Abstract 5120: SPA-1 regulates breast cancer cell adhesion and invasion via interating with integrinβ1 and FAK pathway.
Authors: Su Li , Zhang Yilei 
Published: August 2014

Background: Breast cancer is one of the most frequently diagnosed cancer but with highest mortality rate in females worldwidely because of metastasis. SPA-1 was first identified as an important kind of RapGAPs, which could negative regulate Rap1 activity and play aggregrating roles in cancer invasion and progression such as in human CaP. However, the exact mechanism of SPA-1 regulating cancer metastasis remains elusive. Here we dissected systematically the effect of SPA-1 on breast cancer cell invasion and metastasis as well as the underlying related pathways.

Methods: RT-PCR, western blot and immunohistochemistry were used to detect the SPA-1 expression in tissues and cell lines.The association of SPA-1 expression with clinical features of studied breast cancer patients diagnosed with IDC was analyzed by χ2 test. The function of SPA-1 in MDA-MB-231 cells was assessed by generated stable SPA-1 knockdown cell line using shRNA approach. Morphological change of cells was visualized by confocal microscope after staining with F-actin antibody. Cell adhesion assay, scratch assay and Transwell assay were used to analyze the effect of SPA-1 on cell adhesion, migration and invasion. To study the regulation of MMP9 expression and secretion by SPA-1, we used RT-PCR, western blot, zymography and Elisa assay. To determine whether Rap1 was involved in SPA-1 mediated MMP9 expression, secretion and cellular invasion, Ral-GDS pull down assay was used to monitor the active Rap1.

Results: SPA-1 expression level in tumor tissues is associated with tumor grade(P&lt;0.05). Knockdown of SPA-1 expression reverses invasive phenotype of MDA-MB-231 cells including less invadopodia and focal adhesion formation. In addition, inhibition of SPA-1 expression also suppressed cell adhesion to ECM and ECs as well as cell migration and invasion in vitro. Furthermore, MMP9 expression and secretion, which are required for SPA-1 dependent cellular invasion, dramatically decrease upon SPA-1 down-regulation. Increased phosphorelation of FAK and aberrant FAK/AKT/MMP9 signaling pathway were verified as SPA-1 mediated cell invasion, which is Rap1 independent. In fact, integrin β1 and FAK could be baited out to interact with SPA-1. Importantly, we found parallel expression of SPA-1 and MMP9 in fresh breast cancer tissues.

Conclusions: We have identified that SPA-1 was required for the maintenance of invasive phenotype of breast cancer cells. Besides, SPA-1 can promote breast cancer cell adhesion as well as invasion through FAK/AKT/MMP9 signaling, which is independent of Rap1. Taken together, SPA-1 has a pivotal role in breast cancer cell invasion and progression, which could be a potential therapeutic target for breast cancer metastasis.

Citation Format: Li Su, Yilei Zhang. SPA-1 regulates breast cancer cell adhesion and invasion via interating with integrinβ1 and FAK pathway. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 5120. doi:10.1158/1538-7445.AM2013-5120

Note: This abstract was not presented at the AACR Annual Meeting 2013 because the presenter was unable to attend.