RNAi-mediated ERK2 knockdown inhibits growth of tumor cells in vitro and in vivo

Abstract

The MAPK MEK/ERK pathway is often upregulated in cancer cells and represents an attractive target for development of anticancer drugs. Only few data concerning the specific functions of ERK1 and 2 are reported in the literature. In this report, we investigated the specific role of ERK1 and 2 in liver tumor growth both in vitro and in vivo. DNA synthesis and cells in S phase analysed by flow cytometry, correlated with strong inhibition of Cdk1 and cyclin E levels, are strongly reduced after exposure to the MEK inhibitor, U0126. We obtained a significant reduction of colony formation in soft agar assays and a reduction in the size of tumor xenografts in nude mice treated with U0126. Then, we could specifically abolished ERK1 or 2 expression by small-interfering RNA (siRNA) and demonstrated that ERK2 knockdown but not ERK1 interferes with the process of replication. Moreover, we found that colony formation and tumor growth in vivo were significantly inhibited by targeting ERK2 using stable chemically modified siRNA. Taken together, our results emphasize the importance of the MEK/ERK pathway in liver cancer cell growth in vitro and in vivo and argue for a crucial role of ERK2 in this regulation.

Erk1/2 activation and modulation of STAT3 signaling in oral cancer

“…In particular, Erk1/2 inhibition caused a dose-dependent decrease in the absolute number of living cells along with downregulation of cyclin D1 levels in both OSCC cell lines tested. These findings corroborate previous studies that demonstrated negative regulation of cell growth and cyclin D1 levels following Erk1/2 inhibition by means of U0126 treatment (44,47,55,56).…”

“…Using similar siRNA techniques, Bessard et al underlined the crucial role of the MEK/ERK pathway in liver cancer cell growth in vitro and in vivo demonstrating that RNAi-mediated Erk2 knockdown inhibits tumor cell growth (44). Similarly, Si et al showed that downregulation of Erk1/2 by siRNA inhibited the growth and invasion of human osteosarcoma cells, and found that the knockdown of Erk1/2 made cancer cells more sensitive to cisplatin treatment (57).…”

“…The significance of the MEK/ERK pathway has been shown in various types of cancer, such as liver, prostate and malignant melanoma cancer cell growth in vitro and in vivo (44)(45)(46). For example, knockdown of serine/threonine kinase Mirk/Dyrk1B by siRNA in either ovarian cancer or non-small cell lung cancer (NSCLC) cells led to upregulated activation of c-Raf-MEK-ERK, followed by increased growth rate (47).…”

Identification of a Soluble Factor that Induces Cell Death and Growth Inhibition in Prostate Carcinoma Cells

“…In most cell types, ERK1/2 knockdown is growth-suppressive (42)(43)(44). This effect would prevent our assessment of the role of ERK1 and ERK2 in Raf/MEK-mediated growth suppression.…”

“…Study of ERK signaling is hampered because many cell types are sensitive to the absence of ERK1/2. Apart from the lethal effects of ERK1/2 gene deletion (38,39), decreases in ERK1/2 activity, either through expression of kinase-deficient ERK mutants (40,41) or gene knockdown (42)(43)(44), significantly suppressed cell proliferation in all cell types examined thus far. Accordingly, our knowledge of mechanisms underlying ERK signaling in the context of growth arrest is still limited.…”