Heat shock protein 90-α (Hsp90α) is an intracellular molecular chaperone. However, it can also be secreted with the underlying regulatory mechanism remaining far from clear. Here we show that the secreted Hsp90α is a C-terminal truncated form and its secretion is regulated by the C-terminal EEVD motif via interacting with proteins containing tetratricopeptide repeat domains. We also demonstrate that secretion of Hsp90α is determined by the phosphorylation status at residue Thr-90, regulated by protein kinase A and protein phosphatase 5. We further demonstrate that the secretion of Hsp90α is a prerequisite for its proinvasiveness function and blocking the secreted Hsp90α results in significant inhibition of tumor metastasis. Meanwhile, the level of plasma Hsp90α is positively correlated with tumor malignancy in clinical cancer patients. In sum, our results reveal the regulatory mechanism of Hsp90α secretion, and its function in tumor invasiveness, indicating it can be a promising diagnostic marker for tumor malignancy in clinical application.

Heat shock protein 90α (Hsp90α) is a ubiquitously expressed molecular chaperone that is essential for eukaryotic homeostasis. Hsp90α can also be secreted extracellularly, where it has been shown to be involved in tumor metastasis. Extracellular Hsp90α interacts with and promotes the proteolytic activity of matrix metalloproteinase-2 (MMP-2). However, the regulatory mechanism of Hsp90α on MMP-2 activity is still unknown. Here we show that Hsp90α stabilizes MMP-2 and protects it from degradation in tumor cells. Further investigation reveals that this stabilization effect is isoform-specific, ATP-independent, and mediated by the interaction between the Hsp90α middle domain and the MMP-2 C-terminal hemopexin domain. Moreover, this mechanism also applies to endothelial cells that secrete more Hsp90α in their proliferating status. Furthermore, endothelial cell transmigration, Matrigel plug, and tumor angiogenesis assays demonstrate that extracellular Hsp90α promotes angiogenesis in an MMP-2-dependent manner. In sum, this study provides new insights into the molecular mechanism of how Hsp90α regulates its extracellular client proteins and also reveals for the first time the function of extracellular Hsp90α in promoting tumor angiogenesis.

More sensitive biomarker is urgently needed to reduce the mortality caused by the worldwide prevalent liver cancer. This study aims to assess whether quantitative measurement of heat shock protein 90alpha (Hsp90α) in plasma can improve the diagnosis accuracy and monitor treatment response of liver cancer patients. We analyzed the data from an official (registered at ClinicalTrial.gov: NCT02324127), large-scale (1647 enrollments), and multicenter (three independent hospitals) clinical trial, which quantitatively measured plasma Hsp90α by ELISA for patients with liver cancer, patients with at-risk liver diseases (including hepatitis, liver cirrhosis, focal nodular hyperplasia), and healthy individuals. Diagnostic performance of plasma Hsp90α was evaluated by the calculated sensitivity, specificity, and area under the receiver operating characteristic curve (AUC). ROC curve showed plasma Hsp90α can discriminating liver cancer with a sensitivity of 92.7% and specificity of 91.3% from non-liver cancer control. Similar results were noted in detecting early-stage liver cancer (sensitivity 91.4%, specificity 91.3%). In a parallel study compared with AFP20, plasma Hsp90α exhibited a significantly higher diagnostic performance (sensitivity 93.3% vs 61.1%) in discriminating hepatocellular carcinoma (HCC) from the control. Furthermore, plasma Hsp90α measurement maintained distinctly excellent diagnostic accuracy in distinguishing AFP-negative HCC patients (sensitivity 93.9%, specificity 91.3%) and AFP-limited liver cancer (sensitivity 96.6%, specificity 90.3%). In the efficacy monitoring study, levels of plasma Hsp90α were dramatically decreased after surgery (P=0.005), and correlated significantly with tumor size during interventional therapy (P≤0.05). These findings highlight that plasma Hsp90α as a biomarker for the diagnosis of liver cancer, and can be used to evaluate the therapeutic efficacy of liver cancer patients underwent surgery, or interventional therapy.

Rab GTPases control exocytic and endocytic membrane trafficking such as exosomes release. As a secretory small GTPase, Rab3D is a vital regulator for protein secretion. However, the role of Rab3D in cancer was never systematically studied. The aim of this study is to examine its function and mechanism in cancer, especially metastasis. We detected protein levels of Rab3D in nine cancer cell lines and twelve types of clinical cancer specimens. Subsequently, we established in vitro migration and in vivo orthotopic metastatic mouse models to study the role of Rab3D in tumor metastasis. Here, we reported that the expression levels of Rab3D were dysregulated in cancer cells and highly correlated with tumor malignancies in the clinical samples. Increased expressions of Rab3D led to tumor invasion in vitro and lung metastasis in vivo, whereas Rab3D knockdown suppressed the tumor cell motility. Mechanistic studies revealed that Rab3D activated intracellular the AKT/GSK3β signaling to induce the EMT process. In addition, it also regulated the extracellular secretion of Hsp90α to promote tumor cell migration and invasion. These results prove that Rab3D is a key molecule to regulate tumor metastasis, suggesting that blocking the Rab3D function can be a potential therapeutic approach for cancer metastasis.

Background: Pancreatic cancer is one of the most malignant cancers. The overall 5-year survival rate of its patients is 8%, the lowest among major cancer types. It is very urgent to study the development mechanisms of this cancer and provide potential targets for therapeutics design. Glucose, one of the most essential nutrients, is highly exploited for aerobic glycolysis in tumor cells to provide building blocks. However, the glucose consumption manner in pancreatic cancer cells is unclear. And the mechanism of the substantial metabolic pathway promoting pancreatic cancer development is also unrevealed. Methods: ¹³C₆ glucose was used to trace the glucose carbon flux and detected by mass spectrum. The expressions of PHGDH were determined in cells and pancreatic adenocarcinomas. Knockdown and overexpression were performed to investigate the roles of PHGDH on pancreatic cancer cell proliferation, colony formation and tumor growth. The mechanisms of PHGDH promoting pancreatic cancer development were studied by identifying the interacting proteins and detecting the regulatory functions on translation initiations. Results: Pancreatic cancer cells PANC-1 consumed large amounts of glucose in the serine and glycine de novo synthesis. Phosphoglycerate dehydrogenase (PHGDH) highly expressed and controlled this pathway. Knockdown of PHGDH significantly attenuated the tumor growth and prolonged the survival of tumor bearing mice. The pancreatic adenocarcinoma patients with low PHGDH expression had better overall survival. Mechanistically, knockdown of PHGDH inhibited cell proliferation and tumorigenesis through disrupting the cell-cell tight junctions and the related proteins expression. Besides catalyzing serine synthesis to activate AKT pathway, PHGDH was found to interact with the translation initiation factors eIF4A1 and eIF4E and facilitated the assembly of the complex eIF4F on 5’ mRNA structure to promote the relevant proteins expression. Conclusion: Besides catalyzing serine synthesis, PHGDH promotes pancreatic cancer development through enhancing the translation initiations by interacting with eIF4A1 and eIF4E. Inhibiting the interactions of PHGDH/eIF4A1 and PHGDH/eIF4E will provide potential targets for anti-tumor therapeutics development.