Proteolysis of CD44 at the cell surface controls a downstream protease network.

The cell surface receptor cluster of differentiation 44 (CD44) is the main hyaluronan receptor of the human body. At the cell surface, it can be proteolytically processed by different proteases and was shown to interact with different matrix metalloproteinases. Upon proteolytic processing of CD44 and generation of a C-terminal fragment (CTF), an intracellular domain (ICD) is released after intramembranous cleavage by the γ-secretase complex. This intracellular domain then translocates to the nucleus and induces transcriptional activation of target genes. In the past CD44 was identified as a risk gene for different tumor entities and a switch in CD44 isoform expression towards isoform CD44s associates with epithelial to mesenchymal transition (EMT) and cancer cell invasion. Here, we introduce meprin ß as a new sheddase of CD44 and use a CRISPR/Cas9 approach to deplete CD44 and its sheddases ADAM10 and MMP14 in HeLa cells. We here identify a regulatory loop at the transcriptional level between ADAM10, CD44, MMP14 and MMP2. We show that this interplay is not only present in our cell model, but also across different human tissues as deduced from GTEx (Gene Tissue Expression) data. Furthermore, we identify a close relation between CD44 and MMP14 that is also reflected in functional assays for cell proliferation, spheroid formation, migration and adhesion.

Structural and functional properties of meprin ß metalloproteinase with regard to cell signaling.

The metalloproteinase meprin ß plays an important role during collagen I deposition in the skin, mucus detachment in the small intestine and also regulates the abundance of different cell surface proteins such as the interleukin-6 receptor (IL-6R), the triggering receptor expressed on myeloid cells 2 (TREM2), the cluster of differentiation 99 (CD99), the amyloid precursor protein (APP) and the cluster of differentiation 109 (CD109). With that, regulatory mechanisms that control meprin ß activity and regulate its release from the cell surface to enable access to distant substrates are increasingly important. Here, we will summarize factors that alternate meprin ß activity and thereby regulate its proteolytic activity on the cell surface or in the supernatant. We will also discuss cleavage of the IL-6R and TREM2 on the cell surface and compare it to CD109. CD109, as a substrate of meprin ß, is cleaved within the protein core, thereby releasing defined fragments from the cell surface. At last, we will also summarize the role of proteases in general and meprin ß in particular in substrate release on extracellular vesicles.

A disintegrin and metalloprotease 10 (ADAM10) is a central regulator of murine liver tissue homeostasis.

UNLABELLED: A Disintegrin And Metalloprotease (ADAM) 10 exerts essential roles during organ development and tissue integrity in different organs, mainly through activation of the Notch pathway. However, only little is known about its implication in liver tissue physiology. Here we show that in contrast to its role in other tissues, ADAM10 is dispensable for the Notch2-dependent biliary tree formation. However, we demonstrate that expression of bile acid transporters is dependent on ADAM10. Consequently, mice deficient for Adam10 in hepatocytes, cholangiocytes and liver progenitor cells develop spontaneous hepatocyte necrosis and concomitant liver fibrosis. We furthermore observed a strongly augmented ductular reaction in 15-week old ADAM10(Δhep/Δch) mice and demonstrate that c-Met dependent liver progenitor cell activation is enhanced. Additionally, liver progenitor cells are primed to hepatocyte differentiation in the absence of ADAM10. These findings show that ADAM10 is a novel central node controlling liver tissue homeostasis. HIGHLIGHTS: Loss of ADAM10 in murine liver results in hepatocyte necrosis and concomitant liver fibrosis. ADAM10 directly regulates expression of bile acid transporters but is dispensable for Notch2-dependent formation of the biliary system. Activation of liver progenitor cells is enhanced through increased c-Met signalling, in the absence of ADAM10. Differentiation of liver progenitor cells to hepatocytes is augmented in the absence of ADAM10.