Inducible knock-out of BCL6 in lymphoma cells results in tumor stasis.

Diffuse large B-cell lymphoma (DLBCL) is the most common type of non-Hodgkin lymphomas worldwide and is characterized by a high diversity of genetic and molecular alterations. Chromosomal translocations and mutations leading to deregulated expression of the transcriptional repressor BCL6 occur in a significant fraction of DLBCL patients. An oncogenic role of BCL6 in the initiation of DLBCL has been shown as the constitutive expression of BCL6 in mice recapitulates the pathogenesis of human DLBCL. However, the role of BCL6 in tumor maintenance remains poorly investigated due to the absence of suitable genetic models and limitations of pharmacological inhibitors. Here, we have utilized tetracycline-inducible CRISPR/Cas9 mutagenesis to study the consequences of BCL6 deletion in established DLBCL models in culture and in vivo. We show that BCL6 knock-out in SU-DHL-4 cells in vitro results in an anti-proliferative response 4-7 days after Cas9 induction that was characterized by cell cycle (G1) arrest. Conditional BCL6 deletion in established DLBCL tumors in vivo induced a significant tumor growth inhibition with initial tumor stasis followed by slow tumor growth kinetics. Our findings support a role of BCL6 in the maintenance of lymphoma growth and showcase the utility of inducible CRISPR/Cas9 systems for probing oncogene addiction.

SPINK5 knockdown in organotypic human skin culture as a model system for Netherton syndrome: effect of genetic inhibition of serine proteases kallikrein 5 and kallikrein 7.

Netherton syndrome (NS; OMIM 256500) is a genetic skin disease resulting from defects in the serine protease inhibitor Kazal-type 5 (SPINK5) gene, which encodes the protease inhibitor lympho-epithelial Kazal type inhibitor (LEKTI). We established a SPINK5 knockdown skin model by transfecting SPINK5 small interfering RNA (siRNA) into normal human epidermal keratinocytes, which were used together with fibroblast-populated collagen gels to generate organotypic skin cultures. This model recapitulates some of the NS skin morphology: thicker, parakeratotic stratum corneum frequently detached from the underlying epidermis and loss of corneodesmosomes. As enhanced serine protease activity has been implicated in the disease pathogenesis, we investigated the impact of the kallikreins KLK5 [stratum corneum trypsin-like enzyme (SCTE)] and KLK7 [stratum corneum chymotrypsin-like enzyme (SCCE)] on the SPINK5 knockdown phenotype by generating double knockdowns in the organotypic model. Knockdown of KLK5 or KLK7 partially ameliorated the epidermal architecture: increased epidermal thickness and expression of desmocollin 1 (DSC1), desmoglein 1 (DSG1) and (pro)filaggrin. Thus, inhibition of serine proteases KLK5 and KLK7 could be therapeutically beneficial in NS.

Overexpression of IL-4 alters the homeostasis in the skin.

IL-4 has been implicated to play an important role in the pathogenesis of many inflammatory diseases including skin diseases such as atopic dermatitis. Because it is not clear which pathologic features of atopic dermatitis are dependent on IL-4, we assessed the consequences of IL-4 overexpression in the skin, using transgenic mice overexpressing IL-4 ubiquitously. Although transgenic mice display no clinical signs of skin inflammation, IL-4 induced a wide spectrum of pathologies including an increased number of mast cells and Langerhans cells in dermis and epidermis, respectively, focal deposition of collagen and a considerably reduced adipocyte layer in the dermis as well as an increased mitotic activity of keratinocytes, reflected in acanthosis and hyperkeratosis. The increase in Langerhans cell number may be explained in part by the substantially reduced Langerhans cell emigration from the epidermis in transgenic mice. The molecular mechanism behind this phenomenon remains to be clarified. Under in vitro culture conditions, Langerhans cells from transgenic mice undergo a maturation process similar to that of Langerhans cells from control mice, and their immunostimulatory capacity is also comparable. In contrast, transgenic Langerhans cells are superior to control Langerhans cells in their antigen-processing capacity. We conclude that the overexpression of IL-4 in the skin is, by itself, not sufficient for the induction of a full-blown atopic dermatitis phenotype, but several changes seen in the skin of transgenic mice mirror the cardinal pathologic manifestations of this disease.