Knockdown of endoplasmic reticulum chaperone BiP leads to the death of parvocellular AVP/CRH neurons in mice

Arginine vasopressin (AVP) is expressed in both magnocellular (magnAVP) and parvocellular AVP (parvAVP) neurons of the paraventricular nucleus, and AVP colocalizes with corticotropin-releasing hormone (CRH) only in the parvocellular neurons. The immunoglobulin heavy chain binding protein (BiP) is a major endoplasmic reticulum (ER) chaperone which regulates the unfolded protein response under ER stress. We previously demonstrated that knockdown of BiP in magnAVP neurons exacerbated ER stress, which resulted in the autophagy-associated cell death of magnAVP neurons. Using the same approach, in the present study we examined the role of BiP in mouse parvAVP/CRH neurons. Our data demonstrate that BiP is expressed in mouse parvAVP/CRH neurons under nonstress conditions and is upregulated in proportion to the increase in CRH expression after adrenalectomy. For BiP knockdown in parvAVP/CRH neurons, we utilized a viral approach in combination with shRNA interference. Knockdown of BiP expression induced ER stress in parvAVP/CRH neurons, as reflected by the expression of C/EBP homologous protein. Furthermore, BiP knockdown led to the loss of parvAVP/CRH neurons after 4 weeks. In summary, our results demonstrate that BiP plays a pivotal role in parvAVP/CRH neurons, which function as neuroendocrine cells producing a large number of secretory proteins.

GRP78 secreted by tumor cells stimulates differentiation of bone marrow mesenchymal stem cells to cancer-associated fibroblasts

Cancer-associated fibroblasts (CAFs), one type of tumor-associated stromal cells, have been shown to provide a favorable environment for the malignant tumor progression. Extensive reports have demonstrated that mesenchymal stem cells (MSCs) can function as precursors for CAFs. However, the mechanisms by which tumor cells induce the transition of MSCs to CAFs have not been well established. GRP78, traditionally known as an endoplasmic reticulum (ER) chaperone, has been identified to overexpress in a variety of tumor entities and be involved in promoting survival and chemoresistance of tumor cells. Here, we interrogated the role of GRP78 in the generation of CAFs from MSCs. The results showed that GRP78 treatment induced expression of α-smooth muscle actin (α-SMA), a marker for CAFs, in human bone marrow mesenchymal stem cells (HBMSCs) as well as murine bone marrow mesenchymal stem cells (BMMSCs). This phenomenon was correlated with the stimulated phosphorylation of Smad2/3. Furthermore, the GRP78-induced α-SMA expression in HBMSCs was obviously attenuated by SB431542, a TGF-β type I receptor kinase inhibitor. Taken together, the present data suggested that tumor-derived secreted GRP78 elicited the differentiation of bone marrow-derived mesenchymal stem cells (BMSCs) to CAFs through activating TGF-β/Smad signaling pathway, which may represent a novel mechanism for transition of BMSCs to CAFs and a hitherto unknown function of GRP78 in the tumor microenvironment.