eng Science and Education Publishing American Journal of Medical and Biological Research 2328-4099 2024-12-13 12 2 81 84 10.12691/ajmbr-12-2-7 AJMBR20241227 article Ali Saleh Alharth alharth_a@yahoo.com 1 Musaad Abdullah Alsuliman 2 Waleed Ahmed Alyami 2 Abobaker Alshamarni 2 Zyad M Alsulaiman 3 Abdulaziz M Alsulaiman 4 Regional Laboratory, Ministry of Health, Najran, Saudi Arabia General Health Affairs, Ministry of Health, Riyadh, Saudi Arabia Prince Sultan Military Medical City, Riyadh, Saudi Arabia Almaarefa University, Riyadh, Saudi Arabia Breast cancer is the most diagnosed cancer among women worldwide. Tenascin-C (TNC) is a high glycoprotein which has been shown to be over-expressed in the breast cancer stroma and promotes cancer progression. Thrombospondin 1 (TSP-1) is an adhesive which has been shown to play roles in platelet aggregation, , and . The aim of this study was to investigate the effects of TNC knockdown in TSP-1 expression in highly invasive breast cancer cell lines. Small interfering RNA (siRNA) targeting total TNC and high molecular TNC isoforms (TNC-14 and TNC-14-AD1) were transfected into the highly invasive MDA-MB-231 breast cancer cell line. The alterations caused by TNC knockdown on TSP-1 were analysed at protein level by Western blot using conditioned media. The expression of TSP-1 was significantly up-regulated as a result of TNC down-regulation. In conclusion, TNC knockdown significantly increases TSP-1 expression, confirming their importance in tumorigenesis. https://pubs.sciepub.com/ajmbr/12/2/7/ajmbr-12-2-7.pdf TNC TSP-1 siRNA knockdown