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.
View: Text | PDF
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

×

Figure 2

ERK3 phosphorylates SRC-3 at S857.

Options: View larger image (or click on image) Download as PowerPoint
ERK3 phosphorylates SRC-3 at S857. (A) ERK3 phosphorylates SRC-3 at the ...
(A) ERK3 phosphorylates SRC-3 at the CID region in vitro. SRC-3Flag protein was expressed in Sf9 cells and purified using anti-Flag beads. The N-terminal basic helix-loop-helix domain-containing region of SRC-3 (aa 1–320), serine/threonine-rich region (S/T; aa 321–580), receptor interaction domain-containing region (aa 581–840; lane 5), CID region (aa 841–1080), and histone acetyltransferase domain-containing region (HAT; aa 1081–1424) were expressed as GST-fusion proteins in E. coli. In vitro kinase assay was performed by incubating purified SRC-3Flag (lane 7) or GSTSRC-3 fragment proteins (see Coomassie staining) with purified ERK3 kinase. ERK3 autophosphorylation (arrow, lane 7) and phosphorylation of the substrates (arrowheads, lane 5 and 7) are shown in the autoradiograph in the right panel. (B) ERK3 phosphorylates SRC-3 at S857 within the CID region in vitro. GST, GSTCID, and GSTCIDS857A proteins (see Coomassie staining) were incubated with either purified active ERK3 protein or ERK3KD protein. The arrow and arrowhead indicate ERK3 autophosphorylation and GSTCID phosphorylation, respectively. (C) Knockdown of ERK3 decreases SRC-3 phosphorylation at S857 in H1299 cells. ERK3 was knocked down by transfecting cells with ERK3 siRNA or by transducing cells with lentiviruses expressing ERK3 shRNA. SRC-3 phosphorylation at S857 was analyzed by Western blotting using an Ab that specifically recognizes phosphorylated S857.