Cooperative interaction between protein inhibitor of activated signal transducer and activator of transcription‐3 with epidermal growth factor receptor blockade in lung cancer

Abstract

Epidermal Growth Factor Receptor (EGFR) targeting in nonsmall cell lung cancer (NSCLC) is an established treatment modality; however, it only benefits a minority of patients. STAT3 (signal transducer and activator of transcription-3) plays an important role in the oncogenic signal transduction pathway of NSCLC. Inhibition of STAT3 results in NSCLC growth inhibition and apoptosis. We have previously shown that combined inhibition of EGFR and STAT3 by small molecules resulted in improved therapeutic efficacy as compared with blocking EGFR alone. However, the STAT3 protein has a number of endogenous negative regulators including PIAS3 (Protein Inhibitor of Activated STAT3). In this study, we investigated for the first time the role of PIAS3 in modulating oncogenic EGFR-STAT3 signaling pathway in lung cancer and the anti-proliferative effect of using PIAS3 in conjunction with EGFR blockade in NSCLC. We demonstrate that PIAS3 is expressed in variable degrees in all NSCLC cells. EGF and IL-6 stimulation resulted in the association of PIAS3 with STAT3. The PIAS3/STAT3 complex then bound the STAT3 DNA binding sequence resulting in STAT3 regulated gene expression. Overexpression of PIAS3, using a PIAS3 expression construct, decreases STAT3 transcriptional activity. Furthermore, overexpression of PIAS3 consistently decreased proliferation. EGFR blockade and PIAS3 over-expression in combination had significantly greater anti-proliferative effects as compared with either EGFR blockade or PIAS3 over-expression alone. In conclusion, PIAS3 is expressed in NSCLC cell lines and its over-expression decreased STAT3 transcriptional activity, decreased proliferation of NSCLC cells and when used in conjunction with EGFR inhibitors, increased the anti-proliferative effects. ' 2009 UICC

Identification of STAT3-independent regulatory effects for protein inhibitor of activated STAT3 by binding to novel transcription factors

“…7 This transcriptional repressive activity of STAT3 is thought to be the mechanism by which PIAS3 overexpression leads to growth inhibition in multiple lung cancer cell lines. 16 However other functions for PIAS3 have been recently described. For example, PIAS3 interacts with p65 subunit of NFκB induced by TNFα or IL-1 21 and to MITF resulting in its decreased transcriptional activity.…”

“…15 PIAS3 decreases lung cancer growth and increases the anti-tumor effects of EGFR inhibitors. 16 It is, however, unknown if PIAS3 works uniquely by interacting with STAT3 or other mechanisms of action exist.…”

“…Wnt-mediated signaling has been identified as a critical signaling pathway in non-small cell lung cancer. 32 As several cancers have demonstrated decrease or loss of PIAS3 expression, 13,14,16 restoration of PIAS3 may be a mechanism where one could achieve therapeutic cancer growth control. Our data convincingly shows that in addition to STAT3 mediated effects PIAS3 has a vast STAT3-independent effect by binding to a are important signaling molecules involved in multiple cellular processes such as cell cycle control, proliferation and differentiation.…”

Low PIAS3 Expression in Malignant Mesothelioma Is Associated with Increased STAT3 Activation and Poor Patient Survival

“…PIAS3 was initially found to interact specifically with phosphorylated STAT3, and not STAT1, in IL6-activated murine myeloblast M1 cells and to decrease STAT3 DNAbinding capacity and transcriptional activity (9). We (10,11) and others (12) have demonstrated that overexpression of PIAS3 can inhibit STAT3 transcriptional activity and promote growth inhibition in vitro. If PIAS3 counteracts transactivation by STAT3, it would be conceivable that PIAS3 expression could be decreased in malignant tissues with high STAT3 activation.…”

“…3A), a representative NSCLC cell line (10,11,14,15). Because PIAS3 is thought to be an endogenous inhibitor of STAT3 activity, we examined whether any decreased PIAS3 expression in mesothelioma cells was accompanied by increased p-STAT3 expression.…”