Prognostic impact of activin subunit inhibin beta A in gastric and esophageal adenocarcinomas

PURPOSE

Adenocarcinomas of the esophagus (AEG) and stomach (AS) are among the most common cancers worldwide. Novel markers for risk stratification and guiding treatment are strongly needed. Activin is a multi-functional cytokine with context specific pro- and anti-tumorigenic effects. We aimed to investigate the prognostic role of activin tumor protein expression in AEG/ASs.

METHODS

Tissue from a retrospective cohort of 277 patients with AEG/AS treated primarily by surgery at the Charité - Universitätsmedizin Berlin was collected and analyzed by immunohistochemistry using a specific antibody to the activin homodimer inhibin beta A. Additionally, we evaluated T-cell infiltration and PD1 expression as well as expression of PD-L1 by immunohistochemistry as possible confounding factors. Clinico-pathologic data were collected and correlated with activin protein expression.

RESULTS

Out of 277 tumor samples, 72 (26.0%) exhibited high activin subunit inhibin beta A protein expression. Higher expression was correlated with lower Union for International Cancer Control (UICC) stage and longer overall survival. Interestingly, activin subunit expression correlated with CD4+ T-cell infiltration, and the correlation with higher overall survival was exclusively seen in tumors with high CD4+ T-cell infiltration, pointing towards a role of activin in the tumor immune response in AEG/ASs.

CONCLUSION

In our cohort of AEG/AS, higher activin subunit levels were correlated with longer overall survival, an effect exclusively seen in tumors with high CD4+ cell infiltration. Further mechanistic research is warranted discerning the exact effect of this context specific cytokine.

Increased stiffness of the tumor microenvironment in colon cancer stimulates cancer associated fibroblast-mediated prometastatic activin A signaling

Colorectal cancer (CRC) is the second deadliest cancer in the US due to its propensity to metastasize. Stromal cells and especially cancer-associated fibroblasts (CAF) play a critical biophysical role in cancer progression, but the precise pro-metastatic mechanisms are not clear. Activin A, a TGF-β family member, is a strong pro-metastatic cytokine in the context of CRC. Here, we assessed the link between biophysical forces and pro-metastatic signaling by testing the hypothesis that CAF-generated mechanical forces lead to activin A release and associated downstream effects. Consistent with our hypothesis, we first determined that stromal activin A secretion increased with increasing substrate stiffness. Then we found that stromally-secreted activin A induced ligand-dependent CRC epithelial cell migration and epithelial to mesenchymal transition (EMT). In addition, serum activin A levels are significantly increased in metastatic (stage IV) CRC patients (1.558 ng/ml versus 0.4179 ng/ml, p < 0.05). We propose that increased tumor microenvironment stiffness leads to stromal cell-mediated TGF-β family signaling relying on the induction and utilization of activin A signaling.

Abstract 177: Increased stiffness of the tumor microenvironment in colon cancer leads to an increase in activin and metastatic potential

Colorectal cancer (CRC) is the second deadliest cancer in the US and understanding the switch to metastatic behavior and developing therapeutic strategies to target this process are clinical challenges. Stromal cells and cancer associated fibroblasts (CAF) play a critical biophysical role in cancer progression. CAFs are contractile and mechanosensitive which remodel the tumor microenvironment (TME) by cross linking, deforming and stiffening the matrix and release growth factors, which offers a unique niche for the cancer cells to become metastatic. We hypothesize that CAF-generated mechanical forces lead to metastatic spread directly or indirectly via release of growth factors including a member of the TGFb superfamily, namely activin. We will explore the mechanistic link between fibroblast force, activin release, and the induction of EMT and compare it with the activin serum levels of a CRC patient cohort. We measured activin serum levels by ELISA assay from a retrospective cohort of twenty-eight colorectal cases and twenty-eight polyp free controls. Conditioned media from co-culture of human CRC epithelial cells (FET) and stromal cells (CCD18) was examined by ELISA assay for secreted activin and was also used to culture CRC FET cells to measure induction of metastatic behavior through increase in proteins involved in epithelial-to-mesenchymal transition (EMT). CCD18 were seeded on substrates with increasing stiffness (2kPa, 10kPa, 40kPa) and treated for 72 hours with or without TGFb to generate conditioned media. FET cells were incubated with this media and subjected to trans-well migration and metabolic activity assays.Activin levels were up regulated in serum from stage IV CRC patients. High activin levels may be a predictive marker for metastasis in this cohort, with an Area Under the Curve of 0.8163. CCD18 cells secreted a 10-fold higher level of activin than FET cells alone and co-culture of CCD18 and FET cells resulted in an additional 2-fold increase in activin. Treatment of conditional media from TGFb activated stromal cells with the activin ligand trap, follistatin, leads to a decrease in FET cell migration and reversal of EMT indicating that the activin increase is functionally relevant and critical to the pro-oncogenic stromal response by TGFb. We plated CCD18 cells 2, 10 and 40 kPa polyacrylamide (PA) substrates functionalized by fibronectin with and without TGFb. We found that, with increasing gel substrate stiffness, (a) FET became more migratory, (b) CCD18 contractility increased with increasing stiffness, (c) activin in the condition media increased with increasing force. Inhibiting activin with follistatin decreased the TGFb induced activin secretion and migration in FETs. We suggest that increased TME stiffness leads to stromal cells amplification of TGFb pro-oncogenic function through thus far unrecognized induction and utilization of activin signaling.

