Thymidine phosphorylase mRNA stability and protein levels are increased through ERK-mediated cytoplasmic accumulation of hnRNP K in nasopharyngeal carcinoma cells

Abstract

The cytoplasmic level of heterogeneous nuclear ribonucleoprotein K (hnRNP K) is significantly correlated with the elevated expression of thymidine phosphorylase (TP), and high levels of both proteins are predictive of a poor prognosis in nasopharyngeal carcinoma (NPC). We herein show that TP is highly induced by serum deprivation in NPC cells, and that this is due to an increase in the halflife of the TP mRNA, as shown by nuclear run-on and actinomycin D assays. We further show that the CU-rich element of the TP mRNA directly interacts with hnRNP K, as demonstrated by immunoprecipitation RT-PCR assays, and the nucleus-to-cytoplasm translocation of hnRNP K. Blockade of hnRNP K expression reduces TP expression, suggesting that hnRNP K acts in the upregulation of TP. Mechanistically, both MEK inhibitor and the hnRNP K ERK-phosphoacceptor-site mutant decrease cytoplasmic accumulation of hnRNP K, suggesting that ERK-dependent phosphorylation is critical for TP induction. Furthermore, we found that hnRNP Kmediated TP induction allows NPC cells to resist hypoxia-induced apoptosis. Our results collectively establish the regulation and role of ERK-mediated cytoplasmic accumulation of hnRNP K as an upstream modulator of TP, suggesting that hnRNP K may be an attractive candidate as a future therapeutic target for cancer.

152 EGF-induced acetylation of heterogeneous nuclear ribonucleoproteins is dependent on KRAS mutational status in colorectal cancer cells

“…In agreement with our observations about hnRNPs acetylation, one of the largest acetylome studies showed that the main functional networks modulated by acetylation were related to RNA maturation [35]. All in all, although the prominent role of hnRNPs in tumor progression has been already described [36][37][38], this is the first report showing a relation between KRAS mutational status and hnRNP acetylation. The highest level of acetyl-hnRNPs, and also the largest number of acetylated proteins, was found in cells harboring one single allele of KRAS G13D .…”

A novel role for TNFAIP2: its correlation with invasion and metastasis in nasopharyngeal carcinoma

“…In the tumor microenvironment, TNFa mediates cancer-related inflammation, and may promote tumor progression by increasing angiogenesis and metastasis. [1][2][3]25 The levels of TNFa [6][7] and its downstream genes c-FLIP 18,29 and thymidine phosphorylase [19][20][21][22] are known to be elevated in nasopharyngeal carcinoma tumor tissues. Here, we used Affymetrix chips to identify the 10 TNFa-inducible genes showing the highest upregulation in nasopharyngeal carcinoma tissues vs normal adjacent tissues.…”

“…The primers used to amplify the GAPDH cDNA were as described previously. 22 Quantitative RT-PCR was performed on a Light-Cycler (Roche Diagnostics, Mannheim, Germany), according to the manufacturer's instructions, using the FastStart DNA Master SYBR Green I reagent (Roche Diagnostics). The gene expression results were normalized with regard to the expression of GADPH.…”

“…[19][20][21] We further showed that the upregulation of thymidine phosphorylase in nasopharyngeal carcinoma tumor cells resulted at least in part from cytoplasmic heterogeneous nuclear ribonucleoprotein K (hnRNP K)-mediated stabilization of the thymidine phosphorylase mRNA. 22 High levels of thymidine phosphorylase and cytoplasmic hnRNP K were significantly correlated with overall survival and distant metastasis. 19 On the basis of this success, we have continued to search for other TNFaregulated genes that could serve as potential biomarkers for nasopharyngeal carcinoma prognosis.…”

The antiapoptotic protein, FLIP, is regulated by heterogeneous nuclear ribonucleoprotein K and correlates with poor overall survival of nasopharyngeal carcinoma patients

“…1 However, cytoplasmic accumulation of hnRNP K through ERK-mediated phosphorylation of hnRNP K serines-284 and -353 has been reported in cervical carcinoma HeLa, 7 chronic myelogenous leukemia 8 and NPC 9 cells. The tumorigenic activity of hnRNP K appears to be conferred through its ability to increase proliferation, 10 antiapoptotic effects, 9 clonogenic potential 8 and metastasis. 11 These functions may be due, at least in part, to the ability of hnRNP K to upregulate the c-myc, 8,12 thymidine phosphorylase (TP) 9 and eIF4E 10 genes through transcriptional or post-transcriptional regulation.…”