ERK3 signals through SRC-3 coactivator to promote human lung cancer cell invasion
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
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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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 6

ERK3 promotes the interaction of SRC-3 with PEA3 and occupancy of SRC-3 on the PEA3 binding site of MMP2 gene promoter, which is mediated by the phosphorylation site S857.

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ERK3 promotes the interaction of SRC-3 with PEA3 and occupancy of SRC-3 ...
(A) Knockdown of ERK3 decreases the interaction of SRC-3 with PEA3. H1299 cells were transfected with ERK3 siRNA or nontargeting control siRNA. Coimmunoprecipitation was performed using a SRC-3 Ab or a mouse IgG, followed by Western blotting. (B) ERK3 promotes the interaction of SRC-3 with PEA3, which is mediated by the phosphorylation site S857. H1299 cells were transfected with SRC-3Flag or SRC-3S857AFlag or together with Myc-tagged ERK3 (MycERK3). Coimmunoprecipitation was performed using a Flag Ab. Numbers below the PEA3 immunoblots in Flag immunoprecipitation represent the relative intensity of the protein bands. The band intensity in lane 1 is set as “1.0.” (C) Overexpression of ERK3 enhanced occupancy of SRC-3 on the MMP2 promoter. H1299 cells were stably transduced with either lentiviral vector CDH or lentiviral ERK3 (CDHERK3). ChIP assays were performed using either a SRC-3 Ab or goat IgG. SRC-3 protein occupancy on the PEA3 binding site of MMP2 gene promoter (700-bp upstream of transcription start site; ref. 19) was analyzed by quantitative real-time PCR and presented as the percentage of sheared chromatin input. (D) ERK3 promotes the occupancy of SRC-3, but not the SRC-3S857A mutant, on the MMP2 promoter. A549 cells were singly transduced or cotransduced stably with the lentiviral constructs as indicated. ChIP assays were performed using either a Flag Ab or mouse IgG. *P < 0.01.