Citation Format: Jessica Bauer, Jonas J. Staudacher, Georgina Mancinelli, Nancy Krett, Emon Bashar, Paul Grippo, M Taher A. Saif, Barbara Jung. Increased stiffness of the tumor microenvironment in colon cancer leads to an increase in activin and metastatic potential [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 177.

NFkB is essential for activin-induced colorectal cancer migration via upregulation of PI3K-MDM2 pathway

Colorectal cancer (CRC) remains a common and deadly cancer due to metastatic disease. Activin and TGFB (TGFβ) signaling are growth suppressive pathways that exert non-canonical pro-metastatic effects late in CRC carcinogenesis. We have recently shown that activin downregulates p21 via ubiquitination and degradation associated with enhanced cellular migration independent of SMADs. To investigate the mechanism of metastatic activin signaling, we examined activated NFkB signaling and activin ligand expression in CRC patient samples and found a strong correlation. We hypothesize that activation of the E3 ubiquitin ligase MDM2 by NFkB leads to p21 degradation in response to activin treatment. To dissect the link between activin and pro-carcinogenic NFkB signaling and downstream targets, we found that activin but not TGFB induced activation of NFkB leading to increased MDM2 ubiquitin ligase via PI3K. Further, overexpression of wild type p65 NFkB increased MDM2 expression while the NFkB inhibitors NEMO-binding domain (NBD) and Bay11-7082 blocked the activin-induced increase in MDM2. In conclusion, in colon cancer cell migration, activin utilizes NFkB to induce MDM2 activity leading to the degradation of p21 in a PI3K dependent mechanism. This provides new mechanistic knowledge linking activin and NFkB signaling in advanced colon cancer which is applicable to targeted therapeutic interventions.

Increased Frequency of KRAS Mutations in African Americans Compared with Caucasians in Sporadic Colorectal Cancer

Objectives:

The basis for over-representation of colorectal cancer (CRC) in African-American (AA) populations compared with Caucasians are multifactorial and complex. Understanding the mechanisms for this racial disparity is critical for delivery of better care. Several studies have investigated sporadic CRC for differences in somatic mutations between AAs and Caucasians, but owing to small study sizes and conflicting results to date, no definitive conclusions have been reached.

Methods:

Here, we present the first systematic literature review and meta-analysis investigating the mutational differences in sporadic CRC between AAs and Caucasians focused on frequent driver mutations (APC,TP53, KRAS,PI3CA, FBXW7,SMAD4, and BRAF). Publication inclusion criteria comprised sporadic CRC, human subjects, English language, information on ethnicity (AA, Caucasian, or both), total subject number >20, and information on mutation frequencies.

Results:

We identified 6,234 publications. Meta-analysis for APC, TP54, FBXW7, or SMAD4 was not possible owing to paucity of data. KRAS mutations were statistically less frequent in non-Hispanic Whites when compared with AAs (odds ratio, 0.640; 95% confidence interval (CI): 0.5342–0.7666; P=0.0001), while the mutational differences observed in BRAF and PI3CA did not reach statistical significance.

