Earlier studies revealed an interaction between HSP and

Earlier studies revealed an interaction between HSP90β and ACK1 [15]. In the proteomic approach, we show that ACK1 associates with HSP90α and HSP90β. Additionally, we confirm the existence of a HSP90-ACK1 complex with co-IP experiments. We further analysed whether an inhibition of HSP90 affected the expression of ACK1 and the activation of STATs. We reveal that the HSP90i AT13387 diminishes ACK1 phosphorylation and its expression after 24h. Apparently, inhibiting HSP90 leads to a disruption of the ACK1-STAT1 and ACK1-STAT3 signalling nodes due to a dephosphorylation and destabilization of ACK1. Consistent with these data, the HSP90i Geldanamycin abolished the phosphorylation of constitutively active ACK1 in the prostatic adenocarcinoma cell line LNCaP after 8h [15]. In this experiment, the levels of ACK1 were not significantly lowered [15], which is likely due to the shorter incubation time with the HSP90i. Notably, Geldanamycin treatment can strongly attenuate ACK1-driven LNCaP cell tumourigenesis in vivo[15] and epigenetic drugs of the histone deacetylase inhibitor family induce a caspase-dependent cleavage of ACK1 and a loss of p-STAT3 in leukemic 4 68 synthesis [22]. Moreover, as ACK1 is able to promote tumour growth by regulating tumour suppressors (WWOX) and pro-survival factors (AKT) [15], [36], [37], ACK1 interacting partners and the regulation of STAT signalling by ACK1 appear as promising targets for cancer drug development. Such strategies might be appreciated in light of the fact that recent data illustrate an overexpression of ACK1 and its association with a worse patient outcome, e.g., in pancreatic cancer [30], hepatocellular carcinoma [38], stomach cancer [39], colon cancer [40] and breast cancer [41]. AT13387, which is currently the most potent inhibitor of the N-terminal ATP site of HSP90, is active against lung cancer cells in vitro and in vivo[42]. The reduction of the ACK1-STAT3 signalling axis by this agent may serve as a novel pharmacodynamic marker for HSP90 inhibition. In addition, others found that inhibition of HSP90 attenuates the phosphorylation of STAT3 in autosomal dominant polycystic kidney disease [43]. This finding supports our results, which may have broader implications.
Conclusions The following are the supplementary data related to this article.
Conflict of interest disclosure
Acknowledgements The Wilhelm Sander-Stiftung (#2010.078 to O.H.K) supported the major part of this work. The laboratory of O.H.K is additionally supported by the Deutsche Forschungsgemeinschaft (#KR2291/4-1, KR2291/5-1 and KR2291/7-1 to O.H.K), the Deutsche Krebshilfe (#110909 and 110125 to O.H.K; German Cancer Aid) and intramural funding (University Medical Center Mainz and Naturwissenschaftlich-medizinisches Forschungszentrum Mainz, NMFZ). This work was further supported by the Austrian Science Fund (FWF-P 26011 and FWF-P 29251-B28 to L.K.) and the European Training Network (MSCA-ITN-2015-ETN ALKATRAS No 675712 to L.K.). We thank Elisabeth Gurnhofer for excellent technical assistance.
Introduction Osteosarcoma, as the most frequent malignant primary bone tumor in adolescents, is the leading cause of cancer-related death with the age of 15–19 years [1]. Despite recent improvements in the diagnosis and treatment of osteosarcoma enhanced patient outcomes, the distant metastasis and local relapse also provides high risk for osteosarcoma patients [2], [3]. Recent studies revealed gene therapy could be a rational and promising strategy for patients with various cancers including osteosarcoma. Thus, the identification of the underlying molecular mechanisms of osteosarcoma and novel diagnostic and prognostic biomarkers are critical for osteosarcoma treatment. The human Ack (Activated Cdc42-associated kinase) protein is encoded by the TNK2 gene and is called Ack1 (hAck1). Overexpressed Ack1 has been reported in various human cancers including prostate, gastric, and pancreatic cancers [4], [5], [6]. Recent studies showed that Ack1 is implicated in cell metastasis of cancers. For example, Lei et al. showed the important role of overexpressed Ack1 on the metastasis and poor prognosis of hepatocellular carcinoma [7]. Overexpressed Ack1 also reported to increase the invasive phenotype of breast cancer cells [4]. However, the expression and mechanism of Ack1 involves in osteosarcoma progression remains unclear.