Direct Identification of Proteolytic Cleavages on Living Cells Using a Glycan-Tethered Peptide Ligase.

Proteolytic cleavage of cell surface proteins triggers critical processes including cell-cell interactions, receptor activation, and shedding of signaling proteins. Consequently, dysregulated extracellular proteases contribute to malignant cell phenotypes including most cancers. To understand these effects, methods are needed that identify proteolyzed membrane proteins within diverse cellular contexts. Herein we report a proteomic approach, called cell surface N-terminomics, to broadly identify precise cleavage sites (neo-N-termini) on the surface of living cells. First, we functionalized the engineered peptide ligase, called stabiligase, with an N-terminal nucleophile that enables covalent attachment to naturally occurring glycans. Upon the addition of a biotinylated peptide ester, glycan-tethered stabiligase efficiently tags extracellular neo-N-termini for proteomic analysis. To demonstrate the versatility of this approach, we identified and characterized 1532 extracellular neo-N-termini across a panel of different cell types including primary immune cells. The vast majority of cleavages were not identified by previous proteomic studies. Lastly, we demonstrated that single oncogenes, KRAS(G12V) and HER2, induce extracellular proteolytic remodeling of proteins involved in cancerous cell growth, invasion, and migration. Cell surface N-terminomics is a generalizable platform that can reveal proteolyzed, neoepitopes to target using immunotherapies.

Native Hawaiian and Other Pacific Islanders' Leading Risk Factors for Ischemic Stroke: A Comparative Ethnographic Study.

INTRODUCTION: Hawaii is a multicultural state with many different ethnicities, including Native Hawaiians and other Pacific Islanders (NHOPI). This demographic has not been thoroughly studied, despite its significantly higher prevalence of stroke. This study aimed to characterize risk factors for ischemic stroke in NHOPI compared to other ethnicities. METHODS: An Institutional Review Board (IRB) sanctioned retrospective chart review was conducted at a multi-site community neurology clinic from June 2017 through June 2019. Prospective patients were identified from the database using the International Classification of Diseases 10th Edition (ICD-10) codes for ischemic stroke. 326 patients (99 NHOPI, 116 Asian, 111 Caucasian) with a history of ischemic stroke met the inclusion criteria. Risk factors were determined based on the American Stroke Association guidelines; ethno-racial grouping was based on self-identification; and average household income levels were estimated based on patient zip codes US Census Bureau data. Continuous variable risk factors were analyzed using an analysis of variance (ANOVA) and post-hoc pairwise comparisons using Tukey-Kramer; a multivariate analysis was conducted. RESULTS: Compared to Asians and Caucasians, NHOPI patients were on average 11 years younger at the onset of stroke and more likely to be women. The NHOPI group also had the highest rates of diabetes and obesity. NHOPI average income was significantly lower compared to the Caucasian group. Hypertension and hyperlipidemia were found to be higher in the Asian population. Alcohol consumption was reported more frequently among Caucasian patients. CONCLUSIONS: These results better-characterized risk factors for ischemic stroke among NHOPI in Hawaii. The younger age of stroke onset in NHOPI patients is likely due to the higher burden of cardiovascular risk factors like obesity, smoking, and diabetes. Identifying such disparities in associated risk for NHOPI and other ethnicities can allow targeted stroke prevention and outpatient care in a multicultural setting.

A functional mammalian display screen identifies rare antibodies that stimulate NK cell-mediated cytotoxicity.

Therapies that boost the antitumor immune response have shown a great deal of success. Although most of these therapies have focused on enhancing T cell functions, there is a growing interest in developing therapies that can target other immune cell subsets. Like T cells, natural killer (NK) cells are cytotoxic effector cells that play a key role in the antitumor response. To advance the development of NK-based therapies, we developed a functional screen to rapidly identify antibodies that can activate NK cells. We displayed antibodies on a mammalian target cell line and probed their ability to stimulate NK cell-mediated cytotoxicity. From this screen, we identified five antibodies that bound with high affinity to NK cells and stimulated NK cell-mediated cytotoxicity and interferon-γ (IFN-γ) secretion. We demonstrate that these antibodies can be further developed into bispecific antibodies to redirect NK cell-mediated cytotoxicity toward CD20+ B cell lymphoma cells and HER2+ breast cancer cells. While antibodies to two of the receptors, CD16 and NCR1, have previously been targeted as bispecific antibodies to redirect NK cell-mediated cytotoxicity, we demonstrate that bispecific antibodies targeting NCR3 can also potently activate NK cells. These results show that this screen can be used to directly identify antibodies that can enhance antitumor immune responses.

Cancer-associated protein kinase C mutations reveal kinase's role as tumor suppressor.

Protein kinase C (PKC) isozymes have remained elusive cancer targets despite the unambiguous tumor promoting function of their potent ligands, phorbol esters, and the prevalence of their mutations. We analyzed 8% of PKC mutations identified in human cancers and found that, surprisingly, most were loss of function and none were activating. Loss-of-function mutations occurred in all PKC subgroups and impeded second-messenger binding, phosphorylation, or catalysis. Correction of a loss-of-function PKCß mutation by CRISPR-mediated genome editing in a patient-derived colon cancer cell line suppressed anchorage-independent growth and reduced tumor growth in a xenograft model. Hemizygous deletion promoted anchorage-independent growth, revealing that PKCß is haploinsufficient for tumor suppression. Several mutations were dominant negative, suppressing global PKC signaling output, and bioinformatic analysis suggested that PKC mutations cooperate with co-occurring mutations in cancer drivers. These data establish that PKC isozymes generally function as tumor suppressors, indicating that therapies should focus on restoring, not inhibiting, PKC activity.