ADAM17-mediated EGFR ligand shedding directs macrophage promoted cancer cell invasion

Interactions between cancer cells and tumor-associated macrophages in tumor microenvironment

Tumor microenvironment (TME) refers to the local environment in which various cancer cells grow, encompassing tumor cells, adjacent non-tumor cells, and associated non-cellular elements, all of which collectively promote cancer occurrence and progression. As a principal immune component in the TME, tumor-associated macrophages (TAMs) exert a considerable influence on cancer behaviors via their interactions with cancer cells. The interactive loops between cancer cells and TAMs, including secretory factors derived from both cancer cells and TAMs, are crucial for the proliferation, stemness, drug resistance, invasion, migration, metastasis, and immune escape of various cancers. Cancer cells release paracrine proteins (HMGB1, AREG etc.), cytokines (IL-6, CCL2 etc.), RNAs (miR-21-5p, circPLEKHM1, LINC01812 etc.), and metabolites (lactic acid, succinate etc.) to regulate the polarization phenotype, mediator secretion and function of TAMs. In turn, mediators (TGF-β, IL-10, IL-6 etc.) from TAMs promote cancer progression. This review summarizes recent advancements in the interactive loops between cancer cells and TAMs in TME. Inhibiting the recruitment and M2 polarization of TAMs, reprogramming TAMs from M2 to M1 phenotype, blocking TAMs-mediated immunosuppression and immune escape, and combining with existing immunotherapy can target TAMs to overcome immunotherapy resistance in various cancers. The new breakthroughs lie in identifying effective targets for drug development, improving the drug delivery system to enhance the drug delivery efficiency, and adopting combined therapy. Interventions targeting secretory factors, cell surface receptors, intracellular signaling pathways, and metabolic modulation in the interactive loops between cancer cells and TAMs are expected to suppress cancer progression and improve therapeutic effects.

Fibroblast EGFR signaling mediates ricin toxin-induced acute lung injury via EGR1/CXCL1 axis

Ricin toxin (RT), a highly potent plant-derived toxin, represents a critical threat due to its capacity to induce fatal acute lung injury (ALI) upon inhalation. While the epidermal growth factor receptor (EGFR), a receptor tyrosine kinase predominantly expressed on epithelial cells and fibroblasts, regulates cellular processes such as growth, proliferation, differentiation and inflammation, its involvement in RT-induced ALI remains unexplored. This study investigates this relationship using a mouse model of ALI induced by aerosolized RT at a dose of 2.0 × LD50 (approximately 0.01 mg kg -1). The results demonstrate that damage to alveolar epithelial type II (AT2) cells leads to the release of heparin-binding epidermal growth factor-like growth factor (HB-EGF), which activates EGFR on fibroblasts, exacerbating lung injury pathology and reducing survival. Mechanistically, EGFR activation in fibroblasts induces the early growth response protein 1 (EGR1), which subsequently enhances chemokine C-X-C motif ligand 1 (CXCL1) secretion 24 h post-exposure, promoting neutrophil infiltration in the lung. RNA sequencing analysis corroborates these findings. Notably, pharmacological inhibition of EGFR phosphorylation using Erlotinib (ERL) significantly mitigates the inflammatory response in RT-induced ALI. These results not only illuminate the immune response in lung tissue but also highlight EGFR signaling in fibroblasts as a pivotal mediator of RT-induced ALI. This study identifies a novel therapeutic strategy targeting EGFR signaling in fibroblasts for the treatment of inflammatory lung diseases.

