Abstract 5635: TPM4 overexpression promotes colon epithelial cell tumorigenesis in vitro and correlates with human colon tumor progression in vivo

Abstract

Abstract Because colon cancer still exerts a heavy burden on human health, we are interested in identifying very early events in colon epithelial cell tumorigenesis in order to develop strategies to treat and possibly prevent colon carcinogenesis. We hypothesize that aberrant expression of genes involved in crypt-luminal colon epithelial cell migration, needed for proliferative, undifferentiated stem cells at the crypt bottom to mature into growth arrested, mature effector cells near the lumen, may disrupt normal differentiation and initiate events that can trigger the transition from a normal to premalignant state in colon epithelial cells. Forced upregulation of tropomyosin 4 (TPM4), an actin-binding protein that exerts many effects on contractility and migration, prevents certain aspects of Caco2 maturation induced by contact inhibition of growth, including increased expression of the digestive enzyme sucrose isomaltase and glutathione S-transferase alpha 1. Furthermore, TPM4.2-overexpressing cells exhibit numerous morphological abnormalities. Compared to untransfected Caco2 cells and empty-vector stable transfectant controls, TPM4.2-overexpressing Caco2 cell clones elaborate aberrant thin membrane protrusions and expanded membrane ruffles. Particularly striking are defective maintenance of dome structures at middle (day 14) and late (day 21) time points of induced differentiation in TPM4.2-overeexpressing clones. We further hypothesize that TPM4 is overexpressed in human colon tumors, particularly at early stages of tumorigenesis. In order to test this hypothesis, we examined TPM4 RNA expression in datasets obtained from human colon tissue at premalignant as well as tumorigenic stages. TPM4 trends toward overexpression in premalignant, relative to normal, human colon tissue (uninvolved mucosa from patients with familial adenomatous polyposis, or FAP) and is significantly overexpressed in adenocarcinoma tissue relative to normal controls. Interestingly, TPM4 overexpression may be more pronounced at earlier, rather than later, stages of adenocarcinoma. Our results suggest that aberrant TPM4 overexpression in colon epithelial cells can promote adoption of a tumorigenic state. Certain aspects of Caco2 cell maturation are disrupted by forced TPM4 overexpression during induced differentiation, and TPM4 overexpression correlates with early stages of colon tumorigenesis. Misregulation of TPM4 gene expression may therefore represent a critical molecular event that can block normal differentiation and induce early events in colon epithelial cell tumorigenesis. TPM4 expression level may therefore prove to be a useful biomarker that can, along with other diagnostics, help to determine tumorigenic progression in human colon tissue and to develop novel strategies to prevent colon cancer and treat it at early stages. Citation Format: Giulio Ferrero, Barbara Pardini, Alessio Naccarati, Michael Papetti. TPM4 overexpression promotes colon epithelial cell tumorigenesis in vitro and correlates with human colon tumor progression in vivo [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 5635.