A novel activating role of SRC and STAT3 on HGF transcription in human breast cancer cells

Michelle R Sam,Christopher R Mueller,Bruce E Elliott

doi:10.1186/1476-4598-6-69

Abstract

We have previously determined that the HGF promoter can be transactivated by a combination of activated Src and wild-type Stat3 in the mouse breast cell lines HC11 and SP1. To determine if this pathway is of relevance for the human disease, a series of human breast and other human cells lines were examined, and the status of key proteins in these cells determined. All of the human breast cell lines exhibited strong transactivation by a combination of activated Src and Stat3. This activation was dependent on a Stat3 recognition element present at nt-95. The exception was the ErbB2 over-expressing cell line SK-BR-3 where Stat3 alone could transactivate HGF though Src augmented this effect. Increased phosphorylation of Stat3 tyrosine 705 was also observed in this line. Analysis of three ovarian cell lines revealed that Src/Stat3 expression was not able to activate the HGF promoter in two of these lines (SKOV3 and IOSE-80PC). Src/Stat3 expression did activate HGF transcription in OVCAR3 cells, but this effect was not mediated by the Stat3 site at nt-95. Stat3 phosphorylation at tyrosine 705 was observed in IOSE-80PC cells, but was insufficient to allow for activation of the HGF promoter. Human kidney (HEK293) and cervical carcinoma (HeLa) cells were also not Src/Stat3 permissive, despite high levels of Stat3 phospho-Y705. These results suggest that human breast cells are a uniquely permissive environment for HGF transactivation by Src/Stat3 which may allow for the inappropriate activation of HGF transcription during the early stages of breast transformation. This could lead to paracrine or autocrine activation of the Met receptor in breast carcinoma cells.

Highlights

Hepatocyte Growth Factor (HGF) is a multi-functional cytokine primarily expressed in mesenchymal cells
We have previously shown that activated Src/Signal Transducer and Activator of Transcription 3 (Stat3) co-operativity enhances HGF transcriptional activity and protein expression, and induces HGFdependent scattering in mammary epithelial cells [18,19]
The ability of both Src and Stat3 to activate the HGF promoter was assessed by co-transfection of a mouse HGF proximal promoter construct into a variety of Src responsive mouse and human epithelial cell lines

Summary

Introduction

Hepatocyte Growth Factor (HGF) is a multi-functional cytokine primarily expressed in mesenchymal cells. Molecular Cancer 2007, 6:69 http://www.molecular-cancer.com/content/6/1/69 other human cancers [11,12] Both activated Src and Stat mediate signals downstream of the HGF/Met pathway [13,14], and are key regulators of tumourigenic growth and survival [15,16]. We have characterized a Src/Stat responsive region on the HGF promoter identifying a Stat consensus binding site at nt-95 that has been demonstrated to be required for HGF promoter activation by Src/Stat in mouse mammary carcinoma cells [18] Overall, these observations suggest a model where positive feedback signals in the HGF/Met Src/Stat axis contribute to the transformation process

Methods

Results

Conclusion