Carcinogenesis

About: Carcinogenesis is a research topic. Over the lifetime, 60368 publications have been published within this topic receiving 3192599 citations. The topic is also known as: oncogenesis & tumorigenesis.

p53 gain-of-function cancer mutants induce genetic instability by inactivating ATM

Abstract: Tp53 is the most commonly mutated tumour-suppressor gene in human cancers. In addition to the loss of tumour-suppression function, some missense mutants gain novel oncogenic activities. To elucidate the nature of the gain of function, we introduced the most common p53 cancer mutations (R248W and R273H) independently into the humanized p53 knock-in (HUPKI) allele in mice. Tumour-suppressor functions of p53 are abolished in p53-mutant mice. Several lines of evidence further indicate gain-of-function of p53 mutants in promoting tumorigenesis. p53(R248W) mice rapidly succumb to certain types of cancers not commonly observed in p53(-/-) mice. Interchromosomal translocations, a type of genetic instability rarely observed in p53(-/-) cells, are readily detectable in p53-mutant pre-tumor thymocytes. Although normal in p53(-/-) mouse cells, the G(2)-M checkpoint is impaired in p53-mutant cells after DNA damage. These acquired oncogenic properties of mutant p53 could be explained by the findings that these p53 mutants interact with the nuclease Mre11 and suppress the binding of the Mre11-Rad50-NBS1 (MRN) complex to DNA double-stranded breaks (DSBs), leading to impaired Ataxia-telangiectasia mutated (ATM) activation. Therefore, p53 gain-of-function mutants promote tumorigenesis by a novel mechanism involving active disruption of critical DNA damage-response pathways.

Similarity of the phenotypic patterns associated with BRAF and KRAS mutations in colorectal neoplasia.

Abstract: Activation of the RAS/RAF/extracellular signal-regulated kinase-mitogen-activated protein kinase/extracellular signal-regulated kinase/mitogen-activated protein kinase pathway by RAS mutations is commonly found in human cancers. Recently, we reported that mutation of BRAF provides an alternative route for activation of this signaling pathway and can be found in melanomas, colorectal cancers, and ovarian tumors. Here we perform an extensive characterization of BRAF mutations in a large series of colorectal tumors in various stages of neoplastic transformation. BRAF mutations were found in 11 of 215 (5.1%) colorectal adenocarcinomas, 3 of 108 (2.8%) sporadic adenomas, 1 of 63 (1.6%) adenomas from familial adenomatous polyposis (FAP) patients, and 1 of 3 (33%) hyperplastic polyps. KRAS mutations were detected in 34% of carcinomas, 31% of sporadic adenomas, 9% of FAP adenomas, and no hyperplastic polyps. Eight of 16 BRAF mutations were V599E, the previously described hotspot, and none of these was associated with a KRAS mutation in the same lesion. The remaining eight mutations involve other conserved amino acids in the kinase domain, and 62.5% have a KRAS mutation in the same tumor. Our data suggest that BRAF mutations are, to some extent, biologically similar to RAS mutations in colorectal cancer because both occur at approximately the same stage of the adenoma-carcinoma sequence, both are associated with villous morphology, and both are less common in adenomas from FAP cases. By contrast, colorectal adenocarcinomas with BRAF mutations are associated with early Dukes' tumor stages (P = 0.006) and no such relationship was observed for KRAS mutations. The presence in some colorectal neoplasms of mutations in both BRAF and KRAS suggests that modulation of the RAS-RAF-extracellular signal-regulated kinase-mitogen-activated protein kinase/extracellular signal-regulated kinase/mitogen-activated protein kinase signaling pathway may occur by mutation of multiple components.