Conclusions:

Here, we report the mutational patterns for KRAS, BRAF, and PI3CA in sporadic CRC of AAs and Caucasians in a systematic meta-analysis of previously published data. We identified an increase in KRAS mutations in sporadic CRC in AAs, which may contribute to worse prognosis and increased mortality of CRC in AAs. Future studies investigating health-care disparities in CRC in AAs should control for KRAS mutational frequency.

Activin signaling is an essential component of the TGF-β induced pro-metastatic phenotype in colorectal cancer

Advanced colorectal cancer (CRC) remains a critical health care challenge worldwide. Various TGF-β superfamily members are important in colorectal cancer metastasis, but their signaling effects and predictive value have only been assessed in isolation. Here, we examine cross-regulation and combined functions of the two most prominent TGF-β superfamily members activin and TGF-β in advanced colorectal cancer. In two clinical cohorts we observed by immune-based assay that combined serum and tissue activin and TGF-β ligand levels predicts outcome in CRC patients and is superior to single ligand assessment. While TGF-β growth suppression is independent of activin, TGF-β treatment leads to increased activin secretion in colon cancer cells and TGF-β induced cellular migration is dependent on activin, indicating pathway cross-regulation and functional interaction in vitro. mRNA expression of activin and TGF-β pathway members were queried in silico using the TCGA data set. Coordinated ligand and receptor expression is common in solid tumors for activin and TGF-β pathway members. In conclusion, activin and TGF-β are strongly connected signaling pathways that are important in advanced CRC. Assessing activin and TGF-β signaling as a unit yields important insights applicable to future diagnostic and therapeutic interventions.

Transforming Growth Factor β Superfamily Signaling in Development of Colorectal Cancer

Transforming growth factor (TGF)-β cytokines signal via a complex network of pathways to regulate proliferation, differentiation, adhesion, migration, and other functions in many cell types. A high percentage of colorectal tumors contain mutations that disrupt TGF-β family member signaling. We review how TGF-β family member signaling is altered during development of colorectal cancer, models of study, interaction of pathways, and potential therapeutic strategies.

Expression of an Oncogenic BARD1 Splice Variant Impairs Homologous Recombination and Predicts Response to PARP-1 Inhibitor Therapy in Colon Cancer

BRCA1-associated RING domain protein 1 (BARD1) stabilizes BRCA1 protein by forming a heterodimeric RING-RING complex, and impacts function of BRCA1, including homologous recombination (HR) repair. Although colon cancer cells usually express wild type BRCA1, presence of an oncogenic BARD1 splice variant (SV) in select cancers may render BRCA1 dysfunctional and allow cells to become sensitive to HR targeting therapies. We previously reported association of loss of full-length (FL) BARD1 with poor prognosis in colon cancer as well as expression of various BARD1 SVs with unknown function. Here we show that loss of BARD1 function through the expression of a BARD1 SV, BARD1β, results in a more malignant phenotype with decreased RAD51 foci formation, reduced BRCA1 E3 ubiquitin ligase activity, and decreased nuclear BRCA1 protein localization. BARD1β sensitizes colon cancer cells to poly ADP ribose polymerase 1 (PARP-1) inhibition even in a FL BRCA1 background. These results suggest that expression of BARD1β may serve as a future biomarker to assess suitability of colon cancers for HR targeting with PARP-1 inhibitors in treatment of advanced colon cancer.

Activin and TGFβ use diverging mitogenic signaling in advanced colon cancer

Background

Understanding cell signaling pathways that contribute to metastatic colon cancer is critical to risk stratification in the era of personalized therapeutics. Here, we dissect the unique involvement of mitogenic pathways in a TGFβ or activin-induced metastatic phenotype of colon cancer.

Method

Mitogenic signaling/growth factor receptor status and p21 localization were correlated in primary colon cancers and intestinal tumors from either AOM/DSS treated ACVR2A (activin receptor 2) −/− or wild type mice. Colon cancer cell lines (+/− SMAD4) were interrogated for ligand-induced PI3K and MEK/ERK pathway activation and downstream protein/phospho-isoform expression/association after knockdown and pharmacologic inhibition of pathway members. EMT was assessed using epithelial/mesenchymal markers and migration assays.

