RAS mutations in human cancers: Roles in precision medicine.

Ras proteins play a crucial role as a central component of the cellular networks controlling a variety of signaling pathways that regulate growth, proliferation, survival, differentiation, adhesion, cytoskeletal rearrangements and motility of a cell. Almost, 4 decades passed since Ras research was started and ras genes were originally discovered as retroviral oncogenes. Later on, mutations of the human RAS genes were linked to tumorigenesis. Genetic analyses found that RAS is one of the most deregulated oncogenes in human cancers. In this review, we summarize the pioneering works which allowed the discovery of RAS oncogenes, the finding of frequent mutations of RAS in various human cancers, the role of these mutations in tumorigenesis and mutation-activated signaling networks. We further describe the importance of RAS mutations in personalized or precision medicine particularly in molecular targeted therapy, as well as their use as diagnostic and prognostic markers as therapeutic determinants in human cancers.

Reduced expression of α-L-Fucosidase-1 (FUCA-1) predicts recurrence and shorter cancer specific survival in luminal B LN+ breast cancer patients.

BACKGROUND: The lysosomal enzyme α-L-Fucosidase-1 (FUCA-1) catalyzes the hydrolytic cleavage of terminal fucose residues. FUCA-1 gene is down-regulated in highly aggressive and metastatic human tumors as its inactivation perturbs the fucosylation of proteins involved in cell adhesion, migration and metastases. RESULTS: Negativity to FUCA-1 was significantly related to the development of later recurrences in breast cancer patients with lymph node involvement at diagnosis. Cancer specific survival of luminal B LN+ patients was influenced by FUCA-1 expression as luminal B LN+ patients with positive expression had a longer cancer specific survival. FUCA-1 mRNA expression was inversely related to cancer stage and lymph node involvement. WB and qPCR analysis of FUCA-1 expression in breast cancer-derived cell lines confirmed an inverse relationship with tumor aggressiveness. CONCLUSIONS: This study shows that, within LN+ breast cancer patients, FUCA-1 is able to identify a sub-set of non recurrent patients characterized by the positive expression of FUCA-1 and that, within luminal B LN+ patients, the expression of FUCA-1 predicts longer cancer specific survival. METHODS: We have analyzed FUCA-1 in 305 breast cancer patients by Immunohistochemistry (IHC), and by qPCR in breast cancer patients and in breast cancer cell lines.

FUCA1 is induced by wild-type p53 and expressed at different levels in thyroid cancers depending on p53 status.

Fucose residues of cell surface glycans, which play important roles in growth, invasion and metastasis, are added by fucosyltransferases (FUTs) and removed by α-L-fucosidases (FUCAs). By the differential display method, we isolated a 3' non-coding region of α-L-fucosidase-1 (FUCA1) (a gene coding for the lysosomal fucosidase-1 enzyme) as a wild-type p53-inducible gene: 18S and 20S FUCA1 mRNA species were induced in Saos-2 cells transfected with a temperature-sensitive p53 mutant at the permissive temperature. By microarray analyses of thyroid cancer biopsy samples, FUCA1 RNA expression levels were found to be lower in anaplastic thyroid cancer samples (ATCs), while they were higher in papillary thyroid cancer samples (PTCs) and in normal thyroid tissues. Since most ATCs were reported to carry the mutated form of p53, while PTCs carry mostly the wild-type form of p53, it is likely that FUCA1 expression levels are regulated, at least in part, by the p53 status in thyroid cancers. In order to better understand the role played by FUCA genes in thyroid tumorigenesis, we examined the clonogenic potential in vitro of thyroid cell lines transfected with either FUCA1 or FUCA2 (the latter gene coding for a secreted, non-lysosomal enzyme). We found that α-L-fucosidases did not suppress grossly cell growth. Contrary to what we observed with the expression of FUCA1, the FUT8 expression levels were found high in ATCs but lower in PTCs and normal thyroid tissues. Taken together, these results suggest the possibility that the higher fucose levels on cell surface glycans of aggressive ATCs, compared to those of less aggressive PTCs, may be at least in part responsible for the more aggressive and metastatic phenotype of ATCs compared to PTCs, as the expression levels of FUCA1 and FUT8 were inversely related in these two types of cancers.

Human a-L-fucosidase-1 attenuates the invasive properties of thyroid cancer.

