Activin is a growth suppressive ligand of the TGF? superfamily. It initiates its canonical signaling via a specific receptor, activin receptor 2 (ACVR2) that subsequently phosphorylates activin receptor 1 (ACVR1) to activate a signaling cascade culminating in nuclear translocation of SMAD proteins and growth suppression. We have data showing that ACVR2 protein is lost by distinct mechanisms in human colon cancer regardless of the type of genomic instability and loss is associated with an increase in tumor size in primary colon cancer specimens. Further, activin induces colon cancer cell migration in an ACVR2- dependent manner via activation of mitogenic PI3Kinase signaling, possibly without utilizing SMADs. Additionally, in contrast to TGF?, activin leads to nuclear p21waf down regulation. The goal of this project is to analyze the effects of loss of SMAD-dependent versus SMAD-independent activin signaling on colon cancer characteristics and patient outcomes as well as to dissect mechanisms of activin's distinct effects on migration and cell growth. We hypothesize that mutated ACVR2 interrupts activin signaling causing increased colon cancer cell growth via loss of SMAD-dependent signaling but a decrease in metastatic phenotype via loss of SMAD-independent signaling. Further, we hypothesize that growth suppressive and pro-migratory properties of activin are distinctly regulated via a ligand-specific p21waf1 nuclear export. We will first assess activin and PI3K signaling status in primary colon cancers and metastasis and correlate with patient outcome, followed by assessment of effects of loss of activin and PI3Kinase signaling on intestinal tumors in vivo. Then, using colon cancer cell models with varying ACVR2/PI3K/SMAD4 backgrounds and activin/PI3kinase signaling manipulations, we will examine the specific mechanism of activation of PI3kinase via activin and effects on colon cancer migration in vitro and in vivo employing mouse metastasis models. This will be followed by experiments analyzing the mechanisms of the differential outcome on p21waf1 and its effects on activin-induced SMAD-dependent growth suppression and apoptosis and SMAD-independent migration. This project assesses the specific role of activin signaling and ACVR2 on colon cancer cell growth and migration using human specimens, cellular, and in vivo models.
Colon cancer is the second deadliest cancer in the U.S., with the deaths due largely to metastatic disease. Understanding the genetic mechanisms of how colon cancer metastases form will help to develop better tools to prevent, diagnose, and treat colon cancer.
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