C/EBP-homologous protein (CHOP) is an important component of the endoplasmic reticulum (ER) stress response. We demonstrated the induction of ER stress in response to tunicamycin stimulation, as evidenced by increased expression of chaperone proteins Grp78, Grp94, and enhanced eukaryotic initiation factor 2 subunit 1 (eIF2α) phosphorylation in hepatocellular carcinoma cells. Tunicamycin-induced ER stress resulted in apoptosis and autophagy simultaneously. While inhibition of autophagy mediated by 3-methyladenine pretreatment or direct knockdown of LC3B promoted cell apoptosis, activation of autophagy with rapamycin decreased tunicamycin- induced apoptosis in HCC cells. Furthermore, CHOP was shown to be significantly upregulated upon treatment with tunicamycin in HCC cells. Specific knockdown of CHOP not only enhanced tunicamycin-induced autophagy, but also significantly attenuated ER stress-induced apoptosis in HCC cells. Accordingly, simultaneous inhibition of autophagy in HCC cells with CHOP-knockdown could partially resensitize ER stress-induced apoptosis. Taken together, our data indicate that CHOP may favor ER stress-induced apoptosis in HCC cells via inhibition of autophagy in vitro.

Breast cancer remains the most frequently diagnosed cancer and the leading cause of cancer death in women, both worldwide and in less developed countries. Surgery in conjunction with adjuvant chemotherapy is the main treatment of choice for patients with locally advanced breast cancer, leading to reduce cancer-related symptoms and prolong survival. Paclitaxel as a critical drug in the treatment of breast cancer patients, intrinsic and acquired resistance to paclitaxel represents a significant clinical problem. We had previously demonstrated that increased expression of erbB3 is required for erbB2-mediated paclitaxel resistance in breast cancer cells via PI-3K/Akt/mTOR signaling pathway-dependent upregulation of Survivin. Mesenchymal stem cells (MSCs) are emerging as an important component of tumor microenvironment, which may play an essential role in regulating cancer cell growth, motility, invasion and therapeutic resistance. In the present study, we have explored the possible role of MSCs in regulating the chemo-sensitivity of erbB2-overexpressing breast cancer cells. We show that both human umbilical cord and bone marrow-derived MSCs express significantly higher level of Neuregulin-1 (NRG-1, also Heregulin-β1) as compared with erbB2-overexpressing breast cancer cells themselves. Coculture or treatment with conditioned medium of MSCs not only decreases the anti-proliferation effect of paclitaxel on erbB2-overexpressing breast cancer cells, but also significantly inhibits paclitaxel-induced apoptosis. We further demonstrate that this MSCs-drived paclitaxel-resistance in erbB2-overexpressing breast cancer cells could be attributed to paracrine effect of NRG-1/erbB3 signaling, as specific nutralizaion of NRG-1 or blocking of erbB3 resensitizes erbB2-overexpressing breast cancer cells to paclitaxel treatment. Moreover, overexpression of erbB3 enhances, while knockdown expression of erbB3 abrogates MSCs-drived paclitaxel-resistance. Taken together, our current data indicate that paracrine of NRG-1 by MSCs induce resistance of paclitaxel in erbB2-overexpressing breast cancer cells through activation of erbB3 signaling. Our findings suggest that simultaneously targeting mesenchymal stem cells in tumor microenviroment may be a novel strategy to overcome chemotherapeutic resistance. Citation Format: Ling Zhu, Jin Wang, Weimin Zuo, Rong Lin, Tingting Lin, Yan Lei, Bingshuang Ren, Jun Lu, Huiyue Dong, Lingjing Lin, Lianghu Huang, Qinghua Wang, Yujie Ma, Hui Lyu, Bolin Liu, Jianming Tan, Shuiliang Wang. Mesenchymal stem cells drive paclitaxel-resistance in erbB2-overexpressing breast cancer cells via paracrine of NRG-1. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 4091.