Glycans containing α-L-fucose participate in diverse interactions between cells and extracellular matrix. High glycan expression on cell surface is often associated with neoplastic progression. The lysosomal exoenzyme, α-L-fucosidase-1 (FUCA-1) removes fucose residues from glycans. The FUCA-1 gene is down-regulated in highly aggressive and metastatic human tumors. However, the role of FUCA-1 in tumor progression remains unclear. It is speculated that its inactivation perturbs glycosylation of proteins involved in cell adhesion and promotes cancer. FUCA-1 expression of various thyroid normal and cancer tissues assayed by immunohistochemical (IHC) staining was high in normal thyroids and papillary thyroid carcinomas (PTC), whereas it progressively decreased in poorly differentiated, metastatic and anaplastic thyroid carcinomas (ATC). FUCA-1 mRNA expression from tissue samples and cell lines and protein expression levels and enzyme activity in thyroid cancer cell lines paralleled those of IHC staining. Furthermore, ATC-derived 8505C cells adhesion to human E-selectin and HUVEC cells was inhibited by bovine α-L-fucosidase or Lewis antigens, thus pointing to an essential role of fucose residues in the adhesive phenotype of this cancer cell line. Finally, 8505C cells transfected with a FUCA-1 containing plasmid displayed a less invasive phenotype versus the parental 8505C. These results demonstrate that FUCA-1 is down-regulated in ATC compared to PTC and normal thyroid tissues and cell lines. As shown for other human cancers, the down-regulation of FUCA-1 correlates with increased aggressiveness of the cancer type. This is the first report indicating that the down-regulation of FUCA-1 is related to the increased aggressiveness of thyroid cancer.

Kirsten Ras* oncogene: significance of its discovery in human cancer research.

The KRAS/ K-RAS oncogene is crucially involved in human cancer. The term "oncogene" -- i.e., a gene able to transform a normal cell into a tumor cell - was introduced in 1969, but the word was not used in the human carcinogenesis literature until much later. Transforming Kras and Hras oncogenes from the Kirsten and Harvey sarcoma viruses were not identified until the early 1980s due to the complicated structures of the viral genomes. Orthologs of these viral oncogenes were then found in transforming DNA fragments in human cancers in the form of mutated versions of the HRAS and KRAS proto-oncogenes. Thus, RAS genes were the first human oncogenes to be identified. Subsequent studies showed that mutated KRAS acted as an in vivo oncogenic driver, as indicated by studies of anti-EGFR therapy for metastatic colorectal cancers. This review addresses the historical background and experimental studies that led to the discovery of Kirsten Ras as an oncogene, the role of mutated KRAS in human carcinogenesis, and recent therapeutic studies of cancer cells with KRAS mutations.

Uniform nomenclature for the mitochondrial contact site and cristae organizing system.

The mitochondrial inner membrane contains a large protein complex that functions in inner membrane organization and formation of membrane contact sites. The complex was variably named the mitochondrial contact site complex, mitochondrial inner membrane organizing system, mitochondrial organizing structure, or Mitofilin/Fcj1 complex. To facilitate future studies, we propose to unify the nomenclature and term the complex "mitochondrial contact site and cristae organizing system" and its subunits Mic10 to Mic60.

Genetic deregulation of the PIK3CA oncogene in oral cancer.

The phosphatidylinositol 3-kinase (PI3K)/Akt signaling pathway is one of the most commonly deregulated pathways in human cancers. PI3K comprises a catalytic (p110α) and regulatory subunit (p85), and p110α is encoded by the PIK3CA gene. Here, we summarize the known genetic alterations, including amplifications and mutations, of the PIK3CA oncogene in oral cancer. We discuss in detail PIK3CA mutations and their mutual exclusivity with pathway genes in addition to the incidence of PIK3CA mutations in relation to ethnicity. We describe the constitutive activation of PI3K signaling, oncogenicity, and the genetic deregulation of the PIK3CA gene and its association with oral cancer disease stage. We emphasize the importance of therapeutically targeting the genetically deregulated PIK3CA oncogene and its signaling. We also discuss the implications of targeting Akt and/or mTOR, which are the downstream effectors of PI3K that may possibly pave the way for molecular therapeutic targets for PIK3CA-driven oral carcinogenesis. Furthermore, this critical review provides a complete picture of the PIK3CA oncogene and its deregulation in oral cancer, which may facilitate early diagnosis and improve prognosis through personalized molecular targeted therapy in oral cancer.

Ras oncogenes in oral cancer: the past 20 years.

