Purpose:The standard treatment for organ-confined prostate cancer (PC) is surgery or radiation, and locally advanced PC is typically treated with radiotherapy alone or in combination with androgen deprivation therapy.Here, we investigated whether Stat5a/b participates in regulation of double strand DNA break repair in PC, and whether Stat5 inhibition may provide a novel strategy to sensitize PC to radiation therapy.Experimental Design: Stat5a/b regulation of DNA repair in PC was evaluated by comet and clonogenic TRANSLATIONAL RELEVANCERadiation therapy is a key treatment option for both organ-confined and locally advanced prostate cancer (PC). However, irradiation is often associated with significant toxicities to the neighboring tissues, which can cause debilitating side-effects. In the present study, we demonstrated proof-ofconcept that targeting Stat5a/b signaling sensitizes PC to radiation through regulation of DNA repair.Our results provide, for the first time, mechanistic evidence that Jak2-Stat5a/b signaling is critical for Rad51 expression and Homologous-Recombination DNA repair in PC. Using human PC cell lines, xenograft tumors and ex vivo culture of clinical PCs, we show that genetic or pharmacological inhibition of Stat5a/b sensitizes PC to irradiation while not affecting the radiation sensitivity of the surrounding tissues. These findings provide a strong rationale for development of Stat5a/b inhibitors as adjuvant therapy for radiation treatment of PC.Research.on April 28,

The second-generation antiandrogen, enzalutamide, is approved for castrate-resistant prostate cancer (CRPC) and targets androgen receptor (AR) activity in CRPC. Despite initial clinical activity, acquired resistance to enzalutamide arises rapidly and most patients develop terminal disease. Previous work has established Stat5 as a potent inducer of prostate cancer growth. Here, we investigated the significance of Jak2-Stat5 signaling in resistance of prostate cancer to enzalutamide. The levels of Jak2 and Stat5 mRNA, proteins and activation were evaluated in prostate cancer cells, xenograft tumors, and clinical prostate cancers before and after enzalutamide therapy. Jak2 and Stat5 were suppressed by genetic knockdown using lentiviral shRNA or pharmacologic inhibitors. Responsiveness of primary and enzalutamide-resistant prostate cancer to pharmacologic inhibitors of Jak2-Stat5 signaling was assessed in vivo in mice bearing prostate cancer xenograft tumors. Patient-derived pros-tate cancers were tested for responsiveness to Stat5 blockade as second-line treatment after enzalutamide ex vivo in tumor explant cultures. Enzalutamide-liganded AR induces sustained Jak2-Stat5 phosphorylation in prostate cancer leading to the formation of a positive feed-forward loop, where activated Stat5, in turn, induces Jak2 mRNA and protein levels contributing to further Jak2 activation. Mechanistically, enzalutamide-liganded AR induced Jak2 phosphorylation through a process involving Jak2-specific phosphatases. Stat5 promoted prostate cancer growth during enzalutamide treatment. Jak2-Stat5 inhibition induced death of prostate cancer cells and patient-derived prostate cancers surviving enzalutamide treatment and blocked enzalutamide-resistant tumor growth in mice. This work introduces a novel concept of a pivotal role of hyperactivated Jak2-Stat5 signaling in enzalutamide-resistant prostate cancer, which is readily targetable by Jak2 inhibitors in clinical development.

Edited by Lukas Huber Keywords:Myc promoter-binding protein-1 Breast cancer Endoplasmic reticulum stress Alternative translation a b s t r a c t Myc promoter-binding protein-1 (MBP-1) is a shorter protein variant of the glycolytic enzyme alpha-enolase. Although several lines of evidence indicate that MBP-1 acts as a tumor suppressor, the cellular mechanisms and signaling pathways underlying MBP-1 expression still remain largely elusive. To dissect these pathways, we used the SkBr3 breast cancer cell line and non-tumorigenic HEK293T cells ectopically overexpressing alpha-enolase/MBP-1. Here, we demonstrate that induced cell stresses promote MBP-1 expression through the AKT/PERK/eIF2a signaling axis. Our results contribute to shedding light on the molecular mechanisms underlying MBP-1 expression in non-tumorigenic and cancer cells.

Cell surface expression of alpha-enolase, a glycolytic enzyme displaying moonlighting activities, has been shown to contribute to the motility and invasiveness of cancer cells through the protein nonenzymatic function of binding plasminogen and enhancing plasmin formation. Although a few recent records indicate the involvement of protein partners in the localization of alpha-enolase to the plasma membrane, the cellular mechanisms underlying surface exposure remain largely elusive. Searching for novel interactors and signalling pathways, we used low-metastatic breast cancer cells, a doxorubicinresistant counterpart and a non-tumourigenic mammary epithelial cell line. Here, we demonstrate by a combination of experimental approaches that epidermal growth factor (EGF) exposure, like lipopolysaccharide (LPS) exposure, promotes the surface expression of alpha-enolase. We also establish Heat shock protein 70 (Hsp70), a multifunctional chaperone distributed in intracellular, plasma membrane and extracellular compartments, as a novel alpha-enolase interactor and demonstrate a functional involvement of Hsp70 in the surface localization of alpha-enolase. Our results contribute to shedding light on the control of surface expression of alpha-enolase in non-tumourigenic and cancer cells and suggest novel targets to counteract the metastatic potential of tumours.An increasing number of proteins are being identified as multifunctional 1 . Most of these are enzymes, which in addition to their catalytic function are involved in fully unrelated processes, such as the glycolytic enzyme alpha-enolase, which was one of the first moonlighting proteins to be identified 2 . Multiple subcellular localizations characterize alpha-enolase, which functions as a plasminogen receptor when localized on the cell surface, and available data have demonstrated its interaction with plasminogen in prokaryotic and eukaryotic cells 3 . Mammalian tumour cells use the activation of plasminogen in plasmin to invade tissue and form metastases 4 . Recently, researchers have linked both pericellular plasminogen activation and cell surface alpha-enolase to migration and invasion in lung and pancreatic cancer, and these studies have proposed targeting cancer cells with specific anti-alpha-enolase antibodies as a promising approach to suppress tumour metastasis 5,6 . Due to the large interest in novel therapeutic strategies to counteract cancer spreading, stimuli and signalling pathways that can cooperate to induce the surface localization of alpha-enolase are attractive objects of study.Increased expression of surface alpha-enolase following LPS exposure was originally reported for the U937 macrophage cell line and human blood monocytes 7 . LPS, a component of the outer membrane of Gram-negative bacteria, exerts its biological effects by binding to Toll-like receptor 4 (TLR4), a recognition receptor of the innate immune system. Some evidence shows that functional TLR4 receptors are expressed on a variety of tumours, including breast cancer, where the silencing...