Hans-Jürgen Stark’s research while affiliated with Heidelberg University and other places

MicroRNAs (miRNAs) control organogenesis in mammals but their role in specific cell types is not fully explored. miRNAs exert their function by binding mRNAs and inhibiting translation. Skin is an excellent model to study the role of miRNAs in primary cells of epidermal (keratinocytes) and mesodermal (fibroblasts) origin, because the growth of these cells is tightly controlled at translation. Previous research demonstrated that miRNA-29 family functions during skin repair, however, the exact mRNA targets and the downstream mechanisms of miRNA-29-mediated regulation of cell growth is missing. Here, we use miRNA crosslinking and immunoprecipitation (miRNA-CLIP) method to find the direct targets of miRNA-29 in keratinocytes and fibroblasts from human skin. We uncover previously unrecognized roles of miRNA-29 in protein folding and RNA processing, common to all cell types tested, and determine the cell-specific role of miRNA-29. Using modified anti-sense oligonucleotides (ASO) in 2D and 3D cultures of keratinocytes and fibroblasts, we enhanced cell-to-matrix adhesion and found an autocrine and paracrine mechanism of miRNA-29-dependent cell growth. Our results include a comprehensive list and functional analyses of mRNAs directly bound by miRNA-29 keratinocytes and fibroblasts, determined by miRNA-CLIP and ASO-mediated inhibition of miRNA-29 followed by RNA-seq. We reveal a full transcriptome of human keratinocytes with enhanced adhesion to the wound matrix, which supports regeneration of the epidermis and is regulated by miRNA-29. The functions of miRNA-29 identified in this study can provide a new approach to improve cutaneous repair by restoring and enhancing the endogenous mechanisms through the stage-specific delivery of miRNA-29 ASO.

The BRAF inhibitor vemurafenib, approved for treating patients with BRAF V600E-mutant and unresectable or metastatic melanomas, rapidly induces cutaneous adverse events, including hyperkeratotic skin lesions and cutaneous squamous cell carcinomas (cSCC). To determine, how vemurafenib would provoke these adverse events, we utilized long-term in vitro skin equivalents (SEs) comprising epidermal keratinocytes and dermal fibroblasts in their physiological environment. We inserted keratinocytes with different genetic background [normal keratinocytes: NHEK, HaCaT (p53/mut), and HrasA5 (p53/mut+Hras/mut)] to analyze effects depending on the stage of carcinogenesis. We now show that vemurafenib activates MEK-ERK signaling in both, keratinocytes, and fibroblasts in vitro and in the in vivo-like SEs. As a consequence, vemurafenib does not provide a growth advantage but leads to a differentiation phenotype, causing accelerated differentiation and hyperkeratosis in the NHEK and normalized stratification and cornification in the transformed keratinocytes. Although all keratinocytes responded very similarly to vemurafenib in their expression profile, particularly with a significant induction of MMP1 and MMP3, only the HrasA5 cells revealed a vemurafenib-dependent pathophysiological shift to tumor progression, i.e., the initiation of invasive growth. This was shown by increased proteolytic activity allowing for penetration of the basement membrane and invasion into the disrupted underlying matrix. Blocking MMP activity, by the addition of ilomastat, prevented invasion with all corresponding degradative activities, thus substantiating that the RAS-RAF-MEK-ERK/MMP axis is the most important molecular basis for the rapid switch towards tumorigenic conversion of the HrasA5 keratinocytes upon vemurafenib treatment. Finally, cotreatment with vemurafenib and the MEK inhibitor cobimetinib prevented MEK-ERK hyperactivation and with that abolished both, the epidermal differentiation and the tumor invasion phenotype. This suggests that both cutaneous adverse events are under direct control of vemurafenib-dependent MEK-ERK hyperactivation and confirms the dependence on preexisting genetic alterations of the skin keratinocytes that determine the basis towards induction of tumorigenic progression.

