An essential function of the mitogen‐activated protein kinase Erk2 in mouse trophoblast development

The closely related mitogen-activated protein kinase isoforms extracellular signal-regulated kinase 1 (ERK1) and ERK2 have been implicated in the control of cell proliferation, differentiation and survival. However, the specific in vivo functions of the two ERK isoforms remain to be analysed. Here, we show that disruption of the Erk2 locus leads to embryonic lethality early in mouse development after the implantation stage. Erk2 mutant embryos fail to form the ectoplacental cone and extra-embryonic ectoderm, which give rise to mature trophoblast derivatives in the fetus. Analysis of chimeric embryos showed that Erk2 functions in a cell-autonomous manner during the development of extra-embryonic cell lineages. We also found that both Erk2 and Erk1 are widely expressed throughout early-stage embryos. The inability of Erk1 to compensate for Erk2 function suggests a specific function for Erk2 in normal trophoblast development in the mouse, probably in regulating the proliferation of polar trophectoderm cells

Activation of MEK1 or MEK2 isoform is sufficient to fully transform intestinal epithelial cells and induce the formation of metastatic tumors

<p>Abstract</p> <p>Background</p> <p>The Ras-dependent ERK1/2 MAP kinase signaling pathway plays a central role in cell proliferation control and is frequently activated in human colorectal cancer. Small-molecule inhibitors of MEK1/MEK2 are therefore viewed as attractive drug candidates for the targeted therapy of this malignancy. However, the exact contribution of MEK1 and MEK2 to the pathogenesis of colorectal cancer remains to be established.</p> <p>Methods</p> <p>Wild type and constitutively active forms of MEK1 and MEK2 were ectopically expressed by retroviral gene transfer in the normal intestinal epithelial cell line IEC-6. We studied the impact of MEK1 and MEK2 activation on cellular morphology, cell proliferation, survival, migration, invasiveness, and tumorigenesis in mice. RNA interference was used to test the requirement for MEK1 and MEK2 function in maintaining the proliferation of human colorectal cancer cells.</p> <p>Results</p> <p>We found that expression of activated MEK1 or MEK2 is sufficient to morphologically transform intestinal epithelial cells, dysregulate cell proliferation and induce the formation of high-grade adenocarcinomas after orthotopic transplantation in mice. A large proportion of these intestinal tumors metastasize to the liver and lung. Mechanistically, activation of MEK1 or MEK2 up-regulates the expression of matrix metalloproteinases, promotes invasiveness and protects cells from undergoing anoikis. Importantly, we show that silencing of MEK2 expression completely suppresses the proliferation of human colon carcinoma cell lines, whereas inactivation of MEK1 has a much weaker effect.</p> <p>Conclusion</p> <p>MEK1 and MEK2 isoforms have similar transforming properties and are able to induce the formation of metastatic intestinal tumors in mice. Our results suggest that MEK2 plays a more important role than MEK1 in sustaining the proliferation of human colorectal cancer cells.</p

Functional Redundancy of ERK1 and ERK2 MAP Kinases during Development

ERK1 and ERK2 are the effector kinases of the ERK1/2 MAP-kinase signaling pathway, which plays a central role in transducing signals controlling cell proliferation, differentiation, and survival. Deregulated activity of the ERK1/2 pathway is linked to a group of developmental syndromes and contributes to the pathogenesis of various human diseases. One fundamental question that remains unaddressed is whether ERK1 and ERK2 have evolved unique physiological functions or whether they are used redundantly to reach a threshold of global ERK activity. Here, we show that the extent of development of the mouse placenta and embryo bearing different combinations of Erk1 and Erk2 alleles is strictly correlated with total ERK1/2 activity. We further demonstrate that transgenic expression of ERK1 fully rescues the embryonic and placental developmental defects associated with the loss of ERK2. We conclude that ERK1 and ERK2 exert redundant functions in mouse development

Genetic Demonstration of a Redundant Role of Extracellular Signal-Regulated Kinase 1 (ERK1) and ERK2 Mitogen-Activated Protein Kinases in Promoting Fibroblast Proliferation▿