CD147 regulates the Rap1 signaling pathway to promote proliferation, migration, and invasion, and inhibit apoptosis in colorectal cancer cells

The malignant progression of colorectal cancer (CRC) is intimately associated with the abnormal regulation of transmembrane glycoprotein CD147. However, the molecular mechanism via the Rap1/Rap1GAP signaling axis has not been elucidated. This study, through integrated bioinformatics analysis, discovered that the expression of CD147 in CRC tissues was significantly higher than that in adjacent tissues, and patients with high expression had a shorter overall survival. Immunohistochemistry and Western blot confirmed that the expression level of CD147 protein in CRC tissues was higher than that in adjacent tissues. Moreover, qRT-PCR verified a positive correlation between the expressions of CD147 and Rap1. Immunofluorescence clearly indicated that CD147 was specifically enriched in the cell membrane and cytoplasm of SW620 cells. The knockdown of CD147 mediated by shRNA could inhibit the proliferation of HCT116/SW620 cells, induce apoptosis, and weaken the migration and invasion capabilities. The mechanism involved the downregulation of c-Myc, Bcl-2 and the upregulation of Bax, E-cadherin. The mechanistic study found that the knockdown of CD147 increased the expression of Rap1GAP and inhibited Rap1 activity. Overexpression of Rap1 could reverse the inhibitory effects of CD147 knockdown on proliferation, apoptosis, and EMT phenotypes. This study revealed that CD147 upregulated Rap1 expression while inhibiting Rap1GAP, thereby maintaining Rap1 activity and driving the malignant progression of CRC through the c-Myc/Bcl-2/Bax axis and EMT program, providing experimental evidence for precise treatment targeting the CD147-Rap1 signaling axis.

Targeted approach to determine the impact of cancer-associated protease variants

Several steps of cancer progression, from tumor onset to metastasis, critically involve proteolytic activity. To elucidate the role of proteases in cancer, it is particularly important to consider single-nucleotide variants (SNVs) that affect the active site of proteases, thereby influencing cleavage specificity, substrate processing, and thus cancer cell behavior. To facilitate systematic studies, we here present a targeted approach to determine the impact of cancer-associated protease variants (TACAP). Starting with the semiautomated identification of potential specificity-modulating SNVs, our workflow comprises mass spectrometry-based cleavage specificity profiling and substrate identification, localization, and inhibitor studies, followed by functional analyses investigating cancer cell properties. To demonstrate the feasibility of TACAP, we analyzed the meprin β R238Q variant. This amino acid exchange R238Q leads to a loss of meprin β's characteristic cleavage preference for acidic amino acids at P1' position, accompanied with changes in substrate pool and inhibitor affinity compared to meprin β wild type.

Inhibiting ADAM17 enhances the efficacy of olaparib in ovarian cancer spheroids

Acquired or de novo resistance to poly (ADP-ribose) polymerase inhibitors (PARPi) is a major challenge to ovarian cancer treatment. Therefore, strategies to overcome PARPi resistance are critical to improve prognosis. The purpose of this study is to evaluate whether inhibition of ADAM17 sensitizes ovarian cancer to treatment with olaparib, a PARPi, thereby bypassing resistance mechanisms and improving treatment response. Thus, we analyzed the effect of olaparib in combination with the ADAM17 inhibitor GW280264X in ovarian cancer using a 2D monolayer and a 3D spheroid model followed by a multicontent readout (viability, caspase activation and cytotoxicity). To emphasize the translational aspect of our work, we performed corresponding experiments on primary cells derived from ovarian cancer patients initially screened for their mutation status of the breast cancer gene (BRCA 1/2). In 2D, we observed a significant reduction in cell viability and a subsequent increase in apoptosis of the combined treatment (olaparib + GW280264X) compared with olaparib mono-treatment. The combined treatment allows a substantial dose reduction of olaparib rendering a strong synergistic effect. Using a 3D spheroid model from primary cells, we confirmed the 2D monoculture results and demonstrated not only increased caspase activity under the combined treatment but also a substantial gain in cytotoxicity compared to the mono-treatment. Our study proposes ADAM17 inhibition sensitizing ovarian cancer to olaparib treatment and improving treatment response.

