APC inhibits ERK pathway activation and cellular proliferation induced by RAS

Gene expression profiling: Canonical molecular changes and clinicopathological features in sporadic colorectal cancers

AIM: To investigate alternative or subordinate pathways involved in colorectal tumorigenesis and tumor growth, possibly determining at-risk populations and predicting responses to treatment.

METHODS: Using microarray gene-expression analysis, we analyzed patterns of gene expression relative to canonical molecular changes and clinicopathological features in 84 sporadic colorectal cancer patients, standardized by tumor location. Subsets of differentially expressed genes were confirmed by real-time reverse-transcript polymerase chain reaction (RT-PCR).

RESULTS: The largest number of genes identified as being differentially expressed was by tumor location, and the next largest number by lymphovascular or neural invasion of tumor cells and by mismatch repair (MMR) defects. Amongst biological processes, the immune response was significantly implicated in entire molecular changes observed during colorectal tumorigenesis (P < 0.001). Amongst 47 differentially expressed genes, seven (PISD, NIBP, BAI2, STOML1, MRPL21, MRPL16, and MKKS) were newly found to correlate with tumorigenesis and tumor growth. Most location-associated molecular changes had distinct effects on gene expression, but the effects of the latter were sometimes contradictory.

CONCLUSION: We show that several differentially expressed genes were associated with canonical molecular changes in sporadic colorectal cancers, possibly constituting alternative or subordinate pathways of tumorigenesis. As tumor location was the dominant factor influencing differential gene expression, location-specific analysis may identify location-associated pathways and enhance the accuracy of class prediction.

NM23H2 inhibits EGF- and Ras-induced proliferation of NIH3T3 cells by blocking the ERK pathway

The NM23 family proteins are involved in a variety of biological processes including tumor metastasis, development, and differentiation; however, their functions in the regulation of cellular proliferation are poorly understood. We have investigated the role of one NM23 family protein, NM23H2, in the regulation of cellular proliferation directed by the extracellular signal regulated kinase (ERK) pathway. The activity of ERKs was enhanced by knockdown of endogenous NM23H2 and blocked by overexpression of NM23H2 in both NIH3T3 and HEK293 cells. Additionally, the epidermal growth factor (EGF)- and oncogenic Ras(G12R)-induced proliferation of both HEK293 and NIH3T3 cells was reduced by NM23H2 overexpression. Furthermore, activation of Raf-1, MEK and the ERKs by either EGF or Ras(G12R) was inhibited by NM23H2 overexpression. Together, our data indicate that NM23H2 is a negative regulator of cellular proliferation stimulated by EGF- and Ras-mediated activation of the ERK pathway.

ERK signaling in colorectal cancer: a preliminary report on the expression of phosphorylated ERK and the effects of radiation therapy

OBJECTIVES

Phosphorylated extracellular signal-regulated kinase (ERK) activates cell survival pathways and may promote tumor cell proliferation. The purpose of this study was to determine the level of phospho-ERK staining in pretreatment specimens, and the effect of a short course of radiation therapy (RT) on the levels of phospho-ERK in specimens of colorectal cancer.

METHODS

Specimens of colorectal tumors were obtained from patients beginning RT before surgery. Tumors were graded and histologically staged. Subsequently, tumor samples were reacted with antiphospho-ERK antibodies and the level of staining intensity was assessed.

RESULTS

Of the 12 subjects evaluated, 7 of 12 had tumors that positively stained for phospho-ERK before and/or after RT. Most patients who were phospho-ERK positive before RT converted to ERK negativity after RT.

CONCLUSIONS

The results of this pilot study indicate that phospho-ERK levels may serve as a prognostic marker in colorectal cancer, and further studies are warranted to determine how changes in phospho-ERK staining relate to clinical outcome.

Understanding the somitogenesis clock: what's missing?

