Julian Schardt

Somatic CEBPA Mutations Are a Frequent Second Event in Families With Germline CEBPA Mutations and Familial Acute Myeloid Leukemia

PURPOSE The transcription factor CCAAT/enhancer binding protein-alpha (CEBPA) is crucial for normal myeloid differentiation. Mutations in the CEBPA gene are found in subsets of patients with acute myeloid leukemia (AML). Recently, three families were reported in whom several family members had germline CEBPA mutations and subsequently developed AML. Whereas familial AML is considered a rare event, the frequency of CEBPA germline mutations in AML is not known. PATIENTS AND METHODS In this study, we screened 187 consecutive AML patients for CEBPA mutations at diagnosis. We detected 18 patients (9.6%) with CEBPA mutations. We then analyzed remission samples and constitutive DNA from these patients. RESULTS We found that two (11.1%) of 18 AML patients with CEBPA mutations carried a germline N-terminal frameshift CEBPA mutation. Interestingly, additional members in the families of both of these patients have been affected by AML, and the germline CEBPA mutations were also observed in these patients. Additional somatic mutations in AML patients with germline CEBPA mutations in the two families comprised in-frame C-terminal CEBPA mutations in two patients, two nonsilent CEBPA point mutations in one patient, and monosomy 7 in one patient. CONCLUSION This study shows, for the first time to our knowledge, that germline CEBPA mutations are frequently observed among AML patients with CEBPA mutations. Including the families with germline CEBPA mutations reported previously, additional somatic CEBPA mutations represent a frequent second event in AML with germline CEBPA mutations. Our data strongly indicate that germline CEBPA mutations predispose to AML and that additional somatic CEBPA mutations contribute to the development of the disease.

Complexity of miR-223 regulation by CEBPA in human AML.

microRNA-223 (miR-223) can trigger normal granulopoiesis. miR-223 expression is regulated by two distinct CEBPA (CCAAT/enhancer binding protein-alpha) sites. Here, we report that miR-223 is largely suppressed in cells from acute myeloid leukemia (AML) patients. By sequencing, we found that miR-223 suppression in AML is not caused by DNA sequence alterations, nor is it mediated by promoter hypermethylation. The analysis of the individual contribution of both CEBPA sites to miR-223 regulation identified the site upstream of the miR-223 primary transcript as the predominant regulatory element. Our results suggest that miR-223 suppression in AML is caused by impaired miR-223 upstream factors.

Activation of the Unfolded Protein Response Is Associated with Favorable Prognosis in Acute Myeloid Leukemia

Purpose: The unfolded protein response is triggered by the accumulation of misfolded proteins within the endoplasmic reticulum. Previous studies suggest that the unfolded protein response is activated in some cancer cell lines and involved in tumor development. The role of the unfolded protein response during leukemogenesis is unknown thus far. Experimental Design: Here, we assessed the induction of key effectors of the unfolded protein response in leukemic cells at diagnosis of 105 acute myeloid leukemia (AML) patients comprising all subtypes. We determined the formation of the spliced variant of the X-box–binding protein 1 (XBP1) mRNA, as well as expression levels of calreticulin, GRP78, and CHOP mRNA. Results: The formation of the spliced variant of XBP1s was detectable in 16.2% (17 of 105) of AML patients. Consistent with activated unfolded protein response, this group also had significantly increased expression of calreticulin, GRP78, and CHOP. AML patients with activated unfolded protein response had lower WBC counts, lactate dehydrogenase levels, and more frequently, secondary AML. The incidence of fms-related tyrosine kinase 3 (FLT3) mutations was significantly lower in patients with activated unfolded protein response. In addition, an association was observed between activated unfolded protein response and deletion of chromosome 7. Finally, the clinical course of AML patients with activated unfolded protein response was more favorable with lower relapse rate (P = 0.0182) and better overall (P = 0.041) and disease-free survival (P = 0.022). Conclusions: These results suggest that the unfolded protein response is activated in a considerable subset of AML patients. AML patients with activated unfolded protein response present specific clinical characteristics and a more favorable course of the disease.