B7-H3 enhances colorectal cancer progression by regulating HB-EGF via HIF-1α

Background

B7-H3 (or CD276) represents an important costimulatory molecule expressed in many malignant solid tumors, including colorectal cancer (CRC). The receptor of B7-H3 is not known, and the intracellular function of B7-H3 remains obscure. Herein, we report that B7-H3 upregulated the epidermal growth factor heparin-binding epidermal growth factor (HB-EGF), likely by regulating hypoxia-inducible factor 1α (HIF-1α) and thereby promoting the progression of CRC.

Methods

Lentiviral transfection was performed on CRC cells to establish stable low-B7-H3 expression cells. A mechanistic analysis with an Agilent human gene expression profiling chip was conducted on them. Clinical data and specimens were collected to detect the connection between B7-H3 and HB-EGF in CRC. Quantitative real-time polymerase chain reaction (qRT-PCR) was conducted to detect the messenger RNA (mRNA) level of B7-H3, HB-EGF, and HIF-1α. Chromatin immunoprecipitation (ChIP) quantitative real-time PCR was conducted. The protein level of HIF-1α and the phosphatidylinositide 3-kinases (PI3K)-protein kinase B (AKT) pathway were detected by western blot. HIF-1α was recovered by lentiviral transfection, and the HB-EGF mRNA levels, proliferation, invasion, and angiogenesis ability were detected.

Results

B7-H3 promoted tumor progression through HB-EGF and the PI3K-AKT pathway. As B7-H3 was downregulated, HB-EGF levels were significantly reduced simultaneously, a growth trend that was shown by both CRC cell lines and cancer tissues. In addition, B7-H3 and HB-EGF had significant associations with tumor-node-metastasis (TNM) stage and lymph node metastasis in 50 CRC patients. The binding ability of HIF-1α to the HB-EGF promoter region was significantly decreased in the shB7-H3 RKO group. Western blot revealed that PI3K, AKT, and mammalian target of rapamycin (mTOR) protein amounts and p-AKT and p-mTOR phosphorylation were also downregulated in shB7-H3 RKO cells, suggesting that B7-H3 may regulate HIF-1α via PI3K-AKT signaling. After recovery of the HIF-1α level by lentiviral transfection, the HB-EGF mRNA levels, proliferation, invasion, and angiogenesis in CRC cells recovered as well.

Conclusions

B7-H3 may transmit intracellular signals through PI3K-AKT-mTOR-HIF-1α signaling, upregulating HB-EGF. As the final transcription factor of the pathway, HIF-1α regulates the transcription of the HB-EGF gene, thereby promoting HB-EGF expression, which eventually mediates cell proliferation, invasion, and angiogenesis and promotes the progression of CRC.

Extracellular proteolysis in cancer: Proteases, substrates, and mechanisms in tumor progression and metastasis

A vast ensemble of extracellular proteins influences the development and progression of cancer, shaped and reshaped by a complex network of extracellular proteases. These proteases, belonging to the distinct classes of metalloproteases, serine proteases, cysteine proteases, and aspartic proteases, play a critical role in cancer. They often become dysregulated in cancer, with increases in pathological protease activity frequently driven by the loss of normal latency controls, diminished regulation by endogenous protease inhibitors, and changes in localization. Dysregulated proteases accelerate tumor progression and metastasis by degrading protein barriers within the extracellular matrix (ECM), stimulating tumor growth, reactivating dormant tumor cells, facilitating tumor cell escape from immune surveillance, and shifting stromal cells toward cancer-promoting behaviors through the precise proteolysis of specific substrates to alter their functions. These crucial substrates include ECM proteins and proteoglycans, soluble proteins secreted by tumor and stromal cells, and extracellular domains of cell surface proteins, including membrane receptors and adhesion proteins. The complexity of the extracellular protease web presents a significant challenge to untangle. Nevertheless, technological strides in proteomics, chemical biology, and the development of new probes and reagents are enabling progress and advancing our understanding of the pivotal importance of extracellular proteolysis in cancer.

