Efficient killing of SW480 colon carcinoma cells by a signal transducer and activator of transcription (STAT) 3 hairpin decoy oligodeoxynucleotide – interference with interferon‐γ‐STAT1‐mediated killing

Abstract

The signal transducers and activators of transcription (STATs) convey signals from the membrane to the nucleus in response to cytokines or growth factors. STAT3 is activated in response to cytokines involved mostly in cell proliferation; STAT1 is activated by cytokines, including interferon‐γ, involved in defence against pathogens and the inhibition of cell proliferation. STAT3, which is frequently activated in tumour cells, is a valuable target with respect to achieving inhibition of tumour cell proliferation. Indeed, its inhibition results in cell death. We previously observed that inhibition of the transcription factor nuclear factor‐κB, a key regulator of cell proliferation, with decoy oligodeoxynucleotides results in cell death. We used a similar approach for STAT3. A hairpin STAT3 oligodeoxynucleotide was added to a colon carcinoma cell line in which it induced cell death as efficiently as the STAT3 inhibitor stattic. The hairpin STAT3 oligodeoxynucleotide co‐localized with STAT3 within the cytoplasm, prevented STAT3 localization to the nucleus, blocked a cyclin D1 reporter promoter and associated with STAT3 in pull‐down assays. However, the same cells were efficiently killed by interferon‐γ. This effect was counteracted by the STAT3 oligodeoxynucleotide, which was found to efficiently inhibit STAT1. Thus, although it can inhibit STAT3, the hairpin STAT3 oligodeoxynucleotide appears also to inhibit STAT1‐mediated interferon‐γ cell killing, highlighting the need to optimize STAT3‐targeting oligodeoxynucleotides.

Blockage of Glyoxalase I Inhibits Colorectal Tumorigenesis and Tumor Growth via Upregulation of STAT1, p53, and Bax and Downregulation of c-Myc and Bcl-2

“…The STAT1 protein, composed of 750 amino acids with a size of 91 kDa, has been classified as a tumor suppressor [31,32,33,34,35,36]. STAT1 is involved in defense against pathogens and inhibition of cell proliferation [37]. Recent studies have reported that a stimulus such as ischemia, heat, DNA damage, or oxysterol is required for STAT1 to promote apoptosis [33].…”

A STAT3-decoy oligonucleotide induces cell death in a human colorectal carcinoma cell line by blocking nuclear transfer of STAT3 and STAT3-bound NF-κB

“…Some STAT3 inhibitors are not specific, such as curcumin [15]. In contrast, Stattic, which prevents STAT3 dimerization by specifically interacting with its SH2 domain [16], is highly specific, and efficiently induces tumor cell death [16,17]. Despite its frequent involvement in cancer, which makes it a highly valuable target for inducing tumor cell death, STAT3 still lacks more specific inhibitors.…”

“…They can induce, in vitro , the death of tumor cells whose growth depends on these TFs [19]. This has notably been shown for several TFs, including NF-κB [20,21] and STAT3 [17,22-24]. STAT3-decoy ODN efficiently induced cell death in mouse xenografts of a head and neck squamous cell carcinoma [25].…”

“…For example, in the colon carcinoma cell line SW 480, the constitutive activation of STAT3 contributes to cell survival; its inhibition by STAT3-decoy ODN induces cell death. However, the ODN also blocks IFNγ-mediated cell death through STAT1 activation in the same cell line [17]. The actual mechanism through which decoy ODNs inhibit TFs is still unclear.…”

“…Another study showed that a decoy ODN engineered to contain a nuclear localization signal (NLS) could enter the nucleus and efficiently inhibit p53 [30]. It is not clear yet whether these requirements depend on cellular systems or on the TFs that are targeted, since other studies have found that decoy ODNs did not have to enter the nucleus to exert their inhibitory effect [17,21]. In order to assess their possible use in human cancer, it will be important to understand the mechanism through which the decoy ODNs interfere with TFs and to determine whether nucleo-cytoplasmic shuttling is impaired.…”