Anti-SHARPIN (aa 25-75) polyclonal antibody

Proteins belonging to the linear ubiquitin assembly complex (LUBAC) are believed to be important in tumorigenesis. LUBAC has been demonstrated to be composed of RBCK1, RNF31 and SHARPIN. The aim of this study was to explore all members of the LUBAC complex as novel biomarkers in breast cancer. We have already reported that RNF31 mRNA levels are higher in breast cancer samples compared to adjacent non-tumor tissue. In this study we extend these findings by demonstrating that the mRNA levels of RBCK1 and SHARPIN are also higher in tumors compared to adjacent non-tumor tissue in the same cross sectional study of samples (p < 0.001). In addition, up-regulated mRNA expression of all three members of the LUBAC complex displayed high predictive value in distinguishing tumor tissues from adjacent non-tumor tissue as determined by ROC curve analysis. Furthermore, we investigated whether there is an association between the mRNA and protein expression levels of RBCK1, RNF31 and SHARPIN and clinicopathological parameters including estrogen receptor (ER), progesterone receptor (PR) and human epidermal growth factor receptor (HER2) status and found that RNF31 protein is significantly higher in ERalpha-negative tumors than ERalpha-positive tumors (p = 0.034). Collectively, our findings indicate that up-regulated mRNA expression of RNF31, RBCK1 and SHARPIN could potentially be diagnostic biomarkers of breast cancer and RNF31 might be a drug target for ERalpha-negative breast cancers.

Linear ubiquitination, a newly discovered posttranslational modification, is catalyzed by the linear ubiquitin chain assembly complex (LUBAC), which is composed of three subunits: one catalytic subunit HOIP and two accessory molecules, HOIL-1L and SHARPIN. Accumulating evidence suggests that linear ubiquitination plays a crucial role in innate immune signaling and especially in the activation of the NF-kappa B pathway by conjugating linear polyubiquitin chains to NF-kappa B essential modulator (NEMO, also called IKK gamma), the regulatory subunit of the IKK complex. Porcine reproductive and respiratory syndrome virus (PRRSV), an Arterivirus that has devastated the swine industry worldwide, is an ideal model to study the host's disordered inflammatory responses after viral infection. Here, we found that LUBAC-induced NF-kappa B and proinflammatory cytokine expression can be inhibited in the early phase of PRRSV infection. Screening the PRRSV-encoded proteins showed that nonstructural protein 1 alpha (nsp1 alpha) suppresses LUBAC-mediated NF-kappa B activation and its CTE domain is required for the inhibition. Mechanistically, nsp1 alpha binds to HOIP/HOIL-1L and impairs the interaction between HOIP and SHARPIN, thus reducing the LUBAC-dependent linear ubiquitination of NEMO. Moreover, PRRSV infection also blocks LUBAC complex formation and NEMO linear-ubiquitination, the important step for transducing NF-kappa B signaling. This unexpected finding demonstrates a previously unrecognized role of PRRSV nsp1 alpha in modulating LUBAC signaling and explains an additional mechanism of immune modulation by PRRSV. IMPORTANCE Porcine reproductive and respiratory syndrome (PRRS) is one of the most important veterinary infectious diseases in countries with intensive swine industries. PRRS virus (PRRSV) infection usually suppresses proinflammatory cytokine expression in the early stage of infection, whereas it induces an inflammatory storm in the late stage. However, precisely how the virus is capable of doing so remains obscure. In this study, we found that by blocking the interaction of its catalytic subunit HOIP and accessory molecule SHARPIN, PRRSV can suppress NF-kappa B signal transduction in the early stage of infection. Our findings not only reveal a novel mechanism evolved by PRRSV to regulate inflammatory responses but also highlight the important role of linear ubiquitination modification during virus infection.