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Cancers 2014, 6(4), 2012-2034; doi:10.3390/cancers6042012

Monoclonal Antibodies Specific for STAT3β Reveal Its Contribution to Constitutive STAT3 Phosphorylation in Breast Cancer

1
Section of Infectious Disease, Department of Medicine, Baylor College of Medicine, Houston, TX 77030, USA
2
Department of Molecular & Cellular Biology, Baylor College of Medicine, Houston, TX 77030, USA
3
Department of Pathology & Immunology, Baylor College of Medicine, Houston, TX 77030, USA
4
Department of Biochemistry & Molecular Biology, BCM 286, Room N-1319, Baylor College of Medicine, Houston, TX 77030, USA
*
Author to whom correspondence should be addressed.
Received: 20 June 2014 / Revised: 15 September 2014 / Accepted: 17 September 2014 / Published: 29 September 2014
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Abstract

Since its discovery in mice and humans 19 years ago, the contribution of alternatively spliced Stat3, Stat3β, to the overall functions of Stat3 has been controversial. Tyrosine-phosphorylated (p) Stat3β homodimers are more stable, bind DNA more avidly, are less susceptible to dephosphorylation, and exhibit distinct intracellular dynamics, most notably markedly prolonged nuclear retention, compared to pStat3α homodimers. Overexpression of one or the other isoform in cell lines demonstrated that Stat3β acted as a dominant-negative of Stat3α in transformation assays; however, studies with mouse strains deficient in one or the other isoform indicated distinct contributions of Stat3 isoforms to inflammation. Current immunological reagents cannot differentiate Stat3β proteins derived from alternative splicing vs. proteolytic cleavage of Stat3α. We developed monoclonal antibodies that recognize the 7 C-terminal amino acids unique to Stat3β (CT7) and do not cross-react with Stat3α. Immunoblotting studies revealed that levels of Stat3β protein, but not Stat3α, in breast cancer cell lines positively correlated with overall pStat3 levels, suggesting that Stat3β may contribute to constitutive Stat3 activation in this tumor system. The ability to unambiguously discriminate splice alternative Stat3β from proteolytic Stat3β and Stat3α will provide new insights into the contribution of Stat3β vs. Stat3α to oncogenesis, as well as other biological and pathological processes. View Full-Text
Keywords: Stat3β; Stat3 beta; isoform; alternative RNA splicing; CT7; phosphorylation; monoclonal; oncogenesis; breast cancer; regulation Stat3β; Stat3 beta; isoform; alternative RNA splicing; CT7; phosphorylation; monoclonal; oncogenesis; breast cancer; regulation
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MDPI and ACS Style

Bharadwaj, U.; Kasembeli, M.M.; Eckols, T.K.; Kolosov, M.; Lang, P.; Christensen, K.; Edwards, D.P.; Tweardy, D.J. Monoclonal Antibodies Specific for STAT3β Reveal Its Contribution to Constitutive STAT3 Phosphorylation in Breast Cancer. Cancers 2014, 6, 2012-2034.

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