Upregulation of Eps8 in oral squamous cell carcinoma promotes cell migration and invasion through integrin-dependent Rac1 activation

Abstract

Oral squamous cell carcinoma (OSCC) is a lethal disease and early death usually occurs as a result of local invasion and regional lymph node metastases. Current treatment regimens are, to a certain degree, inadequate, with a 5-year mortality rate of around 50% and novel therapeutic targets are urgently required. Using expression microarrays, we identified the eps8 gene as being overexpressed in OSCC cell lines relative to normal oral keratinocytes, and confirmed these findings using RT-PCR and western blotting. In human tissues, we found that Eps8 was upregulated in OSCC (32% of primary tumors) compared with normal oral mucosa, and that expression correlated significantly with lymph node metastasis (P ¼ 0.032), suggesting a diseasepromoting effect. Using OSCC cell lines, we assessed the functional role of Eps8 in tumor cells. Although suppression of Eps8 produced no effect on cell proliferation, both cell spreading and migration were markedly inhibited. The latter cell functions may be modulated through the small GTP-ase, Rac1 and we used pull-down assays to investigate the role of Eps8 in Rac1 signaling. We found that avb6-and a5b1-integrin-dependent activation of Rac1 was mediated through Eps8. Knockdown of either Eps8 or Rac1, inhibited integrindependent cell migration similarly and transient expression of constitutively active Rac1 restored migration of cells in which Eps8 expression had been suppressed. We also showed that knockdown of Eps8 inhibited tumor cell invasion in an organotypic model of OSCC. These data suggest that Eps8 and Rac1 are part of an integrated signaling pathway modulating integrin-dependent tumour cell motility and identify Eps8 as a possible therapeutic target.

The interplay between Eps8 and IRSp53 contributes to Src-mediated transformation

“…Unlike the involvement of Eps8 in cytoskeletal reorganization is gradually disclosed, the implication of Eps8 in tumorigenesis is well established. Elevated expression of Eps8 was observed in v-Src transformed (IV5) cells (Gallo et al, 1997;Maa et al, 1999), and in a variety of human tumors including colorectal (Maa et al, 2007), cervical (Chen et al, 2008), pituitary (Xu et al, 2009) and oral cancers (Yap et al, 2009). Overexpression of Eps8 conferred the ability of fibroblasts to form focus in culture dish and grow tumor in mice (Maa et al, 2001), corroborating the oncogenic potential of Eps8.…”

High expression of integrin β6 in association with the Rho–Rac pathway identifies a poor prognostic subgroup within HER2 amplified breast cancers

“…The role of Rho–Rac pathway in integrin‐mediated cell adhesion and migration has also been well studied. Integrins have been shown to promote actin assembly by recruiting molecules like Rac3 that activate actin polymerization and RhoA that increase contractility and transmit tension to the sites of integrin ligation leading to increased migratory potential 31, 32, 33. Also, integrin‐mediated production of matrix metalloproteases has been shown to aid tumor cells in degrading the basement matrix leading to invasion 9.…”

EPS8, an Adaptor Protein Acts as an Oncoprotein in Human Cancer

“…Not surprisingly, Eps8 was upregulated in a subset of OSCCs where it correlated significantly with lymph node metastasis. Knockdown of Eps8 suppressed V6-, and 51-integrin-dependent Rac1 activation and inhibited tumor cell invasion in an organotypic model of OSCC [67].…”