The extracellular signal-regulated kinase 1 and 2 (ERK1/2) mitogen-activated protein (MAP) kinase signaling pathway plays an important role in the proliferative response of mammalian cells to mitogens. However, the individual contribution of the isoforms ERK1 and ERK2 to cell proliferation control is unclear. The two ERK isoforms have similar biochemical properties and recognize the same primary sequence determinants on substrates. On the other hand, analysis of mice lacking individual ERK genes suggests that ERK1 and ERK2 may have evolved unique functions. In this study, we used a robust genetic approach to analyze the individual functions of ERK1 and ERK2 in cell proliferation using genetically matched primary embryonic fibroblasts. We show that individual loss of either ERK1 or ERK2 slows down the proliferation rate of fibroblasts to an extent reflecting the expression level of the kinase. Moreover, RNA interference-mediated silencing of ERK1 or ERK2 expression in cells genetically disrupted for the other isoform similarly reduces cell proliferation. We generated fibroblasts genetically deficient in both Erk1 and Erk2. Combined loss of ERK1 and ERK2 resulted in a complete arrest of cell proliferation associated with G1 arrest and premature replicative senescence. Together, our findings provide compelling genetic evidence for a redundant role of ERK1 and ERK2 in promoting cell proliferation

Loss of interleukin-17 receptor D promotes chronic inflammation-associated tumorigenesis.

Interleukin-17 receptor D (IL-17RD), also known as similar expression to Fgf genes (SEF), is proposed to act as a signaling hub that negatively regulates mitogenic signaling pathways, like the ERK1/2 MAP kinase pathway, and innate immune signaling. The expression of IL-17RD is downregulated in certain solid tumors, which has led to the hypothesis that it may exert tumor suppressor functions. However, the role of IL-17RD in tumor biology remains to be studied in vivo. Here, we show that genetic disruption of Il17rd leads to the increased formation of spontaneous tumors in multiple tissues of aging mice. Loss of IL-17RD also promotes tumor development in a model of colitis-associated colorectal cancer, associated with an exacerbated inflammatory response. Colon tumors from IL-17RD-deficient mice are characterized by a strong enrichment in inflammation-related gene signatures, elevated expression of pro-inflammatory tumorigenic cytokines, such as IL-17A and IL-6, and increased STAT3 tyrosine phosphorylation. We further show that RNAi depletion of IL-17RD enhances Toll-like receptor and IL-17A signaling in colon adenocarcinoma cells. No change in the proliferation of normal or tumor intestinal epithelial cells was observed upon genetic inactivation of IL-17RD. Our findings establish IL-17RD as a tumor suppressor in mice and suggest that the protein exerts its function mainly by limiting the extent and duration of inflammation

Copper bioavailability is a KRAS-specific vulnerability in colorectal cancer.

Despite its importance in human cancers, including colorectal cancers (CRC), oncogenic KRAS has been extremely challenging to target therapeutically. To identify potential vulnerabilities in KRAS-mutated CRC, we characterize the impact of oncogenic KRAS on the cell surface of intestinal epithelial cells. Here we show that oncogenic KRAS alters the expression of a myriad of cell-surface proteins implicated in diverse biological functions, and identify many potential surface-accessible therapeutic targets. Cell surface-based loss-of-function screens reveal that ATP7A, a copper-exporter upregulated by mutant KRAS, is essential for neoplastic growth. ATP7A is upregulated at the surface of KRAS-mutated CRC, and protects cells from excess copper-ion toxicity. We find that KRAS-mutated cells acquire copper via a non-canonical mechanism involving macropinocytosis, which appears to be required to support their growth. Together, these results indicate that copper bioavailability is a KRAS-selective vulnerability that could be exploited for the treatment of KRAS-mutated neoplasms

Copper bioavailability is a KRAS-specific vulnerability in colorectal cancer

The oncogene KRAS is frequently mutated in cancer, including colorectal cancer. Here, using a cell-surface proteomics approach, KRAS-mutated colorectal cancer cells are shown to express high levels of the copper transporter ATP7A, which has an essential roles in cancer cell survival and proliferation