The Golgi stress response is a homeostatic mechanism that augments the functional capacity of the Golgi apparatus when Golgi function becomes insufficient (Golgi stress). Three response pathways of the Golgi stress response have been identified in mammalian cells, the TFE3, HSP47 and CREB3 pathways, which augment the capacity of specific Golgi functions such as N-glycosylation, anti-apoptotic activity and pro-apoptotic activity, respectively. On the contrary, glycosylation of proteoglycans (PGs) is another important function of the Golgi, although the response pathway upregulating expression of glycosylation enzymes for PGs in response to Golgi stress remains unknown. Here, we found that expression of glycosylation enzymes for PGs was induced upon insufficiency of PG glycosylation capacity in the Golgi (PG-Golgi stress), and that transcriptional induction of genes encoding glycosylation enzymes for PGs was independent of the known Golgi stress response pathways and ER stress response. Promoter analyses of genes encoding these glycosylation enzymes revealed the novel enhancer elements PGSE-A and PGSE-B (the consensus sequences are CCGGGGCGGGGCG and TTTTACAATTGGTC, respectively), which regulate their transcriptional induction upon PG-Golgi stress. From these observations, the response pathway we discovered is a novel Golgi stress response pathway, which we have named the PG pathway.
Key words: Golgi stress, proteoglycan, ER stress, organelle zone, organelle autoregulation
Ovarian cancer (OC) is one of prevalent tumors and this study aimed to explore CCL20’s effects on doxorubicin resistance of OC and related mechanisms. Doxorubicin-resistant SKOV3 DR cells were established from SKOV3 cells via 6-month continuous exposure to gradient concentrations of doxorubicin. Quantitative PCR and Western blot assay showed that SKOV3 DR cells had higher level of CCL20 than SKOV3 cells, and doxorubicin upregulated CCL20 expression in SKOV3 cells. MTT and cell count assay found that CCL20 overexpression plasmid enhanced doxorubicin resistance of SKOV3 and OVCA433 cells compared to empty vector, as shown by the increase in cell viability. In contrast, CCL20 shRNA enhanced doxorubicin sensitivity of SKOV3 DR cells compared to control. CCL20 overexpression plasmid promoted NF-kB activation and positively regulated ABCB1 expression. Besides, ABCB1 overexpression plasmid enhanced the viability of SKOV3 and OVCA433 cells compared to empty vector under treatment with the same concentration of doxorubicin, whereas ABCB1 shRNA inhibited doxorubicin resistance of SKOV3 DR cells compared to control. In conclusion, CCL20 enhanced doxorubicin resistance of OC cells by regulating ABCB1 expression.
Key words: CCL20, ovarian cancer, doxorubicin resistance, tumor-promoting, ABCB1
PUM2, an RNA binding protein, is known to promote stem cell proliferation via repressing expressions of cell cycle genes. Similar with stem cells, malignant cells are characterized by unlimited proliferation and remote migration. However, roles of PUM2 in cancer development are controversial. Here, we investigated PUM2’s role in glioblastoma development and its relationship with the cell cycle regulator BTG1. Immunoblotting and RT-qPCR were used to evaluate protein expression level and transcript level, respectively. ShRNAs were designed to knock down PUM2 and BTG1 expression. CCK-8 assay was used to evaluate cell viability. Cell migration assay and evasion assay were used to evaluate metastatic capability of glioblastoma cell. RNA pull-down assay and RNA immunoprecipitation assay were used to test the interaction between PUM2 and BTG1 3’UTR. PUM2 expression is elevated in glioblastoma tumor tissues as well as glioblastoma cell lines. PUM2 knockdown remarkably suppresses glioblastoma cell proliferation and migration. In addition, PUM2 knockdown increases BTG1 expression. RNA pull-down assay and RNA immunoprecipitation assay show PUM2 binds to BTG1 3’UTR directly. Furthermore, knockdown of BTG1 reverses the effect of PUM2 knockdown on glioblastoma cell proliferation and migration. Our results suggest that PUM2 promote glioblastoma development via repressing BTG1 expression.
Key words: PUM2, BTG1, glioblastoma, cell proliferation, metastasis