m6A‑modified HOXC10 promotes HNSCC progression via co‑activation of ADAM17/EGFR and Wnt/β‑catenin signaling

The homeobox (HOX) gene family plays a fundamental role in carcinogenesis. However, the oncogenic mechanism of HOXC10 in head and neck squamous cell carcinoma (HNSCC) remains unclear. In the present study, it was revealed that HOXC10 expression was significantly higher in HNSCC tissues than in adjacent tissues, and a high level of HOXC10 was closely associated with worse clinical outcomes. HOXC10 overexpression promoted HNSCC cell proliferation, migration, and invasion, both in vitro and in vivo. Mechanistically, chromatin immunoprecipitation sequencing revealed that HOXC10 drove the transcriptional activation of a disintegrin and metalloproteinase 17 (ADAM17), and the ADAM17/epidermal growth factor receptor (EGFR)/ERK1/2 signaling pathway facilitating the proliferation of HNSCC. Furthermore, mass spectrometric analysis indicated that HOXC10 interacted with ribosomal protein S15A (RPS15A) and enhanced RPS15A protein expression, activating the Wnt/β‑catenin pathway and contributing to invasion and metastasis of HNSCC. Additionally, the methylated RNA immune precipitation and RNA antisense purification assays showed that N6‑methyladenosine (m6A) writer, methyltransferase‑like 3, catalyzed m6A modification of the HOXC10 transcript, m6A reader insulin like growth factor 2 mRNA binding protein (IGF2BP)1 and IGF2BP3 involved in recognizing and stabilizing m6A‑tagged HOXC10 mRNA. In summary, the present study identified HOXC10 as a promising candidate oncogene in HNSCC. The m6A modification‑mediated HOXC10 promoted proliferation, migration, and invasion of HNSCC through co‑activation of ADAM17/EGFR and Wnt/β‑catenin signaling, providing a novel diagnostic and prognostic biomarker and a potential therapeutic target for HNSCC.

Correlation of MR-Based Metabolomics and Molecular Profiling in the Tumor Microenvironment of Temozolomide-Treated Orthotopic GL261 Glioblastoma in Mice

The tumor microenvironment in glioblastoma (GB) is considered to be "cold", i.e., the fraction of cytotoxic T cells, for instance, is low. Instead, macrophages are the major immune cell population in GB, which stem either from tissue response (resident microglia) or recruitment of macrophages from the periphery, thereby undergoing tumor-dependent "imprinting" mechanisms by which macrophages can adapt a tumor-supportive phenotype. In this regard, it is important to describe the nature of macrophages associated with GB, in particular under therapy conditions using the gold standard chemotherapy drug temozolomide (TMZ). Here, we explored the suitability of combining information from in vivo magnetic resonance spectroscopic (MRS) approaches (metabolomics) with in vitro molecular analyses to assess therapy response and characterize macrophage populations in mouse GB using an isogenic GL261 model. For macrophage profiling, expression levels of matrix metalloproteinases (MMPs) and A disintegrin and metalloproteinases (ADAMs) were determined, since their gene products affect macrophage-tumor cell communication by extensive cleavage of immunomodulatory membrane proteins, such as PD-L1. In tumor mice with an overall therapy response, expression of genes encoding the proteases ADAM8, ADAM10, and ADAM17 was increased and might contribute to the immunosuppressive phenotype of GB and immune cells. In tumors responding to therapy, expression levels of ADAM8 were upregulated by TMZ, and higher levels of PD-L1 were correlated significantly. Using a CRISPR/Cas9 knockout of ADAM8 in GL261 cells, we demonstrated that soluble PD-L1 (sPD-L1) is only generated in the presence of ADAM8. Moreover, primary macrophages from WT and ADAM8-deficient mice showed ADAM8-dependent release of sPD-L1, independent of the macrophage polarization state. Since ADAM8 expression is induced in responding tumors and PD-L1 shedding is likely to decrease the anti-tumor activities of T-cells, we conclude that immunotherapy resistance is caused, at least in part, by the increased presence of proteases, such as ADAM8.

