Novel mutations of the HRAS gene and absence of hotspot mutations of the BRAF genes in oral squamous cell carcinoma in a Greek population

Abstract

Abstract. Oral squamous cell carcinoma (OSCC) is the sixth most common cancer in the world. The phosphatidylinositol 3 kinase (PI3K) signalling pathway has been reported to play an important role in OSCC. Since we have previously detected absence of hotspot PIK3CA gene mutations in the Greek population, we hypothesized that BRAF or HRAS may be activated as upstream effectors of the pathway. Furthermore, the status of the HRAS and BRAF mutations in OSCC has never been assessed before in the Greek population. Eighty-six primary paraffin-embedded tumors were screened for BRAF and HRAS hotspot mutations. In HRAS, two hotspot mutations in codon 12 (2.3%) and eight new genetic alterations were detected (8.6% overall). One new missense mutation, Alanine53Valine (Ala53Val), one silent mutation, two mutations in the 5'UTR region and four mutations in intron 1 were detected. No hotspot mutations in BRAF were found. A new silent mutation/polymorphism T1803C was detected at a percentage of 30%. This study is the first to report HRAS mutations in the Greek population. The results suggest that RAS is an important member of the PI3K signalling pathway and may play a role in the tumorigenesis of OSCC. IntroductionOral squamous cell carcinoma (OSCC) is a subset of head and neck squamous carcinoma (HNSCC) involving the oral tongue, upper gingival, lower gingival and alveolus, floor of the mouth, buccal mucosa, retromolar triangle, lip mucosa and hard palate. OSCC is considered to be the sixth most common cancer in the world (1). Smoking and alcohol consumption are major risks for HNSCC but only a fraction of people with these habits actually develop oral cancer, which implies that other genetic factors contribute to the pathogenesis of the disease (2,3). Infection by human papilloma virus has also emerged as a risk factor for HNSCC (4).The RAS family genes consist of three members, HRAS, KRAS and NRAS located on chromosomes 11, 12 and 1, respectively, encoding a 21 kDa membrane protein (p21), which possesses GTPase activity (5,6). HRAS has been shown to activate phosphatidylinositol 3 kinase (PI3K) more efficiently than KRAS and NRAS. Hotspots for RAS mutations are found in codons 12, 13 and 61, causing the mutant protein to lose its ability to exchange GTP with GDP thus remaining activated (7). RAS is also is an upstream regulator of PI3K. Thus an activated RAS could also activate the PI3K signalling pathway, which is shown to be activated in oral cancer (8,9). The incidence of RAS mutations varies greatly among different human tumors and different ethnicities. HRAS mutations are primarily found in cancers of the urinary tract and bladder.

Identification of Key Genes and Pathways in Tongue Squamous Cell Carcinoma Using Bioinformatics Analysis

“…Bouquet et al [ 57 ] demonstrated that AGT had a very powerful antiangiogenic function in vivo , independent of angiotensin II generation, representing a promising novel strategy to inhibit growth and metastasis of primary tumors. HRAS belongs to the Ras oncogene family; obvious mutations of the HRAS gene were found in oral cancer, suggesting that RAS may affect the tumorigenesis process [ 58 ]. There was another interesting finding: activated HRAS mutations could overcome the resistance to erlotinib in an HNSCC cell line with HRAS mutation [ 59 ].…”

Lip cancer and pre-cancerous lesions harbor TP53 mutations, exhibit allelic loss at 9p, 9q, and 17p, but no BRAFV600E mutations

“…In a recent series of 66 intraoral squamous cell carcinoma of the tongue, only 1 sample showed BRAF mutation [41], and in other intraoral squamous cells carcinoma series, BRAF mutation was not detected in any sample [42]. In cutaneous squamous cells carcinomas, BRAF mutations are not detected either in spontaneous or in secondary tumors (occurring in patients under RAF inhibitor or immunosuppression therapy) [43,44].…”

An Ultra-Deep Targeted Sequencing Gene Panel Improves the Prognostic Stratification of Patients With Advanced Oral Cavity Squamous Cell Carcinoma

“… 23 Although HRAS mutations are common in OSCC, BRAF gene mutations are generally found in approximately 3% of such tumors. 24 All of these genes encode for tyrosine kinase receptors that are targeted by pharmacological agents already available or currently under development. 25 …”