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Role of tropomyosin 4 gene misregulation in colon epithelial cell tumorigenesis.

e15184 Background: Ordered migration of colon epithelial cells from the bottom to the top of the crypt is required for their differentiation. Because aberrant colon cell migration may contribute to early stages of colon tumorigenesis, elucidation of how this migration is regulated provides insight into how colon cancer can be prevented and treated before malignancy. Certain actin-binding tropomyosins, including tropomyosin 4 (TPM4), regulate cytoskeletal contractility and migration in many different cell types. Methods: To determine whether aberrant TPM4 regulation may be an early event in colon cell tumorigenesis, we measured TPM4 RNA expression in uninvolved, grossly normal colon tissue from 10 human familial adenomatous polyposis (FAP) patients genetically predisposed to colon cancer versus 7 patients not genetically predisposed (normal). We also examined TPM4 expression in a colon adenocarcinoma cell line (Caco2). These are highly proliferative, undifferentiated cells but can be induced to growth arrest and differentiate, thus acquiring many characteristics of normal absorptive colon epithelial cells. Reporter assays were used to identify sequences that regulate TPM4 gene expression in Caco2 cells. Results: Average TPM4 RNA expression is 2.59 fold higher in the FAP versus normal tissue. TPM4 RNA and protein are highly expressed in proliferating, undifferentiated Caco2 cells but are severely reduced in growth arrested, differentiated cells. Reporter assays have identified genetic regions, near the TPM4 transcriptional start site, that may regulate TPM4 gene expression in proliferating Caco2 cells. Conclusions: This data suggests that aberrantly upregulated TPM4 may be an early event in colon tumorigenesis and that normal TPM4 expression, by fostering ordered colon epithelial cell migration, may promote normal cell differentiation and mitigate adoption of a premalignant state.