Oral squamous cell carcinoma (OSCC) of head and neck is associated with high morbidity and mortality in both Western and Asian countries. Several risk factors for the development of oral cancer are very well established, including tobacco chewing, betel quid, smoking, alcohol drinking and human papilloma virus (HPV) infection. Apart from these risk factors, many genetic factors such as oncogenes, tumor suppressor genes and regulatory genes are identified to involve in oral carcinogenesis with these risk factors dependent and independent manner. Ras is one of the most frequently genetically deregulated oncogene in oral cancer. In this review, we analyze the past 22years of literature on genetic alterations such as mutations and amplifications of the isoforms of the ras oncogene in oral cancer. Further, we addressed the isoform-specific role of the ras in oral carcinogenesis. We also discussed how targeting the Akt and MEK, downstream effectors of the PI3K/Akt and MAPK pathways, respectively, would probably pave the possible molecular therapeutic target for the ras driven tumorigenesis in oral cancer. Analysis of these ras isoforms may critically enlighten specific role of a particular ras isoform in oral carcinogenesis, enhance prognosis and pave the way for isoform-specific molecular targeted therapy in OSCC.

Essential role of caspase-8 in p53/p73-dependent apoptosis induced by etoposide in head and neck carcinoma cells.

BACKGROUND: Caspase-8 is a key upstream mediator in death receptor-mediated apoptosis and also participates in mitochondria-mediated apoptosis via cleavage of proapoptotic Bid. However, the role of caspase-8 in p53- and p73-dependent apoptosis induced by genotoxic drugs remains unclear. We recently reported that the reconstitution of procaspase-8 is sufficient for sensitizing cisplatin- but not etoposide-induced apoptosis, in chemoresistant and caspase-8 deficient HOC313 head and neck squamous cell carcinoma (HNSCC) cells. RESULTS: We show that p53/p73-dependent caspase-8 activation is required for sensitizing etoposide-induced apoptosis by utilizing HOC313 cells carrying a temperature-sensitive p53G285K mutant. Restoration of wild-type p53 function under the permissive conditions, together with etoposide treatment, led to substantial transcriptional activation of proapoptotic Noxa and PUMA, but failed to induce apoptosis. In addition to p53 restoration, caspase-8 reconstitution was needed for sensitization to etoposide-induced apoptosis, mitochondria depolarization, and cleavage of the procaspases-3, and -9. In etoposide-sensitive Ca9-22 cells carrying a temperature-insensitive mutant p53, siRNA-based p73 knockdown blocked etoposide-induced apoptosis and procaspase-8 cleavage. However, induction of p73 protein and up-regulation of Noxa and PUMA, although observed in Ca9-22 cells, were hardly detected in etoposide-treated HOC313 cells under non-permissive conditions, suggesting a contribution of p73 reduction to etoposide resistance in HOC313 cells. Finally, the caspase-9 inhibitor Ac-LEHD-CHO or caspase-9 siRNA blocked etoposide-induced caspase-8 activation, Bid cleavage, and apoptosis in both cell lines, indicating that p53/p73-dependent caspase-8 activation lies downstream of mitochondria. CONCLUSIONS: we conclude that p53 and p73 can act as upstream regulators of caspase-8, and that caspase-8 is an essential mediator of the p53/p73-dependent apoptosis induced by etoposide in HNSCC cells. Our data suggest the importance of caspase-8-mediated positive feedback amplification in the p53/p73-dependent apoptosis induced by etoposide in HNSCC cells.

Association of caspase-8 mutation with chemoresistance to cisplatin in HOC313 head and neck squamous cell carcinoma cells.

Caspase-8 is a critical upstream mediator of apoptosis in the death receptor pathway. However, the relationship between caspase-8 mutation and chemosensitivity remain unclear in head and neck squamous cell carcinoma (HNSCC) carrying p53 mutation. In this study, we identified a caspase-8 nonsense mutation, accompanied by the loss of the second allele, in a drug-resistant HOC313 HNSCC cell line. The nonsense mutation (R68X) leads to truncation of all defined functional domains. Reconstitution of caspase-8 by stable transfection of wild-type caspase-8 sensitized the cells to cisplatin-, but not etoposide-induced apoptosis. Consistent with this, cisplatin, but not etoposide, induced TNF-alpha and TRAIL mRNA in caspase-8 reconstituted HOC313 cells, accompanied by activation of the reconstituted caspase-8 and its downstream caspase-3. These results indicate that the loss of caspase-8 plays an important role in acquisition of chemoresistance to cisplatin in HOC313 cells.

Detection of two novel mutations and relatively high incidence of H-RAS mutations in Vietnamese oral cancer.

