Stat3 Phosphorylation And Bcl-2 Expression As A Predictive Signature For Stratifying Clinical Lymphomas

Overexpression of Bcl-2 presents a major therapeutic challenge in the management of hematopoietic and other malignancies. By conventional dogma Bcl-2 blocks drug-induced apoptosis by inhibiting mitochondrial permeabilization and downstream death amplification. Recently we demonstrated a novel mechanism of death inhibition by Bcl-2 via inducing an increase in mitochondrial oxygen consumption and superoxide production. Interestingly, transfection of cells with a dominant negative mutant of Rac1 or its knockdown sensitized Bcl-2 expressing cells to apoptosis. Furthermore, using a human cancer cell lines and tissue biopsies from patients with a variety of lymphomas revealed that Rac1 was localized at the mitochondria and interacted with Bcl-2. Intrigued by these data from clinical lymphomas we set out to investigate the downstream effector pathways involved in Bcl-2-Rac-1 interaction-mediated survival signaling. We took two independent approaches to address this. Firstly, we employed a computer simulation driven predictive experimental strategy based on the protein pathway dynamic network of cancer physiology created by Cellworks Group Inc. An HCT116 human colorectal cancer cell line with KRAS over-activation, PI3K overexpression, CDKN2A deletion, β-catenin overexpression and Bcl-2 overexpression was created as a baseline. Phenotypic indices of cell proliferation, viability, metastasis, and angiogenesis were amplified in a variant cell line when Rac1 was overexpressed based on the above computer modeled HCT116. Of note, the expression level of the cell proliferation inducer/transcription factor STAT3 and β-catenin were significantly upregulated in the variant cell line; however knockdown of either Bcl-2 or Rac1 in both the base and the variant cell lines resulted in a significant increase in protein involved in apoptosis signaling. Based on these pharmacodynamic computer simulation driven predictions, we set out to verify the correlation between STAT3 signaling (its phosphorylation at Y705 and S727) and Bcl-2-Rac1 interaction. Indeed, we obtain evidence for a cause-en effect relationship between Rac1 activation, Bcl-2 phosphorylation at S70 and the activation of STAT3. More importantly, using primary cells from patients with a variety of lymphomas, we analyzed the activation of STAT3 and Bcl-2 expression and asked if a correlation existed in malignant lymphomas. Interestingly, based on a small number of clinical samples, there appears to be tight correlation between the phosphorylation status of STAT3 and the expression of Bcl-2 in a specific sub-group of B cell lymphomas. These data provide strong translational relevance for a novel predictive signature for stratifying lymphomas with potential clinical implications and validate the use of computer modeling to predict clinical outcomes. Citation Format: Jia Kang, Vignette Z. Q. Ooi, Shireen Vali, Shweta Kapoor, Ansu Kumar, Taher Abbasi, Shazib Pervaiz. STAT3 phosphorylation and Bcl-2 expression as a predictive signature for stratifying clinical lymphomas. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 5577. doi:10.1158/1538-7445.AM2013-5577 Note: This abstract was not presented at the AACR Annual Meeting 2013 because the presenter was unable to attend.