Rocaglates are natural compounds that have been extensively studied for their ability to inhibit translation initiation. Rocaglates represent promising drug candidates for tumor treatment due to their growth-inhibitory effects on neoplastic cells. In contrast to natural rocaglates, synthetic analogues of rocaglates have been less comprehensively characterized, but were also shown to have similar effects on the process of protein translation. Here, we demonstrate an enhanced growth-inhibitory effect of synthetic rocaglates when combined with glucose anti-metabolite 2-deoxy-D-glucose (2DG) in different cancer cell lines. Moreover, we unravel a new aspect in the mechanism of action of synthetic rocaglates involving reduction of glucose uptake mediated by downregulation or abrogation of glucose transporter GLUT-1 expression. Importantly, cells with genetically induced resistance to synthetic rocaglates showed substantially less pronounced treatment effect on glucose metabolism and did not demonstrate GLUT-1 downregulation, pointing at the crucial role of this mechanism for the anti-tumor activity of the synthetic rocaglates. Transcriptome profiling revealed glycolysis as one of the major pathways differentially regulated in sensitive and resistant cells. Analysis of synthetic rocaglate efficacy in a 3D tissue context with a co-culture of tumor and normal cells demonstrated a selective effect on tumor cells and substantiated the mechanistic observations obtained in cancer cell lines. Increased glucose uptake and metabolism is a universal feature across different tumor types. Therefore, targeting this feature by synthetic rocaglates could represent a promising direction for exploitation of rocaglates in novel anti-tumor therapies.

Background: Head and neck squamous cell carcinomas (HNSCC) are phenotypically and molecularly heterogeneous and frequently develop therapy resistance. Reliable patient-derived 3D tumor models are urgently needed to further study the complex pathogenesis of these tumors and to overcome treatment failure. Methods: We developed a three-dimensional organotypic co-culture (3D-OTC) model for HNSCC that maintains the architecture and cell composition of the individual tumor. A dermal equivalent (DE), composed of healthy human-derived fibroblasts and viscose fibers, served as a scaffold for the patient sample. DEs were co-cultivated with 13 vital HNSCC explants (non-human papillomavirus (HPV) driven, n = 7; HPV-driven, n = 6). Fractionated irradiation was applied to 5 samples (non-HPV-driven, n = 2; HPV-driven n = 3). To evaluate expression of ki-67, cleaved caspase-3, pan-cytokeratin, p16INK4a, CD45, ∝smooth muscle actin and vimentin over time, immunohistochemistry and immunofluorescence staining were performed Patient checkup data were collected for up to 32 months after first diagnosis. Results: All non-HPV-driven 3D-OTCs encompassed proliferative cancer cells during cultivation for up to 21 days. Proliferation indices of primaries and 3D-OTCs were comparable and consistent over time. Overall, tumor explants displayed heterogeneous growth patterns (i.e., invasive, expansive, silent). Cancer-associated fibroblasts and leukocytes could be detected for up to 21 days. HPV DNA was detectable in both primary and 3D-OTCs (day 14) of HPV-driven tumors. However, p16INK4a expression levels were varying. Morphological alterations and radioresistant tumor cells were detected in 3D-OTC after fractionated irradiation in HPV-driven and non-driven samples. Conclusions: Our 3D-OTC model for HNSCC supports cancer cell survival and proliferation in their original microenvironment. The model enables investigation of invasive cancer growth and might, in the future, serve as a platform to perform sensitivity testing upon treatment to predict therapy response.

