Inhibition of the Cyclin K-CDK12 complex induces DNA damage and increases the effect of androgen deprivation therapy in prostate cancer.

Androgen deprivation therapy (ADT) is the mainstay of the current first-line treatment concepts for patients with advanced prostate carcinoma (PCa). However, due to treatment failure and recurrence investigation of new targeted therapeutics is urgently needed. In this study, we investigated the suitability of the Cyclin K-CDK12 complex as a novel therapeutic approach in PCa using the new covalent CDK12/13 inhibitor THZ531. Here we show that THZ531 impairs cellular proliferation, induces apoptosis, and decreases the expression of selected DNA repair genes in PCa cell lines, which is associated with an increasing extent of DNA damage. Furthermore, combination of THZ531 and ADT leads to an increase in these anti-tumoral effects in androgen-sensitive PCa cells. The anti-proliferative and pro-apoptotic activity of THZ531 in combination with ADT was validated in an ex vivo PCa tissue culture model. In a retrospective immunohistochemical analysis of 300 clinical tissue samples we show that Cyclin K (CycK) but not CDK12 expression correlates with a more aggressive type of PCa. In conclusion, this study demonstrates the clinical relevance of the CycK-CDK12 complex as a promising target for combinational therapy with ADT in PCa and its importance as a prognostic biomarker for patients with PCa.

N-Cadherin Distinguishes Intrahepatic Cholangiocarcinoma from Liver Metastases of Ductal Adenocarcinoma of the Pancreas.

Carcinomas of the pancreatobiliary system confer an especially unfavorable prognosis. The differential diagnosis of intrahepatic cholangiocarcinoma (iCCA) and its subtypes versus liver metastasis of ductal adenocarcinoma of the pancreas (PDAC) is clinically important to allow the best possible therapy. We could previously show that E-cadherin and N-cadherin, transmembrane glycoproteins of adherens junctions, are characteristic features of hepatocytes and cholangiocytes. We therefore analyzed E-cadherin and N-cadherin in the embryonally related epithelia of the bile duct and pancreas, as well as in 312 iCCAs, 513 carcinomas of the extrahepatic bile ducts, 228 gallbladder carcinomas, 131 PDACs, and precursor lesions, with immunohistochemistry combined with image analysis, fluorescence microscopy, and immunoblots. In the physiological liver, N-cadherin colocalizes with E-cadherin in small intrahepatic bile ducts, whereas larger bile ducts and pancreatic ducts are positive for E-cadherin but contain decreasing amounts of N-cadherin. N-cadherin was highly expressed in most iCCAs, whereas in PDACs, N-cadherin was negative or only faintly expressed. E- and N-cadherin expression in tumors of the pancreaticobiliary tract recapitulate their expression in their normal tissue counterparts. N-cadherin is a helpful marker for the differential diagnosis between iCCA and PDAC, with a specificity of 96% and a sensitivity of 67% for small duct iCCAs and 50% for large duct iCCAs.

Restricted Water Diffusion in Diffusion-Weighted Magnetic Resonance Imaging in Pancreatic Cancer is Associated with Tumor Hypoxia.

Hypoxia is a hallmark of pancreatic cancer (PDAC) due to its compact and extensive fibrotic tumor stroma. Hypoxia contributes to high lethality of this disease, by inducing a more malignant phenotype and resistance to radiation and chemotherapy. Thus, non-invasive methods to quantify hypoxia could be helpful for treatment decisions, for monitoring, especially in non-resectable tumors, or to optimize personalized therapy. In the present study, we investigated whether tumor hypoxia in PDAC is reflected by diffusion-weighted magnetic resonance imaging (DW-MRI), a functional imaging technique, frequently used in clinical practice for identification and characterization of pancreatic lesions. DW-MRI assesses the tissue microarchitecture by measuring the diffusion of water molecules, which is more restricted in highly compact tissues. As reliable surrogate markers for hypoxia, we determined Blimp-1 (B-lymphocyte induced maturation protein), a transcription factor, as well as vascular endothelial growth factor (VEGF), which are up-regulated in response to hypoxia. In 42 PDAC patients, we observed a close association between restricted water diffusion in DW-MRI and tumor hypoxia in matched samples, as expressed by high levels of Blimp-1 and VEGF in tissue samples of the respective patients. In summary, our data show that DW-MRI is well suited for the evaluation of tumor hypoxia in PDAC and could potentially be used for the identification of lesions with a high hypoxic fraction, which are at high risk for failure of radiochemotherapy.

Perilipin 1 Expression Differentiates Liposarcoma from Other Types of Soft Tissue Sarcoma.