Androgen responsive adult human prostatic epithelial cell lines immortalized by human papillomavirus 18

Abstract: Prostate cancer and benign tumors of the prostate are the two most common neoplastic diseases in men in the United States, however, research on their causes and treatment has been slow because of the difficulty in obtaining fresh samples of human tissue and a lack of well characterized cell lines which exhibit growth and differentiation characteristics of normal prostatic epithelium. Non-neoplastic adult human prostatic epithelial cells from a white male donor were immortalized with human papillomavirus 18 which resulted in the establishment of the RWPE-1 cell line. Cells from the RWPE-1 cell line were further transformed by v-Ki-ras to establish the RWPE-2 cell line. The objectives of this study were to: (1) establish the prostatic epithelial origin and androgen responsiveness of RWPE-1 and RWPE-2 cell lines; (2) examine their response to growth factors; and (3) establish the malignant characteristics of the RWPE-2 cell line. Immunoperoxidase staining showed that both RWPE-1 and RWPE-2 cells express cytokeratins 8 and 18, which are characteristic of luminal prostatic epithelial cells, but they also coexpress basal cell cytokeratins. These cell lines show growth stimulation and prostate specific antigen (PSA) and androgen receptor (AR) expression in response to the synthetic androgen mibolerone, which establishes their prostatic epithelial origin. Both cell lines also show a dose-dependent growth stimulation by EGF and bFGF and growth inhibition when exposed to TGF-beta, however, the transformed RWPE-2 cells are less responsive. RWPE-1 cells neither grow in agar nor form tumors when injected into nude mice with or without Matrigel. However, RWPE-2 cells form colonies in agar and tumors in nude mice. In the in vitro invasion assay, RWPE-1 cells are not invasive whereas RWPE-2 cells are invasive. Nuclear expression of p53 and Rb proteins was heterogeneous but detectable by immunostaining in both cell lines. The RWPE-1 cells, which show many normal cell characteristics, and the malignant RWPE-2 cells, provide useful cell culture models for studies on prostate growth regulation and carcinogenesis.

Mutational Inactivation of Transforming Growth Factor β Receptor Type II in Microsatellite Stable Colon Cancers

Abstract: We previously demonstrated that mutational inactivation of transforming growth factor beta type II receptors (RIIs) is very common among the 13% of human colon cancers with microsatellite instability. These mutations principally cluster in the BAT-RII polyadenine sequence repeat. Among microsatellite stable (MSS) colon cancers, we now find that non-BAT-RII point mutations inactivate RII in another 15% of cases, thus doubling the known number of colon cancers in which RII mutations are pathogenetic. Functional analysis confirms that these mutations inactivate RII signaling. Moreover, another 55% of MSS colon cancers demonstrate a transforming growth factor beta signaling blockade distal to RII. The transforming growth factor beta pathway and RII in particular are major targets for inactivation in MSS colon cancers as well as in colon cancers with microsatellite instability.

SIRT1 Is Significantly Elevated in Mouse and Human Prostate Cancer

Abstract: Evidence suggests that the histone deacetylase, SIRT1, is a mediator of life span extension by calorie restriction; however, SIRT1 may paradoxically increase the risk of cancer. To better understand the relationship among SIRT1, energy balance, and cancer, two experiments were done. First, a transgenic mouse model of prostate cancer (transgenic adenocarcinoma of mouse prostate; TRAMP) was used to determine the role of energy balance on SIRT1 expression and the effect of cancer stage on SIRT1 and hypermethylated in cancer-1 (HIC-1). Second, immunohistochemistry was done on human prostate tumors to determine if SIRT1 was differentially expressed in tumor cells versus uninvolved cells. Results show that SIRT1 is not increased in the dorsolateral prostate (DLP) of calorie-restricted mice during carcinogenesis. In contrast, when examined in the DLP as a function of pathologic score, SIRT1 was significantly elevated in mice with poorly differentiated adenocarcinomas compared with those with less-advanced disease. HIC-1, which has been shown to regulate SIRT1 levels, was markedly reduced in the same tumors, suggesting that a reduction in HIC-1 may be in part responsible for the increased expression of SIRT1 in prostatic adenocarcinomas. Furthermore, immunostaining of human prostate tumors showed that cancer cells had greater SIRT1 expression than uninvolved cells. In conclusion, DLP SIRT1 expression from calorie-restricted mice was not altered during carcinogenesis. However, SIRT1 expression was increased in mice with poorly differentiated adenocarcinomas and in human prostate cancer cells. Because SIRT1 may function as a tumor promoter, these results suggest that SIRT1 should be considered as a potential therapeutic target for prostate cancer.