Distinctive gene expression of human lung adenocarcinomas carrying LKB1 mutations

Abstract

LKB1, a tumor-suppressor gene that codifies for a serine/ threonine kinase, is mutated in the germ-line of patients affected with the Peutz-Jeghers syndrome (PJS), which have an increased incidence of several cancers including gastrointestinal, pancreatic and lung carcinomas. Regarding tumors arising in non-PJS patients, we recently observed that at least one-third of lung adenocarcinomas (LADs) harbor somatic LKB1 gene mutations, supporting a role for LKB1 in the origin of some sporadic tumors. To characterize the pattern of LKB1 mutations in LADs further, we first screened for LKB1 gene alterations (gene mutations, promoter hypermethylation and homozygous deletions) in 19 LADs and, in agreement with our previous data, five of them (26%) were shown to harbor mutations, all of which gave rise to a truncated protein. Recent reports demonstrate that LKB1 is able to suppress cell growth, but little is known about the specific mechanism by which it functions. To further our understanding of LKB1 function, we analysed global expression in lung primary tumors using cDNA microarrays to identify LKB1-specific variations in gene expression. In all, 34 transcripts, 24 of which corresponded to known genes, differed significantly between tumors with and without LKB1 gene alterations. Among the most remarkable findings was deregulation of transcripts involved in signal transduction (e.g. FRAP1/mTOR, ARAF1 and ROCK2), cytoskeleton (e.g. MPP1), transcription factors (e.g. MEIS2, ATF5), metabolism of AMP (AMPD3 and APRT) and ubiquitinization (e.g. USP16 and UBE2L3). Real-time quantitative RT-PCR on 15 tumors confirmed the upregulation of the homeobox MEIS2 and of the AMP-metabolism AMPD3 transcripts in LKB1-mutant tumors. In addition, immunohistochemistry in 10 of the lung tumors showed the absence of phosphorylated FRAP1/mTOR protein in LKB1-mutant tumors, indicating that LKB1 mutations do not lead to FRAP1/mTOR protein kinase activation. In conclusion, our results reveal that several important factors contribute to LKB1-mediated carcinogenesis in LADs, confirming previous observations and identifying new putative pathways that should help to elucidate the biological role of LKB1.

Mutations in the LKB1 tumour suppressor are frequently detected in tumours from Caucasian but not Asian lung cancer patients

“…Our study analysed tumours from different histologies and of both a US and Korean origin to determine potential histological and ethnic variation in LKB1 mutational frequency. The large size of our study enabled us to study associations of LKB1 mutations with clinocopathological factors, which have been incompletely characterised in previous studies (Sanchez-Cespedes et al, 2002;Fernandez et al, 2004;Matsumoto et al, 2007;Onozato et al, 2007). In addition, we used a modification of a sensitive mutation screening technique that we have previously developed to facilitate the rapid detection of LKB1 mutations .…”

Mutations in the humanLKB1/STK11gene

“…One 1-bp insertion and one splicing mutation have also been reported [Fernandez et al, 2004;Kuragaki et al, 2003]. Nonsense mutations account for approximately one fourth of the mutations (10/40, 24%).…”

Dysfunctional AMPK activity, signalling through mTOR and survival in response to energetic stress in LKB1-deficient lung cancer

“…We performed immunostaining of LKB1 and pACC proteins in 37 lung primary adenocarcinomas, including seven tumours carrying LKB1 mutations leading to truncated protein (Fernandez et al, 2004). Overall, 13 (35%) of the lung adenocarcinomas, including all LKB1 mutants, were negative for LKB1 immunostaining.…”