The segmentation of vertebrate embryos depends on a complex genetic network that generates highly dynamic gene expression. Many of the elements of the network have been identified, but their interaction and their influence on segmentation remain poorly understood. A few mathematical models have been proposed to explain the dynamics of subsets of the network, but the mechanistic bases remain controversial. This review focuses on outstanding problems with the generation of somitogenesis clock oscillations, and the ways they could regulate segmentation. Proposals that oscillations are generated by a negative feedback loop formed by Lunatic fringe and Notch signaling are weighed against a model based on positive feedback, and the experimental basis for models of simple negative feedback involving Her/Hes genes or Wnt targets is evaluated. Differences are then made explicit between the many 'clock and wavefront' model variants that have been proposed to explain how the clock regulates segmentation. An understanding of the somitogenesis clock will require addressing experimentally the many questions that arise from the study of simple models.

Tautomycetin inhibits growth of colorectal cancer cells through p21cip/WAF1 induction via the extracellular signal-regulated kinase pathway

Tautomycetin is an antifungal antibiotic retaining potent immunosuppressive function. We have identified the roles of tautomycetin on cellular proliferation and transformation of colorectal cancer cells. The proliferation and anchorage-independent growth of HCT-15, HT-29, and DLD-1 colorectal cancer cells were efficiently inhibited without induction of apoptosis by 150 nmol tautomycetin. These growth inhibitory effects were dependent on p21Cip/WAF induction via the extracellular signal-regulated kinase pathway, and the tautomycetin effects were abolished in HCT-116 colon cells and eight other types of cells that did not induce p21Cip/WAF by 150 nmol tautomycetin. The crucial role of p21Cip/WAF1 in the extracellular signal-regulated kinase pathway-dependent antiproliferative responses by tautomycetin was confirmed by using p21Cip/WAF1 gene-deleted HCT-116 cells. The growth inhibitory effect of tautomycetin was acquired by regulation of Raf-1 activity through inhibition of protein phosphatase type 1 and protein phosphatase type 2A with high preference toward protein phosphatase type 1. Tautomycetin could be a potential drug for colorectal cancer.

Axin Inhibits Extracellular Signal-regulated Kinase Pathway by Ras Degradation via β-Catenin

Interactions between the Wnt/beta-catenin and the extracellular signal-regulated kinase (ERK) pathways have been posited, but the molecular mechanisms and cooperative roles of such interaction in carcinogenesis are poorly understood. In the present study, the Raf-1, MEK, and ERK activities were concomitantly decreased in fibroblasts, which inhibit morphological transformation and proliferation by Axin induction. The inhibition of the components of the ERK pathway by Axin occurred in cells retaining wild-type beta-catenin, including primary hepatocytes, but not in cells retaining non-degradable mutant beta-catenin. Axin inhibits cellular proliferation and ERK pathway activation induced by either epidermal growth factor or Ras, indicating a role of Axin in the regulation of growth induced by ERK pathway activation. ERK pathway regulation by Axin occurs at least partly via reduction of the protein level of Ras. Both wild-type and mutant Ras proteins are subjected to regulation by Axin, which occurs in cells retaining wild-type but not mutant beta-catenin gene. The role of beta-catenin in the regulation of the Ras-ERK pathway was further confirmed by Ras reduction and subsequent inhibitions of the ERK pathway components by knock down of mutated form of beta-catenin. The Ras regulation by Axin was blocked by treatment of leupeptin, an inhibitor of the lysosomal protein degradation machinery. Overall, Axin inhibits proliferation of cells at least partly by reduction of Ras protein level via beta-catenin. This study provides evidences for the role of the Ras-ERK pathway in carcinogenesis caused by mutations of the Wnt/beta-catenin pathway components.

PEA-15 inhibits tumor cell invasion by binding to extracellular signal-regulated kinase 1/2

