ERK3 signals through SRC-3 coactivator to promote human lung cancer cell invasion
Weiwen Long, … , Ming-Jer Tsai, Bert W. O’Malley
Weiwen Long, … , Ming-Jer Tsai, Bert W. O’Malley
Published April 16, 2012
Citation Information: J Clin Invest. 2012;122(5):1869-1880. https://doi.org/10.1172/JCI61492.
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Research Article Oncology

ERK3 signals through SRC-3 coactivator to promote human lung cancer cell invasion

Abstract

In contrast to the well-studied classic MAPKs, such as ERK1/2, little is known concerning the regulation and substrates of the atypical MAPK ERK3 signaling cascade and its function in cancer progression. Here, we report that ERK3 interacted with and phosphorylated steroid receptor coactivator 3 (SRC-3), an oncogenic protein overexpressed in multiple human cancers at serine 857 (S857). This ERK3-mediated phosphorylation at S857 was essential for interaction of SRC-3 with the ETS transcription factor PEA3, which promotes upregulation of MMP gene expression and proinvasive activity in lung cancer cells. Importantly, knockdown of ERK3 or SRC-3 inhibited the ability of lung cancer cells to invade and form tumors in the lung in a xenograft mouse model. In addition, ERK3 was found to be highly upregulated in human lung carcinomas. Our study identifies a previously unknown role for ERK3 in promoting lung cancer cell invasiveness by phosphorylating SRC-3 and regulating SRC-3 proinvasive activity by site-specific phosphorylation. As such, ERK3 protein kinase may be an attractive target for therapeutic treatment of invasive lung cancer.

Authors

Weiwen Long, Charles E. Foulds, Jun Qin, Jian Liu, Chen Ding, David M. Lonard, Luisa M. Solis, Ignacio I. Wistuba, Jun Qin, Sophia Y. Tsai, Ming-Jer Tsai, Bert W. O’Malley

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Figure 4

ERK3 promotes A549 cell invasion in a SRC-3–dependent manner, and S857 phosphorylation of SRC-3 is critical in promoting cell invasion.

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ERK3 promotes A549 cell invasion in a SRC-3–dependent manner, and S857 p...
(A) Transwell Matrigel cell invasion assay of A549 cells transiently transfected with Myc-ERK3 or the empty vector or together with either SRC-3 siRNA or nontargeting control siRNA. ERK3 overexpression and SRC-3 knockdown were demonstrated by Western blotting using a Myc Ab and a SRC-3 Ab, respectively. ERK3 lost the capability of promoting A549 cell invasion when SRC-3 was depleted. *P < 0.05. (B) Transwell Matrigel cell invasion assay of A549 cells transiently transfected with SRC-3Flag, SRC-3S857AFlag, or Myc-ERK3 or cotransfected with 2 of the constructs as indicated. Exogenous expression of SRC-3 and/or ERK3 was analyzed by Western blotting using a Flag Ab and a Myc Ab, respectively. Intact S857 is required for SRC-3 to promote cell invasion. (C and D) Inhibition of PAKs by expression of the PID greatly decreased the phosphorylation of SRC-3 at S857 and the effect of ERK3 and SRC-3 expression in cell invasion. GFP or GFP-PID fusion protein was overexpressed in A549 cells. (C) The effect of GFP-PID overexpression on the phosphorylation of SRC-3 at S857 was determined by Western blotting using an Ab that specifically recognizes phosphorylated S857. Numbers represent the relative intensity of the protein bands. The band intensity in the right lane is set as “1.0.” (D) The effect of GFP-PID overexpression on A549 cell invasion that was stimulated by ERK3 and SRC-3 was analyzed by transwell Matrigel cell invasion assay. *P < 0.01.