Protein disulfide isomerase blocks CEBPA translation and is up-regulated during the unfolded protein response in AML

Deregulation of the myeloid key transcription factor CEBPA is a common event in acute myeloid leukemia (AML). We previously reported that the chaperone calreticulin is activated in subgroups of AML patients and that calreticulin binds to the stem loop region of the CEBPA mRNA, thereby blocking CEBPA translation. In this study, we screened for additional CEBPA mRNA binding proteins and we identified protein disulfide isomerase (PDI), an endoplasmic reticulum (ER) resident protein, to bind to the CEBPA mRNA stem loop region. We found that forced PDI expression in myeloid leukemic cells in fact blocked CEBPA translation, but not transcription, whereas abolishing PDI function restored CEBPA protein. In addition, PDI protein displayed direct physical interaction with calreticulin. Induction of ER stress in leukemic HL60 and U937 cells activated PDI expression, thereby decreasing CEBPA protein levels. Finally, leukemic cells from 25.4% of all AML patients displayed activation of the unfolded protein response as a marker for ER stress, and these patients also expressed significantly higher PDI levels. Our results indicate a novel role of PDI as a member of the ER stress-associated complex mediating blocked CEBPA translation and thereby suppressing myeloid differentiation in AML patients with activated unfolded protein response (UPR).

Unfolded protein response suppresses CEBPA by induction of calreticulin in acute myeloid leukaemia

The unfolded protein response (UPR) is triggered by the accumulation of misfolded proteins within the endoplasmic reticulum (ER). The role of the UPR during leukemogenesis is unknown so far. Here, we studied the induction of mediators of the UPR in leukaemic cells of AML patients. Increased expression of the spliced variant of the X‐box binding protein 1 (XBP1s) was detected in 17.4% (16 of 92) of AML patients. Consistent with activated UPR, this group also had increased expression of ER‐resident chaperones such as the 78 kD glucose‐regulated protein (GRP78) and of calreticulin. Conditional expression of calreticulin in leukaemic U937 cells was found to increase calreticulin binding to the CEBPA mRNA thereby efficiently blocking translation of the myeloid key transcription factor CEBPA and ultimately affecting myeloid differentiation. Consequently, leukaemic cells from AML patients with activated UPR and thus increased calreticulin levels showed in fact suppressed CEBPA protein expression. We identified two functional ER stress response elements (ERSE) in the calreticulin promoter. The presence of NFY and ATF6, as well as an intact binding site for YY1 within these ERSE motifs were essential for mediating sensitivity to ER stress and activation of calreticulin. Thus, we propose a model of the UPR being activated in a considerable subset of AML patients through induction of calreticulin along the ATF6 pathway, thereby ultimately suppressing CEBPA translation and contributing to the block in myeloid differentiation.

Comparison of three or fewer high-dose chemotherapy cycles as salvage treatment in germ cell tumors in first relapse

Unique characteristics discriminate germ cell tumors (GCTs) from other solid malignancies. Patients are predominantly young men between 15 and 40 years with few comorbidities (if any); tumors are particularly sensitive to platinum-based chemotherapy; and a cure is still possible with salvage approaches in patients with progression after first-line chemotherapy. Curative salvage strategies involve conventional-dose chemotherapy (CDCT) or, alternatively, high-dose chemotherapy with autologous stem cell transplantation (HDCT/ASCT), which—in contrast to virtually all other types of solid tumors—can be highly effective.1, 2, 3, 4, 5, 6, 7, 8, 9, 10

Pattern of Care Study in Metastatic Renal-Cell Carcinoma in the Preimmunotherapy Era in Switzerland.

