Abstract 4953: Molecular and cellular localization profiles of tristetraprolin in colorectal cancer: Implications for tumor progression in diverse patient populations
Authors: Suswam Esther A. , Putcha Balananda-Dhurjati K. , Tiwari Amit K. , Jadhav Trafina , Walker Kiera D. , Harkins Lualhati , Amer Samir , Eltoum Isam-Eldin , Bae Sejong , Manne Upender 
Published: August 2015

Introduction: Colorectal cancer (CRC) and other solid tumors rely on production of pro-inflammatory cytokines and growth factors to support their rapid growth. Posttranscriptional control of these factors involves interplay between RNA stabilizing and destabilizing factors. We have observed that the protein tristetraprolin (TTP), a RNA destabilizer, is down-regulated in CRCs and that interleukin (IL)-8, a proinflammatory cytokine, is up-regulated. We hypothesized that loss of negative regulation by TTP selectively favors expression of growth factors and protooncogenes that promote tumor progression. Furthermore, new evidence suggests that TTP is associated estrogen receptor-α (ERα) and functions as a co-repressor of ERα activation interaction with histone deacetylases on the gene promoter; nuclear TTP is linked to this tumor suppressor function. Since CRCs of African Americans (AAs) often present worse outcomes relative to those of Caucasian Americans (CAs), we analyzed the expression of TTP and its targets and assessed its subcellular localization in primary CRCs of AA and CA patients and in cultured colon cancer cells. Its effects on disease progression were also determined.

Methods: Paired normal and CRC tissues from 45 patients (AA = 26 and CA = 19), were evaluated by qPCR for mRNA expression levels of TTP, IL-8, and VEGF. Tissue sections were also assayed for immunophenotypic expression by immunohistochemistry, and the staining patterns (nuclear and cytoplasmic) were assessed. To determine TTP effects on the NF-kB pathway, colon cancer cells (CCL235, HCT116 and LoVo) were stimulated with TNF-α, and total RNA was analyzed for TTP, IL-8, VEGF, and cIAP2 expression; interaction of TTP and ERα was also assessed.

Results: In 31 of 45 CRCs, there was down-regulated expression of TTP mRNA, and low TTP levels correlated with advanced tumor stage. Low levels of TTP were present in 21 of 26 AAs and in 12 of 19 CAs. There was an inverse correlation between TTP and IL-8 expression in relation to tumor stage. There was an agreement between mRNA expression and immunophenotypic profiles for TTP and IL-8. Furthermore, there was reduced or a lack of nuclear staining of TTP in malignant cells relative to normal/benign epithelial cells. In cultured colon cancer cells, TTP mRNA levels inversely correlated with levels of IL-8, VEGF, and cIAP2 mRNAs, suggesting interactions of TTP with these cell survival factors.

Conclusions: Reduced expression of TTP was noted in tumors, especially in CRCs of AAs, and a loss or decreased nuclear expression of TTP was observed in malignant cells. Lower TTP levels correlated with advanced tumor stage. These preliminary findings suggest that TTP negatively regulates the expression of cell survival factors in the NF-kB pathway. This work was supported by funds from the NIH/NCI (a career development supplement to grant U54-CA118948).

Citation Format: Esther A. Suswam, Balananda-Dhurjati K. Putcha, Amit K. Tiwari, Trafina Jadhav, Kiera D. Walker, Lualhati Harkins, Samir Amer, Isam-Eldin Eltoum, Sejong Bae, Upender Manne. Molecular and cellular localization profiles of tristetraprolin in colorectal cancer: Implications for tumor progression in diverse patient populations. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 4953. doi:10.1158/1538-7445.AM2015-4953