p90 ribosomal S6 kinase 2 promotes invasion and metastasis of human head and neck squamous cell carcinoma cells
Sumin Kang, … , Dong M. Shin, Jing Chen
Sumin Kang, … , Dong M. Shin, Jing Chen
Published March 15, 2010
Citation Information: J Clin Invest. 2010;120(4):1165-1177. https://doi.org/10.1172/JCI40582.
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Research Article Oncology

p90 ribosomal S6 kinase 2 promotes invasion and metastasis of human head and neck squamous cell carcinoma cells

Abstract

Head and neck squamous cell carcinoma (HNSCC) is one of the most common types of human cancer and frequently metastasizes to LNs. Identifying metastasis-promoting factors is of immense clinical interest, as the prognosis for patients with even a single unilateral LN metastasis is extremely poor. Here, we report that p90 ribosomal S6 kinase 2 (RSK2) promotes human HNSCC cell invasion and metastasis. We determined that RSK2 was overexpressed and activated in highly invasive HNSCC cell lines compared with poorly invasive cell lines. Expression of RSK2 also correlated with metastatic progression in patients with HNSCC. Ectopic expression of RSK2 substantially enhanced the invasive capacity of HNSCC cells, while inhibition of RSK2 activity led to marked attenuation of invasion in vitro. Additionally, shRNA knockdown of RSK2 substantially reduced the invasive and metastatic potential of HNSCC cells in vitro and in vivo in a xenograft mouse model, respectively. Mechanistically, we determined that cAMP-responsive element-binding protein (CREB) and Hsp27 are phosphorylated and activated by RSK2 and are important for the RSK2-mediated invasive ability of HNSCC cells. Our findings suggest that RSK2 is involved in the prometastatic programming of HNSCC cells, through phosphorylation of proteins in a putative signaling network. Moreover, targeting RSK2 markedly attenuates in vitro invasion and in vivo metastasis of HNSCC cells, suggesting that RSK2 may represent a therapeutic target in the treatment of metastatic HNSCC.

Authors

Sumin Kang, Shannon Elf, Katherine Lythgoe, Taro Hitosugi, Jack Taunton, Wei Zhou, Li Xiong, Dongsheng Wang, Susan Muller, Songqing Fan, Shi-Yong Sun, Adam I. Marcus, Ting-Lei Gu, Roberto D. Polakiewicz, Zhuo (Georgia) Chen, Fadlo R. Khuri, Dong M. Shin, Jing Chen

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Figure 7

RSK2 promotes stabilization of actin filaments in HNSCC cells through phosphorylation and activation of Hsp27.

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RSK2 promotes stabilization of actin filaments in HNSCC cells through ph...
(A) RNAi-mediated knockdown of Hsp27 significantly attenuated Tu212 cell invasion conferred by exogenous expression of RSK2. Relative invasion was normalized to the invasion of control Tu212 cells (mean ± SD; **P < 0.01). (B) Stable expression of the phospho-mimetic Hsp27 S78D/S82D double mutant, but not the phospho-deficient Hsp27 S78A/S82A mutant or the Hsp27 S78D and Hsp27 S82D single mutants, led to further significantly enhanced invasion of poorly invasive Tu212 and 686LN cells, compared with Hsp27 WT. Relative invasion was normalized to the invasion of control cells harboring an empty vector (mean ± SD; *P = 0.01–0.05; **P < 0.01). (C) Stable expression of Hsp27 S78D/S82D mutant, but not WT or S78A/S82A mutant, rescued the cell invasion attenuated by stable knockdown of RSK2 in M4e cells. Relative invasion was normalized to the invasion of M4e-pLKO.1 cells (mean ± SD; *P = 0.01–0.05). (D) Actin immunofluorescent staining shows that RNAi-mediated stable knockdown of RSK2 resulted in disruption of actin filaments in 212LN and M4e cells, whereas stable expression of the Hsp27 phospho-mimetic mutant S78D/S82D, but not WT or the phospho-deficient S78A/S82A mutant, rescued the formation of actin filaments. Cells were fixed and stained with phalloidin conjugated with Alexa Fluor 555. The integrity of actin filaments was analyzed by confocal microscopy. Original magnification, ×1,000.