Inhibition of IL‐6‐JAK/Stat3 signaling in castration‐resistant prostate cancer cells enhances the NK cell‐mediated cytotoxicity via alteration of PD‐L1/NKG2D ligand levels

• Published in: Molecular oncology 2018-03, Vol.12 (3), p.269-286
• Main Authors: Xu, LiJun, Chen, XiaoDong, Shen, MingJing, Yang, Dong‐Rong, Fang, Laifu, Weng, Guobin, Tsai, Ying, Keng, Peter C., Chen, Yuhchyau, Lee, Soo Ok
• Format: Article
• Language: English
• Subjects: Androgens; Animals; Antigens; Apoptosis; Aprotinin; B7-H1 Antigen - genetics; B7-H1 Antigen - metabolism; Castration; castration‐resistant prostate cancer; Cell culture; Cell Line, Tumor; Cytotoxicity; Cytotoxicity, Immunologic; Dehydrogenases; Disease susceptibility; Ethylenediaminetetraacetic acid; GPI-Linked Proteins - genetics; GPI-Linked Proteins - metabolism; Heterografts; Humans; IL‐6; Immunotherapy; Intercellular Signaling Peptides and Proteins - genetics; Intercellular Signaling Peptides and Proteins - metabolism; Interleukin-6 - antagonists & inhibitors; Interleukin-6 - genetics; Interleukin-6 - metabolism; Ipilimumab; JAK; Janus Kinases - antagonists & inhibitors; Janus Kinases - genetics; Janus Kinases - metabolism; Killer cells; Killer Cells, Natural - immunology; Kinases; Ligands; Male; Medical prognosis; Metastasis; Mice; Mice, Nude; Mutation; Natural killer cells; NK cell cytotoxicity; NKG2 antigen; NKG2D; PD-L1 protein; Plasmids; Primary Cell Culture; programmed death receptor ligand 1; Prostate cancer; Prostatic Neoplasms, Castration-Resistant - immunology; Prostatic Neoplasms, Castration-Resistant - therapy; Proteins; Signal transduction; Stat3; Stat3 protein; STAT3 Transcription Factor - antagonists & inhibitors; Tumors
• ISSN: 1574-7891; 1878-0261
• DOI: 10.1002/1878-0261.12135

To investigate whether IL‐6 signaling affects the susceptibility of castration‐resistant prostate cancer (CRPC) cells to cytotoxic action of natural killer (NK) cells, CRPC cell lines (having different IL‐6 levels) were developed by lentiviral transduction. While observing no secreted IL‐6 level in parental C4‐2 and CWR22Rv1 cells, we found the IL‐6 expression/secretion in these cells was induced after the transduction process and the IL‐6 level difference in C4‐2siIL‐6/sc and CWR22siIL‐6/sc cell CRPC cell sets could be detected. We then found that IL‐6‐knockdown cells were more susceptible to NK cell cytotoxicity than control cells due to lowered programmed death receptor ligand 1 (PD‐L1) and increased NK group 2D (NKG2D) ligand levels. In animal studies, to concur with the in vitro results, we found that IL‐6‐expressing cell‐derived tumors were more resistant to NK cell action than the tumors of IL‐6‐knockdown cells. Further, we discovered that JAK‐Stat3 is the most critical IL‐6 downstream signaling that modulates PD‐L1/NKG2D ligand levels in CRPC cells. Furthermore, inhibition of the JAK or Stat3 signaling effectively increased the susceptibility of C4‐2sc and CWRsc cells to NK cell cytotoxicity. We observed the most effective cytotoxicity when the PD‐L1 Ab and JAK inhibitor (or Stat 3 inhibitor) were used together. These results suggest that the strategy of targeting IL‐6 signaling (or its downstream signaling) may enhance the NK cell‐mediated immune action to CRPC tumors, thus yielding clinical implications in developing future immunotherapeutics of exploiting this strategy to treat patients with CRPC. IL‐6 signaling, through downstream JAK/Stat3 signaling, plays a significant role in rendering castration‐resistant prostate cancer (CRPC) cells resistant to NK cell cytotoxicity by lowering the programmed death receptor ligand 1 level while increasing the NK group 2D ligand levels. Thus, inhibition of JAK or Stat3 signaling effectively increases the susceptibility of IL‐6‐expressing CRPC cells to NK cell cytotoxicity.