Phosphoprotein enriched in astrocytes of 15 kDa (PEA-15) binds to extracellular signal-regulated kinase 1 and 2 (ERK1/2) mitogen-activated protein (MAP) kinases to alter ERK1/2 cellular localization and target preferences and binds to adaptors in the extrinsic cell death pathway to block apoptosis. Here, we report that PEA-15 protein expression is inversely correlated with the invasive behavior of breast cancer in an immunohistochemical analysis of a breast cancer progression tissue microarray. Short hairpin RNA-mediated inhibition of PEA-15 expression increased the invasion of PEA-15-expressing tumor cells in vitro, suggesting a causative role for PEA-15 in the inhibition of invasion. This causative role was confirmed by the finding that the enforced expression of PEA-15 in invasive tumor cells reduced invasion. The effect of PEA-15 on tumor invasion is mediated by its interaction with ERK1/2 as shown by the following: (a) PEA-15 mutants that fail to bind ERK1/2 did not inhibit invasion; (b) overexpression of ERK1 or activated MAP/ERK kinase (MEK) reversed the inhibitory effect of PEA-15; (c) when an inhibitor of ERK1/2 activation reduced invasion, PEA-15 expression did not significantly reduce invasion further. Furthermore, we find that the effect of PEA-15 on invasion seems to relate to the nuclear localization of activated ERK1/2. PEA-15 inhibits invasion by keeping ERK out of the nucleus, as a PEA-15 mutant that cannot prevent ERK nuclear localization was not able to inhibit invasion. In addition, membrane-localized ERK1, which sequesters endogenous ERK1 to prevent its nuclear localization, also inhibited invasion. These results reveal that PEA-15 regulates cancer cell invasion via its ability to bind ERK1/2 and indicate that nuclear entry of ERK1/2 is important in tumor behavior.

Loss of Apc allows phenotypic manifestation of the transforming properties of an endogenous K-ras oncogene in vivo

Oncogenic mutations in the K-ras gene occur in approximately 50% of human colorectal cancers. However, the precise role that K-ras oncogenes play in tumor formation is still unclear. To address this issue, we have conditionally expressed an oncogenic K-ras(V12) allele in the small intestine of adult mice either alone or in the context of Apc deficiency. We found that expression of K-ras(V12) does not affect normal intestinal homeostasis or the immediate phenotypes associated with Apc deficiency. Mechanistically we failed to find activation of the Raf/MEK/ERK pathway, which may be a consequence of the up-regulation of a number of negative feedback loops. However, K-ras(V12) expression accelerates intestinal tumorigenesis and confers invasive properties after Apc loss over the long term. In renal epithelium, expression of the oncogenic K-ras(V12) allele in the absence of Apc induces the rapid development of renal carcinoma. These tumors, unlike those of intestinal origin, display activation of the Raf/MEK/ERK and Akt signaling pathways. Taken together, these data indicate that normal intestinal and kidney epithelium are resistant to malignant transformation by an endogenous K-ras oncogene. However, activation of K-ras(V12) after Apc loss results in increased tumorigenesis with distinct kinetics. Whereas the effect of K-ras oncogenes in the intestine can been observed only after long latencies, they result in rapid carcinogenesis in the kidney epithelium. These data imply a window of opportunity for anti-K-ras therapies after tumor initiation in preventing tumor growth and invasion.

The PI3 kinase-Akt pathway mediates Wnt3a-induced proliferation

Wnt3a activates proliferation of fibroblasts cells via activation of both extracellular signal-regulated kinase (ERK) and Wnt/beta-catenin signaling pathways. In this study, we show that the phosphatidyl inositol 3 kinases (PI3K)-Akt pathway is also involved in the Wnt3a-induced proliferation. Akt was activated within 30 min by Wnt3a in NIH3T3 cells. By Wnt3a treatment, activated Akt was transiently accumulated in nucleus although beta-catenin was accumulated in the nucleus of cells in a prolonged manner. The Wnt3a-induced Akt activation was not affected by siRNA-mediated reduction of beta-catenin, indicating that Wnt3a-induced Akt activation may occur independently of beta-catenin. The Wnt3a-induced Akt activation was abolished by pre-treatment with PI3K inhibitor, LY294002 and Wortmanin, but not by MEK inhibitor, U0126, indicating that Wnt3a activates Akt via PI3K. The growth and proliferation induced by Wnt3a were blocked by treatments of the PI3K inhibitors. Furthermore, Wnt3a-induced proliferation was blocked by Akt siRNA. These results reveal that the PI3K-Akt pathway mediates the Wnt3a-induced growth and proliferation of NIH3T3 cells.