Oral squamous cell carcinoma is the sixth most common cancer in the world and the seventh most common cancer in Vietnam. The RAS and PI3K-AKT signaling pathways play an important role in oral carcinogenesis. Our previous study on PI3K signaling pathway showed the absence of PIK3CA and PTEN gene mutations in Vietnamese oral cancer. We thus hypothesized that the RAS could be more likely activated as an upstream effector. However, the status of RAS mutations in Vietnamese oral cancer had not been studied. In the present study, Fifty six primary tumor DNA samples were screened for mutations of hot spots in exons 1 and 2 of H-RAS and a part of the samples for exon 7 of ERK2 gene in which we previously reported a mutation in an OSCC cell line. The H-RAS mutations were detected in 10 of 56 tumors (18%). Two novel mutations were found, one was an insertion of three nucleotides (GGC) between codons 10 and 11 resulting in in-frame insertion of glycine (10(Gly)11) and the other was a missense mutation in codon 62 (GAG>GGG). We also found T81C single nucleotide polymorphism in 12 of 56 tumors (22%) and there was no mutation in exon 7 of ERK2 gene. The H-RAS mutation incidence showed significant association with advanced stages of the tumor and also with well-differentiated tumor grade. Our study is the first to report H-RAS mutation from Vietnamese ethnicity, with two novel mutations and relatively high incidence of H-RAS mutations. The results suggest that RAS is an important member in the PI3K-AKT signaling and could play an important role in the tumorigenesis of oral carcinoma.

Monocytic leukemia zinc finger (MOZ) interacts with p53 to induce p21 expression and cell-cycle arrest.

Upon DNA damage, p53 can induce either cell-cycle arrest or apoptosis. Here we show that monocytic leukemia zinc finger (MOZ) forms a complex with p53 to induce p21 expression and cell-cycle arrest. The levels of the p53-MOZ complex increased in response to DNA damage to levels that induce cell-cycle arrest. MOZ(-/-) mouse embryonic fibroblasts failed to arrest in G1 in response to DNA damage, and DNA damage-induced expression of p21 was impaired in MOZ(-/-) cells. These results suggest that MOZ is involved in regulating cell-cycle arrest in the G1 phase. Screening of tumor-associated p53 mutants demonstrated that the G279E mutation in p53 disrupts interactions between p53 and MOZ, but does not affect the DNA binding activity of p53. The leukemia-associated MOZ-CBP fusion protein inhibits p53-mediated transcription. These results suggest that inhibition of p53/MOZ-mediated transcription is involved in tumor pathogenesis and leukemogenesis.

ERK2 CD domain mutation from a human cancer cell line enhanced anchorage-independent cell growth and abnormality in Drosophila.

In a human cancer cell line, we previously found a mutation in codon 322 of the extracellular signal-regulated kinase (ERK2E322K), the protein showed a faster migration when compared to wild-type in SDS-PAGE and constitutive phosphorylation. However, the reason for the faster migration, and the biochemical and biological properties of the mutation is unknown. In this study, we report that the amino acid charge-change mutation in the common docking (CD) domain is important for fast migration. In vitro binding of ERK2E322K to MKP1 and RSK2 was lost, resulting in constitutive activation and possibly contributing to a more efficient colony formation in soft agar. We established transgenic flies by carrying the corresponding CD domain mutation, DERKE335K, which developed smaller and rougher eyes compared with the wild-type. Taken together, these data are consistent with ERK2E322K loss of contact with downstream effectors and its constitutive activation, presenting an oncogenic potential and weak abnormality in differentiation.

SWAP-70 is important for invasive phenotypes of mouse embryo fibroblasts transformed by v-Src.

SWAP-70 is a protein involved in actin rearrangement, especially in membrane ruffling. Mouse embryo fibroblasts (MEFs) deficient in SWAP-70 show impaired membrane ruffling and fail to grow in soft agar after transformation by v-Src. Here, we show that v-Src transformed MEFs expressing SWAP-70 are highly invasive. MEFs expressing SWAP-70 or v-Src alone were far less invasive, suggesting that both proteins were required for the cells to be invasive. Expression of both SWAP-70 and v-Src induced constant membrane ruffling, which may cause vigorous cell movement, probably required for invasiveness of the cells. Expression of v-Src alone morphologically transformed MEFs but formed lamellipodia rather than membrane ruffles, suggesting less aggressive nature of the cells compared with those expressing both SWAP-70 and v-Src. These results suggest that v-Src and SWAP-70 act synergistically in the invasion activity of MEFs.