Loss of cancer cell-derived ADAM15 alters the tumor microenvironment in colorectal tumors

Tumor progression and response to treatment are highly affected by interactions between cancer cells and the tumor microenvironment (TME). Many of the soluble factors and signaling receptors involved in this crosstalk are shed by a disintegrin and metalloproteinases (ADAMs). Upregulation of ADAM15 has been linked to worse survival in cancer patients and a tumor-promoting function both in vitro and in murine cancer models. Although ADAM15 has been involved in cell-cell and cell-extracellular matrix interactions, its role in the crosstalk between cancer cells and the TME in vivo remains unexplored. Therefore, we aimed to understand how ADAM15 regulates the cell composition of the TME and how it affects tumor progression. Here, we showed an upregulation of ADAM15 in tumor tissues from rectal cancer patients. Subcutaneous injection of wildtype and ADAM15-knockout CT26 colon cancer cells in syngeneic mice confirmed the protumorigenic role of ADAM15. Profiling of tumors revealed higher immune cell infiltration and cancer cell apoptosis in the ADAM15-deficient tumors. Specifically, loss of ADAM15 led to a reduced number of granulocytes and higher infiltration of antigen-presenting cells, including dendritic cells and macrophages, as well as more T cells. Using in vitro assays, we confirmed the regulatory effect of ADAM15 on macrophage migration and identified ADAM15-derived CYR61 as a potential molecular mediator of this effect. Based on these findings, we speculate that targeting ADAM15 could increase the infiltration of immune cells in colorectal tumors, which is a prerequisite for effective immunotherapy.

Predictive Roles of ADAM17 in Patient Survival and Immune Cell Infiltration in Hepatocellular Carcinoma

Hepatocellular carcinoma (HCC) is the deadliest malignant tumour worldwide. The metalloproteinase ADAM17 is associated with tumour formation and development; however, its significance in HCC is unclear. This study aimed to investigate the role of ADAM17 in HCC and the correlation between its expression and immune cell infiltration. ADAM17 expression was analysed in pan-cancer and HCC tissues using The Cancer Genome Atlas and Genotype-Tissue Expression datasets. Kaplan-Meier survival analysis displayed a negative association between ADAM17 expression and the overall survival of patients with HCC. High ADAM17 expression was linked to poor tumour/node (T/N) stage and alpha fetoprotein (AFP) levels. Gene Set Enrichment Analysis, Gene Ontology, and Kyoto Encyclopaedia of Genes and Genomes analyses revealed the enrichment of several pathways, including epithelial-mesenchymal transition, inflammatory response, Hedgehog, and KRAS signalling, in patients with upregulated ADAM17. ADAM17 was shown to be positively correlated with immune cell infiltration and immune checkpoint expression via the Tumour Immune Estimation Resource (TIMER) database and immunohistochemistry analyses. Protein-protein interaction (PPI) network analysis revealed that ADAM17 plays a core role in cancer development and immune evasion. In vitro and in vivo experiments demonstrated that ADAM17 influences HCC growth and metastasis. In conclusion, ADAM17 is upregulated in most cancers, particularly HCC, and is critical in the development and immune evasion of HCC.

The exercise IL-6 enigma in cancer

Interleukin (IL)-6 elicits both anticancer and procancer effects depending on the context, which we have termed the 'exercise IL-6 enigma'. IL-6 is released from skeletal muscles during exercise to regulate short-term energy availability. Exercise-induced IL-6 provokes biological effects that may protect against cancer by improving insulin sensitivity, stimulating the production of anti-inflammatory cytokines, mobilising immune cells, and reducing DNA damage in early malignant cells. By contrast, IL-6 continuously produced by leukocytes in inflammatory sites drives tumorigenesis by promoting chronic inflammation and activating tumour-promoting signalling pathways. How can a molecule have such opposing effects on cancer? Here, we review the roles of IL-6 in chronic inflammation, tumorigenesis, and exercise-associated cancer prevention and define the factors that underpin the exercise IL-6 enigma.

