CDK8 is a transcription-regulating kinase that controls TGF-β/BMP-responsive SMAD transcriptional activation and turnover through YAP1 recruitment. However, how the CDK8/YAP1 pathway influences SMAD1 response in cancer remains unclear. Here we report that SMAD1-driven epithelial-to-mesenchymal transition (EMT) is critically dependent on matrix rigidity and YAP1 in a wide spectrum of cancer models. We find that both genetic and pharmacological inhibition of CDK8 and its homologous twin kinase CDK19 leads to abrogation of BMP-induced EMT. Notably, selectively blocking CDK8/19 specifically abrogates tumor cell invasion, changes in EMT-associated transcription factors, E-cadherin expression and YAP nuclear localization both in vitro and in vivo in a murine syngeneic EMT model. Furthermore, RNA-seq meta-analysis reveals a direct correlation between CDK8 and EMT-associated transcription factors in patients. Our findings demonstrate that CDK8, an emerging therapeutic target, coordinates growth factor and mechanical cues during EMT and invasion.

Anoikis, a cell death mechanism triggered upon cell-matrix detachment, is regarded as a physiological suppressor of metastasis that can be regulated by a diverse array of signals. The protein encoded by GDF2 is BMP9 and is a member of the bone morphogenetic protein family and the transforming growth factor (TGF) β superfamily with emerging yet controversial roles in carcinogenesis. In an attempt to identify the function of growth and differentiation factor 2 (GDF2) in epithelial systems, we examined the signaling machinery that is involved and cell fate decisions in response to GDF2 in ovarian and breast epithelia. We find that GDF2 can robustly activate the SMAD1/5 signaling axis by increasing complex formation between the type I receptor serine threonine kinases activin receptor-like kinase (ALK) 3 and ALK6 and the type II receptor serine threonine kinase BMPRII. This activation is independent of cross talk with the SMAD2-transforming growth factor β pathway. By activating SMAD1/5, epithelial cells regulate anchorage-independent growth by increasing anoikis sensitivity that is dependent on GDF2’s ability to sustain the activation of SMAD1/5 via ALK3 and ALK6. Consistent with a role for GDF2 in promoting anoikis susceptibility, the analysis of cell lines and patient data suggests epigenetic silencing of GDF2 in cancer cell lines and increased promoter methylation in patients. These findings collectively indicate an antimetastatic role for GDF2 in ovarian and breast cancer. The work also implicates loss of GDF2 via promoter methylation-mediated downregulation in promotion of carcinogenesis with significant relevance for the use of epigenetic drugs currently in clinical trials.

Resistance to anchorage independent cell death (anoikis) is one of the features of metastasis and can be regulated by a diverse array of growth factors. The protein encoded by GDF2 is BMP9 and is a member of the Bone Morphogenetic protein family and the TGFβ superfamily with defined roles in angiogenesis and emerging yet controversial roles in carcinogenesis. We used normal and oncogenic epithelial systems to examine the role of GDF2 in ovarian and breast epithelia. We find that both normal and transformed epithelial cells are competent to activate the Smad1/5 signaling cascade in response to GDF2. This activation occurs via specific complex formation between the Type I receptor Serine threonine kinases Alk3 and Alk6 and the Type II receptor serine threonine kinase BMPRII. We find that in breast and ovarian epithelial cells GDF2 specifically regulates anchorage independent growth by increasing anoikis sensitivity that is dependent on GDF2's ability to sustain SMAD1/5 activation via Alk3 and Alk6. Analysis of cell lines and patient data indicates epigenetic regulation of GDF2 expression in ovarian and breast cancers. These findings reveal an antimetastatic role for GDF2 in ovarian and breast cancer models of disease with significant implications for the use of epigenetic drugs currently in clinical trials. Citation Format: Archana Varadaraj, Pratik Patel, Anne Serrao, Tirthankar Bandyopadhyay, Nam Y. Lee, Amir Jazaeri, Susan Murphy, Karthikeyan Mythreye. GDF2 promotes anoikis susceptibility in ovarian and breast epithelia. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 3912. doi:10.1158/1538-7445.AM2015-3912