Date Published: April 19, 2018
Author(s): Saoussen Debouki-Joudi, Sonia Mhirsi, Nehla Mokni-Baizig, Nihel Ammous-Boukhris, Hayet Mhamdi, Said Gritli, Raja Mokdad Gargouri, Mohamed Nejib Marzouki.
The transcription factor Krüppel-like factor 6 (KLF6) regulates various cellular functions, such as metabolism, cell proliferation, and differentiation. KLF6 plays a key role in the development and progression of multiple human cancers.
Fifty primary biopsies and 10 normal nasopharyngeal mucosae were used to analyze by RT-QPCR the expression and the copy number of wtKLF6 and the spliced variants (KLF6-SV1, KLF6-SV2, and KLF6-SV3) in Tunisian patients with nasopharyngeal carcinoma. The expression analysis of E-cadherin and cyclin D1 was conducted by RT-QPCR and Western blot, respectively.
The wtKLF6 was significantly downexpressed in tumors compared to normal tissues (p = 0.0015), whereas KLF6-SV1 and KLF6-SV2 were overexpressed in tumors compared to wtKLF6 and KLF6-SV3 (p < 0.0001). Copy number variation was reduced in tumors compared to normal tissues (p = 0.0071). Interestingly, KLF6-SV1 is associated with the juvenile form (p = 0.0003) which is more aggressive than the adult form of NPC. Furthermore, the oncogenic variant KLF6-SV1 was overexpressed in tumors lacking the expression of E-cadherin (p = 0.0022) suggesting its role in metastasis and tumor progression. The wtKLF6 is associated negatively with cyclin D1 in tumor tissues (p = 0.048). The wtKLF6 was downexpressed in contrast with the oncogenic variants. Overexpression of KLF6-SV1 is associated with young patients, and loss of E-cadherin suggests that this variant correlated with the aggressiveness of NPC.
Nasopharyngeal carcinoma (NPC) belongs to head and neck malignant disease with a particular geographical distribution over the world . In Tunisia, NPC represents the most frequent head and neck cancer with a bimodal pattern of age distribution with an annual incidence of about 4 cases per 100,000 persons [1, 2]. There are several clinical and biological characteristics which are specific to the North African patients, especially the two peaks of frequency according to age at diagnosis, the first one around 50 and the second below 30 (20 to 25% of cases). However, in the endemic regions of South-East Asia, there is only one major peak of incidence at about the age of 50 [3–4]. The etiology of the development and progression of NPC is multifactorial such as geographic areas, environmental exposure, diet, Epstein-Barr virus, genetics, and epigenetic factors . Several efforts have been made to identify markers for diagnosis, prognosis, and/or therapy in different types of human cancer including NPC. In this context, we focus on the Krüppel-like factor 6 gene that has been investigated in several cancers but not in NPC except the study of Chen et al., reporting mutation screening of the KLF6 gene in Asian patients .
KLF6 is a Krüppel-like transcription factor ubiquitously expressed and has a key role in human carcinogenesis through regulating several target genes [9, 17]. Indeed, many studies pointed the function of KLF6 as a tumor suppressor because of its ability to reduce cell proliferation through several biochemical mechanisms including regulation of cell cycle, oncogenic products, and apoptosis. Decreased expression of the full length mRNA, mutations, LOH, alternative splicing, and promoter methylation were associated with the development of different human malignancies such as prostate, colorectal, and ovarian cancer and glioblastomas [13, 14, 18, 19]. However, to the best of our knowledge, there is no previous investigation of the KLF6 expression in nasopharyngeal carcinoma except the study of Chen et al. on Chinese patients. Indeed, the authors identify 3 different mutations (Glu75Val, Ser136Arg, and Arg243 Lys) in 3 of 19 NPC tissues . Therefore, in the present study, we investigate the expression levels of the wild-type KLF6 and its oncogenic variants as well as the copy number variation in tumor biopsies and normal nasopharyngeal mucosae of Tunisian patients.
In NPC, the wtKLF6 is downexpressed in tumors compared to normal nasopharyngeal mucosae whereas the levels of the spliced variants KLF6-SV1 and KLF6-SV2 were expressed higher than those of the wild-type isoform in tumors. Interestingly, KLF6-SV1 is positively associated with young patients suggesting that this oncogenic variant contributes to the aggressiveness of the juvenile form of NPC. Furthermore, negative association between the expression of E-cadherin and KLF6-SV1 suggests that the oncogenic variant promotes tumor invasion and metastasis in NPC; nevertheless, further studies should be conducted to elucidate the function of KLF6 and its spliced variants in NPC.