Ectodomain shedding of CD99 within highly conserved regions is mediated by the metalloprotease meprin ß and promotes transendothelial cell migration.

The adhesion molecule CD99 is essential for the transendothelial migration of leukocytes. In this study, we used biochemical and cellular assays to show that CD99 undergoes ectodomain shedding by the metalloprotease meprin ß and subsequent intramembrane proteolysis by γ-secretase. The cleavage site in CD99 was identified by mass spectrometry within an acidic region highly conserved through different vertebrate species. This finding fits perfectly to the unique cleavage specificity of meprin ß with a strong preference for aspartate residues and suggests coevolution of protease and substrate. We hypothesized that limited CD99 cleavage by meprin ß would alter cellular transendothelial migration (TEM) behavior in tissue remodeling processes, such as inflammation and cancer. Indeed, meprin ß induced cell migration of Lewis lung carcinoma cells in an in vitro TEM assay. Accordingly, deficiency of meprin ß in Mep1b-/- mice resulted in significantly increased CD99 protein levels in the lung. Therefore, meprin ß could serve as a therapeutic target, given that in a proof-of-concept approach we showed accumulation of CD99 protein in lungs of meprin ß inhibitor-treated mice.-Bedau, T., Peters, F., Prox, J., Arnold, P., Schmidt, F., Finkernagel, M., Köllmann, S., Wichert, R., Otte, A., Ohler, A., Stirnberg, M., Lucius, R., Koudelka, T., Tholey, A., Biasin, V., Pietrzik, C. U., Kwapiszewska, G., Becker-Pauly, C. Ectodomain shedding of CD99 within highly conserved regions is mediated by the metalloprotease meprin ß and promotes transendothelial cell migration.

Concurrent KRAS p.G12C mutation and ANK3::RET fusion in a patient with metastatic colorectal cancer: a case report.

BACKGROUND: Colorectal cancer (CRC) frequently involves mutations in the KRAS gene, impacting therapeutic strategies and prognosis. The occurrence of KRAS mutations typically precludes the presence of RET fusions, with current medical literature suggesting a mutual exclusivity between these two genetic alterations. We present a unique case that challenges this notion. CASE PRESENTATION: An 85-year-old female with metastatic CRC was found to have a combination of genetic anomalies that is to the best of our knowledge not yet described in the medical literature: a KRAS p.G12C mutation, associated with oncogenesis and treatment resistance, and an ANK3::RET fusion, an infrequent but targetable mutation in CRC. This molecular profile was uncovered through comprehensive genomic sequencing after the patient experienced metachronous tumor dissemination. The presence of both genetic events complicates the treatment approach. CONCLUSIONS: The identification of both a KRAS p.G12C mutation and an ANK3::RET fusion in the same CRC patient adds a new layer to the oncogenic landscape and treatment considerations for CRC. It highlights the intricate decision-making required in the era of precision medicine, where targeted therapies must be carefully chosen and potentially combined to combat complex genetic profiles. The case emphasizes the urgency of investigating the clinical effects of concurrent or sequential use of KRAS p.G12C and RET inhibitors to inform future therapeutic guidelines and improve patient outcomes in similar cases.

Cancer-associated mutations in the canonical cleavage site do not influence CD99 shedding by the metalloprotease meprin ß but alter cell migration in vitro.

Transendothelial cell migration (TEM) is crucial for inflammation and metastasis. The adhesion molecule CD99 was shown to be important for correct immune cell extravasation and is highly expressed on certain cancer cells. Recently, we demonstrated that ectodomain shedding of CD99 by the metalloprotease meprin ß promotes TEM in vitro. In this study, we employed an acute inflammation model (air pouch/carrageenan) and found significantly less infiltrated cells in meprin ß knock-out animals validating the previously observed pro-inflammatory activity. To further analyze the impact of meprin ß on CD99 shedding with regard to cell adhesion and proliferation we characterized two lung cancer associated CD99 variants (D92H, D92Y), carrying point mutations at the main cleavage site. Interestingly, ectodomain shedding of these variants by meprin ß was still detectable. However the cleavage site shifted to adjacent positions. Nevertheless, expression of CD99 variants D92H and D92Y revealed partial misfolding and proteasomal degradation. A previously observed influence of CD99 on Src activation and increased proliferation could not be confirmed in this study, independent of wild-type CD99 or the variants D92H and D92Y. However, we identified meprin ß as a potent inducer of Src phosphorylation. Importantly, we found significantly increased cell migration when expressing the cancer-associated CD99 variant D92H compared to the wild-type protein.