S-Nitrosylation in endothelial cells contributes to tumor cell adhesion and extravasation during breast cancer metastasis

BACKGROUND

Nitric oxide is produced by different nitric oxide synthases isoforms. NO activates two signaling pathways, one dependent on soluble guanylate cyclase and protein kinase G, and other where NO post-translationally modifies proteins through S-nitrosylation, which is the modification induced by NO in free-thiol cysteines in proteins to form S-nitrosothiols. High levels of NO have been detected in blood of breast cancer patients and increased NOS activity has been detected in invasive breast tumors compared to benign or normal breast tissue, suggesting a positive correlation between NO biosynthesis, degree of malignancy and metastasis. During metastasis, the endothelium plays a key role allowing the adhesion of tumor cells, which is the first step in the extravasation process leading to metastasis. This step shares similarities with leukocyte adhesion to the endothelium, and it is plausible that it may also share some regulatory elements. The vascular cell adhesion molecule-1 (VCAM-1) expressed on the endothelial cell surface promotes interactions between the endothelium and tumor cells, as well as leukocytes. Data show that breast tumor cells adhere to areas in the vasculature where NO production is increased, however, the mechanisms involved are unknown.

RESULTS

We report that the stimulation of endothelial cells with interleukin-8, and conditioned medium from breast tumor cells activates the S-nitrosylation pathway in the endothelium to induce leukocyte adhesion and tumor cell extravasation by a mechanism that involves an increased VCAM-1 cell surface expression in endothelial cells. We identified VCAM-1 as an S-nitrosylation target during this process. The inhibition of NO signaling and S-nitrosylation blocked the transmigration of tumor cells through endothelial monolayers. Using an in vivo model, the number of lung metastases was inhibited in the presence of the S-nitrosylation inhibitor N-acetylcysteine (NAC), which was correlated with lower levels of S-nitrosylated VCAM-1 in the metastases.

CONCLUSIONS

S-Nitrosylation in the endothelium activates pathways that enhance VCAM-1 surface localization to promote binding of leukocytes and extravasation of tumor cells leading to metastasis. NAC is positioned as an important tool that might be tested as a co-therapy against breast cancer metastasis.

206 Overexpression of germ cell genes DAZL, STRA8, and BOULE in bovine adipose tissue-derived mesenchymal stem cells for male germ cell derivation

Invitro gamete derivation from stem cells has potential applications as an alternative method for dissemination of elite animal genetics, production of transgenic animals, and conservation of endangered species. Mesenchymal stem cells (MSC) may be suitable candidates for invitro gamete derivation given their differentiation capacity and their potential for cell therapy. DAZL (deleted in azoospermia-like) and BOULE (also called BOLL) encode RNA-binding proteins that control differentiation of germ cells; STRA8 (stimulated by RA-8) encodes a protein required for meiosis. Considering the crucial roles of these factors, the aim of the present study was to evaluate co-overexpression of different combinations of DAZL, STRA8, and BOULE on germ cell gene expression profile in adipose tissue-derived MSC (AT-MSC). AT-MSC were harvested from abattoir-derived male bovine fetuses (n=9; 7-8 months of gestation). The optimal concentration of Lipofectamine 2000 (1, 1.5, 2, 1.5ng µL−1; Invitrogen) was analysed in AT-MSC transfected with plasmid pSIN-EF2-Puro containing DAZL, STRA8, and BOULE coding sequences (pSIN-EF2-DAZL-P2A-STRA8-T2A-BOULE-Puro). Then, AT-MSC were transfected either with plasmids containing DAZL, STRA8, and BOULE genes (pSIN-EF2-DAZL-P2A-STRA8-T2A-BOULE-Puro), DAZL and BOULE genes (pSIN-EF2-DAZL-P2A-STRA8-T2A-Puro), DAZL (pSIN-EF2-DAZL-P2A-T2A-Puro), or empty plasmid at a concentration of 1ng µL−1 of Lipofectamine. Cell samples were obtained from each plasmid treatment and analysed for expression of housekeeping genes ACTB and GAPDH and germ cell genes DAZL, PIWIl2, STRA8, and BOULE by quantitative-PCR using relative values (Quantity) through the ΔΔCT formula. AT-MSC transfected with pSIN-EF2-DAZL-P2A-STRA8-T2A-BOULE-Puro using 1ng µL−1 of Lipofectamine achieved higher (P<0.05) expression of DAZL (13.3-fold) compared with cells transfected with empty vector. Moreover, AT-MSC transfected with pSIN-EF2-DAZL-P2A-STRA8-T2A-BOULE-Puro had higher (P<0.05) levels of DAZL mRNA (3.8-fold) compared with empty vector. Messenger RNA levels of STRA8 (1.4-fold) were only detected in AT-MSC transfected with pSIN-EF2-DAZL-P2A-STRA8-T2A-Puro; PIWIl2 and BOULE were not detected in transfected or untransfected AT-MSC. In conclusion, bovine fetal AT-MSC are amenable for overexpression of germ cell markers DAZL and STRA8. Transfection with plasmid containing three germ cell genes (DAZL, STRA8, and BOULE) allowed overexpression of DAZL, whereas transfection with plasmid containing two germ cell genes (DAZL and STRA8) achieved overexpression of STRA8. This study was supported by Fondecyt grant 1191114, Government of Chile.