Huib Croes

Triplet-repeat oligonucleotide-mediated reversal of RNA toxicity in myotonic dystrophy

Myotonic dystrophy type 1 (DM1) is caused by toxicity of an expanded, noncoding (CUG)n tract in DM protein kinase (DMPK) transcripts. According to current evidence the long (CUG)n segment is involved in entrapment of muscleblind (Mbnl) proteins in ribonuclear aggregates and stabilized expression of CUG binding protein 1 (CUGBP1), causing aberrant premRNA splicing and associated pathogenesis in DM1 patients. Here, we report on the use of antisense oligonucleotides (AONs) in a therapeutic strategy for reversal of RNA-gain-of-function toxicity. Using a previously undescribed mouse DM1 myoblast−myotube cell model and DM1 patient cells as screening tools, we have identified a fully 2′-O-methyl-phosphorothioate-modified (CAG)7 AON that silences mutant DMPK RNA expression and reduces the number of ribonuclear aggregates in a selective and (CUG)n-length-dependent manner. Direct administration of this AON in muscle of DM1 mouse models in vivo caused a significant reduction in the level of toxic (CUG)n RNA and a normalizing effect on aberrant premRNA splicing. Our data demonstrate proof of principle for therapeutic use of simple sequence AONs in DM1 and potentially other unstable microsatellite diseases.

Microscopic localization of PEG-liposomes in a rat model of focal infection.

In the present study the microscopic localization of polyethylene glycol (PEG) liposomes in infected tissues was studied with both light microscopy (LM) and transmission electron microscopy (TEM) in rats with focal intramuscular Staphylococcus aureus infection. PEG-liposomes containing colloidal gold were prepared and injected intravenously in rats with focal S. aureus infection and tissues were dissected at 24 h post injection. Sections were cut and liposomes were visualized for microscopic evaluation using silver enhancement. Uptake of PEG-liposomes was visualized by both scintigraphy and LM in the abscess, liver and spleen. In the infected area, the liposomes were mainly found in the vicinity of blood vessels. TEM showed that the liposomes were localized in the macrophages and to a lesser extent in endothelial cells in the infectious tissue. In the liver, the liposomes appeared mainly localized in Kupffer cells. In the spleen, uptake was only seen in cells of the red pulp and in cells around the central arteries. Our microscopic observations indicate that uptake and retention of PEG-liposomes in the infectious focus is a result of enhanced extravasation due to increased vascular permeability and subsequent phagocytosis of PEG-liposomes by macrophages in the infected tissue.

Cloning and characterization of mCRIP2, a mouse LIM-only protein that interacts with PDZ domain IV of PTP-BL.

Abstract Background: In the mouse submembranous protein tyrosine phosphatase PTP‐BL five PDZ domains are present in between the N‐terminal FERM domain, which directs the protein to the cell cortex, and the C‐terminal catalytic phosphatase domain. To understand more on the physical role of PTP‐BL in this microenvironment, we started to search for PTP‐BL PDZ domain‐interacting proteins.

Characterization of multiple transcripts and isoforms derived from the mouse protein tyrosine phosphatase gene Ptprr

The use of alternative splice sites, promoters and translation start sites considerably adds to the complexity of organisms. Four mouse cDNAs (PTPBR7, PTP‐SL, PTPPBSγ+ and PTPPBSγ−) have been cloned that contain different 5′ parts but encode identical protein tyrosine phosphatase PTPRR catalytic domains. We investigated the genomic origin and coding potential of these transcripts to elucidate their interrelationship. Mouse gene Ptprr exons were identified within a 260 kbp segment on chromosome 10, revealing PTP‐SL‐ and PTPPBSγ‐specific transcription start sites within introns two and four, respectively, relative to the 14 PTPBR7 exons. Northern and RT‐PCR analyses demonstrated differential expression patterns for these promoters. Furthermore, transfection studies and AUG codon mutagenesis demonstrated that in PTP‐SL and PTPPBSγ messengers multiple translation initiation sites are being used. Resulting 72, 60, 42 and 37 kDa PTPRR protein isoforms differ not only in the length of their N‐terminal part but also in their subcellular localization, covering all major PTP subtypes; receptor‐like, membrane associated and cytosolic. In summary, mouse gene Ptprr gives rise to multiple isoforms through the use of distinct promoters, alternative splicing and differential translation starts. These results set the stage for further investigations on the physiological roles of PTPRR proteins.