Promoter hypermethylation analysis in myelodysplastic syndromes: diagnostic & prognostic implication.

BACKGROUND & OBJECTIVE: Myelodysplastic syndromes (MDS) are a heterogenous group of haematopoietic stem cell disorders that are multifactorial in their aetiology. Unique genetic alterations in combinations or in isolation account for a small fraction of MDS suggesting the epigenetic hypermethylation as a possible leading cause for MDS and its transformation to acute myelocytic leukaemia (AML). Therefore, in this study, promoter hypermethylation status of key cell cycle regulators was assessed as markers in MDS patients and association of hypermethylation with clinical progression of disease was also studied. METHODS: Promoter hypermethylation analysis of five tumour associated genes namely p16, p15, MGMT, hMLH1 and E-cadherin were done for 41 MDS patient samples with its various subtype. The hypermethylation analysis was done by using semi-nested multiplex PCR. RESULTS: Eighty per cent of (33/41) of the MDS samples were found to be methylated in any one of the four genes (p16, p15, MGMT and E-cadherin). The p15 methylation was found to be the most frequent 61 per cent (25/41), E-cadherin was methylated in 39 per cent (16/41) and p16 in 37 per cent (15/41) of the cases. MGMT gene showed a low 5 per cent (2/41) methylation whereas hMLH1 gene was not methylated in any one of the samples analysed. INTERPRETATION & CONCLUSION: Differential rate of methylation of the four genes (p16, p15, MGMT and E-cadherin) was observed in MDS samples. All the samples analysed showed the absence of a methylator phenotype in MDS. The methylation frequency of all these genes increased with the clinical severity of the MDS subtypes. Therefore, hypermethylation may be used as a diagnostic and prognostic tool in ascertaining the clinical severity of MDS.

Naf1alpha is phosphorylated in mitotic phase and required to protect cells against apoptosis.

Naf1alpha is an HIV Nef-associated factor expressed ubiquitously in human cells. Previously, we reported that Naf1alpha is phosphorylated with EGF through MEK/ERK2 pathway. In this study, we found an additional phosphorylation of Naf1alpha when cells are in mitotic phase (M phase) or arrested in M phase with anti-mitosis reagents, and disappeared when the cells exit from mitotic phase to G1 phase. Furthermore, we demonstrated that Naf1alpha plays an important role in preventing cells from apoptosis: over-expression of Naf1alpha in Saos-2 cells suppressed trichostatin A (TSA)-induced apoptosis either of random culture or of cell population synchronized in M phase. In addition, knock-down of Naf1alpha expression with small interfering RNA sensitized Saos-2 cells to TSA-induced apoptosis. Physiological significance of these findings is discussed in relation to protection of cells from the apoptosis induction.

Oncogenic mutations of the PIK3CA gene in head and neck squamous cell carcinomas.

Phosphatidylinositol 3-kinases (PI3Ks) are heterodimeric lipid kinases that regulate cellular activities such as proliferation, survival, motility and morphology. Recent studies reported that the p110alpha (PIK3CA), catalytic subunit of PI3-kinase is somatically mutated in human cancers. Hot- spot mutations (E542K, E545K and H1047R) are reported to have higher oncogenic potential. Although PIK3CA mutations were reported in head and neck squamous cell carcinomas (HNSCC) of limited ethnicity, the functional consequences of HNSCC-associated PIK3CA mutations have not been examined. Status of PI3K signaling related genes (PTEN-RAS-EGFR) in the presence of PIK3CA mutation have not been reported. In this study, we analyzed exons 9 and 20 of PIK3CA in 54 samples, including 17 HNSCC cell lines, 19 Indian and 18 Vietnamese primary tumors. We found mutations in 29.4% (5/17) of HNSCC cell lines, 10.5% (2/19) of Indian tumors and no mutation (0/18) in Vietnamese tumors. Two homozygous PIK3CA mutations were found in cell lines and a novel insertion mutation with oncogenicity in Indian tumor. Analysis of PI3K signaling related genes showed that PIK3CA and PTEN mutations were mutually exclusive, though PTEN mutation is uncommon in HNSCC. However, PIK3CA mutation coexisted with H-RAS mutation. Furthermore, PIK3CA mutations were mutually exclusive to EGFR amplification. All the 5 mutants that we found in HNSCC, showed increased PI3 kinase activities, followed by growth factor independent higher colony forming efficiency, changes in morphology, higher rates of migration and invasion compared with PIK3CA wild-type. Our study is the first to examine the oncogenic potential of PIK3CA mutants associated with HNSCC and report on PIK3CA mutations in Indian and Vietnamese ethnicity. These results suggest that PIK3CA mutations in HNSCC are likely to be oncogenic and may significantly contribute to HNSCC carcinogenesis and pave attractive target for therapeutic prevention.

