Silencing of ATPase Inhibitory Factor 1 Inhibits Cell Growth via Cell Cycle Arrest in Bladder Cancer

Abstract

Objective: The role of the ATPase inhibitory factor 1 (IF1) is inhibit the hydrolase activity of F₁F_o-ATPase when oxidative phosphorylation is impaired. It has been demonstrated that IF1 is overexpressed in various carcinomas and mediates tumor cell activities, but the detailed mechanisms of IF1-mediated tumor progression and the link between IF1 and cell cycle progression remain unclear. Herein, we aimed to investigate the potential role of IF1 in cell cycle progression of human bladder cancer (BCa). Methods: The expression of IF1 was analyzed by immunohistochemistry in tumor tissues. Western blot was used to detect protein expression in the cells. Cell proliferation was determined by MTT and colony formation assays. The cell cycle was analyzed using flow cytometry. Results: We firstly showed IF1 was overexpressed in BCa. Silencing of IF1 by small interfering RNA led to a significant decrease in cell proliferation and migration in T24 and UM-UC-3 cells. Importantly, IF1 knockdown caused cell cycle arrest at G₀/G₁ stage and decreased the protein level of cyclin E/cyclin-dependent kinases (cdk) 2 and/or cyclin D/cdk4/cdk6. Conclusion: These results suggest the inhibitory effect of IF1 knockdown on BCa cell proliferation is via the suppression of cyclins and cdks related to G₁/S transition and then induction of G₀/G₁ arrest, and firstly indicate IF1 mediates the tumor cell cycle. We concluded that IF1 may be a novel therapeutic target for BCa.

Regulation of the H+-ATP synthase by IF1: a role in mitohormesis

“…However, upon transformation, the carcinomas arising in these tissues show very high levels of IF1 (Table 1). Interestingly, whereas in bladder [107] and non-small cell lung carcinomas [108] a high expression level of IF1 in the tumor predicts a worse patients’ prognosis, a low tumor expression of IF1 predicts a worse prognosis in colon and breast cancer patients [83]. Consistently, a recent study using mRNA expression levels also suggests that a high IF1 expression predicts the group of low-risk patients in colon cancer [109].…”

“…Tissues, such as bladder, breast, colon, lung and ovary show negligible expression level of IF1 under normal physiological conditions [57, 83, 107] (Table 1). However, upon transformation, the carcinomas arising in these tissues show very high levels of IF1 (Table 1).…”

Overexpression of the ATPase Inhibitory Factor 1 Favors a Non-metastatic Phenotype in Breast Cancer

“…Moreover, overexpression of IF1 triggers in mitochondria a concurrent reactive oxygen species (ROS) signal that switches on the NF-κB pathway favoring invasion and cell survival in colon and lung cancer cells (21, 27). Consistently, a high expression level of IF1 in human hepatocarcinomas (28) and in carcinomas of the lung (29), bladder (30), and stomach (31) and in gliomas (32) is a biomarker of bad prognosis for the patients. In sharp contrast to these findings, a high expression level of IF1 in breast carcinomas positively correlates with less chance to develop metastatic disease; in other words, it is a biomarker of good prognosis for breast cancer patients (21).…”

“…Herein, we report that the overexpression of IF1 in human breast carcinomas, especially in the subgroup of triple-negative breast carcinomas predicts a lower risk for metastatic disease (21). This finding is counterintuitive since (i) the overexpression of IF1 inhibits mitochondrial respiration and enhances glycolysis, which is a metabolic phenotype that is enforced in proliferating invasive cells (2, 3, 5, 6), (ii) a high expression level of IF1 has been recently reported as biomarker of bad prognosis in human hepatocarcinomas (28) and in carcinomas of the lung (29), bladder (30), and stomach (31) and in gliomas (32), and (iii) the overexpression of IF1 in the liver of transgenic mice significantly contributes to an increase in hepatocarcinogenesis (46). To investigate the molecular mechanisms that might support the “non-canonical” behavior of IF1 in breast cancer, which might open up potential new trends in diagnosis and treatment of breast cancer patients, we developed the triple-negative breast cancer BT549-luc cell line that stably overexpresses IF1.…”

“…In gastric (31) and bladder (30) cancer, an increased expression of IF1 has been shown to promote cellular proliferation. Likewise, the overexpression of IF1 in colon cancer cells triggers the transcriptional activation of the NF-κB pathway, thereby favoring proliferation and preventing cell death (27).…”