Cysts of PRKCSH mutated polycystic liver disease patients lack hepatocystin but express Sec63p

Polycystic liver disease (PCLD) is an inherited disorder caused by mutations in either PRKCSH (hepatocystin) or SEC63 (Sec63p). However, expression patterns of the implicated proteins in diseased and normal liver are unknown. We analyzed subcellular and cellular localization of hepatocystin and Sec63p using cell fractionation, immunofluorescence, and immunohistochemical methods. Expression patterns were assessed in fetal liver, PCLD liver, and normal adult liver. We found hepatocystin and Sec63p expression predominantly in the endoplasmic reticulum. In fetal tissue, there was intense expression of hepatocystin in ductal plate, bile ducts, and hepatocytes. However, Sec63p staining was prominent in early hepatocytes only and weak in bile ducts throughout development. In PCLD tissue, hepatocystin was expressed in hepatocytes, bile ducts, and in cyst epithelium of patients negative for PRKCSH mutation. In contrast, the majority of cysts from PRKCSH mutation carriers did not express hepatocystin. Sec63p expression was observed in all cyst epithelia regardless of mutational state. We conclude that hepatocystin is probably required for development of bile ducts and does not interact with Sec63p. The results support the hypothesis that cyst formation in PCLD results from a cellular recessive mechanism involving loss of hepatocystin. Cystogenesis in SEC63-associated PCLD occurs via a different mechanism.

Characterization of a hormone-producing ovarian carcinoma cell line

An ovarian carcinoma cell line (OTN 11) was produced from the ascitic fluid of a patient with a moderately to well differentiated papilliferous cystadenocarcinoma of the ovary. The cell line was characterized using electron microscopy karyotyping, immunohistochemical techniques with monoclonal antibodies against keratins as epithelial markers, and the monoclonal antibodies OV-TL 3 and OC 125 as ovarian carcinoma markers. These techniques revealed the epithelial and adenocarcinomatous nature of the cell line and the presence of ovarian carcinoma-related surface markers. The adenocarcinomatous nature of the cell line also became apparent after heterotransplantation of cell suspensions into nude mice and nude rats, in which adenomatous tumor structures were formed. These xenografts had the same ultrastructural and immunohistochemical properties as the cell line. Despite the adenocarcinomatous character of the tumor the cultured cells release estradiol into the culture medium. We may conclude that OTN 11 is an ovarian carcinoma cell line which has retained highly differentiated functions, such as the production of an ovarian hormone.

Plasmodium berghei Δp52&p36 Parasites Develop Independent of a Parasitophorous Vacuole Membrane in Huh-7 Liver Cells

The proteins P52 and P36 are expressed in the sporozoite stage of the murine malaria parasite Plasmodium berghei. Δp52&p36 sporozoites lacking expression of both proteins are severely compromised in their capability to develop into liver stage parasites and abort development soon after invasion; presumably due to the absence of a parasitophorous vacuole membrane (PVM). However, a small proportion of P. berghei Δp52&p36 parasites is capable to fully mature in hepatocytes causing breakthrough blood stage infections. We have studied the maturation of replicating Δp52&p36 parasites in cultured Huh-7 hepatocytes. Approximately 50% of Δp52&p36 parasites developed inside the nucleus of the hepatocyte but did not complete maturation and failed to produce merosomes. In contrast cytosolic Δp52&p36 parasites were able to fully mature and produced infectious merozoites. These Δp52&p36 parasites developed into mature schizonts in the absence of an apparent parasitophorous vacuole membrane as shown by immunofluorescence and electron microscopy. Merozoites derived from these maturing Δp52&p36 liver stages were infectious for C57BL/6 mice.

