turned OFF by Wnt signal The genes turned on by Wnt signaling are expressed in crypts and those that are turned off are expressed in villi

Wnt signaling turns OFF the transcription of an key cell cycle regulator: the CDK inhibitor p21 mRNA

The effect on p21 expression is indirectly mediated by the transcription factor c-myc. Transcription of the myc gene is directly regulated By TCF/beta-catenin

Stromal cells send Wnt signals Cells that receive them Become stem cells As cells migrate Away from the crypt, they differentiate Let’s put this together to form a picture of normal colon biology and how it is perturbed by APC mutations