RESEARCH ARTICLE Novel mutations and role of the LKB1 gene as a tumor suppressor in renal cell carcinoma Zübeyde Yalniz & Hulya Tigli & Hatice Tigli & Oner Sanli & Nejat Dalay & Nur Buyru Received: 9 May 2014 /Accepted: 25 August 2014 /Published online: 2 September 2014 # International Society of Oncology and BioMarkers (ISOBM) 2014 Abstract The tumor suppressor LKB1 gene is a master kinase and inhibits mammalian target of rapamycin (mTOR) by activating AMP-activated protein kinase (AMPK) and AMPK-related kinases. LKB1 is a critical intermediate in the mTOR signaling pathway, and mutations of the LKB1 gene have been implicated in the development of different tumor types. Recent evidence indicates that LKB1 alterations con- tribute to cancer progression and metastasis by modulating vascular endothelial growth factor (VEGF) production. The Ras homolog enriched in brain (RHEB) protein is a compo- nent of the mTOR pathway and functions as a positive regu- lator of mTOR. However, the mechanisms and effectors of RHEB in mTOR signaling are not well known. In this study, we analyzed the expression of RHEB and HIF1α genes in correlation with LKB1 gene mutations. All coding exons and exon/intron boundaries of the LKB1 gene were analyzed by direct sequencing in 77 renal cell carcinoma (RCC) tumors and 62 matched noncancerous tissue samples. In 51.6 % of the patients, ten different mutations including four novel muta- tions in the coding sequences and six single nucleotide sub- stitutions in the introns were observed. Rheb and HIF1α expression levels were not statistically different between the tumor and corresponding noncancerous tissue samples. How- ever, expression of the Rheb gene was upregulated in the tumor samples carrying the intron 2 (+24 G→T) alteration. Association between the gene expression and tissue protein levels was also analyzed for HIF1α in a subgroup of patients, and a high correlation was confirmed. Our results indicate that the LKB1 gene is frequently altered in RCC and may play a role in RCC progression. Keywords LKB1 . Rheb . HIF1α . Mutation . Expression Introduction Renal cell carcinoma (RCC) accounts for approximately 2 % of all adult malignancies and 90–95 % of the kidney neo- plasms [1]. However, the pathogenesis of renal cell cancer and the signaling pathways and genes associated with RCC are still not well defined. The most frequent tumor is clear cell carcinoma. It is well known that clear cell carcinomas are associated with mutations or inactivation of the von Hippel- Lindau (VHL) gene. Mutations in other genes involved in different pathways have been analyzed only in very small numbers of cases. There has been some evidence in the literature indicating the relevance of the phosphoinositide 3- kinase (PI3K)/AKT/mammalian target of rapamycin (mTOR) signaling pathway in RCC [2]. Recently, two comprehensive studies have shown that a large number of important genes are implicated in the development of renal cell cancer [3, 4]. Both studies have revealed the importance of the PI3K/AKT/ mTOR pathway in renal carcinogenesis which is affected by multiple, but less frequent mutations. mTOR is a serine/ threonine kinase and functions in two multiprotein complexes TORC1 and TORC2 [5]. mTOR kinase and autokinase activ- ities are modulated in cells by growth factors, nutrients, ener- gy levels, and cellular stress [6]. mTOR is inhibited by the tuberous sclerosis complex (TSC)1/TSC2 complex which receives inhibitory and activating signals via the mitogenic PI3K and LKB1/AMP-activated protein kinase (AMPK) Z. Yalniz : H. Tigli : N. Dalay Department of Basic Oncology, Oncology Institute, Istanbul University, Istanbul, Turkey H. Tigli : N. Buyru (*) Cerrahpasa Medical Faculty, Department of Medical Biology, Istanbul University, Kocamustafapasa, 34098 Istanbul, Turkey e-mail: nbuyru@yahoo.com O. Sanli Istanbul Medical Faculty, Department of Urology, Istanbul University, Istanbul, Turkey Tumor Biol. (2014) 35:12361–12368 DOI 10.1007/s13277-014-2550-4