Tumor progression in colorectal cancer (CRC) involves accumulation of genetic and epigenetic changes that ultimately lead to malignancy. E-cadherin downregulation occurs frequently and is widely believed to be a pivotal event in the transition to metastasis. In the majority of E-cadherin-deficient CRCs, p120 localizes aberrantly to the cytoplasm, and E-cadherin-loss / cytoplasmic p120 is strongly associated poor prognosis. p120 itself is downregulated in a subset of CRC but the significance is not yet clear. We have found that p120 ablation in vitro and in vivo destabilizes E-cadherin (and associated catenins) causing severe defects in cell morphology and adhesion. Interestingly, in vitro p120-ablation in many cell types induces constitutive activation of Rho, cell growth in the absence of serum, and loss of contact inhibition. In vivo, similar effects lead to cell autonomous activation of a ROCK/NFKB/COX-2 signaling cascade and chronic inflammation, an observation of potential relevance to the efficacy of NSAIDS and COX-2 inhibitors in CRC. Our data suggest novel co-dependent interactions between p120 and E-cadherin that act through regulation of Rho to suppress metastasis and inflammation. The progress report describes these effects, along with a novel molecular explanation for the relationship between Rho, p120, and E-cadherin.
The aims (below) seek to apply our findings to tumor progression and clinical intervention in CRC.
In aim 1, we will evaluate a simplified p120 KO mouse model to ascertain whether pharmaceutical intervention at the level of pathways activated by p120 (or E-cadherin) downregulation can suppress tumor progression, tumor growth, or metastasis.
Aim 2 explores two separate hypotheses based on novel observations. First, to examine implied relationships between p120 loss, mismatch repair (MMR) deficient CRC, and defects in TGF0IIR signaling, we will perform a head-to-head comparison between well-annotated groups of MMR-deficient and proficient tumors. Second, we will follow up on novel observations of p120 downregulation at the mRNA level in advanced CRC. We will determine whether mRNA levels fall at early stages of CRC progression, whether this phenomenon is associated at any level with tumor type or outcome, and the significance at the molecular level with respect to cause and effect. Finally, in aim 3 we will use chemical genetics to interrogate a well characterized but as yet unknown signaling pathway associated with p120-dependant inactivation of E-cadherin. In collaboration with the Beauchamp lab (project 2) and the Vanderbilt Institute for Chemical Biology (VICB) high throughput screening facility, we have developed a high throughput small molecule screen (HTS) to identify novel compounds that rescue E-cadherin function in CRC model cell lines. The application of HTS represents an innovative approach to delineating signaling pathways that control p1207E-cadherin function, and could lead to identification of novel compounds capable of suppressing tumor progression or metastasis.
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