ABSTRACT
Suppression of detachment-induced cell death, known as anoikis, is an essential step for cancer metastasis to occur. We report here that expression of KLF12, a member of the Kruppel-like family of transcription factors, is downregulated in lung cancer cell lines that have been selected to grow in the absence of cell adhesion. Knockdown of KLF12 in parental cells results in decreased apoptosis following cell detachment from matrix. KLF12 regulates anoikis by promoting the cell cycle transition through S phase and therefore cell proliferation. Reduced expression levels of KLF12 results in increased ability of lung cancer cells to form tumours in vivo and is associated with poorer survival in lung cancer patients. We therefore identify KLF12 as a novel metastasis-suppressor gene whose loss of function is associated with anoikis resistance through control of the cell cycle.
Subject(s)
Anoikis/genetics , Gene Expression Regulation, Neoplastic , Kruppel-Like Transcription Factors/genetics , Lung Neoplasms/genetics , A549 Cells , Animals , Cell Cycle/genetics , Cell Line, Tumor , Cell Proliferation/genetics , Down-Regulation , Flow Cytometry , Humans , Lung Neoplasms/metabolism , Lung Neoplasms/pathology , Mice, Inbred NOD , Mice, Knockout , Mice, SCID , Neoplasm Metastasis , RNA Interference , Reverse Transcriptase Polymerase Chain Reaction , Survival Analysis , Transplantation, Heterologous , Tumor Suppressor Proteins/geneticsABSTRACT
RAS mutations occur frequently in human cancer and activated RAS signalling contributes to tumour development and progression. Apart from its oncogenic effects on cell growth, active RAS has tumour-suppressive functions via its ability to induce cellular senescence and apoptosis. RAS is known to induce p53-dependent cell cycle arrest, yet its effect on p53-dependent apoptosis remains unclear. We report here that apoptosis-stimulating protein of p53 (ASPP) 1 and 2, two activators of p53, preferentially bind active RAS via their N-terminal RAS-association domains (RAD). Additionally, ASPP2 colocalises with and contributes to RAS cellular membrane localisation and potentiates RAS signalling. In cancer cells, ASPP1 and ASPP2 cooperate with oncogenic RAS to enhance the transcription and apoptotic function of p53. Thus, loss of ASPP1 and ASPP2 in human cancer cells may contribute to the full transforming property of RAS oncogene.
Subject(s)
Adaptor Proteins, Signal Transducing/metabolism , Apoptosis Regulatory Proteins/metabolism , Tumor Suppressor Protein p53/metabolism , ras Proteins/metabolism , Adaptor Proteins, Signal Transducing/antagonists & inhibitors , Adaptor Proteins, Signal Transducing/genetics , Animals , Apoptosis Regulatory Proteins/antagonists & inhibitors , Apoptosis Regulatory Proteins/genetics , Cell Line , Humans , MCF-7 Cells , Mice , Protein Binding , RNA Interference , RNA, Small Interfering/metabolism , Recombinant Proteins/biosynthesis , Recombinant Proteins/genetics , Signal Transduction , ras Proteins/antagonists & inhibitors , ras Proteins/geneticsABSTRACT
Somatic mutations within the kinase domain of the epidermal growth factor receptor (EGFR) are present in approximately 10% of non-small-cell lung cancer (NSCLC), with an increased frequency in adenocarcinomas arising in nonsmokers, women, and individuals of Asian ethnicity. These mutations lead to altered downstream signaling by the receptor and appear to define a subset of NSCLC characterized by "oncogene addiction" to the EGFR pathway, which displays dramatic responses to the reversible tyrosine kinase inhibitors gefitinib and erlotinib. The rapid acquisition of drug resistance in most cases, either through mutation of the "gateway" residue in the EGFR kinase domain or by alternative mechanisms, appears to limit the impact on patient survival. Irreversible inhibitors of EGFR display continued effectiveness in vitro against cells with acquired resistance and are now undergoing genotype-directed clinical trials. The molecular and clinical insights derived from targeting EGFR in NSCLC offer important lessons for the broader application of targeted therapeutic agents in solid tumors.