Cell membrane integrity in myotonic dystrophy type 1: implications for therapy

Myotonic Dystrophy type 1 (DM1) is a multisystemic disease caused by toxic RNA from a DMPK gene carrying an expanded (CTG•CAG)n repeat. Promising strategies for treatment of DM1 patients are currently being tested. These include antisense oligonucleotides and drugs for elimination of expanded RNA or prevention of aberrant binding to RNP proteins. A significant hurdle for preclinical development along these lines is efficient systemic delivery of compounds across endothelial and target cell membranes. It has been reported that DM1 patients show elevated levels of markers of muscle damage or loss of sarcolemmal integrity in their serum and that splicing of dystrophin, an essential protein for muscle membrane structure, is abnormal. Therefore, we studied cell membrane integrity in DM1 mouse models commonly used for preclinical testing. We found that membranes in skeletal muscle, heart and brain were impermeable to Evans Blue Dye. Creatine kinase levels in serum were similar to those in wild type mice and expression of dystrophin protein was unaffected. Also in patient muscle biopsies cell surface expression of dystrophin was normal and calcium-positive fibers, indicating elevated intracellular calcium levels, were only rarely seen. Combined, our findings indicate that cells in DM1 tissues do not display compromised membrane integrity. Hence, the cell membrane is a barrier that must be overcome in future work towards effective drug delivery in DM1 therapy.

Tumor cell settling and early invasion of the peritoneum

A Sewall Wright strain-2 guinea pig model producing malignant ascites after injection of a diethylnitrosamine-induced hepatocellular carcinoma cell suspension (Line-10) was used to demonstrate the multilayered settling of tumor cells on the peritoneal surface, frequently followed by the formation of papillary projections and the early invasion in a proliferating submesothelial tissue. At the border of tumor cells and the desmoplastic tissue the malignant cells changed their shape and generally two categories were recognized. Often multilayering, atypical flat cells covered the stromal tissue, while mostly rounded ones invaded using their branched penetration processes, being devoid of cationized ferritin, which was only present on the luminal sides of all cellular elements. Flattened malignant cells, penetrating processes and invading cells lost their microvillous surface pattern. The infiltrating cells were often only detectable with the monoclonal antibody 10 TL 40 and the anti-cytokeratin OV TL 12-5, demonstrating the need for immunohistochemistry in diagnosing solitary invading malignant cells in light microscopy. It appeared that still numerous mesothelial cells were found scattered deeply within the desmoplastic tissue. These former lining cells were identified by their junctions and the presence of remnants of basal lamina as well as by their microvillous 5′-nucleotidase activity.

Targeting CD44v6 for fluorescence-guided surgery in head and neck squamous cell carcinoma

Head and neck squamous cell carcinoma (HNSCC) is an often highly invasive tumor, infiltrating functionally important tissue areas. Achieving complete tumor resection and preserving functionally relevant tissue structures depends on precise identification of tumor-free resection margins during surgery. Fluorescence-guided surgery (FGS), by intraoperative detection of tumor cells using a fluorescent tracer, may guide surgical excision and identify tumor-positive resection margins. Using a literature survey on potential surface molecules followed by immunohistochemical validation, we identified CD44 variant 6 (CD44v6) as a constitutively expressed antigen in the invasion zone of HNSCC lesions. The monoclonal anti-CD44v6 antibody BIWA was labeled with both a near-infrared fluorescent dye (IRDye800CW) and a radioactive label (Indium-111) and dual-modality imaging was applied in a locally invasive tumor mouse model. BIWA accurately detected human HNSCC xenografts in mice with a tumor uptake of 54 ± 11% ID/g and invasion regions with an accuracy of 94%. When dissected under clinical-like conditions, tumor remnants approximately 0.7 mm in diameter consisting of a few thousand cells were identified by fluorescence imaging, resulting in reliable dissection of invasive microregions. These data indicate that CD44v6 is a suitable target for reliable near-infrared detection and FGS of invasive HNSCC lesions in vivo.