Histogenesis of the intravitreal membrane and secondary vitreous in the mouse.

PURPOSE: The intravitreal membrane (IVM) is a membranous structure between the primary and secondary vitreous bodies in developing mammalian eyes. In this study, for the first time the histogenesis of the IVM and the relationship between the hyaloid vasculature and the IVM was characterized in newborn mice. METHODS: Eyes of mice less than 12 days old were fixed and embedded. From these, serial paraffin-embedded sections were made for lectin histochemistry, immunohistochemistry, and picrosirius red (PSR) staining, and ultrathin sections were made for transmission electron microscopy (TEM). Eight biotinylated lectins and antibodies for laminin and type IV collagen were used. RESULTS: Among the eight lectins tested, concanavalin A (Con A) agglutinin, Ricinus communis agglutinin I, and wheat germ agglutinin demonstrated strong positive staining in the IVM and vitreous fibrils of the primary and secondary vitreous bodies. They also bound to the internal limiting membrane (ILM) of the retina. At postgestational day 4, the secondary vitreous first appeared between the ILM and the vasa hyaloidea propria (VHP). Immunohistochemical staining revealed that the IVM consists of extracellular matrix components including laminin and type IV collagen, whereas PSR staining and TEM showed that collagen fibrils in the IVM are bundled and continuous with the basement membrane of hyaloid capillaries or the VHP. CONCLUSIONS: Lectin histochemistry and immunohistochemistry provided good methods for visualizing the structures of the IVM and vitreous fibrils. These results suggest that the IVM is separated from the basement membrane of the retinal ILM along with the vascular network of the VHP when the secondary vitreous begins to form.

Role of caspase 8 as a determinant in chemosensitivity of p53-mutated head and neck squamous cell carcinoma cell lines.

We studied factors that control chemoresistance to 6 head and neck squamous cell carcinoma cell lines carrying p53 mutations. Cell lines were chosen, based on the presence of EGFR amplifications, the presence of H-ras mutations, and the absence of either. WST-1 viability assays showed that, in response to etoposide, Ca922 was most sensitive, HOC313 most resistant, and HSC6 and the others moderately sensitive. A similar tendency was shown by further analyses with cisplatin, 5-fluorouracil, LY294002, and combined treatment with LY294002 and TNF-related apoptosis-inducing ligand (TRAIL). Although both Ca922 and HOC313 had activating mutations upstream of Akt signaling, the constitutive phosphorylation of Akt at S473 was observed in chemosensitive Ca922, but not in chemoresistant HOC313, suggesting that constitutive Akt phosphorylation was not the primary determinant for chemoresistance in these cell lines. Further, by the combined treatment with LY294002 and TRAIL, apoptosis was induced in Ca922 and HSC6 but not in HOC313. Interestingly, caspase 8 was not detected in HOC313, while it was cleaved in the other 2 cell lines. Further, in Ca922 and HSC6 but not in HOC313, caspase 8 inhibitor restored loss of viability induced either with LY294002 and TRAIL or even with etoposide alone. These findings suggest that caspase 8 played an important role in chemoresistance against genotoxic drugs.

A mutation in the common docking domain of ERK2 in a human cancer cell line, which was associated with its constitutive phosphorylation.

The EGFR/Ras/Raf/MEK/ERK pathway is a major pathway involved in the control of growth signals, cell survival and differentiation. Mutations of signaling components, such as EGFR (c-erbB1), Ras, and B-Raf, have been shown to play roles in the genesis of human cancer, while point mutation of ERK has not been reported. In this study, we present evidence for a mutation in an oral squamous cell carcinoma cell line, HSC6. PCR-amplification of cDNA, cloning and sequencing resulted in the identification of glutamic acid to lysine substitution at codon 322 (E322K) that occurred in the common docking (CD) domain of ERK2. The mutant protein contributed towards faster-migration in SDS-PAGE, and constitutive phosphorylation in a MEK-dependent manner. The transient transfection of the mutant ERK2 in 293T cells resulted in the expression of the same faster-migrating band in SDS-PAGE as was detected in HSC6 cells, which was preferentially phosphorylated relative to endogenous wild-type ERK2. The present study is the first to report ERK2 substitution mutation in a human cancer cell line which resulted in constitutive phosphorylation.