Protein inhibitor of activated STAT3 expression in lung cancer

Abstract

Protein Inhibitor of Activated Signal Transducer and Activators of Transcription 3 (PIAS3) is an endogenous inhibitor of STAT3 transcriptional activity. We have previously demonstrated the concentration-dependent negative regulatory effect of PIAS3 on STAT3 signaling and its capacity to decrease lung cancer proliferation and synergize with epidermal growth factor inhibition. We now investigate PIAS3 expression in both non-small cell lung cancer (NSCLC) cell lines and human resected NSCLC specimens. We also investigated the mechanism by which some lung cancers have significantly decreased PIAS3 expression. Expression of PIAS3 is variable in lung cancer cells lines with 2 of 3 squamous cell carcinoma (SCC) cell lines having no or little PIAS3 protein expression. Similarly, the majority of human SCCs of the lung lack PIAS3 expression by immunohistochemistry; this despite the finding that SCCs have significantly higher levels of PIAS3 mRNA compared to adenocarcinomas. High PIAS3 expression generally correlates with decreased phosphorylated STAT3 in both SCC cell lines and human specimens compatible with the negative regulatory effect of this protein on STAT3 signaling. To investigate this variable expression of PIAS3 we first performed sequencing of the PIAS3 gene that demonstrated single nucleotide polymorphisms but no mutations. Exposure of lung cancer cells to 5-azacytidine and trichostatin A results in a significant increase in PIAS3 mRNA and protein expression. However, methylation-specific PCR demonstrates a lack of CpG island methylation in the promoter region of PIAS3. Exposure of cells to an agent blocking proteosomal degradation results in a significant increase in PIAS3. Our data thus shows that SCC of the lung commonly lacks PIAS3 protein expression and that post-translational modifications may explain this finding in some cases. PIAS3 is a potential therapeutic molecule to target STAT3 pathway in lung cancer.

STAT3 inhibition, a novel approach to enhancing targeted therapy in human cancers

“…These include suppressors of cytokine signalling (SOCS) family proteins which are transcriptionally regulated by activated STAT and form a negative feedback loop to suppress STAT signal by binding to or inhibiting JAKs or by targeting bound proteins to the proteasome degradation pathway. Other negative regulators include: protein inhibitor of activated STAT (PIAS), various tyrosine phosphatises (SHP1, SHP2, CD45), phosphatase and tensin homolog (PTEN), GRIM-19 (gene associated with retinoid IFN induced mortality-19) as well as the ubiquitin-proteasome degradation pathway involved in negative regulation of STAT signalling (71)(72)(73)(74)(75)(76)(77)(78)(79)(80)(81). Recently, neurofibromatosis 2 (NF2) tumour suppressor, schwannomin was also demonstrated to inhibit STAT3 phosphorylation (82).…”

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

“…We have also identified a lack of PIAS3 protein expression in the majority of human squamous cell carcinomas of the lung. 14 We have recently demonstrated that PIAS3 binds to STAT3 within minutes of ligand-induced activation and phosphorylation of tyrosine 705 of STAT3, and that PIAS3 negatively regulates STAT3 transcriptional activity in a concentration dependent manner. 15 In addition, we have identified a novel mechanism by which PIAS3 may effect STAT3 signaling, by decreasing STAT3 phosphorylation.…”

Approaching non-canonical STAT3 signaling to redefine cancer therapeutic strategy

“…PIAS expression was reported to be downregulated while reciprocal increase in STAT3 activation and cell proliferation was observed in glioblastoma [37] Another study in lung squamous cell carcinomas also observed an inverse correlation between PIAS and pSTAT3 expression levels [38]. In case of breast cancer miRNA-21 was reported to inhibit PIAS expression and enhances STAT3 oncogenic signaling [39].…”