Results

In primary colon cancers, loss of nuclear p21 correlated with upstream activation of activin/PI3K while nuclear p21 expression was associated with TGFβ/MEK/ERK pathway activation. Activin, but not TGFβ, led to PI3K activation via interaction of ACVR1B and p85 independent of SMAD4, resulting in p21 downregulation. In contrast, TGFβ increased p21 via MEK/ERK pathway through a SMAD4-dependent mechanism. While activin induced EMT via PI3K, TGFβ induced EMT via MEK/ERK activation. In vivo, loss of ACVR2A resulted in loss of pAkt, consistent with activin-dependent PI3K signaling.

Conclusion

Although activin and TGFβ share growth suppressive SMAD signaling in colon cancer, they diverge in their SMAD4-independent pro-migratory signaling utilizing distinct mitogenic signaling pathways that affect EMT. p21 localization in colon cancer may determine a dominant activin versus TGFβ ligand signaling phenotype warranting further validation as a therapeutic biomarker prior to targeting TGFβ family receptors.

Electronic supplementary material

The online version of this article (doi:10.1186/s12943-015-0456-4) contains supplementary material, which is available to authorized users.

Hypoxia-induced gene expression results from selective mRNA partitioning to the endoplasmic reticulum

Protein synthesis is a primary energy-consuming process in the cell. Therefore, under hypoxic conditions, rapid inhibition of global mRNA translation represents a major protective strategy to maintain energy metabolism. How some mRNAs, especially those that encode crucial survival factors, continue to be efficiently translated in hypoxia is not completely understood. By comparing specific transcript levels in ribonucleoprotein complexes, cytoplasmic polysomes and endoplasmic reticulum (ER)-bound ribosomes, we show that the synthesis of proteins encoded by hypoxia marker genes is favoured at the ER in hypoxia. Gene expression profiling revealed that transcripts particularly increased by the HIF-1 transcription factor network show hypoxia-induced enrichment at the ER. We found that mRNAs favourably translated at the ER have higher conservation scores for both the 5'- and 3'-untranslated regions (UTRs) and contain less upstream initiation codons (uAUGs), indicating the significance of these sequence elements for sustained mRNA translation under hypoxic conditions. Furthermore, we found enrichment of specific cis-elements in mRNA 5'- as well as 3'-UTRs that mediate transcript localization to the ER in hypoxia. We conclude that transcriptome partitioning between the cytoplasm and the ER permits selective mRNA translation under conditions of energy shortage.

Shutdown of achaete-scute homolog-1 expression by heterogeneous nuclear ribonucleoprotein (hnRNP)-A2/B1 in hypoxia

The basic helix-loop-helix transcription factor hASH1, encoded by the ASCL1 gene, plays an important role in neurogenesis and tumor development. Recent findings indicate that local oxygen tension is a critical determinant for the progression of neuroblastomas. Here we investigated the molecular mechanisms underlying the oxygen-dependent expression of hASH1 in neuroblastoma cells. Exposure of human neuroblastoma-derived Kelly cells to 1% O2 significantly decreased ASCL1 mRNA and hASH1 protein levels. Using reporter gene assays, we show that the response of hASH1 to hypoxia is mediated mainly by post-transcriptional inhibition via the ASCL1 mRNA 5'- and 3'-UTRs, whereas additional inhibition of the ASCL1 promoter was observed under prolonged hypoxia. By RNA pulldown experiments followed by MALDI/TOF-MS analysis, we identified heterogeneous nuclear ribonucleoprotein (hnRNP)-A2/B1 and hnRNP-R as interactors binding directly to the ASCL1 mRNA 5'- and 3'-UTRs and influencing its expression. We further demonstrate that hnRNP-A2/B1 is a key positive regulator of ASCL1, findings that were also confirmed by analysis of a large compilation of gene expression data. Our data suggest that a prominent down-regulation of hnRNP-A2/B1 during hypoxia is associated with the post-transcriptional suppression of hASH1 synthesis. This novel post-transcriptional mechanism for regulating hASH1 levels will have important implications in neural cell fate development and disease.