Epidermal Growth Factor Receptor Pathway Substrate 8 Is Overexpressed in Human Pituitary Tumors: Role in Proliferation and Survival

Abstract

Based on prior work showing that human pituitary tumors overexpress epidermal and fibroblast growth factor receptors, we hypothesized that downstream components of growth factor signaling pathways may also be dysregulated. Epidermal growth factor pathway substrate number 8 (Eps8) was identified as a transcript overexpressed (5.9-fold) in human pituitary tumors compared with normal pituitary by DNA microarrays. Eps8 mRNA up-regulation was confirmed by semiquantitative RT-PCR. Immunoblot analysis showed that Eps8 protein levels and its downstream target phosphorylated ERK were also up-regulated in human pituitary tumors. Stable overexpression of Eps8 in LbetaT2 gonadotrope pituitary cells augmented colony formation in soft agar at d 21. Eps8 cells proliferated more robustly compared with controls in growth factor replete as well as growth-restricted conditions. In addition, the Eps8 overexpressing cells were protected from serum withdrawal-induced apoptosis compared with controls as assessed by caspase-3 cleavage. Epidermal growth factor activated a robust amplification of ERK and modest up-regulation of Akt in Eps8-overexpressing pituitary cells compared with vector controls. MAPK kinase inhibition or silencing of Eps8 blunted the proliferation of the cells in response to growth factor stimulation. Blockade of the phosphatidylinositol 3-kinase pathway or silencing of Eps8 resulted in a loss of the Eps8 protection from growth factor withdrawal-induced apoptosis. Together these data support a role of Eps8 in amplifying growth factor receptor signaling in human pituitary tumors to promote proliferation and cell survival.

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

“…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. In agreement, Eps8 attenua tion retarded cellular growth in IV5 cells (Leu et al, 2004) and human cancer cells (Maa et al, 2007;Chen et al, 2008;Xu et al, 2009). Remarkably, Eps8 is also a prognostic factor for cervical cancer.…”

“…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.…”

Pituitary tumors contain a side population with tumor stem cell-associated characteristics

“…It is also notable that the EGFR pathway substrate 8 (EPS8) was also overexpressed in the pSP in the present study (four of the five adenomas, P!0.05; Supplementary Table S8). This oncoprotein has previously been found to be upregulated in multiple pituitary tumor subtypes, where it mediates survival, proliferation, and tumorigenicity (Xu et al 2009a). Moreover, the accompanying EGFR was also found to be upregulated and has been shown to be involved in tumor cell migration in some cancers (Hölsken et al 2011).…”

The transcription factors STAT5A/B regulate GM-CSF–mediated granulopoiesis

“…Among these genes was the gene for the antiapoptotic protein Bcl-X (Bcl2l1), which had been proposed as a STAT5A/B target. 45 Epidermal growth factor pathway substrate number 8 (Eps8) had been linked to cell proliferation and survival 46 and enhances epidermal growth factor-dependent mitogenic signals. NIMArelated expressed kinase 6 (Nek6) and other NEK family members contribute to the orchestration of mitotic progression and protect cells from chromosome instability.…”