Heat-shock protein 90 (Hsp90) is a molecular chaperone that plays a key role in the conformational maturation of various transcription factors and protein kinases in signal transduction. Multifunctional ribosomal protein S3 (rpS3), a component of the ribosomal small subunit, is involved in DNA repair and apoptosis. Our data show that Hsp90 binds directly to rpS3 and the functional consequence of Hsp90-rpS3 interaction results in the prevention of the ubiquitination and the proteasome-dependent degradation of rpS3, subsequently retaining the function and the biogenesis of the ribosome. Interference of Hsp90 activity by Hsp90 inhibitors appears to dissociate rpS3 from Hsp90, associate the protein with Hsp70, and induce the degradation of free forms of rpS3. Furthermore, ribosomal protein S6 (rpS6) also interacted with Hsp90 and exhibited a similar effect upon treatment with Hsp90 inhibitors. Therefore, we conclude that Hsp90 regulates the function of ribosomes by maintaining the stability of 40S ribosomal proteins such as rpS3 and rpS6.

Most Hepatocellular carcinoma (HCC) are resistant to conventional chemotherapeutic agents and remain an unmet medical need. Recently, multiple studies on the crosstalk between HCC and their tumor microenvironment have been conducted to overcome chemoresistance in HCC. In this study, we formed multicellular tumor spheroids (MCTS) to elucidate the mechanisms of environment-mediated chemoresistance in HCC. We observed that hepatic stellate cells (HSCs) in MCTS significantly increased the compactness of spheroids and exhibited strong resistance to sorafenib and cisplatin relative to other types of stromal cells. Increased collagen 1A1 (COL1A1) expression was apparent in activated HSCs but not in fibroblasts or vascular endothelial cells in MCTS. Additionally, COL1A1 deficiency, which was increased by co-culture with HSCs, decreased the cell-cell interactions and thereby increased the therapeutic efficacy of anticancer therapies in MCTS. Furthermore, losartan, which can inhibit collagen I synthesis, attenuated the compactness of spheroids and increased the therapeutic efficacy of anticancer therapies in MCTS. Meanwhile, activated HSCs facilitated HCC migration by upregulating matrix metallopeptidase 9 (MMP9) in MCTS. Collectively, crosstalk between HCC cells and HSCs promoted HCC chemoresistance and migration by increasing the expression of COL1A1 and MMP9 in MCTS. Hence, targeting HSCs might represent a promising therapeutic strategy for liver cancer therapy.

UV irradiation has been reported to induce p21^WAF1/CIP1 protein degradation through a ubiquitin-proteasome pathway, but the underlying biochemical mechanism remains to be elucidated. Here, we show that ser-114 phosphorylation of p21 protein by glycogen synthase kinase 3β (GSK-3β) is required for its degradation in response to UV irradiation and that GSK-3β activation is a downstream event in the ATR signaling pathway triggered by UV. UV transiently increased GSK-3β activity, and this increase could be blocked by caffeine or by ATR small interfering RNA, indicating ATR-dependent activation of GSK-3β. ser-114, located within the putative GSK-3β target sequence, was phosphorylated by GSK-3β upon UV exposure. The nonphosphorylatable S114A mutant of p21 was protected from UV-induced destabilization. Degradation of p21 protein by UV irradiation was independent of p53 status and prevented by proteasome inhibitors. In contrast to the previous report, the proteasomal degradation of p21 appeared to be ubiquitination independent. These data show that GSK-3β is activated by UV irradiation through the ATR signaling pathway and phosphorylates p21 at ser-114 for its degradation by the proteasome. To our knowledge, this is the first demonstration of GSK-3β as the missing link between UV-induced ATR activation and p21 degradation.

Background: Breast cancer is one of the leading causes of women's death worldwide. It is important to discover a reliable biomarker for the detection of breast cancer. Plasma is the most ideal source for cancer biomarker discovery since many cells cross-communicate through the secretion of soluble proteins into blood. Methods: Plasma proteomes obtained from 6 breast cancer patients and 6 normal healthy women were analyzed by using the isotope-coded affinity tag (ICAT) labeling approach and tandem mass spectrometry. All the plasma samples used were depleted of highly abundant 6 plasma proteins by immune-affinity column chromatography before ICAT labeling. Several proteins showing differential abundance level were selected based on literature searches and their specificity to the commercially available antibodies, and then verified by immunoblot assays. Results: A total of 155 proteins were identified and quantified by ICAT method. Among them, 33 proteins showed abundance changes by more than 1.5-fold between the plasmas of breast cancer patients and healthy women. We chose 5 proteins for the follow-up confirmation in the individual plasma samples using immunoblot assay. Four proteins, α1-acid glycoprotein 2, monocyte differentiation antigen CD14, biotinidase (BTD), and glutathione peroxidase 3, showed similar abundance ratio to ICAT result. Using a blind set of plasmas obtained from 21 breast cancer patients and 21 normal healthy controls, we confirmed that BTD was significantly down-regulated in breast cancer plasma (Wilcoxon rank-sum test, p = 0.002). BTD levels were lowered in all cancer grades (I-IV) except cancer grade zero. The area under the receiver operating characteristic curve of BTD was 0.78. Estrogen receptor status (p = 0.940) and progesterone receptor status (p = 0.440) were not associated with the plasma BTD levels. Conclusions: Our study suggests that BTD is a potential serological biomarker for the detection of breast cancer.