Background: Interleukin (IL)-8, vascular endothelial growth factor (VEGF), and IL-6 contribute to the colorectal cancer (CRC) progression by inhibiting apoptosis and by promoting angiogenesis and tumor proliferation. We have found that the tristetraprolin (TTP) gene attenuates these processes [J Neurooncol. 2013; 113(2):195-205]. TTP expression is lost or reduced in many cancers, including CRCs, and loss of TTP is thought to contribute to tumorigenesis. We hypothesized that low TTP levels favor expression of growth factors and correlate with CRC progression. In addition, we suggest that TTP modulates CRC growth through negative regulation on cell survival and/or anti-apoptotic factors in the NF-kB pathway. We tested this hypothesis by analyzing mRNA expression of TTP and its targets in primary CRCs of African American (AA) and Caucasian American (CA) patients.

Methods: We analyzed frozen primary tissues from 45 CRC patients (AA=26 and CA=19), each with corresponding normal (benign/control) tissue. cDNAs were reverse-transcribed from total RNA; mRNA levels of TTP and its target genes (IL-8, VEGF, IL-6) were quantified by the qPCR sybr-green method. Expression levels were normalized to GAPDH. To assess TTP effects on the NF-kB pathway, colon cancer cells (CCL235, HCT116, SW480, and LoVo) were stimulated with TNF-α for 0-24 hr, and total RNA was analyzed for TTP, IL-8, IL-6, VEGF, and cIAP2 expression by qRT-PCR. Levels of HuR mRNA in cells were also assessed. Extracts from the cells were immunoblotted with anti-TTP and antiHuR antibodies.

Results: We observed down-regulated expression of TTP mRNA in primary CRCs (31 of 45), and decreased TTP levels correlated with advanced tumor stage. Low levels of TTP were found in 21 of 26 AAs and 12 of 19 CAs. In both racial groups, there was an inverse correlation between TTP and IL-8 expression in relation to tumor stage. Studies with cultured colon cancer cells demonstrated that TTP mRNA levels inversely correlated with levels of IL-8, IL-6, VEGF, and cIAP2 mRNAs, suggesting interactions of TTP with cell survival factors. Western blot analyses confirmed TTP expression levels in these cells.

Conclusions: For both racial groups, TTP expression was lower in tumor tissues relative to normal tissues; the difference was more pronouced in CRCs of AAs. Further, lower TTP levels correlated with advanced tumor stage; and TTP negatively regulated the expression of IL-8, VEGF, and cIAP2 in cultured cells. These studies were supported by a pre-pilot project of the UAB/TU/MSM Partnership grant of NIH/NCI, U54-CA 118948.

Citation Format: Esther A. Suswam, Balanada Dhurjarti Kumar Putcha, Kiera D. Walker, LaJessica Johnson, Jasmine Howard, Edward E. Partridge, Mona N. Fouad, Sejong Bae, Upender Manne. Tristetraprolin suppression is associated with advanced stage colorectal cancer. [abstract]. In: Proceedings of the Sixth AACR Conference: The Science of Cancer Health Disparities; Dec 6–9, 2013; Atlanta, GA. Philadelphia (PA): AACR; Cancer Epidemiol Biomarkers Prev 2014;23(11 Suppl):Abstract nr C77. doi:10.1158/1538-7755.DISP13-C77

©2014 American Association for Cancer Research.
2014