Oncogenic KRAS mutation confers chemoresistance by upregulating SIRT1 in non-small cell lung cancer

Kirsten rat sarcoma viral oncogene homologue (KRAS) is a frequent oncogenic driver of solid tumors, including non-small cell lung cancer (NSCLC). The treatment and outcomes of KRAS-mutant cancers have not been dramatically revolutionized by direct KRAS-targeted therapies because of the lack of deep binding pockets for specific small molecule inhibitors. Here, we demonstrated that the mRNA and protein levels of the class III histone deacetylase SIRT1 were upregulated by the KRASMut-Raf-MEK-c-Myc axis in KRASMut lung cancer cells and in lung tumors of a mouse model with spontaneous KrasG12D expression. KRASMut-induced SIRT1 bound to KRASMut and stably deacetylated KRASMut at lysine 104, which increased KRASMut activity. SIRT1 knockdown (K/D) or the SIRT1H363Y mutation increased KRASMut acetylation, which decreased KRASMut activity and sensitized tumors to the anticancer effects of cisplatin and erlotinib. Furthermore, in KrasG12D/+;Sirt1co/co mice, treatment with cisplatin and erlotinib robustly reduced the tumor burden and increased survival rates compared with those in spontaneous LSL-KrasG12D/+;Sirt1+/+ mice and mice in each single-drug treatment group. Then, we identified p300 as a KRASMut acetyltransferase that reinforced KRASMut lysine 104 acetylation and robustly decreased KRASMut activity. KRASMut lysine 104 acetylation by p300 and deacetylation by SIRT1 were confirmed by LC‒MS/MS. Consistent with this finding, the SIRT1 inhibitor EX527 suppressed KRASMut activity, which synergistically abolished cell proliferation and colony formation, as well as the tumor burden in KRASMut mice, when combined with cisplatin or erlotinib. Our data reveal a novel pathway critical for the regulation of KRASMut lung cancer progression and provide important evidence for the potential application of SIRT1 inhibitors and p300 activators for the combination treatment of KRASMut lung cancer patients.

ADAM12 expression is upregulated in cancer cells upon radiation and constitutes a prognostic factor in rectal cancer patients following radiotherapy

Radiotherapy is one of the most common cancer treatments, yet, some patients require high doses to respond. Therefore, the development of new strategies leans toward personalizing therapy to avoid unnecessary burden on cancer patients. This approach prevents the administration of ineffective treatments or uses combination strategies to increase the sensitivity of cancer cells. ADAM12 has been shown to be upregulated in many cancers and correlate with poor survival and chemoresistance, thus making it a potential candidate responsible for radioresistance. Here, we show that ADAM12 expression is upregulated in response to irradiation in both mouse and human cancer cells in vitro, as well as in tumor tissues from rectal cancer patients. Interestingly, the expression of ADAM12 following radiotherapy correlates with the initial disease stage and predicts the response of rectal cancer patients to the treatment. While we found no cell-autonomous effects of ADAM12 on the response of colon cancer cells to irradiation in vitro, depletion of ADAM12 expression markedly reduced the tumor growth of irradiated cancer cells when subcutaneously transplanted in syngeneic mice. Interestingly, loss of cancer cell-derived ADAM12 expression increased the number of CD31+FAP- cells in murine tumors. Moreover, conditioned medium from ADAM12-/- colon cancer cells led to increased tube formation when added to endothelial cell cultures. Thus, it is tempting to speculate that altered tumor vascularity may be implicated in the observed effect of ADAM12 on response to radiotherapy in rectal cancer. We conclude that ADAM12 represents a promising prognostic factor for stratification of rectal cancer patients receiving radiotherapy and suggest that targeting ADAM12 in combination with radiotherapy could potentially improve the treatment response.

