Tropomyosin 2 Regulates Tumor Cell Proliferation, Immune Suppression, and Activation of the JNK Signaling Pathway in Colitis-Associated Cancer (CAC).

BACKGROUND: Tropomyosin 2 (TPM2) has been linked to the advancement of various tumor types, exhibiting distinct impacts on tumor progression. In our investigation, the primary objective was to identify the potential involvement of TPM2 in the development of colitis-associated cancer (CAC) using a mice model.

METHODS: This study used lentiviral vector complex for TPM2 knockdown ( sh-TPM2 ) and the corresponding negative control lentiviral vector complex (sh-NC) for genetic interference in mice. CAC was induced in mice using azoxymethane (AOM) and dextran sulfate sodium salt (DSS). This study included 6 groups of mice models: Control, Control+sh-NC, Control+sh-TPM2, CAC, CAC+sh-NC, and CAC+sh-TPM2. Subsequently, colon tissues were collected and assessed using quantitative reverse transcription-polymerase chain reaction (qRT-PCR) for TPM2 mRNA levels and flow cytometry for infiltrating immune cells. Tumor number, size, and weight within colon tissues from CAC mice were measured and recorded. The hematoxylin-eosin staining was used for observing tissue pathology changes. The intestinal epithelial cells (IECs) were isolated and analyzed for cell proliferation. This analysis included examining the levels of 5-bromo-2-deoxyuridine (BrdU) and Ki-67 using immunohistochemistry. Additionally, the mRNA levels of proliferating cell nuclear antigen (PCNA) and Ki-67 were detected by qRT-PCR. This study also investigated the activation of the c-Jun N-terminal kinase (JNK) pathway using western blot analysis. Immunogenicity analyses were conducted using immunohistochemistry for F4/80 and flow cytometry.

RESULTS: In 8-week-old mice, AOM injections and three cycles of DSS treatment induced TPM2 upregulation in tumor tissues compared to normal tissues ( p < 0.05). Fluorescence-activated cell sorting (FACS)-isolated lamina CAC adenomas revealed macrophages and dendritic cells as primary TPM2 contributors ( p < 0.001). Lentiviral TPM2 gene knockdown significantly reduced tumor numbers and sizes in CAC mice ( p < 0.01, and p < 0.001), without invasive cancer cells. TPM2 suppression resulted in decreased IEC proliferation ( p < 0.001) and reduced PCNA and Ki-67 expression ( p < 0.05). Western blot analysis indicated reduced JNK pathway activation in TPM2 -knockdown CAC mice ( p < 0.05, p < 0.001). TPM2 knockdown decreased tumor-associated macrophage infiltration ( p < 0.01) and increased CD3+ and CD8+ T cells ( p < 0.01, and p < 0.001), with increased levels of regulator of inflammatory cytokines (CD44+, CD107a+) ( p < 0.01, and p < 0.001), decreased levels of PD-1+ and anti-inflammatory factor (IL10+) ( p < 0.01, and p < 0.001).

CONCLUSIONS: Our results demonstrated that TPM2 knockdown suppressed the proliferation of CAC IECs, enhanced immune suppression on CAC IECs, and inhibited the JNK signaling pathway within the framework of CAC. These findings suggest TPM2 can serve as a potential therapeutic target for CAC treatment.