TROP2 promotes the proliferation of triple-negative breast cancer cells via calcium ion-dependent ER stress signaling pathway

Objective: To explore the molecular mechanisms of tumor-associated calcium signal transduction factor 2 (TROP2) affecting the occurrence and development of triple-negative breast cancer (TNBC). Methods: The TCGA database, immunohistochemical staining, and qRT-PCR were used to analyze the expression of TROP2 in TNBC tissues and cells. The protein expressions of TROP2 and inositol 1,4,5-trisphosphate receptor (IP3R) after TROP2 knockdown were detected by western blot (WB). Cell proliferation was detected by CCK8 and colony formation assay, Annexin V-APC/PI flow cytometry was used to detect apoptosis, and intracellular calcium ion (Ca2+) was detected by flow cytometry with Fura 2-AM fluorescent probe. Finally, the morphological changes of the endoplasmic reticulum (ER) were observed by transmission electron microscopy, and the expression of ER stress (ERS)-related proteins was detected by WB and immunofluorescence staining. Results: TROP2 was up-regulated in TNBC tumor tissues and cells. Silencing TROP2 decreased the proliferation rate and clone formation number, and increased the apoptosis rate and the Ca2+ level in TNBC cells. These phenomena were reversed after the addition of 2-APB. In addition, after TROP2 knockdown, the expressions of IP3R and ERS-related proteins were up-regulated, the ER was cystic dilated, and ERS was activated. And the addition of 2-APB significantly inhibited the activation of ERS induced by TROP2 knockdown. Conclusion: TROP2 regulated the proliferation and apoptosis of TNBC cells through a Ca2+-dependent ERS signaling pathway.