Proteolytic signaling in cancer

INTRODUCTION

Cancer is a disease of (altered) biological pathways, often driven by somatic mutations and with several implications. Therefore, the identification of potential markers of disease is challenging. Given the large amount of biological data generated with omics approaches, oncology has experienced significant contributions. Proteomics mapping of protein fragments, derived from proteolytic processing events during oncogenesis, may shed light on (i) the role of active proteases and (ii) the functional implications of processed substrates in biological signaling circuits. Both outcomes have the potential for predicting diagnosis/prognosis in diseases like cancer. Therefore, understanding proteolytic processing events and their downstream implications may contribute to advances in the understanding of tumor biology and targeted therapies in precision medicine.

AREAS COVERED

Proteolytic events associated with some hallmarks of cancer (cell migration and proliferation, angiogenesis, metastasis, as well as extracellular matrix degradation) will be discussed. Moreover, biomarker discovery and the use of proteomics approaches to uncover proteolytic signaling events will also be covered.

EXPERT OPINION

Proteolytic processing is an irreversible protein post-translational modification and the deconvolution of biological data resulting from the study of proteolytic signaling events may be used in both patient diagnosis/prognosis and targeted therapies in cancer.

Immunomodulatory role of metalloproteinase ADAM17 in tumor development

ADAM17 is a member of the a disintegrin and metalloproteinase (ADAM) family of transmembrane proteases involved in the shedding of some cell membrane proteins and regulating various signaling pathways. More than 90 substrates are regulated by ADAM17, some of which are closely relevant to tumor formation and development. Besides, ADAM17 is also responsible for immune regulation and its substrate-mediated signal transduction. Recently, ADAM17 has been considered as a major target for the treatment of tumors and yet its immunomodulatory roles and mechanisms remain unclear. In this paper, we summarized the recent understanding of structure and several regulatory roles of ADAM17. Importantly, we highlighted the immunomodulatory roles of ADAM17 in tumor development, as well as small molecule inhibitors and monoclonal antibodies targeting ADAM17.

Identification of Molecular Determinants in iRhoms1 and 2 That Contribute to the Substrate Selectivity of Stimulated ADAM17

The metalloprotease ADAM17 is a key regulator of the TNFα, IL-6R and EGFR signaling pathways. The maturation and function of ADAM17 is controlled by the seven-membrane-spanning proteins iRhoms1 and 2. The functional properties of the ADAM17/iRhom1 and ADAM17/iRhom2 complexes differ, in that stimulated shedding of most ADAM17 substrates tested to date can be supported by iRhom2, whereas iRhom1 can only support stimulated shedding of very few ADAM17 substrates, such as TGFα. The first transmembrane domain (TMD1) of iRhom2 and the sole TMD of ADAM17 are important for the stimulated shedding of ADAM17 substrates by iRhom2. However, little is currently known about how the iRhoms interact with different substrates to control their stimulated shedding by ADAM17. To provide new insights into this topic, we tested how various chimeras between iRhom1 and iRhom2 affect the stimulated processing of the EGFR-ligands TGFα (iRhom1- or 2-dependent) and EREG (iRhom2-selective) by ADAM17. This uncovered an important role for the TMD7 of the iRhoms in determining their substrate selectivity. Computational methods utilized to characterize the iRhom1/2/substrate interactions suggest that the substrate selectivity is determined, at least in part, by a distinct accessibility of the substrate cleavage site to stimulated ADAM17. These studies not only provide new insights into why the substrate selectivity of stimulated iRhom2/ADAM17 differs from that of iRhom1/ADAM17, but also suggest new approaches for targeting the release of specific ADAM17 substrates.