Micro‐Abstract A study of the pattern of care in metastatic renal‐cell carcinoma (mRCC) under circumstances with access to all therapeutic options found that the median survival of patients treated with targeted agents for mRCC was 2.0 years when the initial active surveillance periods are excluded. Exposure to more than 2 lines of systemic drugs did not improve outcome of patients with mRCC. Introduction: In metastatic renal‐cell carcinoma (mRCC), physicians have a plethora of therapeutic choices, with the latest addition of checkpoint inhibitors. However, many questions regarding the best use of the respective drugs remain unanswered. Therefore, it is important to examine and summarize the outcome of real‐world experiences to understand the practical value of the various drugs in daily use and foster optimal treatment algorithms for patients with renal‐cell carcinoma. We sought to describe the pattern of care in mRCC under circumstances with access to all therapeutic options for patients. Patients and Methods: We examined the outcome of patients with mRCC who were treated at 8 major centers in Switzerland, mainly with vascular endothelial growth factor–targeted therapy and mammalian target of rapamycin inhibitors. Data from 110 patients with mRCC who had undergone more than one systemic therapy were collected and analyzed. We assessed the pattern of care for patients with mRCC in an unrestricted health care system and outcomes with regard to the respective treatment sequences. We also studied the compliance of individual therapies with published guidelines and correlated the adherence to outcome. Finally, immediate versus deferred treatment and the number of received therapeutic drug lines were analyzed. Results: Median survival of patients treated with targeted agents for mRCC was 2.0 years. Conclusion: Exposure to more than 2 lines of systemic drugs did not improve outcome of patients with mRCC.

Response to first-line treatment and histology are associated with achieving complete remission after the first salvage high-dose chemotherapy in relapsing germ cell tumor patients

Sequential high-dose chemotherapy (HDCT) with autologous stem cell transplantation (ASCT) is a curative option in relapsing germ cell tumor (GCT) patients, and complete remission (CR) after the first ASCT (early CR2) is associated with favorable outcome. Prognostic factors predicting early CR2 have not been investigated so far. We analyzed consecutive patients with a first relapse of GCT treated with three sequential cycles of carboplatin/etoposide-based HDCT with ASCT in the two largest academic centers in Switzerland. The cohort comprised 96 relapsing GCT patients, with 19 (19.8%) patients achieving early CR2 after the first HDCT cycle. The median progression-free survival and overall survival were not reached in patients achieving early CR2, whereas they were 9.6 months (P = 0.0301) and 34.8 months (P = 0.0684) for patients missing early CR2. Patients with early CR2 more often had CR1 after first-line bleomycin, etoposide, and cisplatin chemotherapy (68.4 vs. 31.6%; P = 0.0037) and an interval longer than 2 years between initial diagnosis and first HDCT (36.8 vs. 15.6%; P = 0.0373), but less often a histology of mixed nonseminomatous tumor (46.8 vs. 21.1%; P = 0.0418). These data suggest that response to first-line chemotherapy, late relapse, and histology are associated with achieving early CR2 after a first HDCT with ASCT in relapsing GCT patients.

Functional interplay of SP family members and nuclear factor Y is essential for transcriptional activation of the human Calreticulin gene.

Calreticulin (CALR) is a highly conserved, multifunctional protein involved in a variety of cellular processes including the maintenance of intracellular calcium homeostasis, proper protein folding, differentiation and immunogenic cell death. More recently, a crucial role for CALR in the pathogenesis of certain hematologic malignancies was discovered: in clinical subgroups of acute myeloid leukemia, CALR overexpression mediates a block in differentiation, while somatic mutations have been found in the majority of patients with myeloproliferative neoplasms with nonmutated Janus kinase 2 gene (JAK2) or thrombopoietin receptor gene (MPL). However, the mechanisms underlying CALR promoter activation have insufficiently been investigated so far. By dissecting the core promoter region, we could identify a functional TATA-box relevant for transcriptional activation. In addition, we characterized two evolutionary highly conserved cis-regulatory modules (CRMs) within the proximal promoter each composed of one binding site for the transcription factors SP1 and SP3 as well as for the nuclear transcription factor Y (NFY) and we verified binding of these factors to their cognate sites in vitro and in vivo.