Background. Head and neck squamous cell carcinomas (HNSCC) are histologically and molecularly heterogeneous tumors and frequently develop resistance mechanisms against treatment. Reliable patient-derived 3D tumor models are urgently needed to further study the complex pathogenesis of these tumors and how to overcome treatment failure. Methods. We developed a 3D organotypic co-culture (OTC) model for HNSCCs that maintains the architecture and cell composition of the patients' tumor. A dermal equivalent, composed of healthy, human-derived fibroblasts embedded into viscose fibers, grows in an insert for approximately 10 days in culture and serves as a scaffold for the patient sample. After outgrowth of fibroblast within the dermal equivalent, we cultivated vital HNSCC tumor explants from 13 patients (non-HPV driven, n=7; HPV-driven HNSCC, n=6) by carefully placing them on top of the scaffold. Fractionated irradiation (IR) was applied to 5 samples. To evaluate tumor proliferation and areas of apoptosis, we performed immunohistochemistry and immunofluorescence with antibodies against ki-67, cleaved caspase-3, pan-cytokeratin (PanCK), p16INK4a, and vimentin. Results. All 3D OTC models of non-HPV driven samples encompassed proliferative cancer cells during cultivation for up to 21 days. Proliferation indices of primary and 3D-OTC models were comparable and consistent over time. Overall, tumor explants displayed heterogeneous growth and invasion patterns. Radioresistant and clonally expanding tumor cells were enriched in 3D-OTC models after fractionated IR. HPV DNA was detectable in both primary and OTC (day 14) of HPV-driven tumors; However, p16INK4a expression levels were varying. Conclusion. Our 3D-dimensional organotypic co-culture model for HNSCC supports cancer cell survival and proliferation in their original microenvironment. The model enables investigation of invasive cancer growth as well as clonal expansion of resistant cancer cells upon treatment. In the future, the introduced model might serve as a platform to perform sensitivity testing upon treatment to predict the patients' individual response to therapy. Citation Format: Julia C. Thierauf, Luca Engelmann, Natalia Koerich Laureano, Hans-Jürgen Stark, Elena-Sophie Prigge, Dominik Horn, Kolja Freier, Niels Grabe, Philippe Federspil, Peter K. Plinkert, Magnus von Knebel Doeberitz, Jochen Hess, Annette Affolter. Organotypic co-cultures as a novel 3D model for head and neck squamous cell carcinoma [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr 336.

Microsatellite-unstable (MSI) tumours show a high load of mutational neoantigens, as a consequence of DNA mismatch repair deficiency. Consequently, MSI tumours commonly present with dense immune infiltration and develop immune evasion mechanisms. Whether improved lymphocyte recruitment contributes to the pronounced immune infiltration in MSI tumours is unknown. We analysed the density of high endothelial venules (HEV) and postcapillary blood vessels specialised for lymphocyte trafficking, in MSI colorectal cancers (CRC). HEV density was determined by immunohistochemical staining of FFPE tissue sections from MSI (n = 48) and microsatellite-stable (MSS, n = 35) CRCs. Associations with clinical and pathological variables were analysed. We found elevated HEV densities in MSI compared with MSS CRCs (median 0.049 vs 0.000 counts/mm², respectively, p = 0.0002), with the highest densities in Lynch syndrome MSI CRCs. Dramatically elevated HEV densities were observed in B2M-mutant Lynch syndrome CRCs, pointing towards a link between lymphocyte recruitment and immune evasion (median 0.485 vs 0.0885 counts/mm² in B2M-wild-type tumours, p = 0.0237). Our findings for the first time indicate a significant contribution of lymphocyte trafficking in immune responses against MSI CRC, particularly in the context of Lynch syndrome. High HEV densities in B2M-mutant tumours underline the significance of immunoediting during tumour evolution.

Nonmelanoma skin cancer is the most prevalent cancer worldwide, and a number of cases are steadily increasing. The incidence of skin squamous cell carcinoma, which is the second most frequent tumor in this group of tumors, is markedly increasing in immunosuppressed transplant recipients and under certain cancer treatment modalities. Unfortunately, the aggressiveness of these tumors is also increasing, and once metastasized, the therapies to successfully eradicate these tumors are lacking, thus making research advancements vital. We firstly discuss what is currently known about cutaneous squamous cell carcinomas (cSCCs), an important consideration when designing relevant model systems for further investigation. We continue by reviewing recent studies, which have utilized different models and highlight the importance/requirement for human 3D models to combat this devastating tumor type.

Table S6. 391 Regulated Genes at Day 10 under HIPK4 Knockdown, Related to Figure 3E