Lipid droplets, a morphologic feature of adipocytic tumors, are strongly regulated by associated proteins of the perilipin/PAT (perilipin, adipophilin, and tail-interacting protein of 47 kD) family. So far, the use of perilipins as markers for differential diagnosis of soft tissue tumors has only been studied in a few cases. The aim of this study was to investigate the expression of perilipins in 478 human soft tissue tumors and 60 respective normal tissues. Perilipin 1 was immunohistochemically positive in all studied cases of well-differentiated liposarcomas, >90% of myxoid round cell liposarcomas, and >70% of pleomorphic liposarcomas, whereas only the differentiated components of dedifferentiated liposarcomas were immunohistochemically positive for perilipin 1. All other types of soft tissue sarcomas were negative for perilipin 1. Perilipin 2 was more prominent in dedifferentiated and pleomorphic liposarcomas and nearly all other high-grade sarcomas. In well-differentiated liposarcomas, lipomas, or normal adipose tissue, perilipin 2 was virtually absent. In addition, long-term stimulation of adipogenesis in the liposarcoma cell line LiSa-2 restored perilipin 1 expression, as exhibited in the source tumor. Furthermore, knockdown of perilipin 2 or perilipin 3 in LiSa-2 cells influenced lipid droplet number and size as well as cell vitality. In summary, perilipin 1 is a promising marker for the differential diagnosis of liposarcomas from other soft tissue sarcomas, whereas perilipin 2 correlates negatively with tumor grade and may be therapeutically useful.

Isl2b regulates anterior second heart field development in zebrafish.

After initial formation, the heart tube grows by addition of second heart field progenitor cells to its poles. The transcription factor Isl1 is expressed in the entire second heart field in mouse, and Isl1-deficient mouse embryos show defects in arterial and venous pole development. The expression of Isl1 is conserved in zebrafish cardiac progenitors; however, Isl1 is required for cardiomyocyte differentiation only at the venous pole. Here we show that Isl1 homologues are expressed in specific patterns in the developing zebrafish heart and play distinct roles during cardiac morphogenesis. In zebrafish, isl2a mutants show defects in cardiac looping, whereas isl2b is required for arterial pole development. Moreover, Isl2b controls the expression of key cardiac transcription factors including mef2ca, mef2cb, hand2 and tbx20. The specific roles of individual Islet family members in the development of distinct regions of the zebrafish heart renders this system particularly well-suited for dissecting Islet-dependent gene regulatory networks controlling the behavior and function of second heart field progenitors in distinct steps of cardiac development.

The Isl1/Ldb1 Complex Orchestrates Genome-wide Chromatin Organization to Instruct Differentiation of Multipotent Cardiac Progenitors.

Cardiac stem/progenitor cells hold great potential for regenerative therapies; however, the mechanisms regulating their expansion and differentiation remain insufficiently defined. Here we show that Ldb1 is a central regulator of genome organization in cardiac progenitor cells, which is crucial for cardiac lineage differentiation and heart development. We demonstrate that Ldb1 binds to the key regulator of cardiac progenitors, Isl1, and protects it from degradation. Furthermore, the Isl1/Ldb1 complex promotes long-range enhancer-promoter interactions at the loci of the core cardiac transcription factors Mef2c and Hand2. Chromosome conformation capture followed by sequencing identified specific Ldb1-mediated interactions of the Isl1/Ldb1 responsive Mef2c anterior heart field enhancer with genes that play key roles in cardiac progenitor cell function and cardiovascular development. Importantly, the expression of these genes was downregulated upon Ldb1 depletion and Isl1/Ldb1 haplodeficiency. In conclusion, the Isl1/Ldb1 complex orchestrates a network for heart-specific transcriptional regulation and coordination in three-dimensional space during cardiogenesis.

The LIM protein Ajuba restricts the second heart field progenitor pool by regulating Isl1 activity.

Morphogenesis of the heart requires tight control of cardiac progenitor cell specification, expansion, and differentiation. Retinoic acid (RA) signaling restricts expansion of the second heart field (SHF), serving as an important morphogen in heart development. Here, we identify the LIM domain protein Ajuba as a crucial regulator of the SHF progenitor cell specification and expansion. Ajuba-deficient zebrafish embryos show an increased pool of Isl1(+) cardiac progenitors and, subsequently, dramatically increased numbers of cardiomyocytes at the arterial and venous poles. Furthermore, we show that Ajuba binds Isl1, represses its transcriptional activity, and is also required for autorepression of Isl1 expression in an RA-dependent manner. Lack of Ajuba abrogates the RA-dependent restriction of Isl1(+) cardiac cells. We conclude that Ajuba plays a central role in regulating the SHF during heart development by linking RA signaling to the function of Isl1, a key transcription factor in cardiac progenitor cells.