👤 N Sunaga

Dual specific phosphatases (DUSPs) are a family of phosphatases, including DUSP4, DUSP5, and DUSP6, that function as negative regulators of the RAF/MEK/ERK pathway. These DUSPs have been extensively studied in various human cancers, particularly those with KRAS mutations. Our previous research indicated that these DUSPs are downregulated by KRAS knockdown in KRAS mutant lung cancer cell lines and upregulated in an hTERT/Cdk4-immortalized normal human bronchial cell line HBEC3-KT expressing mutant KRAS Show less

We evaluated the contribution of three genetic alterations (p53 knockdown, K-RAS(V12), and mutant EGFR) to lung tumorigenesis using human bronchial epithelial cells (HBEC) immortalized with telomerase and Cdk4-mediated p16 bypass. RNA interference p53 knockdown or oncogenic K-RAS(V12) resulted in enhanced anchorage-independent growth and increased saturation density of HBECs. The combination of p53 knockdown and K-RAS(V12) further enhanced the tumorigenic phenotype with increased growth in soft agar and an invasive phenotype in three-dimensional organotypic cultures but failed to cause HBECs to form tumors in nude mice. Growth of HBECs was highly dependent on epidermal growth factor (EGF) and completely inhibited by EGF receptor (EGFR) tyrosine kinase inhibitors, which induced G1 arrest. Introduction of EGFR mutations E746-A750 del and L858R progressed HBECs toward malignancy as measured by soft agar growth, including EGF-independent growth, but failed to induce tumor formation. Mutant EGFRs were associated with higher levels of phospho-Akt, phospho-signal transducers and activators of transcription 3 [but not phospho-extracellular signal-regulated kinase (ERK) 1/2], and increased expression of DUSP6/MKP-3 phosphatase (an inhibitor of phospho-ERK1/2). These results indicate that (a) the HBEC model system is a powerful new approach to assess the contribution of individual and combinations of genetic alterations to lung cancer pathogenesis; (b) a combination of four genetic alterations, including human telomerase reverse transcriptase overexpression, bypass of p16/RB and p53 pathways, and mutant K-RAS(V12) or mutant EGFR, is still not sufficient for HBECs to completely transform to cancer; and (c) EGFR tyrosine kinase inhibitors inhibit the growth of preneoplastic HBEC cells, suggesting their potential for chemoprevention. Show less

Constitutive activation of the Wnt signaling pathway as a result of genetic alterations of APC, AXIN1, and CTNNB1 has been found in various human cancers, including those of the colon, liver, endometrium, ovary, prostate, and stomach. To investigate the pathogenetic significance of constitutive activation of the Wnt signaling pathway in human lung carcinogenesis, CTNNB1 alterations in exon 3, a region known to represent a mutation hot spot, were screened in 46 lung cancer cell lines and 47 primary lung cancers. Missense mutations causing substitutions of Ser/Thr residues critical for regulation by GSK-3beta were detected in one (2%) of the cell lines, A427, and two (4%) of the surgical specimens. The three lung cancers with CTNNB1 mutations were adenocarcinomas. To explore the prevalence of constitutive activation of the Wnt signaling pathway in human lung cancer, we assessed 15 lung cancer cell lines representing major histological subtypes of lung cancers for constitutive Tcf transcriptional activity (CTTA). CTTA was observed only in the A427 adenocarcinoma cell line, but not in the remaining 14 cell lines. The data indicate that constitutive activation of the Wnt signaling pathway caused by CTNNB1 mutation is involved in the development and/or progression of a subset of lung carcinoma, preferentially in adenocarcinoma. Show less