Abstract 1487: TPM4 overexpression promotes colon epithelial cell tumorigenesis
Authors: Macwan Rajsumeet , Kozlowski Piotr B. , Papetti Michael 
Published: June 2023

Although much progress has been made in colon cancer treatment and prevention, high morbidity and mortality still associated with this disease are tremendous burdens to human health. Therefore, novel strategies are needed to provide insight into how colon cancer can be prevented and treated, particularly before malignancy. One approach is to identify genes whose misregulation disrupts crypt-luminal colon epithelial cell migration, needed for stem cell progeny at the bottom of the crypt to transition from a highly proliferative, immature state to a growth arrested, mature phenotype near the lumen. Aberrant expression of these genes may contribute to early stages of tumorigenesis, before adoption of a malignant state. Tropomyosins, including tropomyosin 4 (TPM4), are actin-binding proteins that regulate contractility and migration in many cell types. We have shown that TPM4 RNA is overexpressed in premalignant (flat mucosa) of FAP (Familial Adenomatous Polyposis) patients 2.59 fold over the level in normal controls. Furthermore, TPM4 RNA and protein is highly overexpressed in proliferating, undifferentiated Caco2 (human adenocarcinoma) cells relative to growth-arrested, differentiated cells. Therefore, we hypothesize that TPM4 overexpression can block colon epithelial cell differentiation and induce early, premalignant events in colon epithelial cell tumorigenesis. To test this hypothesis, we determined whether Caco2 cell clones stably overexpressing TPM4.2, the TPM4 isoform expressed in Caco2 cells, are defective in the ability to adopt a mature phenotype measured by RNA expression of differentiation-specific genes, including intestinal alkaline phosphatase (ALPi), upon induction of spontaneous differentiation using quantitative real-time polymerase chain reaction (qRT-PCR). Stable TPM4.2 transfectants exhibited a 2.61-fold decreased expression of intestinal alkaline phosphatase (ALPi) relative to control transfectants after 20-21 days of spontaneous induction. Lgr5 RNA was quickly suppressed in both TPM4.2 and control transfectants upon induction of differentiation but was re-expressed in TPM4.2 transfectants 12.3 fold above control levels at day 14 of spontaneous induction. Our results suggest that proper regulation of TPM4 expression in colon epithelial cells is critical to preventing adoption of a tumorigenic state. TPM4 RNA is overexpressed in premalignant human colon tissue, and forced overexpression of TPM4 suppresses maturation and promotes proliferation in an in vitro model of colon epithelial cell differentiation. Misregulation of TPM4 gene expression may therefore block normal differentiation and induce early events in colon epithelial cell tumorigenesis. Based on these studies, we suggest that TPM4 expression levels may be used as diagnostic tools for determining tumorigenic potential and may offer therapeutic strategies for early intervention in colon cancer treatment.

Citation Format: Rajsumeet Macwan, Piotr B. Kozlowski, Michael Papetti. TPM4 overexpression promotes colon epithelial cell tumorigenesis [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 1487.